Arctic Sea Ice : Forum

Cryosphere => Arctic sea ice => Topic started by: interstitial on June 27, 2020, 03:50:42 AM

Title: HYCOM
Post by: interstitial on June 27, 2020, 03:50:42 AM
I think this model deserves its own thread. I was using another thread but I want to focus on this model. Some experienced users don't think it is very good but I want to follow it for a while and see. Because there is conflicting opinions on its value I decided to keep it off the main melting thread and it doesn't really fit elsewhere. To get started if you compare 2019 on 6/25 and 9/25 final area roughly conforms to anything black or thicker on 6/25. I would like to see if 2020 follows the same pattern. In a few days I will compare other years.
Title: Re: HYCOM
Post by: binntho on June 27, 2020, 05:53:04 AM
I am surprised at how well the final extent in the top image (25/9/2019) fits the black thickness boundary three months earlier. So many times have I seen people saying that "everything at such and such color will melt out" but this is the first time I've actually seen anybody doing this sort of comparison after the event.
Title: Re: HYCOM
Post by: interstitial on June 28, 2020, 06:30:06 AM
I have provided a 4/15/2020 map of Piomas vs Hycom as requested. I Also included worldview.

North of Svalbard shows a fair bit of 4 meter ice on Piomas where Hycom shows 2.5 meter ice. In the Beaufort along the Alaska coastline shows a few small pockets of 3 meter ice on Hycom and it does not show on Piomas. The CAA side shows a fair bit of 4 meter ice on Piomas where Hycom shows most of that ice as 3 meter ice with a tiny amount of thicker ice at 4 and even 5 meters. The main body of ice in the Beaufort is between 2 and 3 meters thick according to Piomas. On Hycom that ice looks to be 1.4 to 2.3 meters thick. That is a large volume difference. Near Wrengel island Piomas shows a thick arm starting at 4 meters and thinning to about 2.5 meters. Hycom shows 1.7 meter ice near Wrengel island with the thicker arm shifted south between 1.8 and 2.5 meters thick. Piomas shows a hump in the Greenland sea of thin ice that I could not find on worldview and does not show on Hycom. Overall Piomas shows most of the central Arctic basin being from 2 to 3.4 meters thick. In the same area Hycom shows between 1.4 and 2.3 meters thick.

Most of the differences in shapes can be explained by the difference in resolution between the models. Many of the features are similar though their are some clear differences as noted above. Hycom uses more colors in their scale making a more precise visualization of thickness. Overall Piomas tends to show thicker ice than Hycom. As with any model it needs to validated. Maybe I will track down some Polarstern data and see how it compares.
Title: Re: HYCOM
Post by: interstitial on June 28, 2020, 07:00:03 AM
The June to end of year comparisons are interesting but are not as predictive as 2019.
Title: Re: HYCOM
Post by: interstitial on June 28, 2020, 07:01:41 AM
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Title: Re: HYCOM
Post by: oren on June 28, 2020, 09:41:27 AM
Thank you interstitial for the wealth of data.
I edited the comparative post above and added a Cryosat-SMOS map for mid-April. I am having a hard time comparing them directly but maybe you can do the same visual comparison you did between PIOMAS and Hycom.
I am adding here two maps of April monthly anomalies compared to 2011-2018, one from PIOMAS and one from Cryosat-SMOS, provided by the Polar Science Center as part of their PIOMAS April update. These can help in finding the differences. I wish such a map in the same format  would be available from Hycom, but that would be too much to ask.
Title: Re: HYCOM
Post by: oren on June 28, 2020, 09:46:48 AM
If I may add, the ice distribution in Hycom is very weird, with all the thick ice up to 5m bunched very near to Greenland and the CAA, and the rest of the CAB at a measly 2-2.5m. I find it very hard to believe this represent a true gradient, and Cryosat-SMOS does not support this either.

It now occurs to me that an ASCAT animation, showing where the old ice is and covering the period leading up to mid-April, could be very useful here as well. There should some animations available that uniquorn has posted through the winter and spring, will look for a suitable one.
Title: Re: HYCOM
Post by: Andre Koelewijn on June 28, 2020, 10:21:46 AM
Note that the HYCOM-map serves a specific purpose: to show nuclear submarines operators the maximum probable thickness, to enable safe decisions where to surface.
It is meant as an upper bound throughout the arctic, not an alternative to estimate the actual total ice volume.
Title: Re: HYCOM
Post by: OffTheGrid on June 28, 2020, 08:46:10 PM
If I may add, the ice distribution in Hycom is very weird, with all the thick ice up to 5m bunched very near to Greenland and the CAA, and the rest of the CAB at a measly 2-2.5m. I find it very hard to believe this represent a true gradient, and Cryosat-SMOS does not support this either.

It now occurs to me that an ASCAT animation, showing where the old ice is and covering the period leading up to mid-April, could be very useful here as well. There should some animations available that uniquorn has posted through the winter and spring, will look for a suitable one.
Perhaps we should remember that smos has a 40km grid resolution, and cryosat cannot resolve leads and ridges below a scale of 200-300m. It is unlikely that smos is contributing in the area you reference anyway as it is good at sub 1 m thickness, whole cryosat is better when ice is thicker than that.
So cryosat may assume ridge fields tops as continuous freeboard when things are far more complex at scales below Its resolution. A pity both are confounded during melt season, smos by wet ice, and cryosat by atmospheric moisture, especially cloud and fog, snow, particularly with melted and refrozen layers can cause both to oberestimate freeboard also.

Overall I am fairly impressed by the match between Hycom and crysmos in the april comparison. I am not sure why you find it so weird that the thickest ice is where it gets crushed and stacked by drift pressure against these coastlines, where also it experiences the coldest, with Katabatic winds dropping off tall ice sheets and mountains in midwinter?
At the end i guess, probably the truth may be somewhere in the middle. With unknown it is good I think to keep minds open to All informations, and individuals must balance how many "grains of salt" should each source be taken with.  :P
Title: Re: HYCOM
Post by: interstitial on June 29, 2020, 12:06:41 AM
A number of great comments it may take some time to explore them in detail.


Note that the HYCOM-map serves a specific purpose: to show nuclear submarines operators the maximum probable thickness, to enable safe decisions where to surface.
It is meant as an upper bound throughout the arctic, not an alternative to estimate the actual total ice volume.
I have heard that before on this site and I am not sure where it comes from. I looked for a statement about submarines or maximum probable thickness and found none. I have no doubt that the U.S. Navy is using this model for operations. I would note as of about a year ago the Navy is interested in countering Russian moves in the arctic and is increasing surface operations in the region.
 
In general I wonder how useful it would be for a submarine. I remember talk on this site of using underwater submarines equipped with LIDAR to measure sea ice thickness to validate models. So that statement seems backwards. I have no direct knowledge of U.S. Navel capabilities but I would bet just about anything the submarines have Lidar now and have had it for decades.
 
The objective stated on their website is: he GODAE objectives of three-dimensional depiction of the ocean state at fine resolution in real time, provision of boundary conditions for coastal and regional models, and provision of oceanic boundary conditions for a global coupled ocean-atmosphere prediction model, are being addressed by a partnership of institutions that represent a broad spectrum of the oceanographic community.
 
The partnership does include a number of institutions but I am not naive. Whoever pays most of the bills controls the mission and academic institutions are always looking for funding.
Reading through I also found this bit (Bold is mine): The systems will run efficiently on a variety of massively parallel computers and will include sophisticated data assimilation techniques for assimilation of satellite altimeter sea surface height and sea surface temperature as well as in situ temperature, salinity, and float displacement. They use floats among other things for validation. I am guessing the lidar on submarines is also used for validation though that would be something the navy did internally and would not mention because submarine locations are classified.
 
Finally they finish with this (bold is mine):
This collaborative partnership provides the means to leverage and accelerate the efforts of existing and planned projects, as well as new opportunities for collaboration and cooperation among the partners ranging from research to the operational level. The anticipated results of this effort include integrated analyses/reanalyses for research programs, a foundation for model enhancement based on testing of hypotheses, synthesis of remotely sensed and in situ data, and inputs to coastal, regional, atmospheric, and ice prediction systems. Improved open-ocean nowcasts and forecasts will be applied to search and rescue operations, shipping routes, tracking of icebergs and major pollutants, commercial fisheries, etc.
 
Title: Re: HYCOM
Post by: interstitial on June 29, 2020, 12:08:12 AM
If they are using it for maximum probable thickness and piomas shows thicker ice what does that say?
Title: Re: HYCOM
Post by: interstitial on June 29, 2020, 12:37:15 AM
Thank you interstitial for the wealth of data.
I edited the comparative post above and added a Cryosat-SMOS map for mid-April. I am having a hard time comparing them directly but maybe you can do the same visual comparison you did between PIOMAS and Hycom.
I am adding here two maps of April monthly anomalies compared to 2011-2018, one from PIOMAS and one from Cryosat-SMOS, provided by the Polar Science Center as part of their PIOMAS April update. These can help in finding the differences. I wish such a map in the same format  would be available from Hycom, but that would be too much to ask.

Anomaly maps are a wonderful tool for comparing a point in time with the average of that model. If you compare anomaly maps from different models you are introducing another factor namely the time averaged thickness map for each of the models. If the time averaged thickness varies between models the results get more confused.

It would be nice if Hycom provided anomaly tools.

It may be a good time to mention that the Hycom map varies slightly from Piomas. The differences are not very large.
Title: Re: HYCOM
Post by: interstitial on June 29, 2020, 12:50:48 AM
If I may add, the ice distribution in Hycom is very weird, with all the thick ice up to 5m bunched very near to Greenland and the CAA, and the rest of the CAB at a measly 2-2.5m. I find it very hard to believe this represent a true gradient, and Cryosat-SMOS does not support this either.[/size]

This I think represents the biggest difference between the two models and IMO which gets it right is the better model. I seem to recall that ice grows too about 2 meters and then beyond that it grows slowly. I need actual thickness data to validate the model not comparison with another model.
Title: Re: HYCOM
Post by: interstitial on June 29, 2020, 04:18:07 AM
I used mosaic news post #741 4/19/20 with T62. The difference between thickness on t62 between 4/15 and 4/19 is negligible so I used this date. I found on the 19th T62 was around 84.2N and 15.5E.I used the grid on Hycomm to identify the location and found it shows 1.6 m thickness. Since Piomas does not have a grid and I already made an overlay of the two and checked the same point on Piomas. Piomas says 2.5 m in that location. There is nothing close to 1.4 m in that area everthing else is thicker if anything. This is only one point on one day and not conclusive but I just picked it based on ease of getting the data. This took a long time since I found a point close to that using measurements and angles.
Title: Re: HYCOM
Post by: interstitial on June 29, 2020, 05:11:14 AM
post #1943 by Frivolous in the melting thread includes this comparison of piomas a model to cryosat. Notice piomas has a high bias.
Title: Re: HYCOM
Post by: igs on June 29, 2020, 09:08:11 PM
post #1943 by Frivolous in the melting thread includes this comparison of piomas a model to cryosat. Notice piomas has a high bias.

If Hycom is a tool for the military ( marine / submarines ) I would rather trust military grade data than civil models. They can simply not afford to err, considering what those datasets are used for.

That proves nothing of course, just a thought in case we never get any proof.

I would bet that once the satellites and pictures taken from vessels and airplanes show zero ice, that Piomas will show ice still, just a gut-feeling based on many occurances of that kind, even though they were regional and minor.
Title: Re: HYCOM
Post by: interstitial on June 30, 2020, 02:18:48 AM
Piomass is a fairly simple model it uses wind speed, wind direction, surface air temperature, cloud cover and with the latest update sea surface temperatures. Cloud cover and time of year are used to calculate solar and longwave radiation. Using air temperature and energy input modified by currents, wind and SST’s along with ice thicknesses, concentration and extent are used to calculate ice growth. Currents (from unnamed ocean model) and wind can move ice when the ice is mobile and SST energy. From what I read that is the basics
 
Piomas concerns:
*There is currently no funding to maintain or upgrade Piomas
 *Most of the validation data is older 6 years or older   
  http://psc.apl.uw.edu/sea_ice_cdr/data tables.html (http://psc.apl.uw.edu/sea_ice_cdr/data%20tables.html)
     Exceptions:
BGEP, which is only 4 moored buoys in Beaufort sea.
icebridge quicklook, that prerelease data has a stated accuracy of +/- 1 meter of thickness. The final versions is much more accurate but not the quicklook data.
Cryostat volume is 23% lower than Piomass while this is not thickness it the extent is the similar.
*Piomass shows thin ice in Greenland Sea where none exists.
 
Piomas more info:
*Piomas uses NSIDC ice concentration and snow extent NISE near real time snow and ice extent 25 km
*Reynalds Sea surface temperatures for NCEP/NCAR on ice free areas
*Atmospheric wind, surface air and cloud cover to compute solar and longwave radiation
*Unnamed forced ocean circulation model with input at its open boundaries located at 45 north
*Stated piomas uncertainty +/- 1.35x10^3 km^3 areas in sea of Okhotsk and Gulf of St Lawrence are
   excluded
*spatial coverage 45 N to 90 N grid size 360 x 120 generalized curvilinear coordinate system (Grid shape irregular
Focus only on ice growth
 
Hycom uses hybrid coordinates layered in the open stratified ocean and smoothly transition to terrain following in shallow areas with specific coordinates for mixed layers or unstratified seas. It’s a global ocean model coupled with a global atmospheric model. 
It includes such physical processes as background internal wave breaking, shear instability mixing, double diffusion salt fingering and diffusive instability are parameterized. In the surface boundary layer wind driven mixing, surface buoyancy fluxes and convective instabilities are parameterized. Other factors include nonlocal mixing of temperature and salinity which permits counter gradient fluxes. The Kraus-Turner slab model the dynamical instability model of Price and the MellorYamada level 2.5 turbulence closure of the Prineton ocen model.
 
Hycom algorithms
   advdiff.pdf (horizontal advection/diffusion)
   boundary.pdf (boundary conditions)
   diapycnal.pdf (three interior diapycnal mixing algorithms)
   float.pdf (synthetic floats/drifters/moorings)
   hybrid.pdf (hybrid vertical coordinate adjustment)
   ice.pdf (energy loan ice model)
   KPP.pdf (K-Profile Parameterization vertical mixing)
   KT.pdf (three Kraus-Turner mixed layer models)
   mesh.pdf (horizontal mesh)
   momentum.pdf (momentum equation, including pressure gradient force)
   MY.pdf (Mellor-Yamada level 2.5 turbulence closure vertical mixing)
   PWP.pdf (Price-Weller-Pinkel dynamical instability vertical mixing)
   state.pdf (equation of state, including cabbeling and thermobaricity)
   surface.pdf (surface fluxes, including penetrating shortwave radiation)
   vdiff.pdf (solution of vertical diffusion equation)
   Other algorithms used from MICOM (HYCOM’s precursor) include continuity equation barotropic   
   momentum equation advection algorithm and vertical mode splitting
   https://www.hycom.org/attachments/067_overview.pdf (https://www.hycom.org/attachments/067_overview.pdf)
Hycom does an 8 day run every day.
0.08 degree resolution from 40 N to 40 S and 0.04 degree resolution poleward.
Focus on entire ocean atmosphere with parameterization of many physical interactions.
 
Title: Re: HYCOM
Post by: interstitial on June 30, 2020, 02:28:38 AM
All the buoy information I could find for April 15 showed
ice thickness < 2 m (mostly between 1.5 m and 1.8 m)


Piomas data for the same area > 2.5 m


Hycom varies between 1.6 m and 2 m for the same area
Title: Re: HYCOM
Post by: oren on June 30, 2020, 03:08:07 AM
One thing that PIOMAS does is to model a distribution of ice thicknesses in each grid cell. This enables taking stock of pressure ridges, which contain a lot of volume though only cover a small area. The PIOMAS map shows the average for each cell, but the output files contain the distribution, which Wipneus graphs from time to time.
Looking at the Mosaic buoys, one of them was placed on a 7m thick floe, a real life example of uneven thickness of floes in the same vicinity.
I am sure Hycom models hydrology much much better, but not so sure how well it performs with ice thickness and transport.
Since PIOMAS assimilates NSIDC concentration data, it is rare (but happens) for it to show ice where none exists. I think this mostly stems from coarse resolution and will tend to disappear, so errors don't accumulate. But my knowledge of PIOMAS inner workings is very limited, I just use some of the output provided by Wipneus.
Title: Re: HYCOM
Post by: interstitial on June 30, 2020, 04:07:53 AM
If Hycom was just an intense ocean model it probably wouldn't be as good as Piomass. The Hycom model is coupled with in sophisticated atmospheric model which generates eight day forcasts.
I missed the 7 m data.
The submarine data is interesting with ice spikes pointing down in the water. 


navgem_0.176deg_computagrid_mask_2048x1024.D (ftp://ftp.hycom.org/datasets/force/NAVGEM/navgem2.0_0.176c/navgem_0.176deg_computagrid_mask_2048x1024.D)[/b][/size] is the land-sea mask needed for NAVGEM 2.0.[/font][/size]NAVGEM 2.03-hourly operational output: 20200401 and continuing until it is decommissioned[/color][/size]The 3-hourly files are generally updated once per week (Thursday or Friday) on hycom.org.[/color][/size]navgem2.0_0.176-sea_2020_03hr_mslprs.D[/b]mean sea level pressure (hPa/100 - 1000)navgem2.0_0.176-sea_2020_03hr_soiltm.D[/b]surface (land and ocean) temperature (Kelvin)navgem2.0_0.176-sea_2020_03hr_spchum.D[/b]2 m specific humidity (kg/kg)navgem2.0_0.176-sea_2020_03hr_temp2m.D[/b]2 m air temperature (Kelvin)navgem2.0_0.176-std_2020_03hr_ttlpcp.D[/b]total (large-scale and convective) precipitationnavgem2.0_0.176-sea_2020_03hr_ulwsfc.D[/b]upward surface longwave (W/m2)navgem2.0_0.176-sea_2020_03hr_uswsfc.D[/b]upward surface shortwave (W/m2)navgem2.0_0.176-sec_2020_03hr_dlwsfc.D[/b]downward surface longwave (W/m2)navgem2.0_0.176-sec_2020_03hr_dswsfc.D[/b]downward surface shortwave (W/m2); alias correctednavgem2.0_0.176c-sea_2020_03hr_dswsfc_noaliascorrect.D[/b]downward surface shortwave (W/m2); no alias correctednavgem2.0_0.176-sec_2020_03hr_longwv.D[/b]net surface longwave (W/m2)navgem2.0_0.176-sec_2020_03hr_solrad.D[/b]net surface shortwave (W/m2)navgem2.0_0.176-sec_2020_03hr_uv-10m.D[/b]10 m zonal and meridional wind velocity (m/s)navgem2.0_0.176-sec_2020_03hr_wndspd.D[/b]10 m wind speed (m/s)navgem2.0_0.176c-sec_2020_03hr_Taqa_null.D[/b]Note: no Qr/Qp arrays in this file.[/font][/color]
Title: Re: HYCOM
Post by: interstitial on July 03, 2020, 04:10:52 AM
latest
Title: Re: HYCOM
Post by: johnm33 on July 03, 2020, 10:13:29 AM
The two images show what appears to me to be a massive 'spouting out' incident occuring in the depths of Beaufort, I wouldn't fancy being in a sub caught anywhere in that turmoil.
(https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/beaufortopening/nowcast/opening2020062312_2020062400_930_beaufortopening.001.gif)
(https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/beaufortopening/nowcast/opening2020062312_2020062500_930_beaufortopening.001.gif)
Title: Re: HYCOM
Post by: OffTheGrid on July 04, 2020, 07:28:46 PM
Latest 30 day model run to 11 July.
Signs of thicker ice limbs in coastal Beaufort, ESS, Franz Joseph regions head towards orphaned.
Ice over 2.5m by CAA wilt out. Or export to sure melt zones. Click to animate.
Title: Re: HYCOM
Post by: interstitial on July 04, 2020, 10:20:47 PM
Johnm33 thanks for the information. Any idea what would cause those? Another question I wonder how much mixing and heat those events caused? Any idea if this is normal?
Title: Re: HYCOM
Post by: ajouis on July 05, 2020, 01:12:59 AM
Interstitial, that last hycom run gives you the perfect opportunity to test it against reality, one, in a general manner, given that widespread white “almost gone” areas, that should mean a peak of losses july 15-22, second, some of those very thin areas should be visible from satellite photos, especially for the north of Svalbard, compared to now (provided it is not too cloudy), similarly we could compare with piomas on ice distribution at the mid july release. The quasi arm in Beaufort has shown to be very similar in piomas and hycom, so we can see if they are really parallel or divergent on some important features.
Title: Re: HYCOM
Post by: interstitial on July 05, 2020, 01:41:00 AM
Interstitial, that last hycom run gives you the perfect opportunity to test it against reality, one, in a general manner, given that widespread white “almost gone” areas, that should mean a peak of losses july 15-22, second, some of those very thin areas should be visible from satellite photos, especially for the north of Svalbard, compared to now (provided it is not too cloudy), similarly we could compare with piomas on ice distribution at the mid july release. The quasi arm in Beaufort has shown to be very similar in piomas and hycom, so we can see if they are really parallel or divergent on some important features.
I agree and the more I learn about it the more informative  it is. I will post more on that in a few days. Another big thing it is saying is the bueafort ice is not as stable as it appears. I expect large late season losses there.
Title: Re: HYCOM
Post by: johnm33 on July 05, 2020, 11:36:08 AM
"Any idea what would cause those?" I think massive movements of of water caused by mslp highs/lows passing from land to sea, or vice versa,  or passing over Lomonosov and some by tidal surges in concert with those movements. The movements set up internal waves in deeper layers, these either cancel out or reinforce each other if the second then events like this occur and they're not uncommon in the Canada basin, looking at amsr2 on polarview you can see signs of these events and similar signs elsewhere but without Hycoms model.
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/beaufort.html
Amsr2 data browser (https://seaice.uni-bremen.de/databrowser/#day=24&month=5&year=2020&img=%7B%22image%22%3A%22image-1%22%2C%22sensor%22%3A%22AMSR%22%2C%22type%22%3A%22nic%22%2C%22region%22%3A%22Arctic%22%7D)
 The ice strength gif of Beaufort shows the ice will not hold a crack, suggesting to me it's very weak.
Title: Re: HYCOM
Post by: interstitial on July 07, 2020, 04:31:37 AM
I need to modify my prediction. Hycom does show thicker ice still blocking the northwest passage however it looking at worldview it is thicker floes frozen in place by thinner ice. That thinner ice will allow the channel to clear when the rest of the channel clears.
Title: Re: HYCOM
Post by: interstitial on July 08, 2020, 12:47:27 AM
New Ice thickness. Still on track for melt of large section of Greenland sea and Baffin bay on 7/10-7/17. The CAA can get tricky to predict. I still like this model better.
Title: Re: HYCOM
Post by: ajouis on July 08, 2020, 08:29:06 AM
Today’s bremen comforts the accuracy of the forecast, at least somewhat, the baffin and hudson abrupt losses were even anticipating a bit, but it is to be expected in a predictive model, not everything aligns the model’s way
Title: Re: HYCOM
Post by: interstitial on July 08, 2020, 07:19:52 PM
Agreed. I am thinking a 10 cm especially the last 10 cm is not that much and thinking that it could predict that precisely was to optimistic. That is not what I wanted the model for anyway. Mostly I just like to see how thick the ice is and how much it is actually melting. Otherwise I look at it and wonder why it hasn't melted already or why it all just disappeared. At first I was trying to convince others of its accuracy. After comparing several floats in the CAB I am convinced that it is more accurate than Piomas. Where there are discrepancies I trust Hycom more than Piomas. People have complained it is reporting a maximum thickness but if that is true it still shows thinner ice in more places than Piomas. It is not perfect. In the western side of northwest passage thicker ice froze in place. Hycom shows the thicker ice. Piomas shows it as thinner. Worldview shows reality thicker ice frozen in place.
Title: Re: HYCOM
Post by: interstitial on July 08, 2020, 11:16:23 PM
here
Title: Re: HYCOM
Post by: uniquorn on July 09, 2020, 12:34:00 AM
Another big thing it is saying is the bueafort ice is not as stable as it appears. I expect large late season losses there.
Thanks for the study on Hycom. The model is useful for comparison. Despite repeated assertions by some on the melting thread based on extent, amsr2-uhh doesn't show Beaufort looking stable imho.
jun4-jul8
Title: Re: HYCOM
Post by: johnm33 on July 11, 2020, 11:49:40 AM
The sea ice concentration gif shows imho that the whole pack has softened and will no longer hold a crack, an alternative is that the whole Arctic is becalmed? [18:06-17:07]
(https://media.giphy.com/media/l0FQB0AZDXG4ISsj5U/giphy.gif)
Title: Re: HYCOM
Post by: meddoc on July 11, 2020, 12:02:09 PM
HYCOM- as I stated couple of times before- switched from ArCc to Glb (whatever it should mean) I think back in 2017. They simply ripped off huge Portions of 2m + thick Ice.

I'd have the previous Models' from 2016, but had to make some space available on hard drive.
Title: Re: HYCOM
Post by: Jim Hunt on July 11, 2020, 12:53:25 PM
HYCOM- as I stated couple of times before- switched from ArCc to Glb (whatever it should mean)

It's short for "Global". As in "Global Ocean Forecasting System".

Quote
They simply ripped off huge Portions of 2m + thick Ice.

Not exactly! They started assimilating concentration, amongst other things. Chapter and verse is available at:

https://forum.arctic-sea-ice.net/index.php/topic,1602.msg84108.html#msg84108
Title: Re: HYCOM
Post by: Jim Hunt on July 11, 2020, 12:54:32 PM
I would appreciate a posting of Hycom Apr 15th and Cryosat Apr 15th side by side somewhere, maybe in the new Hycom thread. I would look for differences where the anomalies were supposed to be - near Svalbard, in the Beaufort, and in the ESS.

Here you go:
Title: Re: HYCOM
Post by: interstitial on July 11, 2020, 01:02:53 PM
I rearranged the scale bar to emphasize how inconsistent the fading from one color to the next is. Look at each meter and see how many colors it has. I think they did this to emphasis certain threshold values. That is just a guess. 
Title: Re: HYCOM
Post by: interstitial on July 11, 2020, 04:33:40 PM
HYCOM- as I stated couple of times before- switched from ArCc to Glb (whatever it should mean) I think back in 2017. They simply ripped off huge Portions of 2m + thick Ice.
I'd have the previous Models' from 2016, but had to make some space available on hard drive.
I don’t have many of the old ones but I was able to find some. From what I can see in those areas where thickness was reduced in the new model it was not reduced by a set amount everywhere. The change mostly seemed to affect ice thicker than 2.8 meters.  Some of the thicker ice was left unchanged.
It is my understanding that ice can grow to around 2 meters thick at most in one year. After that growth slows way down. If none of that ice melts how much ice would be added next season? A meter? Maybe but I doubt it. That wouldn’t be ice growth slowing way down. I don’t know the answer. In previous years the oldest ice known as perennial ice could get to 9 years old or older. It took about that long to get to 4 meters thick. https://earthsky.org/earth/decline-of-arctics-thickest-sea-ice (https://earthsky.org/earth/decline-of-arctics-thickest-sea-ice) The amount of ice that is 4 years old or older is almost non existent as shown by graphic below. https://svs.gsfc.nasa.gov/4750 (https://svs.gsfc.nasa.gov/4750)
They updated the model for a reason and the data they got after the update was more accurate than the data they got before. Otherwise they would have stuck with the older model.
Looking at the area from 80N in the quadrant facing Europe and not near an island Hycom shows thickness up to about 2 meters on April 15. The same area on Piomas shows not less than 3 meters. The buoy data I have seen showed in that area at that time ice up to about 2.1 to 2.2 meters thick. Frankly Piomas shows about 2/3rds of the arctic thicker than 2.75 meters in April. It also shows a quarter of the central arctic thicker than 3.5 meters thick. There is almost no ice 4 years old or older and I doubt much if any ice younger than 4 years gets that thick. I think Piomas become an inaccurate model about the time the older ice all melted.
 
Primarily Piomas uses an Ice growth equation based on temperature and time and location when the ice moves. Solar flux ice extent and concentration are also factored in. Recently they added surface ocean temperatures on ice free areas to the mix. Salinity is fixed. A fixed current is used. Sea water under the ice is assumed to be a uniform layer in each grid element. No atmospheric or ocean modeling is done. Near as I can figure it is an academic pursuit probably put together by a professor and grad student around 2003.  It does get updated from time to time but there is no dedicated staff. 
The Hycom model is built from first principles. The atmosphere and ocean are modeled globally.  Currents change as conditions change. It also has more than one full time staff member and a budget. I have written more about in this thread and you can dig into it if you really want to know. The Hycom model is frequently updated so comparisons should be made with the same version. They also do not produce a volume total. Which I find disappointing because we like our spreadsheets on ASIF.     
Title: Re: HYCOM
Post by: interstitial on July 11, 2020, 04:35:43 PM
and the rest
note white bar is the sea ice over 4 years old.
Title: Re: HYCOM
Post by: Comradez on July 11, 2020, 04:56:39 PM
The two look surprisingly similar!  Shouldn't this increase our confidence in HYCOM? 

If so, I think I like HYCOM a little more just because it has such higher resolution. 
Title: Re: HYCOM
Post by: oren on July 11, 2020, 04:59:53 PM
I remind again that PIOMAS models pressures ridges when ice is transported, which is how it can get above the thermodynamic growth limit for ice thickness.
I know nothing of the details but can see the results, e.g. near Svalbard. Is that thick ice really there? I honestly don't know.
Title: Re: HYCOM
Post by: Laurent on July 11, 2020, 05:09:01 PM
Source: https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/arctic.html
(hycom ARC is an older model that allows US ships to choose an ice-free route - it is slightly less accurate than the new model to ensure that ships will not encounter ice).
https://www7320.nrlssc.navy.mil/hycomARC/arctic.html
The data not being available for 2019, I have recovered the image of the proposed 1-year animation.
The comparison data with the ARC model ( the one for 2012) are to be taken with big tweezers, although it is the same color scale! 2012 because the volume record took place in 2012.
Title: Re: HYCOM
Post by: interstitial on July 11, 2020, 06:14:19 PM
I remind again that PIOMAS models pressures ridges when ice is transported, which is how it can get above the thermodynamic growth limit for ice thickness.
I know nothing of the details but can see the results, e.g. near Svalbard. Is that thick ice really there? I honestly don't know.
I think pressure ridges explain thickness near land masses and some elsewhere but I doubt 50% of the central arctic adds a meter by that mechanism. Hycom shows some thick ice in the same areas around land masses but my main concern with Piomas is it shows much thicker ice in the bulk of the Arctic.

I did not start out intending to doubt Piomas I just thought Hycom had value too. It is so much work to write up what I find that I often don't do it. I don't know how fast other are but for me my last post on this thread took about seven hours. AFAIK    few have attempted to countered my claims and they claimed in the area described in my last post that one buoy was tethered on a 7 meter thick chunk of ice. It is certainly possible but I am not sure if is is even true. I think he may have said that because i didn't post the bouy data. Mostly the main anti Hycom comments are someone else said piomas was a better model and I don't think the ice is that thin. Back in 2003 it probably was a great model and that was probably when the opinion was formed. Things change I am constantly trying to explain that what was true then may not be true now. I once had an argument with a guy who insisted that heat pumps did not work below 0 C. Maybe that was true a long time ago but things change. In the Arctic almost all the 4 year old  or older Ice melted. That implies all the thicker ice melted and younger ice normally doesn't get that thick.
Title: Re: HYCOM
Post by: interstitial on July 11, 2020, 06:20:11 PM
Thanks Laurent. I didn't think that data was still available.
Title: Re: HYCOM
Post by: oren on July 11, 2020, 10:05:41 PM
Quote
few have attempted to countered my claims and they claimed in the area described in my last post that one buoy was tethered on a 7 meter thick chunk of ice. It is certainly possible but I am not sure if is is even true. I think he may have said that because i didn't post the bouy data.
A. That was me...
B. That 7 m thick floe is true. The Mosaic people put the buoy there and they measured it. The information was posted by uniquorn in another thread.
C. I really don't know how reliable PIOMAS and/or Hycom is.
D. I will pay more attention to Hycom this melting season.
Title: Re: HYCOM
Post by: interstitial on July 11, 2020, 11:55:15 PM
Oren: At the time I read the 7m commment it struck me as odd. Sometimes I over think these things. Your comments have been helpful. Thank you. My search for buoys was not exhaustive but that is what I found. I wonder if my commentary has been helpful and people do not have a response or if people are just ignoring it. I can get a bit ......       Sigh......    Moving on. End post.
Title: Re: HYCOM
Post by: uniquorn on July 11, 2020, 11:59:10 PM
https://data.meereisportal.de/download/buoys/photos/2020T61_deployment.pdf

There are a lot of other deployment data in the photos directory. Mosaic photos on fomo (https://follow.mosaic-expedition.org/) or twitter show much more ridging than I was expecting but despite being thicker, ridged ice doesn't have the same structural integrity as thermo.

Keep up the good work interstitial :)
Title: Re: HYCOM
Post by: interstitial on July 12, 2020, 12:02:50 AM
Thanks uniquorn.
Title: Re: HYCOM
Post by: oren on July 12, 2020, 12:14:45 AM
Your commentary has been very helpful. I am guessing people have nothing useful to add to it at present.
Title: Re: HYCOM
Post by: uniquorn on July 12, 2020, 12:25:09 AM
Re- ridging, looking back through the mosaic panorama images (https://www.mosaic-panorama.org/?cu=en-GB#) may be useful.
Title: Re: HYCOM
Post by: FishOutofWater on July 12, 2020, 01:02:09 AM
Over the past few decades the loss of thick multi year sea ice, and the presence of more open water and larger waves has led to more ridging. Because Hycom has been updated and improved it is difficult to use it to analyze the changes in Arctic sea ice thickness over the years. The new version of Hycom is probably a better model than PIOMAS to understand what the ice is doing NOW but it is inferior for inter year comparisons that involve years before the change to the GLB - global model. The new GLB version is a major improvement that is hard to compare to the maps of the old Hycom.
Title: Re: HYCOM
Post by: johnm33 on July 12, 2020, 11:44:34 AM
"Keep up the good work interstitial  :)" +1 and thanks.
Title: Re: HYCOM
Post by: interstitial on July 12, 2020, 06:49:48 PM
One of the issues with either model is resolution. Ridging strikes me as something best described on the meter scale and both models only work down to the multiple kilometer scale. Resolution also comes into play when looking at thick ice flows frozen into place. I have included an image of Mclure strait on worldview. Is it as thick as the thick ice flow or more like the fast ice holding it together or an average based on area of each thickness. Hycom’s guiding principle is to indicate the maximum thickness rather than estimating volume. If Hycom made a volume estimate I am confident it would be a lower estimate than Piomas. I made that point before but I have examples of Hycom that are instructive. Hycom shows the Mclure strait at around 2 meters thick  but the fast ice holding it together is probably under a half meter if I had to guess. Not a great image of the Beufort but that ice all appears thicker and does not appear thicker in hycom some of shows thinner. When I looked at the first Chukchi image I was surprised that that boot shape showed up as thick as it did since there is a very low concentration of ice. When I looked above it I was even more surprised as there is almost no ice there at all. Look at the upper left corner. When I look at the Hudson I do not think they factor in concentration at all. In worldview the band of higher concentration on the left that only slightly shows on Hycom. On the other hand looking at worldview there is now indication of a thicker chunk in the middle. That green is around 2 meters thick while the purple around it is closer to half a meter thick. I am not sure why I included Greenland.
The main takeaway here is use a concentration map or satellite image when looking at Hycom thickness. 
Title: Re: HYCOM
Post by: interstitial on July 12, 2020, 06:52:29 PM
and the rest
Title: Re: HYCOM
Post by: interstitial on July 12, 2020, 06:54:04 PM
okay maybe one more
Title: Re: HYCOM
Post by: interstitial on July 12, 2020, 08:13:22 PM
If I can read this right and I am not sure about that. This buoy reads 85 cm of ice on 7/10 for that location hycom shows about 200 cm.
Title: Re: HYCOM
Post by: uniquorn on July 13, 2020, 12:17:05 AM
dtc's are 2cm apart

https://www.cryosphereinnovation.com/simb3
Quote
Bruncin 3.85m DTC
192 dtc values

so maybe 170cm, I didn't check your estimate
Title: Re: HYCOM
Post by: oren on July 13, 2020, 05:08:32 AM
Image of ridging, from Mosaic:

"Heavily ridged sea ice seen off the bow of the ship during ice observations on 14 June (Photo: Luisa von Albedyll / AWI)."
(https://www.meereisportal.de/fileadmin/user_upload/www.meereisportal.de/_processed_/3/5/csm_MeereisportalTicker_40_Bow_Ridged_ice_smaller_f70c1e30c4.jpg)
Title: Re: HYCOM
Post by: interstitial on July 13, 2020, 10:57:14 PM
Thanks for the correction Uniquorn.
Oren: It appears my understanding of ridging may be flawed. I was picturing a line of ridging here and a line there not a region of ridging. Your insights are helpful as always.


To everyone reading. Though it is time consuming and humbling I learn more when I post things and get corrected than when I just read others posts. I am not here to win arguments mostly I just like to know how things work.

Title: Re: HYCOM
Post by: HapHazard on July 13, 2020, 11:03:11 PM

To everyone reading. Though it is time consuming and humbling I learn more when I post things and get corrected than when I just read others posts. I am not here to win arguments mostly I just like to know how things work.

That's why your posts are awesome & I'm sure many more readers here than myself also learn a lot right along with you.  :)
Title: Re: HYCOM
Post by: interstitial on July 16, 2020, 09:43:21 AM
The forecasts do not show when the final bit of ice melts out. The forecasts seem to show white until every spec of ice melts out. This forecast shows a little more melt in a number of places but not all. More melting appears in the central arctic seas in the forecast than in the next day image. This is shown by less purple turning white in the next day compared to the forecast in the central seas the CAA and Hudson.  A bit of 5+ meter ice north of Greenland is reduced to less than 2 meters in the next day but not the forecast. A bit more green (1.8 meter) ice melts in the next day compared to the forecast.


Overall thinner(purple) ice melted more in the forecast than the next day. Specific chunks of thicker ice melted more in the next day than the forecast.
Title: Re: HYCOM
Post by: interstitial on July 19, 2020, 09:30:15 AM
Hycom 7/18/2020
Title: Re: HYCOM
Post by: ajouis on July 19, 2020, 11:12:41 AM
Piomas is getting quite different from hycom, especially on the beaufort and chuchki front
Title: Re: HYCOM
Post by: interstitial on July 19, 2020, 05:47:02 PM
When comparing Piomas to Hycom for 7/15  I note similar things to what I have seen before. Zoom in a bit to compare.
Piomas resolution does not allow it to show some small but thicker chunks amidst thinner ice.
Piomas ignores ice concentration below 15%
Hycom for operational reasons shows the upper limit of possible ice thickness in an area. Piomas is supposed to estimate volume but Piomas shows thicker ice than Hycom.
Hycom shows ice if even one fine chunk is visible. This is frustrating during melting season. I prefer Piomas in this.
Each Piomas color is 0.25 m thick and by counting shades from yellow which is easy to identify thickness ranges can be determined. Piomas shows the ice about 0.5 m thicker than Hycom in Beufort. In Chukchi and ESS Piomas shows thickest ice in the middle where Hycom shows some thicker ice near the edge and around 80 N latitude. North of Laptev to about 85 N shows mostly thinner than 0.5 m thick ice on Hycom and thicker Piomas shows ice mostly thicker than 1 m. To the west of the Anzhu islands Hycom shows a chunk of 2 meter ice. Piomas shows no more than 0.75 M. North of Svalbard Piomas shows 1.75 – 4.00 m thick ice. Hycom shows the ice is not over 1 m thick. North of Greenland and CAA shows a significant swath of over 3 - 4 m thick ice on Piomas. The same location on Hycom shows most of that ice is less than 2.25 m thick with small thicker sections up to 4.5 dispersed throughout. The southern CAA shows no ice in spots that worldview show full of ice with some cracking. Hycom in the same area shows ice 0.25 – 1.75 m thick.
Title: Re: HYCOM
Post by: Tom on July 19, 2020, 10:12:20 PM
Piomas also shows ice that isn’t really there.  I noticed in particular around the islands east of Svalbard.  Attaching a mostly cloud free pic from 2 days before.  Hycom seems to match better what can be seen in worldview.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2F&hash=35d7d5d7526c9897dfb55501e320295a)
Title: Re: HYCOM
Post by: grixm on July 19, 2020, 10:43:53 PM
Piomas also shows ice that isn’t really there.  I noticed in particular around the islands east of Svalbard.  Attaching a mostly cloud free pic from 2 days before.  Hycom seems to match better what can be seen in worldview.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2F&hash=35d7d5d7526c9897dfb55501e320295a)

PIOMAS does not try to accurately model the ice edges, only the average thickness of an area *if* there is ice there. To calculate the volume it uses external data for area and thus it doesn't count ice in locations that the area data says there is no ice in, even if PIOMAS has modeled a thickness above 0 there.
Title: Re: HYCOM
Post by: Tom on July 19, 2020, 11:12:53 PM
Thanks for that info.  It’s been bugging me for a while that the images didn’t seem to reflect reality in worldview, especially since I knew it incorporated area data, but that makes much more sense if it’s using the area data as a mask to produce the volume numbers from the model output.
Title: Re: HYCOM
Post by: oren on July 20, 2020, 02:47:48 AM
Quote
Hycom for operational reasons shows the upper limit of possible ice thickness in an area.

I am certain this is not true. The 7m floe example upthread should have been enough to refute this. But in general pressure ridges in all regions exceed the Hycom thickness, which I assume represents an average, not maximum.
Title: Re: HYCOM
Post by: interstitial on July 21, 2020, 03:25:33 AM
Quote
Hycom for operational reasons shows the upper limit of possible ice thickness in an area.

I am certain this is not true. The 7m floe example upthread should have been enough to refute this. But in general pressure ridges in all regions exceed the Hycom thickness, which I assume represents an average, not maximum.

I respectfully disagree. They searched for thick ice for a long time before they found that particular 7 meter thick chunk or the 6 meter thick one nearby. When I saw images I realized that these were not tiny areas like the size of a house but more like a few kilometers.  Most of the rest of them near the polarstern showed much thinner ice. There was some concern they wouldn't be able to find a good spot to begin. It was ridging which seems to be picked up near shores but maybe not elsewhere? Is it much rarer? Maybe it is more localized? In any case I would consider it more likely to be a model failure than indication of anything. In the Greenland sea it starts should melt quickly. Maybe not this year but most of thickness will probably melt before the freeze season.

The phrasing I used was not precise enough. Looking at submarine lidar scans of the underside of ice sheets show long spike like structures from above. I do not think anybody considers that part of thickness. What is less obvious is how to report the thickness of thicker flows frozen in place by thinner ice. If you are modeling volume a weighted average is appropriate. That is what I think Piomas tries to do. I don't know for certain what either model does. A few weeks back I noticed an area in the CAA that showed much thicker ice in Hycom than Piomas by about a meter or so. Almost everywhere Piomas shows thicker ice than Hycom. Correct me if I am wrong but I believe this is why Oren assumes Hycom must be an average. This location stood out to me. I looked at the location in Worldview and it was clearly thicker ice frozen in place by thinner ice. White chunks surrounded by darker ice thinning to see water underneath and cracking. My interpretation  is Piomas shows the average thickness and Hycom shows thickness of the thicker ice.  I have heard it before on this forum but I looked for and never found any such statement on Hycom. It made sense on an intuitive level that marine vessels would benefit more from over rather than under reporting of ice. That is not the only reason I think it is true. I have heard from some on the forum that really thick sea ice appears to melt quickly. That makes more sense if those are thick ice surrounded by thinner ice. Hycom still shows thin ice when at maximum magnification I see one small spec of ice in a much larger area. Any location that currently shows ice will show at least thin ice (0-5 cm thick) in their forecast. The nowcast mostly shows a thin ribbon of this really thin ice but always in small areas. Once you are aware of it it is easy to spot the difference between a nowcast and an 8 day forecast without looking at the dates. Hycom does not report a volume. If they were showing average thickness I would expect them to report a total volume.  These things together support the idea that the model is looking to over rather than under report thickness IMO.
Title: Re: HYCOM
Post by: oren on July 21, 2020, 04:52:39 AM
Quote
If you are modeling volume a weighted average is appropriate. That is what I think Piomas tries to do. I don't know for certain what either model does. A few weeks back I noticed an area in the CAA that showed much thicker ice in Hycom than Piomas by about a meter or so. Almost everywhere Piomas shows thicker ice than Hycom. Correct me if I am wrong but I believe this is why Oren assumes Hycom must be an average. This location stood out to me. I looked at the location in Worldview and it was clearly thicker ice frozen in place by thinner ice. White chunks surrounded by darker ice thinning to see water underneath and cracking. My interpretation  is Piomas shows the average thickness and Hycom shows thickness of the thicker ice.
Yes, PIOMAS models a weighted average (but divides the volume in a grid cell by its full cell area, not by just the ice area in the cell).
I assume Hycom is an average because it would surely have shown higher thickness if it were to show maximum thickness in a grid cell. Weirdly thick floes are found in various regions of the Arctic, and I am sure the 7m floe was not the only one. I can't prove it as I don't have the data or even the knowledge to back this up in detail.
That PIOMAS shows higher volume than Hycom could be a result of PIOMAS modeling error, Hycom modeling error, or both. I believe the main difference would be the PIOMAS modeling of extra-thick floes resulting from pressure ridges.
Some insight into the PIOMAS model can be gained from the following charts produced by Wipneus from time to time. The distribution shown could be wrong or right compared to physical reality of course. But the model calculated roughly 300-400k km2, and 3000 km3, of ice thicker than 4.2m, as of June 30th last year.

Quote
As some will remember, ice in each gridcell in the PIOMAS model is specified as a discrete distribution: there exist 12 categories of ice thickness (m):
[0.00, 0.26, 0.71, 1.46, 2.61, 4.23, 6.39, 9.10, 12.39, 16.24, 20.62, 25.49]

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=119.0;attach=126765;image)

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=119.0;attach=126766;image)

Another difference between the models is that as far as I am aware, Hycom does not cut off ice below 15% concentration, while PIOMAS does. Maybe Hycom does this for the reason that it is used by navy ships, so it gives maximum ice extent (but not maximum thickness as has been speculated).

As for the anomaly in the CAA, I am quite sure it was caused by anomalous behavior of NSIDC ice concentration data that at some point showed open water in the location, though in real time full ice cover (of very blue color) could be seen on Worldview. NSIDC is sensitive to melt water over the ice, and when the melt water is deep enough and widespread enough it does not "see" the ice in that grid cell. PIOMAS uses NSIDC concentration data as a constraint, so when NSIDC reports zero ice PIOMAS reports zero volume. Later when the melt water drained NSIDC brought the ice back, and PIOMAS brought only some of the volume back. In this case PIOMAS is clearly wrong.
Title: Re: HYCOM
Post by: ajouis on July 21, 2020, 10:33:34 AM
Quote
As some will remember, ice in each gridcell in the PIOMAS model is specified as a discrete distribution: there exist 12 categories of ice thickness (m):
[0.00, 0.26, 0.71, 1.46, 2.61, 4.23, 6.39, 9.10, 12.39, 16.24, 20.62, 25.49]

I think that piomas could do with a tightening of the scale, because apart from ice cap calving (which should not count towards piomas as it is not sea ice), I do not really see the use of the 10+ meters thickness
Title: Re: HYCOM
Post by: oren on July 21, 2020, 01:13:57 PM
From Wikipedia (https://en.wikipedia.org/wiki/Pressure_ridge_(ice)), bolding mine:
Quote
Pressure ridges are the thickest sea ice features and account for about one-half of the total sea ice volume.

Quote
One of the largest pressure ridges on record had a sail extending 12 metres  above the water surface, and a keel depth of 45 metres. The total thickness for a multiyear ridge was reported to be 40 metres. On average, total thickness ranges between 5 metres and 30 metres, with a mean sail height that remains below 2 metres.

I don't know much about the subject, and am unable to evaluate the validity of the quoted numbers, but it seems a volume model must take pressure ridges into account in order to properly estimate total volume.
The end-June >4.2m volume in the chart above was about 25% of total volume in 2019 according to PIOMAS, while in the past it reached 35%-40%, still less than the half cited by Wikipedia.
Title: Re: HYCOM
Post by: ajouis on July 21, 2020, 07:40:07 PM
Oren, I do not doubt the importance of pressure ridges, but it seems to me that given the difficulty of finding a 7 meter floe, and there already vanishing area on the map, the 10+ ones have just melted away, couldn’t find any source one way or the other thiugh 
Title: Re: HYCOM
Post by: interstitial on July 21, 2020, 08:27:32 PM
Oren:
[/color]Yeah I am not an expert either I am just trying to dig up answers in doing so I make assumptions. Your experience helps me to identify at least some of the flaws in my assumptions. I based my opinion of the Piomas model on the description I read and the low resolution image Wipneus supplies. These charts are new to me. Clearly the output by Wipneus is not the model output. Looks like I need to learn more about Piomas to make a reasonable assessment.
[/color]
[/color]Chart by thickness indicate about 5% of the area is thicker than 4.2 m I do not think the map shows that. The scale does not indicate ice thicker than 4 m. My flawed assumption was the average thickness of any grid cell was no greater than 4 m. Ice that was 7 m thick would have to be surrounded by enough thinner ice to bring the average down to 4 m thick.
[/color]
[/color]With pressure ridging creating 50% of volume as you site or 40% of volume as the article cited in the wiki changed to a 2000 paper. I am not sure which is newer or likely to be more accurate.
[/color]
[/color]I do not assume all pressure ridges must be thicker than 4.2 m. The citation that says “On average, total thickness ranges between 5 metres and 30 metres” leads to a book with a 2005 publication date. The book is pay walled but it probably cites an earlier article. This observation is at least as old as 2005 but likely before 2003. 
[/color][/size] [/font]
[/color][/size]In September 2003 when around 1.9 million km2 was 4 years old or older. As compared to September 2019 when around 50,000 is 4 years old or older and [/font]
[/size]https://svs.gsfc.nasa.gov/4750 (https://svs.gsfc.nasa.gov/4750) [/color]It is a different arctic. [/color]
Title: Re: HYCOM
Post by: oren on July 22, 2020, 03:34:46 AM
All good points interstitial. The only thing I know for sure is that PIOMAS calculates an average of the various thicknesses inside a grid cell, and the color shown on the map represents the average in that grid cell. The map shows no more than 4m, but this could be comprised of 10% ice that is 13m, and 90% ice that is 3m. Only someone who can analyze the raw PIOMAS output files can elaborate more than this, or show the distribution rather than just the average. I have long desired this technical ability, but I still lack it.
For example, one could produce a map showing concentration of ice at a given thickness or above. This map could be compared to common sense, to the ice age map by NSIDC and to findings "on the ground". Let's say the map said a certain grid cell had 10% of 13m ice. A research vessel or underwater robot could do statistical sampling and test this in real life.
Or one could produce a map showing concentration of ice <0.26m in each cell, and compare this to actual ice area drops a week or two later, assuming 26cm of thickness are lost in that time period. This could be a predictive tool, or help validate/invalidate the model.

It is very much possible that PIOMAS overestimates the amount of super-thick ice, as it was built at a time when such ice was more prevalent in the Arctic. However my limited knowledge both of PIOMAS and the actual state of the ice prevent me from making this judgement properly.

I remind this thread is about Hycom. Two types of questions arise, PIOMAS vs. Hycom, which we have discussed herein to the best of our abilities, but also Hycom itself, which I think we should try to address:
* Does Hycom model pressure ridges creation in winter and their evolution in summer? Is there a way to find out?
* Does Hycom have numerical outputs, besides the map and animation? Is there a chart of total Hycom volume? If so, how long does it go back in time?
* Does Hycom have a regional breakdown of data? (As Wipneus produces for PIOMAS from the gridded output files)

Assuming that Hycom has been greatly improved and is by now the better model, as has been hinted above, these questions could determine its usefulness within the forum context.
Title: Re: HYCOM
Post by: interstitial on July 22, 2020, 09:52:18 AM
* Does Hycom model pressure ridges creation in winter and their evolution in summer? Is there a way to find out?
* Does Hycom have numerical outputs, besides the map and animation? Is there a chart of total Hycom volume? If so, how long does it go back in time?
* Does Hycom have a regional breakdown of data? (As Wipneus produces for PIOMAS from the gridded output files)
No numerical data I can find of a reasonable size. Your welcome to download the 50+ Gb daily data file and try to extract it from that or convince someone else too. I have a decent internet connection but my internet provider would shut me down if I tried to do that.
Alternatively I have considered writing a script to count pixels for each color however I decided without accounting for map distortion it would be too inacurate. I thought about masking for rings and multiply some scaling factor for each thin ring. I would have to learn more about map types and distortions. I have an inkling of how to proceed but I am not sure I want to know that badly. My coding skills are slow and not great. I would spend more time learning to code than I would coding.

Hycom changes their model occasionally when they do they recalculate some historical data to judge performance. The Last time they went back to 2014.

Yes I get the thickness average idea. The problem is Piomas says they calculate each cell as if conditions were uniform inside the cell. Thats a mess.
Title: Re: HYCOM
Post by: ArcticMelt2 on July 22, 2020, 02:48:42 PM
From Wikipedia (https://en.wikipedia.org/wiki/Pressure_ridge_(ice)), bolding mine:
Quote
Pressure ridges are the thickest sea ice features and account for about one-half of the total sea ice volume.

Quote
One of the largest pressure ridges on record had a sail extending 12 metres  above the water surface, and a keel depth of 45 metres. The total thickness for a multiyear ridge was reported to be 40 metres. On average, total thickness ranges between 5 metres and 30 metres, with a mean sail height that remains below 2 metres.


The compression ridge in the Hudson Bay is now clearly visible. How thick is the ice in it? 2-3 meters?
Title: Re: HYCOM
Post by: johnm33 on July 25, 2020, 09:59:06 PM
(https://media.giphy.com/media/kZiICJdJnntavifNDg/giphy.gif)
Hycomsss main interest here is the outburst from 79N/Zacheriae
Title: Re: HYCOM
Post by: interstitial on July 26, 2020, 01:43:14 AM
<snip same gif as below>
Hycomsss main interest here is the outburst from 79N/Zacheriae
Is this salinity? for what days?
Title: Re: HYCOM
Post by: blumenkraft on July 26, 2020, 07:36:20 AM
Hycomsss = Hycom sea surface salinity i assume.
Title: Re: HYCOM
Post by: johnm33 on July 26, 2020, 09:47:59 AM
Yes current sea surface salinity hind/forecast at time of posting so 03:07-01:08
Title: Re: HYCOM
Post by: be cause on July 26, 2020, 10:44:13 AM
Hi folks can you load gifs as click and play .. the page won't load for me .. too much going on .. b.c.
Title: Re: HYCOM
Post by: blumenkraft on July 26, 2020, 11:02:26 AM
Something Freegrass and i found out only recently: Externally hosted GIFs (via [ img ] tag linked files from other websites) will autoplay (automatically download), no matter the canvas size.

If you want your GIF to behave to forum rules (click to play) you have to upload it to the forum server as an attachment to your post.

A GIF should always be >500 pixels (in at least one direction) in order to save data traffic.

Very small GIFs (smaller than 1MB of file size) can be below this canvas size. It doesn't hurt too much traffic-wise if those would auto-play.
Title: Re: HYCOM
Post by: oren on July 30, 2020, 04:04:29 AM
Discuss Hycom and its reliability here.
Title: Re: HYCOM
Post by: OffTheGrid on July 30, 2020, 04:48:21 AM
Here are todays concentration and thickness charts.
And the same day in 2014 which is the first year the arctic only model was replaced with the global model with weather and ocean data incorporated for prediction purposes.
Does my memory correctly recall that 2014 was the year piomass was updated for the last time? Along with a quiet media release forgotten or missed by most that they believed the piomass model had understated the 2012 minimum, and they revised it upwards?
I think this may be a little charitable for concentration in the central and coastal Beaufort, judging by worldviews.
Title: Re: HYCOM
Post by: OffTheGrid on July 30, 2020, 04:58:58 AM
For comparisons, piomass monthly Thickness averages July/ Aug 2014.

Reverend milkbones 29 July 2012, thickness, also from the previous arctic only Hycom model. Still looking for Pio2012
Title: Re: HYCOM
Post by: interstitial on August 02, 2020, 12:47:28 AM
OffTheGrid
The concentration drops after the recent storm. I suspect that the difference may be in large part due to different timing. I haven’t checked but between time zones and such events labeled the same day could reasonably be almost 48 hours apart. I have included a 7/31 forecast for 8/1 concentration after the storm which seems like a more accurate picture now. The 7/28 concentration forecast for 7/29 does show a significant portion of the Beufort in the 50 to 60% range. To my eyes it shows most of the Beufort less than 85% concentration.
Title: Re: HYCOM
Post by: OffTheGrid on August 04, 2020, 09:00:06 PM
Unfortunate that Hycom has seemingly decided to censor the higher resolution Beaufort model. Its last run on the 24th of July looks like a darn good effort in advance of the accurate picture SMOS is presenting. Bearing in mind that the Soil Moisture/ Ocean Salinity sensor works on detecting the averages over a 40km square grid between the less salty ice surface and the horizon of slush soaked with seawater below.
Its low frequency radar sees straight through ice and water cloud, including fog. The maximum resolution of the higher frequency radars used by Jaxa, etc for their much more promoted extent and area metrics, is at the expense of being badly compromised by cloud effects. And they are still limited to about 500m resolution, so do not see open water below that breadth. A bigger and bigger problem in this season every year. Hycom is probably suffering from falling behind in the need to update algorithims to account for these rapidly crumbling models Its assimilating data from.
Ice crumbling to fields of dispersed slush is far different to solid sheets with crosshatchings of long leads.
Other than the Chukchi not getting the Beaufort arm shoved as far into it, and more ice surging into mckenzie bay from the CAA mega flow than Hycom predicted before the storm, good predictive skill I think. Backed up by what satellite visuals we've had through the clouds and fog.
Still have to click to animate the absurdly small smos gif.
Title: Re: HYCOM
Post by: interstitial on August 05, 2020, 01:54:19 AM
The most recent update I see is May 2020 so I think they update whenever they identify something that needs fixing. I really don't think Hycom incorporates data from other models. It is a global oceanic model coupled with atmospheric forcing from their own atmospheric model. it does use a concentration map but it does not seem to suffer from the same anomalies from storms. They may use the same raw data and filter it I really do not know at this time. I am doing a deeper dive into the system. My real frustration is output data runs about 50 gb a day. I have located some smaller subsets of data but the smallest is 380 mb a day sea surface height.
Title: Re: HYCOM
Post by: JNap on August 06, 2020, 01:23:53 AM
Here is the current August 3rd run from Hycom.  The first pic is the current state of the ice.  The next one is their forecast for the ice on August 11th.  Also attached links for people to navigate there themselves.

https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticict/nowcast/ict2020080312_2020080400_930_arcticict.001.gif (https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticict/nowcast/ict2020080312_2020080400_930_arcticict.001.gif)

https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticict/nowcast/ict2020080312_2020081100_930_arcticict.001.gif (https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticict/nowcast/ict2020080312_2020081100_930_arcticict.001.gif)



Title: Re: HYCOM
Post by: glennbuck on August 06, 2020, 03:05:28 AM
While HYCOM seems accurate around North Greenland for the 11th August. It has 2-2.5 Metre thick ice where it is open sea in the Northern coast of Ellesmere Island in northern Canada, near the Ward Hunt Ice Shelf in the Arctic Ocean, across for 150 miles west on the 6th August!
Title: Re: HYCOM
Post by: Rod on August 06, 2020, 03:12:45 AM
I really have my doubts about that model.

Look at all the ice that it says is less than 1m thick.  If it is correct, then we just need to average about 3cm per day, top and bottom melt combined, to have a BOE (defined as less than 1 million square km) in about a month.

That seems unlikely.
Title: Re: HYCOM
Post by: interstitial on August 06, 2020, 04:24:05 AM
Glenbuck:
Please do not confuse concentration and thickness they are only very loosely correlated. Concentration does not care about thickness it measures only what fraction of ice to open water. 1 meter thick 10 meters thick concentration makes no distinction.

Title: Re: HYCOM
Post by: interstitial on August 06, 2020, 06:57:08 AM
Rod:
It is ok to doubt the model. I do not I doubt the model I doubt your melt assumptions. I have seen melt numbers estimating 5cm a day this season but that seems extremely high to me. At that rate 2 m melts in 40 days. I think we can agree when thick ice gets transported out of the region melt rates are higher than melting in place but we can mostly ignore that.
Looking at piomas model I see ice thinning by 1 m between 4/15 and 7/15. In less central locations the ice thins 1.25 m while in more central locations the ice thins by 0.75m. That is a melt rate of 8mm to 14mm per day. I also looked at Hycom on the same dates and came up with similar numbers. 7/15 includes about 4 weeks after the solstice. We are now almost three weeks beyond that. We are getting close to the time when the CAB normally starts to refreeze. The Beufort will probably melt to the end.
It has been said in past melt seasons that there is enough heat in arctic ocean to melt all of the ice if it mixed thoroughly. The melting along the Greenland CAA coast seems to be from Eckmen pumping of heat from lower down. The right storm could also do it. One of the buoys shows freshwater protection breaking down. This may or may not be happening elsewhere. There was a lot of heat in the ocean in 2019 that did not do much at the end of last season. It could have gone the other way.
I don’t think we are getting a boe this year but looking at that thickness map and saying it will result in a boe is your interpretation and not mine. By the numbers the CAB loses another 400k km^2 of area unless something unusual happens. Even so If all the other seas melts out completely, which has not happened before, the central arctic would still need to lose another 1.6 million km^2 of area in addition to the 400k km^2. The region in which the ice is in makes a huge difference. By the numbers I would expect the Beufort to end with 500k km^2 but due to its location and thickness and concentration 250k km^2 seems likely.
By the way I am using 3.75km area numbers, which I think come from NSIDC, for my estimates. They will be different for other measurements. The more seasons I participate in the more nuances I see in the data. 
Title: Re: HYCOM
Post by: interstitial on August 06, 2020, 07:04:55 AM
The Hycom model grabs data from all the major cryosphere satellites and buoys and incorporates it daily. I also learned that ice thickness is mission critical because US nuclear subs often hide in the arctic under the ice but their wakes (Is it a wake on a submarine or something else?) are clearly evident to satellites when the ice thins. They do not mention what the critical thickness is but they do indicate the ice is too thin for much of the summer and leaves them vulnerable because the area under thick ice is too small to hide. This next bit is pure speculation on my part. I have previously commented on how the color scale clearly shows what ice is thicker or thinner than 135 cm. If I were a betting man I would suggest that is the critical thickness.
Title: Re: HYCOM
Post by: oren on August 06, 2020, 07:43:43 AM
Looking at piomas model I see ice thinning by 1 m between 4/15 and 7/15. In less central locations the ice thins 1.25 m while in more central locations the ice thins by 0.75m. That is a melt rate of 8mm to 14mm per day. I also looked at Hycom on the same dates and came up with similar numbers. 7/15 includes about 4 weeks after the solstice. We are now almost three weeks beyond that. We are getting close to the time when the CAB normally starts to refreeze. The Beaufort will probably melt to the end.

By the way I am using 3.75km area numbers, which I think come from NSIDC, for my estimates. They will be different for other measurements. The more seasons I participate in the more nuances I see in the data.
Thanks for your interesting post interstitial. A few notes:
* The CAB continues to accumulate volume until May 5th-10th, at least according to PIOMAS.
* Peak volume loss rate is between mid-June and end-July. Using Wipneus regional numbers, an area of ~4M km2 loses ~4000 km3, so about 1m over 6 weeks, roughly 2.5 cm/day. Of course this mixes up top melt, bottom melt and export/import.
* CAB normally starts actual freezing in early to mid-Sep, so at least a month away. Earlier we can see effects of melt water freezing on existing ice surfaces.
* If you mean 3.125km grid, it comes from UH (University of Hamburg) AMSR2 data. NSIDC uses a 25km grid.
Title: Re: HYCOM
Post by: Frivolousz21 on August 06, 2020, 07:51:18 AM
Glenbuck:
Please do not confuse concentration and thickness they are only very loosely correlated. Concentration does not care about thickness it measures only what fraction of ice to open water. 1 meter thick 10 meters thick concentration makes no distinction.

It looks really good.

If we had a major dipole we would crush 2012.

The ice is very thin all over.

This year is ending just like  2011
Title: Re: HYCOM
Post by: interstitial on August 06, 2020, 10:16:57 AM
Oren:
That is later than thought for volume but makes sense because the 4/15 date was selected to be prior to any melting so I had the images handy.
Thanks maybe I will try again with different dates but not today.
2.5 cm/day for 6 weeks around the solstice seems more reasonable than 3 cm/day from now until a month from now.
Title: Re: HYCOM
Post by: interstitial on August 06, 2020, 07:23:20 PM
Oren:
This response may not be well put together but it is informed.
JAXA produces their own 25km sea ice extent numbers
The NSDIC  has a 24 km^2 sea ice area and extent product
The NSDIC also has a 4km and 1km Multi-sensor analyzed sea ice extent (MASIE) products
All NSDIC data is archived at University of Colorado Boulder website
MASIE is produced primarily by NOAA utilizing primarily US satelites.
Japanese, US and EU share raw environmental satellite data with each other and coordinate instruments and coverage to maximize resources.
National Oceanic and Atmospheric Administration (NOAA US) operates a series of Polar and Geostationary Operational Environmental Satellites (POES/GOES US) with visible and infrared data. These are supplemented with visible data from Geostationary Meteorological Satellite (GMS Japan), Multifunction Transport Satellite (MTSAT Japan) and Meteorological Satellite (METEOSAT EU) data.
Microwave products from Defense Meteorological Satellite Program (DMSP US) and Advanced Microwave Scanning Radiometer (ASMR-E Japan). 
Synthetic Aperature Radar imagery (from?), surface observations and National Weather Service (NWS US) weather prediction models and whatever other data they can find stuck in the couch cushions are also used.
The above data is used by NOAA analysts to create the Interactive multisensor snow and ice mapping system (IMS US).
NOAA then combines DMSP, AMSR2 and IMS data utilizing an algorithm developed by University of Hamburg researchers to create a 4km and 1km Multi-sensor Analyzed Sea Ice Extent (MASIE US) product. This data is archived at University of Colorado as an NSIDC product and apparently at University of Hamburg.
I would also note that cooperation among NASA, JAXA and ESA on environmental satellites is considerable and will likely increase going forward from what I could tell so assigning countries or organizations is not entirely accurate either.
IMS is an ongoing process utilizing many NOAA algorithms and daily manual interpretation by NOAA analysts. Predominately US satellites and one Japanese satellite are used for data with some data gaps filled in by ESA and JAXA satellites. Data from Japanese and European satellites is processed from raw data with NOAA algorithms.
Looking at University of Hamburg website
 
Beitsch, A.; Kaleschke, L.; Kern, S. developed an algorithm that combined high resolution visible data with lower resolution microwave data in a way that produced a higher resolution product than the old algorithm. Kudos to them they moved the science forward a bit. They did not write the actual algorithm used by NSDIC to produce either the 4km or 1km product.
University of Hamburg researchers use raw data from AMSR2 and AMSR-E to produce a distinct 3.125 km product that would rightly be referred to as a U of Hamburg product.
Title: Re: HYCOM
Post by: interstitial on August 06, 2020, 07:52:13 PM
The university of Hamburg appears to be a sea ice concentration product. Unlike Masie 1km and 4km area products.
Title: Re: HYCOM
Post by: oren on August 07, 2020, 03:09:44 AM
Thanks, interstitial. I am familiar with MASIE but just didn't understand that was what you were referring to. MASIE is less used on the forum because it is not recommended for comparison between years (being based on a manual algorithm), however it is perfectly suitable for making predictions for the current melting season. Note however that MASIE is only about extent, not area, as far as I am aware.
Title: Re: HYCOM
Post by: interstitial on August 07, 2020, 06:09:20 AM
It helped me understand what data was out there. Generally I assume you know about this stuff. Masie does not distinguish between area and extent. If their is ice they count it if not the don't (an approximation of their words not mine). To me that sounds like a description of area though their philosophy on the subject is rather nebulous to me.
Title: Re: HYCOM
Post by: interstitial on August 13, 2020, 05:50:18 PM
To my eyes Hycom is predicting significant losses in Greenland, Beufort and Chukchi seas. As always full screen is best to see the details.
Title: Re: HYCOM
Post by: interstitial on August 13, 2020, 06:03:03 PM
Once again on thickness charts the forecast will always show at least white until it has completely melted out on nowcast.
Concentration charts clear up when it goes to zero. All of the blue and some of the blue green is below the 15% concentration threshold of most products.
Title: Re: HYCOM
Post by: interstitial on August 13, 2020, 06:06:10 PM
The CAA seems to be more resilient than I expected but could flush out.
Title: Re: HYCOM
Post by: oren on August 17, 2020, 03:11:02 AM
Looking at piomas model I see ice thinning by 1 m between 4/15 and 7/15. In less central locations the ice thins 1.25 m while in more central locations the ice thins by 0.75m. That is a melt rate of 8mm to 14mm per day. I also looked at Hycom on the same dates and came up with similar numbers. 7/15 includes about 4 weeks after the solstice. We are now almost three weeks beyond that. We are getting close to the time when the CAB normally starts to refreeze. The Beaufort will probably melt to the end.
Thanks for your interesting post interstitial. A few notes:
* The CAB continues to accumulate volume until May 5th-10th, at least according to PIOMAS.
* Peak volume loss rate is between mid-June and end-July. Using Wipneus regional numbers, an area of ~4M km2 loses ~4000 km3, so about 1m over 6 weeks, roughly 2.5 cm/day. Of course this mixes up top melt, bottom melt and export/import.

According to this interesting article (https://www.meereisportal.de/en/mosaic/sea-ice-ticker/) referenced by A-Team on the Mosaic thread:

Quote
On our transects – regular walks across the floe ... We recorded a gradual decrease in the average ice thickness: a drop of approximately one metre over the course of July.

Quote
...ablation stakes allow us to distinguish between the melting below and melting above. ... We measured an average of ~85cm of ice thinning across our stakes sites from 26 June to 30 July. Surface ablation accounted for seventy-five percent of that thinning, while bottom melting made up the remaining twenty-five percent.

Quote
The remotely operated underwater vehicle (ROV) “Beast” surveys the ice from below ... Comparing the maps produced over several dives showed that not all the ice melted at the same speed. Especially the deep keels that extended more than 8 metres into the comparably “warm” ocean were eroding quickly. In some parts of the ridged ice, keel depth decreased by up to 2 metres in just the first 14 days.

This was in the very southern CAB so fits more or less with the average PIOMAS loss calculated above for the whole CAB.
Title: Re: HYCOM
Post by: vox_mundi on November 15, 2020, 03:48:32 PM
It seems the Navy Lab has discontinued ice concentration updates of HYCOM since the middle of October-Nov 1. Any story to this? Or has the administration ordered an end to all this science stuff?
Title: Re: HYCOM
Post by: Jim Hunt on November 15, 2020, 07:25:04 PM
It seems the Navy Lab has discontinued ice concentration updates of HYCOM

 I see what you mean re the archive, but the "nowcast" still seems to be updating:
Title: Re: HYCOM
Post by: vox_mundi on November 15, 2020, 09:29:30 PM
Do you have a link to that, because here is what I'm using (I'm looking for ice thickness, sorry) and it stops at Nov 2, 2020

https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticictn_nowcast_anim30d.gif

Kinda coincidence that it stopped on election day.
Title: Re: HYCOM
Post by: gerontocrat on November 15, 2020, 10:26:30 PM
Do you have a link to that, because here is what I'm using (I'm looking for ice thickness, sorry) and it stops at Nov 2, 2020

https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticictn_nowcast_anim30d.gif

Kinda coincidence that it stopped on election day.
Try https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticice_nowcast_anim30d.gif

which is a link from the box at the bottom of https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/arctic.html

WHOOPS - but the ice thickness animation does stop at 2nd November. damn
Title: Re: HYCOM
Post by: vox_mundi on November 15, 2020, 11:15:08 PM
Spooky; huh?  ???
Title: Re: HYCOM
Post by: vox_mundi on November 19, 2020, 02:52:07 AM
And now it works!
Title: Re: HYCOM
Post by: gerontocrat on November 19, 2020, 11:23:34 AM
And now it works!
Conspiracy theory

- the US navy won't update the thickness maps until they've processed the latest thickness data from the sonar records of the subs playing cat and mouse with the Russian subs under the Arctic.