Messages

1

Arctic sea ice / Re: The 2020 melting season

« on: September 14, 2020, 05:11:29 AM »

September 13 is one of the year-to-year comparison dates for the U Bremen ASI (from AMSR2) false colour concentration maps, see attached figure  -- and perhaps the one closest to the daily extent minimum.

This year certainly strikes the eye as one of the lowest, along with 2012 of course, and to my eyes with 2007 (in the upper LH corrner) with that vast expanse of blue on the Pacific side.

2

Arctic sea ice / Re: MOSAiC news

« on: September 04, 2020, 09:02:21 AM »

Before it gets too far back, just want to say thanks very much for your detailed & very informative replies to my question on finding the ice bottom from the thermistor strings, SimonF92 and uniquorn.

I'm still digesting your replies & my understanding of the physical situation - things like the fresh water lens - definitely needs some revisions.

3

Arctic sea ice / Re: MOSAiC news

« on: September 03, 2020, 02:04:09 PM »

T78, nearest to PS, has been deployed on ice ~1.5m thick (~therm30-105). Nice to see some below zero air temps there.

Really appreciating seeing actual experimental depth profile data, and very well presented, thanks uniquorn.

The top of the ice is easy to find. But what about the bottom?

I see the temperature remains constant with depth below thermistor 105. Is that definitive?

If it was just one snapshot at a fixed time then the profile could be consistent with some sort of 'freshwater lens' effect, where the gradient was due to increasing salinity with depth. So the actual boundary would not be definitive.

But is it because the gradient above 105 wiggles up and down slightly in time - indicating the better thermal conductivity of ice than of liquid water [UPDATE: ice is 2.2, liquid is 0.6 in MKS units -- not as big a ratio as I had thought], and so reacting more quickly to changes in air temperature - so it must be ice rather than water down to 105 and there is no freshwater lens to be seen at this location?

I think I have just convinced myself. Does that correspond to the actual physics as known by those familiar with this equipment?


Do any of these rigs ever show a freshwater lens below the ice? If not, is that not a real phenomenon in the Arctic?

4

Arctic sea ice / Re: The 2020 melting season

« on: September 03, 2020, 07:57:14 AM »

August 29 - September 2.

The tail is melting quite fast!

5

Arctic sea ice / Re: The 2020 melting season

« on: September 02, 2020, 11:46:40 PM »

September 1 is one of the year-to-year comparison dates for the U Bremen ASI (from AMSR2) false colour concentration maps, see attached figure. Shown are this year, in the lower right corner, and seven of the previous low years. The other 8 recent years can be seen by clicking the link.

This year, the ice is unusually compact for the date.

6

Arctic sea ice / Re: The 2020 melting season

« on: September 01, 2020, 09:30:19 AM »

Always appreciate your ice concentration map gifs, thanks Aluminium.

Very interesting to see [Fig. 1] a couple of places in the ice of 1 August in the Beaufort Sea region where the centre of a Low has left  a 'scar' of reduced concentration -- presumably due to Ekman pumping.

Then look on 31 August [Fig. 2] & the scar is now a hole & the starting point for wider disintegration of the ice. Maybe the "fresh water lens" below the ice is destroyed by the Ekman pumping, and there are also more exposed edges, so further melting is easier in the scar.



Very tentative prediction as it is probably too late in the season, but there was another scar created by a low on 27 August, this time North of Greenland [Fig 3].


It will be interesting to see if it makes a hole.


On 25 August I had suggested it might make a hole ...

... a tight low precisely targeting the ice just north of Greenland. It might even make a big hole in the ice there.

... but for now it's just a scar -- even looking recovered by now & getting squashed against Greenland by the prevailing winds this week.


Anyway, I'm going to claim it as a prediction if, even so, it turns into a hole like the other 2 did! 

7

Arctic sea ice / Re: The 2020 melting season

« on: August 31, 2020, 03:05:52 AM »

Excellent explanation of Arctic Ocean's stratification under threat, thanks ArcTickTock! Excerpt with my bolding ...

...
It gets worse, as I understand it the Arctic surface water in the CAB, specifically over the Amundsen Basin is only slightly less saline that the warmer Atlantic waters below which means it has always been on the razors edge of breaking down.  In the past this did not matter as the central arctic was proof against melting out.  But it is vulnerable, if it ever has a BOE it will start to mix with Atlantic surface water once no more fresh melt water is being added and that Atlantic water is much harder to refreeze.  That being said, we may see freshening of the CAB in the near term as more CAB melt starts to occur each year, delaying things a bit.  However models that suggest we may get a BOE every now and then in the future may be painting a too rosy picture.  BOEs likely create an environment that favors more BOEs, at some point it is probably a runaway phenomenon.

This year at least, it seems the thicker CAB ice is being literally blown away -- in the direction of Alaska. So the ice reservoir of fresh water in the CAB is being partially removed by transport, not just mixed with saline water. (See screenshot figure below.)

What is the relative importance of ice transport (also through the Fram Strait) in this process?

(Yes, aware this is getting a bit detailed for this thread -- but the transport of the thicker ice does seem to be a notable feature of this melt season.)

8

Arctic sea ice / Re: The 2020 melting season

« on: August 26, 2020, 07:28:29 AM »

August 25th is one of the year-to-year comparison dates for the U Bremen ASI (from AMSR2) false colour concentration maps, see attached figure. Shown are this year, in the lower right corner, and seven of the previous low years. The other 8 recent years can be seen by clicking the link.

Most of the ice is in high concentration areas (purple), relative to some of the previous years (those showing more yellow), but the total extent is one of the lower ones. So the guessing game of which ice areas will disappear is mainly confined to the Beaufort ice. The ice north of Greenland still holds some interest though, and the Atlantic side may be pushed in by the forecast winds over the next few days.

9

Arctic sea ice / Re: The 2020 melting season

« on: August 25, 2020, 07:02:29 AM »

Agree with the above posts. The area north of Greenland is looking wrecked already and a ~40 mb dipole is setting up with the high on the Russian side and a tight low precisely targeting the ice just north of Greenland.

 It might even make a big hole in the ice there. If so then that will look visually jarring to those of us remembering that area as having been a permanent ice sanctuary through the years.

10

Arctic sea ice / Re: The 2020 melting season

« on: August 21, 2020, 03:08:01 AM »

Thanks to Neven for kindly updating the year-to-year Bremen map comparison page.

Below is the comparison for 19 August.

You can see this is the first year that the traditional ice sanctuary between Greenland and the North Pole has been wrecked. (Although it has been deteriorating over the years -- see the nice post about 2 pages back by UCMiami.)

To really appreciate how wrecked the sanctuary is though, check out A-team's amazing detailed image on the MOSAIC thread.

11

Arctic sea ice / Re: The 2020 melting season

« on: August 20, 2020, 07:04:09 AM »

Couple of visual predictions for the potential storm: NAVGEM model & Nullschool wind display (uses GFS model).

NAVGEM shows it bottoming out north of Svalbard and at 979 mbar, in the 108-hour prediction.

Nullschool shows 93 km/h winds just north of Greenland, at 0000Z on 2020/08/25! 

Potential for a crazy finish to the melt season. Let's see if this eventuates.

12

Arctic sea ice / Re: Updating the ASIG

« on: August 18, 2020, 10:28:29 AM »

I apologize for being so late with updating the SIC maps. I always tend to procrastinate when it comes to tedious jobs. But it's all updated now, all the way to end of November.

Thanks Neven, much appreciated! One of my favourite ways of trying to understand the trends.

13

Arctic sea ice / Re: The 2020 melting season

« on: August 12, 2020, 07:26:21 AM »

Agree, IILWAR, the U. Bremen AMSR2 map is looking very ratty for the date. The region north of Greenland is freaking me out a bit!

If I may be so bold as to ask a favour, could someone with the ability please update the excellent "Sea Ice Concentration maps" page to include 2019.

It's a favourite page of mine for comparisons. Next day for comparisons is in 2 days time:
https://sites.google.com/site/arcticseaicegraphs/concentration-maps/sic0813

14

Arctic sea ice / Re: PIOMAS 2020 Arctic Sea Ice Volume September Average: August poll

« on: August 10, 2020, 02:53:18 PM »

Dropping down half a bin as the high stayed high & the sun kept shining, & then the wind blew in the Beaufort.

August poll for PIOMAS: 3.50-4.00K km3 VHC (Very high confidence).

That's the bin that centres the 2012 record. This season has been exceptional as well so far so I think it's going to be down there with 2012.

All that sunlight on the ice in July will take its toll. That's direct energy for melting. In my amateur understanding, most will have been absorbed by the ice & some of the high frequency (violet) end will have gone straight through and heated up the water underneath.

Now we're getting to the time of year where there is heat in the water below the ice & how much is transferred to the ice will depend on how much the ice is stirred. So if the next month is windy over the ice then -- in my amateur view -- that would be big factor in pushing towards a record low minimum volume.

15

Arctic sea ice / Re: NSIDC 2020 Arctic SIE September average: August poll

« on: August 10, 2020, 02:45:23 PM »

Dropping down half a bin as the high stayed high & the sun kept shining, & then the wind blew in the Beaufort.

August poll for NSIDC: 3.75-4.25M km2 VHC (Very high confidence)

 I always estimate (guess) the JAXA daily minimum then add 0.5M km2 to predict the NSIDC.

16

Arctic sea ice / Re: JAXA 2020 Arctic SIE September daily minimum: August Poll

« on: August 10, 2020, 02:43:03 PM »

Dropping down half a bin as the high stayed high & the sun kept shining, & then the wind blew in the Beaufort.

August poll for JAXA: 3.25-3.75M km2 VHC (Very high confidence).

Extent depends a lot on the weather in the past couple of weeks of the melt season, so my "very high confidence" is a bit dubious.

The recent slow-down in extent drop is basically irrelevant, if not negatively correlated with the final extent, as was due to the low pressure system in the Beaufort spreading the ice out. At the same time, it basically wrecked it though.

17

Arctic sea ice / Re: September predictions challenge 2020

« on: August 10, 2020, 02:35:58 PM »

Dropping down half a bin on all 3 as the high stayed high & the sun kept shining, & then the wind blew in the Beaufort.

August poll for JAXA: 3.25-3.75M km2 VHC (Very high confidence)
August poll for NSIDC: 3.75-4.25M km2 VHC (Very high confidence)
August poll for PIOMAS: 3.50-4.00K km3 VHC (Very high confidence).

18

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation

« on: August 09, 2020, 01:19:51 AM »

Really amazing graphics above, thanks to those posting!

19

Arctic sea ice / Re: The 2020 melting season

« on: August 08, 2020, 06:20:33 AM »

Why doesn't it feel like third lowest?
Or it does?

Yes, the Bremen AMSR2 map you showed looks much worse than yesterday's map.

Worldview Terra also gives a good view of the Beaufort sector ice eaten away all the way to 80 degrees N.

20

Arctic sea ice / Re: The 2020 melting season

« on: July 20, 2020, 07:55:39 AM »

Here's the year-to-year comparison of the ASI (from AMSR2) maps for 19 July.

This year is unprecedented for the amount of ice cover lost by this date on the Russian side.

21

Arctic sea ice / Re: The 2020 melting season

« on: July 13, 2020, 12:07:08 PM »

...  But the last few days melt across the Atlantic Front from Svalbard to Severnaya Zemlya looks to be more than insolation can do alone.  That looks like Atlantic water attacking the entire front right up to the Nansen ( or even past ) to me!

Remember to also consider the effects of the wind pushing the ice front. It has been pushing it in a somewhat westerly direction and also somewhat north -- see reply #2601 above and its figure, posted by Sambuccu.

22

Arctic sea ice / Re: SMOS

« on: July 11, 2020, 11:15:44 AM »

Very interesting, thanks for the posts and analysis.

23

Arctic sea ice / Re: September predictions challenge 2020

« on: July 08, 2020, 08:34:32 AM »

Thanks for doing this.

I missed June so have some catching up to do!

July poll for JAXA: 3.50-4.00M km2 VHC (Very high confidence)
July poll for NSIDC: 4.00-4.50M km2 VHC (Very high confidence)
July poll for PIOMAS: 3.75-4.25K km3 VHC (Very high confidence).

24

Arctic sea ice / Re: PIOMAS 2020 Arctic Sea Ice Volume September Average: July poll

« on: July 08, 2020, 08:30:46 AM »

I voted [3750,4250] km^3.

That brackets the 2 worst years: 2012 and 2019. I think we will be around there because:

1) This year is currently in the pack of lowest years for today's date;
2) The persistent current high pressure system over the Arctic is pouring in a lot of energy into the ice; and
3) Underneath the noise, the minimum volume is trending progressively lower, year-by-year.

25

Arctic sea ice / Re: NSIDC 2020 Arctic SIE September average: July poll

« on: July 08, 2020, 08:24:17 AM »

Voted [4.0,4.5] M km^2.

For the monthly average I just go 0.5M km^2 up from my choice in the daily minimum poll on the other thread.

26

Arctic sea ice / Re: JAXA 2020 Arctic SIE September daily minimum: July Poll

« on: July 08, 2020, 08:21:48 AM »

Also voted [3.5,4.0]M km^2.

Current extent of 8.0M km^2 is a record for the date by 0.3M km^2.

I actually predict this year will pull away further in the next few days, maybe to 0.5M km^2. The reason is the continuing strong high pressure system sitting squarely over the Arctic basin and which is compacting the ice pack due to the coriolis effect ("Ekman pumping").

Afaik the current extent values still don't correlate that strongly with the September minimum though. My low prediction -- second place behind 2012 -- is instead based more on the heat & low ice thickness on the Russian side -- that side is getting wiped out the earliest on record -- & also on the healthy dose of direct sunlight the Arctic is getting at the moment.

27

Arctic sea ice / Re: Latest PIOMAS update (February 2020)

« on: February 07, 2020, 05:45:40 AM »

Here are volume and volume-anomaly graphs.

It is getting harder to find a new color for a new year. I am trying a new color scheme that I found here:
https://sashat.me/2017/01/11/list-of-20-simple-distinct-colors/

Have a look, I am not sure myself yet, comments are welcome.

Hi Wipneus, you asked the same question a year ago and I replied then with a suggested colour palette.

Did you try those colours and, if so, did they work OK?

28

Arctic sea ice / Re: 2019 sea ice area and extent data

« on: November 08, 2019, 10:57:07 AM »

[ADS NIPR VISHOP (JAXA)] Arctic Sea Ice Extent.

ADS is 45 minutes late on the update.
If someone else can post the new values…
Thank you 

https://ads.nipr.ac.jp/vishop/#/extent

Still hasn't updated.

29

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: October 23, 2019, 06:24:33 AM »

Thanks for all your interesting & some authoritative responses in this discussion.

I still don't understand, how can you use a very thin slice of a full model to approximate the true situation?

I can do it because a) I am only seeking order-of-magnitude accuracy & b) am considering the limited & somewhat artificial situation where the only heat transport mechanism is thermal conduction.

I think I found a better approximation in this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6114986/

This is comparing apples to oranges. You're showing an amount of heat whereas I calculated a rate of heat transfer. That's a lot of heat but it still has to get to the surface to affect the ice.

Have you all forgot the basics of sea ice formation? RoxTheGeologids, macid, slow wing?

Yes, I'm worried that some of the people here may have forgotten more about that than you or I ever knew.

I hope that the current expedition will show how this happens in real time! It's a really interesting theory.. lets see if the real world works that way.

Yes, an exciting prospect!

30

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: October 22, 2019, 02:11:21 PM »

The above discussion suggests a third mechanism whereby incoming storms can retard the start of the refreeze: introducing water vapour to the atmosphere which raises the 'effective temperature' of the sky for long-wave radiation. This lowers the rate of net heat loss from the water and so retards refreeze.

(This 'effective temperature' of the sky is a description I am familiar with from solar water heating applications, and I've also seen it used before in this forum.)

31

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: October 22, 2019, 02:01:04 PM »

Good questions, thank you Macid.


Answering your last question first, my thermal conductivity calculation was for an illustrative 'toy model' that might approximate the true situation in some circumstances. The whole point is to get the magnitude of the heat flux for the process of thermal conduction -- which was found to be of order 1/100 W/m^2.

As you point out, this is negligible compared to the other thermal processes effecting the melting or freezing of the ice, which was what the toy model was intended to illustrate.


The background to my post above has been the common narrative on this forum that excess heat gets stored in the water column over the course of the melt season, together with the assertion that the refreeze cannot proceed to any great extent until that excess heat has first been removed by extraction to the atmosphere.


I've never been comfortable with that explanation because, given the situation of relatively calm water, I can't see how that trapped heat -- which I presumed to extend down by at least several meters and probably tens of meters or more, depending on whether it was sourced from ocean currents or direct sunlight -- can get to the surface to influence the refreeze.


So yes, as you point out, in calm conditions then the long-wave radiation to the cold sky should start the refreeze without noticing how much excess heat has been trapped below. Then, once the ice has formed and grown thick enough, there is no chance for wind and waves to start bringing the excess heat up to the surface. So the re-freeze continues and the trapped excess heat below becomes essentially irrelevant.


My suggestion above concerns the converse situation, where there is wind and waves. I'm suggesting that could mix some of the excess heat up to the surface to replace the heat lost to long-wave radiation and so to retard the start of the re-freeze.

32

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: October 22, 2019, 12:52:31 PM »

It's certainly relevant to the discussion whether or not it has been windy lately in the Arctic basin.

I do have the impression it has been unusually windy over the past month compared to previous years, but nothing quantitative and based only on looking at the weather maps which appeared to show lots of isobar lines in the basin, indicating strong pressure gradients and therefore strong winds. I might be wrong in this.

33

Arctic sea ice / Re: The 2019/2020 freezing season

« on: October 22, 2019, 09:22:11 AM »

.... Nevertheless, it would appear that accumulated heat in the Arctic Ocean/system is an important factor.

It seems to be THE most important factor

Wondering if the record late refreeze may be due, at least in large part, to the Arctic basin having been stormy since the extent minimum?


I have posted my speculation on the importance of storms in the refreeze here on the Stupid Questions thread.

34

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: October 22, 2019, 09:19:09 AM »

From the Freezing Season thread...

.... Nevertheless, it would appear that accumulated heat in the Arctic Ocean/system is an important factor.

It seems to be THE most important factor

Wondering if the record late refreeze may be due, at least in part, to the Arctic basin having been stormy since the extent minimum?


Reason: the thermal conductivity of water is terrible, as I illustrated earlier on this Stupid Questions thread.

So I'm guessing that, to a good approximation, it will only be the action of wind & waves stirring up the water that makes the accumulated sub-surface heat available to retard the refreeze.

Also, ice can't easily form in wind & waves.

Fair?

35

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: October 15, 2019, 11:10:14 AM »

I posted this originally in the Mike Horn expedition thread :

But here is a question. Mike mentions he was about 87 N. Should the sun be below the horizon by this date ? I plugged this lattitude into a couple of online solar angle calculators and they are saying max angle is circa -4 degrees ie below the horizon.

https://keisan.casio.com/exec/system/1224682277

To still see the sun you would need to be near 82 N (according to the online calculations).

Or maybe the calculations are not taking into account the flattening at the poles ?

Agree it is puzzling. However, there is some refraction of sunlight in the atmosphere. Wikipedia says that at sunset it is 35.4' -- so more than half a degree. So that accounts for a small part of the discrepancy.

This website, which includes refraction, says there is no direct sunlight but still 4h19 minutes of "civil twilight" at 87N, even now on 15th October, which is two days after the photo.

36

Arctic sea ice / Re: Latest PIOMAS update (October 2019)

« on: October 06, 2019, 05:35:49 AM »

Thanks Wipneus!

The September monthly volume trend:

Thanks for this plot. There is clearly some year-to-year correlation but, that aside, it seems to me that the Arctic sea ice volume data seems reasonably well described by a linear decline.

Eye-balling, it looks like it reaches zero volume in about 10 years time (and may fluctuate down to that sooner). I wouldn't rule that out!

37

Arctic sea ice / Re: Freeform season chatter and light commentary

« on: September 25, 2019, 03:31:06 PM »

🌍🔥  New #IPCC #ClimateChange report released today: "IPCC Special Report on the Ocean and Cryosphere in a Changing Climate" #SROCC

Press release: https://ipcc.ch/2019/09/25/srocc-press-release/

Full Report, & Summary for Policy Makers: https://ipcc.ch/srocc/chapter/summary-for-policymakers/ 🔥🌍

38

Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves

« on: September 22, 2019, 10:40:24 AM »

It's hard to match the ITP buoys temperature & salinity profiles with their location using the standard plots provided, so I practiced my R and took a stab at it.

Excellent! Much appreciated initiative, MyACIsDying. This is a plot I've wanted to see often.

39

Arctic sea ice / Re: 2019 sea ice area and extent data

« on: September 21, 2019, 06:12:57 AM »

Juan hasn't posted it yet so if I may...

September 20^th, 2019:
     4,054,403 km², an increase of 44,272 km².
     2019 is 2nd lowest on record.

40

Arctic sea ice / Re: The 2019 melting season

« on: September 18, 2019, 09:54:31 AM »

... something I don't really get.

Suggest asking about it in the Stupid Questions thread, as plenty here do get it.


Short answer:

1) Salinity is more important than temperature in determining water density; and

2) The Arctic Ocean at its surface is less saline than the other oceans.

41

Arctic sea ice / Re: 2019 sea ice area and extent data

« on: September 18, 2019, 05:36:30 AM »

Yes, another JAXA extent drop: to 3,964,239 km², so down 26,948 km² from yesterday.

42

Arctic sea ice / Re: 2019 sea ice area and extent data

« on: September 16, 2019, 05:38:13 AM »

September 15^th, 2019:


     4,006,036 km², a drop of -19,682 km².
     2019 is 2^nd lowest on record for this day.


P.S.: 2019 is now the second lowest year for extent on record, now 11,228 km² below the 2016 minimum of 4,017,264 km² and behind only 2012.

43

Arctic sea ice / Re: "Smart" and "Stupid" Questions - Feel Free To Ask

« on: September 15, 2019, 08:35:18 AM »

"The 2019 melting season", Reply #6567

... with melt potentially continuing through this next week given the heat anomalies ... last years min was on 21 Sep!

Three questions I have been wondering about that relate to this melt season:

1) Are the yearly extent minima getting later?

2) Has the Arctic basin been carrying more moisture in the atmosphere at this time of year than in past decades? (Iirc there was an identified step change relating to an extreme weather event in December 2016, was it the 27th? Also, there is more open water in recent years. So this question could include a part 2b: why?)

3) If 'yes' to both 1 & 2, could 2 be at least partially the reason for 1 due to increased moisture in the atmosphere over Arctic basin retarding the loss of heat by long wave radiation?


Have any scientists been watching this and can answer one or more of those questions? Thanks.

44

Arctic sea ice / Re: The 2019 melting season

« on: September 14, 2019, 05:54:20 AM »

13 September is another of the dates on Neven's excellent year-to-year sea ice map comparison

It's easy to see that 2019 is one of the years with the lowest ice extent although that's qualitative.
(I have to admit that 2007 looks about as low as 2012 to me at a first glance, although we know 2012 is actually far lower.)

45

Arctic sea ice / Re: 2019 sea ice area and extent data

« on: September 12, 2019, 06:00:43 AM »

September 11^th, 2019:
     4,110,564 km², a drop of -39,332 km².
     2019 is now 2^nd lowest on record.
     (2007, 2012 & 2016 highlighted).

Thanks Juan, always appreciated.


The forecast winds are so favourable for compaction of the ice pack that extent may well drop all the way below 4 million km² over the course of the next several days, and before freeze-up finally takes hold.

That is so even though 4 million km² has at times been below the predicted range obtained from extrapolating using the progressions to the minima from the previous years on record -- see the plots that gerontocrat has been posting. (After today's drop though, 4 million km² is presumably back within the range from those projections.)


The significance of that, of course, is that 2019 would become only the second year to drop below the 4 million km² marker and it would reach the second lowest minimum extent in the record, below all years except 2012 (all the way down at 3.18 million km²).

46

Arctic sea ice / Re: The 2019 melting season

« on: September 08, 2019, 02:35:57 PM »

The models at Tropical Tidbits are coming into consensus on a high pressure system forming towards the Canadian side of the central Arctic basin by about 4 days from now and then intensifying.

That could potentially bring some compaction of the ice pack and a relatively late minimum extent date for this year.

To illustrate with an example, here is the latest NAVGEM 96h forecast:

47

Arctic sea ice / Re: The 2019 melting season

« on: September 08, 2019, 07:44:07 AM »

7 September is a date displayed in Neven's fine year-to-year comparison of sea ice extent & concentration - here.

2019 is shown at bottom right, along with 7 previous years that Neven has chosen as some of the worst for minimum extent. (Further years are displayed further down on the webpage - not seen in the figure below.)

As expected, 2019 looks like it belongs with the previous worst years.

48

Arctic sea ice / Re: The 2019 melting season

« on: September 06, 2019, 01:16:08 AM »

The weakest ice under full (90° Angle) attack

Windspeeds around 50km/h at a bit of a distance to the "Eye"

Some compaction will be the least impacting extent numbers, some melt still ongoing could
keep area drops in line with extent losses, despite higher concentration.

That's a low pressure system so it causes dispersion -- the opposite of compaction.

On your figure, I suggest you redraw your arrows at 45 degrees to the right of the actual wind directions displayed -- which is the direction the ice goes (Coriolis) -- and then you will see the dispersion.

49

Arctic sea ice / Re: Latest PIOMAS update (September 2019)

« on: September 04, 2019, 09:07:39 AM »

Thanks Wipneus!

Looking at the graph I think 2019 is now guaranteed a 2nd place finish?

Yes, at least. 2nd or 1st.

50

Arctic sea ice / Re: Icesat 2 data now available

« on: September 01, 2019, 10:37:01 PM »

Excellent news, thanks!