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Messages - Steven

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1
Arctic sea ice / Re: The 2020 melting season
« on: May 08, 2020, 08:24:06 PM »
Will you tolerate this thread saying "there are no melt ponds in April" and also saying "no data from CryoSat-2 for 2nd half of April because meltponds confuse sensors"?

There are two separate issues here as the CryoSat-2/SMOS thickness/volume is based on two different sensor types.

CryoSat-2 (radar altimetry): It is common practice to not compute thickness in the Arctic beyond April, since the snow will get wet in May which causes extinction of the radar waves. Open melt ponds that form later are a different issue.

SMOS (L-Band radiometry): Here, the method of thin-ice thickness estimation is based (in essence) on the temperatur difference between the sea water and the ice surface. And this difference can get too small at already in the end of April for reliable ice thickness estimates.

Thus, CryoSat-2 thicknesses stop at April 30 and SMOS (respectively CryoSat-2/SMOS) thicknesses stop at April 15.

Cheers, Stefan

2
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: July 15, 2019, 02:42:53 PM »
BZZT - ambiguous pronoun referents detected!

"It is worse than we thought" = the "we" refers to the climate science community.

"It isn't as bad as we feared" = the "we" refers to members of this board.

Both statements are thus true, because this board is much more alarmist that the community in general.

3
Arctic sea ice / September predictions challenge 2019
« on: June 09, 2019, 10:06:22 AM »
And it's back! Many thanks to Richard Rathbone for setting this up last year. Rules copied over from last year's thread:

Quote
This is a challenge which accumulates scores across all the monthly polls on September sea ice to come up with an overall rating of how good the predictions made are. In addition to making a prediction, entrants are required to rate their confidence in that prediction. The higher the confidence, the narrower the margin of error you are allowed, but the higher score you get if the September ice ends up where you predicted it (and the bigger penalty you take if you miss).

Currently included polls are: JAXA daily minimum area, NSIDC September average.
Other polls may be added during the course of the season if their structure fits this challenge.

Points are scored as follows:
Very High Confidence: 10 points if you pick the correct bin, -10 points for all other bins.
High Confidence: 6 points for the correct bin, 2 points if one bin out, -2 points if two bins out, -6 points for all other bins
Medium Confidence: 4 points for the correct bin, 2 points if one bin out, 1 point if two bins out, -1 if three bins out, -2 if four bins out, -4 points for all other bins
Low Confidence: 2 points for the correct bin, 1 point if within 3 bins, -1 point if 4-6 bins out, -2 points for all other bins
Very Low Confidence: 1 point if in the correct bin, no score (or penalty) for any other bin.

Note on portmanteau and end of range bins: these are excluded from the challenge, you may either select a bin within the portmanteau range, or extend the range beyond the poll endpoint for your challenge entry. If the September values fall out of the normal range, scores will be assessed by extending the bin structure. e.g. an end result of 5.9 counts as two bins out for a 5-5.5 entry.

To enter, post guess and confidence in this thread before the closing date of the poll. Editing a post to change the prediction before the closing date is allowed, editing for any reason after the closing date for a poll will result in disqualification from the challenge.

List of entries

Paddy

June
JAXA:  3.75 - 4.25, medium
NSIDC: 4.25 - 4.75, medium

Oren

June
JAXA: 3.5 - 4, medium
NSIDC: 4 - 4.5, medium

b_lumencraft

June
JAXA: 3.5 - 4, high
NSIDC: 3.75 - 4.25, high

Stephan

June
JAXA: 3.75 - 4.25, high
NSIDC:  4 - 4.5, high

jdallen

June
JAXA: 3.75 - 4.25, high
NSIDC: 4 - 4.5, high

Neven

June

JAXA: 3.5 to 4.0, medium
NSIDC: 4.0 to 4.5, medium


Juan C. García

June

JAXA: 3.5 to 4.0, médium
NSIDC: 3.75 to 4.25, médium

Richard Rathbone

June

Jaxa: 3.75-4.25, Medium
NSIDC 4.0 - 4.5, Medium

Sterks

June

Jaxa: 3.75-4.25, Medium
NSIDC 4.0 - 4.5, Medium

Aluminium

June

JAXA: 3.5-4.0 high.
NSIDC: 4.0-4.5 medium.

Brigantine

June

JAXA 3.75 - 4.25 medium
NSIDC 4.25 - 4.75 medium

slow wing

June

JAXA: 3.75 to 4.25, medium
NSIDC: 4.00 to 4.50, medium

jplotinus

June

JAXA: 4.25-4.75, low
NSIDC: 4.50-5.00, low

Gerontocrat

June

JAXA: 3.75 to 4.25, High
NSIDC: 4.00 to 4.50, High

Steven

June

JAXA: 3.5 to 4.0, medium
NSIDC: 4.0 to 4.5, medium

4
Link to Last year's same poll.

I just came back to ASIF after not keeping up for a few months... because poll season!

I have a lot of reading to do before I decide on a number... things like how well June anomalies correlate with September, what the ice surface is looking like this year and how it compares, etc.

UPDATE: relevant comment on the state of the ice surface, with links to relevant data. [HT Michael Hauber]
UPDATE 2: relevant comments on melt onset / momentum. [HT Neven]
And SMOS 10 year comparison [HT slow wing]

And then here's last year's predict-o-matic [HT Ned W] including confidence intervals. Adjusting for current JAXA data [HT Juan C. Garcia], 2019 minimum should be 4.02 +/- 1.26 (95% CI) based on predictive power of June 7 extent alone.

Provisionally voted for 3.75 - 4.25 atm, I'm thinking medium confidence.
Raised it to 4.00 - 4.50 after looking at that SMOS beige pixel count graph.

5
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: June 02, 2019, 03:18:28 PM »
Since then the ADS have changed their web interface again. I will have to add another flip and a loop to get it now (meaning that it will take some time).

Done the required gymnastics. Should work now, updated to 31st.

6
Arctic sea ice / Re: PIOMAS vs CryoSat
« on: November 08, 2018, 10:19:41 AM »
Just to let you know that the AWI CryoSat-2 data service has been resumed in the past days as can be seen by the PIOMAS - CryoSat-2 figures above. The CryoSat-2 sea ice thickness algorithm has been updated to version 2.1 with a number of changes:

  • Improved snow information for regions outside the central Arctic Ocean
  • new options for automated analysis (NSIDC region codes in gridded and orbit data
  • improved uncertainty for gridded sea ice thickness

We have also added online documentation and anonymous ftp access, you can find the necessary information here:

AWI CryoSat-2 wiki

Whats new in version 2.1


ftp://ftp.awi.de/sea_ice/product/cryosat2/v2p1/nh/

Cheers, Stefan

7
Arctic sea ice / Re: Arctic Image of the Day
« on: August 29, 2018, 09:13:37 PM »
I find the reaction of a lot of people here bewildering.
I like to think this forum is about facts and science. If I make a statement about the xyz ice shelf I should make sure I know what the xyz iceshelf actually is. I certainly do such fact checking because I would hate to make such a mistake.
It did not take me long to find the information I posted above. Maintaining high standards on this forum is certainly worth the effort in my opinion. (of course there are people who think diferently )
JD  and treform have apologized and that is ok, I hope they take more care in the future. Being incentivized to make the extra effort to reduce the risk of making mistakes is a good thing, right? That is not a personal issue, and should not be about hurt feelings.
Can you really not tell the difference between that and mistake about who said what???

8
Arctic sea ice / Re: The 2018 melting season
« on: August 26, 2018, 08:30:18 PM »

Some additional info from 7 years ago.

Thank you, Neven! In addition, a nice animation that summarizes the disintegration of the Ellesmere Island Ice Shelves from 1906 until 2015 can be found here: https://wirl.carleton.ca/research/ice/ice-shelves/ice-shelf-extents/

Great information about the 2011 calving event is also available there: https://wirl.carleton.ca/research/ice/ice-shelves/calving-2011/


9
Arctic sea ice / Re: 2018 sea ice area and extent data
« on: July 28, 2018, 04:07:59 PM »
I've been noting how bizarrely closely 2018's extent has been following 2015.  Neven pointed out that while the two years' extents have been similar, volume has been lower in 2018.

Here's a "snake plot" showing extent vs volume for all years in the 2010s.  It shows how daily extent and volume have evolved during the summer melt season.  It's basically a scatterplot showing the combination of the two variables on each date.

This seems like an interesting data visualization method.  I'd appreciate any feedback on how this could be improved -- so I can do an updated version when the remainder of the July PIOMAS data are published.



The fine print:

Data cover the period from June 1 to July 14 of each year.  The "head" of each year's snake is the end-date (July 14).  Circular "heads" are odd years, squares are even years. 

Volume from PIOMAS via Arctische Pinguin, using the total of CAB+CAA only, and converting each date's volume to an anomaly relative to the 2010-2018 mean for that day of year.  Extent from JAXA, for the entire Arctic, converting each date's extent to an anomaly relative to the 2010-2018 mean for that day of year.  After July 14 of this year, the extent anomaly dropped to right around 0 (i.e., to the average extent for this date).

10
Arctic sea ice / Re: The 2018 melting season
« on: July 08, 2018, 10:03:52 PM »
The most recent on nullschool, we can see that already the cold fresh blob out of the Labrador sea has been swept north to the Faroes Iceland shallow area. Not good news for latter, as it will be preventing underlying Gulfstream water from radiating and evaporating heat, while up taking energy from insolation and the atmosphere better. Also mixing into the saltier hot waters underneath will lighten them, making them more able to stay near surface as they reach the ice.
Nope. There is nothing on Nullschool showing a "fresh blob" out of Labrador sea going towards the "Faroes Iceland shallow area" (which is what exactly?).

The currents go in the opposite direction, flushing the Labrador sea southwards, and SSTA's around Iceland and the Faroes Islands show normal fluctuation.
Repeating your previous image is not proving anything. If you go back in Nullschool you can see that the SSTA in the area between Iceland and the Faroes fluctuates, nothing new happining now. If you set Nullschool to show currents, you can see that the currents from Labrador sea go southwards and there is simply no way that any cold or fresh water could be swept from Labrador sea to the east of Iceland.

It does feel like you are just spouting nonsense, stringing together a series of dubious claims and this particular claim is easily disproved.
Have you heard of storm surges?

Are you suggesting a storm surge from Laptev Sea (against the prevailing currents) to the east of Iceland? How on earth does that work? Which storm did you have in mind? The current (2018-07-08 at 20:00 GMT) does blow out of the Laptev Sea but doesn't reach anywhere near the east of Iceland.

Not only them at work here, but likely the huge surge of Gulfstream waters into the north sea entraining the southward Labrador sea meltflow.

More nonsense. "Likely" the "huge" surge of Gulftsteam waters into the North Sea (? between the UK and Scandinavia?)

Anyway, the Gulf Stream flows up the other side of the Atlantic, nowhere near the Laptev Sea.

And the negative sea surface anomaly in the arctic created by its evacuation, and the cyclonic dispersion and negative atmospheric pressure anomally in the Arctic are behind this situation.
The persistent Greenland vortex low pressure systems are a big part of it also

Which situation? There is no situation - there is nothing happinening now with the SSTA around Iceland that hasn't been ongoing for the last several months. Some daily fluctuations, but that's it.

It takes a specific kind og hyperimagination to see cold freshwater being "entrained" 1500 km against surface currents on the basis of a slightly bluer than usual color in an SSTA map where the colors change daily anyway!

On a lighter note. Here's an example of a pyramid wave field caused by waves from the latest Greenland vortex low refracting around  Iceland. Some reflection off Greenland is culpable too.

Do you honestly think you can see pyramid waves on that picture? "Refracting around Iceland" ... please! Do you imagine it's a duck in a bathtub?

And when did the normal stream of low-pressure areas flowing up the Atlantic, as they do every year more or less non stop, become "caused by the Greenland vortex"? The lows flow all the time, non stop, all year round, and any purported "Greenland vortex" has nothing to do with it.

Currently the lows tend to flow in over Iceland because they are pushed to the west by the unusual high pressure area over the United Kingdom. Greenland has nothing to do with it.

11
Arctic sea ice / Re: Land snow cover effect on sea ice
« on: July 08, 2018, 12:37:48 PM »
Rob: I think your model is fun and interesting, so I spent some time with it.

Assuming I've correctly re-produced your results...

The question above is, roughly:  what's the probability that the actual result is 0.7M km2 or more away from the predicted result?  This occurred in: 1980, 1982, 1983, 1986, 1988, 1991, 2001, and 2006.  That's 8 out of 39 years, or about a 20% chance.

Eyeballing the graph you published pretty much agrees that both 2001 and 2006 predictions are off by around 0.7M km2.


We can slightly simplify your approach by noting that you are predicting minimum extent as a linear combination of three variables: June snow area, June ice area, and June ice extent.  The multi-variable linear regression package that I'm using (XL miner in google sheets) notes that the 'extent' parameter isn't very useful in this prediction.  The software suggests there's a 6% probability that 'extent' should really be part of the equation.

Also, graphing the trend lines through the minimum and the predicted minimum, suggests that the prediction is diverging from actual (getting larger) as each year passes.  Since both snow cover and minimum extent trend downward year by year, it might be interesting to add 'year' as a parameter to better explore how well snow cover helps explain minimum extent.

Overfitting a model based on year, snow area, and ice area to all data from 1979 through 2017, we get the second attached picture.  And a forecast of 4.58 M km2 for the 2018 min extent.  (With a 360 K km2 geometric mean error.)  (Overfitting Dekker's model gives a forecast of 4.76 M km2 with a 435 K km2 geometric mean error.)  (If I train the year-based model on just 1992 through 2015, the forecast is 4.64 M km2 with a 386 K km2 geometric mean error.)

My simple physical explanation for the year-based model would be: heat is accumulating worldwide year by year due to greenhouse gases; the snow and ice area (or lack thereof) takes into account how much insolation is absorbed in the northern hemisphere in June.  Together, this suggests the amount of heat available for melting ice, subject to the vagaries of weather.




12
Arctic sea ice / Re: Don't read this thread
« on: July 07, 2018, 08:53:35 AM »
Maybe it's like with the Roman empire. No Roman saw it collapse. The big system shock is too slow for us impatient humans.
The collapse of the Roman empire took centuries, and I suspect it didn't become a "collapse" until historians began looking at in modern times.

Other than that I totally agree with Ned W after only some three or four years of watching this forum. Every year we get a chorus of doomsayers that think they understand everything so much better than everybody else. Funnily enough, every year the chorus has new members - wonder if the unusually noisome pack of doomsayers this year will still be so cock-sure next year.

On the other hand, the Ice will melt out eventually, and I (and many others apparently) think that the end could be quite sudden. But this year? Nope.

13
Arctic sea ice / Re: Land snow cover effect on sea ice
« on: July 07, 2018, 04:47:33 AM »
Most of you will know that since 2013, I use I use the "whiteness" of the Arctic in June as a predictor for how much ice will melt out between June and September.

http://neven1.typepad.com/blog/2013/07/problematic-predictions-2.html

Specifically, I use three variables to make this prediction :
- Land snow cover in June
- Ice 'area' in June
- (Extent - Area) in June, which represents the amount of 'water' in the ice pack in June.

A combination of these variables, each one of which affects the 'albedo' of the Northern Hemisphere, represents how much solar energy gets absorbed by the Northern Hemisphere in summer, and this correlates remarkably well with September sea ice cover.

Details of this method is described in one of my entries into Arcus Sea Ice Prediction Network :

https://www.arcus.org/files/sio/25738/sio-2016-july_dekker.pdf

This year, land snow cover in June was quite high compared to recent years :



Also, ice 'area' is quite high in June (in between 2014 and 2015) and the ice is still fairly compact.

As a result, prediction for Sept 2018 September sea ice extent is quite high at 5.19 km2, with a standard deviation of 340 k km2.

My gut feeling this year tells me that this an upper bound, but it's fairly clear that given the past performance of this method, it is highly unlikely (less than 2.5% chance) that Sept 2018 will end up below 4.5 M km2.

Here is what this hind-cast method did for the past 26 years :

14
For the July poll, I take momentum indicators into account as well as the long term trend. These are awful for melt, the CPOM June SIPN entry, based on May melt pond modelling is calling for the highest September extent since 2006, 5.3 (+- 0.5)

I'd prefer to see their June analysis, but my crude June indicators (NSIDC area anomaly cliff and PIOMAS volume anomaly cliff) also point to low momentum as does the late appearance of general surface melt on SMOS and high NSIDC compactness.

So, I have to go up a lot, the question is just how many bins. For the moment, just 3, but if the CPOM SIPN July entry is out before the closing date (it normally just misses this) and their June analysis backs up their May analysis, it'll be 4.

4.75 - 5.25

15
Arctic sea ice / Re: Arctic sea ice minimum early prediction
« on: June 01, 2018, 06:45:37 PM »
Here's a graph showing (for 2018) the standard error of regression, when relating each day's extent to the ensuing minimum, based on data from 2007-2017:



Here is a similar graph, using sea ice area on a given day as a predictor of the extent minimum.  As above, the graph shows the standard error of the regression based on data for 2007-2017:



Between about day 140 and day 220 (i.e., from late May to mid-August), the values in this graph are substantially lower than in your graph above.  So sea ice area is a better predictor than extent during that period (based on 2007-2017 data).

Source for the sea ice area data: https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/data/nsidc_arc_nt_main.txt.

Hey, that is very cool.  Here are both (area and extent) on the same graph:



This is the standard error for estimating the end-of-season JAXA daily extent minimum, based on each day's JAXA extent or NSIDC area.

I'm not sure what to make of those dips and spikes in June/July in the area data.

16
Arctic sea ice / Re: Arctic sea ice minimum early prediction
« on: May 31, 2018, 06:23:31 PM »
The reason why I asked this, is that I'm unable to reproduce the 4.33 (or 4.22) million km2 that you mentioned.  I assume you used the JAXA extent for 28 May 2018, minus the average extent loss for the years 2007 to 2017 from 28 May to minimum.  But that would give an estimate of 3.96 million km2 for the 2018 minimum, rather than 4.33 million km2.  So I am wondering if you changed something to your methodology?

Thanks for reminding me about this, Steven.  Yes, I did change something in the methodology, relative to last year's.  But the change wasn't really deliberate, and I might go back to last year's way instead. 

The 4.33 (or 4.22) x 10^6 km2 comes from using OLS regression to predict the minimum based on the current date's extent in each year from 2003 to present (or 2007 to present).  The 3.95 comes from calculating the average drop to the minimum from the current date, and subtracting that from the current extent.  The latter is what I used last year, and I'll probably go back to that ... I think.  Actually, I'm not sure which is better conceptually.  This version has a slightly better mean absolute error over the past decade.  But I liked last year's version.

The difference between the two boils down to this: is the drop from day X to the minimum independent of whether day X's extent is unusually high/low?  I can see arguments for both sides of this question.

17
Arctic sea ice / Re: The 2018 melting season
« on: May 04, 2018, 07:59:21 PM »
Even though 80N is only a small part of the Arctic, I still regard the DMI temperature graph as somewhat indicative of what's going on, a precursor of sorts. In this sense, the current high temperatures there may prove to be significant. Emphasis on 'may'.

Below is what I would consider the most important graph in the latest NSIDC summary. According to the summary there's a record high amount of FYI and record low amount of MYI:

Quote
As averaged over the Arctic Ocean (Figure 4d), the multiyear ice cover during week nine has declined from 61 percent in 1984 to 14 percent in 2018, the least amount of multiyear ice recorded. In addition, only 1 percent of the ice cover is five years or older, also the least amount recorded. This is rather striking since September 2017 did not set a new record low minimum extent. The proportion of first-year versus multiyear ice in spring will largely depend on the amount of open water left at the end of summer over which first-year ice forms. How much ice is transported out of the Arctic through Fram Strait in winter also plays a role. The unusually high amount of first-year ice this March suggests that there was a strong Fram Strait ice export this past winter. Given that (in the absence of ridging) first-year ice grows to about 1.5 to 2 meters (4.9 to 6.6 feet) thick over a winter season, the ice age data point to a fairly thin ice cover. Nevertheless, how much ice melts out this coming summer will depend strongly on summer weather conditions.

I'm not sure how accurate this is. For instance, I'm not seeing the band of MYI extending across the Beaufort towards Chukchi. A-Team, are you reading? What do you think?

I'm afraid Tschudi et al. forgot the ice "birthday" on September 2017,  when 1st year ice (dark blue) becomes 2nd year ice (light blue) , light blue becomes green (3rd year ice), etc.

ftp://ccar.colorado.edu/pub/tschudi/iceage/data/

Look for instance at weeks 30, 38, 45:

ftp://ccar.colorado.edu/pub/tschudi/iceage/images/iceage_browse_week_n_2017_30_nrt.png
ftp://ccar.colorado.edu/pub/tschudi/iceage/images/iceage_browse_week_n_2017_38_nrt.png
ftp://ccar.colorado.edu/pub/tschudi/iceage/images/iceage_browse_week_n_2017_45_nrt.png


This could be affecting the results displayed at the time series on http://nsidc.org/arcticseaicenews/2018/05/

I've just sent a message to Mark Tschudi to let him know.





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