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Rob Dekker
California
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Hi Bill, On July 5 you posted the September SIE numbers using the 'daily average' method as opposed to the standard NSIDC method of calculation. On the Forum you asked me to run these numbers through my method to see if the 'daily average' method is better 'predictable'. I just posted the results on the forum here : http://forum.arctic-sea-ice.net/index.php/topic,1834.msg121896.html#msg121896 Result is that no, the 'daily average' method is not better predictable than the standard NSIDC SIE numbers. However, NSIDC 'area' numbers ARE better predictable, obtaining a beautiful 270 k km^2 SD of the residuals. That method still predicts that 2017 will end up where 2013 and 2014 were, so it still predicts a 'rebound' year. But, as noted above, we really should be starting to see a major 'stall' in SIE decline really soon now for that prediction to remain somewhat believable...
Toggle Commented 3 days ago on Melting momentum: May 2017 at Arctic Sea Ice
2017 is still dropping rapidly, keeping pace with 2007 and 2012. If this continues much longer then my hypothesis that June land snow cover and ice concentration are a good predictor for September SIE will be debunked.
Toggle Commented Jul 15, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
P-maker, back in the 80's, in June the melt line would be outside the Arctic Basin, where there is no MYI.
Toggle Commented Jul 15, 2017 on PIOMAS July 2017 at Arctic Sea Ice
I have another theory, and one we can possibly test : Notice that the reduction in volume loss since the 80's happens mostly during July (see Wipneus' "Arctic Ice Volume Anomaly" graph here) : https://sites.google.com/site/arctischepinguin/home/piomas And remember that in recent years, July is when the melt starts to eat seriously into the Arctic Basin, which during the 80's the melt line was still outside the Basin. So if PIOMAS underestimates the thickness of ice in the periphery of the Arctic Basin (and possibly overestimates the thickness of ice outside the Basic), then PIOMAS would record less ice loss during July in recent years, compared to earlier decades. The estimate does not need to be much : just a 20% error in thickness would explain the (PIOMAS recorded) reduced ice volume melt during July. Does that make sense ?
Toggle Commented Jul 15, 2017 on PIOMAS July 2017 at Arctic Sea Ice
Excellent points, D. Thinner ice could indeed imply increased sensitivity on insolation. That could explain the rapid decline of volume during June of the recent years that is so clearly visible in Wipneus' volume anomaly graphs : https://sites.google.com/site/arctischepinguin/home/piomas But that still does not explain why volume loss in the second half of the melting season (July to September) is actually less than in the 80's.
Toggle Commented Jul 14, 2017 on PIOMAS July 2017 at Arctic Sea Ice
Sorry guys, I'm not sure about that last claim. I'm not sure which year had the least volume loss since the start of July through September. Yet the first claim (that volume loss seems to decrease over time) still stands.
Toggle Commented Jul 13, 2017 on PIOMAS July 2017 at Arctic Sea Ice
And may I note that the volume loss line with the LEAST volume loss is 2012, which happens to be the year with the MOST extent loss.
Toggle Commented Jul 13, 2017 on PIOMAS July 2017 at Arctic Sea Ice
There is something puzzling about the Sea Ice Volume Projection graph as shown by Jim Pettit : http://neven1.typepad.com/.a/6a0133f03a1e37970b01b8d29304f5970c-pi Notice that the recent years (2010-2016) show significantly LESS volume melt than the earlier years (80's or 90's line). Does anyone have a physical reason for that odd difference ?
Toggle Commented Jul 13, 2017 on PIOMAS July 2017 at Arctic Sea Ice
AnotherJourneybyTrain, I am a great admirer of (the late) Drew Slater's probabilistic model. Also note that his model tends to bounce around a bit on the short term, since it is based on ice concentration only, which varies rapidly. For example, it just bounced back sharply to 4.93 for August 29. Let us see where the ice takes us.
Toggle Commented Jul 11, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
Neven said suggests still 5.41 M km^2 for September 2017 Wow, Rob, that's even higher than David Schröder's 5.1 (4.6 to 5.6) million km2. Higher than every ear since 2006, and higher even than rebound years 2013 and 2014. I know. It's a pretty outlandish projection, but that is what comes out if you run the numbers. Very important to note is that my model does not include "ice thickness" (or "ice volume"). Since we had a pretty unprecedented warm winter, ice may be 10% thinner than previous years, which is is not captured in my model. So we may end up in the "happy middle" as was posted before, where volume and albedo effects even out. Something in the mid 4's.
Toggle Commented Jul 8, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
Let me add that in June, there were two periods of a week each that created a dipole with some serious ice compaction. That brought the extent numbers down considerably. The data on 'area' and land snow cover and ice concentration suggest that once the weather turns more neutral or cyclonic, 'extent' will start to stall, and there is not enough heat (melting momentum) to continue the rapid extent decline that we have seen so far.
Toggle Commented Jul 7, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
I seem to be one of the few with an rather optimistic outlook for September minimum. A month again, my entry (based on May data) for SIPN was 5.4 M km^2 for the NSIDC average September : https://www.arcus.org/files/resize/sio/27252/sio2017_june_fig1_n33-700x509.png That was mostly caused by a very large land snow anomaly (4 million km^2) in land snow cover, and moderate 'area' and 'ice concentration' numbers over May. Now the June numbers are in, and the land snow cover anomaly was still there. Here is the Rutger's snow lab data : http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=6 The anomaly is still huge : some 3.5 M km^2 more than last year and a larger amount of land snow cover than since 2004. This anomaly has to have an impact on the albedo feedback in June, and thus the amount of heat that warms the Arctic never made it this year. Most of us know that ice 'extent' is not a very good predictor, and 'area' is better. There NSIDC's 'area' number for June came in pretty high (8.51 which is 8.54 after the 'pole hole' adjustment) is higher than most years over the past decade. As a result, the formula I use for June prediction of Sept average (explained here) : https://www.arcus.org/files/sio/25738/sio-2016-july_dekker.pdf suggests still 5.41 M km^2 for September 2017. The difference with May numbers is that the standard deviation of the (hindcast) prediction is 342 k km^2, which is considerably better than the 550 k km^2 SD for a linear trend. This year appears to be a serious test for my (mostly land-snow cover based) prediction method.
Toggle Commented Jul 7, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
Sea Ice Prediction Network finally published the June report (based on May data) https://www.arcus.org/sipn/sea-ice-outlook/2017/june The median Outlook value for September 2017 sea ice extent is 4.43 million square kilometers. Looks like an "in-the-middle" prediction, possibly balancing low volume data with low melting pond data.
Toggle Commented Jul 4, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
A bit dated, but since PIOMAS numbers are now released mid-month as well (thank you Dr. Zhang!) we had a PIOMAS update June 15. Wipneus reports on the PIOMAS forum thread : the volume gap with 2012 has been deminished from about 1. 48 down do 0.38 [1000 km3] Which is quite surprising, but explains a lot : It appears that 2017 has lost much of its lead in volume loss due to moderate melt in the Arctic over the first weeks of June. I can't suppress the notion that this is caused by the lack of melting momentum that Neven already talked about, and I believe that this is at least partially caused by the land snow cover anomaly, which keep things cool in the Arctic. We are not out of the woods yet though. The latest PIOMAS numbers are still record low, and although a significant land snow cover remains, it is still too early to exclude an extreme outcome in September. If this (persistent) land snow cover is an indication, 'extent' should really start to level off over the coming weeks, away from its current position among the top three. We will see...
Toggle Commented Jun 23, 2017 on PIOMAS June 2017 at Arctic Sea Ice
Hans, Why not explain your prediction beforehand ? Is it PIOMAS record low volume ? Also, 2012 doesn't decline that much over the next 10 days. Only 67 k/day if I recall. If you claim a significant decline over the next 10 days, why not go with 2010 ?
Toggle Commented Jun 18, 2017 on Melting momentum: May 2017 at Arctic Sea Ice
Another problem with incorporating 'remaining volume' or 'FYI thickness' in my linear regression method against 'extent' is that there may be non-linear effects : if ice melts, it adds to 'extent' as long as it has ANY thickness. After that it disappears quite suddenly.
Toggle Commented Jun 12, 2017 on PIOMAS June 2017 at Arctic Sea Ice
Jim, yes, I did consider using PIOMAS to find out FYI thickness, and use that as an additional variable that affects the melting season. However, I did not have time yet to set up the data stream for that and validate that variable (check how strongly it really shows up in the September extent data).
Toggle Commented Jun 12, 2017 on PIOMAS June 2017 at Arctic Sea Ice
To add to that last sentence : If the snow cover excess and the volume deficit even out, we may end up in what Hans called the "happy medium".
Toggle Commented Jun 8, 2017 on PIOMAS June 2017 at Arctic Sea Ice
DeanB, regarding where the May land snow anomaly resided : http://climate.rutgers.edu/snowcover/chart_vis.php?ui_year=2017&ui_month=5&ui_set=2 The excess snow in May seems to mainly form a ring around the Arctic, with most excess on the Siberian side. Explanation : It was just a rather cool May in the Arctic. Bill said but that suggests that your algorithm perhaps places undue significance on snow cover Perhaps. Or maybe not. Check out the pan-Arctic situation here on MODIS : https://lance3.modaps.eosdis.nasa.gov/imagery/subsets/?mosaic=Arctic.2017157.terra.4km and notice the pristine white ice and snow covered land all along the Siberian coastline. Compare that to the situation last year : https://lance3.modaps.eosdis.nasa.gov/imagery/subsets/?mosaic=Arctic.2016157.terra.4km where a snow-free Siberia and blue ice suggest that melting was in full swing all along Siberia. It is still early to make predictions. But if that land snow anomaly holds through June, then melting onset in the Arctic will be seriously delayed, which makes 5.4 left over in September not an unlikely scenario. Let us see what June brings, but I for one am hopeful that this land snow anomaly will compensate for the record low ice volume numbers.
Toggle Commented Jun 8, 2017 on PIOMAS June 2017 at Arctic Sea Ice
While average volume melt suggests that a record low is in the works this melting season, land snow cover is on the other extreme. May land snow cover is out, and it is a whopper : http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=5 May left the highest snow cover since 1996, an astonishing 4 million km^2 more than last year. That has got to leave a mark on Arctic amplification, and my regression formula (based on snow cover and ice extent/area) suggests that September SIE average will be some 5.4 M km^2. Note that May is really a bit too early for this method, since the SD is not much better than for a linear trend. But since volume is pointing radically one way, and snow cover is pointing radically the other way, this melting season is going to put some theories to the test...;o)
Toggle Commented Jun 7, 2017 on PIOMAS June 2017 at Arctic Sea Ice
NeilT, Yes. If we are to believe PIOMAS (and there is no reason not to), then we can expect (even with an average melting season) about a 10% steeper decline of 'extent' over June/July than in prior years. And that should be amplified by Arctic amplification. Let's see what will happen, but the low volume numbers suggest its going to be a hell of a ride...
Toggle Commented Jun 6, 2017 on PIOMAS June 2017 at Arctic Sea Ice
Diablo, thanks ! The interesting thing about that April comparison between PIOMAS and Cryosat is that Cryosat seems to project even less ice volume than PIOMAS, while in the Jan projection it was the other way around.... So what to believe ? : When I look at Nico's FDD measures : https://sites.google.com/site/cryospherecomputing/fdd that suggests that the 2016/2017 winter accumulated some 4200 FDDs and prior years hovered around 5000. That is a fraction of 4200/5000=0.84. Ice thickness is approximately the SQRT(FDD) which means 2017 ice thickness is SQRT(0.84)=0.91 of prior years. Which suggests 10% decline in FYI thickness. Now when I look at that PIOMAS/Cryosat April image you linked to, PIOMAS April 2017 has 20k km^3, and prior years are about 22k km^3. Which is indeed a 10% decline. Cryosat April (and also Jan) seem to be less consistent, and in fact 'all-over-the-place'. This makes be have more confidence in the PIOMAS numbers than in the Cryosat numbers.
Toggle Commented Jun 6, 2017 on PIOMAS June 2017 at Arctic Sea Ice
Thanks Navegante, Poster "Michael" is doing amazing work on the ASIF regarding the differences and similarities between PIOMAS and Cryosat. The latest difference plot https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=8.0;attach=46167;image indeed suggest that the differences are minor, although the blue (more ice volume in Cryosat) still appears to dominate the field.
Toggle Commented Jun 5, 2017 on PIOMAS June 2017 at Arctic Sea Ice
Thanks Neven. Indeed, if we follow PIOMAS numbers, the outlook for September does not look good at all ; even for an average melting season we end up below 2012. The only hope is that PIOMAS is wrong. There is some hope there, since Cryosat does not confirm PIOMAS numbers this year : http://psc.apl.uw.edu/wordpress/wp-content/uploads/schweiger/ice_volume/cryosat_piomas_awi_ts.2011.2017.Jan.png So who is right ? PIOMAS or Cryosat ? I have to admit that I personally feel that, considering the very warm winter we just went through, that I think PIOMAS is more accurate than Cryosat, and FYI (the ice that will likely melt out over the summer) this year is thin and fragile. If that is the case, we must see some evidence of that in the "extent" record as we move into June and July, in the form of a 'cliff' as the thin FYI melts out faster than other years.
Toggle Commented Jun 4, 2017 on PIOMAS June 2017 at Arctic Sea Ice
Looks like it going to be a test of NSIDC (extent graph) against PIOMAS (volume graph) this year.
Toggle Commented May 7, 2017 on PIOMAS May 2017 at Arctic Sea Ice