Overview Winter Climate for NH

The diagram represents how Dr. judah Cohen pictures the Northern Hemisphere wintertime climate system.  He leads research regarding Arctic and NH weather patterns for AER.  He explains the dynamics in an interview at Washington Post (here):

My colleagues, at AER and at selected universities, and I have found a robust relationship between two October Eurasian snow indices and the large-scale winter hemispheric circulation pattern known as the North Atlantic or Arctic Oscillation pattern (N/AO).

The N/AO is more highly correlated with or explains the highest variance of winter temperatures in eastern North America, Europe and East Asia than any other single or combination of atmospheric or coupled ocean-atmosphere patterns that we know of. Therefore, if we can predict the winter N/AO (whether it will be negative or positive) that provides the best chance for a successful winter temperature forecast in North America but certainly does not guarantee it.

[Of the two indices we’ve analyzed], the first and longer [more data points] index is simply the monthly mean snow cover extent (SCE) for the entire month [of October] as measured from satellites. This record dates back to at least 1972 and is available on the Rutger’s Global Snow Lab website.

The second index that we developed last year, with the support of NSF and NOAA grants, measures the daily rate of change of Eurasian snow cover extent also during the entire month of October, which we refer to as the Snow Advance Index or SAI.

There have been recent modeling studies that demonstrate that El Nino modulates the strength and position of the Aleutian Low that then favors stratospheric warmings and subsequently a negative winter N/AO that are consistent with our own research on the relationship between snow cover and stratospheric warmings. So the influence of ENSO on winter temperatures in the Mid-Atlantic and the Northeast may be greater than I acknowledge or that is represented in our seasonal forecast model.

How It Works

Conceptual model for how fall snow cover modifies winter circulation in both the stratosphere and the troposphere–The case for low snow cover on left; the case for extensive snow cover on right.

1. Snow cover increases rapidly in the fall across Siberia, when snow cover is above normal diabatic cooling helps to;
2. Strengthen the Siberian high and leads to below normal temperatures.
3. Snow forced diabatic cooling in proximity to high topography of Asia increases upward flux of energy in the troposphere, which is absorbed in the stratosphere.
4. Strong convergence of WAF (Wave Activity Flux) indicates higher geopotential heights.
5. A weakened polar vortex and warmer down from the stratosphere into the troposphere all the way to the surface.
6. Dynamic pathway culminates with strong negative phase of the Arctic Oscillation at the surface.

From Eurasian Snow Cover Variability and Links with Stratosphere-Troposphere
Coupling and Their Potential Use in Seasonal to Decadal Climate Predictions by Judah Cohen

Extensive 2016 Siberian snowfall led to unusually rapid recovery of Arctic sea ice following relatively low September 2016 minimum.

What About Winter 2017-2018?

Dr. Cohen’s Winter Outlook for NH  September 18, 2017

Many important markers are currently being set indicating the atmosphere is beginning in earnest the transition from summer to winter. There are four features that I am monitoring closely over the coming weeks and months to gauge the evolving atmospheric circulation pattern and resultant weather across the NH.

The first is the nascent stratospheric polar vortex (PV). The PV has returned to the NH polar stratosphere. Much recent research including my own has shown that the relative strength of the PV if not forces, certainly leads prolonged periods of temperature anomalies across key regions of the NH. A strong PV is related to relatively milder temperatures across the mid-latitudes of the NH while a weak PV is related to relatively colder temperatures across the mid-latitudes of the NH. This relationship is strongest in mid-winter. Early signs are that the PV will start off relatively weak similar to last fall. This is somewhat surprising because increasing greenhouse gases favor colder stratospheric temperatures and hence a stronger PV. Poleward heat flux or vertical wave activity flux is predicted to be unusually active in the coming two weeks, which is likely the reason for the predicted relatively weak start to the PV.  (my bolds)

The active poleward heat flux is also likely related to the second feature that I will be following – high latitude blocking. The negative AO state is often a manifestation of strong high latitude blocking while the positive AO often reflects a lack of high latitude blocking. The predicted negative AO in the coming two weeks is a result of predicted strong high latitude blocking with the dominant block predicted to reside in the region of Scandinavia and the Barents-Kara seas. In the near term this will lead to a cold and snowy period across most of Siberia. Blocking in this region is favorable for weakening the stratospheric polar vortex and will likely lead to weakening of the PV over the next two weeks. If similar blocking occurs later on during the late fall and early winter it will favor a sudden stratospheric warming (SSW). SSW in the winter often precedes extended periods of severe winter weather across the continents of the NH. (my bolds)

The third feature is Arctic sea ice extent. The minimum in Arctic sea ice extent is achieved this time of year and if the minimum has not already been reached it should occur relatively soon. The past two blogs I suggested the possibility that the sea ice minimum could be similar to the years 2008 and 2010 and that is looking likely. Sea ice extent is extremely low compared to climatology but will not be a new record low. The largest anomalies are in the North Pacific side of the Arctic in the Beaufort Sea. This pattern matches recent Septembers. Typically, the largest anomalies migrate with the progression of fall to the North Atlantic side of the Arctic. It is my opinion that low sea ice favors high latitude blocking but the nature of the blocking is regionally dependent. For example, low sea ice in the Barents-Kara Seas favors blocking in the northwest Eurasia sector resulting in cold temperatures in parts of Asia. (my bolds)

The fourth feature is Siberian snow cover. My, along with my colleagues and others, research has shown that extensive Siberian snow cover in the fall favors a trough across East Asia with a ridge to the west near the Urals. The atmospheric circulation pattern favors more active poleward heat flux, a weaker PV and cold temperatures across the NH. With a predicted strong negative AO in the coming weeks, snow cover is likely to advance relatively quickly heading into October. It is very early in the snow season but recent falls have been snowy across Siberia and therefore I do expect another upcoming snowy fall across Siberia. Though admittedly, recent Siberian snow cover as a predictor of winter temperatures has been mixed.

Summary

Uh oh.  Now where did I put away my long johns?

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Arctic Ice Exceeds at Minimum

It is the most typical day this decade for the annual Arctic ice extent minimum. Some take any year’s slightly lower minimum as proof that Arctic ice is dying, but the image below shows extents from 2007, mostly smaller than 2017.

While the daily average extent for the last 10 years bottomed out on day 260, years like 2016 and 2009 hit minimum on day 254.  This year’s extent was at 4.7M km2 for a week, hit bottom at 4.6M on day 253, then rose up and over 4.8M km2.  SII (Sea Ice Index) 2017 is similar to MASIE, though a bit lower lately. The graph below shows September comparisons through day 260.
Note that as of day 260, 2017 has gone 300k km2 above average, 500k km2 more than 2016, 700k km2 higher than 2007, and 1400k km2 greater than 2012.  All regions have added ice, with Central Arctic the only exception.  That is likely due to Central Arctic sea already full of ice at 3.1M km2.

The table shows ice extents in the regions for 2017, 10 year averages and 2007 for day 260.

Region 2017260 Day 260
Average
2017-Ave. 2007260 2017-2007
 (0) Northern_Hemisphere 4757445 4449204 308241 4045776 711669
 (1) Beaufort_Sea 411648 468835 -57187 481384 -69736
 (2) Chukchi_Sea 106342 145834 -39492 22527 83815
 (3) East_Siberian_Sea 320193 257482 62711 311 319882
 (4) Laptev_Sea 241780 123163 118617 235869 5912
 (5) Kara_Sea 21251 20846 405 44067 -22816
 (6) Barents_Sea 1664 24778 -23114 7420 -5756
 (7) Greenland_Sea 90072 213695 -123622 333181 -243109
 (8) Baffin_Bay_Gulf_of_St._Lawrence 65653 26566 39086 26703 38950
 (9) Canadian_Archipelago 430824 247034 183790 225526 205299
 (10) Hudson_Bay 1932 6975 -5042 2270 -338
 (11) Central_Arctic 3071252 2912912 158339 2665244 406008

The largest deficits to average are in BCE and Greenland Sea, more than offset by huge surpluses in Central Arctice, CAA and Laptev.  Note the strong growth in East Siberian offsetting the Beaufort deficit.

Over this decade, the Arctic ice minimum has not declined, but looks like fluctuations around a plateau since 2007. By mid-September, all the peripheral seas have turned to water, and the residual ice shows up in a few places. The table below indicates where  ice is found in September. (Shows day 260 amounts with 10 year averages)

Arctic Regions 2007 2010 2012 2014 2015 2016 2017 Average
Central Arctic Sea 2.67 3.16 2.64 2.98 2.93 2.92 3.07 2.91
BCE 0.50 1.08 0.31 1.38 0.89 0.52 0.84 0.87
LKB 0.29 0.24 0.02 0.19 0.05 0.28 0.26 0.17
Greenland & CAA 0.56 0.41 0.41 0.55 0.46 0.45 0.52 0.46
B&H Bays 0.03 0.03 0.02 0.02 0.10 0.03 0.07 0.03
NH Total 4.05 4.91 3.40 5.13 4.44 4.20 4.76 4.45

BCE (Beaufort, Chukchi and East Siberian) on the Asian side are quite variable as the largest source of ice other than the Central Arctic itself.   Greenland Sea and CAA (Canadian Arctic Archipelago) together hold almost 0.5M km2 of ice at minimum, fairly consistently.   LKB are the European seas of Laptev, Kara and Barents, a smaller source of ice, but a difference maker some years, as Laptev was in 2016 and 2017.  Baffin and Hudson Bays are almost inconsequential.  The biggest contributors to 2017 success are Central Arctic, Canadian Archipelago and Laptev.

For context, note that the average maximum has been 15M, so on average the extent shrinks to 30% of the March high before growing back the following winter.

Update Sept. 20

Dave Burton asked a great question in his comment below, and triggered this response:

Dave, thanks for asking a great question. All queries are good, but a great one forces me to dig and learn something new, in this case a more detailed knowledge of what goes into MASIE reports. My answer above refers only to a sub-product which combines MASIE with JAXA.

You asked, where do they get their data? The answer is primarily from NIC’s Interactive Multisensor Snow and Ice Mapping System (IMS). From the documentation, the multiple sources feeding IMS are:

Platform(s) AQUA, DMSP, DMSP 5D-3/F17, GOES-10, GOES-11, GOES-13, GOES-9, METEOSAT, MSG, MTSAT-1R, MTSAT-2, NOAA-14, NOAA-15, NOAA-16, NOAA-17, NOAA-18, NOAA-N, RADARSAT-2, SUOMI-NPP, TERRA

Sensor(s): AMSU-A, ATMS, AVHRR, GOES I-M IMAGER, MODIS, MTSAT 1R Imager, MTSAT 2 Imager, MVIRI, SAR, SEVIRI, SSM/I, SSMIS, VIIRS

Summary: IMS Daily Northern Hemisphere Snow and Ice Analysis

The National Oceanic and Atmospheric Administration / National Environmental Satellite, Data, and Information Service (NOAA/NESDIS) has an extensive history of monitoring snow and ice coverage.Accurate monitoring of global snow/ice cover is a key component in the study of climate and global change as well as daily weather forecasting.

The Polar and Geostationary Operational Environmental Satellite programs (POES/GOES) operated by NESDIS provide invaluable visible and infrared spectral data in support of these efforts. Clear-sky imagery from both the POES and the GOES sensors show snow/ice boundaries very well; however, the visible and infrared techniques may suffer from persistent cloud cover near the snowline, making observations difficult (Ramsay, 1995). The microwave products (DMSP and AMSR-E) are unobstructed by clouds and thus can be used as another observational platform in most regions. Synthetic Aperture Radar (SAR) imagery also provides all-weather, near daily capacities to discriminate sea and lake ice. With several other derived snow/ice products of varying accuracy, such as those from NCEP and the NWS NOHRSC, it is highly desirable for analysts to be able to interactively compare and contrast the products so that a more accurate composite map can be produced.

The Satellite Analysis Branch (SAB) of NESDIS first began generating Northern Hemisphere Weekly Snow and Ice Cover analysis charts derived from the visible satellite imagery in November, 1966. The spatial and temporal resolutions of the analysis (190 km and 7 days, respectively) remained unchanged for the product’s 33-year lifespan.

As a result of increasing customer needs and expectations, it was decided that an efficient, interactive workstation application should be constructed which would enable SAB to produce snow/ice analyses at a higher resolution and on a daily basis (~25 km / 1024 x 1024 grid and once per day) using a consolidated array of new as well as existing satellite and surface imagery products. The Daily Northern Hemisphere Snow and Ice Cover chart has been produced since February, 1997 by SAB meteorologists on the IMS.

Another large resolution improvement began in early 2004, when improved technology allowed the SAB to begin creation of a daily ~4 km (6144×6144) grid. At this time, both the ~4 km and ~24 km products are available from NSIDC with a slight delay. Near real-time gridded data is available in ASCII format by request.

In March 2008, the product was migrated from SAB to the National Ice Center (NIC) of NESDIS. The production system and methodology was preserved during the migration. Improved access to DMSP, SAR, and modeled data sources is expected as a short-term from the migration, with longer term plans of twice daily production, GRIB2 output format, a Southern Hemisphere analysis, and an expanded suite of integrated snow and ice variable on horizon.

http://www.natice.noaa.gov/ims/ims_1.html

Footnote

Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used. This is false in fact and in logic. Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year? Researchers do this, including Walt Meier in charge of Sea Ice Index. That said, I understand his interest in directing people to use his product rather than one he does not control. As I have said before:

MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies. More on this at my post Support MASIE Arctic Ice Dataset

 

Arctic Ice Refreezing

We are about 4 days away from the annual Arctic ice extent minimum, which typically occurs on or about day 260 (mid September). Some take any year’s slightly lower minimum as proof that Arctic ice is dying, but the image below shows day 260 over the last 10 years. The Arctic heart is beating clear and strong.

Click on image to enlarge.

Recent posts noted that 2017 Arctic ice extents were stabilizing and then coasting to a halt.  Now we are seeing a reversal with ice growing in all but one region.  While the daily average extent over the last 10 years bottomed out on day 260, years like 2016 and 2009 hit minimum on day 254.  This year’s extent was at 4.7M km2 for a week, hit bottom at 4.6M on day 253, and 3 days later is now up to 4.8M km2.  SII (Sea Ice Index) 2017 is similar to MASIE, though a bit lower lately. The graph below shows September comparisons.
Note that as of day 256, 2017 has gone 250k km2 above average, 500k km2 above 2007 and 2016, and 1300k km2 greater than 2012.  All regions are adding ice, with Central Arctic the only exception.  That is likely due to Central Arctic sea already full of ice at 3.1M km2.  The image below shows impressive refreezing in the Canadian Archipelago.

Click on image to enlarge.

Over this decade, the Arctic ice minimum has not declined, but looks like fluctuations around a plateau since 2007. By mid-September, all the peripheral seas have turned to water, and the residual ice shows up in a few places. The table below indicates where we can expect to find ice this September. (Shows day 260 amounts with 10 year averages)

Arctic Regions 2007 2010 2012 2014 2015 2016 Average
Central Arctic Sea 2.67 3.16 2.64 2.98 2.93 2.92 2.91
BCE 0.50 1.08 0.31 1.38 0.89 0.52 0.87
LKB 0.29 0.24 0.02 0.19 0.05 0.28 0.17
Greenland & CAA 0.56 0.41 0.41 0.55 0.46 0.45 0.46
B&H Bays 0.03 0.03 0.02 0.02 0.10 0.03 0.03
NH Total 4.05 4.91 3.40 5.13 4.44 4.20 4.45

BCE (Beaufort, Chukchi and East Siberian) on the Asian side are quite variable as the largest source of ice other than the Central Arctic itself.   Greenland Sea and CAA (Canadian Arctic Archipelago) together hold almost 0.5M km2 of ice at minimum, fairly consistently.   LKB are the European seas of Laptev, Kara and Barents, a smaller source of ice, but a difference maker some years, as Laptev was in 2016.  Baffin and Hudson Bays are almost inconsequential.

For context, note that the average maximum has been 15M, so on average the extent shrinks to 30% of the March high before growing back the following winter.

Footnote

Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used. This is false in fact and in logic. Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year? Researchers do this, including Walt Meier in charge of Sea Ice Index. That said, I understand his interest in directing people to use his product rather than one he does not control. As I have said before:

MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies. More on this at my post Support MASIE Arctic Ice Dataset

 

Arctic Ice Coasting Sept. 12

Crystal Serenity touring in the Arctic Northwest Passage 2016 and 2017.

With the most typical day for annual minimum a week away, watching Arctic ice is like watching an ocean liner coasting to a halt before reversing engines.  A recent post reported that ice extents  are stabilizing around 4.7M km2 in recent days, and more importantly, some refreezing in the central seas.  As discussed in Arctic Heart Beat, the marginal shelf seas seldom have ice at annual minimum, typically on or about day 260.  The image below shows the progression of ice extents from 2007 to 2017 on day 254 with six days to go.

Click on image to enlarge.

 

Yesterday was day 254 and the graph below shows 2017 compared with other years and the decadal average during the last 3 weeks.

For the last week MASIE and SII are showing the same extent, now about 70k km2 above the 10 year average.  Only four years in the decade had more ice on this day.  2007 is 300k km2 lower, 2016 500k km2 lower, and at the bottom is 2012 1.1M km2 below 2017.  A recent post on August storms discussed the dramatic impact on 2012 and 2016, which is evident as well in the chart.  The table compares 2017, decadal average and 2007 for the regions containing ice at this time.

Region 2017254 Day 254
Average
2017-Ave. 2007254 2017-2007
 (0) Northern_Hemisphere 4652293 4583359 68934 4349612 302681
 (1) Beaufort_Sea 393863 480306 -86443 599679 -205815
 (2) Chukchi_Sea 131705 173275 -41570 74733 56973
 (3) East_Siberian_Sea 279268 286737 -7468 311 278957
 (4) Laptev_Sea 205794 149612 56182 247496 -41702
 (5) Kara_Sea 18486 29190 -10705 62274 -43788
 (6) Barents_Sea 4313 25209 -20896 7384 -3071
 (7) Greenland_Sea 107969 211322 -103353 324789 -216820
 (8) Baffin_Bay_Gulf_of_St._Lawrence 45146 22235 22911 21406 23740
 (9) Canadian_Archipelago 370958 262283 108675 210083 160875
 (10) Hudson_Bay 1432 11057 -9625 16552 -15120
 (11) Central_Arctic 3092201 2931173 161028 2783651 308551

The deficits continue to be on the Pacific side, especially Beaufort, and also Greenland Sea is down this year.  These are more than offset by large surpluses in the Central Arctic and Canadian Archipelago, and also Laptev.  East Siberian sea also has surplus ice this year compared to 2007.

aer Atmospheric and Environmental Research

September 5, 2017 Dr. Judah Cohen of AER posted his monthly forecast for the Arctic and NH based on the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO).  Excerpts below.

The AO is currently slightly negative (Figure 1), reflective of mostly positive geopotential height anomalies across the Arctic and mixed geopotential height anomalies across the mid-latitudes of the NH (Figure 2). Geopotential height anomalies are mostly negative across Greenland and Iceland (Figure 2), and therefore the NAO is slightly positive.
Figure 1. (a) The predicted daily-mean near-surface AO from the 00Z 5 September 2017 GFS ensemble. Gray lines indicate the AO index from each individual ensemble member, with the ensemble-mean AO index given by the red line with squares.

The AO is predicted to straddle neutral next week as geopotential height anomalies remain mixed across the Arctic. Similarly, with mixed geopotential height anomalies stretching across Greenland and Iceland, the NAO will likely be near neutral as well.  

(Note: AO and NAO are signed differently than one might expect; the reference point is outside the Arctic itself.  Thus negative phases of these indices mean higher pressures in the Arctic and lower outside, while positive phases indicate lower pressures in the Arctic.  Now that the Arctic sun is setting, the main issue for ice extent is storminess which requires low Arctic pressures.)

Impacts

It is the first week of fall, a season of transition from summer to winter. One important sign IMO of this seasonal transition is the return of the polar vortex in the stratosphere. The models predict the possible formation of the polar vortex sometime next week. Starting in October, I will be watching variability in the polar vortex for signs of pattern changes in the weather across the NH.

Another sign of the seasonal transition is the minimum in Arctic sea ice extent, which will be achieved in the coming days and/or weeks. The trajectory of sea ice melt has slowed since early August. In my last blog I suggested the possibility that the sea ice minimum could be similar to the years 2008 and 2010 and that is looking more likely but is difficult to predict. Over the coming months, I will be following Arctic sea ice variability for signs of the severity of the upcoming winter. Our understanding for how anomalies in sea ice extent influence the weather in the mid-latitudes is still immature IMO but I do think that important progress has been made recently.

Another sign of the transition from summer to winter is the return of snowfall to the NH. Snowfall over the sea ice in August probably helped retard the melt of sea ice and snowfall is now even occurring over Siberia and Alaska but is still very regionalized. Again I will be monitoring the advance of snow cover extent across the continents for signs of the strength of the polar vortex and the possible resultant weather.

Finally I find it interesting that while the atmospheric circulation has transitioned from the dominant summer pattern across Eurasia it has not across North America. The dominant summer pattern across Eurasia was ridging across Europe (with the exception of Northern Europe) and East Asia but with troughing in Western Asia. The forecast for the coming weeks is the opposite with troughs across Europe and East Asia but ridging in Western Asia. This is an overall cooler pattern than the dominant summer pattern. However across North America there are no similar signs of transition. The dominant summer pattern was strong ridging across western North America and troughing in eastern North America and at least for now that pattern looks to continue for much of the month of September. I don’t know the reason behind the persistent western ridge/eastern trough pattern across North America but how long this pattern can persist will obviously have important implications for the weather across North America in the coming months.

Summary

Bottom line, looks like September weather will be ordinary in the Arctic with seasonal cooling in the NH.  Dr. Cohen also thinks the annual ice extent minimum will be near average for the decade.  While the monthly average is final only at September end, this week will set the tone and likely result.

 

 

Early Arctic Minimum?

It is a few days earlier than usual, but MASIE shows ice extents  stabilizing near 4.7M km2 in recent days, and more importantly, some refreezing in the central seas.  As discussed in Arctic Heart Beat, the marginal shelf seas seldom have ice at annual minimum, typically on or about day 260.  The image below shows the progression of ice extents from 2007 to 2017.

Yesterday was day 251 and the graph below shows 2017 compared with other years and the decadal average during the last 3 weeks.

At this point MASIE and SII are showing the same extent, about 100k km2 above the 10 year average.  2007 is 250k km2 lower, 2016 500k km2 lower, and at the bottom is 2012 1.1M km2 below 2017.  The table compares 2017, decadal average and 2007 for the regions containing ice at this time.

Region 2017251 Day 251
Average
2017-Ave. 2007251 2017-2007
 (0) Northern_Hemisphere 4716948 4619900 97048 4467771 249177
 (1) Beaufort_Sea 409067 492365 -83298 643868 -234801
 (2) Chukchi_Sea 133345 185601 -52257 95240 38105
 (3) East_Siberian_Sea 279966 301146 -21180 311 279655
 (4) Laptev_Sea 196236 152840 43396 252479 -56243
 (5) Kara_Sea 22449 30277 -7828 59593 -37144
 (6) Barents_Sea 23123 20028 3095 5882 17240
 (7) Greenland_Sea 116132 196719 -80586 315125 -198993
 (8) Baffin_Bay_Gulf_of_St._Lawrence 46799 21575 25224 17173 29626
 (9) Canadian_Archipelago 374084 268736 105348 236583 137501
 (10) Hudson_Bay 1191 11933 -10743 22646 -21455
 (11) Central_Arctic 3113399 2937746 175653 2817614 295785

The deficits continue to be on the Pacific side, especially Beaufort, and also Greenland Sea is down this year.  These are more than offset by large surpluses in the Central Arctic and Canadian Archipelago, and also Laptev.  East Siberian sea also has surplus ice this year compared to 2007.

aer Atmospheric and Environmental Research

September 5, 2017 Dr. Judah Cohen of AER posted his monthly forecast for the Arctic and NH based on the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO).  Excerpts below.

The AO is currently slightly negative (Figure 1), reflective of mostly positive geopotential height anomalies across the Arctic and mixed geopotential height anomalies across the mid-latitudes of the NH (Figure 2). Geopotential height anomalies are mostly negative across Greenland and Iceland (Figure 2), and therefore the NAO is slightly positive.
Figure 1. (a) The predicted daily-mean near-surface AO from the 00Z 5 September 2017 GFS ensemble. Gray lines indicate the AO index from each individual ensemble member, with the ensemble-mean AO index given by the red line with squares.

The AO is predicted to straddle neutral next week as geopotential height anomalies remain mixed across the Arctic. Similarly, with mixed geopotential height anomalies stretching across Greenland and Iceland, the NAO will likely be near neutral as well.  

(Note: AO and NAO are signed differently than one might expect; the reference point is outside the Arctic itself.  Thus negative phases of these indices mean higher pressures in the Arctic and lower outside, while positive phases indicate lower pressures in the Arctic.  Now that the Arctic sun is setting, the main issue for ice extent is storminess which requires low Arctic pressures.)

Impacts

It is the first week of fall, a season of transition from summer to winter. One important sign IMO of this seasonal transition is the return of the polar vortex in the stratosphere. The models predict the possible formation of the polar vortex sometime next week. Starting in October, I will be watching variability in the polar vortex for signs of pattern changes in the weather across the NH.

Another sign of the seasonal transition is the minimum in Arctic sea ice extent, which will be achieved in the coming days and/or weeks. The trajectory of sea ice melt has slowed since early August. In my last blog I suggested the possibility that the sea ice minimum could be similar to the years 2008 and 2010 and that is looking more likely but is difficult to predict. Over the coming months, I will be following Arctic sea ice variability for signs of the severity of the upcoming winter. Our understanding for how anomalies in sea ice extent influence the weather in the mid-latitudes is still immature IMO but I do think that important progress has been made recently.

Another sign of the transition from summer to winter is the return of snowfall to the NH. Snowfall over the sea ice in August probably helped retard the melt of sea ice and snowfall is now even occurring over Siberia and Alaska but is still very regionalized. Again I will be monitoring the advance of snow cover extent across the continents for signs of the strength of the polar vortex and the possible resultant weather.

Finally I find it interesting that while the atmospheric circulation has transitioned from the dominant summer pattern across Eurasia it has not across North America. The dominant summer pattern across Eurasia was ridging across Europe (with the exception of Northern Europe) and East Asia but with troughing in Western Asia. The forecast for the coming weeks is the opposite with troughs across Europe and East Asia but ridging in Western Asia. This is an overall cooler pattern than the dominant summer pattern. However across North America there are no similar signs of transition. The dominant summer pattern was strong ridging across western North America and troughing in eastern North America and at least for now that pattern looks to continue for much of the month of September. I don’t know the reason behind the persistent western ridge/eastern trough pattern across North America but how long this pattern can persist will obviously have important implications for the weather across North America in the coming months.

Summary

Bottom line, looks like September weather will be ordinary in the Arctic with seasonal cooling in the NH.  Dr. Cohen also thinks the annual ice extent minimum will be near average for the decade.  While the monthly average is final only at September end, the next week will set the tone and likely result.

 

 

Sept. Weather Forecast Arctic & NH

aer Atmospheric and Environmental Research

September 5, 2017 Dr. Judah Cohen of AER posted his monthly forecast for the Arctic and NH based on the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO).  Excerpts below.

The AO is currently slightly negative (Figure 1), reflective of mostly positive geopotential height anomalies across the Arctic and mixed geopotential height anomalies across the mid-latitudes of the NH (Figure 2). Geopotential height anomalies are mostly negative across Greenland and Iceland (Figure 2), and therefore the NAO is slightly positive.
Figure 1. (a) The predicted daily-mean near-surface AO from the 00Z 5 September 2017 GFS ensemble. Gray lines indicate the AO index from each individual ensemble member, with the ensemble-mean AO index given by the red line with squares.

The AO is predicted to straddle neutral next week as geopotential height anomalies remain mixed across the Arctic. Similarly, with mixed geopotential height anomalies stretching across Greenland and Iceland, the NAO will likely be near neutral as well.  

(Note: AO and NAO are signed differently than one might expect; the reference point is outside the Arctic itself.  Thus negative phases of these indices mean higher pressures in the Arctic and lower outside, while positive phases indicate lower pressures in the Arctic.  Now that the Arctic sun is setting, the main issue for ice extent is storminess which requires low Arctic pressures.)

Impacts

It is the first week of fall, a season of transition from summer to winter. One important sign IMO of this seasonal transition is the return of the polar vortex in the stratosphere. The models predict the possible formation of the polar vortex sometime next week. Starting in October, I will be watching variability in the polar vortex for signs of pattern changes in the weather across the NH.

Another sign of the seasonal transition is the minimum in Arctic sea ice extent, which will be achieved in the coming days and/or weeks. The trajectory of sea ice melt has slowed since early August. In my last blog I suggested the possibility that the sea ice minimum could be similar to the years 2008 and 2010 and that is looking more likely but is difficult to predict. Over the coming months, I will be following Arctic sea ice variability for signs of the severity of the upcoming winter. Our understanding for how anomalies in sea ice extent influence the weather in the mid-latitudes is still immature IMO but I do think that important progress has been made recently.

Another sign of the transition from summer to winter is the return of snowfall to the NH. Snowfall over the sea ice in August probably helped retard the melt of sea ice and snowfall is now even occurring over Siberia and Alaska but is still very regionalized. Again I will be monitoring the advance of snow cover extent across the continents for signs of the strength of the polar vortex and the possible resultant weather.

Finally I find it interesting that while the atmospheric circulation has transitioned from the dominant summer pattern across Eurasia it has not across North America. The dominant summer pattern across Eurasia was ridging across Europe (with the exception of Northern Europe) and East Asia but with troughing in Western Asia. The forecast for the coming weeks is the opposite with troughs across Europe and East Asia but ridging in Western Asia. This is an overall cooler pattern than the dominant summer pattern. However across North America there are no similar signs of transition. The dominant summer pattern was strong ridging across western North America and troughing in eastern North America and at least for now that pattern looks to continue for much of the month of September. I don’t know the reason behind the persistent western ridge/eastern trough pattern across North America but how long this pattern can persist will obviously have important implications for the weather across North America in the coming months.

Summary

Bottom line, looks like September weather will be ordinary in the Arctic with seasonal cooling in the NH.  Dr. Cohen also thinks the annual ice extent minimum will be near average for the decade.

 

 

Arctic Ice Uncertainties

Northern Hemisphere Spatial Coverage

As noted in the September Outlook Arctic Ice, NOAA’s Sea Ice Index (SII) typically shows less ice than MASIE from National Ice Center (NIC). SII is a satellite product processed from passive microwave sensors. MASIE (Multisensor Analyzed Sea Ice Extent) adds other sources such as satellite imagery and field observations to produce high resolution ice charts for navigational purposes.

A post in 2016 NOAA Is Losing Arctic Ice showed how discrepancies between the two datasets vary considerably throughout the year, usually lower in SII except for October. Walt Meier directs the SII production and published a study in October 2015 comparing SII and MASIE, also discussed in that post.

In 2016 NOAA upgraded from SII version 1 to version 2, and later to version 2.1. The latest documentation says few datapoints were changed in v2.1, and that anomalies were unchanged. My cursory look seemed to confirm that. However, on closer inspection, there are significant differences between v1 and v2 (which carry over to v2.1). This post describes those differences.

I prepared two spreadsheet arrays for SIIv1 and SIIv2.1 and then a third array to calculate the differences. The graph below shows the results for 2006 to 2015 inclusive, being the years for which datapoints can be compared with MASIE.

It is clear that V2.1 is systematically lower than V1, on average -200k km2. The differences are less than 100k km2 the first four months, then increase May, June, July, before shrinking again in August and September. The big changes come in the last months, especially October. The October correction is not surprising. The comparison by Meier and in my post discussed large SII surpluses over MASIE in October that did not appear credible.

The graph is limited to one decade since that is the period to be compared with MASIE. The spreadsheet shows that the differences are typical of the whole dataset going back to 1979, albeit with considerable variety through the years. The graph below shows the month by month differences for all years through 2015.

As stated before, the average all years difference in green is comparable to the last decade. Differences were calculated by subtracting v1 from v2, since v2 is mostly lower. However, as the Min Diff line shows, v2 was higher for some datapoints, notably in July. The Max Diff shows that some Octobers were changed by as much as 1M km2. The dotted lines show the standard deviation for the average differences, which averaged  +/- 90k km2.

Summary

It is challenging to estimate Arctic ice extents. NOAA is to be commended for recognizing the erroneous October values, and correcting them. Clearly some of that overall diminishing of extents by 200k km2 derives from removing the bogus surpluses.

Those claiming that SII is for certain and MASIE is dubious need to reconsider. MASIE has its own challenges but is reasonably consistent in recent years. Meanwhile SII had to improve its product, resulting in changes to past values in the dataset. While error ranges are not available for these statistics, the standard deviation gives some indication of the variability in the estimates.

Fortunately, it appears that the critical months of March and September have not changed much in the new SII version.  However, it is not encouraging to see SII averages for the last two months -500k km2 below MASIE.  See September Outlook Arctic Ice

It is a good thing that several agencies and methods are involved in the effort to measure and understand Arctic ice dynamics. It is not good to claim certainty for a single record or to ignore the errors that are found along the way. It is wise to remember that measuring anything in the Arctic is difficult.

September Outlook Arctic Ice

2017: August Report from Sea Ice Prediction Network

For the August Report there were 37 contributions with the median Outlook value for September 2017 Arctic sea ice extent of 4.5 million square kilometers with quartiles of 4.2 and 4.8 million square kilometers (See Figure 1 in the Overview section, below). These values are unchanged from the July Report, which is consistent with the moderating impact of summer 2017 Arctic weather. The range is 3.1 to 5.5 million square kilometers in August, unchanged from the July Outlook. To place this Outlook in context, recently observed values were 4.3 million square kilometers in 2007, 3.6 million square kilometers in 2012, and 4.7 million square kilometers in 2016. 

These are predictions for the September 2017 monthly average ice extent as reported by NOAA Sea Ice Index (SII). This post provides a look at the 2017 Year To Date (YTD) based on monthly averages comparing MASIE and SII datasets. (10 year average is 2007 to 2016 inclusive)

The graph puts 2017 into recent historical perspective. Note how 2017 was below the 10-year average for the first 4 months, then recovered to match average in May and has maintained average through August. The outlier 2012 provided the highest March maximum as well as the lowest September minimum, coinciding with the Great Arctic Cyclone that year.  2007 began the decade with the lowest minimum except for 2012.  SII 2017 is running below MASIE and is currently just below MASIE 2007 and 2012.

The table below provides the numbers for comparisons.

Monthly 2017 2017 2017 2017-10yr Ave 2017-10yr Ave 2017-
2007
Averages MASIE SII SII
Deficit
MASIE SII MASIE
Jan 13.503 13.174 -0.329 -0.418 -0.512 -0.259
Feb 14.478 14.112 -0.366 -0.363 -0.440 -0.173
Mar 14.509 14.273 -0.236 -0.544 -0.542 -0.114
Apr 13.941 13.760 -0.180 -0.412 -0.446 0.246
May 12.838 12.618 -0.220 0.075 -0.138 0.412
June 10.975 10.720 -0.255 0.069 -0.218 0.148
July 8.383 7.901 -0.482 0.024 -0.206 0.367
Aug 6.006 5.472 -0.533 0.051 -0.185 0.421

The first two columns are the 2017 YTD shown by MASIE and SII, with the SII deficits in column three.  The difference has doubled the last two months and averaged -325k km2 for the YTD. Column four shows MASIE 2017 compared to MASIE 10 year average, while column five shows SII 2017 compared to SII 10 year average.  YTD MASIE is -190k km2 to average and SII is -336k km2 to average.  The last column shows MASIE 2017 holding an August surplus of 421k km2 over 2007.  For the YTD 2017 is 131k km2 higher than 2007, overcoming this year’s deficits in the early months.

For more on SII versions 1 and 2 differences see Arctic Ice Uncertainties

Summary

The experts involved in SIPN are expecting SII 2017 September to be higher than 2007 and slightly lower than 2016.  The way MASIE is going, this September looks to go higher than 2016 unless some bad weather intervenes.

Footnote:

Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used. This is false in fact and in logic. Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year? Researchers do this, including Walt Meier in charge of Sea Ice Index. That said, I understand his interest in directing people to use his product rather than one he does not control. As I have said before:

MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies. More on this at my post Support MASIE Arctic Ice Dataset

MASIE: “high-resolution, accurate charts of ice conditions”
Walt Meier, NSIDC, October 2015 article in Annals of Glaciology.

Arctic Ice September Strong

Click on image to enlarge.

The image above shows ice extents for yesterday, day 244, from 2007 to 2017.  Particularly interesting is the variation in the CAA (Canadian Arctic  Archipelago), crucial for the Northwest Passage.  (The region is located north of the word “Extent” in gold.)  While 2016 was a fine year for cruising with the passage completely open at day 244 that was not the case in 2014, and this year also has places frozen solid. By September 1, ice is still clogging some channels.

The graph of August NH ice extents shows 2017 has remained above the decadal average in recent days. (Ten-year average is for 2007 to 2016 inclusive).

This year is now 600k km2 greater than 2016 and exceeds the 10 year average by 50k km2.  SII (Sea Ice Index) 2017 is closer now, only 200k km2 lower.  2007 is running 400k km2 lower.  A previous post Beware the Arctic Storms of August discussed how late summer storms have dramatic impacts, and the graph shows both 2012 and 2016 plummeting in late August.  Note that just 2 weeks ago 2012 was tied with 2017, and then lost 1.6M km2.  2016 lost 1.3M km2 in the same period.

The table below compares 2017 with 2007 and the 10-year averages for Arctic regions.

Region 2017244 Day 244
Average
2017-Ave. 2007244 2017-2007
 (0) Northern_Hemisphere 4934548 4884191 50357 4525136 409412
 (1) Beaufort_Sea 424479 542957 -118477 629454 -204974
 (2) Chukchi_Sea 204972 225008 -20036 96232 108740
 (3) East_Siberian_Sea 314746 348577 -33831 196 314550
 (4) Laptev_Sea 216679 182883 33796 245578 -28899
 (5) Kara_Sea 34099 45628 -11528 74307 -40208
 (6) Barents_Sea 16638 23603 -6965 11061 5577
 (7) Greenland_Sea 142702 183941 -41239 288223 -145521
 (8) Baffin_Bay_Gulf_of_St._Lawrence 55689 24864 30825 32804 22885
 (9) Canadian_Archipelago 384879 294120 90759 234389 150490
 (10) Hudson_Bay 3848 23575 -19727 28401 -24553
 (11) Central_Arctic 3135439 2988097 147342 2883201 252238

2017 has deficits mainly in BCE, especially Beaufort Sea, but those are more than offset by surpluses in Central Arctic and CAA (Canadian Arctic Archipelago).  As shown in the post Arctic Heart Beat Central Arctic and CAA are the two regions providing most of the ice extent at annual minimum.

Footnote

Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used.  This is false in fact and in logic.  Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year?  Researchers do this, including Walt Meier in charge of Sea Ice Index.  That said, I understand his interest in directing people to use his product rather than one he does not control.  As I have said before:

MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies.  More on this at my post Support MASIE Arctic Ice Dataset

Serenity Faces Ice Aug.30

Click on image to enlarge.

August 31 and Sept. 1 Updates Below

h/t to angech for asking an interesting question:  What are the chances of an early refreezing in the Northwest Passage?  It provoked me to look more into the recent history of ice extents in the CAA (Canadian Arctic Archipelago).

The image above shows the years in the last decade closest to 2017 in terms of ice present in the CAA.  Only 2014 had more ice in that region than this year: 513k km2 compared to 464k km2 at day 240.  It appears that CAA annual minimum typically occurs at day 260, the same as the overall NH minimum.  The image above also shows that 2009 with 388k km2 provides the closest analog to this year for the amount of ice in McClintock Bay just in front of Serenity. The image below gives the progression in 2009 from day 244 to 270.

As of 10:30 EST this morning Serenity is located as shown in image below along with ice extent reported by MASIE for yesterday.  Ship tracking is provided by marinevesseltraffic.com  and shows that Serenity is now in convoy with two icebreakers ahead of her.

Canadian ice chart from yesterday showing Serenity and escort worked their way through the water and thinner green ice, but with some thicker stuff ahead.

Serenity will make it through with such assistance, which was largely unnecessary last year.  And as the above shows, 2014 would have been close to impossible.

UPDATE 16:30 EST

The convoy has reached the southern tip of Prince of Wales Island and are turning northeast. It appears they will sail along the thin shore ice, presumably headed for the western entrance of Bellot Strait which passes through to Prince Regent channel.

UPDATE 7:00AM EST AUG. 31

Serenity convoy is about to enter Bellot Strait.  Waiting for a cargo ship to exit the channel.

UPDATE 9:00AM EST Aug. 31

Cruisemapper shows Serenity has entered the Strait following her icebreaker.

Update 12:00 PM EST Aug. 31

Serenity and icebreaker escort have emerged from Bellot Strait into Prince Regent channel and are turning north.  Next destination may well be Devon Island with some interesting things that were seen last year.  See Mars in the Arctic

Update 7:00 AM EST Sept. 1, 2017

Serenity and icebreaker are anchored just off Beechey Island at the southwestern tip of Devon Island.