Wednesday, 17 August 2016

Arctic Sea Ice Update

2016 Arctic cyclone, update 1

Arctic Sea Ice Blog

As announced in ASI 2016 update 5 a very large cyclone is raging in the Arctic, as we speak. According to Environment Canada the storm's current central pressure is 970 hPa, but it was 968 hPa 12 hours ago, which is probably the lowest it will go. I've combined the weather map with yesterday's Uni Bremensea ice concentration map, for geographical orientation and the storm's position in relation to the ice pack:
  Arctic Cyclone 968 hPa
There hasn't been a marked effect on the ice as of yet. On the Forum Wipneus reports a large drop of 170K in the Cryosphere Today sea ice area numbers he calculates. CTSIA20160816 
This is the third largest August daily drop in the last decade, but Wipneus explains it is partly due to flash melting in the Canadian Arctic Archipelago. A large drop in NSIDC SIE numbers of 122K is entirely due to the CAA, but it would be even larger if it weren't for ice in the Laptev Sea 'unflashing' into the view of the SSMIS satellite sensor aboard the DSMP F18 satellite.
I expect some more flashing tomorrow in the regions that are directly affected by the storm. Not only is there a lot of ice jutting out towards the East Siberian and Chukchi Seas, there is also a 'bite' developing towards the pole. It can clearly be seen on this animation of Uni Bremen SIC maps. Also note the movement in the last two frames, due to the storm. This movement will become more marked in the next 2-3 days:
But back to the storm. As explained in the ASI update, a pressure of 968 hPa isn't as low as the 963 hPa of the Great Arctic Cyclone of 2012 (GAC-2012), but it is very low nonetheless. It's difficult to classify the storm, especially as it is still ongoing, but soon after GAC-2012 a paper was published by Simmonds and Rudeva to ascertain the storm's ranking according to their methodology:

The plot shows that AS12 was at the tail of the distribution and, at 966.38 hPa, was the lowest in our record, beating the previous deepest (966.94 hPa) (for a storm at 06UTC 7 August 1995) by 0.56 hPa. The next lowest central pressure, 969.23 hPa, was associated with a cyclone at 06UTC 22 August 1991, followed by the fourth lowest storm central pressure in the earlier part of that month 00UTC 7 August 1991 (970.47 hPa).
Their central pressure of 966 hPa is 3 hPa higher than the one reported by Environment Canada while the storm was ongoing. If the same applies to this storm, a central pressure of 971 hPa means there have been at least four stronger Augusts storms in their 1979–2012 database. However, they do not look at central pressure only, but also at intensity, radius, depth and longevity.
In this regard it's interesting to have a look at what the  ECMWF model is forecasting for the next 6 days (click for a larger version, and go to the ASIGForecasts page for daily forecasts):
The storm loses strength, but doesn't fade away completely. In fact, the forecast beyond these 6 days is showing a re-intensification of the storm. Below is an animation of the entire 11-day ECMWF forecast, as provided by the Tropical Tidbits website, which shows the cyclone's forecast central pressure: