Friday Map Discussion: 14 September 2007

Hi Folks,

Motivated by yet another record minimum in Arctic Ocean sea ice extent (2.92 x 10+6 km2 as of 12 Sep; previous all-time record minimum was ~4.0 x 10+6 km2 in 2005) the focus of Friday map discussion for 14 Sep'07 was on the poles.

The Arctic sea ice measurements were obtained from "The Cryosphere Today (TCT)" at the University of Illinois (first link below). Noteworthy is that a new historic sea ice *maximum* was set around Antarctica on the same day(12 Sep) as the historic sea ice *minimum* in the Arctic Ocean. Go figure. How do you say that the results are (forgive me) "poles" apart? No one ever said that the process of climate change is linear.

I have attached a NH sea ice *anomaly* time series from 1 Jan'79 to the present as downloaded from the TCT link (caution: this is an anomaly time series relative to the 1979-2000 mean; a time series of mean sea ice extent was not available). The historical record shows that sea ice anomalies fluctuated between +/- 1.0 x 10+6 km2 between 1979 and 1995. Subsequently, negative sea ice extent anomalies have dominated the time series after the (last?) hurrah for a positive million km2 ice anomaly in roughly October 1996.

Of interest, is the net 2.0 x 10+6 km2 change (positive to negative) in sea ice anomaly in November 1996. Both Ryan Torn (phone call) and Tom Galarneau noted that this huge swing from positive to negative sea ice anomalies coincided with the extratropical transition (ET) of SuperTyphoon Dale. As discussed in Eric Kelsey's master's thesis on this storm, a huge surge of modified tropical air reached the North Pole ahead of Dale and the resulting intense (944 hPa) extratropical cyclone that resulted from the Dale ET. Other deep cyclone events prior and subsequent to the Dale ET also contributed to large positive heat fluxes at higher latitudes of the NH. Coincidence or enemy action?

Also attached is a time series of monthly temperature anomalies from late 1992 through August 2007 for land areas of the NH, SH and the globe. This time

series was obtained from the Climate Diagnostics Bulletin (CDB) at the Climate Prediction Center (CPC) link (second link below). >From this image it is readily apparent that positive temperature anomalies have dominated both hemispheres and the globe over continental areas with the great El Nino year of 1998 still the positive anomaly champ. Of interest is that SH land areas have experienced three consecutive months (unique to the time series) of slightly below normal temperatures for JJA 2007. The question arises as to whether continental coolness in the just-concluded SH winter is a result and/or a cause (or neither) of the record maximum SH sea ice extent this winter.

Images of the mean and forecast (GFS) spread of the Antarctic Oscillation index (AAO) as obtained from the CPC (third link below) are also attached. From early June until mid-August the AAO was negative (anomalously weak polar westerlies). Remarkably, the AAO index pegged at a -4.0 sigma value in late July when major cold air outbreaks were common around the SH (e.g., the first snow in Buenos Aires in 80 years). Note also that the GFS control/ensemble forecasts had difficulty capturing the negative plunge of the AAO index in the latter part of July (the observed value of the AAO was outside the range of the ensemble spread for more than a week even in the 7-day forecasts).

A fascinating research project would be to investigate the possible atmospheric causes for the observed daily NH sea ice anomaly since 1979. This is a good opportunity to take synoptic meteorology in a new direction. At issue is to what extent the observed sea ice anomalies at higher northern latitudes respond to internal factors (e.g., Arctic wind patterns, Arctic cloud cover changes) versus external factors (e.g., enhanced poleward heat fluxes in conjunction with storminess in middle and higher latitudes, changes in oceanic heat fluxes, and general climate change). The attached NH sea ice anomaly time series suggests that changes in sea ice anomalies are mostly occurring on synoptic and intraseasonal time scales superimposed on a long-term downward trend.

Lance

http://arctic.atmos.uiuc.edu/cryosphere/

http://www.cpc.ncep.noaa.gov/products/CDB/

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/teleconnections.shtml