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2008.02.18
North Pacific Winter Conditions Increasingly Severe !
(Comparing 2006 & 2007 conditions to average conditions)
There have been several heavy weather events across the major shipping lanes of the North Pacific so far this year – the second year in a row of notably heavy conditions. This prompted us to ask: How does the winter of 2007 (so far) compare to last year?
Figure 1. Sea Level Pressure (mb) composite anomaly for November - December 2007, as compared to climatogical mean 1968-1996. From NCAR/NCEP global Reanalysis Data provided by Earth System Research Laboratory.
Figure 2. Sea Level Pressure (mb) composite mean for November - December 2007. From NCAR/NCEP global Reanalysis Data provided by Earth System Research Laboratory.
Figure 1 shows the mean sea level pressure anomaly for the months of November and December of this winter season. This figure shows sea level pressures were lower than average across the Bering Sea and through the western portions of the basin, with pressures higher than average across the eastern portions of the basin and into the southern Gulf of Alaska.
Figures 2 and 3 show the composite mean sea level pressure for the months of November-December, for 2007 and for the years 1968-1996, which we can take to be the climatological mean. Comparing the two figures, one will note that the composite mean sea level pressure for Nov.-Dec. 2007 is fairly similar to the climatological mean, with a few small, but important, differences.
Comparing November-December of 2006 to 2007, the overall pattern across the basin is almost exactly opposite from year to year: An amplified trough-ridge pattern over the basin in 2007, with an amplified ridge-trough pattern over the basin in 2006.
All in all, for the period November-December, the Bering Sea and Gulf of Alaska have seen more days with heavy weather in 2007 – the weather appears to have been worse this winter compared to last winter. And while it is not yet possible to determine whether the winter of 2007 in the North Pacific as a whole is worse than the whole winter of 2006, one conclusion that can be made is that it appears that this year, the conditions experienced in the Gulf of Alaska this year have indeed been worse than last year.
