Seasonal evolution of Aleutian low-pressure systems: Implications for the North Pacific sub-polar circulation
Pickart, R. S., G. W. K. Moore, A. M. Macdonald, J. E. Walsh and W. S. Kessler
Journal of Physical Oceanography, 39, 1316-1339.
Abstract The development of Aleutian low storms, and how this evolves from early fall to early winter, is analyzed using a combination of meteorological fields and satellite sea surface temperature (SST) and wind data. The time period of this study is September-December 2002, although results are shown to be representative of the longterm climatology. Charateristics of the storms were documented as they propagated across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to spin up in two distinct geographical locations - the Gulf of Alaska in early fall, and the western North Pacific in late fall - seemingly related to the seasonal evolution of the SST field in both regions. In the Gulf of Alaska, a "notch" in the SST distribution seems to be of primary importance by optimizing differential heating of the storm and allowing air-sea fluxes to energize the storm more effectively. As winter approaches and the Sea of Okhotsk becomes partially ice-covered and cold, the air emanating from the Asian continent leads to cyclogenesis in the region near Kamchatka. The impact on the oceanic circulation of the windstress curl pattern resulting from these two regions of storm development is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may in part be responsible for the two distinct North Pacific sub-Arctic gyres.
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Dr. William S. Kessler
NOAA / PMEL / OCRD
7600 Sand Point Way NE
Seattle WA 98115 USA