Recorded presentation7A.6
Seasonal evolution of Aleutian Low-Pressure Systems: Implications for the North Pacific Ocean Sub-Polar Circulation
R. S. Pickart, WHOI, Woods Hole, MA; and G. W. K. Moore, A. Macdonald, I. A. Renfrew, J. E. Walsh, and W. S. Kessler
The seasonal change in the development of Aleutian low-pressure systems from early-fall to early-winter is analyzed using a combination meteorological re-analysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September--December, 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations---the Gulf of Alaska in early fall, and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent ``notch'' in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the windstress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific sub-Arctic gyres.
Session 7A, Ocean-atmosphere interactions and influences on tropical and extratropical storms: Part 2
Tuesday, 13 January 2009, 3:30 PM-5:00 PM, Room 128A
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