85th AMS Annual Meeting

Tuesday, 11 January 2005: 9:15 AM
Seasonal comparisons of strong western North Pacific cyclones and the SST anomalies beneath them
Richard E. Danielson, Dalhousie University, Halifax, NS, Canada; and J. R. Gyakum
Studies have long emphasized the importance of western ocean boundary currents and their strong sea surface temperature (SST) gradients to the development of midlatitude cyclones, especially strong ones. However, they have also emphasized that the net role of surface heat fluxes in cyclones is not well understood. Prompted by an unexplained atmospheric phenomenon over the North Pacific Ocean, called the midwinter storm track suppression, the hypothesis of a seasonal variation the role of surface heat and moisture fluxes in small groups of strong western North Pacific cyclones is examined. Their net effect is examined using SST anomalies as a proxy. Composite SST anomalies are constructed for each cyclone group, where groups are defined only by their occurrence during midwinter or during the early and late cold season. Systematic differences in sea surface temperature anomalies are interpreted as differences in preconditioning by the upper-oceanic mixed layer. It is suggested that the role of preconditioning heat fluxes in cyclones varies because of large-scale seasonal changes in baroclinicity, or perhaps more specifically static stability, and in the role of the ocean as a local source of water vapour.

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