Dependence of winter precipitation over Portugal on NAO and baroclinic wave activity

作者：Ulbrich U^*; Christoph M; Pinto JG; Corte Real J

来源：International Journal of Climatology, 1999, 19(4): 379-390.

DOI：10.1002/(SICI)1097-0088(19990330)19:4<379::AID-JOC357>3.0.CO;2-8

• precipitation
• North Atlantic Oscillation
• Portugal
• surface low
• storm track
• baroclinic wave
• EOF-analysis

The relationship between winter (DJF) rainfall over Portugal and the variable large scale circulation is addressed. It is shown that the poles of the sea level pressure (SLP) field variability associated with rainfall variability are shifted about 15 degrees northward with respect to those used in standard definitions of the North Atlantic Oscillation (NAO). It is suggested that the influence of NAO on rainfall dominantly arises from the associated advection of humidity from the Atlantic Ocean, Rainfall is also related to different aspects of baroclinic wave activity, the variability of the latter quantity in turn being largely dependent on the NAG.
A negative NAO index (leading to increased westerly surface geostrophic winds into Portugal) is associated with an increased number of deep (p(s)<980 hPa) surface lows over the central North Atlantic and of intermediate (980 A separate influence of local surface cyclones over the Iberian peninsula which may, for instance, arise from the large scale ascent of air, is revealed by the statistics: for a given advection, rainfall amounts for months with local cyclone cores over the considered region tend to exceed those without.

• 出版日期1999-3-30