ABSTRACT

High-frequency variability in the stratocumulus cloud cover at the eastern rim of the subtropical anticyclone of the southeast Pacific constitutes a central element of the regional climate as it deeply modulates longer period fluctuations. This variability is especially marked over the coastal strip due to the diurnal solar radiation cycle and to the existence of a generic phenomenon known as coastal lows.

Based on weather charts (Reanalysis) together with sur face and upper-air data obtained during the CIMAR 6 cruise, the effect of synoptic-scale variability on the stratocumulus within the marine boundary layer and the inversion layer above it, is documented and discussed. This variability was outstanding during the first half of CIMAR 6, due to the projection of mid-latitude disturbances over the subtropical sector of the southeastern Pacific. The amplitude of these disturbances was more pronounced over the coastal strip, possibly in connection with enhanced up and down flows by the Andes. The warm easterlies and the descent of the subsidence inversion associated with the onset of upper-air ridges that followed those disturbances, extended as far as 800 km offshore, though winds in a shallow surface layer maintained the south (equatorward) direction. It can be concluded that, at a local level, there is no simple relationship between large scale subsidence and depth of the marine boundary layer, probably due to the warm advection produced by the easterlies as they flow down the Andes slope.

Key words: Marine boundar y layer, Stratocumulus, Southeastern Pacific, Subtropical anticyclones.