The Diurnal Cycle in Circulation and Cloudiness over the Subtropical Southeast Pacific: A Modeling Study

Abstract The extensive and persistent deck of stratocumulus (Sc) over the subtropical southeast Pacific (SSEP) plays an important role in the regional and global climate. As in other subtropical regions, the Sc form at the top of a marine boundary layer (MBL), capped by the subsidence inversion. A distinctive feature of this subtropical deck is its pronounced dawn-to-afternoon decrease in cloud amount and liquid water path, partially associated with a regular and marked descent of the inversion base and the warming of the lower troposphere. Furthermore, coastal observations in this area reveal a diurnal cycle in air temperature encompassing up to 5 km MSL. In this work, 15-day regional numerical simulations using the fifth-generation PSU–NCAR Mesoscale Model (MM5) in November (austral spring), May (late fall), and January (summer) 2001 were used to document the mean diurnal cycle in circulation and low-level cloudiness over the SSEP. The simulated amplitude, depth, and phase of the diurnal cycle in air te...

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