Effects of the Andes on Eastern Pacific Climate: A Regional Atmospheric Model Study*

Abstract

Abstract A regional atmospheric model is used to study the effects of the narrow and steep Andes on the eastern Pacific climate. In the Southern Hemisphere cold season (i.e., August–October 1999), the model reproduces key climatic features, including the intertropical convergence zone (ITCZ) north of the equator and an extensive low-level cloud deck capped by a temperature inversion to the south. Blocking the warm easterly winds from South America, the Andes help maintain the divergence and temperature inversion and, hence, the stratocumulus cloud deck over the southeast Pacific off South America. In an experiment where the Andean mountains are removed, the warm advection from the South American continent lowers the inversion height and reduces the low-level divergence offshore, leading to a significant reduction in cloud amount and an increase in solar radiation that reaches the sea surface. In March and early April 1999, the model simulates a double ITCZ in response to the seasonal warming on and south ...