CONICET | Buscador de Institutos y Recursos Humanos

The impact of changes in soil moisture in subtropical Argentina in rainfall distribution and low level circulation is studied with a state-of-the art regional model in a downscaling mode, with different scenarios of soil moisture for a 10 day period. The selected case (starting January 29, 2003) was characterized by a Northwestern Argentina Low event associated with well defined low level northerly flow that extended east of the Andes over subtropical latitudes. Four tests were conducted at 50 km horizontal resolution with 31 sigma levels, decreasing and increasing the soil moisture initial condition by 50% over the entire domain, 50 % reduction over northwest Argentina and 50% increase over South East South America. A control run with NCEP/GDAS initial conditions was used to assess the impact of the different soil moisture configurations. It was found that land-surface interactions are stronger when soil moisture is decreased, with a coherent reduction of precipitation over southern south America. Enhanced northerly winds result form an increase in the zonal gradient of pressure at low levels. In contrast, when soil moisture is increased, no circulation changes are found, though there appears to be a local feedback effect between the land and precipitation The combined effects of changes in the circulation and in local stratification induced by soil wetness modifications, through variations in evaporation and CAPE, are in agreement with what has been found by other studies, resulting in coherent modifications of precipitation when variations of CAPE and moisture flux convergence mutually reinforce.