Influence of the background wind on the local soil moisture-precipitation feedback

Abstract

The importance of soil moisture anomalies on airmass convection over semiarid regions has been recognized in several studies. The underlying mechanisms remain partly unclear. An open question is why wetter soils can result in either an increase or a decrease of precipitation (positive or negative soil moisture-precipitation feedback, respectively). Here an idealized cloud-resolving modeling framework is used to explore the local soil moisture-precipitation feedback. The approach is able to replicate both positive and negative feedback loops, depending on the environmental parameters. The mechanism relies on horizontal soil moisture variations, which may develop and intensify spontaneously. The positive expression of the feedback is associated with the initiation of convection over dry soil patches, but the convective cells then propagate over wet patches where they strengthen and preferentially precipitate. The negative feedback may occur when the wind profile is too weak to support the propagation of convective features fromdry towet areas. Precipitation is then generallyweaker and falls preferentially over dry patches. The results highlight the role of themidtropospheric flowin determining the sign of the feedback.Akey element of the positive feedback is the exploitation of both low convective inhibition (CIN) over dry patches (for the initiation of convection) and high CAPE over wet patches (for the generation of precipitation). © 2014 American Meteorological Society.