The influence of soil moisture anomalies on variability of the North American monsoon system

Abstract

We examine the influence of land-atmosphere interactions, as moderated by soil moisture anomalies, on variability of the North American Monsoon System (NAMS). Sensitivity experiments, in which soil moisture was prescribed to field capacity, were completed with the MM5 mesoscale model linked to the OSU land surface scheme. Our results demonstrate that the NAMS precipitation response to soil moisture forcing depends critically on the location of anomalous surface conditions. Wet soil in the southern Rocky Mountains (SRM) during July, which could result from the melt of an above-normal snowpack, inhibits precipitation in the NAMS region. This is consistent with the observed negative correlation between SRM spring snowcover and NAMS summer precipitation [Gutzler and Preston, 1997]. In contrast, wet soil in the NAMS region enhances July precipitation within that area-a positive soil moisture-rainfall feedback exists. Our findings must be tested with experiments that incorporate anomalies constrained by regional-scale soil moisture observations.