Local and Remote Atmospheric Responses to Soil Moisture Anomalies in Australia

Three sets of model experiments are performed with the Community Earth System Model to study the role of soil moisture anomalies as a boundary forcing for the formation of upper-level Rossby wave patterns during the Southern Hemisphere summer. In the experiments, soil moisture over Australia is set to +/- 1 standard deviation (STD) of an ERA-Interim-derived soil moisture reconstruction for the years 2009-16 and 50 ensemble members are run. The local response is a positive heating anomaly in the dry simulations that results in a thermal low-like circulation anomaly with an anomalous surface low and upper-level anticyclone. Significant differences in convective rainfall over Australia are related to differences in convective instability and associated with changes in near-surface moisture and moisture advection patterns. A circum-hemispheric flow response is identified both in the upper-level flow and in the surface storm tracks that overall resembles a positive southern annular mode-like flow anomaly in the dry simulations. The structure of this atmospheric response strongly depends on the background flow. The results point to a modulation of the hemispheric flow response to the forcing over Australia by El Nino-Southern Oscillation. Significant changes of precipitation over the Maritime Continent and South Africa are found and significant differences in the frequency of surface cyclones are present all along the storm tracks.

Automated summary

Model experiments show that soil moisture anomalies in Australia during the Southern Hemisphere summer can influence upper-level Rossby wave patterns, resulting in temperature anomalies and convective rainfall differences in the region, which in turn affect circulation patterns and storm tracks.