Seasonal and regional responses to changes in Australian soil moisture conditions

Abstract

This paper addresses the interaction of large scale soil moisture anomalies and the atmospheric circulation. This approach is based on a suite of GCM experiments in which the soil was instantaneously saturated and desiccated over the entire Australian continent. These conditions were imposed on the first day of each of the 12 calendar months and anomaly simulations integrated for 4 months. The ‘memory’ of these changes as reflected in the important climate elements was analysed. The subsequent anomalies of soil moisture exhibited the greatest persistence of up to and beyond 4 months. This persistence was most apparent for the simulations initiated in winter. The surface latent heat flux anomalies showed comparable, if slightly smaller, levels of persistence. Somewhat smaller amounts of perseverance were found for the anomalies of surface air temperature, even less in the precipitation (and indeed none in the desiccated case), and very modest amounts in the mean sea level pressure. The results shown here demonstrate substantial asymmetry in the transient response of the climate system to these wet and dry soil moisture conditions. Also apparent is a seasonal and regional dependence in the way in which the model recovers from the perturbations to the moisture. These three characteristics are seen to be connected to some extent. The explanation for the behaviours lies in the many nonlinear processes in the land-atmosphere system and the complex roles played by convection, cloud, circulation regimes (including the monsoon), thermal conditions, and horizontal moisture transports. © 1998 Royal Meteorological Society.