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. (C) 1998 Royal Meteorological Society. [References: 66]