SMEX04

In much of the interior of the North American continent, summer precipitation is a dominant feature of the annual cycle. Surface boundary conditions play an important role in initiation and maintenance of the North American Monsoon System (NAMS), which controls summer precipitation over much of this region.

Understanding these processes is a focus for the North American Monsoon Experiment. A working hypothesis is that among the land surface antecedent boundary conditions that control the onset and intensity of the NAMS is soil moisture. The influence of the land surface is relayed through surface evaporation and associated surface cooling (dependent on soil moisture), terrain, and vegetation cover. Soil moisture and, in particular, surface wetness, can change dramatically after heavy rain events. Increased soil moisture after precipitation promotes evapotranspiration between storm events. This may contribute to enhanced convection and further precipitation.

As part of NAME there will be an intensive observing period in the summer of 2004 over the Tier I domain. The intention of SMEX04-NAME is to enhance the terrestrial hydrology component of NAME by facilitating development of soil moisture. Specific activities include the provision of soil moisture products from the existing insitu network in Arizona and the development of an equivalent network within a study region in Mexico, and soil moisture products derived from existing satellite sensors on Aqua and TRMM. An intensive ground and aircraft field campaign will take place during August 2004 that will provide validation of the insitu and satellite products. SMEX04-NAME will also address important algorithm and validation issues for existing satellite based soil moisture products from the Advanced Microwave Scanning Radiometer and future low frequency instruments.