The Daily Cycle in and below the Lower Troposphere Along the Gulf of California During the North American Monsoon

The North American Monsoon (NAM) is an important seasonal feature of the continent's climate, but many details of it are poorly understood. Recent studies suggest that the simulated daily cycle of convection is out of phase with observations in part because the daily cycle of land/sea breezes and moisture transport is not adequately represented in the models. In order to provide a very detailed look at changes in the lower troposphere and the surface below it during the NAM, a suite of instruments was deployed at Estacion Obispo, Sinaloa, Mexico during the North American Monsoon Experiment (NAME) 2004 field program. Estacion Obispo is located along the west coast of Mexico near the mouth of the Gulf of California. A 915-MHz wind profiling radar with RASS, a sonic anemometer and Licor gas analyzer, Eppley pyranometers and pyrgeometers, and soil heat flux plates and thermistors were deployed during much of the 2004 North American Monsoon season. The resolution of the resulting datasets ranges from 1 minute (soil temperature, soil moisture, and radiation) to 30-minutes (profiler winds and RASS-derived virtual temperatures). This high temporal resolution allows us to study in great detail the daily cycle of the lower troposphere and the upper half-meter of the underlying land.

Analysis of these data in conjunction with other observations collected during the NAME Extended Observing Period show that some aspects of the daily cycle in this region were largely invariant over the time period, while others exhibited quite different characteristics during active and break monsoon episodes. These resuls will be presented and placed in the larger context of the 2004 NAM season. Data collected during a similar deployment in the summer of 2005 may also be presented in order to allow discussion of interannual variability.