Satellite observations of Pacific moisture surges associated with the North American Monsoon

A substantial portion of the total annual precipitation in northwestern Mexico and the southwestern United States occurs during the monsoon season of July through mid-September. Rainfall events of highest intensity also occur during the monsoon period, making the region vulnerable to damaging flash floods throughout the summer months. Nevertheless, the regional atmospheric dynamics leading to severe monsoon storm events remain poorly understood.

Satellite observations provide a synoptic view of moisture circulation in the North American Monsoon region that is not provided by traditional meteorologic records. The dynamics of large-scale atmospheric moisture circulation during the 1997 through 2000 monsoon seasons were examined using a variety of satellite data sets including upper-tropospheric water vapor measurements from GOES and passive microwave sensors, and estimated rainfall and total precipitable water from SSM/I.

Previous researchers have identified “moisture surges” as a common monsoon-season mechanism for moisture transport up the Gulf of California and into the southwestern United States. Satellite observations reveal that these surges are frequently associated with large-scale systems whose moisture originates in the tropical eastern Pacific. Analysis of moisture movement up the Gulf of California using satellite-derived water vapor observations shows a significant correlation between the arrival of the surges and intense rainfall events in nearby cities in Mexico and the southwestern United States. Investigations of the genesis, timing and evolution of these events have helped identify conditions that may initiate a moisture surge and result in severe storm events in this region.