AGU: Geophysical Research Letters

 

Editors' Highlight

The dynamics of North American monsoons

The North American Monsoon Experiment is an international research program aimed at learning more about summertime precipitation over North America to improve precipitation prediction in models. In particular, several scientists interested in understanding more about summer precipitation over southwestern North America conducted a field study during the summer of 2004. For this study, scientists used GPS receivers, surface barometers, and surface thermometers to calculate the daily precipitable water vapor (PWV) content over northwestern Mexico. Through analyzing these data, Kursinski et al. (2008) found that the onset of the monsoon season can be seen by a large increase in PWV over several days, beginning in early July. Data from the Sierra Madre Occidental foothills revealed a dynamical transition in mid-August from smaller local convection patterns to larger, more regional scales. During the small-scale phase, a positive feedback helps precipitation-supplied moisture to initiate more moist convection. The authors noted that precipitation is usually preceded by a rapid PWV rise and a sharp surface temperature decrease, implying that models must include moist convective downdrafts in the NAM area.

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