The low-level circulation of the North American Monsoon as revealed by QuikSCAT
Five years (1999–2003) of near-surface QuikSCAT ocean winds over the Gulf of California and northeast Pacific Ocean are used to characterize the changes in the low-level circulation associated with the North American Monsoon. Our analysis shows that the onset of the summer season is accompanied by a seasonal reversal of the flow along the Gulf of California, with the establishment of a time-mean southerly wind throughout the gulf. This reversal, not evident in the global reanalysis products, occurs in late spring and precedes the onset of the monsoonal rains. In the core of the monsoon, the time-mean flow is found to be modulated by transient events, namely gulf surges, detected in the near-surface wind field as periods of enhanced southerly flow which typically originate at the southern end of the gulf and propagate northward. The histogram of the summertime along-shore winds identifies these surges as a distinct population of events, readily distinguishable from the background flow.
Additional Information© 2004 American Geophysical Union. Received 16 March 2004; accepted 22 April 2004; published 29 May 2004. The QuikSCAT Level 3 Ocean Wind Vector data were obtained from the Physical Oceanography Distributed Active Archive Center (PO.DAAC) at NASA JPL in Pasadena, CA. (http:/ podaac.jpl.nasa.gov). The interpolated Seaflux winds are obtained from the NASA/NOAA sponsored data system Seaflux, at JPL through the courtesy of W. Timothy Liu and Wenqing Tang. (http://airsea-www.jpl. nasa.gov/seaflux). This work was supported by NASA through Fellowship NGT530499 and Grant NAG512559 and by NOAA/PACS under Grant NA17RJ1228. We would also like to thank Rit Carbone and Hugo Berbery for their constructive reviews.
Published - 2004GL020009.pdf