Principal Component Analysis of the Summertime Winds over the Gulf of California: A Gulf Surge Index

Creators: Bordoni, Simona; Stevens, Bjorn

Abstract

A principal component analysis of the summertime near-surface Quick Scatterometer (QuikSCAT) winds is used to identify the leading mode of synoptic-scale variability of the low-level flow along the Gulf of California during the North American monsoon season. A gulf surge mode emerges from this analysis as the leading EOF, with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence. This index is used as a reference time series for regression analysis and compositing meteorological fields of interest, to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon, as well as the manifestation of these transient events in the large-scale circulation. It is found that, although seemingly mesoscale features confined over the Gulf of California, gulf surges are intimately linked to patterns of large-scale variability of the eastern Pacific ITCZ and greatly contribute to the definition of the northward extent of the monsoonal rains.

Additional Information

© 2007 American Meteorological Society. (Manuscript received 29 July 2005, in final form 21 February 2006) The QuikSCAT level 3 ocean wind vector data were obtained from the Physical Oceanography Distributed Active Archive Center (PODAAC) at NASA JPL in Pasadena, California (information online at http:/podaac.jpl.nasa.gov). The blended global GPCP 1DD product was provided by the NASA Goddard Space Flight Center's Laboratory for Atmospheres (ftp://rsd.gsfc.nasa.gov/pub/1dd), which develops and computes the 1DD as a contribution to the GEWEX GPCP. The ECMWF ERA-40 data were obtained from the data system section at NCAR. The NCEP–NCAR renalaysis data are provided by the NOAA–CIRES Climate Diagnostics Center, Boulder, Colorado, via their Web site (http://www.cdc.noaa.gov). The authors thank Dennis Shea for his help with the satellite products, Roger Wakimoto for motivating interest in the monsoon, George Kiladis for discussions during the early stages of this work, and Tapio Schneider for helpful comments and suggestions through the course of this study. Comments by Mike Douglas and one anonymous reviewer helped improve this manuscript. This work was supported by NASA through Fellowship NGT530499 and Grant NAG512559.

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