Modes of Monsoon Precipitation in Arizona and New Mexico

While recent studies have linked strong NA monsoons to summer drought in the U.S. mid-west, the sequence of events which produce the NA monsoon remains unclear. It is important to show how the NA monsoon may operate in two modes: one mode producing anomalously wet conditions in New Mexico (but not Arizona), the other mode producing wet conditions in Arizona (but not New Mexico). Before mechanistically understanding any possible linkage between the NA monsoon and mid-western precipitation patterns, it may be necessary to understand the processes responsible for these two apparent modes. Our previous studies provide evidence that Gulf of California (GOC) sea surface temperatures (SST) are a factor determining the timing and westward extent of the North American (NA) monsoon within the United States. For this to be true, GOC SSTs must influence NA monsoon rainfall, and evidence to this effect is presented. Some results described in this study are from our paper published in Journal of Climate (Mitchell and Ivanova, 2002). The SST data used were derived from the NOAA Advanced Very High Resolution Radiometer (AVHRR), which measures fluxes of emitted and reflected radiance from five channels in the visible, near-infrared and thermal infrared (see McClain et al. 1995). The question can be asked, “are wet monsoon seasons for AZ also wet for NM, and vice-versa?” The results of this study show that in wet AZ years, wet conditions are extensive throughout the southwest, extending into Utah, Nevada and California, while eastern NM is slightly drier than normal. In wet NM years, AZ in near normal for the monsoon season, and wet conditions are confined to NM and parts of Colorado and Texas. Hence, a strong monsoon year for NM will generally not benefit other parts of the desert southwest. While both AZ and NM are affected by the monsoon, the means by which they are affected appears to be different, since wet monsoons in AZ tend not to be anomalously wet in NM, and vice-versa. Based on our previous work, we suggest that the dominant moisture source for wet AZ monsoon seasons is the N. Gulf of California, while this moisture source does not appear likely for wet NM seasons. Also, as shown in Higgins et al. (1999), the monsoon begins in western NM about a week earlier on average than in western AZ. If the NM monsoon moisture comes from the Pacific (which various satellite imagery suggest), it apparently comes from lower regions of the GOC or the eastern Pacific near Acapulco, Mexico. In these regions, SSTs warm earlier than in the N. GOC, and may explain the earlier onset times in NM. Poster Presentatio