Characteristics of Precipitation in Mountainous Terrain in Northern Mexico and the Southwest United States Using the TRMM Precipitation Feature Database

The University of Utah Precipitation Feature (PF) Database is an invaluable tool for examining the characteristics of PFs all over the world. This database, which includes the last 10 years of TRMM data, is used to describe PFs in mountainous areas of northern Mexico and the southwest United States. Asking what types of PFs are responsible for precipitation in this region can contribute to the creation of a regional climatology. In this study, we divided terrain into three categories based on elevation and examined PFs in each regime. The study region was also divided into boxes based on the location of the topography. The boxes are examined individually to determine properties of precipitation in each area using descriptive statistical methods. Some of the properties examined include the seasonal and diurnal cycle; numbers and locations of PFs; and area, lightning flash count, rain volume, and other characteristics that serve as proxies for intensity. A distinct pattern emerges showing a greater number of convectively intense features with higher volumetric rainfall at lower elevations, while PFs at higher elevations remain weaker and greater in number.

The presentation focuses on the occurrence, convective intensity, and convective fraction of PFs in northern Mexico and the southwest United States as a function of PF size and the location of the centroid of the PF with respect to topography. Preliminary results indicate that with increasing elevation, a greater percentage of precipitation is produced by smaller PFs. It has been previously shown that there are differences in PFs with elevation in west central Mexico (the area of the NAME field project), but this study shows that these patterns hold for mountainous areas to the north where the high terrain is more complex than it is in the part of the Sierra Madre observed during NAME. We are also very interested in the convective/stratiform percentage of the PFs and the locations of storms that produce heavy rainfall or storms that are considered to be convectively intense. In the future, we hope to offer quantitative comparisons between the study region and the area of the NAME field project. The results could then be compared with model simulations and used to help evaluate rainfall retrieving algorithms at a range of elevations.