**Diurnal Variability and Energetics of the North American Monsoon

The North American Monsoon System (NAMS), although smaller in size and magnitude than its Asian counterpart, is an important feature of summertime climate over the southwestern United States and Mexico. The monsoon activity, extending from July through September, exhibits considerable variability on a diurnal time scale. Prominent is the presence of a late afternoon or evening maximum in convection and rainfall. To better understand this variability and the processes that control it, this study utilizes model simulations of the 1998 NAMS to analyze the diurnal variability in the components of differential heating and the related moisture and motion fields. The Florida State University Global Spectral model (FSUGFSM) was employed at the resolution T126 (126 waves triangular truncation) to run 21 three-day model simulations. The diurnal response in the resultant wind, moisture, and heating fields was compiled from the first day of each simulation. Also calculated were the velocity potential and divergent wind fields. Analysis of these fields reveals that during the afternoon there is strong low level moisture along the western side of the Sierra Madre Occidental coupled with an area of wind convergence along the axis of the mountains. In addition, the mountainous terrain provides an area of strong heating for the region. The influence of the strong daytime heating, upslope winds, and moisture transport over the higher terrain is essential for the development of monsoon convective activity. Further analyses will examine the monsoon energetics in order to illustrate the features responsible for the maintenance of the monsoon system. Also, an analysis of the moisture transport resulting from the divergent and rotational components of the wind will be conducted. The question of the origin of moisture for monsoon activity is an important one in NAMS research with several possible sources under debate, including the tropical Pacific, the Gulf of California, and the Gulf of Mexico. Through use of high resolution model output, this study hopes to provide a better understanding of the diurnal variability of the NAMS as well as of the moisture sources and energetics responsible for the development of monsoon activity.