The diurnal cycle of cloud and precipitation associated with the North American Monsoon System (NAMS) has been examined for 2003 using the global full resolution IR data of Janowiak et al. (2001), the CMORPH satellite precipitation estimates of Joyce et al. (2004), and the 3-dimensional precipitation data observed by the TRMM Precipitation Radar (PR). Three-hourly fields of cloud amounts and mean precipitation are computed on a 0.25 deg lat/lon grid over the North American and its nearby oceans for a 6-month period from May to October 2003. A comprehensive diagnostic study is performed to describe the temporal-spatial structure of the mean state and diurnal cycle of the NAMS cloud and precipitation systems over the period. Our results are:

1) Variations of cloudiness and precipitation assoiated with the North American Monsoon System (NAMS) are dominated by diurnal cycle;

2) Clouds and precipitation start from higher elevation in the morning, move toward the coast as they reach the maximum in late afternoon;

3) The phase of the diurnal cycle is relatively stable, while the magnitude presents changes of synoptic and intraseasonal time scales; and

4) Maximum of deep convection and precipitation appear 50-100km west to the mountain crests.

Further work is underway to extend the examination for other years and to investigate the relationship with large-scale circulation and moisture fields. Detailed results will be reported at the workshop.