Diurnal Cycle of Cloud Systems over Norht America as Observed by Satellite Infrared Data

Diurnal Cycle of Cloud Systems over North America as Observed by Satellite Infrared Data

Yelena Yarosh, Pingping Xie, Mingyue Chen, Robert Joyce, John E. Janowiak, and Phillip A. Arkin

The diurnal cycle of cloud associated with the North American Monsoon System (NAMS) has been examined for 2003 using the global full resolution IR data set created and archived at NOAA Climate Prediction Center (Janowiak et al. 2001). Defined by merging and inter-calibrating infrared observations from multiple geostationary satellites, this IR data set covers a global domain from 60S to 60N with a spatial resolution of 4km x 4 km and is available in 30 min intervals on a quasi real-time basis since February 2000.

In this study, 3-hourly mean cloud fields, defined as the mean cloud top temperature and fractional coverage of cold cloud for several threshold temperatures, are computed on a 0.25 deg lat/lon grid over the North America and its nearby oceans [150W-50W; 10N-60N] for the 6-month period from May to October 2003. A diagnostic study is then performed to describe the temporal-spatial structure of the mean state and diurnal cycle of the NAMS cloud systems over the period. Our preliminary results are:

1) Cloud systems associated with the North American Monsoon System are influenced significantly by topography so that both the coverage and the height of the clouds increase sharply as the system moves inland;

2) Variations of cloudiness are dominated by the diurnal cycle which experiences its minimum and maximum at 10LST and 19LST, respectively;

3) The phase of the diurnal cycle is relatively stable throughout the period, while the magnitude varies on synoptic and intra-seasonal time scales.

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 conference.