Diurnal Cycle of Cloud and Precipitation Associated with the North American Monsoon System Pingping Xie, Yelena Yarosh, Mingyue Chen, Robert Joyce, John Janowiak, and Phillip A. Arkin

Objective: To examine the diurnal cycle of cloudiness and precipitation over the NAME domain using the GOES IR and CMORPH precipitation data

Target Area and Period: Target Area: Mexico 22 o N – 32 o N; (circulation patterns south of 22 o N seem different) Target Period: Warm Season 2003 May 1 – Oct. 31, 2003

Precipitation Data:  CMORPH (Joyce et al. 2004)  Precipitation estimates based on satellite observations;  Original CMORPH data produced on a resolution of 30-min / 8-km over the globe;  3-hourly mean precipitation calculated on 0.25 o lat/lon grid in this work;

Cloudiness Data [1]:  GOES Full Resolution IR data (Janowiak et al. 2001);  Surface / cloud top temperature on a resolution of 30-min / 4-km;  Fractional coverage of clouds colder than 215K, 235K, and 255K is calculated on a resolution of 3-hourly / 0.25 o lat/lon;

Cloudiness Data [2]:  Clouds are classified into 3 kinds for convenience purpose:  Low Clouds:255K – 235K  Middle Clouds:235K – 215K  High Clouds:<215K  Cloudiness is shown in percentage (%).

Mean Precipitation and Topography Heavy rainfall is observed over both the west and east coasts of Mexico

Mean Precipitation and Cloudiness Low Middle Clouds High Precip. Clouds [mm/day] Clouds have wider and smooth distribution than precipitation; There is an east-west shift in the maximum positions;

3-Hourly Mean Precipitation Precipitation starts at morning time; It reaches maximum in late afternoon; Diurnal cycle over the west and east coasts is in phase;

3-Hourly Mean Low Clouds [235K-255K] The maximum amount of low clouds appears ~3 hours later than that for the precipitation

3-Hourly Mean Mid Clouds [215K-235K] The diurnal cycle of middle and high clouds is basically in phase with that of the precipitation;

Diurnal Cycle of Cloudiness and Precipitation Relative to the Mountain Mean values are calculated over a latitude band 22 o N – 32 o N, relative to the mountain ridge; Cloud / precip. Starts over high elevation in the morning, moves toward coast as it reaches maximum; High clouds are located over west of low clouds

Mean Diurnal [22 o N-32 o N; 5 o W/E to the Ridge] Diurnal cycle of low clouds has a flatter tail than that for the high/middle clouds and the precip.

Summary:  Cloud and precipitation start from higher elevation in the morning, move toward the coast as they reach the maximum in late afternoon;  The position of maximum higher clouds is located west to that for the lower clouds;  All data used here are available to NAME scientists;

Future Work:  Differences in diurnal cycle for different months in a monsoon season;  Year-to-year variations;  Diurnal cycle for regions south of 22 o N;  3-D structure of diurnal cycle of precipitation using TRMM data;  Connection to large-scale circulation patterns of intraseasonal to interannual time scales;  Relation to findings by other NAME scientists;

3-Hourly Mean Amount of High Clouds

East-West Section of Mean cloudiness / Precipitation