A case study of diurnal variation of convection and mesoscale modeling during TOGA-COARE

Abstract

Infrared satellite images from the TOGA-COARE domain have been objectively processed to reveal the distribution of cloud clusters with temperatures of a given threshold for two 48-h periods (14-15 January and 18-19 January 1993). old cloudiness is examined with a threshold of less than 2O8K and moderately cold cloudiness is examined with a threshold of less than 235K. Cloud cluster sizes are found to have a log-normal distribution. Cluster size ranges for the given temperature thresholds are found to be smaller for 14-15 January than for 18-19 January, and smaller overall than previous climatological studies. Due to synoptic scale variability, the diurnal cycle is more apparent during 18-19 January with deep convection peaking before dawn, and then moderately cold cloud area expanding in the afternoon. Smaller clusters have a smaller diurnal signal than larger clusters. The NPS/NRL mesoscale model demonstrates skill in the forecast of total cloud cover with a model integration of up to 24 hours. The model is found to over forecast cloud cluster size and to show minimal skill in depicting a diurnal signal in convection.