American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 2231773 bytes)    Cited by

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D17105, doi:10.1029/2004JD004818, 2004

Diurnal cycle of tropical precipitation in a general circulation model

J. Craig Collier

Department of Atmospheric Sciences, Texas A & M University, College Station, Texas, USA


Kenneth P. Bowman

Department of Atmospheric Sciences, Texas A & M University, College Station, Texas, USA


Abstract

Hourly averaged precipitation rates from an ensemble of the Community Climate Model version 3 (CCM3) simulations for the 44-month period from January 1998 through August 2001 are compared to observations from the Tropical Rainfall Measuring Mission (TRMM) satellite. In order to have adequate sampling by the satellite, comparisons are made for 15° longitude × 10° latitude boxes and for larger geographical areas within the tropics. The temporally and spatially averaged hourly precipitation rates from CCM3 and from TRMM are fit to the diurnal harmonic by the method of linear least squares regression, and the phases and the amplitudes of the diurnal cycles are compared. The model's diurnal cycle is too strong over major land masses, particularly over South America (200% too large), and is too weak over many oceans, particularly the northwestern tropical Pacific (57% too small). The model-satellite phase differences tend to be more homogeneous. The peak in the model's diurnal harmonic consistently precedes that of the observations nearly everywhere. Phase differences are large over Australia, Papua New Guinea, and Saharan Africa, where CCM3 leads TRMM by 4 hours, 5 to 6 hours, and 9 to 11 hours, respectively. The model's phase and amplitude biases likely have effects on its hydrologic cycle and its surface and atmospheric energy budgets. Thus the causes for the model's biases need to be investigated.

Received 25 March 2004; accepted 29 June 2004; published 14 September 2004.

Keywords: diurnal; precipitation; general; circulation; model; GCM.

Index Terms: 1610 Global Change: Atmosphere (0315, 0325); 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854); 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation.

Read Full Article (file size: 2231773 bytes)    Cited by

Citation: Collier, J. C., and K. P. Bowman (2004), Diurnal cycle of tropical precipitation in a general circulation model, J. Geophys. Res., 109, D17105, doi:10.1029/2004JD004818.