Representation of the Caribbean mean diurnal cycle in observation, reanalysis, and CMIP3 model datasets

This study explores how the Caribbean mean diurnal cycle is represented in observed, reanalyzed, and general circulation model data of the CMIP3 generation, with a focus on the central Antilles Islands (18-21A degrees N, 80-66A degrees W). Their trade wind climate, high solar forcing, and eastward decrease in size challenge dataset ability to represent a diurnal cycle of sufficient amplitude and correct phase. The mean difference between maximum and minimum temperature (Delta T) provides a useful metric, and values of 5-12A degrees C are observed at stations around the Caribbean basin. The Delta T in various reanalyses and CMIP3 models generally yield correct values over South America, but few exhibit elevated Delta T over the central Antilles Islands. NCEP2 and ECMWF reanalyses differ in their representation despite similar resolution, the latter reflecting elevated Delta T. Only one of the four CMIP3 models evaluated correctly simulates Antilles Delta T, but does so with a dry bias. An intercomparison of mean diurnal rainfall in the Antilles is conducted. According to satellite and high-resolution reanalysis, the rain rate doubles in the afternoon. However NCEP2/ECMWF reanalysis and CMIP3 models yield an amplitude about half the observed and exhibit a nocturnal peak typical of marine climates. The reason for the variety of outcomes is related to model parameterizations that translate surface fluxes to boundary layer responses, and to horizontal resolution that affects the representation of sea breeze confluence over large islands.