Abstract
This study investigates the diurnal variation of the warm season precipitation simulated by the Goddard Earth Observing System version 5 atmospheric general circulation model for 2 years (2005–2006) at a horizontal resolution of 10 km. The simulation was validated with the satellite-derived Tropical Rainfall Measuring Mission (TRMM) 3B42 precipitation data and the Modern-Era Retrospective analysis for Research and Applications atmospheric reanalysis for atmospheric winds and moisture. The simulation is compared with the coarse-resolution run in 50 km to examine the impacts driven by resolution change. Overall, the 10 km model tends to reproduce the important features of the observed diurnal variation, such as the amplitude and phase at which precipitation peaks in the evening on land and in the morning over the ocean, despite an excessive amplitude bias over land. The model also reproduces the realistic propagation patterns of precipitation in the vicinity of ocean coasts and major mountains. The regional characteristics of the diurnal precipitation over two regions, the Bay of Bengal and the Great Plains in North America, are examined in detail, where the observed diurnal cycle exhibits a systematic transition in the peak phase due to the development and propagation of regional-scale convective systems. The model is able to reproduce this pattern as well as the diurnal variation of low-level wind and moisture convergence; however, it is less effective at representing the nocturnal peak of precipitation over the Great Plains. The model results suggest that increasing the horizontal resolution of the model to 10 km substantially improves the representation of the diurnal precipitation cycle. However, intrinsic model deficiencies in topographical precipitation and the accurate representation of mesoscale convective systems remain a challenge.
Highlights
Diurnal variation of precipitation is a fundamental component of the global climate system, especially in warm seasons
The ITCZs in the Pacific and the Atlantic are overall weaker in the model simulation, they are abnormally strong in the eastern ends near the continents
This study examines the realism of the diurnal variation of warm-season precipitation simulated by the Goddard Earth Observing System version 5 (GEOS-5) atmospheric general circulation model (AGCM) at a 10 km horizontal resolution
Summary
Diurnal variation of precipitation is a fundamental component of the global climate system, especially in warm seasons. Previous studies analyzing observation data have demonstrated that there are large differences in the diurnal variation between the continent and the ocean continental and oceanic environments, such that the continental deep convection produces precipitation more frequently in the late afternoon to evening, whereas the oceanic precipitation develops more typically during the early morning (Yang and Slingo 2001; Dai et al 2007; Kikuchi and Wang 2008). They indicate that the diurnal (24-h) component has a greater influence than the semidiurnal (12-h) component both on land and on the ocean. The Bay of Bengal and its adjacent coastal regions exhibit a strong diurnal variation, introduced by the propagation of convective systems that initiate near the coastal region and migrate offshore (Zuidema 2003; Liu et al 2008)
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