Global precipitation diurnal variations depicted in the observation and the CFS Reanalysis

Diurnal cycle of global precipitation and its representation in the NCEP/CFS reanalysis is examined using the newly completed high-resolution CPC Unified Gauge-Satellite Merged Precipitation Analysis for a 12-year period from 1998 to 2009. The gauge-satellite merged precipitation analysis used here is defined by adjusting the original CMORPH high-resolution satellite estimates against two sets of long-term climate records, i.e., the CPC unified daily gauge analysis over land and the pentad GPCP over ocean, respectively. The adjusted CMORPH is integrated from its original resolution of 8kmx8km / 30-min to T382 / hourly resolution to facilitate the verifications of the precipitation fields.

Diurnal cycle represents a large portion of precipitation variations over most parts of the globe. Diurnal cycle of precipitation is characterized by a single peak at local afternoon over land areas where/when precipitation is dominated by heat convections, while maximum amount of rainfall is observed in early morning over most of the tropical ocean. Diurnal cycle of precipitation may be modulated by large-scale circulation systems. Over CONUS and eastern China, diurnal cycle of precipitation is produced largely by the east-ward migration of meso-scale systems. At the conference, a detailed description of the magnitude and phase and their seasonal, regional variations will be reported.

Comprehensive examinations showed substantial improvements in the spatial distribution patterns of precipitation in the CFSR. Precipitation structures associated with the large-scale topography are well reproduced when compared against the observation. In particular, evolution of precipitation patterns with the development of transient weather systems is well captured by the CFSR. Overall, the diurnal cycle of the precipitation is reasonably well reproduced by the CFSR over many global regions. The magnitude of the diurnal variations presents biases and phase differences in some regions. Particularly noticeable is the fluctuations in the CFS mean diurnal cycle that are absent in the observations.