Abstract
The role of the Himalayan orography representation in a Regional Climate Model (RegCM4) nested in NCMRWF global spectral model is examined in simulating the winter circulation and associated precipitation over the Northwest India (NWI; 23°–37.5°N and 69°–85°E) region. For this purpose, nine different set of orography representations for nine distinct precipitation years (three years each for wet, normal and dry) have been considered by increasing (decreasing) 5, 10, 15, and 20% from the mean height (CNTRL) of the Himalaya in RegCM4 model. Validation with various observations revealed a good improvement in reproducing the precipitation intensity and distribution with increased model height compared to the results obtained from CNTRL and reduced orography experiments. Further it has been found that, increase in height by 10% (P10) increases seasonal precipitation about 20%, while decrease in height by 10% (M10) results around 28% reduction in seasonal precipitation as compared to CNTRL experiment over NWI region. This improvement in precipitation simulation comes due to better representation of vertical pressure velocity and moisture transport as these factors play an important role in wintertime precipitation processes over NWI region. Furthermore, a comparison of model-simulated precipitation with observed precipitation at 17 station locations has been also carried out. Overall, the results suggest that when the orographic increment of 10% (P10) is applied on RegCM4 model, it has better skill in simulating the precipitation over the NWI region and this model is a useful tool for further regional downscaling studies.
Highlights
The short-term climate over mountain region is modulated mainly by complex topographical features and land surface characteristics (Pielke and Avissar 1990; Giorgi and Mearns 1991; Giorgi and Avissar 1997; Im and Ahn 2011) as well as non-linear interactions between small scales to planetary scale physical processes (Namias 1960; Smith 1979; Kasahara 1980; Wallace 1987)
The results suggest that when the orographic increment of 10% (P10) is applied on RegCM4 model, it has better skill in simulating the precipitation over the Northwest India (NWI) region and this model is a useful tool for further regional downscaling studies
The influence of the Himalayan orography representation in regional climate model (RegCM4) on winter circulation and associated precipitation is studied over the NWI region
Summary
The short-term climate over mountain region is modulated mainly by complex topographical features and land surface characteristics (Pielke and Avissar 1990; Giorgi and Mearns 1991; Giorgi and Avissar 1997; Im and Ahn 2011) as well as non-linear interactions between small scales to planetary scale physical processes (Namias 1960; Smith 1979; Kasahara 1980; Wallace 1987). A number of theoretical studies are made to understand the upper air circulation features and associated precipitation over the mountain region (Fraser et al 1973; Hobbs et al 1973; Kasahara 1980). Most of the studies are carried out with the assumptions of with and without orography using GCMs. A few modeling studies (Abe et al 2003; Song et al 2010) are conducted using GCMs as well as regional climate models (RCMs) to understand the changes in precipitation with the degree of changes in the mountain height. A few modeling studies (Abe et al 2003; Song et al 2010) are conducted using GCMs as well as regional climate models (RCMs) to understand the changes in precipitation with the degree of changes in the mountain height They found an increase in intensity of precipitation with the increase of model orography. It is demonstrated in various studies that the modulation of rainfall over mountain region varies from low to high orographic features (Barros and Lettenmaier 1994)
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