Surface and Upper Air Fields During Extreme Winter Precipitation Over the Western Himalayas

Abstract

Surface and upper air circulation features associated with extreme precipitation years are demonstrated during winter season viz., December, January, February and March (DJFM) to examine winter weather affecting the western Himalayas. These circulations are studied over the domain 15°S–45°N and 30°E–120°E. This domain is considered particularly to illustrate the distribution of precipitation due to a wintertime eastward moving synoptic weather system called western disturbances. Surplus and deficient years of seasonal (DJFM) precipitation are identified using ± 20% departure from mean from uninitialized daily reanalysis data of forty (1958–1997) years of the National Center For Environmental Prediction (NCEP), US. The years 1965–1969, 1973 and 1991 are found to be surplus years and the years 1962, 1963, 1971, 1977, and 1985 are found to be deficient years. Comparative study between composites of these two categories is made using students t-test of significance. Significant differences in sea-level pressure, zonal and meridional component of wind at surface and upper levels, total precipitable water content, geopotential height and temperature are observed in the two contrasting seasons.