The impacts of the approaching western disturbances (WDs) on the surface meteorological variables over the north-west Himalaya (NWH), India

Abstract

Eastward-moving upper air troughs in the subtropical westerlies, commonly known as the western disturbances (WDs) in the Asian subcontinent, are primary sources of precipitation over the north-west Himalayan (NWH) region and the northern plains of India during winter. Many simulation case studies with the help of numerical weather prediction models and a few observational case studies have been conducted to understand the spatial structure, dynamics, energy and weather associated with the WDs over the NWH in the past. However, studies using in situ observations on the impacts of the approaching WDs on various surface meteorological variables at a local scale in the high-altitude mountainous regions of the NWH are lacking. The objectives of this study are to examine the impacts of the approaching WDs on various surface meteorological variables for 11 stations in the NWH and the associated precipitation amount in a 24-hr time interval. Changes (departures) in the values of various meteorological variables are examined on the first precipitation day of the occurrence of active WDs to study the impacts of the approaching WDs and the associated precipitation amount in the 24-hr time interval which are found to depend on the altitude and geographic location of a station. The mean drop in the maximum and ambient air temperatures are found to be \(2.0{^{\circ }}\) and \(0.7{^{\circ }}\hbox {C}\), respectively, while the mean rise in the minimum air temperature was found to be \(0.8{^{\circ }}\hbox {C}\). A mean drop in the surface atmospheric pressure and a mean increase in the relative humidity are found to be 0.9 hPa and 19.5%, respectively, in a 24-hr time interval. The mean precipitation amount and mean maximum precipitation amount associated with the active WDs in the 24-hr time interval are found to be 8.9 and 68.8 mm, respectively. The results are briefly discussed in the paper. The findings of this study can be useful for operational weather forecasting and a selection of precursor variables for developing a real-time local scale weather forecast model(s) for remote areas of the NWH for the winter season.