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In this study, a detailed diurnal climatology of thunderstorms, precipitation spell and visibility are prepared using the hourly thunderstorm, precipitation spell and surface visibility data from four stations, viz., Mukteshwar and Tehri stations in hills and Dehradun and Pantnagar stations in plains of Uttarakhand. The charts, thus prepared, containing the hourly mean monthly frequency of occurrence (FO) and the hourly diurnal probability of occurrence (PO) of these three weather events can be utilised to identify the most or least probable day and hour of a day for the occurrence of these weather events over a specific region in Uttarakhand. The FO of thunderstorms is found to be higher over the hills of Uttarakhand during pre-monsoon season and plains during monsoon season. The analysis of the temporal characteristics of thunderstorms reveals higher PO during morning and afternoon/evening hours over plains and afternoon/evening hours over hills of Uttarakhand. The precipitation over Uttarakhand, as rain and drizzle, starts increasing in June, with peak FO of precipitation spells in July and August months. The FO of rain is substantially larger than the FO of drizzle throughout the year in stations of the Garhwal region, whereas over the Kumaun region, the difference in FO of rain and drizzle is not large. The study results show that the occurrence of fog over hills is more often during daytime in the monsoon season, whereas the PO of fog is higher during morning and late-night hours from the second fortnight of December till February over plains of Uttarakhand. [ABSTRACT FROM AUTHOR]

The monsoon low-level jet (MLLJ) originates at Mascarene high and after traveling thousands of kilometers enters India from the western boundary causing deep convection, cloudiness, and rainfall. Although its core lies at 850 hPa, it has a large vertical extent; therefore, different meteorological parameters at different levels have a large influence on the Indian summer monsoon rainfall. This study aims to examine the upper-air climatology of 9 stations on the west coast and central Peninsular India and to find out the effects of various parameters at different standard pressure levels on the Indian summer monsoon rainfall variability. We used the 34-yr (1971–2004) actual upper-air radiosonde/radio wind and standard synoptic surface observations data from these 9 stations and reported some new aspects of the MLLJ. The NCEP/NCAR and ECMWF reanalysis wind data have also been used to holistically study the features of MLLJ over sea and land areas. This study, as opposed to some recent studies, confirms the splitting of MLLJ into two branches, which can be seen on a few days during the monsoon season. Further analyses show that the change in geopotential height between 800 and 900 hPa has a strong bearing on the strength of MLLJ. The change in the upper-air pressure gradient force over the Indian landmass can cause a change in the wind speed of MLLJ during the monsoon season. [ABSTRACT FROM AUTHOR]