In recent years, the upper air radiosounding system based on Global Positioning System (GPS) is used as an effective method. GPS receiving device in a Radiosonde improves observation accuracy, allowing simplification of ground equipment. To get improved quality of upper air data, ten stations have been upgraded with new upper air systems based on GPS. This paper describes the upper air radiosounding system that adopts the GPS. After the introduction of GPS Radiosonde in the network at 10 places, data quality has improved substantially at these stations, which has been validated by National Centre for Medium Range Weather Forecasting (NCMRWF) and European Centre for Medium-Range Weather Forecasts (ECMWF). In all cases the quality change has been remarkable and as a result black list tag is removed by ECMWF for the Indian GPS stations.

Lkkj & xqokgkVh gokbZ vM~Ms ij vk, paMokr ls tqM+s okf"kZd vkSj ekfld ckjEckjrk dk forj.k] xtZ ds lkFk vk, rwQkuksa  vkSj paMokrksa ds vkjEHk gksus dk le; vkSj mudh vof/k rFkk i;kZoj.kh; ifjorZuksa dk fo’ys"k.k fd;k x;k gSA rwQku vkSj paMokr lcls T;knk ebZ ds eghusa esa vkrs gSa vkSj mlds ckn viSzy ds eghus esa vkrs gSaA rwQkuksa vkSj paMokrksa dh vko`fr;k¡ lcls T;knk ebZ ds eghusa esa gksrh gSa vkSj mlds ckn vizSy ds eghus esa gksrh gSaA vf/kdk¡’k rwQku ekulwu _rq ls iwoZ vkSj ekulwu _rq ds nkSjku vkrs gSa rFkk paMokr Qjojh ls ebZ ds eghuksa ds nkSjku vkrs gSaA ekulwu _rq ls iwoZ vkus okys vf/kdk¡’k rwQku e/; jkf= ls ysdj rM+ds lqcg ds le; esa vkrs gSa tcfd ekulwu _rq ds nkSjku vkus okys rwQku 0600&1200 ;w- Vh- lh- ds chp vk;k djrs gSa  vf/kdk¡’k rwQkuksa dh vof/k rhu ?kaVksa ls Hkh de dh gksrh gSA vf/kdk¡’k paMokrksa dh vof/k pkj feuVksa ls Hkh de dh gksrh gS] fn’kk mÙkj if’pe vkSj ;s 0900&2100 ;w- Vh- lh- ds le; vkrs gSaA xqokgkVh gokbZ vM~Ms ij paMokr ds vkus ls i;kZoj.kh; rkieku vkSlru 2-2° lsa- rd fxj tkrk gS] lkisf{kd vknzZrk 8-5 izfr’kr rd c<+ tkrh gS vkSj nkc 1-6 gSDVkikLdy rd c<+ tkrk gSA xqokgkVh gokbZ vM~Ms ij paMokr ds vkus ls vf/kdre iou xfr vkSlru yxHkx 39 ukWV~l gksrh gSA fiNys v/;;uksa ls rqyuk djus ij ;g irk pyrk gS fd fiNys dqN o"kksZa esa rQkuksa vkSj paMokrksa ds y{k.kksa esa fo’ks"k ifjorZu ugha vk;k gSA  The annual and monthly frequency distribution, time of commencement and duration of thunderstorms & squalls and environmental changes associated with occurrence of squall at Guwahati Airport have been analyzed. The frequencies of thunderstorms and squalls are maximum in the month of May followed by April. Most of the thunderstorms occur during premonsoon and monsoon season and squalls occur during Feb-May. Most of the premonsoon thunderstorms commence during midnight to early morning while the thunderstorms during monsoon season have preference to commence between 0600-1200 UTC. Majority of thunderstorms is of the duration of less than three hours. Majority of squalls have the duration of less than four minutes, direction as northwesterly and occur during 0900-2100 UTC. On the average, environmental temperature falls by 2.2° C, the relative humidity rises by 8.5%, and the pressure increases by 1.6 hPa due to squall over Guwahati Airport. The average maximum wind speed associated with a squall over Guwahati Airport is about 39 knots. Comparison with the past studies indicates that characteristics of thunderstorms and squalls have not changed significantly over the years.

Extreme weather events, interacting with vulnerable human and natural systems, can lead to disasters, especially in absence of responsive social system. Accurate and timely monitoring and forecast of heavy rains, tropical cyclones, thunderstorms, hailstorms, cloudburst, drought, heat and cold waves, etc. are required to respond effectively to such events. Due to extreme weather events, crops over large parts of the country are adversely affected reducing production of total food grains, fodder, cash crops, vegetables and fruits which in turn affect the earnings and livelihood of individual farmers as well as the economy of the country. In situ observational network are the vital component for skilful prediction of extreme weather events. Current observational requirements for extreme weather prediction are met, to varying degrees by a range of in-situ observing systems and space-based systems. The augmentation of in-situ observational network is continuously progressing. IMD now has a network of Doppler Weather Radars (DWRs), Automatic Weather Stations (AWSs), Agro AWSs, Automatic Rain Gauges (ARGs), GPS upper air systems etc. These observations along with non-conventional (satellite) data are now being used to run its global and regional numerical prediction models on High Performance Computing Systems (HPCS). This has improved monitoring and forecasting capabilities for extreme weather events like cyclones, severe thunderstorm, heavy rainfall and floods in a significant manner. This paper provides an overview of the role of in-situ observational network for extreme weather events in India, framework for further augmentation to the network and other requirements to further enhance capabilities for high impact & extreme weather events and natural hazards.

No abstract

Some empirical formulae have been attempted in the past to compute mean daily global solar radiation from sunshine or cloud data. The instruments measuring solar radiation, depending on the method used measure either direct or diffuse radiation. It is possible to correlate the sunshine hours measured and the direct solar radiation received. An empirical formula has been attempted and tested using one year(1971) data for Delhi. The correlation is found to be high except in the month of April.