On the Variability of Cold Wave Episodes Over Northwest India Using an NGFS Retrospective Analysis

摘要

A retrospective analysis of 17 years of NCMRWF Global Forecast System (NGFS) data was conducted to understand the state and variability of cold wave episodes over northwest India. During the 2000-2016 period, a total of 21 cold wave episodes (202 cold nights) were detected, out of which 5 severe cold episodes (63 cold nights) were registered. The 10 (6) episodes occurred during La Nina (El Nino) years suggesting that both phases of El Nino-Southern Oscillation provide a favourable background for the occurrence of cold waves. The average duration of a cold wave episode was ~ 9.6 days, with the longest (shortest) episode, seen in the year 2008 (2006), lasting for 26 (6) consecutive days. The average duration of a severe cold wave episode is approximate to 4 days longer than that of a normal cold wave. In the year 2005, both the earliest (11 December) and latest (16 February) onsets of cold waves were seen. The omnipresence of intense Siberian anticyclone and the presence of western disturbance brought cold winds to the study region. Also, temperature advection and geo-potential height anomalies play vital roles in the maintenance of cold waves. The cold waves exhibit a significant intra-annual variability over northwest India. The intensity of cold waves has shown an increase of 0.11 degrees C per cold episode.