Unusual long & short spell of fog conditions over Delhi and northern plains of India during December-January, 2009-2010

Abstract

Sheet of fog is a common scenario during December-January months, which not only occurs in northern India but also in Bangladesh and Pakistan. Maximum fog frequency is noticed in Delhi and adjoining areas. This also affected the maximum temperature during January 1969-88, it varied between 20.6-21.5° C and during 2005 it was 18.9° C and 19.03° C during 2010. Formation of fog and its sustainability mainly depends upon surface wind, relative humidity, minimum temperature and persistency. Maximum dense fog was 285, 190 and 176 hours in 1998-99, 2002-03 and in 2009-10 respectively. During the month of January 2010 there were 5 western disturbances which enhanced the moisture over northern India, surface wind speed remained around 5 kt or less. Inversion in lower levels and freezing level has also been taken into consideration. No significant relation was found between fog and freezing level. However, inversion layer played an important role in formation of fog. Visible satellite imageries have also been taken into consideration to monitor fog over vast area of northern India, Bangladesh and Pakistan.