How air pressure change in Arctic is causing fog in Delhi

PUNE: A new study of the Indian Institute of Tropical Meteorology (IITM), Pune, has found that abnormal air circulation patterns in two far-away regions — the Arctic and Eurasia — have links to fog over the Indo-Gangetic plains of north India. Based on an analysis of 105 cases of fog events in the period between 1979 and 2013, the study reported that widespread fog conditions over the Indo-Gangetic plains were connected to the abnormal movement of high pressure systems over the Arctic Circle and the Eurasian middle latitudes.

The Arctic is approximately 9,240km away from India. About 2,910km separates India from Eurasia. “When an environment with lower air pressure surrounds the Arctic region, the cold air stays locked-up within the Arctic Circle. The development of high air pressure over the Arctic Circle, combined with east-west movements of air circulation over Eurasia, can cause more cold air to advance towards the tropical latitudes and the Indo-Gangetic plains,” said Ramesh Vellore, a scientist from IITM involved in the study.

Sinking of cold air coming from the Arctic and Eurasian regions over the Indo-Gangetic plains allows development of high pressure and favours fog formation in the presence of moisture close to the surface. Fog scenario in the Indo-Gangetic plains commonly occurs because of the development of a highpressure environment over the Himalayan valley.

Researchers suggested a suitable methodology could be devised to improve fog forecast assessment by combining the Arctic and Eurasian aspects. Number of studies in the past have associated the region’s fog lifecycle in this region to increasing pollution particulate matter arising from growing population, rapid urbanisation, biomass burning, and industrial and vehicular activities in the Indo-Gangetic plains.

The study period for the research was December and January months from 1979 to 2013. Daily summaries of surface meteorological observations (temperatures, humidity, winds, surface pressure, rainfall and other indicators of local weather phenomena like thunderstorms, fog and dust storms) documented by the National Data Centre, India Meteorological Department, Pune, were used in the study. Twenty-six stations, three each from Punjab, Haryana, and Bihar, two from New Delhi, 14 from Uttar Pradesh and one from Uttarakhand, were chosen for the study.