"Hence it is always better to adopt a precautionary stand while formulating policies dealing with extreme climatic conditions," he adds. "It is difficult to pinpoint the cause - natural unpredictability of climate or changes occurring in it due to anthropogenic activities," avers S M Kulshrestha, former director general of imd. Some experts wonder whether the occurrence can be attributed to natural inherent variability of the climate alone or there is more to it. Groping in the dark Is it a case of reading too much into a natural phenomenon? Even scientific opinion seems to be divided on the issue. But De says that fog can be dense at higher temperatures also, provided the moisture and wind conditions are conducive. The ideal temperature range in which a fog is formed is 1 c to 5 c, subject to there being abundant moisture and weak winds. Besides, fog droplets are at least 100 times smaller than those that are contained by clouds. Firstly, unlike clouds which are formed at higher altitudes, fog condensation takes place a few hundred metres above the ground. While there are many similarities between a cloud and a fog, there are a few differences as well. But scientists at the National Centre for Medium Range Weather Forecast ( ncmrwf), New Delhi, are baffled by the persistent foggy conditions. This is one of the reasons for the unrelenting cold wave. "This time, however, the number of such disturbances was almost one in three days which is unusually high," reveals U S De, former assistant director general of imd. A cold wave spawns these westerly disturbances, but it does not last more than a few days. While Delhi and its neighbouring areas are experiencing radiation fog, the advective form is enveloping the Uttar Pradesh and Bihar regions.įor many years, westerly winds (often accompanied by showers) originating from the Mediterranean Sea have been lashing north India in the winter months. In another commonly experienced form of the phenomenon, known as advective fog, a layer of haze is formed by the movement of moist air over a cold surface such as a waterbody or freshly fallen snow. Under their combined effect, the heat radiated by the ground spreads to the cold sky leading to condensation around minute particles in the atmosphere. Aerosols are minute particles in the atmosphere.īare facts Fog is a natural phenomenon and the elements that cause it to occur are quite common: clear, calm nights and high humidity.
Such an occurrence over polluted areas can lead to a serious problem as it can trap aerosols - both natural such as mineral dust, and human-made like suspended particulate matter. Some of them concede that such foggy conditions have been on the rise in winter months during the past six years.
The fog and an accompanying bitter cold wave - which has so far claimed over 600 lives in north India - are almost unprecedented in magnitude, point out Indian meteorologists. Its intensity is such that visibility levels drop to near zero soon after dusk and sunlight is blocked out well into noon. Barely had it recovered from the embarrassment of forecasting the monsoon incorrectly when the winter wrong-footed it.Īn unusually severe nightly fog, enveloping a vast stretch of the Indo-Gangetic belt from Punjab to Kolkata, has confounded the imd as much as it has disrupted normal life across northern India. The weather gods seem hell-bent on proving the India Meteorology Department ( imd) wrong.
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