Fog formation in Northeast India

Winter season announces its arrival by the formation of fog in the early morning and late evening hours. The nature of fog in Northeast India is different from fog in North India which extends up to the eastern states of Uttar Pradesh and Bihar. In these regions radiation fog predominates. When the heat absorbed by the earth’s surface during the day is radiated into space, the surface cools down and if a deep layer of moist air is present near the ground, the humidity will reach 100% and fog will form. This type of fog is generally formed on a clear sky with calm winds.

Fog in Northeast India

Bestowed with a homogeneous terrain comprising of mountains, valleys, undulations and proximity to water bodies, nature of fog in Northeast India varies from place to place.

Northeast India includes the state of Assam, located south of the eastern Himalayas, along the banks of the river Brahmaputra and Barak valley. The state is surrounded by six of the other Seven Sister States of Arunachal Pradesh, Meghalaya, Nagaland, Manipur, Mizoram, and Tripura. A narrow strip of land called the Siliguri Corridor, in West Bengal connects these states to rest of the country.

Here’s a detailed study of the composition and formation of fog in the four main airfields of Siliguri, Guwahati, Agartala and Imphal.

Siliguri- Also known as the ‘Gateway of Northeast India’, Siliguri is situated in the foothills of sub-Himalayan West Bengal and around 80 kilometres away from Darjeeling. Fog here is vulnerable to wind patterns such as uphill, anabatic winds and downhill, katabatic winds. During the day when slopes receive sunlight, the air above them becomes warm and travels uphill. Inversely at night, as heat is lost from here, colder and denser air from the hills drains into this region. Siliguri also has proximity to water body as it is located on the banks of the Mahananda River.

Guwahati- The Brahmaputra River plays a major role in the formation of fog in Guwahati, Assam. The induced influence of moisture when temperature and wind patterns remain conducive, fog forms. This advection fog transpires when relatively warm moist air from the river blows over the cooler surface of the land.

Agartala-The capital of Tripura is in the plains and also has fair proximity to the sea. Here, southerly winds from the sea increases the moisture level and in low temperatures coupled with light winds, leads to the formation of fog. A lot of greenery around also makes the air heavy with moisture.

Imphal-Imphal at an elevation of750 metersabove the sea level is an ideal place for fog formation.

Today morning, fog in Northeast India was fairly widespread with dense in pockets. The visibility in Agartala was 100 meters, Siliguri 250 meters, Guwahati 800 meters and visibility in Imphal was good.

picture courtesy- Dhurjati Chatterjee