The Problems of fog in Manipur

N Munal Meitei *

A thick smog enveloped Imphal city, especially along the airport road, reducing visibility to near zero from about 9 pm on Dec 11 2012
Pix - TSE

In Manipur for the last few weeks or so there has been the news for thick fogs all over State thereby causing many road accidents and also cancellation of Flights coming to this state. As an unusual phenomenon, sometimes the Sun could be seen only in the late hours of the day. These are some of the present Environmental issues faced by the State from the word of Climate Change. There are reports that more than 10,000 vehicles got registered in Manipur every year. We also know that while one litre of petrol burns, it produces about 3 kg of CO2. Only about 29.7% of the households in the State are using cooking gas and around 70.30% are still using the traditional cooking style such as firewood, hay and cow-dung etc.

There are numerous brick fields in the State where both inferior quality coal and firewood are burnt all the year round. The mushrooming stone crushing centers are also producing quite a few quantity of dusts into the atmosphere. After the harvesting most of the farmers used to brunt the hay stock in the field which has also caused not only lost of biomass but a huge amount of pollutants into the air. In the vast open valleys, wind carried away such polluted air from one place to another.

But in our Manipur valley which is surrounded by hills, the phenomenon cannot be happened and polluted air confined for longer period. As such the pollution level of the State is comparatively high that sometimes the pollutant content i.e. the Particulate matters of the air is found to be around 581 micrograms per cu. m. which is 381 micrograms above the permissible level as given by the National Pollution Control Board.

Fog is a meteorological phenomenon caused by a supersaturation of the air, so that it can no longer hold water vapor. Formation of Fog is directly related to Dew point. Fog forms when the difference between temperature and dew point is generally less than 2.5 °C. The lower the dew point, the drier the air is, and vice versa. Air can cool in several ways.

First, the air can be lifted by flowing over a hill, by convection or by the convergence of two air streams. Secondly, it can be cooled by contact with a cold ground. The processes are similar to those which make clouds, although fog forms close to the ground, rather than higher up in the atmosphere. There are many names such as mist, fog and smog etc. The difference between mist and fog also lies in their thickness – and how far we can see through them i.e. the visibility. If we could see less than 1 km through the cloud of water droplets, it is known as fog. If we can see between 1 and 2 km, we call it mist.

Drivers while driving with high beams will simply reflect from the water droplets and create glare. Therefore for a Driver in foggy night, should use preferably the down light. Clear skies mean that the ground gets cold faster and the air close to it also. This cool air gets condense on condensation nuclei such as dust, ice, and salt in order to form clouds and water droplets from the water vapour in the air. Fog is formed more readily when there are more condensation nuclei in the air. These nuclei are provided by the large quantities of particles in the air. These particles come from nature and anthropogenic agents such as vehicle exhausts, fires and dust etc.

All types cloud formation requires very minute hygroscopic particles upon which water vapor can start its condensation. Another recently-discovered source of condensation nuclei for coastal fog is kelp. Researchers have found that under stress i.e. intense sunlight, strong evaporation, etc., kelp release particles of iodine which in turn become nuclei for condensation of water vapor. Fogs are thickest when the air can hold maximum moisture.

Mist, however, usually stays closer to the ground and you can see over the top of it. Mist is often seen on autumn mornings when nights get longer and cooler again. This is particularly true in valleys, because cold air sinks down and collects in the valley during the night. Mist and fog also form over areas where there is plenty of moisture, such as river alleys, lakes and harbours. This explains the example of high hills with good vegetation cover is often surrounded by mist and fog. Dust and smoke make fog much worse.

In the early twentieth century, London was a very dirty city as a result of heavy industry and millions of coal fires. It was then famous for its fogs, which were "as thick as pea-soup". They were so thick and polluted that visibility would drop to 15 m or less. As a result, the government was forced to try and clean up the city – and coal fires were banned in the 1950s. This dramatically reduced the number of fogs. However some cities still suffer from polluted fogs called smog. Sometimes due to more precipitation this moisture falls to the ground in the form of rain, or even snow or hail.

A scene of Foggy morning

In Manipur, the thick foggy situation what we are experiencing for the last few days may be termed as Radiation Fog. Since the magnitude of the fog level is higher in and around the valley, the phenomenon is more significance. After the Sunset, Infrared Radiation from the ground escapes out into the space, the ground cools and, in turn, cools the air in contact with it. As the evening starts, condensation continues to occur on the ground to form dew.

As the pollution level is already higher, with slight air movement, sufficient condensation forms on condensation nuclei to form the very small droplets of water - mist or fog which spread all over the valley. This happens for two primary reasons. First, the low-lying valley areas of Manipur have maximum moisture, sometimes around 96%. Lakes, Wetlands and numerous Streams are located in valley region and the soil moisture is also quite high.

Vegetations growing in these valley areas having better water accessibility also contribute more moisture by the process of evapotranspiration. Secondly, cooled air sinks to the lowest elevation. Cool air is denser than warm air and will thus, under gravity, pool into the lowest elevation from the surrounding hilly regions. Since cool air does not have to evaporate as much moisture as warm air to reach saturation, fog will form in the coolest air first.

The cooler air will sink into the low-lying valley areas. This combined with more moisture in the valley areas will lead to formation of most dense fog in the regions, especially where the lakes, wetlands, streams, soil moisture and vegetation is highest. Radiation fog is also most common when nights get longer than daytime. Again, this applies best to fog that develops on a clear night with light winds. Radiation fogs occur at night, and usually do not last long after sunrise, though can persist all day in the winter months especially in areas bounded by high ground.

Another name of the probable fogs in Manipur may be Advection Fog. Along the areas having more water bodies and wetlands, Advection Fog may form when moist air from the nearby water bodies passes over the cooler surface of the land. Frequently, warmer inland weather sucks the moist air across the land, creating a thick blanket of fog. This happens most frequently around the Lake and wetlands.

For clouds, that cooling is almost always as the result of rising altitude, which cools from expansion, but for fog, which occurs next to the ground, there are usually other reasons for this cooling. During the long winter night, both the air and land cooled down, at the same time the water is still heated up. In order to keep temperature in equilibrium, warm water surface release the latent heat in the form of evaporation which when contact with the chilled air also enhanced thick fogs.

Another probable contribution for the present fog in Manipur is Tule fog. This happens when cold Mountain or hill air sinks into a valley at night. Warmer air above presses the colder air down, causing fog to form and linger for days. This type of fog occurs when conditions on the hills are also cold. Ground fog also usually begins on clear, calm nights.

But, first, during the day, you need the sun to warm the ground. This fog is more common in valleys because cold air sinks, it tends to pool in low-lying areas and makes it easier to reach saturation point. Fog has also some of the usefulness to us. Though fog has caused many inconveniences, some of the plants get their water requirement from fog. Most of the xerophytes plants took the advantages of fog. Some coastal communities use fog nets to extract moisture from the atmosphere where groundwater pumping and rainwater collection are insufficient.

As time passed, the Climatic conditions of Manipur have changed. In the recent past, we have experienced extreme climatic conditions in the State. Last year itself, there was scanty rainfall thereby causing much hardship especially to the poor farmers. The cultivators are yet to recoup for their lost. These are just the beginning but a lot more challenges are still following in the near future if we do not understand and value the importance of Nature and Environment. In our time itself, we have came across so much of unusual challenges and hence please feel, what will be the Environment that we will be handing over to our future generations. Therefore, let's think twice before we do anything that causes harm to our Environment from this moment onwards.