Why FOG happens in winter | Explained

WHAT IS FOG:

According to Britannica fog is acloud of small water droplets that is near ground level and sufficiently dense to reduce hori- zontal visibility to less than 1,000 metres (3,281 feet).

HOW IS IT FORMED:

Fog shows up when water vapour, or water in its gaseous form, condenses. During condensation, molecules of water vapour com- bine to make tiny liquid water droplets that hang in the air. You can see fog because of these tiny water droplets. Fog happens when it's very, very humid. There has to be a lot of water vapour in the air for fog to form. Fog begins to form in the early hours of the morn- ing, when the temperature is at its lowest. The most stable fogs occur when the surface is colder than the air above; that is, in the presence of a temperature inversion.

ARE FOG AND MIST THE SAME:

Fog is denser than mist. There are more wa- ter molecules in the same amount of space in a fog. Fog cuts visibility down to one kilo- metre, meaning it will prevent you from see- ing further away than one kilometre from where you're standing. Mist can reduce vis- ibility to between one and two kilometres

TYPES OF FOG: 

Radiation fog: Forms in the evening when heat absorbed by the Earth's surface during the day is radiated into the air. As heat is trans- ferred from the ground to the air, water droplets form. Sometimes people use the term "ground fog" to refer to radiation fog. Ground fog does not reach as high as any of the clouds overhead It usually forms at night. Fog that is said to "burn off" in the morning sun is radiation fog. Advection fog forms when warm, moist air passes over a cool surface. This process is called advection, a scientific name describing the movement of fluid. In the atmosphere, the fluid is wind.

When the moist, warm air makes con- tact with the cooler surface air, water vapour condenses to create fog. Advection fog shows up mostly in places where warm, tropical air meets cooler ocean water.

 Valley fog: Forms in mountain valleys, usu- ally during winter. Valley fog develops when mountains prevent the dense air from escapin The fog is trapped in the bowl of the Valley In 1900, vapour condensed around particles of atr pollution in the Meuse Valley, Belgium. More than 60 people died as a result of this deadly valley fog.

Freezing fog:  This happens when the liquid fog droplets freeze to solid surfaces Mountaintops that are covered by clouds are often covered in. freezing fog. As the freezing fog lifts, the ground, the trees, and even objects like spider webs, are blanketed by a layer of frost. The white land- scapes of freezing fog are common in places with cold, moist climates, such as Scandinavia or Antarctica.

Why Northern part India has more foggy conditions:

According to the India Meteorological Department (IMD), the fall in temperature along with moisture and light winds over the Indo-Gangetic plain has resulted in dense fog over the region. Western disturbances, which are storms that originate in the Mediterranean Sea, bring moisture- bearing winds to northwest India.

 This results in increased moisture levels over the region. In the absence of western disturbances, local moisture sources like water vapour from rivers and soil moisture cause fog. The Indo Gangetic plain is most vulnerable to fog occurrences, with major, weeks long spells of dense fog in the months of December and January. These foggy spells are linked to wind and temper- ature patterns.

   

                           

(Source: National Geographic)