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FOG: What is Fog | How Fog is Formed | Types of Fog | Where Does Fog Occur | What Fog can Produce | Effects & Benefits of Fog | Effect on Human Health.


Advection fog layer in San Francisco
Advection fog layer in San Francisco
Written by Prevail Dias

FOG

What is the Fog?
It is a low-lying cloud that consists of tiny water droplets or ice crystals, present close to the earth's surface reducing visibility.

How Fog is Formed? 
When the difference between air temperature and dewpoint is less than 2.5°C. The water vapor present in the air condenses into tiny water droplets that are suspended in the air, which results in the formation of a low lying cloud which reduces visibility.

Types of Fog?

Radiation Fog: 
It is formed after the sunset when the land starts cooling by infrared thermal radiation in clear sky and calm conditions. It usually occurs at night, It does not last long after the sunrise. Radiation fog is commonly seen during autumn and winter.

Ground Fog: 
It is a fog that conceals less than 60% of the sky. It does not extend to the base of any cloud present above it.

Advection Fog: 
It is formed when air consisting of moisture moves over a cool surface or water bodies by the advection process. It is commonly seen over the sea.

Evaporation Fog:
It forms over the water bodies which has cooler air above it. It is also called steam fog.

Precipitation Fog:
It forms when the water droplets fall below the cloud into drier air which causes these droplets to convert into water vapor then these water vapor cools and at the dew point, it condenses and fog is formed.

Some other types of fog are:
Hail Fog
Freezing Fog
Upslope Fog

Where Does Fog Occur?
Fog usually occurs where the relative humidity is near 100%. This happens due to added moisture in the air or falling ambient air temperature. The fog sometimes fails to form at relative humidity at 100%, but can sometimes even form at lower humidities.

What Fog can Produce?
1) Precipitation in the form of drizzle.
2) Precipitation in the form of light snow.
This occurs when the humidity of fog attains 100%, which causes small droplets to come together to form large droplets.

How water vapor is added to the air?
There are many ways through which water vapor is added to the air, some are as follows:
  • Evaporation of water from the surface of oceans, water bodies or wetlands.
  • Transpiration from plants.
  • Wind convergence.
  • When cool or dry air passes over warmer water.
  • Lifting air over mountains.

Effects of Fog
  1. Reduces visibility.
  2. A partial or complete halt to air, road, rail & water transportation.
  3. Fog does not cause any health problem but when it mixes with the pollutants in the air it triggers health problems.
  4. Fog can cause financial loss.

Benefits of Fog
  1. Benefits winter crops.
  2. Decreases surface temperature.
  3. Reduces heat & water stress for vegetation.

Does Fog cause Health Problems?
No, fog does not cause any health problem as it only consists of tiny water droplets but when it mixes with the pollutants in the air it triggers health problems.


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