Clouds and Fog

Clouds And Fog

Clouds: The cotton-like envelope suspended in the sky.

What are clouds?

A cloud is a suspended mass of water droplets or ice crystals in the atmosphere. Clouds form as a result of condensation of water in the sky. Clouds can differ in size, composition, color, etc. The Climatic system of the Earth is highly influenced by clouds.

Myths about clouds

Since time immemorial, clouds have been a subject of various myths:

  • According to an ancient Hindu tradition, clouds were regarded as the relatives of white elephants, who roamed on Earth and brought rain. 
  • According to a Native American tribe in Nebraska, clouds were referred to as the cloths of Gods residing in heaven.   
  • According to ancient Greek beliefs, clouds were a group of nymphs or Nephelai who collected water from the rivers, carried the water to heaven and poured back to Earth in the form of rain. 

Cloud Temperature:

The temperature of clouds depends on a number of factors like:

  • Altitude- The higher the cloud, the lower is the temperature as temperature decreases at an approximate rate of 3 degrees Fahrenheit per 1000ft. 
  • Humidity- The humidity level in the air also contributes to cloud temperature. The more humid the air, the cooler is the temperature. 
  • Air composition- The presence of considerable amounts of CO2 and other greenhouse gases contribute to the increase in cloud temperature. 

Cloud cover

Cloud cover (also referred to as cloudiness, cloud amount or cloudage) is the portion of the sky concealed by clouds when observed from a specific location. The general unit of measurement of cloud cover is Okta. Cloud cover is directly associated with the duration of sunshine. The least cloudy locations are the sunniest while the areas with a large cloud cover receive minimal sunlight.

Clouds are responsible for playing several critical roles in the climate system. They effectively reflect light to space and aids the cooling of the planet. Cloud plays a crucial role in maintaining the energy balance of the atmosphere and climate change.                                                       

From year to year, the cloud cover values vary just by 0.03. Whereas the local day to day cloud cover value rises to 0.3 across the earth typically. According to a number of data sets, the land is generally covered by 0.1-0.15 less could than oceans.

According to the satellite recordings studied over the years, the continents of Europe, South America, North America and significant parts of Asia are more dominated by cloudy skies than Africa, Australia and the Middle East. 

South America’s Amazon rainforest experiences extensive cloud cover domination throughout the year. In contrast, Africa’s the Sahara Desert experiences a clear-sky condition almost all the time. 

Cloud Pattern

Clouds can be found in a variety of patterns. The atmospheric conditions. Wind speed, temperature etc. determines the pattern of clouds formed.

  1. Wave clouds 
wave clouds
Image Source: Wikimedia Commons

Wave clouds are formed as a result of internal atmospheric waves. When air mass travels in the form of a wave, if there is enough moisture present in the atmosphere, then clouds are formed following the pattern of the air. 

Wave clouds range from smooth to scattered depending on the water vapour conditions. 

These clouds generally reside in the middle to upper troposphere layers. At times the lower part of such clouds contains supercooled water. 

  • Swirling Clouds

Swirling clouds are generally formed when off-shore winds and ocean currents force the air above the ocean to organise chunks of ice and water droplets into swirling eddies. 

These clouds can have diameters ranging from several hundred feet to hundreds of miles depending on the intensity of winds and amount of ice chunks present. 

  • Honeycomb clouds
honeycomb clouds
Image Source: Wikimedia Commons

Honeycomb cloud patterns are formed as a result of simple convection where warm air rises and cold air falls through an envelope of clouds. 

These type of clouds are generally seen above the ocean surfaces. The uneven heating of oceans results in the imperfect formation of the clouds. 

  • Roll clouds

Roll clouds are called so because they seem to be rolling along a horizontal axis. These are a rare pattern of clouds formed due to a solitary wave movement in which a wave moves with a single crest without changing shape or speed.

Such clouds are generally seen in the coastal areas. 

  • Shelf clouds

Shelf clouds are a form of a low-level convective cloud. These clouds are formed when cold, sinking air from a storm cloud spreads across the surface. A shelf cloud appears like an approaching wall of clouds leading a storm. 

Shelf clouds are considered to be an indicator of storms and are often accompanied by rising dust. 

  • Mammatus Clouds
mammatus clouds
Image Source: Wikipedia Commons

Mammatus clouds are pouch-like clouds suspended in the air. These clouds are generally made up of ice and are thunderstorm anvils. These pouches can extend hundreds of miles and are visible for 10-15 minutes at a time. 

  • Cloud Hole

A cloud hole, also known as a fallstreak hole refers to a large gap between cirrocumulus or altocumulus clouds. Such holes are formed when the temperatures in the clouds are below the freezing levels. These clouds are often formed after the passage of an aircraft. 

Cloud Height

As long as there is sufficient moisture for condensation, clouds can be found at any atmospheric level.

There are three different types of clouds based on the atmospheric level.

Cloud typeHeightCloud types
High clouds5 – 13 km (16,000 – 43,000 ft)Cirrus, Cirrocumulus, Cirrostratus
Middle clouds2 – 7 km (7,000 – 23,000 ft)Altocumulus, Altostratus
Low cloudsSurface – 2 km (surface – 7,000 ft)Stratus, Stratocumulus, Nimbostratus
cloud height
Image Source: Valentin de Bruyn / Coton This illustration has been created for Coton, the cloud identification guide for mobile., Cloud types enCC BY-SA 3.0

What is the Fog?

fog
Image Source: F Mira from Lisbon, Portugal, Ponte Vasco da Gama 25CC BY-SA 2.0

Fog refers to a visible aerosol composed of tiny ice crystals or water droplets suspended near the surface of the Earth. Fog is primarily a low-lying cloud. Formation of fog takes place when the temperature difference between dew point and air is less than 2.5 °C.

The formation of Fog is influenced by 

Topography- Hill fog forms when cool winds blow up the slope and cause moisture to condense. Valley fog forms mainly during winters.

Temperature- Cold temperatures aids the condensation process thereby enabling the heavy cold air to evolve into fog and mist.

Wind condition- Cool and calm breeze aids the formation of fog.

Nearby water bodies- Near water bodies fog can form even at dry air conditions. The main reason behind this is cold air passing over the warm water surfaces.

Types of Fog:

1. Radiation Fog

Radiation fog is formed when the land cools after sunset because of infrared thermal radiations in a calm sky. 

2. Ground Fog

The ground fog has a depth of about tens of centimetres and doesn’t extend to the base of the clouds.

3. Advection Fog

Advection fog is formed when advection or wind brings moist air over a cold surface. 

4. Steam or Evaporation Fog

Steam fog is formed over water bodies enveloped by relatively more cooling air. 

5. Frontal Fog

Frontal Fog has formed raindrops from warm air falls above a frontal surface and evaporates into a more relaxed air near the surface.

6. Precipitation Fog

Precipitation fog is formed when the precipitation falls on the drier air below a cloud. In this, the water droplets evaporate into water vapour.

7. Hail Fog

Hail fog is formed when cold temperature results in the accumulation of hail.

To know more about the types of clouds and cloud formation visit https://lambdageeks.com/cloud-formation-types-of-clouds-cumulonimbus-cloud/

About Sanchari Chakraborty

Clouds and FogI am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

Let's connect through https://www.linkedin.com/in/sanchari-chakraborty-7b33b416a/

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