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Clouds
A cloud is an aerosol consisting of a visible mass of minute liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may compose the droplets and crystals.
Types of clouds:
- High clouds:
- Cirrus: indicate fair weather and a good sunset. Look fibrous or wispy.
- Cirrocumulus: Appear like white globular mass.
- Cirrostratus: resemble thin white sheet or veil.
- Medium clouds:
- Altocumulus: indicate fair weather
- Altostratus; dense, grayish clouds
- Low clouds:
- Stratocumulus: rough, bumpy cloud
- Stratus: Brings dull weather with light drizzle.
- Nimbostratus: Rain clouds. It also brings snow or sleet.
- Clouds with great vertical height:
- Cumulus: Typically seen in tropical, humid regions.
- Cumulonimbus: Thunder cloud brings rain with thunder and lightning.
Haze:
It is caused by smoke or dust in industrial areas or when there is unequal refraction of light in the air of different densities in the lower atmosphere. This is seen in regions of low humidity [Relative humidity < 75%].
Mist:
It occurs in areas of high humidity where the relative humidity is 75% +. Condensation of water vapor in the air causes small water droplets to float about in the lower atmosphere forming clouds.
Fog:
These are formed when water vapors condense on smoke or dust particles. A dense ground cloud is formed reducing visibility. Although fogs are seen in tropics and temperate areas, they are denser in high and middle latitudes than in tropics. Fogs are more common overseas than land and prevalent in coastal areas.
Different types of rainfall
Conventional rainfall
This type of rainfall occurs in areas of high temperature, particularly during the summer months. When solar intensity increases during the afternoon, large-scale moisture is evaporated rapidly and they condense at high altitudes forming intensive rainfall usually restricted to a small region. This rainfall is of short duration and will subside as fast as it started.
Ex: In India, this type of rainfall can be seen in plains especially in northern India during the summer months.
Orographic rainfall
This form of rainfall happens at the foot and windward sides of a mountain. As moisture-laden clouds approach high mountains, they ascend along the slope, and as a result, they condense and form rainfall. This rainfall usually results in some areas on the other side of the mountain become drought-prone.
Ex: The Western Ghats are the perfect example of orographic rainfall in India. This can also be found in the Meghalaya hills and foothills of the Himalayas.
Frontal rainfall
Frontal rainfall occurs when pressure difference creates storms and cyclones. The cyclonic system will bring a large amount of rainfall as it approaches land. Similarly, temperate cyclones form rainfall at the border of warm and cold fronts.
Ex: Coastal India, especially the Bay of Bengal states receives frontal rainfall.
Monsoonal Rainfall
This type of precipitation is characterized by seasonal reversal of winds which carry oceanic moisture (especially the southwest monsoon) with them and cause extensive rainfall in the south and Southeast Asia.
Cyclonic Rainfall
Cyclonic Rainfall is convectional rainfall on a large scale.
The precipitation in a tropical cyclone is of convectional type while that in a temperate cyclone is because of frontal activity.
Threats due to excessive rainfall
Flash floods
The biggest threat through excessive rainfall is the occurrence of flash floods. The high amount of rainfall in a short duration will create destruction of property and life.
Landslides
Landslides become regular if rainfall increases its limits. The landslides may result in the destruction of forests, properties, and even life.
Pressure Belts of Earth
On the earth’s surface, there are seven pressure belts. They are the Equatorial Low, the two Subtropical highs, the two subpolar lows, and the two Polar highs. Except for the Equatorial low, the others form matching pairs in the Northern and Southern Hemispheres. There is a pattern of alternate high and low-pressure belts over the earth. This is due to the spherical shape of the earth—different parts of the earth are heated unequally. The Equatorial region receives a great amount of heat throughout the year. Warm air being light, the air at the Equator rises, creating low pressure. At the poles the cold heavy air causes high pressure to be created/formed. It is also due to the rotation of the earth. In the Subpolar region around latitudes 60° to 65° North and South of the Equator, the rotation of the earth pushes up the bulk of the air towards the Equator, creating a low-pressure belt in this region.
Equatorial Low-Pressure Belts
This low-pressure belt extends from 0 to 5° North and South of the Equator. Due to the vertical rays of the sun here, there is intense heating. The air, therefore, expands and rises as convection current causing low pressure to develop here. This low-pressure belt is also called a doldrums because it is a zone of total calm without any breeze.
Subtropical High-Pressure Belts
At about 30°North and South of the Equator lies the area where the ascending equatorial air currents descend. This area is thus an area of high pressure. It is also called as the Horse latitude. Winds always blow from high pressure to low pressure. So the winds from the subtropical region blow towards the Equator as Trade winds and another wind blow towards Sub-Polar Low-Pressure as Westerlies.
Circum-Polar Low-Pressure Belts
These belts located between 60° and 70° in each hemisphere are known as Circum-Polar Low-Pressure Belts. In the Subtropical region, the descending air gets divided into two parts. One part blows towards the Equatorial Low-Pressure Belt. The other part blows towards the Circum- Polar Low-Pressure Belt. This zone is marked by the ascent of warm Subtropical air over cold polar air blowing from poles. Due to the earth’s rotation, the winds surrounding the Polar region blow towards the Equator. Centrifugal forces operating in this region create the low-pressure belt appropriately called the Circumpolar Low-Pressure Belt. This region is marked by violent storms in winter.
Polar High-Pressure Areas
At the North and South Poles, between 70° to 90° North and South, the temperatures are always extremely low. The cold descending air gives rise to high pressures over the Poles. These areas of Polar high pressure are known as the Polar Highs. These regions are characterized by permanent IceCaps.
Climate
Climate is the average weather conditions in a place over a long period of time—30 years or more.
Hot regions are normally closest to the equator. T
The climate is hotter there because the Sun’s light is almost directly overhead at the equator. And the North and South Poles are cold because the Sun’s light and heat are least direct there.
Five main types of climates.
A: Tropical. In this hot and humid zone, the average temperatures are greater than 64°F (18°C) year-round and there are more than 59 inches of precipitation each year.
B: Dry. These climate zones are so dry because moisture is rapidly evaporated from the air and there is very little precipitation.
C: Temperate. In this zone, there are typically warm and humid summers with thunderstorms and mild winters.
D. Continental. These regions have warm to cool summers and very cold winters. In the winter, this zone can experience snowstorms, strong winds, and very cold temperatures—sometimes falling below -22°F (-30°C)!
E: Polar. In the polar climate zones, it’s extremely cold. Even in summer, the temperatures here never go higher than 50°F (10°C)!
