Humidity And Clouds

(A) Cirrus – (ii) Higher altitude – (d) Snow flake clouds

Explanation- Cirrus is a high-level cloud with an altitude of 7000 to 14000 metres. They are called snow flake clouds because they are composed of ice particles.

(B) Cumulonimbus – (i) Vertical extent in the sky- (a) roaring clouds

Explanation- Cumulonimbus are mountain-like huge vertical clouds which are formed as a result of strong upward water vapour currents in the atmosphere.

They are known as roaring clouds as they are responsible for thunderstorms and lightening.

(C) Nimbostratus – (iv) Low altitude – (c) continuous rain.

Explanation- Nimbostratus clouds are low-level clouds with an altitude of fewer than 2000 metres. They are dark and have dense layers which block the sun and hence cause continuous and persistent rains.

(D) Alto-cumulus – (iii) Medium altitude – (b) floating clouds

Explanation- Alto-cumulus is a mid-level cloud with an altitude of about 2000 to 7000 metres. They contain water droplets and appear puffy. Due to condensation, the clouds become light weight and float in the air. Hence they are called floating clouds.

(a) Moisture-holding capacity

Explanation: The moisture holding capacity of air is dependent on the temperature of the air. The capacity of the air to hold moisture increases with an increase in the temperature. For example, at 40°C, the moisture holding capacity of the air is 51.12 gm/cu.m.

(b) Absolute humidity

Explanation: Absolute humidity is the amount of water vapour in 1 cu.m of the atmosphere. For instance, near coastal regions, absolute humidity in the air is likely to be higher than near the poles.

(c) Relative humidity

Explanation: Relative humidity is less in desert regions. This is because high temperature reduces the relative humidity of a particular place.

(d) Cumulonimbus

Explanation: Cumulonimbus clouds are indicators of the storm. They are huge and appear dark in colour. They cause rain accompanied by storm and tornadoes.

(e) Condensation

Explanation: In a free environment, the condensation of the vapour present in the atmosphere takes place around dust particles. This is because minute particles of dust, salt, smoke etc. soak water easily.

The air in a region is dry primarily due to low moisture content. Moreover, distance from the sea, the high speed of the wind and increased rate of evaporation contribute to a decrease in the moisture holding capacity of the atmosphere.

For example, in Rajasthan, the air is dry and hot leading to the low moisture content in the air.

Humidity is measured in grams per cubic metres. The air is considered to be dry when the humidity in the air is 0 gm/cu.m. Whereas the air is saturated when the humidity at 30°C temperature is 37gms/cu.m.

Condensation is a process by which water vapour is converted into water. The following are the prerequisites for condensation to take place:

1. Firstly, the presence of water vapour in the atmosphere is required for condensation to occur.

2. Secondly, low temperature is important as it decreases the moisture holding capacity of the air which leads to condensation.

3. Finally, fine particles such as dust, salt etc. need to be present around which condensation happens.

A cloud is a collection of water vapour and fine particles at a greater height in the sky formed due to the process of condensation.

According to international classification, clouds are divided into three main types based on their altitudes above sea level:

1. High clouds: The clouds which are at the height of 7000 to 14000m and contain ice particles are known as high clouds. They include Cirrus, Cirrocumulus and Cirrostratus clouds.

2. Medium clouds: These clouds have a general altitude of 2000 to 7000 metres. They comprise alto-stratus and alto-cumulus clouds.

3. Low clouds: These are at an altitude of fewer than 2000 metres. They are divided into five types.

a) Strato-cumulus

b) Stratus Clouds

c) Nimbostratus clouds

d) Cumulus clouds

e) Cumulonimbus clouds.

A cloud is a collection of water vapour, and fine particles at a greater height in the sky formed due to the process of condensation.

Nimbostratus clouds lead to uninterrupted precipitation and even snowfall. These low-level clouds have thick layers and are grey in colour which blocks out the sun.

Relative humidity is determined by the amount of water vapour in the atmosphere (called absolute humidity) in proportion to the vapour holding capacity at the same temperature and same volume.

Relative humidity (%)

Relative humidity is inversely proportional to the temperature. When the temperature decreases, Relative humidity increases. It is low when the temperature is high.

Therefore, Relative humidity is usually higher in mornings and nights but lower in afternoons due to the increase in temperature.

Due to the process of condensation, fine water and ice particles float in the air at higher elevation as they are light in weight. These particles gather around to form clouds. Clouds float in the sky due to the vertical flow of the air.

Relative humidity changes with a change in the temperature and altitude of a particular region. As the altitude of a place increases, the air gets thin and the moisture holding capacity of the air decreases (low atmospheric pressure) which results in reduced humidity.

When the water evaporates from the earth, it is released into the air. The air has a maximum ability to hold moisture in a certain quantity and at a particular temperature only. When this ability is reached, and relative humidity reaches 100%, the air is considered to have reached its saturation point.

In other words, when the proportion of water vapour and the vapour holding capacity is equal, the air is said to be saturated.

Cumulus and cumulonimbus clouds are low clouds. These are at an altitude of fewer than 2000 metres. Cumulus clouds are responsible for pleasant weather. Due to an increase in the vertical flow of air, cumulus clouds get turned into cumulonimbus clouds which leads to rain.

Given:

Temperature- 30°C

Vapour holding capacity- 30.37 gms/cu.m.

Absolute Humidity- 18 gms/cu.m.

Relative humidity

Absolute humidity is defined as “the amount of water vapour in 1 cu.m. of air.”

Given, water vapour= 4.08 gms

Volume of air= 1 cu.m.

Thus, absolute humidity =

= 4.08 gm/m³

For the month of July 2018 in Mumbai, high temperatures were usually around 31°C, hardly falling below 27°C or exceeding 33°C.

While low temperatures for the month were around 27°C, hardly falling below 23°C or rising above 27°C.

Table 1.1 shows the high and low temperatures with their respective average temperatures and humidity percentage levels for the month of July.

According to the weather reports of Mumbai, July 2018 was the most humid month of the year.

In the first picture, the day is hot, and the people are predicting that a sandstorm is on the rise.

In the second picture, the day is very hot, it must be a summer noon and the people are indeed feeling very hot. Also, the weather conditions are very humid, the humidity is high in the air and hence it is very sweaty.

In the third picture, the day is very cold, mostly the winter season in on the go over there. To prevent the children from catching cold, the mother advices them to wear the sweater and play.

In the above discussion, the words hot, moist, cool etc. show the condition of the air. They relate to the content of the moisture in the air.

For precipitation to occur, the conditions should be humid and the moisture content in the air must be high.

In winters, the air that we exhale, is hotter than the air that is present surrounding the window glass. Hence, when the hot air from our mouth touches the cool surface of the window glass, it precipitates to form water droplets.

In summers, the air that we exhale, is cooler than the air that is present surrounding the window glass. Hence, when the cool air from the mouth touched the hot surface of the window, no precipitation occurs and no water droplets are formed.

Precipitation usually occurs only when hot air touches cooler surfaces.

Just subtract the previous vapour holding capacity from the present one to get the difference in the capacities in the third column.

For eg, at the temperature of 0 degree, to get the difference in capacities, subtract the vapour holding capacity at -5 degree from the vapour holding capacity at 0 degree= 4.85-3.26=1.59

Continue the process for all the remaining blanks.

With the decrease in temperature from 20 degree C to 10 degree C there will be a relative fall in humidity. With the change in temperature the humidity content of the air changes.

The cold air is capable of holding less water content than that of warmer air even when fully saturated. The temperature fall will make the air lose its moisture content and reduce the humidity index.

Saturation level is that point where no further addition can be made to the present state.

• The colour of the clouds is white and they are not huge in size.

• The altitude is less, so I think they might be cumulonimbus clouds or cumulus clouds

• Yes, these clouds can bring continuous rainfall. The low altitude clouds consist of five types of clouds. They are also called as Strato-cumulus clouds. They have layers. Their colour is white to earthy. Round clusters of clouds can be here. Stratus clouds also have layers. They are ash coloured and their base is uniform. Nimbo-stratus has thick layers. They are grey-ash in colour and cause continuous rainfall and even snowfall.