Water in the Atmosphere| Class 11 Geography Notes (2024)

Water in the Atmosphere is a major part of our climate system. Water is present in our atmosphere in three forms gaseous, liquid, and solid. In the circulation process of water in the atmosphere, evaporation is really important. It is a process where water changes its form from liquid state to vapor and moves to the Earth’s surface into the atmosphere.

In this article, we are going to discuss the Water in the Atmosphere in detail.

Water in the Atmosphere

There are three different forms of water in our atmosphere gaseous, liquid, and solid. The gaseous form of water is called vapor. It is the only distributed form that is present in our atmosphere.

• Vapor is the source of all types of precipitation.
• Vapor affects the meteorological phenomena. Its volume ranges from 0-4% in general.
• Atmosphere gains the moisture due to the evaporation and the process of transpiration from the plants.
• With increasing height, the water levels in vapor drop and they become small.
• The vapor is important for the stability of the air.

Evaporation and Condensation

Evaporation: Evaporation is the process by which water changes from a liquid state to a gaseous state, forming water vapor. Heat is the primary driver of evaporation. When the temperature rises, water molecules gain energy and move faster, eventually breaking free from the liquid surface and becoming vapor in the air. The temperature at which water starts to evaporate is known as the latent heat of vaporization. This process is vital for the water cycle as it replenishes moisture in the atmosphere.

Condensation: Condensation is the opposite process of evaporation, where water vapor in the air changes back into liquid water. This occurs when moist air cools down, reducing its capacity to hold water vapor. The excess water vapor then condenses into liquid form. Condensation also occurs when moist air comes into contact with a colder surface, causing the air temperature to drop below its dew point. Additionally, condensation can happen around very small particles in the air called condensation nuclei, such as dust, smoke, or salt particles. These particles provide surfaces for water vapor to condense onto, forming clouds or fog.

1. Dew: Dew forms when moisture in the air condenses onto cooler surfaces, such as grass, leaves, or stones, during the night. This process occurs when the temperature is above freezing and the dew point is higher than the freezing point. Ideal conditions for dew formation include clear skies, calm air, high relative humidity, and long, cold nights.
2. Frost: Frost occurs when condensation takes place below the freezing point of water, resulting in the formation of ice crystals instead of liquid water droplets. This typically happens on cold surfaces, such as grass or car windshields, when the air temperature is at or below freezing. Similar to dew, frost formation requires clear skies, calm conditions, and high humidity, but with temperatures below freezing.
3. Fog and Mist: Fog is a type of cloud that forms near the ground when the temperature of an air mass containing a large quantity of water vapor suddenly drops, causing condensation to occur within the air mass itself. Mist is similar to fog but contains more moisture, with each condensation nucleus holding a thicker layer of moisture. Fog and mist reduce visibility and often occur in urban or industrial areas where smoke or pollution provides condensation nuclei.
4. Clouds: Clouds are masses of minute water droplets or tiny ice crystals formed by the condensation of water vapor in the atmosphere at considerable elevations. Clouds can take various shapes and forms depending on their height, density, and transparency. The four main types of clouds are cirrus, cumulus, stratus, and nimbus, each with distinct characteristics and formations. Clouds play a crucial role in weather patterns and the Earth’s energy balance.
   1. Cumulus: Cumulus clouds resemble cotton wool and are often seen scattered across the sky in patches. They form at lower altitudes, usually between 4,000 and 7,000 meters. Cumulus clouds have a flat base and can appear in various shapes, adding texture to the sky.
   2. Stratus: Stratus clouds are layered clouds that cover large portions of the sky. These clouds form due to the loss of heat or the mixing of air masses with different temperatures. They often create overcast conditions and can be found at different altitudes, depending on the atmospheric conditions.
   3. Nimbus: Nimbus clouds are dark gray or black in color and typically form at middle levels or very close to the Earth’s surface. These clouds are dense and opaque, blocking sunlight and causing dim lighting conditions below. Nimbus clouds often bring precipitation, and when they are low to the ground, they can create fog-like conditions.

Different combinations of the four basic types of clouds can result in various cloud formations categorized into different levels of the atmosphere:

1. High clouds – These include cirrus, cirrostratus, and cirrocumulus clouds. They form at high altitudes and are often wispy or thin in appearance.
2. Middle clouds – Examples are altostratus and altocumulus clouds. These clouds occupy the middle layers of the atmosphere and typically have a layered or patchy appearance.
3. Low clouds – Stratocumulus and nimbostratus clouds are considered low-level clouds. They form closer to the Earth’s surface and can appear in layers or sheets, sometimes bringing precipitation.
4. Clouds with extensive vertical development – This category includes cumulus and cumulonimbus clouds. These clouds can build vertically through the atmosphere and often produce intense weather phenomena such as thunderstorms and heavy rainfall.

Precipitation

Continuous condensation in the atmosphere leads to the growth of condensed particles, which eventually become too heavy to remain suspended in the air and fall to the Earth’s surface. This process is known as precipitation. Precipitation can occur in the form of liquid or solid particles. Rainfall refers to precipitation in the form of liquid water, while snowfall occurs when temperatures are below freezing, causing water vapor to crystallize into hexagonal snowflakes.

In addition to rain and snow, other forms of precipitation include sleet and hail, although these are less common and occur sporadically. Sleet occurs when raindrops freeze into small pellets of ice as they pass through a subfreezing layer of air near the ground. Hailstones, on the other hand, form when raindrops are carried upward into colder atmospheric layers, causing them to freeze and accumulate layers of ice. Hailstones can have multiple concentric layers of ice, resulting in their characteristic rounded shape.

Types of Rainfall

Rainfall can be classified into three main types based on its origin: convectional, orographic (relief), and cyclonic (frontal).

Convectional Rain: When air is heated, it becomes lighter and rises in convection currents. As it ascends, it cools, leading to condensation and the formation of cumulus clouds. This type of rainfall often occurs with thunder and lightning and is typically short-lived. It is common in equatorial regions and interior parts of continents, especially in the northern hemisphere.

Orographic Rain: When a saturated air mass encounters a mountain, it is forced to rise. As it ascends, it expands and cools, causing moisture to condense and form precipitation. One notable characteristic of orographic rain is that the windward slopes of mountains receive more rainfall, while the leeward slopes, after giving rain on the windward side, remain dry due to descending air. This phenomenon creates a rain-shadow area on the leeward side of the mountain.

Cyclonic Rain: Cyclonic rainfall occurs in association with extratropical cyclones, as discussed in Chapter 9. For more information on cyclonic rainfall, please refer to Chapter 9.

World Distribution of Rainfall

Different regions of the world experience varying amounts of rainfall throughout the year and across different seasons.

Generally, as we move away from the equator towards the poles, rainfall gradually decreases. Coastal areas typically receive more rainfall compared to inland regions due to their proximity to large bodies of water, which serve as significant moisture sources.

Between the latitudes of 35° and 40° North and South of the equator, rainfall is heavier on eastern coasts and decreases towards the west. However, between 45° and 65° North and South of the equator, rainfall is initially higher on the western margins of continents due to the influence of westerly winds, gradually decreasing towards the east. In regions where mountains run parallel to the coast, rainfall is greater on the windward side of the mountains, decreasing on the leeward side.

Precipitation regimes across the world can be categorized based on the total annual precipitation:

1. Equatorial regions, windward slopes of mountains along western coasts in cool temperate zones, and coastal areas experiencing monsoons receive heavy rainfall exceeding 200 cm annually.
2. Interior continental areas receive moderate rainfall ranging from 100 to 200 cm annually.
3. Coastal areas of continents receive a moderate amount of rainfall.
4. Central parts of tropical regions and eastern and interior parts of temperate lands receive rainfall ranging between 50 and 100 cm annually.
5. Areas located in the rain shadow zone of continental interiors and high latitudes receive very low rainfall, typically less than 50 cm annually.

The seasonal distribution of rainfall also plays a crucial role. In some regions, rainfall is evenly distributed throughout the year, such as in the equatorial belt and western parts of cool temperate regions.

Also Read:

1. Rainfall in India
2. Trapping Rain Water
3. Humidity And Precipitation
4. Which region receives Heavy Rainfall in India?
5. Which winds bring rainfall in India? Why is it so important?

Class 11 Chapter 10 Water in the Atmosphere- FAQs

What is the water in the atmosphere class 11th geography?

Water vapour present in the air is known as humidity. It is expressed quantitatively in different ways. The actual amount of the water vapour present in the atmosphere is known as the absolute humidity. It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.

What is the summary of water in the atmosphere?

Water at the Earth’s surface evaporates into water vapor, then rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.

What are the three types of precipitation Class 11?

The most common types of precipitation are rain, hail, and snow. Rain is precipitation that falls to the surface of the Earth as water droplets.

What is dew class 11?

Dew is formed when the air has high relative humidity and the temperature of the air near the earth’s surface becomes very low. This causes condensation of water vapour into water droplets.

See Also

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Why water is important in the atmosphere?

Water vapor is the most prevalent greenhouse gas. It causes roughly half of the warming of the planet. Like other greenhouse gases, it lets almost all of the sunlight reach the earth’s surface but absorbs heat radiated upward from the earth.

How does water leave the atmosphere?

In the cool air, water vapor is more likely to condense from a gas to a liquid to form cloud droplets. Cloud droplets can grow and produce precipitation (including rain, snow, sleet, freezing rain, and hail), which is the primary mechanism for transporting water from the atmosphere back to the Earth’s surface.