Evaporation-and-condensation/”>Evaporation and Condensation: dew, frost, fog, mist and cloud, rainfall types
Evaporation
Evaporation is the process of which water changes from its liquid state to gaseous form. This process takes place at all places, at all times and at all temperatures except at dew point or when the air is saturated. The rate of evaporation is affected by several factors. Important among them are as under:
(i) Accessibility of water bodies :-The rate of evaporation is higher over the Oceans than on the continents.
(ii) Temperature :-when the temperature of an air is high, it is capable of holding more moisture in its body than at a low temperature. It is because of this that the rate of evaporation is more in summers than in winters. That is why wet clothes dry faster in summers than in winters.
(iii) Air moisture :-If the relative humidity of a sample of air is high, it is capable of holding less moisture. On the other hand if the relative humidity is less, it can take more moisture. Hence, the rate of evaporation will be high. Aridity or dryness of the air also increases the rate of evaporation. During rainy days, wet clothes take more time to dry owing to the high Percentage of moisture content in the air, than on dry days.
(iv) Wind :-If there is no wind, the air which overlies a water surface will get saturated through evaporation. This evaporation will cease once saturation point is reached. However, if there is wind, it will blow that saturated or nearly saturated air away from the evaporating surface and replace it with air of lower humidity. This allows evaporation to continue as long as the wind keep blowing saturated air away and bring drier air.
(v) Cloud cover :-The cloud cover prevents solar radiation and thus influences the air temperatures at a place. This way, it indirectly controls the process of evaporation.
Condensation
Condensation the process by which water vapor (gas) in the Atmosphere turns into water (liquid state). It is the opposite of evaporation. This stage is very important because it is the cloud formation stage. Cool temperatures are essential for condensation to happen, because as long as the temperature in the atmosphere is high, it can hold the water vapor and delay condensation.
When a gas is cooled sufficiently or, in many cases, when the pressure on the gas is increased sufficiently, the forces of attraction between Molecules prevent them from moving apart, and the gas condenses to either a liquid or a solid.
- Example: Water vapor condenses and forms liquid water (sweat) on the outside of a cold glass or can.
- Example: Liquid carbon dioxide forms at the high pressure inside a CO2 fire extinguisher.
The temperature of the air falls in two ways. Firstly, cooling occurs around very small particles of freely floating air when it comes in contact with some colder object. Secondly, loss in air temperature takes place on a massive scale due to rising of air to higher altitudes. The condensation takes place around the smoke, salt and dust particles which attract water vapour to condense around them. They are called hygroscopic nuclei. When the relative humidity of an air is high, a slight cooling is required to bring the temperature down below dew point. But when the relative humidity is low and the temperature of the air is high, a lot of cooling of the air will be necessary to bring the temperature down below dew point. Thus, condensation is directly related to the relative humidity and the rate of cooling.
here are four types of condensation and the worst period for such problems is September to May:-
1. Surface condensation. This is the most familiar type of condensation, taking the form of water on window panes, cold wall surfaces and tiles.
2. Interstitial condensation. This is condensation forming between walls or within the building structure.
3. Reverse condensation. This is also called “Summer condensation”. If rains drenches a wall and strong sunlight then dries it, the heat can actually force water vapour into the wall. When it then meets an insulated surface, it forms condensation at that barrier.
4. Radiation condensation. This is sometimes called “clear night condensation“. If there is a sudden temperature drop at night, it can cause condensation on the underside of roof coverings, for example: often this drips onto the insulation quilting and causes a distinctive mottled effect upon the quilting.
Dew, Frost, Fog, Mist and Cloud
Dew: When the atmospheric moisture is condensed and deposited in the form of water droplets on cooler surface of solid objects such as grass blades, leaves of Plants and trees and stones, it is termed as dew. Condensation in dew form occurs when there is clear sky, little or no wind, high relative humidity and cold long nights. These conditions lead to greater terrestrial radiation and the solid objects become cold enough to bring the temperature of air down below dew point. In this process the extra moisture of the air gets deposited on these objects. Dew is formed when dew point is above freezing point. Dew formation can be seen if the water is poured into a glass from the bottle kept in a refrigerator. The outer cold surface of the glass brings the temperature of the air in contact with the surface down below dew point and extra moisture gets deposited on the outer wall of the glass.
Frost: When the dew point is below freezing point, under above mentioned conditions, the condensation of extra moisture takes place in the form of very minute particles of ice crystals. It is called frost. In this process, the air moisture condenses directly in the form of tiny crystal of ice. This form of condensation is disastrous for standing crops such as potato, peas, pulses, grams, etc. It also creates problems for road transport system.
Mist and Fog: When condensation takes place in the air near the earth’s surface in the form of tiny droplets of water hanging and floating in the air, it is called mist. In mist the visibility is more than one kilometer and less than two kilometers. But when the visibility is reduced to less than one kilometer, it is called fog. Ideal conditions for the formation of mist and fog are clear sky, calm and cold winter nights.
Cloud: Clouds are visible aggregates of water droplets, ice particles, or a mixture of both along with varying amounts of dust particles. A typical cloud contains billions of droplets having diameters on the or- der 060.01 to 0.02 mm; yet liquid or solid water accounts for less than 10 parts per million of the cloud volume. Clouds are generally classified on the basis of their general form or appearance and alti- tude.
Rainfall types.
Precipitation or Rainfall is defined as water in liquid or solid forms falling to the earth. It happens when continuous condensation in the body of air helps the water droplets or ice crystals to grow in size and weight that the air cannot hold them and as a result these starts falling on the ground under the force of gravity.
Different types of Rainfall are:-
- Convectional Rainfall :-Excessive heating of the earth’s surface in tropical region results in the vertical air currents. These currents, lift the warm moist air to higher strata of atmosphere. When-the temperature of such a humid air starts falling below dew point continuously, clouds are formed. These clouds cause heavy rainfall which is associated with lightning and thunder. This type of rainfall is called conventional rainfall. It is very common in equatorial region where it is a daily phenomenon in the afternoon
(b) Orographic or Relief Rainfall :-Orographic rainfall on formed where air rises and cools because of a topographic barrier. When their temperature fall below dew point, clouds are formed. These clouds cause widespread rain on the windward slopes of the mountain range. This type of rain is called orographic rainfall. However when these winds cross over the mountain range and descend along the leeward slopes, they get warm and cause little rain. Region lying on the leeward side of the mountain receiving little rain is called rainshadow area (see figure 12.4). A famous example of orographic rainfall is Cherrapunji on the southern margin of the Khasi Hills in Meghalaya India.
(c) Convergence or Cyclonic Rainfall:-Convergence rainfall, produced where air currents converge and rise. In tropical regions where opposing air currents have comparable temperatures, the lifting is more or less vertical and is usually accompanied by con- vention. Convectioned activity frequently occurs along fronts where the temperature of the air masses concerned are quite different. Mixing of air along the front also probably contributes to condensation and therefore to the frontal rainfall. When two large air masses of different densities and temperature meet, the warmer moist air mass is lifted above the colder one. When this happens, the rising warm air mass condenses to form clouds which cause extensive down pour. This rainfall is associated with thunder and lightning. ‘This type of rainfall is also called frontal rainfall. This type of rainfall is associated with both warm and cold fronts, (fig. 12.5) It is gener- ally steady and may persist for a whole day or even longer.
Evaporation is the process by which water changes from a liquid to a gas or vapor. It is the primary way that water moves from the Earth’s surface to the atmosphere. Evaporation occurs when water molecules at the surface of a liquid have enough energy to escape the attraction of other water molecules and enter the air as a gas. The rate of evaporation depends on several factors, including the temperature of the water, the amount of wind, and the humidity of the air.
Condensation is the process by which water vapor in the air changes into liquid water. It occurs when water vapor molecules come into contact with a surface that is cooler than the air. The water vapor molecules then lose energy and condense onto the surface. Condensation is the opposite of evaporation, and it is the main way that water returns to the Earth’s surface.
Dew is water that condenses on objects on the Earth’s surface, such as grass, leaves, and cars. It forms when the air temperature drops below the dew point, which is the temperature at which the air can no longer hold all of the water vapor it contains. The water vapor then condenses on the surface of objects, forming droplets of dew.
Frost is a type of dew that forms when the temperature drops below freezing. It forms when water vapor in the air condenses on objects on the Earth’s surface and then freezes. Frost can be a beautiful sight, but it can also be a problem for plants and crops.
Fog is a cloud that forms at or near the Earth’s surface. It is made up of tiny water droplets or ice crystals that are suspended in the air. Fog can form when warm, moist air meets cold air. The warm air rises and cools, and the water vapor in the air condenses to form fog. Fog can also form when cold air moves over a warm surface. The cold air picks up moisture from the warm surface, and the water vapor condenses to form fog.
Mist is a type of fog that is made up of very small water droplets. It is so thin that it often does not obscure objects more than a few feet away. Mist is most common in the early morning or evening, when the air is cool and moist.
Clouds are made up of tiny water droplets or ice crystals that are suspended in the air. They form when water vapor in the air condenses around tiny particles, such as dust or salt. Clouds are classified according to their shape, height, and appearance.
There are four main types of rainfall: rain, snow, sleet, and hail. Rain is the most common type of rainfall. It occurs when water vapor in the air condenses around tiny particles and falls to the Earth’s surface as liquid water. Snow is a type of precipitation that occurs when water vapor in the air condenses around tiny particles and falls to the Earth’s surface as ice crystals. Sleet is a type of precipitation that occurs when raindrops freeze as they fall through cold air. Hail is a type of precipitation that occurs when water droplets freeze and grow into large ice balls.
Dew
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What is dew? Dew is water that condenses on objects on the ground at night.
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How does dew form? Dew forms when water vapor in the air condenses on objects that are cooler than the air.
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What are the benefits of dew? Dew can help to water plants and can also be used to collect drinking water.
Frost
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What is frost? Frost is a thin layer of ice that forms on objects when the temperature drops below freezing.
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How does frost form? Frost forms when water vapor in the air condenses on objects that are at or below freezing.
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What are the benefits of frost? Frost can help to protect plants from the cold and can also be used to create beautiful patterns on windows.
Fog
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What is fog? Fog is a cloud that forms at ground level.
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How does fog form? Fog forms when water vapor in the air condenses around tiny particles in the air, such as dust or smoke.
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What are the benefits of fog? Fog can help to reduce Air Pollution and can also create a beautiful atmosphere.
Mist
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What is mist? Mist is a thin layer of fog that is close to the ground.
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How does mist form? Mist forms when water vapor in the air condenses around tiny particles in the air, such as dust or smoke.
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What are the benefits of mist? Mist can help to reduce air pollution and can also create a beautiful atmosphere.
Cloud
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What is a cloud? A cloud is a visible mass of water droplets or ice crystals in the atmosphere above the Earth.
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How do clouds form? Clouds form when water vapor in the air condenses around tiny particles in the air, such as dust or smoke.
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What are the benefits of clouds? Clouds help to regulate the Earth’s temperature and can also provide shade from the sun.
Rainfall types
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What are the different types of rainfall? There are three main types of rainfall: frontal rainfall, convective rainfall, and orographic rainfall.
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What is frontal rainfall? Frontal rainfall occurs when two air masses of different temperatures meet. The warm air rises and the cold air sinks, causing the water vapor in the air to condense and form clouds.
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What is convective rainfall? Convective rainfall occurs when the air near the ground is heated, causing it to rise. As the air rises, it cools and the water vapor condenses to form clouds.
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What is orographic rainfall? Orographic rainfall occurs when air is forced to rise over a mountain range. As the air rises, it cools and the water vapor condenses to form clouds.
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Which of the following is not a type of precipitation? (A) Rain (B) Snow (C) Dew (D) Hail
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Which of the following is not a type of cloud? (A) Cirrus (B) Stratus (C) Cumulus (D) Dew
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Which of the following is not a type of fog? (A) Advection fog (B) Radiation fog (C) Upslope fog (D) Dew
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Which of the following is not a type of frost? (A) Hoar frost (B) Rime frost (C) Dew (D) Rain
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Which of the following is not a type of mist? (A) Sea fog (B) Valley fog (C) Radiation fog (D) Dew
Answers: 1. (D) Dew is not a type of precipitation. It is a form of condensation that occurs when water vapor in the air condenses on objects that are cooler than the air. 2. (D) Dew is not a type of cloud. Clouds are made up of tiny water droplets or ice crystals that are suspended in the atmosphere. 3. (D) Dew is not a type of fog. Fog is a cloud that forms at or near the ground. It is caused by the condensation of water vapor in the air onto small particles, such as dust or salt. 4. (D) Dew is not a type of frost. Frost is a form of dew that forms when water vapor in the air condenses on objects that are colder than the air. 5. (D) Dew is not a type of mist. Mist is a type of fog that is less dense than fog. It is caused by the condensation of water vapor in the air onto small particles, such as dust or salt.