Physical Geography 3 Flashcards
(37 cards)
Humidity and how is it expressed, what does it depend upon
Water vapour present in the air is known as humidity. Absolute and relative humidity. Depends upon temperature
Absolute humidity
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.
Relative humidity
The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.
Saturation and dew point
The air containing moisture to its full capacity at a given temperature is said to be saturated. It means that the air at the given temperature is incapable of holding any additional amount of moisture at that stage. The temperature at which saturation occurs in a given sample of air is known as dew point.
Evaporation and causes
process by which water is transformed from liquid to gaseous state. Heat is the main cause for evaporation.
latent heat of vapourisation
The temperature at which the water starts evaporating is referred to as the latent heat of vapourisation.
Condensation and causes
The transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat.
Sublimation
Change of water from gaseous into solid form, a form of condensation
Hygroscopic nuclei
In free air, condensation results from cooling around very small particles termed as hygroscopic condensation nuclei. Particles of dust, smoke and salt from the ocean are particularly good nuclei because they absorb water.
The relationship between temperature and humidity
is inversely proportional. The relationship between temperature and humidity is inversely proportional: Warmer air can hold more water vapor than colder air. This means that if the temperature increases, the relative humidity decreases, and the air becomes drier. Colder air has a lower capacity to hold water vapor than warmer air. This means that if the temperature decreases, the relative humidity increases, and the air becomes wetter.
What form does water take after condensation in the atmosphere aka types?
dew, frost, fog and clouds.
Discuss Dew
When the moisture condenses in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew. The ideal conditions for its formation are clear sky, calm air, high relative humidity, and cold and long nights. For the formation of dew, it is necessary that the dew point is above the freezing point (0 degree C).
Discuss Frost
Frost forms on cold surfaces when condensation takes place below freezing point (0 degree C), i.e. the dew point is at or below the freezing point. The excess moisture is deposited in the form of minute ice crystals instead of water droplets. The ideal conditions for its formation are clear sky, calm air, high relative humidity, and cold and long nights.
Discuss Fog, Mist and Smog
When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden, condensation takes place within itself on fine dust particles. So, the fog is a cloud with its base at or very near to the ground. Mist has more moisture. Smog is when fog is mixed with smoke.
Clouds and types
Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types : (i) cirrus; (ii) cumulus; (iii) stratus; (iv) nimbus.
Discuss Cirrus Clouds
Cirrus clouds are formed at high altitudes (8,000 - 12,000m). They are thin and detached clouds having a feathery appearance. They are always white in colour.
Discuss Cumulus Clouds
They are generally formed at a height of 4,000 - 7,000 m. Cumulus clouds look like scattered cotton wool with flat base.
Discuss Stratus Clouds
As their name implies, these are layered clouds covering large portions of the sky. These clouds are generally formed either due to loss of heat or the mixing of air masses with different temperatures.
Discuss Nimbus Clouds
Nimbus clouds are black or dark gray and shapeless. These are extremely dense and opaque to the rays of the sun. They form at middle levels or very near to the surface, almost touching ground.
Combo clouds
A combination of these four basic types can give rise to the following types of clouds: 1. high clouds – cirrus, cirrostratus, cirrocumulus; 2. middle clouds – altostratus and altocumulus; 3. low clouds – stratocumulus and nimbostratus and 4. clouds with extensive vertical development – cumulus and cumulonimbus.
Precipitation
Release of moisture in free air post condensation. May be liquid aka rainfall, or solid aka snowfall when temp below 0 degrees.
Sleet
is frozen raindrops and refrozen melted snow-water. When a layer of air with the temperature above freezing point overlies a subfreezing layer near the ground, precipitation takes place in the form of sleet. Raindrops, which leave the warmer air, encounter the colder air below. As a result, they solidify and reach the ground as small pellets of ice not bigger than the raindrops from which they are formed.
Hail
Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the earth are called hailstones. These are formed by the rainwater passing through the colder layers. Hailstones have several concentric layers of ice one over the other.
Types of Rainfall
On the basis of origin, rainfall may be classified into three main types – the convectional, orographic or relief and the cyclonic or frontal.
