Elements of Climate

7/28/2019 Elements of Climate

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Climatology is the study of the long-term

state of the atmosphere, orclimate.

The long-term state of the atmosphere

is a function of a variety of interacting

elements.

Elements Of Climate

Temperature

Humidity

Wind

Solar radiation

Precipitation

Cloud Cover

Climate


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Temperature is defined as the thermal state of matter with referenceto its tendency to communicate heat to the matter in contact with it.

Temperature is an index of the thermal energy content of materials

disregarding energies stored in chemical bonds and in the atomic

structure of matter.

Temperature of air is measured in degree Celsius, degree Kelvin,

degree Fahrenheit.

Instruments to measure temperature are Mercury or Alcohol

Thermometer Maximum and Minimum Thermometer, Bimetallic

Thermograph.


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Differences in solar radiation gives rise to temperaturevariation.

Variation in temperatures affect the air pressure andgives rise to convectional winds.

Temperature variations affect the amount and nature ofprecipitation.

In presence of water body, rise in temperature raises the

humidity in the air.


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Temperature data can be simplified

by finding out following values.

Mean monthly Temperature

Monthly mean Maxima

Monthly mean Minima

Monthly Extreme maxima

Monthly Extreme minima

These five values give reasonablyaccurate picture of temperature

conditions of the Location.

Temprature Data For Important Cities In

India


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Humidity of air can be described as the amount of

moisture present in the air.

Absolute humidity is defined as the weight of moisture inthe unit volume of air.Unit Of Measurement is gram /cu.mt.

Relative humidity is the ratio of actual amount ofmoisture present to amount of moisture the air could holdat the given temperature.It is expressed in percentage(%)

Humidity is measured by Wet and Dry bulb Hygrometer.


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The relative humidity depends on the air temperature and the water

vapours present in the air.

During the day, if the temperature at ground is high, The RH gets

lowered. The rate of evaporation increases. And in presence of

water, vegetation, more evaporation takes place and AH at ground

increases.

At night, if the temperature at ground is low, The RH is high. The rate

of evaporation decreases. The point of saturation is reached and

with further cooling moisture condenses in dew.

Air movement increases the rate of evaporation. When humid airgets cooled by lowering temperature or by mixing of cool winds, the

moisture gets condensed and the rate of precipitation increases.

Effects Of Humidity


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Humidity, vapour pressure, rainfall are

mutually dependant factors.

To give an indication of prevailing

humidity conditions, it is sufficient to

establish monthly mean maximum and

monthly mean minimum relative

humidity values.

Early morning values are fairly high, the

afternoon values are more

characteristic of the given location. So

they are used to brief humidity

conditions.

Humidity Data For Important Cities In India


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Winds are basically convection currents in the atmosphere tending toeven out the differential heating of various zones.

The pattern of air movements is modified by earths rotation. Windrefers to the horizontal motion of the air.

Also unequal heating of the Earth's surface creates pressure gradientsthat result in wind.

Wind velocity is measured by anemometer.Unit is m./s. or km./hr or knot (nautical mile per hour)

The directions of wind can be established asN,S,E,W (cardinal poins)

N-E, S-E, N-W, S-W (semi cardinal points),

NNE, ENE, ESE ,SSE, SSW, WSW, WNW and NNW( tertiary points)


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Effects on Macro level:

The atmosphere rotates with the earth. Due tothe thermal forces and Coriolis force, a pattern

of wind is formed on the earths surface.

Polar winds, westerlies and trade winds are

the resulting wind patterns.

Effects on micro level:

Mountain breeze, valley breeze.

Sea breeze and land breeze

They occur due to difference in temperature over the respective areas.


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By determining directions of the wind,

daily or seasonal shifts and pattern ofwind velocities one can know the

calm period in each month.

Many different methods of graphical

presentation of wind patterns, windvelocities, wind frequencies are

evolved.

Wind Data For Important Cities In India


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Solar radiation is the radiantenergy from the sun.

The Solar radiation which strikesthe Earth is called as Insolation.*Solar radiation the most importantelement of climate.*The unit of measurement of solarradiation is W/sq.mt,Btu/sq.ft,kcal/sq.mt., mj/sq.mt.

Solar energy can be measuredwith instruments like solarimeter,heliometer, actinometer,pyranometer.*It comprises of ultraviolet, visibleand infra-red wavelengths.*It heats the Earth's surface whichin turn determines the

temperature of the air above.*The solar radiation is in the form ofwaves. The range of wavelengthsis solar spectrum.


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Average daily amount of solar radiation ( mJ/sq.mt.day) for each month of theyear would give a fair indication of climatic conditions including seasonal

variations of the location.

*Solar radiation reaching the outer limits of the atmosphere depends on

Energy output of the sun

distance from the earth to the sun

dust in the solar system.

*Solar radiation reaching the earths surface depends on

Transparency of earths atmosphere

Duration of the day

Angle at which the sunrays strike the earths surface.

Unequal heating of the Earth's surface creates pressure gradients that result inwind. The spectral energy distribution varies with altitude due to the filteringeffect of atmosphere. The receipt of solar radiation drives evaporation


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The Case Of India


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Precipitation

Precipitation is defined as water in liquid or solid forms falling to the earth.

It s always preceded by condensation or sublimation or a combination of the two and

is primarily associated with rising air.

The common precipitation forms are rain, drizzle, snow and their modifications.

Types of precipitation:

Convectional precipitation eg. Rain, snow, etc.

Orthographic precipitation -rains due to topography. Eg. Cherapunji.

Convergence precipitation-mixing of opposite air currents.


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Effects of precipitation


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Cloud Cover

A cloud is physically an aerosol that is a suspension of minute

water droplets or ice crystals and other particles in the air.

Clouds are visible aggregates of water droplets, ice particles or a

mixture of both along with varying amounts of dust particles.

Clouds form when rising air cools to what is known as the dew

point, where it can no longer hold its water vapor. The vapor then

condenses around particles of dust forming tiny droplets which

combine together, lifting into the air as a result of warm or coldfronts, convection or by encountering obstacles, such as hills and

mountains.

Cloud Cover is Measured in % Area occupied of Clear sky.

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Elements of Climate