meteorology & geography

8/7/2019 Meteorology & Geography

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Composition of Atmosphere

Up to an altitude of 90 km it is uniform in termsof N2, O2 and Ar

The O2 & N2 make about 99% of the clean air

(in addition of it small amount of CO2 & watervapour, ozone and inert gases and huge amountof solid and liquid particles)

N2 & O2 are climatically of little consequence(N2 does not enter into chemical union but fixed

into soil- it serve mainly as diluents and regulatecombustion


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O2 combines with all the elements and is

most combustible

CO2 is an important gas in atmosphericprocesses. It absorb heat, use in

photosynthesis etc.

O3 is found in stratosphere between 20 &

25 km from the earth surface and absorb

UV rays thus protect life


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The water vapour and dust particles areimportant variables of weather and climate

They are sources of all forms of condensationand principal absorber of heat

Water vapour does not exceed 3- 4% andnearly 90% lies below 6 km (decreases fromequator towards poles)

Here dust particles, salt, pollens etc are also

present (they act as positive charge and entrapthe negatively charged water vapours toproduce cloud)


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In the upper layer of atmosphere the

microscopic dust (solid) particles scatter

incoming solar radiation and absorb allcolor except blue. The larger particles are

responsible for red and orange colors


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STRUCTURE OF ATMOSPHERE

On the basis of chemical compositionthere are two main layers

Homosphere and heterosphere

Homosphere: Extends upto 90 kms, characterised by

uniformity in chemical composition. There arethree thermal layers

Troposphere, stratosphere and mesosphere. Eachlayer is separated from the adjoining layer by ashallow transitional zone. The heterosphere hasheterogeneous chemical composition with layeredstructure of N2, O2, He and H2 respectively


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STRUCTURE OF ATMOSPHERE

Troposphere: 16 km thick at equator and10 km at poles, temperature decreaseswith altitude

The temperature decreases with altitude(0.65 0C per 100 m). A minimum of -60 0Ctemp. is reached at the tropopause.

Most of the atmospheric processesresponsible for the weather and climaticconditions take place here.


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Tropopause

The normal lapse rate ceases to function

It separates troposphere from stratosphere

This layer is quite and calm The altitude of tropopause depends upon

temperature of lower layer, cyclonic

activities etc. (10 to 15 km at tropic ofcancer and tropic of Capricorn, 18 km at

equator, 08 km at poles)


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Stratosphere

Lies between 10- 16 to 50 km

Free from violent weather so it is preferred

by jet liners Tendency of rise of temperature with

altitude due to presence of ozone

Water vapour is absent which prevent thecloud formation providing finest visibility

Ozone layer lies in this zone


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Stratosphere

Temperature rises from -60 0C to 00C

Ozone layer shield the UV rays

Ozone layer is not of uniform thickness(highest at equator and lowest at poles). It

is very thin, about 1/8 of an inch

At the upper boundary of stratosphere,stratopause is found


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Mesosphere

It extends from 50 to 90 km

The temperature decreases with altitudeand reaches a minimum of 110 0C

It displays high wispy clouds in highlatitudes during summer due to reflectedsunlight from meteoritic dust particle

After that mesopause is found. It is thinand extremely cold, separates themesosphere from thermosphere


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Heterosphere

It is layered thermosphere extending

above the mesopause and continues to

the edge of the space, about 60000 km

above the earth surface

Temperature rises spectacularly and

reaches upto 900 0C at 350 km

In the lower part, ionization of atmospheric

gases takes place (100 to 400 km)


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Weather and climate

Weather is the condition of atmosphere at

any place at a specific time with respect to

the various elements (temp., sunshine,

wind, clouds, fog, precipitation etc.)

Climate is the total complex of weather

conditions, its average characteristics and

range of variation over it


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Weather and climate

Principal elements of weather and climate

Principal elements

of weatherand climate

Temperature Pressure and wind Moisture and ppt


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Weather and climate

Temperature and precipitation are main

elements

Temperature expresses intensity of heat Unequal distribution of heat causes

differences in atmospheric pressure which

causes wind

Moisture is present in atmosphere as

water vapour (temperature dependent)


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Weather and climate

The climatic controls vary from place to place

due to climatic controls

These are- Latitude

Distribution of land and water

High and low pressure belts

Winds

Altitude Mountain barriers

Ocean currents

Storms


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Solar radiation

Source of all energy on the earth is the sun

The energy radiated from sun comes fromnuclear reactions in its core (1.5 x 107 0 C)

Only half of the billionths fraction of the energyradiated from the sun is intercepted by earth

We commonly call it the energy of the sun heatand light

It is transmitted in the form of electromagneticwaves which are commonly known as shortwaves


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Solar radiation

About 41% of these waves are in the formof visible light

About half of this is in the form of higherwaves

Remaining 9% are in the form of x rays,gamma rays and UV rays

The UV forms only 6% of the insolationand is consumed in photochemicalreactions


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Solar radiation

The infra red though invisible form only 43% ofthe total insolation. They are largely absorbed bywater vapour

Insolation is greatest at equator. It decreasespole wards

The total insolation received at the equator isroughly four times that of the poles

The energy is radiated into space by sun at a

steady rate. The earths atmosphere intercept anamount of energy equivalent to 1.94 cal/ cm2/min.


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Effects of atmosphere on insolation

Atmospheric gases are essentially

transparent to visible light, suspended

particles of liquid or solids can absorb or

reflect light

A thick cloud may allow less than 10% of

sunlight hitting it to reach the earths

surface (cloud generally behave likemirror)

Blue colour of sky is due to scattering of

light


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Heat budget on earth


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Heat budget on earth


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Terrestrial absorption and reflection

The sun heats the earth and earth heats

the atmosphere

Nearly 51% of solar energy reaches theearth directly or indirectly

The absorbed energy causes increase in

temperature

The earth radiates long wave which is

known as terrestrial radiation


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Methods of Terrestrial heat transfer

Radiation- transfer of most energy throughspace (long wave radiation) which heatedthe lower atmosphere

Conduction- The transfer of heat from oneobject to another by touching them(through molecular movement). It occursat the interface of the atmosphere and theearths surface (air is not a good conductorbut good insulator)


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Methods of Terrestrial heat transfer

Convection- Vertical transfer of heat

Advection- Horizontal transfer of heat.

Wind is the transfer agent Latent heat of condensation- The

evaporated water vapour stored heat as

latent heat. This energy released in

atmosphere when it changes to liquid

water through condensation


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Heat energy budget at earths

surface

Out of 47% of earths heat, 14% is sent to

the atmosphere in the form of long wave

radiation (6% to outer space and 8% to the

atmosphere)

The 10% is transferred through

conduction and convection

The remaining 23% is reaches through

latent heat of condensation


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Heat energy budget in the

atmosphere

About 60% of the solar radiation intercepted bythe earth system is temporarily retained by theatmosphere

This includes 19% absorbed by clouds andozone layer, 8% is emitted by long waveradiation, 10% is transferred from conductionand convection, and 23% is by latent heat ofcondensation

Some of these energy is recycled and most ofthem is lost to the outer space after beingreplaced by another solar energy.


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Variations in the heat energy

budget

For any particular place, the heat budget maynot be in balance (the above are averages only)and adjustments may be made within the entire

earth system It is due to the differences in latitude and

seasonal fluctuations

High insolation in tropical zone throughout the

year In the Arctic and Antarctic zones, there is little

insolation


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Variations in the heat energy

budget

Places in the middle latitude have lower deficit orsurplus

At about 380 latitude, the heat budget is in

balance At any particular place, the heat budget varies

throughout year according to season with atendency toward a surplus and deficit six month

later Seasonal differences may be small near the

equator, very great in mid and higher latitude


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Vertical distribution of temperature

The temperature varies with altitude at thenormal lapse rate (0.6 0 C/ 100 m) belowthe tropopause and that decreases with

altitude The air changes its temperature either by

heating or cooling. If the air is dry, thetemperature of rising and expanding airwill decrease at the rate of 10.2 0 C/ 1000m , for wet air it is 5.8 0 C/ 1000 m


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Vertical distribution of temperature

There is temperature inversion also. It

increases under certain unusual

conditions. The most noticeable inversion

are occur near the earth surface when the

earth cools off the lowest layer of air

through conduction and radiation


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Horizontal distribution of

temperature

The temperature distribution on earth depends

upon insolation, land and sea, seasonal

changes, winds and currents and the nature of

the land The places having similar temperature

conditions are joined by means of isotherms.

These lines run from east to west

The break in these may occurs when land meets

to sea.


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temperature

The isothermal lines passing from a continentstowards the oceans bend towards the equatorduring summer and towards the poles during

winter. The local currents further modify thesebends

Over land surfaces which have no vertical forms,isothermal lines run parallel to the equator

The hottest regions are the equatorial landmasses and the coldest regions are interior ofNorth America and Asia


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temperature

On the basis of latitudinal temperature

distribution, the earth is divided into torrid,

frigid and temperate zones

Torrid zone is bounded by tropic of cancer

and tropic of Capricorn

The temperate zone is lies between tropic

of cancer to the arctic circle and tropic of

Capricorn to the Antarctic circle


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July isotherm

July isotherms in Northern hemisphere areirregular, zigzag and widely spaced shows warmseason and summer conditions

350

C isotherm passes over North Africa, SouthWest Asia and North West part of America

In Southern hemisphere, it bends towards poleson continents and towards equator on oceans.

The continents are warmer than oceans. Theisotherms are more regular, straight and closelyspaced (wintry condition)


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temperature

The arctic circle forms the southern

boundary in northern hemisphere and the

Antarctic circle forms the northern

boundary in southern hemisphere


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Atmospheric pressure and wind

Air pressure and winds are the invisibleelements of weather which influence otherelements in significant way. They control

temperature and precipitation The weight of air on unit area of the earth

is called air pressure. It is expressed inbar, millibar orPascal or Newton/ m2. Theaverage pressure over earth surface atsea level is 1013. 25 millibar


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The atmospheric pressure is measured by

an instrument known as barometer

The amount of pressure exerted by air at aparticular point is determined by

temperature and density. It means that

change in either temperature or density

will cause corresponding change inpressure


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Distribution of atmospheric pressure is

shown on map by isobars. These are

imaginary lines drawn through places

having equal atmospheric pressure at sea

level

The spacing of isobars expresses the rate

and direction of the pressure changes andis referred to as pressure gradients


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There are two type of pressure systems- highpressure and low pressure

Temperature is the most common cause of

pressure differentiation. Air that is cooled at thebottom will sink and increase pressure, whereaswarming will cause air to rise thus lower thepressure

The change in temp. is caused either by solarradiation or induced by some external dynamicagencies like friction or by force producedthrough earth rotation


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Thus pressure change takes place either

by thermal or dynamic processes

Distribution of atmospheric pressure is notuniform over the earths surface

There are vertical and horizontal pressure

distributions on earths surface


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Vertical pressure distribution

It is according to temperature and altitude

For first few thousands meter above thesea level, the pressure decreases at the

rate of 1 mb for every 10 m. It drops to halfof its surface value (from 1013.25 mb to540.4 mb) at 5 km altitude

The rates of fall of pressure with altitude isdetermined partly by the rate of fall intemperature


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Vertical pressure distribution

At mount Everest, the air pressure is about twothird less than it is at sea level

The air pressure also changes through time for a

particular location, rather than being solelyrelated to altitude

At sea level, the air pressure is intimately relatedto the intensity of radiation, the general

movement of global circulation and also to thelocal humidity and precipitation. A change in airpressure for a given locality is nearly always asign of a change in the weather


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Horizontal distribution of pressure

It presents an alternate belt of low andhigh pressure areas

There is inverse relationship between

pressure and temperature The equatorial region having high

temperature has slow pressure. The polar

region has high pressure These pressure belts are thermally

induced


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There should have been a gradual increase in

pressure from the equator towards the poles.

But this is not so

There are two intermediate zones of subtropicalhighs in the vicinity of 300 N and S and two sub

polar lows in the vicinity of 600 N and S

Formation of these pressure belts is due to

pressure gradient force and rotation of earth


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The warm air of equatorial low pressure

belt gradually gets cool in its ascent, upon

reaching upper layers, it starts moving

towards the pole. It further cools and

begins to subside in a zone between 20

and 350 of latitudes (due to cooling and

earths rotation). The pole ward directedwind deflected eastward


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On rotating earth, the particle moves

fastest at equator and the speed

decreases, if we go towards the pole. The

moving particle towards the equator or

away from the equator, may get deflected

due to coriolis force


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Ferrell's law

All moving bodies like wind and oceancurrents get deflected from their normalpaths towards right in the Northern

hemisphere and towards left in theSouthern hemisphere

The rate deflection increases with thedistance from the equator

It produces a blocking effect and the airpiles up aloft


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Pressure belts of world

There are seven pressure belts in thewhole world

Equatorial trough of low pressure

Subtropical high pressure belt of NH Subtropical high pressure belt ofSH

Sub tropical- low pressure belt of NH

Subtropical low pressure belt ofSH

Polar high of NH

Polar high ofSH


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Pressure belts of the worlds


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Equatorial trough of low pressure

Located up to 10 0 latitude on either side of

the equator in NH and SH

It is thermally produced low pressure belt Pressure is more uniform than other belts

Surface winds are generally absent

It is a region of extremely calm air and iscalled as doldrums


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Subtropical high pressure belt

Located between tropics and 35 0 latitude

Broken into many pressure cells

The high pressure is caused due to thesubsidence and pilling of the air

A calm condition with variable and feeblewinds is created

These regions are also referred as horselatitude as the sailing vessels with thecargo of horse found it difficult to sail.


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Sub pressure low pressure belt

Located between 45 0 and 66.5 0 latitudein NH and SH

Well developed in North Atlantic and North

Pacific regions The low pressure is caused by converging

and rising air

Due to contrast between temp. ofsubtropical and polar source of air,cyclonic storms are produced


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Polar highs

Well developed high pressure zones due

to persistent low temperature

Thos gives rise to cap of high pressure.The prevailing easterly winds blow out of

these caps


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Seasonal distribution of pressure

The pressure conditions vary according to

weather conditions also

The horizontal distribution of pressure is

shown by isobars

The pressure gradient is right angle to the

isobars

Closely spaced isobars shows steep

pressure gradients


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Seasonal distribution of pressure

In summer the hot continents intensify the

low pressure cells and in the similar

condition the colder oceans intensify the

high pressure cells

In winter the situation is reversed


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January isobars

In Northern hemisphere, the polar highs in the

form of ridges extending from northeastern

Eurasia to Yukan of North America. The isobars

have extensive high pressure. The subtropicallow pressure belt is represented by individual

oceanic cells developed in north Atlantic and

Pacific. The subtropical highs is well developed

over the cold continents. The highest pressure iscentered on central Asia


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January isobars

In southern hemisphere, the equatorial low

pressure is mainly south of the equator. It

extends over warm continent. The

subtropical high over southern oceans is

broken into three cells namely Pacific,

Atlantic and Indian ocean


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July isobars

In NH the polar highs has weakened

substantially and it separates Asiatic low.

The sub polar low is also weakened. The

subtropical high is well developed in

oceans. The equatorial low pressure is lies

north of equator. The center of low

pressure is well developed over the oceanbetween 10 to 150


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July isobars

In southern hemisphere, the subtropical

high pressure is strongly developed over

oceans than over cold continents. Sub

polar low is a continuous belt over 65 to

750 south latitude. The polar high is weak

and extends to smaller degree over

oceans


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Winds

Air moving parallel to the ground is calledas wind

The vertical air movement is called as

current Air movement is caused by differences in

air pressure

Wind moves from high pressure to lowpressure region following barometricslope.


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Winds

Air moving down the pressure gradient followsthe law of gravitation

Wind set once in, it flows from high to lowpressure but follows somewhat a devious course

due to the coriolis force The wind is known by the direction from which it

is blowing

The direction of wind is known by wind vane.

The wind velocity is measured by anemometerand expressed in km/ hr on land and knot/hr inthe ocean


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Types of wind

The pressure varies from place to place in response tolocal temperature wind conditions and distribution of landand sea

There are three different air circulation systems. These

are primary, secondary and tertiary The primary circulation pattern, prepares the broad

framework for other circulatory patterns. The primarywinds are also known as planetary wind eg. Tradewinds, westerlies and polar winds. Secondary wind

include monsoon, cyclones, anticyclones, air massesand fronts. Tertiary wind include local winds like land andsea breezes. They affect only local weather and climate


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Primary wind

These wind constitute large scale motion

of atmosphere under the influence of

pressure gradient, coriolis force and

frictional force

It ignores seasonal heating and land water

contrast on the earth surface. These are

doldrums, trade winds, westerlies andpolar easterlies


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Primary wind

Doldrums- are feeble and have least

surface movement. They are dominant

towards both the sides equator


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Atmospheric moisture

Water vapour is one of the most important

atmospheric gases

It is odorless and invisible. Human body

can sense only in conjunction with air

temp.

The atmosphere gathers moisture through

evaporation and looses it throughcondensation and ppt.


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Atmospheric moisture

The water has a number of unique properties

like high specific heat and the highest surface

tension

The water needs a lot of heat to change intovapour

The heat stored in water vapour as latent heat

Due to high surface tension, the water molecule

attract and form droplets, dew, fog, mist etc.


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Source and distribution of water

vapour

All the three forms of water are interchangeable

The surface of the ocean is the greatest sourceof water vapour

Much of the water vapour evaporated from theoceans is carried by winds to the land surfacewhere is ppted and delivered back to the oceans

The amount of water vapour in the atmosphere

is highly variable from place to place and fromtime to time, ranging almost upto 5% in anyplace. It decreases with altitude


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Evaporation

The solid and liquid water changes into

water vapour

It occurs whenever energy is transported

to an evaporated surface and temperature

rises

The molecules become more mobile and

overcome the forces binding them to watersurface and break away


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Evaporation

The heat removed from the immediate

surrounding is trapped in water vapour as

latent heat

It means the evaporation decreases the

temp. of remaining liquid by an amount

proportional to latent heat of vapour


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Evaporation

The rate of evaporation is related to the

difference between saturation vapour

pressure at surface temp. and the vapour

pressure at the air above

Tropical seas and forests are by far the

greatest contributors of moisture

The polar ice caps and tropical deserts arelargely without evaporation


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Potential evapotranspiration

Evapotranspiration is the amount ofmoisture transferred to the atmosphere byevaporation of liquid and solid water plus

transpiration from living tissues of plants Potential evapotranspiration is idealized

conditions in which there would be enoughrainfall to provide sufficient moisture for all

possible evapotranspiration for any place


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Humidity

Humidity refers to the condition of the air

with regard to water vapour

Absolute humidity refers to the actual

amount of water vapour present per unit

volume of air (expressed in g/ cu. M)

It is greater near the equator during

summer

It is greater over the oceans


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Relative humidity

It is amount of water vapour in the aircompared with the amount that would bepresent if air were saturated at that temp.

It is expressed in percentage determinedby dividing the absolute humidity by waterholding capacity of air

If air saturated, its RH will be 100%

The RH can be altered by changing temp.without changing the amount of moisture


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Relative humidity

The dew point is also at 100% RH because any

further cooling will result in condensation. It

means the dew point is where condensation

begins as cooling continues If this point is above freezing point, condensation

will be in the form of rain, if below freezing point,

will be in the form of snow consequently cooling

will result in continued condensation


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Condensation

In this process, the water vapour changesinto liquid, if the air is cooled below its dewpoint

Any amount of cooling of the saturated airstarts the process of condensation

Whenever the dew point temperature fallsbelow the freezing point, water vapourmay convert directly into ice by theprocess of crystallization


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Condensation

Condensation may start with the addition

of any further water vapour to the

saturated air or with the reduction of its

temperature

Condensation depends upon two factors-

RH and degree of cooling

In arid lands larger degree of cooling isnecessary before the dew point is reached


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Condensation

In humid climates a lesser degree of

cooling will starts the process of

condensation

In condensation, equal amount of energy

is transferred into the atmosphere

There can be no condensation unless

there is a surface on which the liquid cancondense


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Condensation

The abundant supply of microscopic

particles of sea salt, SO2, oxides of N2,

volcanic dust and fine dust particles are

capable attracting or absorbing the liquid


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Dew and frost

On cool nights in early winters, whenradiation from the ground is relativelyrapid, the air in contact with the ground

may be chilled to dew point and moisturecondenses on the leaves and grass in theform of dews

If dew point is at or below the freezing

point, the condensation takes the form oftiny ice crystals or frost


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Dew and frost

Dew and frost form on grass quite rapidly

because grass is a good radiator and

therefore cools quickly

Furthermore, grass and other plants give

off moisture which is not readily

evaporated at nights when the air cools

The formation of D & F impeded by dry air,wind and clouds


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Dew and frost

Low ground moisture and also cold air

from the uplands flow down the slope into

valleys causing the formation of dew and

frost on low flat ground rather than onslope


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Clouds and fog

Clouds are formed by condensation of

water vapour around nuclei of dust

particles in the air

In most cases, cloud consists of tiny

droplets of water but they may also consist

of ice particles if the temp. is below

freezing point


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Clouds and fog

Most of the clouds are formed by risingwarm and moist air. The ascending airexpands and cools until the dew point is

reached and some of the moisturecondenses into clouds

Other clouds result from mixing betweentwo air masses of different temp.

The clouds at and near the earths surfaceare known as fog


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Clouds and fog

About 10 genera of clouds are combined

into three groups based on the average

height of the cloud base High clouds (5- 10 kms)- Cirrus, cirrostratus,

cirrocumulus

Middle clouds (2- 7 kms)- Altostratus, altocumulus

Low clouds (below 2 kms)- Stratocumulus, stratus,

nimbostratus, cumulus, cumulonimbus


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Clouds and fog

The high clouds are composed entirely of

ice crystals. The clouds formed by vertical

development, have a water droplet

composition in their lower part, but thosewith a very large vertical extent have tops

with entirely of ice crystals


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Precipitation

It is a Latin word, precipitatio means head long

falling down. In meteorological language, it

means condensed or frozen water vapour that

falls on the ground. It not only includes rain orsnow but also other hydrometer like hail, slit or

fog

The ppt depends upon- temp. at which

condensation takes place, condition of the air,height of the cloud and the process generating

phenomenon


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Forms of precipitation

Precipitation results from the continued

condensation and growth of the moisture

particles until they become too large to remain

suspended in the air If condensation takes place at a temp. above 00

C, resulting precipitation will be in the form of

rain.

If rain passes through a layer of colder air on theway down, it may freeze and fall as sleet


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Forms of precipitation

In strong turbulent currents of thunder storms,

water drops may be carried upwards into

freezing and fall as hail

Snow is not frozen rain but forms when moisturecrystallizes directly from vapour at a temp. below

freezing point

Ice storms result when rain, already near the

freezing point, falls on the colder ground andvegetation freezes upon contact


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Types of precipitation

There are three types of precipitation- 1.convectional, Orographic and cyclonic

Convectional occurs when moist air over

the heated ground becomes warmer thanthe surrounding air and is forced to rise,expand, cool and release some moisture

It is most common in low latitudes andusually comes in the form of short heavyshowers just after hottest part of the day


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Thunder and lightening is general

Orographic precipitation- when moist air isforced to rise over a mountain or other

elevation in its path Thus the wind ward side of the most of the

mountain receives heavy ppt. where asthe leeward sides receives lesser rain falleg. Western India, North America andSouth America


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The moist air of Arabian sea is forced to

rise above the hills, expand and become

cool and there is the rain fall

The other side of the maintain, the

descending wind is devoid of moisture

hence does not give rain. This is known as

rain shadow


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Cyclonic precipitation- In the low pressure

areas where cyclonic winds coming from

various direction converge and force the

large volume of light air and rise to causerain


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Temperate (D) climate

Found in micro-thermal zones (40- 650 N-S)

Climatic bands of severe winters is found

between subtropical and boreal types of

climate. There are two sub climates Temperate marine (Do)

Temperate continental (Dc)

Do has mild winters and fairly clear summers.

Av. Temp. is more than 00 C, rain through outthe year


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Temperate continental

There is harsh winter and cool summers

Extreme cooling is associated with

anticyclone

Annual ppt is low though it takes place

throughout the year eg. North eastern

Asia, Eastern Canada & Eurasia


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Boreal Climate (E)

Found in higher middle latitudes

Summers are short and cool, winters are

long and cold with a very short frost free

season

Annual temp. 0 to 100 C, annual ppt. is

meager and most it occur during summer

in coniferous forest of the world


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Polar climate (F)

Found in high altitudes and higher reaches

of the Himalayas and the Alps

Average temp. does not exceed 100 C in

any month

There is no summer

On the basis of temp., the polar climates

are classified into Tundra (Ft) and ice cap

(Fi)


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Tundra

Only in NH where it occupies the coastalfringes of Arctic ocean, ice free shores ofNorthern Iceland, Southern Greenland and

higher reaches of Himalayas and Alps Extreme cold, average temp. does not rise

above 00 C, associated with permanentfrost leading to frozen sub soil

During summer, the ppt. is in the form ofsnow and rain


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Ice caps

Average temp. is less than freezing point

Associated with the phenomenon of

permanent ice and snow

Summer and winter are windy and chilly,

ppt is meager


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Dry (B) climate

On the Western margins of A

Higher rate of moisture is there (loss

through evaporation)

Temp. range from -25 0C to 30 0C

Two types Desert (Bw) and Semiarid (Bs)


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Tornado

Violent whirlwind of cyclonic type- anticlock wisein NH and clock wise in SH

The axis of wind is vertical, extending from thecloud base downwards and often reachingground level, width is 50- 500 m and travels atthe speed of 10- 30 knot, the wind velocity is upto 200 knot in the centre

It may last from few minutes to a few days,

covering a track between a few hundred m tofew hundred miles


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Storm warning signals

A tropical revolving storm is small area ofvery low pressure around which windblows spirally inwards, anticlockwise in NH

and clockwise in SH In case of violent tropical revolving storms,

wind speeds upto 130 knots have beenexperienced

TRS originate between 5- 20 0 latitude andtravel between w and wn inNH

S i i l


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Storm warning signals

meteorology & geography

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