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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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Composition of Atmosphere
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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Composition of Atmosphere
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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Composition of Atmosphere
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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Horizontal distribution of
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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Horizontal distribution of
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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Horizontal distribution of
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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Atmospheric pressure and wind
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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Atmospheric pressure and wind
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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Atmospheric pressure and wind
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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Atmospheric pressure and wind
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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Horizontal distribution of pressure
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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Horizontal distribution of pressure
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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Horizontal distribution of pressure
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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Types of precipitation
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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Types of precipitation
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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Types of precipitation
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 sub- tropical 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