Heat Budget

Facts

  • The annual mean temperature on the surface of the earth is always constant
  • Balance between insolation and terrestrial radiation is termed as heat budget of the earth

Latitudinal variation

  • latitudinal heat balance
  • The amount of insolation received is directly related to latitudes
  • Insolation creates an imbalance of heat at different latitudes
  • Tropical region
  • Amount of insolation received is higher than the amount of terrestrial radiation, resulting in surplus heat
  • Polar region
  • Amount of insolation received is lesser than the amount of terrestrial radiation, resulting in heat deficit

Let the incoming solar radiation be 100 units

  • 35 units are reflected back into space before reaching the earth’s surface
  • 6 units by atmosphere
  • 27 units by clouds
  • 2 units by snow and ice
  • 65 units
  • 51 units reach the earth’s surface
  • 14 units are absorbed by the various gases, dust particles and water vapour
  • Earth radiates back the 51 units in the form of terrestrial radiation
  • 34 units are absorbed by the atmosphere
  • 17 units directly go to space
  • Atmosphere radiates 48 (14+34) units of absorbed radiation back to space
  • 48+17 + 65 units
  • Total outgoing radiation : 65+35 = 100 units

 

Factors responsible for uneven distribution of temperature

Factors

  1. Latitude
  • Angle of incidence of sun’s rays decrease gradually from equator towards the poles
  • Due to this, higher temperatures are found in tropical regions and decreases gradually towards the poles
  1. Land and Sea Contrast
  • Land gets heated and cooled more rapidly than water
  • Temperature is relatively higher on land during day and it is higher in water during night
  • During winter the air above oceans has higher temperature than landmasses
  • Vegetation covered land does not get excessively heated because of evaporation of water from the plants
  1. Relief and Altitude
  • Relief features such as mountains, plateaus and plains affect the distribution of temperature
  • Temperature decrease gradually from the sea level
  • Rate of decrease of temperature also varies with time of a day, season and location
  1. Ocean Currents
  • Warm currents and cold currents distributes the temperature accordingly
  1. Winds
  • Winds transfer heat from one region to another though advection
  1. Vegetation Cover
  • vegetation cover absorbs much of sun’s heat and prevents quick radiation from the earth
  1. Nature of the Soil
  • Black, yellow and clayey soils absorb more heat than sandy soils
  • Heat radiates more rapidly from sandy soils than from black, yellow and clayey soils
  1. Slope and Aspect
  • Amount of insolation varies with the Angle of the slope and its direction
  • Temperature in gentle slopes is higher than steep slopes
  • southern slopes of the Himalayas are warmer than the northern ones

Temperature Distribution

Basics

  • Distribution of temperature on earth’s surface is uneven
  • Isotherms
  • Imaginary lines on a map joining the places of equal temperature, reduced to sea level are called Isotherms
  • Isotherms are regular and widely spaced in the southern hemisphere due to large expanse of water in southern hemisphere
  • Isotherm are irregular and closely spaced in northern hemisphere due to large expanse of landmasses
  • Annual range of temperature
  • Difference between the average temperature of warmest and the coldest months is known as annual range of temperature
  • Equatorial regions have insignificant annual range of temperature
  • due to constant insolation throughout the year
  • Warm and cold ocean currents influence the annual range of temperature significantly
  • Seasonal extremes are most obvious in northern and southern hemispheres during January and July
  1. Horizontal distribution
  • Latitudinal distribution of temperature over the surface of the earth is called horizontal distribution
  • January
  • Sun shines vertically overhead near the Tropic of Capricorn
  • Summer in southern hemisphere and winter in northern hemisphere
  • High temperature is found over three regions
  • North-west Argentina
  • East-Central Africa
  • Central Australia
  • Isotherms
  • bend towards poles when they cross the oceans in northern hemisphere and towards equator when they cross the landmasses
  • bend towards equator when they cross the oceans in southern hemisphere and towards poles when they cross the landmasses
  • July
  • Sun shines vertically overhead near the Tropic of Cancer
  • Summer in northern hemisphere and winter in southern hemisphere
  • Isotherms
  • bend towards poles when they cross the oceans in northern hemisphere and towards equator when they cross the landmasses
  • bend towards equator when they cross the oceans in southern hemisphere and towards poles when they cross the landmasses
  1. Vertically distribution
  • Temperature decrease gradually with altitude in troposphere
  • Rate of temperature decrease in troposphere is 6 C per km, extending to the tropopause
  • This vertical gradient of temperature is called standard atmosphere or normal lapse rate
  1. Temperature Inversion

Anomalous increase in temperature with height in the troposphere

  • Process

Step 1: Quick radiation of heat from the earth’s surface

Step 2 : Quick radiation results in cooling of the air near the earth’s surface

Step 3: upper layers which lose their heat not so quickly are comparatively warm

Step 4: cooler air is near the earth and the warmer air is above

Result: Normal condition in which temperature decreases with increasing height, is reversed

  • The phenomenon of inversion of temperature is observed generally in intermontane valleys
  • Frames cultivate on upper slopes and avoid the lower slopes of the mountains to escape winters frost

Distribution of Atmospheric pressure

Facts

  • Atmospheric pressure on the surface of the earth not uniform, it varies both vertically and horizontally
  • An isobar is a line connecting points that have equal values of pressure
  • cooking in high mountainous areas takes long time because, low pressure reduces the boiling point of water
  1. Vertical Distribution
  • The columnar distribution of atmospheric pressure is known as vertical distribution of pressure
  • Lower layers are more dense due to the compressive pressure exerted by the mass of air in the upper layers
  • Three factors determine the air pressure of a given place and at given time
  1. Temperature of the air
  2. Amount of water vapour present in the air
  • Gravitational pull of the earth
  1. Horizontal Distribution
  • The distribution of atmospheric pressure over the globe is known as horizontal distribution of pressure
  • The spacing of isobars expresses the rate and direction of change in air pressure or pressure gradient
  • Factors affecting the horizontal distribution of pressure
  1. Air temperature
  2. The earth’s rotation
  • Pressure of water vapour
  1. Air Temperature
  • There is an inverse relationship between air temperature and air pressure
  • The higher air temperature, the lower is the pressure
  • Pressure does not increase latitudinally in a regular fashion from equator to the poles
  • there are regions of high pressure in subtropics and regions of low pressure in the subpolar areas
  1. The Earth’s Rotation
  • The earth’s rotation generates centrifugal force, which deflects the air from its original place, causing a decrease in air pressure
  • low pressure belts of the subpolar regions and the high pressure belts of the sub-tropical regions are created as a result of the earth’s rotation
  • Pressure of Water Vapour
  • Air with higher quantity of water vapour has lower pressure and vice versa
  • Important
  • Continents experience low pressure in summer and high pressure in winter
  • Oceans experience low pressure in winter and high pressure in summer

Pressure Belts

Facts

  • ITCZ
  • Inter Tropical Convergence Zone (ITCZ)
  • is the area encircling the earth near the equator where the northeast and southeast trade winds come together
  • is known by sailors as the doldrums
  • ITCZ moves back and forth across the equator following the sun’s Zenith point
  • Pressure belts shift northward in July and southward in January
  • High pressure belts are dry while low pressure belts are humid

Pressure Belts

  1. Equatorial Low Pressure belt
  • Formation

Step 1: Sun shines almost vertically on the equator throughout the year

  • This belt is termed doldrums due to its erratic weather patterns with stagnant calms and violent thunderstone
  1. Sub-tropic High Pressure Belts
  • Sub-tropical high pressure belts extent from the tropics to about 35 degree latitudes in both the Hemispheres
  • 2 belts
  • North sub-tropical high pressure belt
  • South sub-tropical high pressure belt
  • formation

Step 1: Sun shines almost vertically on the equator throughout the year

step 2: Air gets warm and rises over the equatorial region

step 3: up rising air of the equatorial region is deflected towards poles due to the earth’s rotation

step 4: After becoming cold and heavy, it descends into-tropic regions with high pressure

  • Regions of divergence
  • Winds from these areas diverge towards equatorial and subpolar low pressure belts
  • Calm conditions with feeble and variable winds are found here
  • These belts or latitudes are also called horse latitudes
  • Warm and dry conditions of horse latitudes is responsible for formation of temperature deserts
  • Sub-polar Low Pressure Belts
  • Extends between
  • 450C N latitude and the Arctic Circle in the northern hemisphere
  • 450 N latitude and the Antarctic Circle in the southern hemisphere
  • Winds from sub-tropical and the polar high belts converge here to produce cyclonic storms or low pressure conditions
  • The zone of convergence is also known as polar front
  1. Polar High Pressure Belts
  • High pressure is found in polar regions
  • 2 Belts
  • North polar high pressure belt
  • South polar high pressure belt
  • Winds from these belts blow towards sub-polar low pressure belts

 

Winds

Facts

  • Horizontal movement of air in response to difference is termed as wind
  • Vertical movement of air is called air current

Factors affecting wind

  1. Pressure Gradient
  • Pressure gradient and speed of the wind is higher, if the difference in air pressure between the two points is  High
  • Pressure gradient and speed of the wind is lower, if the difference in air pressure between the two points is low
  1. Coriolis Effect
  • Winds get deflected from their original paths due to deflection in wind direction caused by the earth’s rotation on its axis
  • Ferrel’s law – Coriolis force tend to deflect the winds
  • Corriolis force is absent along the equator but increases gradually towards the poles
  • Coriolis force is maximum at poles

Types of winds

  1. Planetary winds or permanent winds
  2. periodic winds and
  3. local winds

 

Planetary winds

Facts

  • Planetary or permanent winds blow from high pressure belts to low pressure belts in the same direction throughout the year
  • As the trade winds tend to blow mainly from the east, they are also known as the Tropical easterlies
  1. Easterlies
  • Blows from sub-tropical high pressure areas towards equatorial low pressure areas
  • Also called as trade winds ‘to blow steadily and constantly in the same direction’
  • trade winds
  • North-east trade winds
  • South-east trade winds
  • In northern hemisphere trade winds move away from the subtropical high in north-east direction
  1. Westerlies
  • Winds that move poleward from the sub-tropical high pressure belt
  • Also termed as antitrade winds due to their direction opposite to trade winds
  • Due to Coriolis force
  • Westerlies blow with higher force in southern hemisphere than in northern hemisphere due to absence of land
  • Velocity of westerlies increase towards south and become stormy
  • Polar easterlies
  • Polar esterlies blow from polar regions towards sub-polar low pressure regions
  • Direction of winds is form
  • North-east to south-west in the northern hemisphere
  • South-east to north-west in the southern hemisphere

 

Periodic and Local Winds

Periodic winds

  • Monsoon Winds
  • The word ‘Monsoon’ has been derived from the Arabic word ‘Mausim’ meaning season
  • The winds that reverse their direction with the change of seasons are called monsoon winds
  • During
  • Summer the monsoon winds blow from sea towards land
  • winter the monsoon winds blow from land towards seas
  • Monsoon winds are found in
  • India, Pakistan, Bangladesh, Myanmar, Sri Lanka, North Australia, China and Japan

Local winds

  • These are winds that affect local weather and are confined to the lower levels of the troposphere
  1. Land and Sea Breezes
  • Land and sea breezes are prevalent on the narrow strips along the coasts or lake
  • Sea breeze
  • Sea breeze beings to develop shortly before noon and generally reaches its greatest intensity during mid-day to late afternoon
  • Formation

step 1: differential heating of land and water products low and high pressures

Step2: a local low pressure area is developed on land

Step3: sea breeze or high pressure winds blow from the water surface towards the low pressure land surface

  • Land breeze
  • formation

step1: During night, the land and the air above it cools more quickly than the nearby water body

step2: land develops high pressure area while the sea develops a low pressure area

step3: wind begins to blow from land towards sea

  1. Mountain and Valley Breezes
  • Valley breeze
  • formation

Step1: After sunset, the rapid radiation takes place on the mountain slopes

step2: high pressure develops more rapidly on slopes than on the valley floor

  • Hot winds
  1. Loo
  • Loo are hot and dry winds
  • Blow over the northern plains of India and Pakistan in the months of May and June
  • Their temperature varies between 450 C to 500 C
  1. Foehn
  • Foehn is strong, dusty, dry and warm local wind which develops on the leeward side of the Alps
  • The temperature of the winds vary from 150 C to 200 C which help in melting snow
  1. Chinook
  • Chinook or snow eater is the hot and dry local wind moving down the eastern slopes of the Rockies in USA and Canada
  1. Cold Winds
  2. Mistral
  • Mistral are cold, dry, and high velocity local winds originating on the Alps
  • They move over France towards the Mediterranean sea through the Rhone valley
  • They bring down temperature below freezing point in areas of their influence

Cyclones

Facts

  • Air masses with uniform characteristics of temperature, pressure and moisture are necessary to form cyclones
  • Major regions forming air masses are the high latitude polar or low latitude tropical regions
  • Types of air masses
  • Cold polar air mass
  • Warm tropical air mass
  • cyclones
  • Cyclones are rapid inward circulation of air masses about a low pressure centre
  • Direction
  • Anti clockwise in the northern hemisphere
  • Clockwise in the southern hemisphere
  • Types
  1. Temperature or mid latitude cyclones
  2. Tropical or low latitude cyclones
  • Anticyclones
  • Anticyclones are winds spiralling outward from a high pressure centre
  • Direction
  • Clockwise in the northern hemisphere
  • Counter clockwise in the southern hemisphere
  1. Temperature Cyclones
  • Temperature cyclones are formed along a front in mid-latitudes between 350 and 650 N and S
  • They blow from west to east and are more pronounced in winter season
  • Major regions
  • Atlantic Ocean
  • North West Europe
  • Weather Conditions
  • Cyclone
  • Anticyclone
  1. Tropical Cyclones
  • tropical cyclones are formed along the zone of confluence of north-east and south-east trade winds
  • This zone is known as the Inter Tropical Convergence Zone(ITCZ)
  • These are not extensive and have the diameters smaller than temperature cyclones
  • Major regions
  • Mexico
  • South-Western and North Pacific Ocean
  • North Indian ocean
  • South pacific ocean
  • Weather conditions
  • Cyclone
  • no clear warm and cold front
  • no well-defined pattern of winds
  • These are shallow depressions and the velocity of winds is weak
  • High velocity and torrential rainfall combine to create distructive storms
  • Anticyclones
  • tropical cyclones are not accompanied by anticyclones
  • Tropical cyclones strike Indian coasts in summer and autumn months
  • Eye of tropical cyclones remains calm and rainless

Humidity

Facts

  • Proportion of water vapour varies from zero to four percent by volume in the atmosphere
  • The amount of water vapour present in the air affects standing crops favourably
  • Humidity indicates the degree of dampness or wetness of the air
  • The temperature at which a given sample of air becomes fully saturated is called the dew point or saturation point

Humidity of the air is expressed as

  1. Absolute humidity
  • Absolute humidity is the ratio of the mass of water vapour actually in the air to a unit of air, including the water vapour
  • it is expressed in grams per cubic metre of air
  1. Relative humidity
  • The ratio of the amount of water in the air at a given temperature to the maximum amount it could hold at that temperature
  • it is expressed as percentage
  • The relative humidity of an air at saturation point is 100%
  • Relative humidity
  • increases when the temperature of the air decreases or when more moist air is added to it
  • decreases when the temperature of the air increases or when less moist air is added to it

Evaporation and Condensation

Evaporation

  • Evaporation is the change in state of water from liquid to gaseous form
  • Latent heat
  • Heat required to convert a solid into a liquid or vapour, or a liquid into a vapour, without change of temperature
  • Energy released during the release of latent heat causes significant changes in weather
  • Transpiration
  • loss of water from leaf and stem tissues of growing vegetation
  • combined losses of moisture by evaporation and transpiration is termed as evapo-transpiration
  • Factors affecting evaporation
  1. Accessibility of water bodies
  2. Temperature
  • Air moisture
  1. Wind
  2. Cloud cover

Condensation

  • Condensation is the process by which atmosphere water vapour changes into water or ice crystals
  • The temperature of the air falls in two ways
  • cooling around small particles suspended in the atmosphere such as smoke, salt and dust particles
  • cooling due to rising of air into the higher altitudes
  • Process

step1: the temperature of saturated air falls below dew point

step2: the air cannot hold the amount of humidity which it was holding earlier at a high temperature

step3: extra amount of humidity changes into water droplets or crystals of ice

  • Condensation takes place in two situations
  • when dew point is below freezing point or 00 C
  • Frost
  • Snow
  • when the dew point is above freezing point
  • Dew
  • Mist
  • Fog
  • Smog
  • Forms of Condensation
  1. Dew
  • Dew is the tiny drops of water that from on cool surfaces at night, when atmospheric vapour condenses
  • Favourable conditions
  • clear sky
  • little or no wind
  • high relative humidity
  • cold long nights
  • Process

step1: solid objects become rapidly cold due to terrestrial radiation

step2: this brings the temperature of air down below dew point

step3: extra moisture of the air gets condensed and deposited on these objects

  1. Frost
  • Frost is the deposition of small white ice crystals on the ground or other surfaces when the temperature falls
  • The air moisture condenses directly in the form of tiny crystal of ice
  • Frost effects crops such as potato, peas, pulses, grams etc.
  • Mist
  • a cloud of tiny water droplets suspended in the atmosphere at or near the earth’s surface
  • litmits visibility to a lesser extent than fog; strictly, with visibility remaining above 1 km
  1. Fog
  • a thick cloud of tiny water droplets suspended in the atmosphere at or near the earth’s surface
  1. Smog
  • fog or haze intensified atmospheric pollutants such as smoke dust carbon monoxide sulphur dioxide and other fumes
  1. Cloud
  • clouds are visible mass of water or ice particles suspended at a considerable altitude
  • liquid or solid water accounts for less than 10 parts per million of the cloud volume

Precipitation

Facts

  • From of precipitation depends on the method of formation and temperature during the formation

Forms of Precipitation

  1. Drizzle
  • very light rain, stronger than mist but less than a shower
  • Drizzle is composed of fine drops of water with diameter less than 0.5 mm
  1. Rain
  • When the droplets of size 0.5 mm are widely spaced, then it is called rain
  • Snowfall
  • precipitation falling from clouds in the form of ice crystals
  • Condensation takes place below freezing point and the water vapour changes directly into ice crystals
  1. Sleet
  • Sleet is frozen rain, formed when rain before falling on the earth, passes though a cold layer of air and freezes
  • it’s usually a combination of small ice balls and rime
  1. Hail
  • Precipitation of ice pellets of frozen rain, when there are strong rising air currents in showers from cumulonimbus clouds
  • diameters range from 5 mm to 50 mm and fails either isolated or in irregular lumps
  • Hailstones are composed of a series of alternating layers of transparent and translucent ice

 

Types of Rainfall

  1. Convectional Rainfall
  • Convectional rainfall is common in equatorial region where it is a daily phenomenon in afternoon
  • Formation

step1: heating of the earth’s surface in tropical region results in vertical air currents

step2: air currents, lift the warm moist air to the upper layers of atmosphere

step3: temperature of humid air starts falling below dew point continuously forming clouds

step 4: clouds cause heavy rainfall along with lightning and thunder

  1. Orographic or Relief Rainfall
  • Orographic rainfall occurs where air rises and cools against a topographic barrier
  • Region lying on the leeward side of the mountain receiving less rainfall is called rain-shadow region
  1. Convergence or Cyclonic Rainfall
  • Convergence rainfall is produced where air currents converge and rise
  • Tropical regions
  • the vertical lifting and mixing of opposing air masses with contrasting temperatures causes convectional Rainfall
  • Frontal Rainfall

step1. two large air masses of different densities and temperature meet

step2. the warmer moist air mass is lifted above the colder one

step3. the rising warm air mass condenses to form clouds, which causes extensive down pour

Frontal rainfall is associated with thunder and lightning and may persist for a whole day or even longer

 

Distribution of Precipitation

Facts

  • land receives lesser amount of rainfall than the oceans
  • Precipitation decreases from equatorial region towards the polar region
  • Coastal areas adjacent to cold currents are drier than coastal areas near warm currents
  1. Regions of Heavy Precipitation
  • Regions receiving more than 200 cm of annual precipitation
  • Regions include
  • equatorial coastal areas of tropical zone
  • Coastal regions of temperature zone
  1. Regions of Moderate Precipitation
  • regions receiving more than 100 to 200 cm of annual precipitation
  • Regions include
  • Eastern coastal regions of sub-tropical zone
  • Coastal regions of the warm temperature zone
  1. Regions of Less Precipitation
  • Regions receiving more than 50 to 100 cm of annual precipitation
  • Regions include
  • Interior parts of tropical zone
  • Eastern interior parts of temperature zone
  1. Regions of Scanty Precipitation
  • Regions receiving less than 50 cm of annual precipitation
  • Regions include
  • Tropical, temperature and cold deserts of the world
  • Rain shadows regions
  • Interior parts of continents
  • Western margins of continents along tropics
  • Reason: easterlies become dry winds
  • Western margins of continents along high latitudes
  • Reason: polar winds are cold and dry

Factors Affecting Rainfall Distribution

  1. Moisture supply
  • Equatorial and tropical regions receive heavy rainfall due to highest evaporation
  • Coastal areas have more moisture than interior parts of continents
  • Frigid regions have very low evaporation hence very scanty precipitation
  1. Wind direction
  • Winds blowing from sea to land cause rainfall
  • Land bearing winds are dry
  • Sub-tropical deserts have very little rainfall because they have off-shore winds
  • Ocean currents
  • Warm currents carry warm moist winds which cause rainfall
  • Cold current carries cold dry winds without moisture which doesn’t cause rainfall
  1. Presence of mountain
  • Mountains cause rainfall on the windward side and rain shadow on the leeward side
  1. Pressure belts
  • Areas of low pressure attract rain bearing winds
  • Areas of high pressure does not attract rain bearing winds
  1. Seasons
  • Equatorial regions receive convectional type of precipitation throughout the year
  • Western parts of temperature lands receive cyclonic and Orographic type of precipitation through westerlies
  • Coramandel Coast of India receives precipitation only in winter

 

Weather and Climate

Weather

  • Weather is the state of atmosphere at a particular place and time influenced by the interaction of elements such as temperature, pressure, wind, humidity, heat etc.
  • Weather is expressed as sunny, hot, warm, cold, fine etc.. based upon the atmosphere conditions
  • weather changes very often
  • A place can experience different types of weather conditions in a year

Climate

  • The weather in some location averaged over some long period of time is called as climate
  • average of these weather conditions is calculated from the data collected for several years
  • Climate of a region is more or less permanent
  • A place can experience only one type of climate

 

Factors affecting Climate

Latitude

  • Distance from the equator: the places near the equator are warmer than the places in higher latitudes
  • Vertical rays in equatorial regions are concentrated over a small area than the slanting rays in higher latitudes
  • Lower latitudes receive higher temperature, as the vertical rays pass through a shorter distance in the atmosphere before reaching the earth’s surface

Altitude

  • The temperature decreases with altitude

Distance from the Sea

  • Coastal regions have low range of temperature and high humidity due to moderating effect of the seas
  • Moderating effect of seas: slower heating and cooling of water in seas positively influences the temperature and humidity
  • The places far from the sea or interior regions of continents have higher range of diurnal and annual temperatures

Prevailing Winds

  • On-shore winds bring the moisture from the sea and cause rainfall
  • Off-shore winds coming from the land are dry and cause evaporation

Cloud Cover

  • Regions with cloudless skies experience higher range of temperatures
  • Regions with cloudy skies experience small range of temperatures

Ocean Currents

  • Winds blowing over warm current carry warm air to the interior and raise the temperature of the inland areas
  • Winds blowing over cold current carry cold air to the interior and create fog and mist
  • Cold currents lower the temperature in Coastal areas and causes fog

Aspect

  • Mountain slopes facing the sun are warmer than the slopes facing away from the sun

Slope

  • Gentler slope raises the temperature of air above them
  • Steeper slopes lowers the temperature of air above them

Nature of the Soil

  • Sandy soils are good conductor of heat while black clay soils absorb the heat quickly
  • deserts are hot in the day and cold in the night

Vegetation cover

  • bare surface re-radiate the heat easily
  • forest areas have lower range of temperature throughout the year

Direction of Mountain Chains

  • The mountain chains act as natural barrier for the wind
  • Himalayas blocks the
  • moisture laden monsoon winds from crossing over to Tibet (reason for which northern plains of India get rains)
  • polar cold winds from entering into India

 

Climatic Types

Koeppen climate

  • Most widely used system of climate classification is developed by Vladimir koeppen
  • It is based upon the climate factors and also the relationship of climate with the vegetation
  • Koeppen classification divides world into five climatic groups and sub-divided into 13 climatic types
  • He introduced the use of capital and small letters to designate climate groups and types
  • Four of the climatic groups are based on temperature and one precipitation
  • Humid climates – A, C, D and E
  • Dry climates – B
  • Seasons of dryness are indicated by the small letters
  • f-no dry season
  • m- monsoon climate
  • w – winter dry season
  • s – summer dry season
  • The small letters a, b, c and d refer to the degree of severity of temperature

Climate groups

  1. Tropical humid climates
  2. Af-tropical rain forest
  • Found near the equator
  • Major areas
  • Amazon basin in south America
  • Western equatorial Africa
  • Islands of East Indies
  • Temperature is uniformly high
  • Annual range of temperature is negligible
  • Temperature –Max -300 C min – 200 C
  • Vegetation: tropical evergreen forests
  1. Aw – Savanna Climate
  • Found north and south of Af types climate regions
  • Annual rainfall is less than Af and Am climate types
  • diurnal ranges of temperature are greatest in the dry season
  • vegetation
  • Deciduous forest
  • Tree-shredded grasslands
  • Am-Monsoon Climate
  • Major areas
  • Indian sub-continent
  • North Eastern part of South American
  • Northern Australia
  • Heavy rainfall in summer but dry Winter
  1. Dry climates
  2. Bw-Desert climate
  • Extends over large latitudes from 150-600 north and south of the equator
  • Also found in the areas of subtropical high due to less rainfall caused by
  • subsidence
  • Inversion of temperature
  • Maximum temperature in the summer is very high
  1. Bs-Steppe Climate
  • subtropical steppe receive slightly more rainfall than the desert
  • spare grasslands grow in steppe climate
  1. Warm temperature climates
  2. Cs-Mediterranean Climate
  • Major areas
  • areas around Mediterranean sea
  • west coast of continents in subtropical latitudes
  • Climate includes hot, dry summer and mild, rainy winter
  • average temperature in summer is around 250 C and in winter below 100 C
  • Cfa-Humid subtropical
  • Found in eastern parts of the continent in subtropical latitudes
  • rainfall throughout the year
  • Thunderstorms in summer and frontal precipitation in winter
  • Cfb-Marine west coast Climate
  • located poleward from the Mediterranean climate on the west coast of the continents
  • Due to marine influence, the temperature is moderate
  • In winter it is warmer than for its latitude
  • annual and daily ranges of temperature are small
  • Precipitation occurs throughout the year from 50-250 cm
  1. Dw-Taiga Climate
  • occurs mainly over North-eastern Asia
  • Poleward summer temperatures are lower and winter temperatures are extremely low
  • many places experience below freezing point for up to seven months in a year
  • Precipitation occurs in summer
  • The annual precipitation is low from 12-15 cm
  1. Df-Humid continental
  • Cold climate with humid winter
  • occurs poleward of marine west coast climate and mid latitude steppe
  • annual ranges of temperature are large
  • weather changes are abrupt and short
  1. The Continental Climate
  • Polar climates
  • Tundra Climate
  • Vegetation-low growing mosses, lichens and flowering plants
  • region of permafrost where the sub soil is permanently frozen
  • Very long duration of day light in summers
  • Ef-Ice-cap Climate
  • Found over interiors of Greenland and Antarctica
  • temperature is below freezing point
  • very little precipitation

Seasons

Basics

  • Season is a period of the year characterized by particular climate features and weather patterns
  • Seasons occur as a result of inclination, rotation and revolution of the earth

Seasons

  • Summer
  • Summer solstice marks the beginning of summer season
  • On June 21, the sun reaches its northern most point touching the tropic of Cancer
  • Northern hemisphere experience summer as it is inclined towards the sun
  • In the northern hemisphere days get longer while the nights get shorter
  • southern hemisphere experience winter as it is inclined away from the sun
  • In the southern hemisphere days get shorter while the nights get longer
  • Winter
  • Spring

Regional Variations

  • Seasons are insignificant on or near the equator due to same temperature throughout the year
  • Oceanic influence reduces the seasoned variations in coastal regions
  • Polar regions have two seasons
  • Long winter
  • short winter
  • Temperature regions follow 4 seasons

India follows 3 seasons

  • Summer
  • Winter
  • Rainy

Indian Meteorological Department recognize 4 seasons

  • Cold weather season (December to February)
  • Hot weather seasons (March to May)
  • Advancing monsoon season or rainy season (June to September)
  • Retreating monsoon season (October to November)