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Page 1: Geography--Atmosphere: Lecture one

Horizontal Distribution of Temperature

Page 2: Geography--Atmosphere: Lecture one

The line connecting the areas of same temperature:• Isotherms

Page 3: Geography--Atmosphere: Lecture one

Factors

• Latitude• Nature of the surface• Continental/Maritime effect• Altitude• Cloudiness• Ocean currents and winds

Page 4: Geography--Atmosphere: Lecture one

Latitude because….

Determines the:• Angle of sun’s rays

Page 5: Geography--Atmosphere: Lecture one
Page 6: Geography--Atmosphere: Lecture one
Page 7: Geography--Atmosphere: Lecture one
Page 8: Geography--Atmosphere: Lecture one

Nature of surface:

• Water always has a moderate temperature as compared to land

Reasons?• Specific heat of land is lower than water: The heat required to raise

the temperature of the land is much smaller than that of water• Radiation penetrates deep into water, but only the top portion of land• Evaporation keeps the water cool

Page 9: Geography--Atmosphere: Lecture one

Continental/Maritime effect

Page 10: Geography--Atmosphere: Lecture one

• The land areas near the water bodies have moderate temperatures than those without any water body nearby• Temperature made moderate by winds from the water bodies

Page 11: Geography--Atmosphere: Lecture one

Altitude

Page 12: Geography--Atmosphere: Lecture one

• The temperature decreases with altitude due to decline in atmospheric pressure

Page 13: Geography--Atmosphere: Lecture one

Cloudiness

Page 14: Geography--Atmosphere: Lecture one

• The clouds can block the incoming solar radiation, reducing the temperature• Though they also block the outgoing radiation from the earth

Page 15: Geography--Atmosphere: Lecture one

Ocean currents and Winds

• The Presence of Warm or Cold Ocean currents affects the temperature of nearby landmasses• The Winds from the colder or hotter areas also affect the

temperatures of the places

Page 16: Geography--Atmosphere: Lecture one
Page 17: Geography--Atmosphere: Lecture one

Diurnal Temperature

• The sun is at its peak in the sky at noon, therefore at this time the solar radiation is at its maximum• However the maximum temperature during the day doesn’t occur at

noon• Why? Because air temperature is determined by both the solar radiation

and the radiation from the earth. The sum of the total radiation from the sun and the earth is maximum a few hours after noon• After sunset the Temperature starts decreasing; the minimum

temperature occurs right before the sunrise when the earth has lost the maximum of its heat

Page 18: Geography--Atmosphere: Lecture one

Annual Temperature

• During June 21st the sun is directly above the tropic of cancer and the northern hemisphere receives its maximum solar radiation• However the hottest time comes after a month of summer solstice

when the sum of the radiation from the sun and the earth is maximum• Similarly, though the solar radiation in northern hemisphere is

minimum at December 22; the coldest month is often the January

Page 19: Geography--Atmosphere: Lecture one

Atmospheric Pressure and Winds

Page 20: Geography--Atmosphere: Lecture one

Atmospheric Pressure

• the force per unit area exerted on a surface by the weight of air above that surface in the atmosphere of Earth

Page 21: Geography--Atmosphere: Lecture one
Page 22: Geography--Atmosphere: Lecture one

• Unit:• Milibar

• Instrument:• Barometer

• The line joining the areas of similar pressure• Isobar

• Standard sea-level air pressure• 1013 mb

Page 23: Geography--Atmosphere: Lecture one

Wind

• Movement of air relative to earth’s surface• The winds are often named by the direction they come from

Page 24: Geography--Atmosphere: Lecture one
Page 25: Geography--Atmosphere: Lecture one

Factors that create and affect the wind• Pressure gradient• Coriolis Effect• Friction

Page 26: Geography--Atmosphere: Lecture one

Pressure Gradient

• The difference of pressure at any two places• Acts as a force that drives air to move from places of higher pressure

to the places of lower pressure• Cause of difference in pressure: Air temperature Warm air rises

creating a low pressure zone; cold air descends creating a high pressure zone

Page 27: Geography--Atmosphere: Lecture one
Page 28: Geography--Atmosphere: Lecture one
Page 29: Geography--Atmosphere: Lecture one
Page 30: Geography--Atmosphere: Lecture one

Coriolis Effect/Force

• Coriolis effect is the result of the rotation of the earth• It causes the wind in the northern hemisphere to turn to the right of

its direction; i.e. clockwise• Causes the wind in the southern hemisphere to turn to the left of its

direction; i.e. anti-clockwise• Remember: it doesn’t cause the wind or affects its speed; just affects

the direction

Page 31: Geography--Atmosphere: Lecture one

Surface friction/Drag

• The surface of the earth resists the movement of the wind; casing it to slow down

Page 32: Geography--Atmosphere: Lecture one
Page 33: Geography--Atmosphere: Lecture one

Winds

Page 34: Geography--Atmosphere: Lecture one

Geostrophic Wind

Page 35: Geography--Atmosphere: Lecture one

Frictional Winds: The Cyclones and Anti-CyclonesCyclone:• A Low pressure area where the wind converges from all sides and is forced up• In northern hemisphere this convergence is anti-clockwise• In Southern hemisphere it is clock-wise

Anti-cyclone:• A high pressure area where the wind descends and diverges in all directions• In Northern Hemisphere anticyclones have clockwise motion• In S.hemisphere they have anti-clockwise motion

Page 36: Geography--Atmosphere: Lecture one

Cyclones Anticyclones

Page 37: Geography--Atmosphere: Lecture one

Local Winds

Page 38: Geography--Atmosphere: Lecture one

Land and sea breeze

• Due to contrasting thermal responses of the land and the water• Reversal of the circulation in the day and the night

Page 39: Geography--Atmosphere: Lecture one

Sea Breeze

Page 40: Geography--Atmosphere: Lecture one

Land Breeze

Page 41: Geography--Atmosphere: Lecture one

Mountain/Valley Breeze

• Also Day/Night local circulation system• Due to contrasting temperatures of the valley and the mountain

Page 42: Geography--Atmosphere: Lecture one

Day

• During the day, the air over the mountain slope heats up more than the air at the foot of the mountain• The warm air rises• A low pressure is created at the top of the mountain and high

pressure from the cool air below forces a cool breeze to move upward• This condition generates a breeze which we call Valley breeze

Page 43: Geography--Atmosphere: Lecture one
Page 44: Geography--Atmosphere: Lecture one

Night

• In the night the air at the upper slope of the mountain cools off very quickly and becomes dense• A high pressure is created• At this time, the air at the valley floor is a lot warmer (low pressure)

and is forced to give way to colder air moving down the slope towards the valley floor• This is called mountain breeze

Page 45: Geography--Atmosphere: Lecture one
Page 46: Geography--Atmosphere: Lecture one

Planetary Winds

Page 47: Geography--Atmosphere: Lecture one

• All the movement of air around the earth• Redistributes heat and moisture across the earth's surface• Without it earth’s surface would be either too dry, too wet, too cold,

or too hot

Page 48: Geography--Atmosphere: Lecture one

Idealized Model

• Suppose the earth doesn’t have tilt• Suppose the whole earth is made up of only land or only water• Suppose there are no mountains or valleys

Page 49: Geography--Atmosphere: Lecture one

The elements of planetary winds

• Equatorial low and Subtropical high pressure belts• The Trade Winds and the Westerlies• Polar Highs, Polar Easterlies and Polar fronts

Page 50: Geography--Atmosphere: Lecture one

Equatorial Low and Subtropical Highs• Maximum radiation at equator would cause the air to rise, creating a

low pressure belt along the equator: “The Equatorial Low” or “ITCZ”• The air rises to the Tropopause, diverges, and flows polewards• This pole-ward air cools, descends at 300 North and South• This descending air creates high pressure belts in both northern and

southern hemispheres: The “Subtropical Highs”

Page 51: Geography--Atmosphere: Lecture one

The Trade Winds and the Westerlies

• The air descending at 300 Latitude would diverge and flow towards equator and poles• Wind returning to equator deflect to west due to coriolis force

Become “Northeast Trade winds” in the northern hemisphere, and “Southeast Trade winds in the southern hemisphere• The trade winds converge at the equator and complete a loop known

as Hadley cell• The air moving pole-wards from the 300 Latitude are deflected to the

east by coriolis force and become “Westerlies”.. They prevail between 300 N and S

Page 52: Geography--Atmosphere: Lecture one

Polar Highs, Polar Easterlies and Polar fronts• Extreme cold at Poles Air descends High pressure• Wind flows equator-wards• Diverge due to the west due to coriolis force and become “Polar

Easterlies”• Polar Easterlies meet Westerlies coming from subtropical highs at 600

Latitude and form “Polar Front”• Warm Westerlies forced to rise over cold polar air, creating a low

pressure belt: “midlatitude low”

Page 53: Geography--Atmosphere: Lecture one
Page 54: Geography--Atmosphere: Lecture one
Page 55: Geography--Atmosphere: Lecture one

Actual

• The location of maximum solar heating shifts from 23 N to 23 S; therefore the Inter-tropical convergence zone migrates North and South of equator throughout the year• Presence of continents and oceans• The presence of mountains