Transcript
Horizontal Distribution of Temperature
The line connecting the areas of same temperature:• Isotherms
Factors
• Latitude• Nature of the surface• Continental/Maritime effect• Altitude• Cloudiness• Ocean currents and winds
Latitude because….
Determines the:• Angle of sun’s rays
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
Continental/Maritime effect
• 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
Altitude
• The temperature decreases with altitude due to decline in atmospheric pressure
Cloudiness
• The clouds can block the incoming solar radiation, reducing the temperature• Though they also block the outgoing radiation from the earth
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
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
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
Atmospheric Pressure and Winds
Atmospheric Pressure
• the force per unit area exerted on a surface by the weight of air above that surface in the atmosphere of Earth
• Unit:• Milibar
• Instrument:• Barometer
• The line joining the areas of similar pressure• Isobar
• Standard sea-level air pressure• 1013 mb
Wind
• Movement of air relative to earth’s surface• The winds are often named by the direction they come from
Factors that create and affect the wind• Pressure gradient• Coriolis Effect• Friction
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
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
Surface friction/Drag
• The surface of the earth resists the movement of the wind; casing it to slow down
Winds
Geostrophic Wind
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
Cyclones Anticyclones
Local Winds
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
Sea Breeze
Land Breeze
Mountain/Valley Breeze
• Also Day/Night local circulation system• Due to contrasting temperatures of the valley and the mountain
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
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
Planetary Winds
• 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
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
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
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”
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
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”
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
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