Upload
antionette-frankie
View
16
Download
0
Tags:
Embed Size (px)
DESCRIPTION
WEATHER AND CLIMATE LECTURE 1. Atmosphere: Structure and Composition. Atmosphere is made up of layers: 1. Troposhere - decreases by 6.4 degrees Celsius for every 1000m increase in height ( Environmental Lapse Rate ) - contains most of the water vapour, cloud, dust, pollution - PowerPoint PPT Presentation
Citation preview
WEATHER AND CLIMATE
LECTURE 1
Atmosphere: Structure and Composition
Atmosphere is made up of layers:
1. Troposhere- decreases by 6.4 degrees Celsius for every1000m increase in height (Environmental Lapse Rate)- contains most of the water vapour, cloud,dust, pollution- tropopause: upper limit of the troposhere. - temperatures remain constant with heightincrease
Atmosphere: Structure and Composition
2. Stratosphere- steady increase in temp due to ozone concentration- winds increase with height- pressure decreases with height- stratopause: layer above stratosphere- no change in temp with increasing height
Atmosphere: Structure and Composition
3. Mesosphere- temperatures fall rapidly - no gases or particles present to absorb radiation- mesopause: layer above mesosphere where no change in temperature with height is seen
HEAT/ENERGY BUDGET
Before looking at the earth’s budget, let us see what happens to incoming solar radiation:
3 General Processes act upon incoming radiation:
a) Absorption
b) Radiation
c) Reflection
HEAT/ENERGY BUDGET
Absorption.
- by gases in the upper atmosphere as well as ice particles and dust
Reflection.
- by clouds and the earth’s surface back to space
- dependent on the albedo of clouds and earth’s surface
- gas molecules also scatter radiation back to space. The rest reaches surface by diffuse radiation (scattered energy)
HEAT/ENERGY BUDGET
Scattering and Diffuse Radiation
Scattered insolation is either:
Scattered Back to Space
Absorbed by earth’s surface as diffuse radiation
HEAT/ENERGY BUDGET
Incoming radiation converted to heat energy
- radiates back to the atmosphere
- absorbed by water vapour/carbon dioxide to retain heat near the surface (Greenhouse Effect)
HEAT/ENERGY BUDGET
The amount of radiation the earth receives:
A system of inputs and outputs
Balances on the global level, but not necessarily so on a local scale
HEAT/ENERGY BUDGET
Eg: At night, no incoming radiation, yet heat is still lost, especially on cloudless days
- at any one place and time, more radiant energy is being lost than gained, vice versa
Heat Escapes to Space
HEAT/ENERGY BUDGET
This can be determined by the net radiation: difference between all incoming and outgoing radiation
surplus: radiant energy flowing in faster than it is flowing out
deficit: radiant energy flowing out faster than it is flowing in
HEAT/ENERGY BUDGET
What prevents tropics from overheating?
1 Horizontal Heat Transfers
- winds carry heat energy away from the tropics
2. Vertical Heat Transfers
Radiation, conduction, convection and transfer of latent heat
- supplementary reading
Factors Affecting Temperature
Amount of insolation varies through time and space, and from point to point
a) Long-term factors
b) Short-term factors
c) Local influences
Long-Term factors
Height above sea-level
- atmosphere heated from earth’s surface by conduction and convection
- dependent on surface area of landmass
Surface
Atmosphere
ConductionWarm, rising Air
Convection
- as heights increase on mountains, less land mass present to give off heat by above process, hence lower temperatures
Long-Term factors
Height above sea-level
- at the same time, pressure/density of air decreases with altitude
- less air molecules present to absorb and retain heat, hence as air thins with altitude, temperatures decrease Decreasing
Density of Air Molecules with Increasing HeightSurface
Long-Term factors
Altitude of the sun
- temperatures decrease with decreasing angle of the sun
SunA
B
-Less loss of energy atA as ray at A travels a shorter distance than at B
Long-Term factors
SunA
B
Therefore, the higher the latitude (moving from Poles to Equator), the higher the temperatures, vice versa
Long-Term factors
Nature of Surface (Land/sea)
- Land and water differ in their abilities to absorb heat
- specific heat capacity: the amount of energy needed to raise 1kg of a substance by 1 degree Celsius
- water has a higher S.H.C. than land/soil
Long-Term factors
Nature of Surface (Land/sea)
- water requires more energy to raise its temperature by 1 degree Celsius as compared to continents
- In summer, sea heats up more slowly than land
- In winter, land loses energy more rapidly than the sea
Long-Term factors
Nature of Surface (Land/sea)
Illustration of different rates of energy gain/loss between land and water
Swimming Pool on a hot day:- air temperatures warm
- water seems to be ‘icy’ cold when you jump in
A chilly afternoon immediately after a heavy rain:
- air temperatures cool
- water in the pool seems to be ‘nice and warm’
Long-Term factors
Nature of Surface (Land/sea)
- Continental areas therefore are more responsive to temperature changes as compared to water bodies
- this is also why coastal areas have smaller annual temperature ranges than inner continents
Long-Term factors
Prevailing winds
- where winds come from
- and characteristics of surface over which they blow
Winter:
- winds blowing from sea tend to be warmer
- coastal areas experiencing such breezes will be warmer than areas not experiencing such breezes
Long-Term factors
Prevailing winds
Warmer Sea Breeze
Cold Surface (Winter)
Warms coastal areas. Warm wind eventually cools with distance into continents
Inner Continents will be colder than coastal areas even if they may be within the same climatic region
Long-Term factors
Ocean Currents
Equator
S. Pole
N. Pole Warm Currents
Cold Currents
Short-term factors
Seasonal Changes
- due to earth’s tilt, Northern Hemisphere receives more insolation during Summer solstice (21 June) than Southern Hemisphere
- Northern Hemisphere receives less insolation during Winter Solstice (22 December)
N
S
Earth’s axis onwhich it rotatesnot on the SouthPole
N
SBut is tilted atan angle
Short-term factors
Equator
Earth during Winter Solstice
- Northern Hemisphere - less insolation (cooler ie Winter)
- Southern Hemisphere - more insolation (warmer ie Summer)
Short-term factors
Earth’s Elliptical Orbit around the sun therefore sets up the different seasons
Summer Winter
Spring
Autumn
Short-term factors
Length of Day and night
- areas experiencing longer days tend to havehigher temperaturesEquator: - Equal lengths of day and night every 24 hours
Poles: - experience 24 hours of darkness for parts ofwinter- during summer, experience up to 24 hours ofday
Local Influences on Insolation
Slope Aspect
- northern hemisphere: north-facing slopes (adret) receive less sunshine
- cooler than south-facing slopes (ubac)
In addition, steeper slopes receive more insolation due to their higher angle of incidence
Local Influences on Insolation
Cloud Cover
- reduces both incoming and outgoing insolation
- thicker cloud cover, more absorption, reflection, scattering and terrestrial radiation (radiation back to space) during daytime
- cooler temperatures during day with thick cloud cover, higher with no/little cloud cover
Local Influences on Insolation
Cloud Cover
- Night:
- Thick cloud cover during night time can act as an insulating blanket to trap heat
- lack of cloud cover during the night, loss of heat from surface by terrestrial radiation, cool/cold temperatures
Local Influences on Insolation
Urbanisation
- alters the albedo of natural landscape
- buildings, concrete and black roads tend to reflect less insolation and therefore absorb more heat
- hence higher temperatures in urban areas than grass or natural landscape
Finito