VALLEY AND
URBAN CLIMATES
MATRIC IEB
GEOGRAPHY
, Valley climates
Aspect
north facing slope south facing slope
soils warmer and drier= direct sun rays moist= in the shade
and evaporation natural vegetation= trees and shrubs
grass/hardier vegitation commercial plantations
houses here= light, decrease heating costs
valley winds
mountain winds
valley winds
day-anabatic winds night-katabatic winds
after midnight= cold,clear,calm
occurs after noon mountain top cools rapidly due to terrestrial
insolation warms slope radiation air
cold air subsides,warm air rises above slope is cold and dense and gravity
above thus upslope causes it to move down slope
temperature inversion and frost pocket
form
speed=steepness
, Temperature inversions in a valley
Temperature inversions occur on cold, calm, conditions nessasary
cloudless evenings. Long night- for land and air to cool
The valley slopes cool rapidly due to terrestrial Calm conditions- so warm and cold air do
radiation losses. not mix
Cold air drains into the valley due to gravity Clear skies- so terrestrial radiation
flow. heat loss is at a maximum
Warmer air on the valley floor is displaced Cold night- temperature differences
upwards. are exaggerated
Thermal Belt:
The warm air is trapped between the cold air at the bottom of
the valley, and the cooler air which subsides due to radiation
loss at night. This creates a warmer layer about mid-way
upslope. This layer is referred to as the thermal belt.
Frost pocket:
A frost pocket often forms in winter. The lowest point in
the valley is the coldest (gravity pulls the cold, dense air
downwards). If the dew point temperature cools to below
zero at the bottom of the valley, water vapour changes into
ice crystals and as a result frost forms on the valley floor
instead of dew.
URBAN CLIMATES
MATRIC IEB
GEOGRAPHY
, Valley climates
Aspect
north facing slope south facing slope
soils warmer and drier= direct sun rays moist= in the shade
and evaporation natural vegetation= trees and shrubs
grass/hardier vegitation commercial plantations
houses here= light, decrease heating costs
valley winds
mountain winds
valley winds
day-anabatic winds night-katabatic winds
after midnight= cold,clear,calm
occurs after noon mountain top cools rapidly due to terrestrial
insolation warms slope radiation air
cold air subsides,warm air rises above slope is cold and dense and gravity
above thus upslope causes it to move down slope
temperature inversion and frost pocket
form
speed=steepness
, Temperature inversions in a valley
Temperature inversions occur on cold, calm, conditions nessasary
cloudless evenings. Long night- for land and air to cool
The valley slopes cool rapidly due to terrestrial Calm conditions- so warm and cold air do
radiation losses. not mix
Cold air drains into the valley due to gravity Clear skies- so terrestrial radiation
flow. heat loss is at a maximum
Warmer air on the valley floor is displaced Cold night- temperature differences
upwards. are exaggerated
Thermal Belt:
The warm air is trapped between the cold air at the bottom of
the valley, and the cooler air which subsides due to radiation
loss at night. This creates a warmer layer about mid-way
upslope. This layer is referred to as the thermal belt.
Frost pocket:
A frost pocket often forms in winter. The lowest point in
the valley is the coldest (gravity pulls the cold, dense air
downwards). If the dew point temperature cools to below
zero at the bottom of the valley, water vapour changes into
ice crystals and as a result frost forms on the valley floor
instead of dew.
