Valley Climates Flashcards
(22 cards)
Aspect
The direction of hill slopes in relation to the suns rays
Shadow zone
The area where there is no direct warming from the sun (faces poles)
Anabatic winds
Winds that blow upslope (during the day)
Katabatic winds
Winds that blow downslope (at night)
Valley winds
Winds that blow up valley (during the day)
Mountain winds
Winds that blow down valley (at night)
Temperature inversion
When air temperature increases with increasing altitude
Frost pocket
The bottom of a valley where cold air collects and causes frost to form
Radiation fog
Fog formed due to terrestrial radiation
Comment on aspect of slopes
Slopes facing the equator are warmer than those facing the poles
Aspect affect on vegetation and human settlement (north facing)
Soils are dryer
Grasses and shrubs
Houses built on these slopes because they are warmer.
Crops like grapes which like hot, sunny conditions
Aspect affect on vegetation and human settlement (south facing)
Soils are wetter
Shade-loving plants such as trees, ferns and mosses.
Not popular
Suited to forestry
Winter wheat in SW Cape
Valley winds during the day
Slopes and air above heat them.
Warm, less dense air above the slopes rises (anabatic winds)
Winds also blow up the valley during the day (valley winds)
Warm, less dense air above the slopes rises
Valley winds at night
Slopes and air above them are cooled
Cold, dense air on slopes sinks (katabatic winds)
Winds also blow down the valley at night (mountain winds)
Normal temperature lapse rate
Where temperature decreases with increasing altitude
Temperature inversion
NTLR reversed, when temperature increases with increasing altitude
Frost
Still, clear winter night the land cools quickly.
No clouds prevent terrestrial radiation from escaping
No wind to mix the air
The cold air drains down to the valley floor, displacing the warm air upwards. This causes a temperature inversion where temperature increases with an increase in altitude.
If dew point is below freezing, then water vapour changes into ice crystals and frost is formed on the valley floor (frost pocket)
Effects of temperature inversions on settlement and farming
People will build their houses halfway up the slope of a valley to be in the warmer thermal belt
Crops which need warm, frost-free condition will be planted in the thermal belt, e,g. Sugar cane
Thermal belt
The zine where warm air is trapped between colder air masses (usually middle part of slope)
Why are settlements in SH usually halfway up north facing slopes where it is warmest?
Gets direct perpendicular rays of sun (faces equator)
Avoids the top (temp decreases with increased altitude)
Avoids valley floor (cold pocket of air)
Effects of frost pockets on settlement and farming
Crops which can withstand cold conditions can be planted at the bottom of the valley e.g. potatoes
Pollution is trapped in the cold air below the temperature inversion at night
Radiation fog
Forms in valley on cold, clear, windless nights.
Rapid cooling to dew point (>0) through a great vertical depth causes condensation
Water droplets are so small that they are suspended in the air.
This is known as radiation fog because it forms as a result of cooling due to terrestrial radiation .
The densest fog forms in the lowest part of the valley where air is coldest
As the earths surface starts to heat up during the morning, the fog evaporates from below and appears to “lift”.
