defining hot enviroments
- high temperatures, low precipitation, sparse vegetation, little cloud cover, long hours of sunlight, high day and low night temperatures.
desert= an area with less than 25 cm of rainfall per year.
hot desert= (sahara) winter 13 degrees, summer 37 degrees 37mm rain per year
semi desert= (Kalahari) winter 10 degrees, summer 23 degrees, 363mm rain per year.
factors causing aridity- temperature
effected by latitude and insolation levels
- lower latitudes have higher levels of insolation, so the sun is higher in the sky.
- this is due to radiation not having to travel so far through the earths atmosphere reducing the amount refected (albedo effect). also radiation is more concentrated as it isn't spread out like up at the poles.
lack of precipitation
little rainfall only about 10-500mm per year
hot deserts have rainfall due to strong convectional storms
semi deserts have seasonal rainfall
subtropical high pressure cells found 30 degrees N and S of equator.
air subsides and becomes compressed and drys out.
this also stops warm air from ground rising and creating clouds, leading to little rainfall.
when land is far away from ocean
large distance means that offshore winds can't carry moisture for that length of time so most is lost before it reaches inland areas.
the only wind that reaches is dry and warm.
mountains form a barrier for cool air which is then forced up the mountain side where it condenses at the top forming rain.
this leaves only dry air to carry on over the mountain creating a dry desert area the other side called a rain shadow.
cold ocean currents
cool air above ocean currents holds less moisture, these currents travel close to land.
once this cool air hits the land it heats up and evaporates any moisture in it, leaving a coastal fog. the air that then travels further inland is dry and warm.