A gently sloping extension of a hill (inselberg) or plateau formed from scarp retreat. See Inselberg Formation
Precipitation (rainfall, snow, sleet, hail)
Precipitation refers to any deposition
of moisture(liquid) to the ground.
Precipitation beginning at high elevation
includes rain, snow, sleet, hail while some
Precipitation originating from ground level
include dew, frost, rime, fog and mist.
Deposition of liquid from high
up in the clouds.Types of Rainfall
when moisture (air) originating mostly from
the ocean encounters a barrier such as
a mountain causing it to rise, cool and expand.
This generates heavy rainfalls on the
windward side of the mountain e.g the
windward side of Inyangani mts experiences
high Rainfall in Zimbabwe due to moisture from
the Indian ocean. The leeward side is
dry because air is descending and compressing.
This is another factor causing deserts e.g
Atacama in S America and The Great Basin in west USA caused by the Sierra Nevada mountains blocking off moisture from the Pacific Ocean.
air parcels by the ground becomes buoyant
and light therefore start rising. The air parcel is warmer than the surrounding air therefore it is unstable and continues to rise, producing towering cumulonimbus clouds.
When two air masses meet (cold and
one is forced aloft causing it to cool and
expand generating heavy rainfalls and thunderstorms.NB: cloud type and rainfall differ depending on the type of front (See Fronts)
Another type of rainfall whereby
two bodies of air usually originating from
the sea rises together on a low pressure area over land where friction reduces speed. A good example is the ITCZwhere North east and South west trade winds meet on a low pressure belt. Lifting or convergence on warm waters can give birth to tropical storms
Snow forms by a process of
aggregation whereby slicky ice crystals with their liquid coating
stick with solid ice crystals forming hexagonal snowflakes. Snow is a form
of theBergeron Findeisen but instead of the snowflakes melting they
remain solid given that low level temperatures are also low.
Hail is formed by a process of accretion
in a high updraught cloud(cumulonimbus) with high convectional currents. For hail to form water droplets
are carried high up in the cloud where they freeze, they are
then sent downwards where water droplets freeze on the ice. The
cycle continues until the ball of ice is big enough to be dropped as
hail. Layers of ice can be seen when a hail ball is peeled off. Hail balls are usually 4mm-6mm in diameter, but some hail can be as large as 50cm which can kill humans, animals or plants.
Snowflakes may encounter high temperatures at lower levels as they fall resulting in their partial melting, thus the sleet will be a mixture of snow and rain.