Why is a microburst (weather)

Just curious.

Ok , during a storm when it is raining heavily, espescially in a dry region, the rain can induce a downdraft(which a microburst is an example of). Some of the water on the rain droplets will evaporate before hitting the ground, this evaporation cools the air, in the same way that rubbing alcohol feels cold as it evaporates on your skin. Cool air is more dense than warm air, so the air cooled by the heavy rain will sink (heat rises remember, cold air sinks). the descending air gains kinetic energy as it approaches the ground . This is an example of a downdraft. and a microburst is just a very localized downdraft (micro specifies the size scale). Descending air eventually reaches a barrier (the ground) and spreads out. This produces straight line winds (as opposed to rotational-as is the case in a tornado) away from the downdraft. It can do damage.

Its different from a tornado because a tornado is a rising collumn of rotating air while a microburst is sinking air that is not rotating

The AMS Glossary of Meteorology defines a microburst as...
" (A) downburst that covers an area less than 4 km along a side with peak winds that last 2–5 minutes."
http://amsglossary.allenpress.com/glossa…

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There are two kinds of microbursts - wet and dry.
Wet and dry microbursts are both a result of rapidly descending air originating inside a convective cloud (cumulonimbus).

All rain has evaporated when a dry microburst impacts the ground.
The downward speed is accelerated by evaporative cooling.

Wet microbursts are accompanied by heavy rainfall.
The rain accompanying the intense down draft contributes to its intensity.

A microburst is a localized column of sinking air that can produce damaging divergent and straightline winds.

a powerful short lasting down draft of wind that takes place in a small localized area