Question

what are the causes of rain

Answer 1

Ultimately, what causes rain in our atmosphere is the ascent of air containing water vapor. During ascent,the pressure decreases (as a result of gravity), so rising air then expands, cooling as itdoes so. When the air starts out with a relative humidity less than 100%, thi coolingby expansion causes the relative humidity to increase, until the point of saturation. At the saturation point, condensation of the water begins (Itusually begins a bit before reaching 100%, actually, as a result of trace amounts of hygroscopic condensation nuclei in the air.) and the air remains saturated as it ascends further, resulting in continuing condensation. Condensation initiallyforms tiny cloud droplets that are numerous but are far too small to fall to theground as rain. Thereare processes that can go on in clouds (this gets rather technical) that cause the cloud droplets (and ice particles, for clouds tall enough to have some part of thecloud be above the 0 deg C level in the atmosphere), to grow in size and eventually they become large enough to fall as rain.

Answer 2

It is caused by condensation of vapour in the cloud.