# Understanding Convectional Rainfall

Consider the following explanation of convectional rainfall given in a VII grade textbook.

When air comes in contact with the hot surface of the earth, it gets heated, becomes light and rises in the form of air current. After the warm air current reaches the upper layers of the atmosphere, it expands adiabatically and loses heat. This leads to condensation and the formation of cumulus and cumulonimbus clouds which soon become heavy with condensed water vapour and cause rainfall.

On searching online, most easily found sources give the explanation on the same lines.

There are a few things I don't understand:

1. Which air is responsible for the rainfall? Is it just the moisture-laden air present above the oceans and the water itself that evaporates from water bodies or even the air present above land surface?
Obviously, all the air mass which receives sunlight whether above land or water becomes hotter and goes up but the air above oceans already has water-molecules while the air above the land is just the normal mixture of air with some percentage of oxygen, nitrogen etc molecules. Do the molecules from this normal mixture also combine at higher altitudes to form water molecules and add to the precipitation process?

2. How do we know that the expansion at higher altitudes is adiabatic and would precipitation in the form of rain not happen if it were not adiabatic and something else?

3. What exactly is meant when it is said that clouds become very heavy and can't hold on to water and therefore cause rain?

• Trying that again: “It expands adiabatically and loses heat”. Adiabatic means no heat. Heat is flowing thermal energy. They mean loses energy. Or loses temperature. (It loses energy by doing expansion work under pressure with no heat coming in, and pressure, and loses temperature). But it does not technically lose heat. “Lose heat” isn’t even right. “Heat” is energy flowing from a high temperature thing/region to a lower temperature thing/region. Temperature difference drives heat flow. Not Temp diff no heat flow (ie no thermal transfer of energy). Aug 18, 2021 at 8:42
• It’s possible that in this particular field, people say that. But technically it is what I wrote. Engineers and thermal -hydraulic and thermodynamic experts all have such definitions. Losing thermal energy by heat transfer is not “losing heat”, but that doesnt happen if adiabatic anyway - adiabatic = no heat, no losing energy via heat transfer, no heat transfer Aug 18, 2021 at 8:46