The Precipitation Duration Ratio

We all know that water evaporates from the earth's surface and then condenses into tiny droplets around particles such as dust, which serve as condensation nuclei, when the vapor (vapour) reaches a certain altitude. This is because the air gets colder as we move higher and the colder air cannot hold as much water as the warmer air near the surface.

Many millions of these tiny condensed droplets of water form clouds. When the cloud gets full of water droplets, they are in close proximity to one another so that they collide and join together into larger drops by hydrogen bonding. This happens because water molecules are assymetrical, one side is more negatively-charged and the opposite side more positively-charged, and the molecules line up negative-to-positive.

These larger drops of water are too heavy to be held aloft by the air and begin to fall as rain. This applies to sleet, as well as rain, and also to snow, although the snow formation process is somewhat more complicated. There is rain in places where little or no water evaporates because clouds move with the wind, and in doing so bring water from sea to land.

Have you ever wondered why water evaporates all of the time, but precipitation occurs only a fraction of the time? This ratio, the precipitation duration ratio, can only be explained by the fact that process of water falling must be more efficient than that of water rising. I would like to give my explanation of this and it provides insight into the processes of weather and what goes on inside clouds.

Both the upward movement of water during evaporation and the downward movement during precipitation is driven by gravity. Water evaporates, when it breaks free of the hydrogen bonding with other water molecules, because water is actually lighter than air by molecule. Water falls as precipitation because when water molecules do bond by hydrogen bonding, after coming close enough to one another, water is 800 times as heavy as air at sea level.

Water molecules rise one by one after evaporation. But when they fall, snowballing takes place and this makes the process of falling more rapid than that of rising.

When a drop forms high up in the cloud that is heavy enough to fall, it collides with and incorporates molecules below it, including droplets that were not yet heavy enough to fall. Eventually, these lower droplets would most likely combine with other molecules and droplets until they became heavy enough to fall, but the snowballing greatly accelerates the process.

The result is the precipitation duration ratio, the fact that water evaporates all of the time but there is precipitation only a fraction of the time. The rising of the water is addititive, while the falling of the water is multiplicative.

It is not possible for water to fall at the same rate it rises because it rises by molecule, which are lighter than air. If clouds were thin in the vertical plane so that this snowballing could not take place, it would have to be raining virtually all of the time, albeit very lightly. There can be no such snowballing process for rising water vapour (vapor) because it would produce droplets that would be large enough to fall, rather than rise.

This is why there tends to be only light rain from those horizontal stratus clouds. Rain clouds are the towering cumulus and cumulonimbus clouds. There is a tremendous snowball effect due to the great vertical height of cumulonimbus clouds. Vertical currents of air in the cloud produce the static electricity which results in lightning.

I find it logical to presume that small droplets high up in the cloud are most likely to begin falling first because the air is cooler and thinner the higher we go, meaning that it has less capacity to support water. But this is not strictly true and some drops lower in the cloud do fall first.

We cannot use the precipitation duration ratio to actually measure the snowball effect that does take place because it does not always occur from the top of the clouds. But the ratio does tell us the overall effect that it has on the evaporation-precipitation process.