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Author Topic: size of raindrops  (Read 9139 times)

Offline vidya

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size of raindrops
« on: 11/08/2007 12:46:50 »

Hello, I was wondering if there is a generalization in the size of raindrops between the tropics and temperate regions. For a fixed volume of rain, are raindrops in the tropics larger and the density of raindrops smaller usually? Also, what determines the size of raindrops?



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size of raindrops
« Reply #1 on: 11/08/2007 22:05:00 »
what determines the size of raindrops? The raindrops of a heavy pattering summer shower are large about a tenth of an inch in diameter. Fine rain is made of drops one twentieth to one fiftieth of an inch in size.

I suppose you could equate this to different regions. Where they only have light showers, as opposed to regions that have heavy rains - monsoons for example.

Here in the UK, we are "lucky" enough, to experience lots of differing rainfall.

was that any help?

Offline DoctorBeaver

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size of raindrops
« Reply #2 on: 11/08/2007 22:10:50 »
I remember reading somewhere that temperature can affect their size.

  • Guest
size of raindrops
« Reply #3 on: 11/08/2007 22:37:36 »
I remember reading somewhere that temperature can affect their size.

This is true, The higher the temperature, the greater the capacity to hold water vapor. The more water vapor can be held in the same volume without condensing.


An interesting side-light to the process is that
  >when water vapor changes state to liquid, the
  >water vapor molecules give up the kinetic energy
  >that they had when they were moving. This warms
  >the remaining free molecules in the air and tends
  >to delay further condensation. However, this
  >process actually enhances condensation
  >of water vapor in the atmosphere because a warmed
  >parcel of air rises more rapidly, thus expands
  >more rapidly, thus cools more rapidly, and thus
  >condenses more rapidly than if the parcel had
  >stayed in one place and the temperature were
  >decreased. The enormous growth of towering
  >cumulonimbus clouds demonstrates this dramatically.

David Cook
  >Meteorologist working in ER Division
  >Argonne Nat. Lab.

Also, i think different cloud types produce different sized raindrops. The different cloud types are produced by different weather patterns/events. You also have to account for geography and topography.

As i tried, somewhat clumsily, to say earlier. Rainfall is heavier in areas where there is abundant atmospheric moisture, such as in the tropics, near an ocean coastline, near an area of an ocean where there are seasonal monsoon rains

Little rainfall occurs where there is little available moisture because an area is located far from an ocean

On a personal note, and i think i have said this before. I love clouds.
« Last Edit: 14/10/2007 19:16:07 by »


  • Guest
size of raindrops
« Reply #4 on: 08/10/2007 17:40:29 »
I read that the size of raindrops is often related to the strength of the updrafts inside the clouds where they're formed. The raindrops accrete tiny droplets of water until they are heavy enough to lose the support of the updraft. Then they fall out.
'Thunder drops' come from thunder clouds in which there are huge updrafts - which also cause build up of charge by electrostatic induction.
Mizzy rain falls out of stratus clouds in which there are only small currents of air.

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size of raindrops
« Reply #5 on: 09/10/2007 15:48:31 »
Many observations have been made of size distributions of raindrops, aggregated snowflakes, graupel and hailstones under various meteorological conditions. The size distributions have been studied in conjunction with upper air soundings which were used to determine the original shape or snow crystal form of the hydrometeors. It was concluded that the size distribution of raindrops is dependent on that of the precursor snowflakes which is controlled by the shape of the snowflakes and the upper air conditions.

further reading here:

  • Guest
size of raindrops
« Reply #6 on: 14/10/2007 14:28:20 »
To understand why raindrops came in different sizes, we need to go back and understand what a raindrop is and how it is formed.

where does rain come from? Clouds you say, so what are the clouds made of? A cloud is made from water vapour and other particles, say dust or smoke. These are called condensation nuclei.

Condensation occurs when the water vapor attaches to and wraps itself around the tiny particles. Each particle becomes a tiny droplet between 0.0001 and 0.005 cm in diameter. Why the difference? Well, the particles (of smoke, dust...) are different sizes so each droplet will be a different size.

This size of droplet is too small and light to fall as rain, so it has to gain weight and size, this is called coalescence. Coalescence, is when tiny droplets join or bump in to other droplets to become one single, bigger droplet.

soon the droplet will become too heavy and big for the cloud, at this point it will start to fall. As it falls, it begins to further coalesce. Once the droplet has reached as size of 0.5mm it is officially a raindrop.

This will continue to fall and there you have your rain, if on the way down it reaches a size of or greater than 4mm in will then split in to two single raindrops.

As the raindrop falls it may encounter an updraft, this will take it back up in to the cloud where it once again coalesces with other drops / droplets.

So when we have smaller raindrops, we can say that there was not much coalescing going on and that there was no or very little in the way of updrafts.
When the raindrops are bigger, we can say that there was an updraft and plenty of coalescing.

Another way to look at it is, that low clouds generally produce smaller raindrops (not much distance to fall, which will prevent much coalescing and reduce the effectsof any updraft). Where higher clouds will generally produce larger raindrops as they have further to fall so they can coalesce more and be influenced by updrafts. Generally these are associated with thunderstorms.


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size of raindrops
« Reply #6 on: 14/10/2007 14:28:20 »


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