How much time It Takes For a Drop of Rain to Reach the Ground from the Cloud

How much time does It Take For a Drop of Rain to Reach the Ground from the Cloud ?

Meteorology is Very fascinating part of Science . One Side It looks Simple another but side Very Complicated . As We all Know Cloud Is formed as Water Evaporates in the form of its vapour , these vapour is wafted up to colder regions of the atmosphere where it condenses and forms clouds. Drops of moisture in the cloud are very tiny , its diameter is about 0.02 mm or less . They are Sustained up there due to collisions with air molecules. If the atmosphere were completely still and the cloud base low it would take them up to 10 hours to descend to the surface , But these are not a drop of  Rain just droplets of moisture .

So How much time a drop of rain takes to reach the Ground  ?

These 0.02 mm of diameter of moisture droplets in cloud coalesce together to become a reasonable - Sized rain drop of 0.2mm diameter . Such drops can start descending with increasing speed till they reach a terminal velocity when the air resistance becomes equal to the downward force of gravity. For a rain drop of 0.2 mm diameter , the terminal velocity is about 4 m/s . Terminal velocity will be higher for bigger drops and lower for smaller drop . 

So the time of descent will depend on the height of the cloud and the size of the raindrop .

Hence, for a drop of rain (average diameter of 0.2mm ) coming down with a speed (Terminal Velocity ) of 4 m/s from a cloud that is one kilometer high takes 4 minutes . The bigger size drop,diameter more than 0.2 mm will take less time while smaller size drop, diameter less than 0.2 mm will take more time .