Zoom April 2011

It gets cloudy and it rains—that’s the way of the world. Depressing as it is, the processes that go into rainfall are actually multifaceted and fascinating. On a global scale, our atmosphere is a complex interaction of air masses, each varying in temperatures, pressures, altitudes and many other variables. The boundary between two air masses of differing densities is known as a weather front, and this area is the crucible for all metrological phenomena, including rainfall. It all begins with the formation of a cloud, which is a visible collection of water and ice particles suspended in the atmosphere. This happens when a volume of air cools and becomes saturated with water vapor, reaching its dew point. The impetus for the collecting water vapor varies, the most common are the upward motion of wind, precipitation from a higher altitude, evaporation from bodies of water or land, plant transpiration, the movement of cool or dry air over water and air lifted by mountains. Now at the dew point, the water vapor condenses into liquid form on condensation nuclei, usually dust, ice or salt and a visible cloud is formed. Next, actual rainfall begins with coalescence, when air turbulence causes water droplets to fuse to each other or to ice crystals. Eventually, the droplets/ice crystals become heavy enough to overcome air resistance and begin their fall to the surface of the Earth. As the ice crystals fall into warmer air, they will melt and become raindrops or fall to the ground as freezing rain. On average, raindrops are between .1 and 9 millimeters in diameter and never teardrop-shaped. The smallest are spherical and as they grow larger, air resistance comes back into play and they become oblate and at their largest resemble parachutes. Not factoring in the effect of wind, the mass of the largest droplets causes them to impact the ground at around 20 mph while the smallest droplets hit at around 4.5 mph.

michael isenbek

Michael Isenbek, Associate Editor, dabbles in both fiction and nonfiction writing, coordinates the Pulse event listings and writes the text for "Zoom," among other editorial tasks. He has a Master's Degree in Liberal Studies and a Bachelor's Degree in Cultural Studies with a concentration in Journalism from SUNY Empire State College.