NASA has finally unravelled the mystery about why it often drizzles rather than raining. “There was a previous hypothesis that the updrafts could be important. But the hypothesis had never been tested”, said Hanii Takashi the research team leader, who came up with the reason behind drizzling. Updraft is an upcurrent or draught of air that rises up from the land or sea due to heat. The research team has laid the cause of drizzle on these currents of air.
Water that is evaporated from the land and sea and other water bodies form aerosols, which are microscopic particles. The scientist have studied the nature and functions of these aerosols in contributing to the rainfall patterns. There is more abundance of aerosols in the clouds over the land than the clouds over the sea. It would then drizzle more frequently on lands than on the sea. But the case is quite the contrary. There’s something additional to aerosols that acts to effect the pattern of rainfall.
The research was led by the scientists of NASA’s Jet Propulsion Laboratory in Pasadena, California: UCLA and the University of Tokyo. They concentrated mainly on the updrafts which in higher thunderstorm clouds play a distinct role in rain formation. However, in lower clouds the warm air currents are much weaker. It was never discovered until this time that updrafts could control the size of the rain droplets. The updrafts closer to the land being weaker can only hold water particle that are smaller in size, and when they tend to grow, the currents no longer being able to hold them, lets them go and hence, it drizzles. The updrafts over the seas are even weaker than those above the land, and hence they let go of the water particles more frequently and so it drizzles much more in sea areas.