Chasing showers
NIVEDITA GANGULY
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A shower of rain during the hot season is a blessing indeed.
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The sun god’s fury has left everyone craving for those teasing showers of rain.
Ray of hope
Summer rains are a mysterious phenomenon that comes down as heavenly blessings from the skies above, providing the much needed relief to the dry Earth. Sometimes it threatens with menacing clouds overhead, only to fizzle into a drizzle. But, whatever said and done, there is something magical when the first drops of rain touch the parched ground after a long and sizzling summer.
Summer showers are a typically localised spell that leaves footprints of soaked and scorched earth alternating within a few hundred metres of each other in the city.
Summer rains are a result of the interaction of a number of favourably pre-disposed parameters such as raised humidity levels and optimum ambient temperature ably supported by concomitant smooth upward drift of hot air.
Atmosphere act
Director of Cyclone Warning Centre V.L.Prasad says that summer showers depend on the level of moisture present in the atmosphere and presence of low-pressure trough that precipitates the lean season showers.
Summer showers normally occur due to the process of convection. The Earth gets heated up due to solar radiation and emits long wave terrestrial radiation into the atmosphere.
"This is when convection takes place resulting in the formation of cumulonimbus clouds, also known as thunderstorm clouds, that are primarily responsible for the summer showers," says Prasad.
These clouds form at 16-18 km from the Earth’s surface. However, the summer rains take place in short spells and last for about three hours. "The short spells occur due to a single cell of clouds, unlike the monsoon period when a chain of clouds are set up in the horizon causing heavy rains," he explains.
Experience of the last three years reveals that the showers normally occur during April and May. There has not been any specific pattern of summer showers observed over the years.
On record
The rainfall figures of the last two years indicate the instability of this phenomenon.
In 2004, 64.6 mm of rainfall was recorded during April and 16.2 mm in May. The year 2005 recorded 36.5 mm rainfall in April and 7.7 mm in May. Last year’s figures too stress on this unsteady trend wherein April recorded 30.5 mm rainfall and signed off in style with the rainfall figures touching 80.7 mm in May. “Due to the unpredictable nature of the rainfall pattern, there is no yardstick to prognosticate on its likely performance,” says Prasad.
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