SYLLABUS SECTION: GS I (GEOGRAPHY)

WHY IN THE NEWS?

Recently, the US states of Nebraska, Minnesota and Illinois were hit by a storm system called a derecho.

MORE DETAILS:

• The US National Weather Service describes a derecho as a widespread, long-lived, straight-line windstorm that is associated with a band of rapidly moving showers or thunderstorms.
• The name comes from the Spanish word la derecha, which means straight.
• Unlike a tornado or cyclone, winds in straight-line storms have no rotational motion.
• Being a warm-weather phenomenon, a derecho generally occurs during summer time beginning May, with most storms hitting in June and July.
• they are a rare occurrence compared with other storm systems like tornadoes or hurricanes.
• For a storm to be classified as a derecho it must have wind gusts of at least 93 km per hour, and a wind damage swath extending more than 400 km.
• the time gap between successive wind damage events should not be more than three hour.

GREEN SKY

• Severe thunderstorms can result in a green sky due to light interacting with the huge amount of water they hold.
• Big rain drops and hail can scatter all but the blue wavelengths, because of which primarily blue light penetrates below the storm cloud.
• This blue then combines with the red-yellow of the afternoon or evening sun to produce green.

AMERICAN STORM:

• Derechos mostly occur over the central and eastern United States.
• The super derecho of May 8, 2009 was one of the most intense and unusual derechos ever observed in the country as it swept from Kansas to Kentucky with windspeeds reachingupto170 km/hr.
• In2010, Russia documented its first derecho. They have occurred in Germany and Finland, and more recently in Bulgaria and Poland.
• Meteorologists classify derechos as progressive, serial and hybrid.
• A progressive derecho is associated with a Shortline of thunderstorms that may travel for hundreds of miles along a relatively narrow path. It is a summer phenomenon.
• A serial derecho has an extensive squall line wide and long sweeping across a large area. It usually occurs during the spring or fall.
• Hybrid ones have the features of both progressive and serial derechos.

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Source: INDIAN EXPRESS