Monday, July 9, 2012

NASA Satellites Examine a Powerful Summer Storm

As a powerful summertime storm, known as a derecho, moved from Illinois to the Mid-Atlantic states on June 29, expanding and bringing destruction with it, NASA and other satellites provided a look at various factors involved in the event, its progression and its aftermath.

According to NOAA's Storm Prediction Center web site, a derecho (pronounced "deh-REY-cho") is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Damage from a derecho is usually in one direction along a relatively straight track. By definition an event is classified a derecho if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length.

These storms are most common in the United States during the late spring and summer, with more than three quarters occurring between April and August. They either extend from the upper Mississippi Valley southeast into the Ohio Valley, or from the southern Plains northeast into the mid-Mississippi Valley.

The movie begins on June 28 at 1515 UTC (11:15 a.m. EDT) and ends on June 30, 2012 at 1601 UTC (12:01 p.m. EDT). In the animation, the derecho's clouds appear as a line in the upper Midwest on June 29 at 1432. By 1602 UTC, they appear as a rounded area south of Lake Michigan. By 2132, the area of the derecho's clouds were near Lake Erie and over Ohio expanding as the system track southeast. By 0630 UTC, the size appears to have almost doubled as the derecho moves over West Virginia, Maryland, Pennsylvania and Virginia. At 0232 UTC on June 30 (10:32 p.m. EDT), the Derecho was over the mid-Atlantic bringing a 100 mile line of severe storms and wind gusts as high as 90 mph to the region.

The process of a derecho can become self-sustaining as hot and humid air is forced upward by the gust front and develops more (reinforcing) towering clouds. When one adds in a rear low level jet stream, there is nothing to stop the repeating process.

NASA's Aqua satellite flew over the derecho on June 29 and June 30, using the Atmospheric Infrared Sounder instrument (AIRS) onboard to capture infrared imagery of the event.

The AIRS images for June 29, shows the crescent shape of the initial stage of the derecho as it gathered strength on the Michigan-Indiana-Ohio border and began its rapid eastward movement. "The AIRS infrared image shows the high near-surface atmospheric temperatures blanketing the South and Midwestern U.S., approaching 98 degrees Fahrenheit," said Ed Olsen of the AIRS Team at NASA's Jet Propulsion Laboratory.


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