Monday, May 2, 2011

Weather Radar Technology Captures Tornado Activity

The devastating tornadoes last week were tragic, but I saw some amazing photos of the intense storms while watching the news. Many of these photos and animations are enabled by advanced radar technologies that our industry has developed.

One NASA platform that provided vital information is the Tropical Rainfall Measuring Mission (TRMM). The TRMM has several instruments including a Precipitation Radar that was the first space borne instrument designed to provide 3D maps of storm structure. These measurements yield information on the intensity and distribution of the rain, on the rain type, on the storm depth and on the height at which the snow melts into rain. It can provide vertical profiles up to 12 miles and detect fairly light rain rates down to about .027 inches per hour. The Precipitation Radar uses a frequency 3 times higher than similar ground based systems in order to obtain high resolution images. It uses 128 solid state power amplifiers to provide a robust design and minimize power consumption (it only uses 224 W). As the beam size is small, it also utilizes scanning phased array technology to steer the beam over the target area.

The TRMM also has a Microwave Imager (TMI) whichi is a passive microwave sensor designed to provide quantitative rainfall information over a wide swath under the TRMM satellite. By carefully measuring the minute amounts of microwave energy emitted by the Earth and its atmosphere, TMI is able to quantify the water vapor, the cloud water, and the rainfall intensity in the atmosphere. The TMI measures the intensity of radiation at five separate frequencies: 10.7, 19.4, 21.3, 37 and 85.5 GHz. Calculating rainfall rates from TMI requires fairly complicated calculations using Planck’s radiation law, which describes how much energy a body radiates given its temperature.

The primary instruments for measuring precipitation are the Precipitation Radar, the TMI, and the Visible and Infrared Scanner. Additionally, TRMM carries the Lightning Imaging Sensor and the Clouds and the Earth’s Radiant Energy System Instrument. These instruments can all function individually or in combination with one another. TRMM is part of NASA’s Mission to Planet Earth, a long-term, coordinated research effort to study the Earth as a global system. The following images and description were taken from the NASA website:

The TRMM satellite saw severe weather over the eastern United States for the third day in a row on 27 April 2011. TRMM Microwave Imager (TMI) and Precipitation Radar data from this orbit shows numerous intense thunderstorms stretching from Louisiana to the Ohio valley. By 2:53 PM, four tornadoes had been reported as this stormy weather moved through Alabama and Mississippi (Images and Captions by Hal Pierce - SSAI/NASA GSFC).

Ground radar systems have added the capability to create very detailed 3D images of severe weather. One reason for this is the use of dual polarization radar. The images and descriptions below were taken from an article written by Jason Samenow in the Washington Post:

Radar sequence of tornado supercell thunderstorms that tracked from western Mississippi into southwest North Carolina. (Brian Tang, a post doctoral research fellow at the National Center for Atmospheric Research)

It is a Radar montage of the most impressive supercell from the large tornado outbreak. This cell traveled about 450 miles and lasted over 8 hours. It also was responsible for the large, violent tornado that caused the destruction in Tuscaloosa. The National Weather Service reported that the tornado spawned by this supercell from Tuscaloosa to Birmingham was on the ground for 80 miles and reached high-end EF-4 intensity (winds to 190 mph).

Vertical cross section of radar when tornado was in the vicinity of Tuscaloosa, Alabama on April 27. (@iwitnessweather and The Weather Channel via Twitter)

The above three-dimensional radar image shows not only the hook echo across the horizontal plane but also see the “debris” generated by the tornado right as it’s in the vicinity of Tuscaloosa. The debris is depicted by the “ball” of pink (indicating the high reflectivity) at the point of the hook echo. In the vertical, you can see the radar’s reflection of the actual funnel.

These newer tools should help scientists learn more about these storms and improve our warning systems. All these images and capabilities enabled by RF engineering!

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