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The Lightningof El Nino

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see captionMarch 8, 2000: Just as children count the seconds between a flash of lighting and the boom of thunder to guess an approaching storm's distance, scientists are now recognizing the merits of lightning as a valuable indicator of the path and power of storms.

But Steven Goodman's analysis of lightning is a bit more sophisticated than the childhood amusement of watching a storm roll in.

Goodman is a scientist at the Global Hydrology and Climate Center (GHCC) in Huntsville, Alabama. From his office he is able to monitor lightning summaries that paint a picture of the electrical behavior of storms. One of his most fascinating discoveries was the correlation between the El Nino effect and intensified lightning in the Gulf Coast region.

Above: Number of winter days when lightning hit the Earth's surface during a strong El Niño period (left) and during La Niña (right). (Credit: Steven Goodman, Global Hydrology & Climate Center.)

El Nino, a periodic warming of the tropical eastern Pacific Ocean, alters the course of the jet stream, pushing it as far south as Alabama or the Gulf of Mexico. In a normal winter the jet stream is usually located over Virgina. Storms tend to track along the edge of the jet stream where the rift between cool and warm air creates a contrast that fuels storm activity.

Aware of the enhanced precipitation and fuss about El Nino in the winter of 1997-1998, Goodman and his colleagues scrutinized two years of satellite data and discovered abnormally high amounts of lightning during three of the past four El Nino cycles. The number of days of lightning during an El Nino year can reach 33 and during La Nina, the opposite effect, it can be less than 15.

The 1997-1998 El Nino season was unique, mostly due to the jet stream's position along the southeast Gulf Coast, hovering just south of Tallahassee, Florida. Each El Nino year is different, said Goodman, making it difficult to predict precise weather changes based solely on the general
effect.

"If you want to look at impacts of storms...it's not enough to say "I'm forecasting El Nino"...[because] each El Nino event is somewhat different."

Without El Nino to spice up life along the Gulf Coast this year, Goodman says it's been "a boring year" as far as thunderstorm activity. The average in the Southeast is 16 thunderstorm days each winter. Although he has not looked at any hard data yet, Goodman expects the number to be "well below normal."

see captionRight: The Lightning Imaging Sensor (LIS), is a space based instrument used to detect the distribution and variability of total lightning (cloud-to-cloud, intracloud, and cloud-to-ground lightning) that occurs in the tropical regions of the globe. The LIS is a science instrument aboard the TRMM Observatory, which was launched on 28 November 1997 from the Tanegashima Space Center in Japan. For more information about space-based lightning detectors, click here.

Goodman is a member of the GHCC Lightning Team, formed in the late '70s and early '80s as a product of NASA's interest in lightning imaging sensors. To observe lightning activity from space requires optical measurement in low-earth or geostationary orbit. The Lightning Team's first installation was the Optical Transient Detector (OTD), which has been observing global lightning since April 1995. The Lightning Imaging Sensor (LIS) stationed on the Tropical Rainfall Measuring Mission (TRMM) was launched in November of 1997 to study the distribution and variability of global lightning. Together they produce unbiased climatology of Earth's lightning day and night and enable scientists to investigate the relationship of lightning to precipitation and thunderstorm convection. With two satellites already in orbit, Goodman and the rest of the Lightning Team have accomplished part of their original objectives.

One goal remains elusive.

"The pot of gold at the end of the rainbow for us is to be in geosynchronous orbit."

The realization of this goal may one day come in the form of the Lightning Mapping Sensor (LMS). Rather than catch a glimpse of storms for a segment of 90 seconds to three minutes -- only a fraction of a much longer thunderstorm life cycle -- the scientists are banking on continuous real-time data from LMS to complement the OTD and LIS data. Although they are still waiting for funding for the proposal, Goodman believes the system could be functioning by 2003.

Meteorologists and climatologists are anxious for innovations to provide cues as to storm evolution and prediction. At any given moment there are 2,000 thunderstorms active around the world and 100 flashes of lightning per second. Each year lightning causes deaths, injuries, property damage, brush fires, downed power lines and systems disruptions.

While current forecasting technology can take 12 minutes to calculate storm characteristics, Goodman says that monitoring lightning helps better assess “rapidly changing lightning rates and rapidly changing characteristics of storms.” Lightning can suggest which storms are going to intensify and which will weaken.

see captionRight: Storm clouds from nighttime thunderstorm Illuminated by cloud-to-cloud lightning. Credit: NOAA Photo Library, NOAA Central Library

Using lightning data "gives [us] more confidence and information," Goodman said.

The scientists at GHCC look at the actual data and try to match lightning flash rates with certain aspects of storms such as total rainfall and ice content amounts. The satellite images are used more for summary and are posted on the GHCC web site at www.ghcc.msfc.nasa.gov/GOES/.

Another way the scientists at GHCC manipulate lightning data is to examine boundary interactions at low levels. When a storm runs into a boundary such as a gust front or a thermal boundary and the air spins upward, lightning indicates this upwelling and helps identify boundaries. The new technology allows for measurements of humidity, hills and darkness – tornadoes often occur in conjunction with these conditions.

The Global Hydrology and Climate Center is a joint venture between government and academia to study the global water cycle and its effect on Earth's climate. Jointly funded by NASA and its academic partners, and jointly operated by NASA's Marshall Space Flight Center in Huntsville, Ala., and the University of Alabama in Huntsville, the Center conducts research in a number of critical areas.
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