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Thought this might be of interest..
Michael Boschat
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JOHN F. KENNEDY ASTRONOMICAL OBSERVATORY
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==========================================================================
Don Savage
Headquarters, Washington, DC June 7, 1995
(Phone: 202/358-1547)
Kathy Berry
Geophysical Institute, University of Alaska, Fairbanks
(Phone: 907/474-7798)
SPRITES CONFIRMED OVER STORMS OUTSIDE U.S. FOR FIRST TIME
NASA researchers have captured on videotape the
first conclusive evidence that the mysterious flashes of
red light called sprites -- which extend up to 55 miles
above electrical thunderstorms -- are not limited to the
United States.
The research team from the Geophysical Institute of
the University of Alaska, Fairbanks, recorded the unusual
flashes above thunderstorms near the equator in South
America last February and March. Previously, they had seen
the recently discovered sprites above storms only in the
U.S., leading some scientists to question whether or not
they occur in other parts of the world.
Geophysical Institute researchers Davis Sentman,
Gene Wescott and Daniel Osborne used special low-light-
level cameras aboard a Westwind-2 jet aircraft to record
the brief flashes. The flights, part of a NASA-sponsored
investigation into the phenomenon, were coordinated with
the Peruvian Air Force. The researchers recently completed
an analysis of the footage gained during their flights.
In form and in visual appearance, the sprites over
South America look similar to flashes recorded by the team
over storms in the central U.S. last summer. About 500
sprites were recorded last June and July, many on color
video for the first time. None of the sprite groups seen
this winter over South America were as large or as intense
in color as some of the larger groups recorded over the U.S.
Less intense thunderstorms may have contributed to
the smaller number and desultory appearance of the sprites
in South America. In the southwestern-central U.S., the
storms form along a quickly moving frontal system, but the
convective storms in South America are nearly stationary;
they tend to grow in place, develop slowly into large
systems like boiling water, then dissipate.
Some scientists had speculated that sprites might
not exist over equatorial regions because thunderstorms
there frequently do not get larger than about 100 miles,
which some thought was the minimum size needed to produce a sprite.
Pilots and others also have reported seeing blue or
greenish columns propagate upward at great speed from the
top of thunderstorms. Wescott and Sentman were the first
to report the video capture and the characteristics of
"blue jets" from 1994 flights over the U.S. No blue jets
were seen over South America.
Sprites can be seen from the ground after dark with
the unaided eye under the right conditions. To encourage
pilots and others to report sprite sightings around the
world, Sentman is establishing a Sprite Watcher's Homepage
on the World Wide Web. The homepage will give brief
information about sprites, the conditions needed to view
sprites from the ground or air, and simple directions to
follow when recording a sighting. All public sightings
will be incorporated into a scientific database, and then
displayed on a global map for Web users.
Researchers from government laboratories, universities,
and Federal agencies will continue to investigate sprites and other
phenomena associated with thunderstorms this summer during two main
campaign efforts. A team from the Geophysical Institute will observe
storms from Colorado mountain tops to support optical observations
of sprites made from the Yucca Ridge Field State east of Fort Collins,
CO. Research into what causes sprites will be made using radio
frequencies, radar, and other measuring techniques at additional
sites across the eastern half of the U.S.
More than two dozen scientists from across the
country will participate in a second major campaign, which
will focus on thunderstorms around northern Florida.
Facilities and capabilities at NASA's Kennedy Space Center
will be used in the study.
-end-
EDITOR'S NOTE: Individuals interested in participating
in the sprite research or receiving further information via
the internet can access the Sprite Watchers Homepage at the
following URL: http://elf.gi.alaska.edu/
SPRITES AND JETS
Information presented is based primarily on the Sprites '94 Campaign.
Analysis of data acquired during a spring campaign over South America
is in progress. A Sprites Watchers Guide is under construction and
will be referenced on this page.
The Sprites '94 Campaign represents work done by researchers from the
Geophysical Institute of the University of Alaska Fairbanks.
Sprites are optical emissions which occur above thunderstorms. So far,
only Mesoscale Convective Systems (large storm systems) have been
analyzed in detail. However, recent data collected over South America
suggests sprites also appear above smaller storm systems. Sprites have
been observed to have tops at approximately 90 km (+/- 10 km).
In addition to documenting sprites, the Sprites '94 campaign
documented blue jets. The blue jets have tops at approximately 40 km.
Another difference between jets and sprites is the time scale of the
phenomena. The sprites are very brief (less than 17ms) emissions. (The
persisentence of the sprites for more than a single frame is primarily
due to the camera system). The jets propagate upwards over several
video frames. This can be seen in the movies below. One reason sprites
and jets are very interesting is the possible effects of the energy on
the chemical reactions in the upper atmosphere.
References
- Lyons, W.A., Characteristics of luminous structures in the
stratosphere above thunderstorms as imaged by low-light video,
Geophys. Res. Letts., 21, 875-878 (1994).
- Millikh, G.M., et. al., On the physics of high altitude lightning
Geophys. Res. Lett., 22, 85-88 (1995).
- Sentman, D.D. and E.M. Wescott, Red Sprites & Blue Jets,
Geophysical Institute Video Production, University of Alaska
Fairbanks, 9 July 1994.
- Sentman, D.D. and E.M. Wescott, Observations of upper atmospheric
optical flashes recorded from an aircraft, Geophys. Res. Lett.,
20, 2857-2860 (1993).
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