New observations of sprites from the space shuttle
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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D15201, doi:10.1029/2003JD004497, 2004
New observations of sprites from the space shuttle
Yoav Yair,1 Peter Israelevich,2 Adam D. Devir,2 Meir Moalem,3 Colin Price,2
Joachim H. Joseph,2 Zev Levin,2 Baruch Ziv,1 Abraham Sternlieb,4 and Amit Teller2
Received 30 December 2003; revised 3 May 2004; accepted 3 June 2004; published 6 August 2004.
[1] We present the results of space-based observations of sprites obtained during the
Mediterranean Israeli Dust Experiment (MEIDEX) sprite campaign conducted on board
the space shuttle Columbia during its STS-107 mission in January 2003. A total of
6 hours of useful data were saved from 21 different orbits, of which 1/5 contained
lightning. We imaged sprites from an altitude of 280 km using a calibrated multispectral
camera above thunderstorms in various geographical locations, mainly in central Africa,
northern Australia, and South America, and also over the Pacific and Indian Oceans.
In this paper we report on sprites observed from ranges 1600–2000 km from the shuttle, at
altitudes of 40–90 km above the ground. Their brightness was in the range of 0.3–
1.7 mega-Rayleighs (MR) in the 665 nm filter and 1.44–1.7 MR in the 860 nm filter. On
the basis of the frequency of observed events and the number of tropical thunderstorms,
we estimate the sprite rate in the tropics to be of the order of several per minute. INDEX
TERMS: 0342 Atmospheric Composition and Structure: Middle atmosphere—energy deposition; 2427
Ionosphere: Ionosphere/atmosphere interactions (0335); 3304 Meteorology and Atmospheric Dynamics:
Atmospheric electricity; 3324 Meteorology and Atmospheric Dynamics: Lightning; KEYWORDS: sprites, space
shuttle, thunderstorms
Citation: Yair, Y., P. Israelevich, A. D. Devir, M. Moalem, C. Price, J. H. Joseph, Z. Levin, B. Ziv, A. Sternlieb, and A. Teller
(2004), New observations of sprites from the space shuttle, J. Geophys. Res., 109, D15201, doi:10.1029/2003JD004497.
1. Introduction [3] Early images of TLEs from space were obtained in
conjunction with the mesoscale lightning experiment that
[2] Transient luminous events (TLEs) is the collective
was conducted in 1989 – 1991 [Boeck et al., 1994, 1998].
name given to a wide variety of optical emissions which
The analysis of hundreds of hours of video identified
occur in the upper atmosphere above active thunderstorms.
17 events of vertical flashes that appear to connect cloud
These very brief colorful phenomena were discovered in
top and the ionosphere. These events were geolocated by
1989 [Franz et al., 1990] and have been studied since from
using stars and ground lights and were found to occur over
the ground [Lyons, 1994a, 1996], aircraft [Sentman and
Africa, South America, USA, Australia, Borneo, and the
Wescott, 1993], balloons, the space shuttle [Boeck et al.,
Pacific Ocean. The oblique view of the illumination inside
1994, 1998], and the International Space Station [Blanc et
the cloud (caused by strong lightning flashes) from the
al., 2004]. Distinct classes and names were given for the
space shuttle provided the first unambiguous optical link
various forms of TLE, all of which allude to their fleeting,
between the parent stroke and the subsequent TLE.
unpredictable nature: jets, sprites, elves, and haloes, to name
Recently, the Lightning and Sprite Observations experiment
but a few. Sprites seem to play an important role in
(LSO), which consisted of automatic nadir-view observa-
mesosphere-troposphere coupling [Pasko et al., 2001] that
tions of thunderstorms conducted from the International
bears on the global electrical circuit [Rycroft et al., 2002].
Space Station, succeeded in separating the weak sprite
Indeed, recent observations suggest that TLEs connect the
signal from the bright lightning light preceding it by using
top of thunderstorms to the ionosphere [Pasko et al., 2002;
a camera with a very narrowband filter in the 756– 766 nm
Su et al., 2003].There is a growing body of literature which
range. This filter allowed only the sprite light from the
covers the phenomenology and theory of TLE generation,
molecular nitrogen band N2 1 PG (3-1) at 762.7 nm to enter
and we refer the interested reader to recently published
the camera. In total, ten events were detected in several
reviews [Lyons et al., 2000, 2003; Rodger, 1999].
hours of automatic undirected observations [Blanc et al.,
2004].
1
Department of Natural Sciences, Open University of Israel, Tel-Aviv,
[4] In this paper we report results of space-based obser-
Israel. vations of sprites, obtained during the Mediterranean Israeli
2
Department of Geophysics and Planetary Sciences, Tel-Aviv Uni- Dust Experiment (MEIDEX), that was conducted on board
versity, Tel-Aviv, Israel. the space shuttle Columbia during its STS-107 mission in
3
Space Branch, Israeli Air Force, Hakirya, Tel-Aviv, Israel.
4
Israel Ministry of Defense, Hakirya, Tel-Aviv, Israel.
January 2003. The mission lasted 16 days and was per-
formed in a 39 inclination at an altitude of 280 km (150
Copyright 2004 by the American Geophysical Union. nautical miles (NMs)), passing over the major thunderstorm
0148-0227/04/2003JD004497$09.00 producing regions on our planet. Nocturnal observations of
D15201 1 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
daytime dust over-flight in the Atlantic and the Mediterra-
nean regions, most of the nighttime TLE observations were
conducted in the SE Pacific (Australia and Fiji), Africa, the
southern Indian Ocean, and South America. The necessary
shuttle attitude maneuvers and camera gimbal changes were
deduced 24 hours in advance on the basis of a forecast
method [Ziv et al., 2004] that evaluated the probability of
lightning activity in the regions of interest (ROI) on the
basis of significant weather maps (SIG maps) used for
aviation.
[8] The necessary shuttle attitude maneuvers and camera
gimbal changes were deduced based on almost real-time IR
satellite images that were available on the Web (http://
www.bom.gov.au/weather/satellite/) and on VLF lightning
locations from the Tropical Ocean-Global Atmosphere
(TOGA) network (http://ritz.otago.ac.nz/~sferix/TOGA_
network.html) operated by the University of Otago, New
Figure 1. A schematic representation of the observation Zealand. These were used for short-term corrections of the
geometry during a MEIDEX sprite orbit showing the shuttle 24 hour forecast. This ‘‘now-casting’’ method allowed us to
attitude in tail-to-Earth (or nose-to-Earth), with the vertical request of mission control an adjustment of the shuttle
axis out of the payload bay tilted 15 degrees from the local attitude, which was generally granted, provided that it was
horizontal (17 and 19 degrees were also used in several calculated no later than 4.5 hours ahead of an observation
orbits). The accuracy of pointing was 1 degree, owing to the (i.e., the time of three revolutions).
drift in the space shuttle’s attitude in orbit. [9] Most of the observations were conducted with filter 5
(665 ± 50 nm), a spectral range in which considerable
radiation from sprites is expected from the N2(1 PG) system
the mesosphere above these storms were conducted as a [Heavner et al., 2000]. The transmittance of this filter was
secondary objective of the MEIDEX. between 80 and 95%. Additional measurements were con-
ducted with filter 6 (860 ± 40 nm), which was considered to
2. Instruments be prospective for near-infrared (NIR) emissions [Clodman
[5] A detailed description of the MEIDEX science payload and Yair, 2003].
and of its technical specification had already been described [10] The payload was commanded alternatively from the
[Yair et al., 2003]. Spectral data from earlier studies crew cabin and from the ground according to a predeter-
[Hampton et al., 1996] showed that at least five out of the mined schedule. Time stamping on the Xybion image was
six wavelengths chosen for the MEIDEX were adequate for inserted from the ground as part of the camera setting and
TLE observations. We used an image-intensified Xybion was corrected by the crew if the lag was greater than 2 s.
IMC-201 camera, with a rectangular field of view (FOV) Thus the accuracy of event timing may be considered to be
measuring 10.76 vertical and 14.04 horizontal (diagonal ±2 s. January 2003 was rich in Intertropical Convergence
17.86), with a 486 704 pixels CCD, where each pixel Zone (ITCZ) lightning activity, with major storm centers
corresponds to 1.365 10 7 steradian. The camera was found in the summer hemisphere around northern Australia,
calibrated before flight at the Laboratory for Atmospheres Indonesia, Fiji, and south of the equator over the Pacific
at NASA Goddard Space Flight Center and during the Ocean. Intense storms were also observed over Argentina,
mission using the Moon as a calibration source, enabling the Amazon Basin, and the Congo Basin in central Africa.
us to obtain calibrated images of the observed phenomena. Most observations were conducted before local midnight,
The camera was mounted on a single-axis gimbal and when convective activity had not yet subsided. The obser-
allowed a 44 scan of the limb, which in terms of potential vations relied on the astronauts’ visual observations and
coverage gave us a 1600 km arc across the horizon. real-time adjusting of the camera pointing angle, which
[6] The geometry of observation is shown in Figure 1. For were based on initial storm location forecasts transmitted
a limb distance of 1900 km the camera field of view covered beforehand.
the altitude range 0– 150 km, where all known TLEs occur.
During sprite observations, the shuttle was pointed such that 4. Results
the center of the FOV was pointing 50 km above the limb
(17 below local horizontal of the shuttle).The camera was [11] TLE observations during the MEIDEX were per-
operated in the ‘‘locked’’ mode, each time on a specific filter formed in 24 dedicated observation windows, each
with a fixed integration time of 33 ms. Filter choice and approximately 20 min long. A total of 583 min were
camera gain settings evolved throughout the mission to recorded on board, out of which 458 min were transmitted
enhance the probability of registering TLEs. to the ground. In some orbits the data were downlinked
(live) during the actual observation and recorded simulta-
neously on board and on the ground, and in other orbits it
3. Operational Methodology was recorded on board and re-played to the ground at a
[7] Owing to the MEIDEX orbital constraints for its later time. Nonoverlapping data from 21 orbits constitute
primary objective, i.e., dust measurements which required our 357 min database, with a possible addition of 11 min
2 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
Table 1. MEIDEX-Sprite Campaign Data Set Summarya
MET/Start MET/Stop Useful Analyzed
Orbit Time, UT Time, UT Start Time, UT Data, min Status Orbits
44 02/1705 02/1745 19/01/2003, 0844 22 saved yes
45 02/1835 02/1910 19/01/2003, 1014 15 saved yes
46 02/2000 02/2040 19/01/2003, 1139 18 saved no
47 02/2146 02/2221 19/01/2003, 1325 26 saved yes
48 02/2310 02/2340 19/01/2003, 1449 26 saved yes
61 03/1835 03/1915 20/01/2003, 1014 31 saved no
66 04/0205 04/0235 20/01/2003, 1744 28 saved yes
67 04/0335 04/0405 20/01/2003, 1914 03 saved yes
76 04/1705 04/1745 21/01/2003, 0924 41 saved no
77 04/1835 04/1915 21/01/2003, 1014 7 saved no
87 05/0950 05/1015 22/01/2003, 0129 19 saved yes
87 05/1115 05/1145 22/01/2003, 0254 31 saved yes
110 06/2015 06/2045 23/01/2003, 1154 5 saved no
112 06/2305 06/2335 23/01/2003, 1444 lost
113 07/0020 07/0125 23/01/2003, 1559 11 saved yes
114 07/0210 07/0230 23/01/2003, 1749 01 found no
124 07/1710 07/1740 24/01/2003, 0854 19 saved yes
140 08/1710 08/1740 25/01/2003, 0854 13 saved yes
156 09/1705 09/1730 26/01/2003, 0844 lost
160 09/2300 09/2330 26/01/2003, 1439 lost
161 10/0030 10/0100 26/01/2003, 1609 lost
162 10/0208 10/0244 26/01/2003, 1747 17 saved yes
235 14/1520 14/1550 31/01/2003, 0659 lost
239 14/2120 14/2150 31/01/2003, 1259 24 saved yes
Total 357
a
The ‘‘useful data’’ column refers to the video in minutes transmitted by the shuttle, either by the analog or digital downlink
systems, which was recorded in the Payload Operations Control Center (POCC) at NASA GSFC and/or at NASA Johnson
(overlapping times excluded). ‘‘Status’’ denotes if the data was saved on the ground or lost in the accident. The ‘‘analyzed’’ column
marks the orbits whose data has been analyzed thus far.
in tapes recovered on the ground by search teams after the of the MEIDEX filters 5 and 6. The procedure is detailed
Columbia accident. A summary of the MEIDEX-sprite in Appendix A.
observations is presented in Table 1. Mission elapsed time
(MET) denotes the observation windows (note that on the 4.1. Detection of Sprite Emission in the NIR Orbit 66:
images presented in the next sections the format of the 20 January 2003, 1824:32 UT, Filter 6 (860 nm)
time stamp is 01/xx/03, where ‘‘xx’’ is the mission day, [13] The shuttle flew across the southern Indian Ocean
and the time is the MET). ‘‘Start’’ and ‘‘stop’’ refer to and eastern Australia crossing the northeastern coast. At
ingress and egress into and out of the predetermined sprite that time, two main lightning activity centers were located
ROI and do not always match the actual recording times. within a mesoscale convective system (MCS) on the
On some occasions the recording continued well outside northwestern Australian coastline to the west of our
of the ROI, as long as it did not violate the mission flight planned observation area. At 1824:32 UT the shuttle was
rules or interfered with other shuttle activities. located at 36.07S 158.12E, with the payload bay pointed
[12] Only part of the data set covered stormy regions directly backward (no bias; Figure 2a). The recorded image
where TLEs are generated. Here we report the results of (Figure 2b) shows a very large sprite above the lightning
the analysis of 2/3 of our data set, concentrating on the illuminated cloud top. On the basis of an estimated range of
detection of sprites. A separate report on our elves 1800 km from the shuttle to the flash, we calculated the
observations is presented in the work of Israelevich et sprite to occupy the altitude range 45 –90 km, with a lateral
al. [2004]. The total energy of each sprite event was dimension of 30 km. This detection of sprite emission in the
calculated from the average of the radiance-exposure NIR spectral range complements the EXL98 observations
product, obtained in a region that matches the shape of reported by Siefring et al. [1998] and Bernhardt et al.
the sprite by the use of a closely fitted polygon. The total [1998]. The detected emissions in filter 6 confirm spectral
area of this polygon in pixels was determined, and the analysis work by Bucsela et al. [2003] and arise from the
average of its radiance-exposure product was calculated in N2 1 PG. The calculated brightness of this event was 0.96 ±
mJ m 2 sr 1. Since an atmospheric background emission 0.1 MR (Figure 2c). Interestingly, the airglow layer (Meinel
exists, it was necessary to subtract its radiance-exposure OH emission bands 6-2 and 7-3) [Chamberlain, 1961] is
product from that of the sprite. We assumed that for clearly visible in this image as a diffuse glow parallel to
sprites detected in filter 5, the main source of the emis- Earth’s surface, and the sprite seems to pierce through it.
sions was from red first positive group (1 PG) bands Bakans [2002] evaluated the emission intensity of these
of neutral molecular nitrogen at 662.4 nm (N2 1 PG) airglow spectral bands to be 680 ± 40 and 880 ± 50 R. Less
[Heavner et al., 2000]. An estimation of the range of each than a minute later (at 1825:25.26 UT), we observed two
event from the shuttle, based on its location within our additional sprites located above the horizon (Figure 2d). No
FOV, enabled us to accurately calculate the energy and the visible lightning-induced cloud illumination was associated
brightness of the sprite in each of the given spectral bands with these sprites; presumably, the causative ground flash
3 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
was behind the geometrical horizon at a range exceeding
2000 km. It is worth noting that no previous sprite event
was ever recorded at such a large range. The calculated
emission from these two sprites was 0.78 ± 0.08 MR. These
events were separated by more than 500 km from the first
one and originated from a different part of the storm
system.
4.2. A Sequence of Meteors and Sprites Orbit 87:
22 January 2003, 0153:14 UT, Filter 5 (665 nm)
[14] In this orbit we started sprite observations over
Argentina, crossing the Atlantic Ocean, continuing south
of the equator over Africa, and terminating in the Indian
Ocean. When flying eastward into continental Africa over
Namibia, a strong storm was observed over the Congo
Basin. In the span of less than 2 min, two meteors and
several bright TLEs (sprites and elves) were observed
(Table 2). Although the space shuttle traversed some
900 km northeastward during that period of time, the fact
that the astronaut kept tilting the camera toward the center
of lightning activity ensured that we approximately imaged
the same storm system. Figure 3a presents the overlapping
footprints (on the ground) of 40 s of the orbit on the basis
of the fact that the shuttle was tilted with respect to the
velocity vector, enabling an almost cross-track observation.
The first meteor (marked M1 in Figure 3a) was observed at
0152:47.23 UT and penetrated the upper atmosphere in
what appears in the image as a steep angle (Figure 3b). It
is hard to establish the exact trajectory of this meteor from
the visible trail because it can be either coming toward or
receding with respect to our line of sight. On the basis of a
comparison with visible background stars, we estimate this
meteor to peak at magnitude +1.5, and the estimated range
for the termination of the visible track was 1200 km. The
second meteor (marked M2 in Figure 3a) was brighter
(+1.0) and occurred at 0153:05.32 UT. Figure 3c shows
the trajectory of the second meteor, consisting of 14 super-
imposed frames spanning a total duration of 0.462 s. The
trajectory shows that the meteor entered the atmosphere Figure 2. (a) The coverage of field of view of the
between the shuttle and the limb, as Earth is clearly visible Xybion camera from the space shuttle, superimposed on
in the image due to the illumination by the Moon (phase an IR weather satellite image for the time of the
68.5%) and was seen in an oblique angle from the northeast. observation. (b) Enhanced image of the sprite recorded
The computed range for the termination point is 800 km during orbit 66 by Astronaut Ilan Ramon over north
from the shuttle. Australia. We used filter 6, centered at 860 nm. Time on
[15] The sequence shown in Figure 3d illustrates the raw the image is expressed in mission elapsed time (MET), in
data obtained from the Xybion camera. The triple columni- the format 01/xx/03, where xx is the mission day.
form sprite was recorded at 0153:15.89 UT, less than 30 s (c) Color-enhanced detail of the sprite, with a color-coded
after the first meteor penetrated that same atmospheric radiance-exposure product in mJ m 2 sr. X and Y
volume. This event (marked S1 in Figure 3a) was located coordinates are the pixel numbers in the image. (d) Raw
near the limb 1500 km away from the shuttle. Another image of two sprites above the horizon (upper left side).
small sprite was detected at 0154:17.96 UT. A subsequent The causative lightning is beyond the horizon, a distance
image from 0156:01.60 UT (Figure 3e) shows a carrot- exceeding 2000 km from the shuttle.
shaped sprite with a distinct bright body and a dimmer set
of branches extending upwards toward the ionosphere. [Fullekrug and Price, 2002], and so there is little surprise in
Some tendrils also appear to protrude from below the main the discovery of sprites over Africa.
sprite body. These tendrils are known to occur no later
than 10 ms after sprite initiation with speeds of the order of 4.3. Sprites Over an Oceanic Storm Orbit 48:
106 –107 m s 1 [Moudry et al., 2003], but our camera was 19 January 2003, 1513:50 UT, Filter 5 (665 nm)
unable to resolve this downward evolution. The bright spot [16] The shuttle passed to the east of the Australian
to the right of the sprite is the star B-Tauri, and Saturn southeastern coast observing a massive storm centered at
appears on the left-hand margin of the image. This area of 38S, 138E near Tasmania. At 1513:50 UT the shuttle was
Earth was already predicted to be a major producer of TLE located at 36.07S, 158.12E, with nose down the payload
4 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
Table 2. Timing and Sequence of Events During the Observation and 87) of thunderstorms in different locations, we have
in Orbit 87 Over a Thunderstorm in Central Africa located seven sprite events, which occurred above different
Event Time, UT Type of TLE cells separated by hundreds of kilometers. If we consider the
1 0152:10.86 elves
number of sprite elements in each event, the total is 11.
2 0152:47.06 meteor Although it is known that sprites tend to appear in places
3 0153:05.32 meteor preceded by other sprites [Stenbaek-Nielsen et al., 2000;
4 0153:15.89 three sprites Moudry et al., 2003], we presume that these events were
5 0153:16.13 elves separate and independent.
6 0153:34.78 elves
7 0154:17.96 sprite [19] Only approximately 1/5 of the data we analyzed
8 0156:01.60 sprite (254 min) was actually over stormy weather and contained
lightning. This means that the average detection rate of
TLEs during the MEIDEX was 0.33 events per minute. This
bay pointed in azimuth 268.7 (meaning that Earth is seen on is a much higher rate than reported after the MLE [Boeck et
top in the video images). An IR satellite image shows an al., 1998] or in the International Space Station (ISS)
extended cold front emanating from Antarctica toward SE observations [Blanc et al., 2004]. If we only consider sprite
Australia, with cloud bands over the ocean (Figure 4a). The events (and not elements), the detection rate is 0.13 sprites
crew gimbaled the camera by 7.48 to observe a lightning per minute. We assume that our camera had detected only
flash located near the limb. The recorded image shows Earth the high-energy tail of the sprite brightness distribution,
occupying the upper part of the frame and the limb at the being biased toward bright events that were located near
bottom third, a brightly illuminated cloud top, and two the limb when the shuttle was pointed in that direction. Thus
distinct sprites at a height of 80 km above the ground. The the reported value sets a lower limit on the occurrence rate.
main body of the sprites and diffuse elongated branches are [20] To date, there is no reliable quantitative assessment
clearly seen (Figure 4b). The bright line at the middle left- of the prevalence of sprites on a global scale. Reports by
hand side of the image is light coming out of cities on the Lyons [1994b, 1996] during summer observation campaigns
southeastern coast of Australia. Lightning activity around from Yucca Ridge Field Station (YRFS) in Ft. Collins,
Australia for this UT day is shown in Figure 4c. These Colorado, stated a number of the order of 1000 sprites for a
lightning observations come from the experimental World 6-week campaign. This yields an average of 25 events per
Wide Lightning Location network [Rodger et al., 2004], night, which translates to 4 per hour. However, this value
which uses linked VLF receivers to locate discharges from probably represents only summer conditions above that
the electromagnetic pulses they radiate. The compilation of region of the United States with a bias toward large
lightning locations from the network clearly shows the mesoscale convective systems (MCSs). Fullekrug and Price
lightning activity organized along the cold front. A search [2002] estimated a sprite rate of 60 – 70 per night (or
for correlation with the lightning data showed that the only 10 per hour) over the African continent. Heavner et al.
flash detected within the 2 s accuracy of the image time [2000] suggested that the upper limit for the global rate is
stamp was at 1513:51.26 UT and was located at 33.19S, 1 sprite per second on the basis of the assumption that the
132.89E, well outside the camera FOV. Thus it cannot be global sprite distribution corresponds to the lightning
the parent lightning seen in the image. Figure 4d presents distribution that exhibits a ground flash rate of 10– 14 s 1.
the radiance-exposure product for the two sprites in mJ m 2 [21] If we consider that there are approximately 1000
sr 1. Assuming an average duration of 10 ms for the sprites storms globally at any given time [Rycroft et al., 2002],
(observed in a single video frame), we computed a total with a total global flash rate of 44 ± 5 s 1 [Christian et al.,
(surface) brightness of 1.14 ± 0.1 (left element) and 0.79 ± 2003], and if we assume that only a quarter of these are
0.08 (right) MR. The present observation of sprites above ground flashes (CGs), we get 750 CGs per minute world-
the ocean is a significant addition to the limited number of wide. Since sprites are exclusively produced by strong +CGs
oceanic sprites reported thus far. (though some observations report otherwise) [Sao-Sabbas et
al., 1999], we can estimate that only 1% of those are +CGs
that have large enough charge moments to generate sprites,
5. Discussion so that the statistical overall global rate is of the order of
5.1. Detection and Occurrence Rates 7.5 sprites per minute.
[17] The MEIDEX sprite campaign was limited in dura- [22] The average global sprite rate cannot be accurately
tion and was considered a secondary science objective for calculated from the limited MEIDEX set of observations.
the primary dust experiment. In order to achieve the However, the wide geographical distribution of sprites
maximum yield out of the very limited set of observations, found during the mission and the relatively high detection
we developed a forecast method and a pointing capability rate can assist in estimating a lower limit. On the basis of
that helped the shuttle crew conduct targeted observations our forecast method products and analysis of satellite
toward areas with a high probability of TLE occurrence. In images during the mission [Ziv et al., 2004], we conclude
addition, the real-time pointing by camera maneuvers was a that the storms we observed were not special in any
significant success factor that greatly enhanced the detection meteorological aspect. Thus we can assume that they
rate. represent the ordinary, ambient condition of tropical light-
[18] The total number of TLEs (elves and sprites) we ning activity for the Southern Hemisphere summer. Multi-
have discovered so far in the data is 17 out of 254 min of plying the detection rate of sprites (0.12) by a conservative
observing time analyzed. The summary of detected sprites is estimate of simultaneous tropical thunderstorms (100), we
presented in Table 3. In three 5 min samples (orbits 48, 66, get a rate of 12 sprites per minute in the tropics. This value
5 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
Figure 3. (a) Shuttle locations and pointing of the camera FOV during the observations of meteors and
TLEs during orbit 87 (22 January 2003) over Africa. M1 and M2 denote the locations of the two meteors.
S1 corresponds to the location of the first sprite group (see Figure 3d). (b) A composite Xybion image
showing the first meteor trail at 0152:47.23 UT. The meteor is seen as the bright smudge at the upper left
side of the image. (c) A composite Xybion image showing the second meteor trail at 0153:05.32 UT. The
meteor is seen as an oblique line on the right-hand side of the image (d) A sequence of video frames
(33 ms per frame) of the Xybion camera showing the appearance of a ‘‘triple’’ sprite in conjunction with
the first meteor penetration at 0153:15.89 UT. (e) Image of a sprite with visible branches and tendrils at
0154:46.08 UT.
6 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
Figure 4. (a) The coverage of field of view of the Xybion camera from the space shuttle, superimposed
on an IR weather satellite image for19 January 2003 at 1500 UT. At the time of the observation the
shuttle was located at 158E, 36S. (b) Raw image of sprites recorded during orbit 48 by astronaut
William McCool over the ocean near Tasmania. Earth is on top (the Columbia was flying nose-down).
We used filter 5, centered at 665 nm. (c) Lightning location (black dots) detected by the TOGA network
on 19 January 2003. The lightning activity near Tasmania was the source of the sprites detected.
(d) Color-enhanced and re-oriented detail of the sprites, with a color-coded radiance-exposure product in
mJ m 2 sr. X and Y coordinates are the pixel numbers in the image.
7 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
Table 3. Summary of MEIDEX Confirmed Sprite Events, Found After Analysis of 2/3 of the Dataa
MEIDX Number
Orbit MET Time, UT Time, UT Location Filter of Sprites Brightness, MR
48 02/2334:50.09 19/1/03, 1513:50.09 Tasmania 5 2 1.14 ± 0.10
0.79 ± 0.08
66 04/0245:32.07 20/1/03, 1824:32.07 northern Australia 6 1 0.96 ± 0.10
66 04/0246:25.26 20/1/03, 1825:25.26 northern Australia 6 2 0.78 ± 0.08
87 05/0953:29.39 22/1/03, 0132:29.39 Argentina 5 1 N/Ab
87 05/1014:15.89 22/1/03, 0153:15.89 central Africa 5 3 0.34 ± 0.03
87 05/1015:17.96 22/1/03, 0154:17.96 central Africa 5 1 N/A
87 05/1017:01.60 22/1/03, 0156:01.60 central Africa 5 1 1.20 ± 0.10
a
There were 20 additional suspected events not listed here.
b
N/A, not available.
is of the same order of magnitude as the one reported by Alpha Hydrids, and Alpha Leonids). Thus it is reasonable to
Heavner et al. [2000] and corresponds well with the expect that the two meteors we observed represent only a
statistical analysis above. Obviously, only long-term obser- part of the total meteoritic flux and that they were preceded
vations from orbiting space platforms can retrieve a reliable and succeeded by other events not observed by our camera.
estimate of the global sprite rate. The termination height of a specific meteor depends, among
other factors, on its composition, size, velocity, and trajec-
5.2. Meteors and Sprite Formation tory and is different for various showers and sporadic
[23] Elves and sprites were already observed in conjunc- meteors. For example, during the 1999 Leonid storm,
tion with meteor activity during the Leonid Meteor Shower Brown et al. [2000] found termination heights between 75
Airborne Campaign in 1999 [Yano et al., 2001]. There, and 110 km (mean 95 ± 0.56 km). Slower meteors end at a
11 sprites and 33 elves were observed in 1.06 hours above a lower altitude.
European thunderstorm in the Balkans at the time when the [25] The termination altitude of the light emission from
Leonid flux was near its peak [Jenniskens et al., 2000, the first meteor (85 km) approximately coincided with the
Figure 6]. A meteor was also reported to initiate a blue-jet height of the triple sprite observed less than 30 s later.
event in association with the occurrence of a sprite during Indeed, it is hard to establish that this specific meteor
the SPRITES’98 campaign [Suszcynsky et al., 1999]. Still, a triggered the observed sprite, being separated laterally by
relation between the meteoritic flux and the occurrence of 200 km and because the position of the meteor in the
TLEs has not been uniquely established [Wescott et al., image does not correspond to a specific feature in any of the
2001]. At least one theory [Symbalisty et al., 2000] suggests three sprite elements shown in Figure 3d. Presumably,
a direct link between meteor ablation in the mesosphere and particles deposited along the trail of similar meteors served
the formation of Columniform (or C-) sprites. According to as the source of mesospheric irregularities and sought to
model calculations, the flux of particles in the meteor trail explain sprite appearance [Wescott et al., 2001], but this
reduces the ambient atmospheric conductivity so that a cannot be verified from our image.
strong cloud-to-ground stroke occurring within 1 hour [26] Thus, even though no direct causative relationship
of the formation of the meteor trail can trigger a temporally between sprites and TLEs was found during our observa-
brief column of light known as a C sprite. Zabotin and tions, the proximity of our observed events (e.g., meteors
Wright [2001] have suggested that the presence of small and TLE) in time and space supports existing theoretical
particles of meteoric origin in the mesosphere and strato- studies about the role that meteors play in TLE generation
sphere explains features in sprite formation and fine struc- and evolution and may not be a mere coincidence. More
ture. Presumably, the surfaces of these conducting dust observation campaigns of sprites are needed during known
particles contain microspires that amplify the electrostatic peak dates of meteor showers.
field, leading to explosive emission of electrons. Similarly,
Belevkina et al. [2002] suggest that cosmic dust particles
can act as seeds for the formation of sprite tendrils. 6. Summary and Conclusions
Especially, solid iron and magnesium grains can magnify [27] In the video from the 13 orbits analyzed thus far, we
the ambient electric field by a factor of 105 – 106, making the have positively identified 17 TLEs in less than 51 min of
atmosphere at mesospheric heights more susceptible to accumulated thunderstorm data (7 sprites, 10 elves together
electrical breakdown. However, no clear evidence has been with 20 suspected events), a significantly higher detection
obtained linking meteors and sprites. Sao-Sabbas et al. rate compared to the MLE and LSO observations. The
[2004] had suggested that conductivity inhomogeneties in geographical distribution of these events shows that when
the mesosphere, caused by (among other factors) meteoritic there are thunderstorms in the tropics, there is a high
dust particles, may play an important role in the observed probability that some form of accompanying TLE exists.
lateral displacement of sprites with respect to their parent We have obtained images over the Pacific and Indian
ground stroke. Oceans, in the central south Atlantic and over Argentina,
[24] On the basis of the American Meteor Society data- Brazil, north Australia, Tasmania, Congo, Nigeria, and the
base, 22 January coincides with the activity period of Borneo and Fiji peninsula. If we consider the limited
several meteor showers (Delta Cancrids, Canids, Eta observation time and detection efficiency of the MEIDEX
Carinids, Eta Craterids, January Draconids, Rho Geminids, payload, the wide geographical distribution of our success-
8 of 10D15201 YAIR ET AL.: SPRITE OBSERVATIONS FROM SPACE D15201
ful observations provides evidence to the wide-spread flux (photons s 1 m 2 sr 1) at the TLE plane by dividing it
nature of TLE occurrence on a global scale. by the total area of the TLE (the total number of its pixels
[28] In conclusion, the MEIDEX sprite campaign suc- multiplied by the pixel area, m2). The result is insensitive to
ceeded in recording various types of TLE in numerous the distance between the observer and the TLE because we
geographical locations and obtained a considerable amount multiply and divide by the square of the distance from
of new observations. Contrary to remote-controlled or detector to target.
automatic robotic observations, the human factor played a [33] The Rayleigh is a unit of luminous flux used to
significant and indispensable role in the real-time target measure the brightness of the airglow and the aurora,
acquisition, greatly enhancing the probability of capturing first proposed by Hunten et al. [1956]. One Rayleigh is
TLEs. The mission proved the flexibility and global cover- 106/4p quanta (photons) per square meter per second per
age of sprite observations from space and set a benchmark steradian (or 7.96 104 photons s 1 m 2 sr 1). We
for future satellite- and ISS-based TLE observations, such convert the luminous flux (photons s 1 m 2 sr 1) at the
as the global survey by the ROCSAT-2 satellite [Chern et TLE plane to Rayleigh units by dividing the result by
al., 2003] and other missions presently in the planning 7.96 104 photons s 1 m 2 sr 1.
stage, such as the French TARANIS mission [Blanc et al.,
2004]. The novel human-based ‘‘hunting technique’’ for [34] Acknowledgments. This research was made possible by the
TLEs from space proved to be very efficient and may be devotion and enthusiasm of the Columbia crew: Rick Husband, William
adapted in future space-based campaigns from satellites and McCool, Michael Anderson, David Brown, Laurel Clark, Kalpana Chawla,
and Ilan Ramon. The MEIDEX is a joint project of the Israeli Space
from the ISS. Agency and NASA. We wish to thank S. Janz and E. Hilsenrath of
the Laboratory for Atmospheres at NASA GSFC for their help in the
calibrations of the Xybion cameras. Special thanks to the Hitchhiker team
Appendix A: Calibration Procedure of Sprite at NASA GSFC: T. Dixon, M. Wright, K. Barthelme, S. Applebaum,
C. Knapp, K. Harbert, and to A. Lalich and T. Schneider, STS-107 flight
Images planners at NASA JSC, for making this experiment possible. The WWLL
[29] Here we describe the extraction of radiance data from network map came courtesy of Craig J. Rodger, University of Otago, New
Zealand, supported by Marsden Fund contract 02-UOO-106. Thanks also to
the MEDIEX calibrated sprite images. During the preflight Martin Fullekrug, University of Frankfurt, for his help with the Wetterdienst
calibration process at NASA GSFC Laboratory for Atmo- IR satellite images.
spheres, each pixel of the camera CCD was filled by the
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