SPRITES 99 YUCCA RIDGE FIELD STATION
FMA Research
JD 99226 14 AUGUST 1999
PRELIMINARY SPRITE LOG
The following is a very preliminary listing of the times of sprites imaged at the
Yucca Ridge Field Station. These are based solely on real-time visual inspection of
the video monitoring system. There are most likely some additional sprites not listed
and not all those below may in fact be sprites. All times are UTC. Times are likely
to be within ±5 seconds of actual time.
SUMMARY: Convection over the north central US was muted. However, a short wave on the
jet stream moving through Montana and Wyoming spawned a few late afternoon storms. One
cluster maintained itself beyond sunset and continued to propagate east-southeast
through Montana, Wyoming and into South Dakota. The cell had reflectivities of 55-60 dBZ
for several hours after sunset and only slowly weakened after midnight. Flash rates were
above 1000 /hr and the positive rate was under 10% almost all the time. The system
produced a steady stream of very bright sprites for more than a two hour period. The
sprites started when the percent +CGs were less than 3%. The sprite activity actually
stopped when the system began to weaken after 0700ZX, even though the + positive was
rising to near 10%. The storm was also unusual in that the cause of its long persistence
was not obvious (it was still producing lightning in eastern SD at damn). There were a
fair number of Perseid meteors imaged. This storm was classical of the small storms in
the northern High Plains which produce sprites even though not particularly large nor
electrically active. They tend to occur with northwest flow aloft.
The balloon mission was scrubbed due to strong winds. Custer saw some sprites before
being blocked by clouds. The MM5 forecast run ran without problems.
Total TLEs from Yucca Ridge This Campaign: 1656
(S) = Sprite; (E) = Elve; (B) = Blue Jet; (CF/CG) = Cloud/Ground flash; (M)=Meteor
JD 99226 - 14 AUGUST 1999
0400. Start LLTV Observations
0450.20 [S+]
0500.27 [S]
O515.40 [S+]
O517.30 [S?]
O524.10 S+]
O534.01 [S]
0538.52 [S+]
0550.55 [S]
0558.04 [S]
0603.26 [S+]
0612.10 [S]
0620.40 [S-]
0623.35 [S+]
0627.58 [S]
0630.27 [S+]
0632.10 [S-]
0635.00 [S+]
0635.57 [S]
0639.29 [S+]
0651.20 [S]
0654.20 [???]
0710.45 [S-]
0713.16 [S-]
0814 End LLTV Observations