X. Qiea,4, X. Konga, G. Zhanga, T. Zhanga, T. Yuana, Y. Zhoua,
Y. Zhanga, H. Wanga, A. Sunb
2004
Abstract
 Most of the intracloud (IC) flashes occurred in the lower part and only a few
occurred in the upper part of the thunderstorm.
 As most of the graupels fell to the ground in the dissipating stage of the storm,
the lower positive charge in the thunderstorm tripole decreased, and negative
cloud-to ground (CG) flashes overwhelmingly dominated.
 The lower positive charge was estimated to be located at about 1.7 km above the
ground, while the main negative charge was located higher than about 2.2 km
above the ground.
Qinghai–Tibetan Plateau.
Six stations cover an area of about 11x8 km^2.
Site 1 is located at (101°35’E, 37°303’N).
The altitude of this area is about 2650 m above sea level.
Fig. 1. Sketch map of the measurement sites. Site 1 was located at .The mean elevation is 2650 m above sea level.
The thunderstorm on August 4, 2002 developed locally southwest of Site
5 (in the direction of Site 4) at 18:10 Beijing time (BT) and then moved
very slowly northeastward toward Site 1. The thunderstorm was just over
Site 5 during its mature stage and died out near Site 5 in the direction of
Site 1.
AND
The downward directed field is defined as positive
according to the “atmospheric electricity “ convention, i.e.,
positive field corresponds to a positive charge overhead.
Instrumentation
 Field mill
 Slow antenna and Fast antenna systems (with 6 s and 2 ms
with a frequency bandwidth of 2 MHz and 5 MHz,
respectively)
 A high-speed digital camera (the sensor is 256x256 CCD array)
The evolution of surface E-field and Efield change revealed a tripole charge
structure of storm in the developing
and mature stage of the storm, and the
lower dipole was the main source of
lightning flashes. This suggested that
the charging in the lower part of the
storm was more vigorous than that in
the upper part.
Fig. 2. The evolution of surface electric field at Site 5 (a) and flash rate on August 4, 2002. (b)
Total flash (IC and CG), (c) positive CG flash, (d) negative CG flash, (e) lower level IC flash
and (f) possible upper level IC flash. All the CG flashes are marked by arrows in (a). The
downward-directed field is defined as positive according to the atmospheric electricity sign
convention, i.e., positive field corresponds to a positive charge overhead.
Flash A
The two IC discharge
processes produced
negative-going E-field
changes at Site 5,
which is opposite to the
negative return stroke,
indicating both IC
processes occurred
between the lower dipole,
which is consistent with
the optical observation.
Fig. 3. Surface electric field changes and relative optical intensity produced by flash A at 19:02:28. (a) Slow
E field change at Site 5, (b) slow E-field change at Site 1, (c) fast E-field change at Site 5, and (d) relative
optical intensity from high-speed digital camera at Site 1. The discharge was just overhead Site 5 and 5 km
away from Site 1.
The hails or graupels at the base of the cloud had a very important
effect on the positive surface E-field. After most of the hail or graupel
fell to the ground, the positive surface E decreased rapidly and became
negative in 2 min.
0.85x10^5 m/s,
0.85x10^5 m/s,
0.85x10^5 m/s and
0.95x10^5 m/s
from left to right, in the
frame of 333 ms,
Fig. 4. One of the video pictures at 333 ms (the same 0 ms reference as in Fig. 3) showing the stepped leader
progression of Flash A based on high-speed digital camera with 1 ms time resolution.
Fig. 5. The time-expanded surface electric field change produced by the return stroke of Flash A recorded by fast
antenna at Site 1. The 4 peaks, marked by a, b, c, and d, are produce by 4 possible grounded branches.
Flash B
Fig. 6. Same as Fig. 3 but for Flash B at 19:08:48. The discharge was about 3 km form Site 5,
and 7 km from Site 1.
1.1x10^5 m/s
Fig. 7. One of the video frames during the stepped leader progression at 206 ms (same 0 ms reference as in
Fig. 6), which showed large horizontal developing component with multiple channel branches.
Conclusion
 The thundercloud was a normal-polarity tripole with a larger-than-usual lower
positive charge region in the mature stage of the thunderstorm. The IC flashes
occurred between charges in the lower dipole more frequently than between
charges in the upper dipole.
 Negative CG flashes dominated overwhelmingly in the dissipating stage as the
magnitude of the lower positive charge became much smaller.
 The slow antenna and high-speed digital camera observation showed that
long-duration IC processes often occurred just before and after the negative
CG flash.
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Charge structure