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Krehbiel, Paul R. >
Please use this identifier to cite or link to this item:
http://hdl.handle.net/10136/92
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| Title: | An Analysis of the Electric Field Change Produced by Lightning |
| Authors: | Krehbiel, Paul R. |
| Keywords: | Atmospheric Physics
Lightning
Electric Field |
| Issue Date: | Dec-1981 |
| Publisher: | Geophysical Research Center, Research and Development Div., New Mexico Tech |
| Citation: | Geophysical Research Center Report T-11, 1981 |
| Series/Report no.: | GRC Report
T-11 |
| Abstract: | Ten cloud-to-ground (CG) flashes, 21 intracould (IC) flashes and 3
hybrid flashes from five storms have been analyzed in detail to determine
the locations of the lightning charge and charge transfer. This has been
done using simultaneous observations of the electrostatic field change at
9-11 observing locations on the ground beneath and around the storm. Some
of the results are as follows: a) The (negative) charge sources for the
initial strokes of CG flashes were found to coincide with strong
precipitation in the part of the storm having the greatest vertical
development, at temperatures usually between -15 and -20 degrees C; b)
Time-resolved analyses of first and other strokes initiated by stepped-type
leaders showed that the leader and stroke sources were co-located; c) The
charge sources for subsequent strokes of multi-stroke flashes often
overlapped that of the initial stroke, as if the initial stroke had only
partially discharged that part of the cloud; d) For two CG flashes where
overlap did not occur, the initial stroke removed a large amount of charge
from the cloud and the interstroke interval after the stroke was quiet, as
if the stroke had reduced the large-scale electric stress in the cloud; e)
The later strokes of CG flashes tended to originate in regions of weaker
precipitation echo that were horizontally displaced from the earlier stroke
sources; f) when not quiet, the interstroke charge transfer was nearly
horizontal (or affected by the leader for the next stroke), even for the
flash which Rustan et al. (1980) reported the interstroke activity to be
almost vertical and at high altitude in the cloud; g) The charge transfer
of IC flashes was nearly vertical on average, and upward-divergent from
within or near strong precipitation to above the precipitation. Positive
charge was effectively lowered or negative charge was raised; h) Analysis
of the first 15 discharges in a small, developing storm showed that the
negative charge sources of the IC flashes remained at the same temperature
levels throughout the 7 minute interval of the flashes, between -10 and -20
degrees C, and were co-located with the negative charge sources of two CG
discharges that occurred toward the end of the sequence; i) Onset of the
lightning activity in this storm followed vertical growth of the 30 dBZ
echo top from the -10 degree C level to -20 or -30 degrees C over a
6-minute time interval. 45 dBZ reflectivity values were detected to -20
degrees C at the time and in the vicinity of the first discharges in the
storm; j) the lightning discharged the storm at an average rate of 200 mA
at the beginning, and the 400-600 mA by the end of the 15-discharge sequence.
The moment discharge rate was found to increase in an approximately linear
manner with time, from values of about 0.5 Coul-km/sec at the beginning and
2.0 Coul-km/sec at the end of the sequence; k) Six IC discharges were
analyzed from an 8 second time interval in a storm whose discharge rate was
60/min and whose wind field evolution had been determined by Lhermitte.
The discharges produced small but measurable moment changes, 1-5 Coul-km
(vs. 15-200 Coul-km changes for the other IC flashes studied), and were
located both where an upper-level downdraft entered strong precipitation
and in the updraft region. The comparison was subject to uncertainties
associated with the time skew of the wind field measurements and coordinate
transformation however; 1) horizontal IC discharges were observed in the dissipating stages of a large storm system, and for the 10th flash of the
15-discharge sequence. The charge transfer of vertical intracloud flashes tended to develop horizontal components in the final part of the discharge,
and in one large intracloud flash this resembled the interstrsoke activity
of CG flashes – in agreement with the observations of Kitagawa and Brook
(1960); m) The dissipating-storm flashes removed positive charge from just
above the radar brightband and also produced one or two positive strokes to
ground as they propagated through the large storm system; this result
suggested that a different, lower-rate electrification process was
occurring in the dissipating storm.
The results indicate that the lightning charge sources reflect the
location of net negative charge in the storm, and agree with Wilson’s
vertical dipole model that positive charge is located above the negative in
growing storms. The negative charge sources are more concentrated that the
positive, and are mostly (but not entirely) associated with strong
precipitation between temperature levels of -10 and -20 or -25 degrees C. |
| Description: | This report reproduces the author's Ph.D. Thesis submitted to the Department of Pure and Applied Physics at the University of Manchester Institute of Science and Technology (UMIST), Manchester, England, with only a few minor corrections to the original manuscript. |
| URI: | http://hdl.handle.net/10136/92 |
| Appears in Collections: | Krehbiel, Paul R.
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Files in This Item:
| File |
Description |
Size | Format |
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| KREHBIEL PT 2.pdf | Volume II | 17952Kb | Adobe PDF | View/Open | | KREHBIEL PT 1.pdf | Volume I | 37633Kb | Adobe PDF | View/Open |
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