http://hdl.handle.net/10136/80 Community home page Search the Channel search http://dspace.nmt.edu/dspace/simple-search http://hdl.handle.net/10136/350 Title: New Mexico thunderstorms observed by the Lightning Mapping Array: An overview of one season <br/> <br/>Authors: Thomas, R J; Behnke, S; Hamlin, T; Harlin, J; Krehbiel, P; Rison, W <br/> <br/>Description: Poster http://hdl.handle.net/10136/346 Title: Thunderstorm Charge Studies Using a Simple Cylindrical Charge Model, Electric Field Measurements, and Lightning Mapping Observations <br/> <br/>Authors: Krehbiel, P.; Rison, W.; Thomas, R.; Marshall, T.; Stolzenburg, M.; Winn, W.; Hunyady, S. <br/> <br/>Description: Poster http://hdl.handle.net/10136/92 Title: An Analysis of the Electric Field Change Produced by Lightning <br/> <br/>Authors: Krehbiel, Paul R. <br/> <br/>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. <br/> <br/>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.