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LIGHTNING PHENOMENOLOGY 23 1 Lightning Phenomenology Richard E. Orville State University of New York at Albany INTRODUCTION Severe weather phenomena that disrupt our lives include tornadoes, hail, high winds, hurricanes, snowstorms, and lightning. It is not well known that in most years, lightning ranks as the number one killer, followed closely by tornadoes. Much less dramatic than a tornado passing through an area or a severe snowstorm that paralyzes a city, a lightning ground strike can quickly kill one or two people in less than a second with little or no warning. Annually in the United States about 100 people are killed by lightning strikes, and reliable estimates for the world would be in the thousands. Lightning on a global and regional scale is an area of science that brings together the interests of the atmospheric physicist, chemist, and meteorologist in an effort to learn its characteristics. The phenomenology of lightning involves the frequency of lightning observed over large spatial and time scales. It involves the maximum and average flashing rate per unit area and the variation of flash characteristics with location and storm type. Studies of lightning phenomenology can now be discussed in terms of both satellite and ground-based observations. With the use of satellites, we obtain data on the global lightning flash rates and the distribution of lightning with respect to the continents and oceans. With the extensive use of ground-based observations, we can determine the flashing rates and flash characteristics of individual storms. In addition, we can monitor the variations of the ground flashes as a function of location and storm type. SATELLITE OBSERVATIONS OF LIGHTNING Optical Detectors Significant advances in obtaining a better estimate of global flash rates and distribution have occurred as the result of satellite lightning observations in the last decade. Turman (1978,1979), Turman et al. (1978), and Turman and Edgar (1982), using optical detectors on the Defense Meteorological Satellite Program (DMSP) satellites, showed the distribution of lightning at dawn and dusk for a period of 1 year. One example of this recent result is shown in Figure 1.1, where the dusk lightning distribution for November-December 1977 demonstrates the spatial distribution and the rate. Note that the lightning is found mostly in the southern hemisphere, but significant activity still occurs in the northern hemisphere. The latitudinal and seasonal variation of the lightning activity is best shown by examining Figure 1.2 (Kowalczyk, 1981; Turman and Edgar, 1982). In this histogram, the lightning rate has been summed over
LIGHTNING PHENOMENOLOGY 24 Figure 1.1 Lightning activity recorded by a DMSP satellite for the period November 6-December 2, 1977. The dawn and dusk distribution as well as the lightning rates can be compared. From Turman and Edgar (1982) with permission of the American Geophysical Union.