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Journal of Atmospheric Electricity, 25, No.2, 2005, 55 – 68
Diurnal variations of electric activity of global thunderstorms deduced fromOTD data. M. Hayakawa1, M. Sekiguchi1, A.P. Nickolaenko2 1
The University of Electro-Communications, Chofu-shi, Tokyo, Japan Email:
[email protected] 2 Usikov Institute for Radio-Physics and Electronics, Ukrainian National Academy of Sciences, Kharkov, Ukraine, Email:
[email protected]
Abstract General properties of the global thunderstorm activity are obtained from the OTD diurnal data. It is shown that variations of the net number of lightning flashes observed from the space support common geophysical concept of the thunderstorm development. Close similarity exists between the old WMO data and modern optical observations. Key words: Global lightning flash rate, OTD observations, Diurnal variations of lightning activity, Carnegie curve. -----------------------------------
Fig. 1. Spatial distribution of the global lightning activity for each hour of a day (UT). ------------------------------------2.1. Latitudinal distribution We show the latitudinal distribution of the global lightning activity in Fig. 2 in a traditional form: the cumulative number of strokes is given here as a function of latitude summed over the day span. To obtain the distribution, we computed cumulative number of flashes for the whole day and summed the result over the longitudes, i.e. with the fixed latitude. Thus the cumulative number of strokes was obtained for the given latitude varying in correspondence with 2.5° resolution of initial data. The plot shown in Fig. 2 practically coincides with the data published by Christian, et al., [2003] thus indicating on internal correspondence of OTD data sets.
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Fig. 3. Daily variations of distribution lightning strokes within the 2.5° latitudinal belts.
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Fig. 3a. Cumulative latitudinal distribution of lightning strokes (additional).
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Two distinct zones are seen in Fig. 2: the narrow near-equatorial activity is concentrated in tropics with maximum number of flashes, and a wider, probably bimodal, distribution is observed over the middle latitudes having a smaller peak value. By applying maps corresponding to different moments of time, we can single out the south – north drift of sources, see Fig. 3.
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Universal Time hr Fig. 4. Latitudinal dynamics of lightning activity, no daily drift is apparent The contour map of the global lightning activity is shown in Fig. 3 surveying the latitudinal redistribution of flashes during the day. Time (UT) is depicted on the abscissa in hours, the latitude is plotted on the ordinate (south is at the bottom), and the cumulative number of flashes is shown by color computed in the given latitude belt (integrated over the longitudes). The map reveals three distinct areas. The first one is marked by tilted line ‘Australia – Asia’. Activity here tends to drift from the Northern Australia (around 6 hr UT) through Indonesia to Himalayas and Karakorum (8 – 12 hr). The second zone occupies the central dark area representing African storms (8 – 20 hr). These are characterized by a very high level and an absence of distinct north–south motion, except an isolated maximum around Madagascar at 14 hr UT. The third area contains the activity drifting from the South to the North America (18 – 24 hr UT) shown by the second tilted line in Fig. 3. The relevant routes could be recognized when we turn to the maps of Fig. 1, however, Fig. 3 shows these trends more clearly. Optical observations show that the north – south diurnal drift is pertinent to Asian and American lightning activity, while African storms occur within the same latitudinal belt. Probably, the feature reflects geometrical structure and positioning of continents over the globe.
