On the basis of data from 3 days in 1978 this paper investigates the relation between thunderstorm dimensions and electrical activity to determine the relative importance of thunderstorm size and thunderstorm environment on the sferics rate. Sferics were recorded continuously by a wide-band (100 + 50 kHz) crossed-loop radio direction finder located at the radar site' precipitation data during the corresponding period came from the radar volume scan. The number of sferics associated with specific storms and recorded in 5-min intervals varied from a few tens to a few thousands, depending on the dimensions of the source storm and on its distance from the sferics receiver. For four thunderstorm situations this variation was reduced to a small scatter, with standard deviations corresponding to factors of 1.17-1.47, by fitting the data with the empirical relation' S oc A" x I(F n x 10 -:r, where S is the observed number of sferics per 5 min, A the cross-sectional area, H the height, and r the range of the storm. For three of the four sets of data analyzed, x was just over unity, giving a nearly linear relation between the sferics rate and the storm's area' for a supercell storm the relation was higher than linear. For thunderstorms between 50 and 300 km distant the number of recorded sferics decreased exponentially, by a factor of about 2 every 45 km, or with z = 0.0068 + 0.0011 per km. Thunderstorm height appeared the dominant parameter determining the rate of electrical activity' values of y for the 3 days were between 0.13 and 0.28 per km, the greater effect of thunderstorm height was found associated with a stronger wind shear in the 7.5-to 12-km layer. 1. INTRODUCTION Until recent years, few studies related the frequency of lightning to the radar-observed thunderstorm features. Vonnegut and Moore [1959] have reported the high rate of electrical activity associated with large thunderstorms, and results of Shackford [1960] indicate that the lightning rate increases significantly with the height reached by intense precipitation. More recently, Fitzgerald [1978] considered the existence of radar reflectivity levels between 25 and 30 dBZ the necessary threshold for the onset of lightning, and Grosh [1978] reported that the period of the maximum lightning rate coincided with the time of maximum storm height and the maximum of precipitation-filled volume. In a detailed analysis of severe thunderstorms, Rust et. al. [1981] found that the lightning rate coarsely followed the Doppler-derived updraft velocity, and Williams [1985] reported that the number of cloud-to-ground lightning flashes increased as the fifth power of thunderstorm size. [1973] and Larsen and $tansbury [1974] compared radio-located lightning to the radar-observed precipitation pattern and found cores of intense precipitation that reached over ? km height, associated with the bearings of the observed lightning. At the McGill Radar Weather Observatory, Larsen Results of Marshall and Radhakant [1978] support the strong correlation between the occurence of ...
Triangulation from paired sferics (100 ± 50 kHz) received at stations 57 km apart gave 42 map locations of lightning flashes belonging to a thunderstorm well-defined on weather radar. This storm was one of many in a long line along the leading edge of a band of light stratiform precipitation (snow above 3 km). The band was 9 km high and 60 km wide, and the storms were embedded in it. The convective region of the storm studied had a north-south extent of 20 km, the east-west extent averaging two-thirds as much. Cumulus heights progressed from 3 km on the west to 7 ± 1 km on the east. Two-thirds of the lightning flashes were in the convective region. The remaining third were in 160 km 2 of the light stratiform precipitation immediately west of it. RÉSUMÉ La triangulation d'atmosphériques conjuguées (100 ± 50 kHz) reçues à des stations distantes de 57 km a donné sur la carte 42 endroits d'éclairs appartenant à un orage bien défini sur radar météorologique. Cet orage était l'un des nombreux orages observés le long du bord antérieur d'une bande de précipitations stratiformes légères (neige au-dessus de 3 km). Cette bande avait 9 km de hauteur sur 60 km de largeur et les orages y étaient enchâssés. La région convective de l'orage étudié avait un axe nord-sud de 20 km et un axe est-ouest représentant les deux tiers de cette distance. La hauteur des cumulus allait de 3 km à l'ouest à 7 ± 1 km à l'est. Les deux tiers des éclairs ont eu lieu dans la région convective. Le reste s'est produit dans 160 km 2 de la bande de précipitations stratiformes légères immédiatement à l'ouest de cette région.
An empirical relationship between radar reflectivity levels exceeding 32 and 40 dBZ at a height of 6 km and sferics data is used to generate maps that indicate regions of thunderstorms. These radar maps serve as ground truth when compared with colocated GOES visible and infrared imagery. A threshold computed to equalize the radar and satellite thunderstorm areas delineates the region in visible‐IR space that is most probably associated with electrical activity. The locations of satellite‐delineated storms beyond radar range, on the synoptic scale, show good agreement with sources of lightning determined from sferics detectors. The skill of the extrapolation of these areas for short‐range forecasting is discussed.
A technique has been developed for generating “shadow maps” (the shadow that an array of showers would cast on the earth's surface) in the microwave radiation from a hypothetical source in a geostationary satellite at specified azimuth and altitude. The input data for this technique are weather‐radar records on digital magnetic tape. To describe and demonstrate the technique and its intended use, this paper contains just one shadow map at high resolution (approaching that of the radar record), one sequence of maps at a lower resolution covering the three hours of one storm‐array passage, and an analysis of the effect that one passage would have had on an earth station and on various path‐diversity pairs. We hope to generate high‐resolution maps for a whole season (summer 1976) and to use them to catalogue and compare the various storm‐array passages that would have a significant effect on slant‐path microwave links.
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