The lightning data were obtained from the Global Atmospherics, Inc., Tucson, Arizona. Data handling at Texas A&M University is under the direction of Jerry Guynes and Robert White and we thank them for their assistance. We thank the United States Air Force for supporting Major Huffines during this research. Special thanks go to Barbara Orville for her editing assistance. This project is part of a lightning program supported by the National Science Foundation (ATM-9806189) and the National Oceanic and Atmospheric Administration (Cooperative Agreement NA87WA0063).
Changnon, S. A., 1985: Secular variations in thunder-day frequencies in the twentieth century. J. Geophys. Res.,90, 6181–6194.
——, 1988a: Climatography of thunder events in the conterminous United States. Part I: Temporal aspects. J. Climate,1, 389–398.
——, 1988b: Climatography of thunder events in the conterminous United States. Part II: Spatial aspects. J. Climate,1, 399–405.
——, 1989: Relations of thunderstorms and cloud-to-ground lightning frequencies. J. Climate,2, 897–921.
——, 1993: Relations between thunderstorms and cloud-to-ground lightning in the United States. J. Appl. Meteor.,32, 88–105.
——, D. Changnon, and R. Pyle, 1988: Thunder event and cloud-to-ground lightning frequencies. J. Geophys Res.,93, 9495–9502.
Cummins, K. L., M. J. Murphy, E. A. Bardo, W. L. Hiscox, R. B. Pyle, and A. E. Pifer, 1998: A combined TOA/MDF technology upgrade of the U.S. National Lightning Detection Network. J. Geophys. Res.,103(D8), 9035–9044.
Krider, E. P., R. C. Noggle, and M. A. Uman, 1976: A gated, wideband magnetic direction finder for lightning return strokes. J. Appl. Meteor.,15, 301–306.
——, ——, A. E. Pifer, and D. L. Vance, 1980: Lightning direction finding systems for forest fire detection. Bull. Amer. Meteor. Soc.,61, 980–986.
MacGorman, D. R., M. W. Maier, and W. D. Rust, 1984: Lightning strike density for the contiguous United States from thunderstorm duration records. NUREG/CR-3759, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, D.C., 44 pp. [Available from NSSL, 1313 Halley Circle, Norman, OK 73609.].
Mach, D. M., D. R. MacGorman, W. D. Rust, and R. T. Arnold, 1986:Site errors and detection efficiency in a magnetic direction-finder network for locating lightning strikes to ground. J. Atmos. Oceanic Technol.,3, 67–74.
Orville, R. E., 1991: Lightning ground flash density in the contiguous United States—1989. Mon. Wea. Rev.,119, 573–577.
——, 1994: Cloud-to-ground lightning flash characteristics in the contiguous United States: 1989–1991. J. Geophys. Res.,99 (D5), 10 833–10 841.
——, and A. C. Silver, 1997: Lightning ground flash density in the contiguous United States: 1992–95. Mon. Wea. Rev.,125, 631–638.
Reap, R. M., and R. E. Orville, 1990: The relationships between network lightning locations and surface hourly observations of thunderstorms. Mon. Wea. Rev.,118, 94–108.
U.S. Department of Commerce, 1975: Federal Meteorological Handbook. No. 1. NOAA/National Weather Service, 256 pp.