FAST LOW-LEVEL LIGHT-PULSES FROM THE NIGHT-SKY OBSERVED WITH THE SKYFLASH PROGRAM

This paper presents further discussion of and new data on fast subvisu al increases in the luminosity of the night sky described in our previ ous papers. A detailed technical description of the simple telescopic photometers used in the project SKYFLASH and their mode of operation i ncluding the detection of polarized Rayleigh-scattered flashes is prov ided. Distant lightning storms account for many of the events, and the complex relations between short and long luminous pulses with and wit hout sferics are shown by examples from a new computerized data system , supplemented by two low-light-level TV cameras. Of particular intere st are the previously observed ''long'' events having a slow rise and fall, 20-ms duration, and showing small polarization and no coincident sferic. A group of such events on September 22-23 during the invasion of U.S. coasts by Hurricane Hugo, is discussed in detail. The recentl y observed ''plume'' cloud-top-to-stratosphere lightning event is sugg ested as a possible source type for these flashes. An alternative sour ce may be exploding meteors, recently identified during SKYFLASH obser vations by low-light-level television techniques as the origin of some sky-wide flash events described herein.