TRANS-IONOSPHERIC PULSE PAIRS (TIPPS) - THEIR GEOGRAPHIC DISTRIBUTIONS AND SEASONAL-VARIATIONS

Since November 1993 the Blackbeard instrument aboard the ALEXIS satell ite has detected pairs of pulses in the VHF band, known as Trans-Ionos pheric Pulse Pairs (TIPPs). These pulses exhibit dispersion consistent with a source of sub-ionospheric origin. As of January 1997 over 850 TIPPs have been detected. The source of these emissions still remains a mystery, although it is believed that TIPPs are in some way related to thunderstorms as such storms provide a strong sub-ionospheric sourc e and produce radiation in the same frequencies observed by Blackbeard . In an attempt to establish this connection we compare the geographic occurrence of TIPPs to that of lightning flashes observed from space by the Optical Transient Detector (OTD) on the Microlab-1 spacecraft. TIPP data run from 2 November 1993 to 19 November 1996. OTD data run f rom 1 May 1995 to 30 November 1996. The geographical occurrence of TIP Ps and that of lightning flashes is strongly correlated. TIPPs occur l ess frequently during the winter months and their region of production moves southward in the North American sector similar in behavior to l ightning activity.