One-month periodicity in lightning activity and tropical cloud variations

Summary form only given. It has been recognized that lightning activity is an excellent proxy of atmospheric circulation in thunderstorm. GEON, the global ELF observation network, is the first continuously-operated lightning observation network covering while globe with uniform sensitivity for charge moment change. Here we show that in the period from February to June 2004 the variation of the number of lightning strokes in Asia Maritime Continent (hereinafter: MC) shows one-month oscillation clearly correlated with Outgoing Longwave Radiation (OLR) in Western Pacific Warm Pool (hereinafter: WPWP) with amplitudes of few 10s of percent but without apparent phase shift. In other words, when the thunderstorm activity in MC is enhanced, the OLR in WPWP becomes large, namely, less cloudy. Moreover, OLR in most part of other tropical region, such as those in Africa, Pacific Ocean and Atlantic Ocean, shows prominent negative correlation with the number of lightning strokes in MC, implying the activities of thunderstorms in tropical regions oscillate in the same phase. It was also found that such global oscillation seems to be synchronized with parameters that reflect solar activity, such as galactic cosmic ray or F10.7 index, but shifted by about 8 days. These results are probably related to the phenomena reported by Takahashi et al. (ACP in 2010), namely, a 27-day variation of OLR in WPWP, which is only seen in the solar maximum years of the 11-year cycle, for 3 cycles.