LIGHTNING AND CLIMATE: THE WATER VAPOR CONNECTION C. Price (1) and M. Asfur (2) (1) Tel Aviv University, Geophysics and Planetary Sciences, Ramat Aviv, 69978, Israel, (cprice@flash.tau.ac.il ) (2) As in (1), but e-mail: mustafa@flash.tau.ac.il ABSTRACT The amplitude of future global warming will depend strongly on how upper tropospheric water vapor (UTWV) changes in response to greenhouse gas forcings. However, monitoring long-term changes in water vapor is very difficult, and no single method is in place, or planned, to deal with this problem. In this paper new evidence is presented showing the close link between UTWV variability and global lightning activity. Continental deep convective storms that transport large amounts of water vapor into the upper troposphere dominate the variability of global UTWV, while also being the storms that produce the majority of our planet’s lightning. Furthermore, integrated global lightning activity can be continuously observed from a single location on the earth’s surface via the Schumann Resonances (SR), an electromagnetic phenomenon in the atmosphere produced by global lightning. INTRODUCTION Tropospheric water vapor is a key element of the earth’s climate. It has direct effects as a greenhouse gas, as well as indirect effects through the interaction with clouds, aerosols, and tropospheric chemistry. Small changes in upper tropospheric water vapor (UTWV) have a much larger impact on the greenhouse effect than small changes in water vapor in the lower atmosphere [1]. Both climate models and observations support the idea that higher temperatures will increase the amount of UTWV [2, 3]. Recent observations indicate that UTWV may already be increasing [4]. Some climate models predict UTWV to increase by 20% for every 1 K increase in surface temperatures [3]. This sensitivity is greater than that predicted by the Clausius-Clapeyron equation (6% per 1 K at 300 K) since UTWV is influenced not only by temperature, but also by transport from the lower atmosphere. As a result, the water vapor feedback could amplify the surface temperature change due to a doubling of carbon dioxide by 60% [5]. UTWV is transported aloft by deep convection, to be later redistributed zonally and meridionally in the upper atmosphere [6]. The stronger the updrafts, the deeper these cloud and precipitation particles are transported into the upper levels of clouds. Not only does the intensity of the convection influence the volume of water transported aloft, but it simultaneously influences the electrification processes in these convective clouds. The eventual sublimation of the large ice-filled anvils results in a major source of water vapor into the upper troposphere [7]. In this paper a new diagnostic is presented for studying global UTWV variability. It involves using the global atmospheric electric circuit that is regulated by global lightning activity. The use of the global electric circuit to monitor climate variability has previously been suggested [8]. However, previous studies focused on using the global electric circuit and lightning activity to study tropical and global surface temperature changes. Here we build on a previous study by [9] and consider the connection between global lightning and UTWV. METHODOLOGY A relatively simple and cheap method for continuously observing global lightning variability is via the Schumann Resonance (SR) [10]. Each lightning discharge emits electromagnetic radiation at all frequencies and in all directions. The lower the frequency of the radiation, the less the attenuation of the electromagnetic waves in the atmosphere, and the greater the propagation distance. At extremely low frequencies (ELF: 1Hz<f<100Hz) the radiation can propagate a few times around the globe before dissipating. This is achieved by electromagnetic waves being trapped in the earth-ionosphere waveguide. The resonant frequencies are excited by lightning discharges in the lower atmosphere, and since there are approximately 50- 100 lightning flashes per second around the globe, the variability of the SR intensity represents a continuous measure of the variability of global lightning activity [11]. Simultaneous measurements on opposite sides of the globe show remarkable agreement (Figure 1), implying that a single station can be used to track global lightning variability. At present a SR observation site in the Negev Desert, Israel, is continuously providing magnetic and electric field data. There are a number of other stations around the world that also continuously monitor the SR, including Rhode Island (USA), Japan, Hungary,