Collaborative Research: Balloon Campaign to Quantify Thunderstorm Effects on the Global Electric Circuit

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This grant would quantify the role of thunderstorm activity as a driver of Earth's global electric circuit. The required measurements of the fair weather vertical electric field and current density would be obtained over a period of several days. The time series of the fair weather electric field and vertical current density at high altitude, above weather, orographic, and other influences, obtained by using the well-proven technique of double Langmuir probes on a stratospheric balloon platform would be compared to properties of the contemporaneous global thunderstorm activity. With the recent development and characterization of ground-based global lightning detection networks, it is now possible to retrieve global thunderstorm area, and its uncertainty, on a timescale of minutes. The objective of the proposed work is to test the hypothesis, at unprecedented accuracy and depth, that thunderstorm activity is the primary driver for the global circuit. intellectual merit. Nearly 100 years after C. T. R. Wilson suggested thunderstorms are an important driver of the global electric circuit. Achieving this goal would require a quantitative evaluation of the drivers for the fair weather electric field. This goal has remained elusive due to a long-standing difficulty in measuring the various candidates: thunderstorms, electrified clouds, or other middle atmosphere current sources. Furthermore, there has been only very limited observational work on the short time response of the global circuit to variations in the thunderstorm source. This proposal will test thus connection hypothesis, at times scales of order 100 seconds. A straightforward comparison of the two time series of global active thunderstorm area and vertical fair weather electric current density would enable significant progress on this classic question. Because the high time resolution measurements are a substantial advance over previous investigations, this work will likely lead to new insights and questions about the global electric circuit. A graduate student's dissertation research would be supported as a result of the proposed effort. Moreover, an undergraduate student participating in the sub-contract effort relating to the flight deployment of the balloons each summer would be supported as well.Students will be trained in development and calibration of instrumentation, field campaign logistics, collating and analyzing multiple types of data, and modeling as a means to understand measurements. This grant would provide important measurements, and likely also insights, for ongoing efforts to model the global electric circuit. The anticipated improvement in our understanding of the thunderstorm driver component is also critical to achieving progress on understanding other global electric circuit variations such as from solar wind effects, solar protons events, or large scale atmospheric temperature change. If a robust relation between global thunderstorm activity and stratospheric vertical current density is identified as expected from the grant, this would open the possibility to the prospects of being able to monitor total global thunderstorm activity using a small number of instrumented balloons.