Award Abstract #0619941
Development of ADELE--Airborne Detector for Energetic Lightning Emissions

NSF Org:	ATM Division of Atmospheric Sciences
Initial Amendment Date:	September 5, 2006
Latest Amendment Date:	September 5, 2006
Award Number:	0619941
Award Instrument:	Standard Grant
Program Manager:	Bradley F. Smull ATM Division of Atmospheric Sciences GEO Directorate for Geosciences
Start Date:	September 15, 2006
Expires:	August 31, 2009 (Estimated)
Awarded Amount to Date:	$467220
Investigator(s):	David Smith dsmith@scipp.ucsc.edu (Principal Investigator) Joseph Dwyer (Co-Principal Investigator)
Sponsor:	University of California-Santa Cruz 1156 High Street SANTA CRUZ, CA 95064 831/459-5278
NSF Program(s):	MAJOR RESEARCH INSTRUMENTATION
Field Application(s):	0000099 Other Applications NEC
Program Reference Code(s):	OTHR, 4444, 1525, 1522, 1189, 0000
Program Element Code(s):	1189

ABSTRACT

The Airborne Detector for Energetic Lightning Emissions (ADELE) is being developed to study x-ray and gamma-ray emissions from within and around thunderstorms. These phenomena include terrestrial gamma-ray flashes (TGFs), minute-scale enhancements in gamma-ray background, and intense bursts of lower-energy hard x-rays associated with lightning leaders. ADELE will consist of three modules to be mounted at the front, top, and bottom of a research aircraft capable of flight around and possibly over thunderstorms. The modules will contain several types of scintillation counters, some optimized for performance at low to medium count rates and others optimized to capture data at the extremely high fluxes and count rates predicted when flying near a thunderstorm in the path of TGF emission. The combination of geometrical effects and spectra observed by the modules will help distinguish both the altitude of origin and direction of propagation (direct or backscattered) of the radiation. The primary technological developments for ADELE involve the extremely fast sampling and resulting large data handling task associated with the need to observe extremely high count rates predicted during TGFs observed from close quarters.

The intellectual merit of this work derives from the fact that few x-ray/gamma-ray observations have been made at thundercloud altitudes where the largest electric fields exist and many of these emissions are thought to originate. Relativistic runaway, which produces MeV-range gamma-rays, is a leading candidate for the basic lightning-initiation process. It also is a candidate mechanism for generating TGFs, which may themselves turn out to be a signature of initiation. But (with one possible exception), TGFs have only been seen from orbit, where only gamma rays emitted at the very highest levels of the storm, near cloud tops, can escape and be observed. If gamma rays are being emitted during the much more frequent initiation of lightning lower in storms they cannot be observed by detectors at the surface or in orbit. ADELE will provide a permanent facility for hard x-ray and gamma-ray observations that can be deployed to the most interesting altitudes (above and alongside thunderclouds) and to a variety of sites for joint observations with ground-based systems. It will also have the largest dynamic range and highest throughput of any such instrument on the ground, in the air, or in space, opening up a new discovery space for understanding these emissions.

The broader impacts of the development and eventual operations of ADELE are invaluable

hands-on experimental training to graduate and undergraduate students at the University of California, Santa Cruz, the Florida Institute of Technology, and the other institutions collaborating on future science missions. The high-speed digitization and large data throughput of the electronics to be developed will be of interest to other users of scintillation detectors. ADELE data will demonstrate for the first time the true energy content of TGFs, allowing a determination of whether the ionization they produce has any impact on atmospheric chemistry and climate.

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