首页|Radar Diagnosis of the Thundercloud Electron Accelerator
Radar Diagnosis of the Thundercloud Electron Accelerator
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NSTL
Amer Geophysical Union
Thunderstorm Ground Enhancements (TGEs) refer to correlated enhancements in surface electric field and gamma ray flux that are manifestations of electron runaway in the storm overhead. The electric field enhancements can be of positive or negative polarity. In this study, altitude-resolved S-band radar observations of graupel are used to demonstrate distinct differences in storm structure linked with these “positive” and “negative” TGEs. The physical interpretation rests on the well-established temperaturedependent tripole structure of thunderstorms, with the main negative charge of the tripole acting as an electron repeller. This interpretation is supported by case studies showing altitude-stable convection, with shallow (deep) development linked with “positive” (“negative”) TGEs, and by case studies of collapsing storms that show upper dipole dominance early and lower inverted dipole dominance later when graupel particles descend from a colder to warmer temperature domain. In the case of many TGEs on Mt Aragats (3.2 km MSL), the temperature-dependent altitude of downward electron acceleration and avalanching may be sufficiently distant (>500 m) from surface detectors that the energetic electrons (1–10 MeV) are not likely avalanche/runaway electrons. Instead, they are Compton-scattered and pair-produced electrons from bremsstrahlung gamma radiation emanating from the high-field avalanche region aloft. These inferences are consistent with GEANT4 calculations that identify the physical origins of energetic electrons at the surface.
Radar DiagnosisThundercloud Electron Acceleratorsurface electric
E. Williams、H. Mkrtchyan、B. Mailyan、G. Karapetyan、S. Hovakimyan
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Massachusetts Institute of Technology, Cambridge, MA, USA
A. Alikhanian National Science Lab, Yerevan, Armenia
Antihail Service, Hydrometeorology and Monitoring Center, Yerevan, Armenia
NSTL
Amer Geophysical Union
