Premium
Comment on “Can gamma radiation be produced in the electrical environment above thunderstorms”
Author(s) -
Papadopoulos K.,
Milikh G.,
Valdivia J.
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/96gl00770
Subject(s) - thunderstorm , radiation , environmental science , meteorology , lightning (connector) , gamma ray , atmospheric sciences , climatology , geology , physics , nuclear physics , power (physics) , quantum mechanics
In a recent letter Chang and Price [1995] (subsequently referred to as CP) set forward the claim that runaway electron acceleration followed by runaway discharge [Gurevich, 1961; Connor and Hastie, 1975] can take place at the altitude of about 70 km in the ionosphere in the presence of a vertical laminar electric field E of the order of 500 V/m. Furthermore, they speculate that the 7-ray flashes observed when the Compton 7-ray observatory overflies the equatorial region [Fishman et al., 1994] and the short-pulse radio bursts detected by the ALEXIS satellite [Massey and Holden, 1995] can be attributed to such a runaway discharge occurring at an altitude of 70 km corresponding to neutral density of 7 x 10 TM #/cm 3. The purpose of this comment is to demonstrate that the conclusions of the CP paper are based on physical principles inconsistent with the fact that for the relevant ionospheric parameters the electron mean free path is much longer than its gyroradius. It is easy to see that for runaway electrons the mean free path is far larger than the gyroradius. For example, a 1 MeV electrons in the Earth's magnetic field has a gyroradius of approximately 80 m, while the mean free path at 70 km is tens of kilometers. The CP paper states that an acceleration distance of 3.7 km is required for the electrons to reach 1 MeV. This is forty times longer than the relevant gyroradius. As noted by Papadopoulos and Milikh [1994] and Book et al. [1995], for mean free paths longer than the gyroradius proper analysis requires inclusion of the magnetic field in the equations of motion. The problems with the CP model become apparent by a simple physics analysis which considers acceleration of an electron in the presence of an electric field perpendicular to a magnetic field. Such a configuration is expected for runaway acceleration over thunderstorms in the equatorial region. We study the runaway acceleration of a test electron in crossed static electric and magnetic fields by transforming the equations of motion to a reference frame moving with the velocity 3c relative to the ionospheric frame in which the transformed fields E and are parallel. In this frame the electrons can be treated as unmagnetized.