An explanation for parallel electric field pulses observed over thunderstorms

Abstract

Every electric field instrument flown on sounding rockets over a thunderstorm has detected pulses of electric fields parallel to the Earth's magnetic field associated with every strike. This paper describes the ionospheric signatures found during a flight from Wallops Island, Virginia, on 2 September 1995. The electric field results in a drifting Maxwellian corresponding to energies up to 1 eV. The distribution function relaxes because of elastic and inelastic collisions, resulting in electron heating up to 4000–5000 K and potentially observable red line emissions and enhanced ISR electron temperatures. The field strength scales with the current in cloud‐to‐ground strikes and falls off as r−1 with distance. Pulses of both polarities are found, although most electric fields are downward, parallel to the magnetic field. The pulse may be the reaction of ambient plasma to a current pulse carried at the whistler packet's highest group velocity. The charge source required to produce the electric field is very likely electrons of a few keV traveling at the packet velocity. We conjecture that the current source is the divergence of the current flowing at mesospheric heights, the phenomenon called an elve. The whistler packet's effective radiated power is as high as 25 mW at ionospheric heights, comparable to some ionospheric heater transmissions. Comparing the Poynting flux at the base of the ionosphere with flux an equal distance away along the ground, some 30 db are lost in the mesosphere. Another 10 db are lost in the transition from free space to the whistler mode.

Effects of lightning and sprites on the ionospheric potential, and threshold effects on sprite initiation, obtained using an analog model of the global atmospheric electric circuit

“…Similar processes due to fields radiated by lightning are investigated by Inan et al [1993] and Parrot et al [2007, 2008]. Recently, from rocket observations above a thunderstorm, Kelley and Barnum [2009], page 7, show that electron heating of up to 5000 K occurs and that “the whistler packet's effective radiated power is 25 mW at ionospheric heights, comparable to some ionospheric heater transmissions.” Sauvaud et al [2008] observe that radiation from the NWC transmitter at 19.8 kHz in Australia scatters Van Allen radiation belt electrons into the drift‐loss cone. They also show that a first‐order cyclotron resonance between whistler mode waves and electrons of ∼200 keV could occur at in the equatorial plane at a magnetic L value of 1.7.…”

Electron heating and airglow emission due to lightning effects on the ionosphere

“…In the main ionosphere, the whistler mode pulse begins to disperse but the leading edge has the parallel electric field mentioned above, characterized by a few ms pulse with a peak amplitude of 1 to 10 mV m −1 . Each strike has these two components, 4 to 9 per flash, separated by 40 to 80 ms. As discussed by Kelley and Barnum [2009], these parallel fields are mysterious owing to the high conductivity parallel to the magnetic field, but there is evidence that they are real. Here we consider this phenomenon to be real and predict measurable effects in the ionosphere, for example, by airglow or incoherent scatter radar methods.…”

“…Pulsed electric fields parallel to the geomagnetic field have been observed at mesospheric and thermospheric heights in several rocket flights [Kelley et al, 1985[Kelley et al, , 1990 and accelerated electrons were detected on one satellite [Burke et al, 1992] in conjunction with an electric field pulse. A detailed study from another flight is presented in a companion paper [Kelley and Barnum, 2009]. A brief summary of these results follows.…”

“…[6] According to the rocket data [Kelley and Barnum, 2009], a pulsed electric field induced by lightning can penetrate into the F2 layer. This field is characterized on average by a pulse with an electric field of 3 mV m À1 and an e-folding time of 1.5 ms, followed by an electric field with opposite sign of À0.5 mV m À1 during 6 ms. in an opposite direction.…”

“…Each strike has these two components, 4 to 9 per flash, separated by 40 to 80 ms. As discussed by Kelley and Barnum [2009], these parallel fields are mysterious owing to the high conductivity parallel to the magnetic field, but there is evidence that they are real. Here we consider this phenomenon to be real and predict measurable effects in the ionosphere, for example, by airglow or incoherent scatter radar methods.…”