Modification of the lower ionospheric conductivity by thunderstorm electrostatic fields

Abstract

This paper reports a modeling study of the modifications of the nighttime lower ionospheric conductivity by electrostatic fields produced by underlying thunderstorms. The model used combines Ohm's law with a simplified lower ionospheric ion chemistry model to self‐consistently calculate the steady state nighttime conductivity above a thunderstorm. The results indicate that although the electron density is generally increased, the lower ionospheric conductivity can be reduced by up to 1–2 orders of magnitude because electron mobility is significantly reduced due to the electron heating effect. For a typical ionospheric density profile, the resulting changes in the reflection heights of extremely low frequency and very low frequency waves are 5 and 2 km, respectively.

Lower Ionospheric Conductivity Modification Above a Thunderstorm Updraught

“…The mechanism suggested agrees with previous observations of the lower ionosphere above thunderstorms (Lay et al, 2014;Shao et al, 2013) and growing modeling evidence for the ionospheric heating effect of thundercloud charge (Pasko et al, 1998;Salem et al, 2016). The mechanism suggested agrees with previous observations of the lower ionosphere above thunderstorms (Lay et al, 2014;Shao et al, 2013) and growing modeling evidence for the ionospheric heating effect of thundercloud charge (Pasko et al, 1998;Salem et al, 2016).…”

“…Previous modeling studies show that thunderstorm electrostatic fields can reduce conductivity in the nighttime D region by electron heating at altitudes of ∼70-90 km (Pasko et al, 1998;Salem et al, 2016), affecting the nighttime reflection heights of sub-ionospheric VLF radio waves (∼80-90 km). The heating effect is dependent on the atmospheric conductivity above the thundercloud and thundercloud charge configuration, including charge density and altitude.…”

“…Thundercloud electrostatic field extends upward where it is attenuated by the finite conductivity of the atmosphere above (e.g., Park & Dejnakarintra, 1973;Tonev & Velinov, 2002;Velinov & Tonev, 1995). In the lower layer of the ionosphere (D region, ∼50 to 100 km altitude), the presence of weak thundercloud electrostatic fields is proposed to heat ionospheric electrons and alter the conductivity profile of the D region (Kabirzadeh et al, 2015;Pasko et al, 1998;Salem et al, 2016). Observations using lightning atmospherics have shown that D region conductivity profiles differ during thunderstorm conditions compared to fair weather (e.g., Han & Cummer, 2010;Lay et al, 2014;Shao et al, 2013).…”

Elves Accompanying Terrestrial Gamma Ray Flashes

“…The electron mobility used to calculate the conductivity depends on electric field, and it decreases rapidly with increasing electric field. In our model, we adopt the electron mobility formula introduced by Salem et al () to account for the field dependence of electron mobility. According to this formula, the electron mobility is reduced by a factor of ∼42 when electric field increases from zero to 0.5 E k .…”

“…Therefore, the change in the conductivity due to the EMP is dominated by the change in electron mobility. In addition, electron mobility from various sources often differs more than 10–20% (Salem et al, ). We thus ignore the change in the electron density caused by the EMP.…”