Infrared glow above thunderstorms?

Abstract

Sustained heating of lower ionospheric electrons by thundercloud fields, as recently suggested by Inan et al. [1996], may lead to the production of enhanced infrared (IR) emissions, in particular 4.3‐µm CO2 emission. The excitation rate for N2(v) via electron collisions is calculated using a new steady‐state two‐dimensional electrostatic‐heating (ESH) model of the upward coupling of the thundercloud (TC) electric fields. The vibrational energy transfer to CO2 and 4.3‐µm radiative transfer are then computed using a line‐by‐line non‐LTE (non‐local thermodynamic equilibrium) radiation model. Limb‐viewing radiance profiles at 4.3‐µm and typical radiance spectra are estimated for five different TC charge distributions and ambient ionic conductivities. Broadband 4.3‐µm enhancements of greater than a factor of two above ambient nighttime levels are predicted for tangent heights (TH) in the range ∼80 to >130 km for the most perturbed case, with larger enhancements in selected narrower spectral regions. The predicted IR enhancements should be observable to an orbiting IR sensor.