Global occurrence of Elves and lightning-induced heating of the ionosphere from ground-based observations

Abstract:

Elves are the optical signature of the lightning electromagnetic pulse (EMP) interaction with the lower ionosphere. Simultaneously, the lightning EMP induces collisional heating of the lower ionosphere and deposits energy in the D-region. We use a database of elve observations from the ground-based PIPER photometer instrument, together with VLF/LF observations of the causative sferics, to assess the probability of elve production for different lightning source parameters. We find that the lightning peak current alone predicts the occurrence of elves with 90% accuracy, and there is a 50% probability of elve production for peak currents of 88 kA. Using the resulting probability regression curve together with one year of global lightning peak current data from GLD360, we estimate that 0.8% of all lightning across the globe produces elves, for a total of ~5 x 10⁶ elves per year globally. 

Next, using the Stanford EMP model, we calculate the total energy deposited in the lower ionosphere due to lightning, as a function of peak current and other source parameters. Again, we find that the lightning peak current provides the majority of the variation and is a good predictor of the total heating in the ionosphere. We find that the energy deposited in the lower ionosphere is 70-80% of the total radiated energy in the EMP, the variation depending on day vs. night and only weakly dependent on peak current. Integrating over the total annual lightning activity, we find a total of ~60 TJ of energy deposited in the lower ionosphere per year due to lightning.