Comparison of ionospheric reflection heights for LEMPs produced by lightning return strokes of different polarity

Abstract

Apparent ionospheric reflection heights estimated using electric field waveforms of negative and positive cloud-to-ground lightning return strokes (-CGs and +CGs) that occurred during the same thunderstorms have been compared. We analyzed electric field waveforms of 101 -CGs and 74 +CGs that were recorded in August 2016 in Florida. For daytime conditions, the mean ionospheric reflection height for lightning electromagnetic pulses (LEMPs) produced by + CGs is larger than that for LEMPs produced by -CGs for either first or subsequent strokes, although the difference is statistically significant only for subsequent strokes. For nighttime conditions, the trend is the same, but the sample sizes are too small to draw meaningful conclusions. For daytime conditions, the mean ionospheric reflection height for subsequent strokes in -CGs is smaller than that for first strokes, while for + CGs the mean reflection heights for first and subsequent strokes are essentially the same. This disparity is related to the fact that subsequent strokes in –CGs usually develop in the channel of the first stroke, while subsequent strokes in +CGs usually form new terminations on ground and, hence, are similar to first strokes. In our dataset, NLDN-reported peak currents for + CGs tend to be higher than for –CGs for both daytime and nighttime conditions and for either first or subsequent strokes.