Variance of transionospheric VLF wave power absorption

TLDR: In this article, the power reduction of very low frequency (VLF) waves propagating through the ionosphere with a very large IRI and in situ observational data was investigated.

Abstract: To investigate the effects of D ‐region electron density variance on wave powerabsorption, we calculate the power reduction of very low frequency (VLF) wavespropagatingthroughtheionospherewithafullwavemethodusingthestandardionosphericmodel IRI and in situ observational data. We first verify the classic absorption curves ofHelliwell’susingourfullwavecode.ThenweshowthattheIRImodelgivesoverallsmallerwave absorption compared with Helliwell’s. Using D‐region electron densities measuredbyrocketsduringthepast60years,wedemonstratethatthepowerabsorptionofVLFwavesissubjecttolargevariance,eventhoughHelliwell’sabsorptioncurvesarewithin±1standarddeviation of absorption values calculated from data. Finally, we use a subset of therocket data that are more representative of the D region of middle‐ and low‐latitude VLFwave transmitters and show that the average quiet time wave absorption is smaller thanthat of Helliwell’s by up to 100 dB at 20 kHz and 60 dB at 2 kHz, which would make themodel‐observation discrepancy shown by previous work even larger. This result suggeststhat additional processes may be needed to explain the discrepancy.