Power Transmission of Whistlers in the Lunar Ionosphere

Abstract This study investigates the power transmission ratio of lunar whistlers below 10 Hz for the first time by solving full wave equations that incorporate collisional effects for waves propagating upward from the surface to 100 km high in an ionosphere with four dominant ion species at temperatures of 150 K and 400 K in the lunar crustal field environment. The results indicate that increasing wave frequencies lead to decreasing power transmission ratios. This trend is consistent with the satellite observations near the Moon, which predominantly detect peak wave intensities at lower frequencies. Stronger magnetic field intensities and larger angles between the field and the surface led to an increase in power transmission ratios. This finding is consistent with the increased detection of waves in regions with higher field intensities and the more frequent occurrence rate of broadband whistlers linked to larger angles. As the temperature increases, the power transmission ratio increases, consistent with the higher occurrence rates of broadband whistlers at regions with smaller solar zenith angles. Incorporating the Doppler shift effect from solar wind on the observed wave frequency, the selenographic distribution of power transmission ratios exceeding −3 dB within the instrumentally detectable frequency range shows a heightened northern–southern asymmetry, aligning with the established patterns of wave intensities and occurrence rates. The preference to measure harmonic whistlers at lower altitudes can be attributed to the attenuation of the higher-frequency component at higher altitudes. The fact that the intensities of left-hand polarized components are more pronounced can also be interpreted.