Propagation characteristics of ELF/VLF electromagnetic waves in the Martian ionosphere and the possibility for detection of Martian atmospherics by NOZOMI observations

A feasibility study has been made of the detection possibility of radio wav e noises, i.e., Martian atmospherics, emitted from discharges in the Martia n atmosphere during large dust storms. The spacecraft NOZOMI, which was lau nched in 1998, is to be placed on an elliptic orbit around Mars with perige e of 150-200km. An onboard-equipment LFA (Low Frequency Plasma wave Analyze r) has capability to measure the low frequency plasma waves in the frequenc y range from 10 Hz to 32 kHz. In order to know if the LFA can detect the at mospheric radio noises, the propagation characteristics of electromagnetic waves through the Martian ionosphere are studied theoretically by using a f ull-wave method. The ionosphere is modeled as a magneto-ionic medium based on the recent observations of magnetic anomaly by Mars Global Surveyor spac ecraft, and the atmospheric constituent and electron density by Viking obse rvations. Our calculation shows that the waves at frequencies less than a h undred hertz; can propagate with low attenuation and reach to altitudes abo ve 200 km in the whistler-mode in the regions of magnetic anomalies in the dayside ionosphere. It is shown that the radio noises emitted from electric discharge in an intense dust storm, with the intensity over -30 dBV/m/root Hz at the ionospheric entry point, can be sensed by the LFA. The observati onal identification of Martian atmospherics will contribute to the physical study of charge/discharge process in the Martian atmosphere.