ROLE OF THE MODE THEORY ON LIGHTNING GENERATED WAVES PROPAGATING IN VENUS-IONOSPHERE WAVE-GUIDE

The wave mode either electromagnetic or electrostatic of the OEFD measured signals is unknown and needs to be ascertained by indirect means. Considering these waves to be generated by global Venus lightning, the wave attenuation along the Venus-ionosphere wave-guide has been computed. The effective wave attenuation versus frequency shows a ''knee'' characterizing minimum attenuation 6 kHz. This ''knee'' is consistent with the amplitude spectral peak of OEFD signals around this frequency. This feature of the OEFD signals implies that the Venus lightning may have global occurrence. The lightning generated signals may travel considerable distance within the Venus-ionosphere waveguide. The encounter of these signals with plasma ''holes'' or ion ''troughs'' in the nightside of Venus wake region results in the leakage of the signals out of the shielding ionosphere. These signals are occasionally recorded by the OEFD. The occurrence rate statistics shows that the leakage of 5.4 kHz signals through the plasma ''holes'' in the vicinity of PVO periapsis are most effective. The maximum occurrence rate of higher frequency signals change in altitude slightly from one PVO season to another.