Investigation of whistler waves associated with a flux rope near Venus

Whistler waves are electromagnetic plasma waves with a characteristic frequency and mode of propagation. These waves can be generated by various means in the planetary plasma environment, including atmospheric lightning on Venus and Earth. Whistler waves have therefore been considered as potential evidence of lightning activity on Venus and are predominantly observed in the nightside ionosphere, possibly associated with lower-atmospheric sources. On Earth, these waves are frequently observed in the magnetic reconnection region, with only limited observations reported in association with flux rope structures, where they are generated under local plasma conditions such as temperature anisotropy. Flux rope structures have been reported on Venus since the Pioneer Venus Orbiter (PVO) mission in the ionosphere and induced magnetosphere. However, the link between flux ropes and whistler wave generation at Venus remains unexplored, and the role of this local plasma instability as an alternative to lightning-driven mechanisms has not been quantitatively tested. In this study, we investigate whistler waves observed in the vicinity of a Venusian flux rope and perform a quantitative linear instability analysis to test whether the anisotropic electron distributions within the flux rope can drive the observed wave activity. Our results show that the calculated anisotropy exceeds the whistler instability threshold by a factor of approximately three, and the predicted growth time is considerably shorter than the observed wave burst duration, suggesting that local anisotropy-driven instability may be a plausible generation mechanism. This work infers flux ropes as identifiable, in situ wave source regions at Venus and demonstrates that a portion of the whistler waves observed in the Venusian ionosphere may be attributed to local plasma instabilities. This work provides new insight into Venusian whistler wave activity and may lead to further studies of whistler waves driven by local plasma instabilities.