Jupiter Lightning‐Induced Whistler and Sferic Events With Waves and MWR During Juno Perijoves

Abstract

During the Juno perijove explorations from 27 August 2016 through 1 September 2017, strong electromagnetic impulses induced by Jupiter lightning were detected by the Microwave Radiometer (MWR) instrument in the form of 600‐MHz sferics and recorded by the Waves instrument in the form of Jovian low‐dispersion whistlers discovered in waveform snapshots below 20 kHz. We found 71 overlapping events including sferics, while Waves waveforms were available. Eleven of these also included whistler detections by Waves. By measuring the separation distances between the MWR boresight and the whistler exit point, we estimated the distance whistlers propagate below the ionosphere before exiting to the magnetosphere, called the coupling distance, to be typically one to several thousand of kilometers with a possibility of no subionospheric propagation, which gives a new constraint on the atmospheric whistler propagation.

A Survey of Small‐Scale Waves and Wave‐Like Phenomena in Jupiter's Atmosphere Detected by JunoCam

“…The overwhelming majority of wave-like features are clustered between 7°S and 6°N latitude, the relatively bright EZ. These features are dominated by long wave packets with short wave crests, the type of waves detected by Hunt and Muller (1979) and discussed by Simon, Li, and Reuter (2015) as mesoscale waves observed at low latitudes by previous imaging experiments. These waves fall within the relatively bright EZ and appear to be subclustered with fewer waves between 1°S and the equator than between either 7°S and 1°S or the equator and 6°N.…”

“…Time-delayed integration of multiple pixel rows builds up the signal-to-noise ratio. Hansen et al (2017) provide details of the instrument Hunt and Muller (1979), Flasar and Gierasch (1986) 27°S to 27°N 7 0 -430 Galileo (1996) Bosak and Ingersoll (2002) 13°S 300 Galileo (1999) Arregi et al (2009), Simon, Li, and Reuter (2015) 0. 2°N, 3.6°N 155-205 Galileo (2001) Arregi et al 20091.…”

“…We have used JunoCam's coverage over a wide range of latitudes, coupled with its high spatial resolving power, to examine all of our images for various phenomena in Jupiter's clouds. Small-scale waves, with wavelengths (distances between wave crests) less than~300 km, were first detected in 1979 by Voyager (Hunt & Muller, 1979) and have been detected by Galileo (e.g., Bosak & Ingersoll, 2002) and New Horizons (e.g., Reuter et al, 2007) since then, as well as by the near-infrared JIRAM instrument on Juno Fletcher et al, 2018). Larger waves, with scales of 1,200 km or greater, have since also been detected from the Earth using Hubble Space Telescope (HST) and ground-based imaging .…”

Atmospheric Electricity at the Ice Giants

“…This detection was very surprising since no HF sferics were detected at Jupiter (probably due to ionospheric absorption, as pointed out by Zarka (1985)), and radio emissions of terrestrial lightning in the ultra-high frequency band (UHF, 300-3000 MHz) have rarely been studied due to the decline of intensity with increasing frequency. The MWR high frequency observations have been confirmed by parallel observations of whistlers with the Juno Waves instrument (Kolmasova et al, 2018;Imai et al, 2018). Modern receivers with low noise figures and wide bandwidth should allow good observations of impulsive radiation of lightning at microwave frequencies (Petersen and Beasley, 2014).…”

Evidence for low density holes in Jupiter’s ionosphere

“…Another indirect observational study of the Jovian ionosphere was carried out via dispersion analysis using Juno’s detections of lightning-induced whistlers. In this analysis, for some cases, it was necessary to reduce the ionospheric plasma density model by 10 to 30% 7,24 . In other words, the Jovian ionosphere changes dynamically.…”