Evidence for low density holes in Jupiter\u2019s ionosphere

Masafumi Imai,Ivana Kolmašová,John E P Connerney,Scott J Bolton,George B Hospodarsky,William S Kurth,Donald A Gurnett,Steven M Levin,Ondřej Santolík,Shannon T Brown

doi:10.1038/s41467-019-10708-w

Abstract

Intense electromagnetic impulses induced by Jupiter’s lightning have been recognised to produce both low-frequency dispersed whistler emissions and non-dispersed radio pulses. Here we report the discovery of electromagnetic pulses associated with Jovian lightning. Detected by the Juno Waves instrument during its polar perijove passes, the dispersed millisecond pulses called Jupiter dispersed pulses (JDPs) provide evidence of low density holes in Jupiter’s ionosphere. 445 of these JDP emissions have been observed in snapshots of electric field waveforms. Assuming that the maximum delay occurs in the vicinity of the free space ordinary mode cutoff frequency, we estimate the characteristic plasma densities (5.1 to 250 cm−3) and lengths (0.6 km to 1.3 × 105 km) of plasma irregularities along the line of propagation from lightning to Juno. These irregularities show a direct link to low plasma density holes with ≤250 cm−3 in the nightside ionosphere.

Highlights

Intense electromagnetic impulses induced by Jupiter’s lightning have been recognised to produce both low-frequency dispersed whistler emissions and non-dispersed radio pulses
We present dispersed millisecond pulses with a lower frequency cutoff between 20 and 150 kHz recorded by the Juno radio and plasma wave (Waves) instrument[11] during eight perijove passes from perijove 1 (PJ1) on 27 August 2016, through PJ9 on 24 October 201712–15
We have carried out a survey of the Juno wave instrument (Waves) burst mode data from the Low Frequency Receiver High (LFR-Hi) channel in the form of frequency-time spectrograms below 150 kHz (Methods) on PJ1 and PJ3 to PJ9

Summary

Introduction

Intense electromagnetic impulses induced by Jupiter’s lightning have been recognised to produce both low-frequency dispersed whistler emissions and non-dispersed radio pulses. Assuming that the maximum delay occurs in the vicinity of the free space ordinary mode cutoff frequency, we estimate the characteristic plasma densities (5.1 to 250 cm−3) and lengths (0.6 km to 1.3 × 105 km) of plasma irregularities along the line of propagation from lightning to Juno. A lightning-induced non-dispersed electromagnetic pulse was observed at Jupiter by the Galileo Probe in a magnetic field waveform in the frequency range from 10 Hz to 100 kHz5. Since their discovery intense electromagnetic impulses induced by Jupiter’s lightning have been recognised to produce both low-frequency dispersed whistler emissions[2,6,7] and non-dispersed radio pulses[5,8]. On the basis of the theory of lightning-induced microsecond trans-ionospheric pulse pairs on Earth[16,17,18], we suggest that the upper limit of the vertical height between the thunderstorm and the reflection layer in the Jovian atmosphere might be less than 500 km

Methods

Results

Conclusion