Prevalent lightning sferics at 600 megahertz near Jupiter’s poles

Abstract

Lightning has been detected on Jupiter by all visiting spacecraft through night-side optical imaging and whistler (lightning-generated radio waves) signatures. Jovian lightning is thought to be generated in the mixed-phase (liquid-ice) region of convective water clouds through a charge-separation process between condensed liquid water and water-ice particles, similar to that of terrestrial (cloud-to-cloud) lightning. Unlike terrestrial lightning, which emits broadly over the radio spectrum up to gigahertz frequencies, lightning on Jupiter has been detected only at kilohertz frequencies, despite a search for signals in the megahertz range . Strong ionospheric attenuation or a lightning discharge much slower than that on Earth have been suggested as possible explanations for this discrepancy. Here we report observations of Jovian lightning sferics (broadband electromagnetic impulses) at 600 megahertz from the Microwave Radiometer onboard the Juno spacecraft. These detections imply that Jovian lightning discharges are not distinct from terrestrial lightning, as previously thought. In the first eight orbits of Juno, we detected 377 lightning sferics from pole to pole. We found lightning to be prevalent in the polar regions, absent near the equator, and most frequent in the northern hemisphere, at latitudes higher than 40 degrees north. Because the distribution of lightning is a proxy for moist convective activity, which is thought to be an important source of outward energy transport from the interior of the planet, increased convection towards the poles could indicate an outward internal heat flux that is preferentially weighted towards the poles. The distribution of moist convection is important for understanding the composition, general circulation and energy transport on Jupiter.

Jupiter's Turbulent Power Spectra From Hubble Space Telescope

“…Many features resemble those seen in the Earth's atmosphere, where they are primarily driven by convective processes. A similar origin is almost certainly true for Jupiter's atmosphere where there is evidence of lightning and scant water ice detections (Brown et al, ; Gierasch et al, ; Kolmašová et al, ; Little et al, ; Simon‐Miller et al, ).…”

“…These higher transitions could indicate a real “forcing scale” where energy is injected into the atmosphere to drive changes in 24°N jet speed, or it could indicate a small scale at which enstrophy is being dissipated by the Great Red Spot as it is shrinking (Simon et al, ; Tollefson et al, ). The Juno mission has found observations showing lightning at higher latitudes, which could be connected to moist convection as a source for injecting energy at these locations (Brown et al, ; Gierasch et al, ; Kolmašová et al, ). This is another result of our analysis that finds unique power spectra features corresponding to dynamic areas on the planet.…”

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

“…As a result of the comparison of the Waves catalogue of 1,627 Jovian low-dispersion whistlers within 1,311 waveform snapshots (Kolmašová et al, 2018) and the MWR sferic catalogue of 383 lightning events (Brown et al, 2018), we found 11 MWR sferic 100-ms events that overlap with eight Waves 122.88-ms snapshots in which we detected low-dispersion whistlers, hereafter called concurrent events at altitudes between 6,340 and 22,050 km. In addition, we use the term non-concurrent event when the MWR sferic event occurs without any detection of whistlers in the Waves waveforms.…”

“…Concurrent whistler and sferic events using data set of whistler detections by Waves (Kolmašová et al, ) and sferic detections by Microwave Radiometer (MWR) (Brown et al, ). The borders of the blue bars indicate the beginning and end time of MWR sferic events (100‐ms integration intervals), which overlap the times of Waves whistler detections.…”

“…This means that the lightning-induced impulses may escape without any subionospheric propagation, just vertically above the lightning location and form both detected sferics and low-dispersion whistlers. However, these impulses might also propagate for some limited distance below (Kolmašová et al, 2018) and sferic detections by Microwave Radiometer (MWR) (Brown et al, 2018). The borders of the blue bars indicate the beginning and end time of MWR sferic events (100-ms integration intervals), which overlap the times of Waves whistler detections.…”