High‐Spatiotemporal Resolution Observations of JupiterLightning‐Induced Radio Pulses Associated WithSferics and ThunderstormsMasafumi Imai1,2 , Michael H. Wong3,4 , Ivana Kolmašová5,6 , Shannon T. Brown7 ,Ondřej Santolík5,6 , William S. Kurth1 , George B. Hospodarsky1 , Scott J. Bolton8 , andSteven M. Levin7

1Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA, 2Department of Electrical Engineeringand Information Science, National Institute of Technology (KOSEN), Niihama College, Niihama, Japan, 3SETI Institute,Mountain View, CA, USA, 4Center for Integrative Planetary Science, University of California, Berkeley, CA, USA,5Department of Space Physics, Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czechia,6Faculty of Mathematics and Physics, Charles University, Prague, Czechia, 7Jet Propulsion Laboratory, CaliforniaInstitute of Technology, Pasadena, CA, USA, 8Space Science and Engineering Division, Southwest Research Institute, SanAntonio, TX, USA

Abstract Jupiter lightning discharges produce various kinds of phenomena including radio wave pulsesat different frequencies. On 6 April 2019, the Juno Waves instrument captured an extraordinary series ofradio pulses at frequencies below 150 kHz on timescales of submilliseconds. Quasi‐simultaneousmulti‐instrument data show that the locations of their magnetic footprints are very close to the locations ofultrahigh frequency (UHF) sferics recorded by the Juno MWR instrument. Hubble Space Telescopeimages show that the signature of active convection includes cloud‐free clearings, in addition to theconvective towers and deep water clouds that were also recognized in previous spacecraft observations oflightning source regions. Furthermore, the detections of 17 very low frequency/low‐frequency (VLF/LF)radio pulses suggest a minimum duration of lightning processes on the order of submilliseconds. Theseobservations provide new constraints on the physical properties of Jupiter lightning.

Plain Language Summary Jupiter lightning illuminates clouds and produces a strong pulse atradio wavelengths. Juno's radio observatory (consisting of two onboard instruments) in a broad radiorange made several detections of extraordinary radio pulses on 6 April 2019. The high‐temporal observationsof such radio pulses detected below 150 kHz indicate variations of the lightning related processes on theorder of submilliseconds. Observations of these radio pulses and direct lightning‐induced radio emissions at600MHz come from the same area, very close to deep water clouds detected by the Hubble Space Telescope(HST) in the Jovian atmosphere. The coordinated Juno‐HST lightning observations provide a new way ofunderstanding the lightning processes and lightning source regions associated with the cloud featuresat Jupiter.

1. Introduction

Lightning at Jupiter generates a strong electromagnetic impulse in the atmosphere, producing three kindsof radio signatures. The first is comprised of Jovian whistlers typically observed at frequencies below 20kHz with several seconds long dispersed falling tones when detected in the Io torus (Gurnett et al., 1979;Kurth et al., 1985) or with fast signatures lasting from a few milliseconds to a few tens of milliseconds inthe upper ionosphere (Kolmašová et al., 2018). In the strongly magnetized plasma near Jupiter, the whis-tler frequency is limited below the local electron plasma frequency due to the orientation of the wave pro-pagation with respect to the local magnetic field line (Stix, 1992). These radio signals may possiblypropagate up to several thousand kilometers horizontally away from lightning strokes below the iono-sphere before ultimately escaping into the inner magnetosphere, but their direct vertical propagation can-not be excluded (Imai et al., 2018). The second kind consists of dispersed millisecond pulses called Jupiterdispersed pulses (JDPs), observed at frequencies below 150 kHz but above the maximum plasma fre-quency encountered during the wave propagation through the ionosphere. JDPs propagate directly fromlightning strokes but can leak into the inner magnetosphere only at places where the ionospheric density

©2020. American Geophysical Union.All Rights Reserved.

RESEARCH LETTER10.1029/2020GL088397

Key Points:• First common observations of

VLF/LF radio pulses, UHF sferics,and thunderstorms were carried outusing Juno and the Hubble SpaceTelescope

• New high‐time resolutionmeasurements of radio pulsesassociated with Jovian lightningprocesses resolve submillisecondvariations

• Cloud structure with juxtaposeddeep water clouds, convectivetowers, and clearings is the signatureof active convection

Supporting Information:• Supporting Information S1

Correspondence to:M. Imai,m.imai@niihama.kosen-ac.jp

Citation:Imai, M., Wong, M. H., Kolmašová, I.,Brown, S. T., Santolík, O., & Kurth, W.S., et al. (2020). High‐spatiotemporalresolution observations of Jupiterlightning‐induced radio pulsesassociated with sferics andthunderstorms. Geophysical ResearchLetters, 47, e2020GL088397. https://doi.org/10.1029/2020GL088397

Received 15 APR 2020Accepted 10 JUL 2020Accepted article online 17 JUL 2020

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is sufficiently low, either in localized holes or over the nightside (Imai et al., 2019). The third kind of sig-nal is a nondispersed sferic, recorded by the Galileo Probe at frequencies <100 kHz below the Jovianionosphere (Rinnert et al., 1998) and by Juno at 600MHz and 1.2 GHz leaking into the inner magneto-sphere (Brown et al., 2018). The latter ultrahigh frequency (UHF) sferics freely traverse the ionospherefrom the lightning strokes as straight‐line propagation. Note that, in the atmospheric electricity commu-nity, the term “sferic” is traditionally used for impulsive radio pulses propagating in the Earth‐ionospherewaveguide, but lately, it has also been used for transionospheric radio pulses of lightning from Jupiter,Saturn, or Uranus (Aplin et al., 2020). Monitoring these three kinds of lightning‐induced radio wavesyields a global lightning map on both the dayside and nightside of Jupiter and puts constraints on theplasma environment near the planet.

For terrestrial lightning wemeasure the duration of a lightning flash from the first initial breakdown pulse tothe last return stroke pulse. This lightning durationmight vary frommilliseconds to tens or even hundreds ofmilliseconds (Rakov & Uman, 2003). Different processes within the duration of a lightning flash areobserved on Earth at shorter timescales decreasing down to microseconds in the case of stepped or dart lea-der pulses, tens of microseconds for initial breakdown pulses, or hundreds of microseconds for returnstrokes. Not knowing yet the details of development of lightning flashes at Jupiter, we refer to these collec-tively as “lightning processes” in this paper.

Another set of Jupiter lightning observations prior to Juno came from the optical detections of illuminatedclouds on the nightside of the planet fromVoyager 1 (Borucki &Williams, 1986; Cook et al., 1979), Voyager 2(Borucki & Magalhães, 1992), Galileo (Dyudina et al., 2002; Gierasch et al., 2000; Little et al., 1999), Cassini(Dyudina et al., 2004), and New Horizons (Baines et al., 2007). Nightside lightning from Juno has also beendetected by navigation cameras: the SRU (Becker et al., Views of lightning on the darkside of Jupiter byJuno's Stellar Reference Unit, EGU General Assembly Abstract 6393, 2019) and the Advanced StellarCompass (ASC) (Joergensen et al., Juno ASC observations of low light phenomena on the Jovian nightside,AGU Fall Meeting Abstract P24B‐04, 2018). The nightside lightning images suggested that (1) the deepestlightning flashes were situated within or below the water cloud layer (≥5‐bar level), (2) the lateral extentof thunderstorms typically ranges from 100 to 2,000 km, and (3) some of the thunderstorms may have light-ning activity exceeding several minutes. It is still questionable how many lightning strokes comprise theimaging detections (with ≥5‐s exposure time (Baines et al., 2007)). A scanned Galileo imager frame gaveaverage flash rates of about 0.3 flashes/s in two storm clusters, but multiple strokes may have been includedin individual measured flashes because of the 1.5 s/pixel effective temporal resolution of the scanned frame(Little et al., 1999). Multifilter dayside imaging of lightning storm locations (separated by 2–4 hr from night-side lightning imaging) has demonstrated the presence of both deep clouds associated with water condensa-tion and tall, high‐opacity convective towers in the vicinity of lightning flashes (Dyudina et al., 2004;Gierasch et al., 2000).

In this paper, we present colocated observations of lightning detected at radio wavelengths and cloud fea-tures captured at visible and near‐infrared wavelengths during Juno's nineteenth perijove on 6 April 2019.During this interval, unique detections of very low frequency/low‐frequency (VLF/LF) radio pulses below150 kHz were made and the magnetic footprints of these were spatially very close to the sources of UHF sfe-rics at 600MHz and thunderstorms. These observations with 2.67‐μs time sampling allow the investigationof lightning processes at submillisecond scales.

2. Description of Instruments and Measurements

Since 5 July 2016, the Juno spacecraft has been in polar orbit around Jupiter (Bolton et al., 2017). DuringJuno perijoves every 53 days, synoptic observations of lightning at radio wavelengths are made by the radioand plasma wave instrument (Waves; Kurth et al., 2017) and by the Microwave Radiometer (MWR; Janssenet al., 2017). Constraints from operational modes and geometrical considerations mean that the two instru-ments rarely achieve truly simultaneous coverage. The reception of lightning‐induced radio waves is depen-dent on the topology of Jupiter's magnetic field lines for Jovian whistlers and on the orientation of thespacecraft spin plane with respect to the planet's atmosphere for UHF sferics detected by the MWR. Herewe investigate quasi‐simultaneous Waves and MWR data acquired around noon UTC on 6 April 2019.During this pass, Juno's onboard imaging instruments were shut down to accommodate an MWR

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cross‐track scanning orientation (Bolton et al., Initial results of Juno's microwave imaging of Jupiter's atmo-sphere at multiple depths, AGU Fall Meeting Abstract P21G‐3455, 2019), so we use Hubble Space Telescope(HST) imaging for atmospheric context.

The Waves instrument is capable of collecting electric field data in a frequency range of 50 Hz to 41MHzwith an electric dipole antenna and magnetic field data in a frequency range of 50 Hz to 20 kHz with amagnetic search coil sensor, through three onboard receivers. In this study, the effective length of the dipoleantenna is assumed to be 0.5 m, instead of 2.4 m for the geometrical effective length (Kurth et al., 2017). Oneof the receivers—the Low Frequency Receiver (LFR)—is divided into two frequency bands: the low‐bandfrequency channels of electric and magnetic fields (LFR‐Lo) from 50 Hz to 20 kHz and the high‐bandfrequency channels of electric fields (LFR‐Hi) from 10 to 150 kHz. The LFR‐Lo and LFR‐Hi burst modesrecord snapshots containing 6,144 points at a cadence of one snapshot per second. The 6,144‐pointLFR‐Lo and LFR‐Hi snapshots have respective durations of 122.88 ms (at 20‐μs resolution) and 16.384 ms(at 2.67‐μs resolution). These frequency bands conduct interleaved observations due to the instrumentaldesign. The LFR‐Lomode was utilized for the previous studies of Jovian low‐dispersion whistlers (Imai et al.,2018; Kolmašová et al., 2018). As described in the work of Kolmašová et al. (2018) and Imai et al. (2018,2019), we converted waveform data on the ground into spectral data by means of a 256‐point fast Fouriertransform for identifying Jupiter's lightning‐induced wave morphology. In measuring an emission duration,we limit the time domain waveforms using the fourth‐order Butterworth filter between 40 and 100 kHz.This process allows us to remove most of the dispersed signals at the low‐band frequency that contain themajority of delays accumulated during the wave propagation through the ionospheric plasma.

The MWR instrument is designed to detect one linearly polarized electric field component with twopatch‐array antennas at 600MHz and 1.25 GHz, three slot‐array antennas at 2.6, 5.2, and 10.0 GHz andone corrugated horn antenna at 22.0 GHz. Electric field strengths are sampled with a fixed temporal resolu-tion of 100ms (corresponding to 1.2° of spacecraft spin per sample) and converted into antenna tempera-tures TA in K. The antenna beams lie in the spacecraft spin plane, with the high‐band frequency antennascoaligned on one side of the spacecraft, and the 600‐MHz antenna on a separate side resulting in a 120°pointing offset. Although MWR has detected UHF sferics in the 1.2‐GHz channel, we concentrate on themuch more common UHF sferics at 600MHz in this paper. The selection of the UHF sferic events is madeby finding a signal higher than six standard deviation above the noise floor, after the background signal isdetermined via a low‐pass filter (Brown et al., 2018). The −10‐dB level (about 90% received power) of the600‐MHz antenna forms a 17° beam half‐angle that we use to define the uncertainty of the sferic position.Using straight‐line propagation, we estimate the MWR boresight of the lightning source mapped onto the5‐bar atmosphere.

Jupiter atmospheric context observations have been acquired with the HST as part of the Wide FieldCoverage for Juno (WFCJ) program (Wong et al., 2020). The first observation was made during Juno's thirdperijove on 11 December 2016 (Tollefson et al., 2017). This program utilizes filters from ultraviolet (UV) tonear‐infrared wavelengths in the Wide Field Camera 3 (WFC3/UVIS) instrument, including 631‐nm,727‐nm, and 889‐nm narrow filters sensitive to cloud and haze particles at different altitudes. Imaging dataare mapped to the 1‐bar level in Jovigraphic System III coordinates as described in Wong et al. (2020). At60°N, the spatial resolution is about 400 km in the east‐west direction and 700 km in the north‐southdirection, with a mapping accuracy of about 80 × 160 km.

3. Observations

From 11:58:00 through 12:00:30 on 6 April 2019, the Juno Waves LFR‐Hi and LFR‐Lo channels indepen-dently detected a multitude of lightning‐induced radio pulses below 150 kHz shown in Figures 1a and 1d.At that time, Juno's position changed in altitude above the 1‐bar level from 17,630 to 14,730 km in the north-ern hemisphere, crossing magnetic field lines connecting to the middle radiation belt (Kollmann et al., 2017)atM= 2.34 – 2.87 (pink line of Figure 1a inset).M is defined as the magnetic equatorial radius mapped alongJuno's magnetic field line using the JRM09 magnetic field model (Connerney et al., 2018) with the currentsheet (Connerney et al., 1981), divided by the equatorial radius of Jupiter (1 RJ = 71,492 km). M is used inthe same way as the dipole L but with nondipole field lines.

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Of the 150 available snapshots each in the LFR‐Hi and LFR‐Lo channels (asynchronously acquired), 7LFR‐Hi snapshots and 56 LFR‐Lo snapshots contained one or more radio pulses. Figure 1e shows two whis-tlers in a single 122‐ms LFR‐Lo snapshot, with one whistler appearing to extend to frequencies higher thanthe 20‐kHz cutoff of the LFR‐Lo channel. Of the 93 whistlers detected in the LFR‐Lo data, 26 appeared toextend to frequencies above the 20‐kHz cutoff. In the LFR‐Hi data, 17 VLF/LF radio pulses were observed,extending as high as 128 kHz. A single 16.384‐ms snapshot contained 10 discrete VLF/LF radio pulses(Figure 1b), while the details of the time domain waveform for one such pulse at 40–100 kHz gives a durationof 0.392 ms in Figure 1c. Six other snapshots containing VLF/LF radio pulses are illustrated in Figure 2 andlisted in Table 1.

As the definitive mode of 17 VLF/LF radio pulses acquired from LFR‐Hi data is unclear, they may be eitherJDPs or Jovian whistlers. Some of the observed pulses show signatures of a lower cutoff and dispersed fea-tures close to it. Therefore, they might not be whistlers below the plasma frequency but JDPs above theplasma frequency. Recall that the plasma frequency corresponds to the upper frequency of Jovian whistlersand the lower cutoff frequency of JDPs. However, this distinction may not be stated with certainty for all ourobservations, as the determination of the local plasma frequency is not always possible. In some cases, wecan also examine positions of observations. For example, in Figure S1 in the supporting information, themaximum observable range (or radio horizon) overlaps with a small portion of nightside region, and thiscondition might be unfavorable for the JDP assumption because most of the observable region faces the day-side and the previous JDP observations were concentrated near the terminator (Imai et al., 2019).

Because the electromagnetic impulse generated from lightning is the source of whistlers and/or JDPs, thesewaveform durations give upper bounds on the duration of lightning processes, which generated the observedpulses. We measured the time domain LFR‐Hi waveform at 40–100 kHz to identify discrete wave packetswithin seven samples. According to Table 1, all measured wave packet durations vary from 0.277 ms through0.715 ms. These timescales fit well within the range of observed durations of lightning generated radio pulseson the low‐Earth orbit. The whistlers at frequencies <1.25 kHz exhibit dispersion over a few tens of millise-conds above the nightside ionosphere (Santolík et al., 2009) and longer on the dayside (Santolík et al., 2008),

Figure 1. Waves data in the high‐ and low‐band frequency channels of the low‐frequency receiver (LFR‐Hi and LFR‐Lo) combine to give new constraints on thehighest frequencies and shortest durations associated with lightning at frequencies below 150 kHz. Snapshots were obtained with 1‐s cadence over the period from11:58:00 to 12:00:30 on 6 April 2019 in LFR‐Hi (a) and LFR‐Lo (d). Note that each snapshot in LFR‐Hi and LFR‐Lo cannot be overlapped in time due to theinstrumental design and the lightning signatures last on the timescale of submilliseconds. These constraints do not allow us to directly compare thetransient emissions seen in LFR‐Hi and LFR‐Lo. Inset (a): the black line shows Juno's positions in Jovicentric coordinates, while the pink linecorresponds to the interval of interest. (b) A train of VLF/LF radio pulses from 10 to 150 kHz is depicted as a spectrogram converted from a16.384‐ms waveform snapshot, with details of a wave packet of an isolated VLF/LF pulse at 40–100 kHz displayed in (c). The labels in (a) and(b) coincide with the event names listed in Table 1. (e) Whistlers below 20 kHz captured from a 122.88‐ms waveform snapshot are illustrated.The black lines in (d) and (e) represent the local proton cyclotron frequency, fcp, based on Juno's onboard magnetometer (Connerney et al., 2017).

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Figure 2. (a–f) Seven events recorded in six LFR‐Hi waveform snapshots on 6 April 2019. All labels next to panel names correspond to the event names shown inTable 1 and Figure 1. The orange dots indicate the selected upper frequencies of the impulsive radio pulses, whereas the brown dots correspond to startand end periods of the observed wave packets in the frequency range of 40 through 100 kHz.

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while these time intervals become progressively shorter at VLF range (Parrot et al., 2008, 2015). On the otherend of the wide frequency range of lightning radio signals, dispersed transionospheric pulse pairs generatedby intracloud discharges (e.g., Jacobson & Light, 2003) have a duration between a few tens and one hundredmicroseconds.

The magnetic footprints of the observed VLF/LF radio pulses overlapped with detections of UHF sferics in aregion shown by HST maps to host active moist convection. The MWR instrument detected nine UHF sfericsignals between 12:02:14 and 12:04:16 on 6 April 2019, with TA varying from 3.7 to 179.0 K. Recall that thesetimes are not aligned with the VLF/LF radio pulse times because the UHF sferic times are limited to timeswhen the MWR boresight rotates around and aligns with the direction of the thunderstorms. MWR bore-sight positions for these UHF sferics, together with the LFR‐Hi VLF/LF radio pulse magnetic footprints,are superimposed on HST maps in Figure 3 and listed in Table 1.

Localization of radio signal source regions is not precise enough to associate the signals with specific cloudfeatures, and in fact, we cannot rule out the possibility that all of the signals originated from a single cloudfeature. However, HST maps of the general area of the radio signal source region show a particular juxtapo-sition of three cloud structure types that are commonly found in regions with active convection and light-ning: deep water clouds, tall convective towers, and cloud clearings. Figures 3a and 3c use three HSTfilters probing different depths to show the presence of these three cloud structures in the vicinity of theradio signal source regions.

Deep clouds appear as red in this representation and correspond to pressure levels >4 bar at normalincidence (Banfield et al., 1998; Li et al., 2006; West et al., 2004) where only water can condense. The shallowHST viewing angle near 60°N means that these deep clouds could be at slightly lower pressures, but anycloud material at P > 2.5 bar can still only be composed of water given our knowledge of Jupiter's composi-tion (e.g., Wong et al., 2015). Water clouds indicate the potential for moist convection, while adjacent thickand tall clouds suggest active convective towers. Thewater cloudsmay also be rendered visible by downdraftssurrounding the convective towers that clear material from the levels at P < 4 bar. HST cloud‐depth color‐ratio maps in Figures 3b and 3d show both very deep and very high clouds in the lightning source region.

Cloud‐free clearings are the third element of the cloud structure that observationally signifies moist convec-tion and lightning. The other two elements (convective towers and deep water clouds) have been noted inlightning source regions in the Great Red Spot turbulent wake (as observed by the Galileo Orbiter in

Table 1Summary of VLF/LF Radio Pulse and UHF Sferic Events on 6 April 2019

Event Start recordSource locationa in Jovigraphic

Detected Upper Emission Antennanameb time (UTC)c longitude latitude number frequency duration (ms)d temperature TA (K)

R1 11:58:13.692 84.36 61.39 1 57 kHz 0.277 —

R2 11:58:39.692 84.61 60.60 1 60 kHz 0.443 —

R3 11:58:53.667 84.75 60.19 1 75 kHz 0.493 —

R4 11:59:01.692 84.84 59.95 10 128 ± 14 kHz 0.335 ± 0.118 —

R5 11:59:33.667 85.21 59.01 1 65 kHz 0.715 —

R6 11:59:42.667 85.32 58.75 2 55 ± 5 kHz 0.256 ± 0.064 —

R7 11:59:45.667 85.35 58.66 1 65 kHz 0.638 —

S1 12:02:13.838656 79.81 62.06 1 600MHz ≤100 54.2S2 12:02:14.038653 78.50 62.02 1 600MHz ≤100 7.6S3 12:02:43.838618 82.86 60.26 1 600MHz ≤100 179.0S4 12:02:44.638621 78.23 60.11 1 600MHz ≤100 11.5S5 12:03:15.738588 75.17 58.13 1 600MHz ≤100 3.7S6 12:03:45.438059 80.19 56.52 1 600MHz ≤100 8.6S7 12:03:45.538050 79.70 56.51 1 600MHz ≤100 21.5S8 12:04:15.138004 84.04 54.88 1 600MHz ≤100 15.8S9 12:04:16.138003 79.67 54.73 1 600MHz ≤100 11.2

aThe first character of R and S, respectively, stands for VLF/LF radio pulses and UHF sferics, and the second character is an event number in chronologicalorder. bThe interval of observations is 16.384ms forWaves/LFR‐Hi and 100ms forMWR. cThemagnetic footprint of the VLF/LF radio pulse is mapped alonga JRM09 magnetic field line (Connerney et al., 2018) onto 300‐km altitude above the 1‐bar level and the UHF sferic position is MWR boresight location at the5‐bar level. dUsing the fourth‐order Butterworth filter between 40 and 100 kHz, we measure the emission durations for Events R1–R7.

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Gierasch et al., 2000) and in both individual discrete storms as well as cyclonic vortices (as observed by theCassini Orbiter in Dyudina et al., 2004, and by the HST in Wong et al., 2020). Although the deep waterclouds and convective towers in these lightning source regions dominated previous attention, we nowrecognize that cloud‐free clearings are a third element shared among these source regions. The three‐waysignature of lightning and active convection—convective towers, deep water clouds, and clearings—appears as a combination of white, red, and black areas in the color scheme shared by Figure 1 ofGierasch et al. (2000), Figure 9 of Dyudina et al. (2004), Figures 9 and 11 of Wong et al. (2020), and ourFigure 3c. The significance of clearings as an element of the cloud structure of active convective areas isnot yet known. Clearings could either be an indication of thermal conditions that promote convectiveoutbreaks (e.g., Sugiyama et al., 2014) or an after‐effect due to convective downdrafts (e.g., Lunine &Hunten, 1987; Li & Ingersoll, 2015).

4. Discussion and Conclusions

This paper reports the detections of VLF/LF lightning‐induced radio pulses (10–150 kHz) from the JunoWaves instrument on 6 April 2019. These VLF/LF radio pulses may be either whistlers or JDPs. Their mag-netic footprints were spatially colocated with UHF sferic locations recorded at 600MHz by the Juno MWRinstrument. In the lightning source region, HST maps isolated deep clouds (presumably water), as well as

Figure 3. Polar‐projected maps from the Hubble Space Telescope show that the general source area for Juno lightning events includes the three cloud structureelements that are typical of active convection: deep water clouds, high convective towers, and cloud clearings. Color composites of 631 nm (red channel),727 nm (green channel), and 889 nm (blue channel) in panels (a) and (c) give cloud/haze height information in color and opacity information inbrightness. In this composite, deep clouds appear red, high and thick clouds such as convective towers appear white, and clearings appear dark.Tropospheric clearings have a bluish cast at high latitudes because polar stratospheric haze scattering is strong in the 889‐nm filter. Color ratio inpanels (b) and (d) shows cloud depth information (but not opacity information), with high values (red) where clouds are deeper than ∼4 bar and lowvalues (blue) where opacity is dominated by higher‐altitude particulates. The magnetic footprints of VLF/LF radio pulses using the JRM09 magneticfield model (Connerney et al., 2018) are spatially correlated with nine MWR UHF sferic boresight pointings (blue circles in panels c and d; see Table 1).UHF sferic observations are shown as yellow stars. The strongest UHF sferic (S3 event in Table 1) is plotted in (d) with the lightning stroke positionaluncertainty, defined by the −10 dB (or ∼90% received power) contour (Janssen et al., 2017). HST time stamps give the range over which individualframes were acquired (Wong et al., 2020); comparing these with Juno timestamps requires taking into account the one‐way light time of 40.4 min.However, cloud feature morphology and position is not expected to change by more than a few HST pixels over such a short timespan.

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compact opaque clouds extending to high altitudes. The durations of VLF/LF radio pulses range from 0.277through 0.715 ms after the fourth‐order Butterworth filter between 40 and 100 kHz, while their upper fre-quencies reach as high as 128 kHz.

The lightning flash rate from optical and radio detections is still controversial at Jupiter. The optical flashaverage rate for all flashes stronger than the optical energy of 2 × 108 J is 4 × 10−3 flashes/year/km2 usingGalileo images with an exposure time of 6.4–179.2 s (Little et al., 1999) and the flash rate from MWR UHFsferic 100‐ms events is less than 0.03 flashes/year/km2 (Brown et al., 2018). These values are much lowerthan 1–30 flashes/year/km2 based on Jupiter whistlers detected byWaves (Imai et al., 2018; Kolmašová et al.,2018). The HST maps link lightning to meteorologically distinct areas with signs of both deep water cloudsand high/thick clouds extending at least one scale height above them. These localized areas of intense moistconvection may dominate the lightning activity, leading to systematic errors in flash rates determined fromsurveys that are not global in scope.

We found radio signatures of lightning processes lasting ≤0.277 ms, implying that many previousvisible‐imaging lightning detections (as well as MWR UHF sferic detections at timescales of 100 ms) mayhave been integrated over multiple events. The total durations of JDPs are also short, with the majority(95% of 445 detections) within 3.2 ms (Imai et al., 2019). Hence, the optical and microwave radio estimatesof lightning flash rates are probably underestimated, in contrast to the whistler‐based lightning flash ratefrom Waves. The cluster of VLF/LF radio pulses and UHF sferics during Juno's nineteenth perijove effec-tively links lightning (and thus moist convection) to particular patterns of cloud structure (from HSTmaps),which may be used to extend studies of the broader spatial variability of the lightning flash rate on Jupiter.

Data Availability Statement

The data used in this study are publicly accessible via the Planetary Data System (https://pds.nasa.gov) forJuno Waves and MWR instruments and the Wide Field Coverage for Juno program (https://doi.org/10.17909/T94T1H) for the Hubble Space Telescope. The processed data for each figure can be found throughZenodo (https://doi.org/10.5281/zenodo.3930085)

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AcknowledgmentsThe authors are pleased to acknowledgeall members of the Juno mission team.They are also grateful to AndrewIngersoll and an anonymous reviewerfor their helpful suggestions. M. I. alsothanks C. W. Piker and J. B. Faden formany helpful discussions about JunoWaves data calibrations and datavisualization via Autoplot (http://autoplot.org). The research at theUniversity of Iowa was supported byNASA through Contract 699041X withthe Southwest Research Institute.M. H. W. was supported by NASA'sJuno Participating Scientist programand by NASA through grants from theSpace Telescope Science Institute(operated by the Association ofUniversities for Research inAstronomy, Inc., under NASA contractNAS 5‐26555) for Programs GO‐14661,15159, and 15665. I. K. and O. S.acknowledge support from the MSMTLTAUSA17070 grant and from theCzech Academy of Sciences through thePraemium Academiae award. I. dePater graciously shared data used inFigure 3.

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