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Spectral Structures of Jovian Broadband Kilometric Radiation Revealed by Cassini and Juno.

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Title: Spectral Structures of Jovian Broadband Kilometric Radiation Revealed by Cassini and Juno.
Authors: Fischer, G.1,2 (AUTHOR) georg.fischer@uni-graz.at, Taubenschuss, U.3 (AUTHOR), Píša, D.3 (AUTHOR), Imai, M.3 (AUTHOR), Kurth, W. S.4 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Jan2025, Vol. 130 Issue 1, p1-26. 26p.
Subject Terms: Gas giants, Lunar phases, Radio waves, Juno (Space probe), Rotational motion
Abstract: Cassini flew past Jupiter in 2000/2001, and Juno has been orbiting the gas giant since mid‐2016. Here we focus on the spectral properties of Jovian broadband kilometric radiation (bKOM), and we classified them according to their slope in the time–frequency spectrum and distinguish four categories with negative, positive, mixed, or no slope in frequency. These bKOM structures had mostly negative slopes during the inbound portion of the Cassini Jupiter flyby, whereas they were mostly positive for the outbound. The reason for this could be higher intensities of bKOM emissions from midnight to dawn local times. We interpret the semi‐circles of the Jovian radio emission nicknamed "bullseyes" as negatively sloped bKOM connected with positively sloped bKOM, and we detected 40 bullseyes in Juno Waves data until the end of 2017. Cassini and Juno show similar distributions of bKOM with respect to the Jovian Central Meridian Longitude like the Voyagers and Ulysses. This means that bKOM has not changed over several decades and "rotates" with the system III period. Several features of the bKOM structures suggest emission cones with thick mantles and moderate beaming angles around 50° $50{}^{\circ}$. We found an enhancement of the occurrence probability of southern bKOM for certain phases of Ganymede and Callisto. Plain Language Summary: In this paper we investigated the spectral properties of Jovian broadband kilometric radiation (bKOM) with the radio wave instruments of the spacecraft Cassini and Juno. bKOM emissions have a wavelength of a few kilometers. We classified bKOM spectral structures according to their slope in the time–frequency spectrum and distinguish four categories of bKOM with negative, positive, mixed, or no slope. We detected 40 so‐called "bullseye" radio emissions in the Juno data until the end of 2017. These semi‐circles were previously detected by the Ulysses spacecraft, and we interpret them as bKOM in which negatively sloped bKOM is immediately followed by positively sloped bKOM. We found that bKOM is very stable and occurs and rotates with the Jupiter system III period. We also detected a possible influence of the moons Ganymede and Callisto on the occurrence probability of bKOM, which is somewhat enhanced at certain moon phases. We draw conclusion about the beaming properties of bKOM, which is most likely emitted in emission cones with thick cone mantles and moderate beaming angles. Key Points: We classified Jovian broadband kilometric radiation (bKOM) into 4 categories with negative, positive, mixed, or no slope in dynamic spectraRadio "bullseyes" might be special bKOM structures of negatively sloped bKOM followed by positively sloped bKOMThe occurrence probability of southern bKOM was enhanced during certain moon phases of Ganymede and Callisto [ABSTRACT FROM AUTHOR]
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Abstract:Cassini flew past Jupiter in 2000/2001, and Juno has been orbiting the gas giant since mid‐2016. Here we focus on the spectral properties of Jovian broadband kilometric radiation (bKOM), and we classified them according to their slope in the time–frequency spectrum and distinguish four categories with negative, positive, mixed, or no slope in frequency. These bKOM structures had mostly negative slopes during the inbound portion of the Cassini Jupiter flyby, whereas they were mostly positive for the outbound. The reason for this could be higher intensities of bKOM emissions from midnight to dawn local times. We interpret the semi‐circles of the Jovian radio emission nicknamed "bullseyes" as negatively sloped bKOM connected with positively sloped bKOM, and we detected 40 bullseyes in Juno Waves data until the end of 2017. Cassini and Juno show similar distributions of bKOM with respect to the Jovian Central Meridian Longitude like the Voyagers and Ulysses. This means that bKOM has not changed over several decades and "rotates" with the system III period. Several features of the bKOM structures suggest emission cones with thick mantles and moderate beaming angles around 50° $50{}^{\circ}$. We found an enhancement of the occurrence probability of southern bKOM for certain phases of Ganymede and Callisto. Plain Language Summary: In this paper we investigated the spectral properties of Jovian broadband kilometric radiation (bKOM) with the radio wave instruments of the spacecraft Cassini and Juno. bKOM emissions have a wavelength of a few kilometers. We classified bKOM spectral structures according to their slope in the time–frequency spectrum and distinguish four categories of bKOM with negative, positive, mixed, or no slope. We detected 40 so‐called "bullseye" radio emissions in the Juno data until the end of 2017. These semi‐circles were previously detected by the Ulysses spacecraft, and we interpret them as bKOM in which negatively sloped bKOM is immediately followed by positively sloped bKOM. We found that bKOM is very stable and occurs and rotates with the Jupiter system III period. We also detected a possible influence of the moons Ganymede and Callisto on the occurrence probability of bKOM, which is somewhat enhanced at certain moon phases. We draw conclusion about the beaming properties of bKOM, which is most likely emitted in emission cones with thick cone mantles and moderate beaming angles. Key Points: We classified Jovian broadband kilometric radiation (bKOM) into 4 categories with negative, positive, mixed, or no slope in dynamic spectraRadio "bullseyes" might be special bKOM structures of negatively sloped bKOM followed by positively sloped bKOMThe occurrence probability of southern bKOM was enhanced during certain moon phases of Ganymede and Callisto [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2024JA032826