Rotational Modulation of the High Frequency Limit of Saturn Kilometric Radiation

The high frequency limit (HFL) of the Saturnian Kilometric Radiation (SKR) can probe the deepest SKR sources, closest to Saturn's ionosphere. In this study, we determined and analyzed the SKR HFL throughout the entire Cassini Saturn orbital tour. The maximum frequency of the northern SKR, whose distribution peaks at ∼625 kHz, is shifted by +100 to +200 kHz from the distribution of southern SKR HFL, consistent with the magnetic field offset toward the northern hemisphere at Saturn. The uniformly observed SKR HFL in the vicinity of Saturn suggests a broad extent and beaming of the SKR source. When the observer is confined to certain locations, the rotational modulation of the SKR HFL is clearly observed. This modulation feature of the SKR HFL is statistically established and analyzed in this study. The modulation of HFL is best observed at mid‐latitudes between 10° and 40° and at almost all local times. We perform a simulation that suggests that the modulation of HFL requires the superposition of a “clock” like and a rotating source behavior. By comparing the derived HFL modulation using different longitudes with variable and fixed rotation periods, we can exclude the existence of a magnetic anomaly that was proposed in a previous study based on the Voyager data. The calculation of the least‐square periodogram confirms that the modulation observed in HFL is similar to the ones previously detected at Saturn.

[1]  P. Zarka,et al.  Observations of the First Harmonic of Saturn Kilometric Radiation During Cassini's Grand Finale , 2022, Journal of Geophysical Research: Space Physics.

[2]  C. Jackman,et al.  Saturn Anomalous Myriametric Radiation, a New Type of Saturn Radio Emission Revealed by Cassini , 2022, Geophysical research letters.

[3]  B. Cecconi,et al.  Statistical Study on Spatial Distribution and Polarization of Saturn Narrowband Emissions , 2021, The Astrophysical Journal.

[4]  M. Dougherty,et al.  The landscape of Saturn’s internal magnetic field from the Cassini Grand Finale , 2019, Icarus.

[5]  Thomas A. Burk,et al.  Saturn’s magnetic field revealed by the Cassini Grand Finale , 2018, Science.

[6]  B. Cecconi,et al.  The low-frequency source of Saturn’s kilometric radiation , 2018, Science.

[7]  Emma J. Bunce,et al.  Planetary Period Oscillations in Saturn's Magnetosphere: Cassini Magnetic Field Observations Over the Northern Summer Solstice Interval , 2018 .

[8]  M. Kivelson,et al.  Coupled SKR Emissions in Saturn's Northern and Southern Ionospheres , 2018 .

[9]  D. Gurnett,et al.  An SLS5 Longitude System Based on the Rotational Modulation of Saturn Radio Emissions , 2018, Geophysical Research Letters.

[10]  L. Lamy.  The Saturnian Kilometric Radiation before the Cassini Grand Finale , 2017, 1709.07693.

[11]  G. Provan,et al.  Planetary period modulations of Saturn's magnetotail current sheet during northern spring: Observations and modeling , 2017 .

[12]  C. Jackman,et al.  Low‐Frequency Extensions of the Saturn Kilometric Radiation as a Proxy for Magnetospheric Dynamics , 2016 .

[13]  S. Cowley,et al.  Planetary period oscillations in Saturn's magnetosphere: Further comments on the relationship between post-equinox properties deduced from magnetic field and Saturn kilometric radiation measurements , 2016 .

[14]  D. Gurnett,et al.  Rotational modulation of Saturn's radio emissions after equinox , 2016 .

[15]  Emma J. Bunce,et al.  Field‐aligned currents in Saturn's northern nightside magnetosphere: Evidence for interhemispheric current flow associated with planetary period oscillations , 2015 .

[16]  D. Gurnett,et al.  Saturn kilometric radiation periodicity after equinox , 2015 .

[17]  Stanley W. H. Cowley,et al.  The origin of Saturn's magnetic periodicities: Northern and southern current systems , 2014 .

[18]  P. Zarka,et al.  Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux , 2013 .

[19]  D. G. Mitchell,et al.  Multispectral simultaneous diagnosis of Saturn's aurorae throughout a planetary rotation , 2013, 1307.4675.

[20]  D. Gurnett,et al.  Analysis of Saturn kilometric radiation near a source center , 2011 .

[21]  Baptiste Cecconi,et al.  Planetary period oscillations in Saturn's magnetosphere: Evidence in magnetic field phase data for rotational modulation of Saturn kilometric radiation emissions , 2011 .

[22]  C. Jackman,et al.  Statistical properties of the magnetic field in the Kronian magnetotail lobes and current sheet , 2011 .

[23]  C. Russell,et al.  Saturn's very axisymmetric magnetic field: No detectable secular variation or tilt , 2011 .

[24]  L. Lamy.  Variability of southern and northern periodicities of Saturn Kilometric Radiation , 2011, 1102.3099.

[25]  P. Louarn,et al.  Emission and propagation of Saturn kilometric radiation: magneto-ionic modes, beaming pattern and polarization state , 2011, 1101.3666.

[26]  J. Slavin,et al.  In situ observations of the effect of a solar wind compression on Saturn's magnetotail , 2010 .

[27]  Donald A. Gurnett,et al.  CMI growth rates for Saturnian kilometric radiation , 2010 .

[28]  P. Schippers,et al.  Properties of Saturn kilometric radiation measured within its source region , 2010, 1101.3842.

[29]  Donald A. Gurnett,et al.  A north‐south difference in the rotation rate of auroral hiss at Saturn: Comparison to Saturn's kilometric radio emission , 2009 .

[30]  R. Prangé,et al.  An auroral oval at the footprint of Saturn's kilometric radio sources, colocated with the UV aurorae , 2009 .

[31]  P. Zarka,et al.  Elliptical polarization of Saturn Kilometric Radiation observed from high latitudes , 2009 .

[32]  Philippe Zarka,et al.  On the character and distribution of lower-frequency radio emissions at Saturn and their relationship to substorm-like events , 2009 .

[33]  P. Zarka,et al.  Source locations of narrowband radio emissions detected at Saturn , 2009 .

[34]  Philippe Zarka,et al.  Goniopolarimetric study of the revolution 29 perikrone using the Cassini Radio and Plasma Wave Science instrument high‐frequency radio receiver , 2009 .

[35]  Philippe Zarka,et al.  Modeling of Saturn kilometric radiation arcs and equatorial shadow zone , 2008 .

[36]  Philippe Zarka,et al.  Saturn kilometric radiation: Average and statistical properties , 2008 .

[37]  R. Mutel,et al.  Cluster multispacecraft determination of AKR angular beaming , 2008, 0803.0078.

[38]  Philippe Zarka,et al.  Modulation of Saturn’s radio clock by solar wind speed , 2007, Nature.

[39]  J. Steinberg,et al.  Linear prediction studies for the solar wind and Saturn kilometric radiation , 2006 .

[40]  R. Treumann.  The electron–cyclotron maser for astrophysical application , 2006 .

[41]  Emma J. Bunce,et al.  In situ observations of a solar wind compression‐induced hot plasma injection in Saturn's tail , 2005 .

[42]  William M. Farrell,et al.  A nightside source of Saturn's kilometric radiation: Evidence for an inner magnetosphere energy driver , 2005 .

[43]  P. Zarka,et al.  Direction finding and antenna calibration through analytical inversion of radio measurements performed using a system of two or three electric dipole antennas on a three‐axis stabilized spacecraft , 2005 .

[44]  B. Cecconi,et al.  An Earth-like correspondence between Saturn's auroral features and radio emission , 2005, Nature.

[45]  M. L. Kaiser,et al.  The Cassini Radio and Plasma Wave Investigation , 2004 .

[46]  P. Zarka.  Auroral radio emissions at the outer planets: Observations and theories , 1998 .

[47]  J. Scargle.  Studies in Astronomical Time Series Analysis. V. Bayesian Blocks, a New Method to Analyze Structure in Photon Counting Data , 1997, astro-ph/9711233.

[48]  P. Zarka,et al.  Reply [to “Comment on ‘Evidence of Saturn's magnetic field anomaly from saturnian kilometric radiation high‐frequency limit’”] , 1992 .

[49]  P. Zarka,et al.  Evidence of Saturn's magnetic field anomaly from Saturnian kilometric radiation high‐frequency limit , 1991 .

[50]  M. Desch,et al.  The relationship between Saturn kilometric radiation and the solar wind , 1983 .

[51]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[52]  M. L. Kaiser,et al.  Saturnian kilometric radiation: Source locations , 1982 .

[53]  M. Desch.  Evidence for solar wind control of saturn radio emission , 1982 .

[54]  M. Desch,et al.  Planetary radio astronomy observations from voyager 1 near saturn. , 1981, Science.

[55]  M. Desch,et al.  Voyager Detection of Nonthermal Radio Emission from Saturn , 1980, Science.

[56]  Lou‐Chuang Lee,et al.  A theory of the terrestrial kilometric radiation , 1979 .

[57]  N. Lomb.  Least-squares frequency analysis of unequally spaced data , 1976 .

[58]  Carl E. McIlwain.  Magnetic coordinates , 1966 .