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Solar Wind influence on Jupiter Hectometric and Decametric Radiation

Problem description:

Case of Jovian decametric emissions:

The first investigations have examined the possibility of some relationship between Jupiter?s decametric radio emissions (DAM) as observed by ground-based radiotelescope and solar activity. Gallet (1957) was the first who foresaw the possibility of a long term anti-correlation (Fig.1 ? left panel) between the sunspot cycle and the DAM probability of occurrence. Carr et al. (1958) also noted that the most intense DAM noise storms seemed to occur at roughly 7- to 8-days intervals.

Fig.1: Annual variation of Jupiter burst activity (left panel) compared with the sunspot cycle (Roberts, 1963), and the corresponding idealized geometry configuration (right panel) where solar wind velocity spirals could produce coincidences or negative delays immediately before opposition (Barrow, 1985).

 

Barrow (1972) found a significant correlation when he combined the daily geomagnetic Cp-index and Jovian decametric emissions recorded from 1961 to 1968. The author estimated the delay in days between the arrival of particles at the Earth and at Jupiter and found a delay of about 9-days and 12-days depending on the geometry configuration of Earth-Sun-Jupiter. These and other earlier correlation studies were reviewed by Carr and Desch (1976) who discuss the conflicting results indicating anti-correlation, no solar influence, or positive correlations. One can note that these investigations are based on the assumption that solar particles disturb the Earth?s magnetic field and later on the Jovian magnetosphere where they trigger by some means the decametric radio emissions (Fig.1 ? right panel). More detailed analysis of Genova et al. (1989) showed that only emission not controlled by the Io satellite (so-called non-Io-controlled emissions) could be subject to solar effect.

Case of Jovian hectometric emissions:

The space era allowed us to realize the existence of other Jovian radio emissions which are not observable from ground-based radio stations. One of them is the Jovian hectometric (HOM) radiation which was detected by early space-borne radio telescopes (Brown, 1974).

Fig.2: Variation of the hectometric relative intensity measured by Galileo as a function of the time (top panel). The intensity (at 800 kHz with a time resolution of 0.8 min) has been normalized to a distance of 60 RJ and averaged over each Jovian rotation. The vertical bars indicate the standard deviation over each rotation. Variation of the solar wind flow speed, measured near the Earth?s orbit by Wind/SWE, as a function of the time, moved forward 153 days (middle panel). The data have been averaged over 10 hours. Variation of the hectometric intensity measured by Wind for the same time period (bottom panel). The intensity (at 680 kHz manually picked every 1 min) has been averaged over each Jovian rotation. ??HOM events?? are marked by arrows and observed by Galileo and Wind with a time lag (indicated by A), almost simultaneously by both spacecraft (indicated by B), and only by Galileo (indicated by C).
Fig.3: Occurrence probability of the Jovian hectometric emissions versus the central meridian longitude ? CML ? (left panel). These HOM histograms are derived from data recorded by the Wind/WAVES and Galileo/PWS experiments where the two specific Jovian longitudes (CML ~ 120° and CML ~ 320°) coincide with occurrence of the ?particle events?. Right panel shows a schematic representation of the connection between the equatorial ?particle events? location and the aurora region where the hectometric emissions are supposed to be generated.

 

Using Voyager data, Desch and Barrow (1984) investigated the correlation between HOM energy and the solar wind density and velocity fluctuations at Jupiter. A significant positive correlation was found between variations in the HOM energy and the solar wind density but not the solar wind velocity. Galopeau and Boudjada (2005) confirmed this relationship between the HOM intensity and the solar wind parameters by combining WAVES and PWS experiments onboard Wind and Galileo spacecraft (Fig.2). They also showed that the HOM intensity is occurring at two specific Jovian longitudes (Fig.3 - left panel) where in addition ?particle events? took place as reported by Mauk et al. (1997). A scenario of the physical process occurring in the Jovian magnetosphere is shown in Fig.3 - right panel (from Mauk and Sauer, 2007) where the ?particle events? observed mainly in the equatorial magnetic plan of the planet are connected to the auroral region where the Jovian hectometric emissions are generated. In this scenario the electrons associated to the HOM and the ?particle events? seem to have a solar wind origin.

References:

  • Barrow, C.H., The influence of the Sun on Jupiter?s radio emission, in Planetary Radio Emissions I, Ed.: H.O. Rucker and S.J. Bauer, Austrian Academy of Sciences, p. 148, 1985.
  • Barrow, C. H., Decametre wave radiation from Jupiter and solar activity, Planet. Space Sci., 20, 2051, 1972.
  • Brown, L. W., Spectral behavior of Jupiter near 1 MHz, Astrophys. J., 194, L159? L162, 1974.
  • Carr, T. D., M. D. Desch, and J. K. Alexander, Phenomenology of magnetospheric radio emissions, in Physics of the Jovian Magnetosphere, edited by A. J. Dessler, pp. 226?284, Cambridge Univ. Press, New York., 1983.
  • Carr, T.D., Smith, A.G., Pepple, R. et al. 18-Megacycle observations of Jupiter in 1957, Astrophys. J., 127, 274?284, 1958.
  • Desch, M. D., and C. H. Barrow, Direct evidence for solar wind control of Jupiter?s hectometer-wavelength radio emission, J. Geophys. Res., 89, 6819? 6823, 1984.
  • Gallet, R. M., Results of the observations of Jupiter's radio emission on 18 and 20 Mc/s in 1956 and 1957, Trans. Inst. Rad., 5, 327, 1957.
  • Galopeau, P.H.M., and M.Y. Boudjada, Solar wind control of Jovian auroral emissions, J. Geophys. Res., 110, A09221, doi:10.1029/2004JA010843, 2005.
  • Genova, F., P. Zarka, and A. Lecacheux, Jupiter decametric radiation, in Time Variable Phenomena in the Jovian System, Rep. NASA SP-494, edited by M. J. S. Belton, R. A. West, and J. Rahe, pp. 156? 174, NASA, Greenbelt, Md, 1989.
  • Mauk, B. H., D. J. Williams, and R. W. McEntire, Energy-time dispersed charged particle signatures of dynamic injections in Jupiter?s inner magnetosphere, Geophys. Res. Lett., 24, 2949 ? 2952, 1997.
  • Mauk, B., and J. Saur, Equatorial electron beams and auroral structuring at Jupiter, J. Geophys. Res., 112, A10221, doi:10.1029/2007JA012370, 2007.
  • Roberts, J. A., Radio emission from the planets, Planet. Space Sci., 11, 221, 1963.