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Planetary Period Oscillations in Saturn's Magnetosphere: Comments on the Relation Between Post-equinox Periods Determined from Magnetic Field and Skr Emission Data : Volume 33, Issue 7 (24/07/2015)

By Cowley, S. W. H.

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Book Id: WPLBN0004002593
Format Type: PDF Article :
File Size: Pages 12
Reproduction Date: 2015

Title: Planetary Period Oscillations in Saturn's Magnetosphere: Comments on the Relation Between Post-equinox Periods Determined from Magnetic Field and Skr Emission Data : Volume 33, Issue 7 (24/07/2015)  
Author: Cowley, S. W. H.
Volume: Vol. 33, Issue 7
Language: English
Subject: Science, Annales, Geophysicae
Collections: Periodicals: Journal and Magazine Collection (Contemporary), Copernicus GmbH
Historic
Publication Date:
2015
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Provan, G., & H. Cowle, S. W. (2015). Planetary Period Oscillations in Saturn's Magnetosphere: Comments on the Relation Between Post-equinox Periods Determined from Magnetic Field and Skr Emission Data : Volume 33, Issue 7 (24/07/2015). Retrieved from http://www.ebooklibrary.org/


Description
Description: Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK. We discuss the properties of Saturn planetary period oscillations (PPOs) deduced from analysis of Saturn kilometric radiation (SKR) modulations by Fischer et al. (2014), and from prior analysis of magnetic field oscillations data by Andrews et al. (2012) and Provan et al. (2013), with emphasis on the post-equinox interval from early 2010 to early 2013. Fischer et al. (2014) characterize this interval as showing single phase-locked periods in the northern and southern SKR modulations observed in polarization-separated data, while the magnetic data generally show the presence of separated dual periods, northern remaining shorter than southern. We show that the single SKR period corresponds to the southern magnetic period early in 2010, segues into the northern period in late 2010, and returns to the southern period in mid-2012, approximately in line with changes in the dominant magnetic oscillation. An exception occurs in mid-February to late August 2011 when two periods are again discerned in SKR data, in good agreement with the ongoing dual periods in the magnetic data. Fischer et al. (2014) discuss this change in terms of a large jump in the southern SKR period related to the Great White Spot storm, which the magnetic data show is primarily due instead to a reappearance in the SKR data of the ongoing southern modulation in a transitory interval of resumed southern dominance. In the earlier interval from early April 2010 to mid-February 2011 when Fischer et al. (2014) deduce single phase-locked periods, we show unequivocal evidence in the magnetic data for the presence of separated dual oscillations of approximately equal amplitude. We suggest that the apparent single SKR periods result from a previously reported phenomenon in which modulations associated with one hemisphere appear in polarization-separated data associated with the other. In the following interval, mid-August 2011 to early April 2012, when Fischer et al. (2014) again report phase-locked northern and southern oscillations, no ongoing southern oscillation of separate period is discerned in the magnetic data. However, the magnetic amplitude data show that if a phase-locked southern oscillation is indeed present, its amplitude must be less than ~ 5–10 % of the northern oscillation.

Summary
Planetary period oscillations in Saturn's magnetosphere: comments on the relation between post-equinox periods determined from magnetic field and SKR emission data

Excerpt
Andrews, D. J., Bunce, E. J., Cowley, S. W. H., Dougherty, M. K., Provan, G., and Southwood D. J.: Planetary period oscillations in Saturn's magnetosphere: Phase relation of equatorial magnetic field oscillations and SKR modulation, J. Geophys. Res., 113, A09205, doi:10.1029/2007JA012937, 2008.; Andrews, D. J., Cowley, S. W. H., Dougherty, M. K., and Provan, G.: Magnetic field oscillations near the planetary period in Saturn's equatorial magnetosphere: Variation of amplitude and phase with radial distance and local time, J. Geophys. Res., 115, A04212, doi:10.1029/2009JA014729, 2010a.; Andrews, D. J., Coates, A. J., Cowley, S. W. H., Dougherty, M. K., Lamy, L., Provan, G., and Zarka, P.: Magnetospheric period oscillations at Saturn: Comparison of equatorial and high-latitude magnetic field periods with north and south SKR periods, J. Geophys. Res., 115, A12252, doi:10.1029/2010JA015666, 2010b.; Andrews, D. J., Cowley, S. W. H., Dougherty, M. K., Lamy, L., Provan, G., and Southwood, D. J.: Planetary period oscillations in Saturn's magnetosphere: Evolution of magnetic oscillation properties from southern summer to post-equinox, J. Geophys. Res., 117, A04224, doi:10.1029/2011JA017444, 2012.; Badman, S. V., Andrews, D. J., Cowley, S. W. H., Lamy, L., Provan, G., Tao, C., Kasahara, S., Kimura, T., Fujimoto, M., Melin, H., Stallard, T., Brown, R.H., and Baines, K.H.: Rotational modulation and local time dependence of Saturn's infrared H3+ auroral intensity, J. Geophys. Res., 117, A09228, doi:10.1029/2012JA017990, 2012.; Burch, J. L., DeJong, A. D., Goldstein, J., and Young, D. T.: Periodicity in Saturn's magnetosphere: Plasma cam, Geophys. Res. Lett., 36, L14203, doi:10.1029/2009GL039043, 2009.; Carbary, J. F., Mitchell, D. G., Krimigis, S. M., and Krupp N.: Electron periodicities in Saturn's outer magnetosphere, J. Geophys. Res., 112, A03206, doi:10.1029/2006JA012077, 2007.; Cowley, S. W. H. and Provan, G.: Saturn's magnetospheric planetary period oscillations, neutral atmosphere circulation, and thunderstorm activity: Implications, or otherwise, for physical links, J. Geophys. Res., 118, 7246–7261, doi:10.1002/2013JA019200, 2013.; Fischer, G., Ye, S.-Y., Groene, J. B., Ingersoll, A. P., Sayanagi, K. M., Menietti, J. D., Kurth, W. S., and Gurnett, D. A.: A possible influence of the Great White Spot on Saturn kilometric radiation periodicity, Ann. Geophys., 32, 1463–1476, doi:10.5194/angeo-32-1463-2014, 2014.; Fischer, G., Gurnett, D. A., Kurth, W. S., Ye, S.-Y., and Groene, J. B.: Saturn kilometric radiation periodicity after equinox, Icarus, 254, 72–91, 2015.; Galopeau, P. H. M. and Lecacheux A.: Variations of Saturn's radio rotation period measured at kilometer wavelengths, J. Geophys. Res., 105, 13089–13101, 2000.; Gurnett, D. A., Kurth, W. S., and Scarf, F. L.: Plasma waves near Saturn: Initial results from Voyager 1, Science, 212, 235–239, 1981.; Gurnett, D. A., Lecacheux, A., Kurth, W. S., Persoon, A. M., Groene, J. B., Lamy, L., Zarka, P., and Carbary, J. F.: Discovery of a north-south asymmetry in Saturn's radio rotation period, Geophys. Res. Lett., 36, L16102, doi:10.1029/2009GL039621, 2009.; Gurnett, D. A., Groene, J. B., Averkamp, T. F., Kurth, W. S., Ye, S.-Y., and Fischer, G.: The SLS4 longitude system based on a tracking filter analysis of the rotat

 

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