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Saturn's Nightside Dynamics During Cassini's F Ring and Proximal Orbits: Response to Solar Wind and Planetary Period Oscillation Modulations.

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Title: Saturn's Nightside Dynamics During Cassini's F Ring and Proximal Orbits: Response to Solar Wind and Planetary Period Oscillation Modulations.
Authors: Bradley, T. J.1 tb252@le.ac.uk, Cowley, S. W. H.1, Bunce, E. J.1, Melin, H.1, Provan, G.1, Nichols, J. D.1, Dougherty, M. K.2, Roussos, E.3, Krupp, N.3, Tao, C.4,5, Lamy, L.6, Pryor, W. R.7, Hunt, G. J.2
Source: Journal of Geophysical Research. Space Physics. Sep2020, Vol. 125 Issue 9, p1-39. 39p.
Subject Terms: *Solar activity, Space vehicles, Magnetosphere, Magnetic fields, Rotation of the Sun
Abstract: We examine the final 44 orbits of the Cassini spacecraft traversing the midnight sector of Saturn's magnetosphere to distances of ~21 Saturn radii, to investigate responses to heliospheric conditions inferred from model solar wind and Cassini galactic cosmic ray flux data. Clear storm responses to anticipated magnetospheric compressions are observed in magnetic field and energetic particle data, together with Saturn kilometric radiation (SKR), auroral hiss, and ultraviolet auroral emissions. Most compression events are associated with corotating interaction regions, producing ~2-3.5 day intervals of magnetospheric activity that are recurrent with the ~26 day solar rotation period (one or two such events per rotation), though one on the final pass is related to a nonrecurrent interplanetary shock possibly associated with an earlier X-class solar flare. The response to compressions is modulated by the concurrent relative phasing of the northern and southern planetary period oscillation (PPO) systems, with long (>1 planetary rotation) SKR low-frequency extension (LFE) intervals associated with strong field-aligned coupling currents being favored when the two PPO systems act together to thin and thicken the tail plasma sheet during each PPO cycle. LFE onsets/intensifications are then favored at thin plasma sheet phases most unstable to reconnection, producing energetic nightside particle injections and poleward contractions of dawn-brightened auroras. Correspondingly, solar rotation recurrent intervals of magnetospheric quiet conditions also occur with weak energetic particle fluxes and auroral emissions, associated with extended solar wind rarefactions. Overall, the results emphasize how strongly activity in Saturn's magnetosphere is modulated by concurrent heliospheric conditions. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Saturn's Nightside Dynamics During Cassini's F Ring and Proximal Orbits: Response to Solar Wind and Planetary Period Oscillation Modulations.
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  Data: <searchLink fieldCode="AR" term="%22Bradley%2C+T%2E+J%2E%22">Bradley, T. J.</searchLink><relatesTo>1</relatesTo><i> tb252@le.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Cowley%2C+S%2E+W%2E+H%2E%22">Cowley, S. W. H.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Bunce%2C+E%2E+J%2E%22">Bunce, E. J.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Melin%2C+H%2E%22">Melin, H.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Provan%2C+G%2E%22">Provan, G.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Nichols%2C+J%2E+D%2E%22">Nichols, J. D.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Dougherty%2C+M%2E+K%2E%22">Dougherty, M. K.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Roussos%2C+E%2E%22">Roussos, E.</searchLink><relatesTo>3</relatesTo><br /><searchLink fieldCode="AR" term="%22Krupp%2C+N%2E%22">Krupp, N.</searchLink><relatesTo>3</relatesTo><br /><searchLink fieldCode="AR" term="%22Tao%2C+C%2E%22">Tao, C.</searchLink><relatesTo>4,5</relatesTo><br /><searchLink fieldCode="AR" term="%22Lamy%2C+L%2E%22">Lamy, L.</searchLink><relatesTo>6</relatesTo><br /><searchLink fieldCode="AR" term="%22Pryor%2C+W%2E+R%2E%22">Pryor, W. R.</searchLink><relatesTo>7</relatesTo><br /><searchLink fieldCode="AR" term="%22Hunt%2C+G%2E+J%2E%22">Hunt, G. J.</searchLink><relatesTo>2</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Space+Physics%22">Journal of Geophysical Research. Space Physics</searchLink>. Sep2020, Vol. 125 Issue 9, p1-39. 39p.
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  Data: *<searchLink fieldCode="DE" term="%22Solar+activity%22">Solar activity</searchLink><br /><searchLink fieldCode="DE" term="%22Space+vehicles%22">Space vehicles</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetosphere%22">Magnetosphere</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+fields%22">Magnetic fields</searchLink><br /><searchLink fieldCode="DE" term="%22Rotation+of+the+Sun%22">Rotation of the Sun</searchLink>
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  Data: We examine the final 44 orbits of the Cassini spacecraft traversing the midnight sector of Saturn's magnetosphere to distances of ~21 Saturn radii, to investigate responses to heliospheric conditions inferred from model solar wind and Cassini galactic cosmic ray flux data. Clear storm responses to anticipated magnetospheric compressions are observed in magnetic field and energetic particle data, together with Saturn kilometric radiation (SKR), auroral hiss, and ultraviolet auroral emissions. Most compression events are associated with corotating interaction regions, producing ~2-3.5 day intervals of magnetospheric activity that are recurrent with the ~26 day solar rotation period (one or two such events per rotation), though one on the final pass is related to a nonrecurrent interplanetary shock possibly associated with an earlier X-class solar flare. The response to compressions is modulated by the concurrent relative phasing of the northern and southern planetary period oscillation (PPO) systems, with long (>1 planetary rotation) SKR low-frequency extension (LFE) intervals associated with strong field-aligned coupling currents being favored when the two PPO systems act together to thin and thicken the tail plasma sheet during each PPO cycle. LFE onsets/intensifications are then favored at thin plasma sheet phases most unstable to reconnection, producing energetic nightside particle injections and poleward contractions of dawn-brightened auroras. Correspondingly, solar rotation recurrent intervals of magnetospheric quiet conditions also occur with weak energetic particle fluxes and auroral emissions, associated with extended solar wind rarefactions. Overall, the results emphasize how strongly activity in Saturn's magnetosphere is modulated by concurrent heliospheric conditions. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1029/2020JA027907
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        Text: English
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      – SubjectFull: Solar activity
        Type: general
      – SubjectFull: Space vehicles
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      – SubjectFull: Magnetosphere
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      – SubjectFull: Rotation of the Sun
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