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Solar wind dynamic pressure upstream from Saturn: Estimation from magnetosheath properties and comparison with SKR

Solar wind dynamic pressure upstream from Saturn: Estimation from magnetosheath properties and comparison with SKR
Solar wind dynamic pressure upstream from Saturn: Estimation from magnetosheath properties and comparison with SKR

An analytical method is developed by which measurements made by the Cassini spacecraft in Saturn's magnetosheath can be used to infer the upstream solar wind parameters, specifically the solar wind speed (Vsw) and the dynamic pressure (Pd). The method is validated by comparing the results with other estimates of these parameters, including the mSWiM MHD model and magnetopause and bow shock models applied to observed boundary crossings. The comparisons suggest that the new inferred Vsw are on average ~40 km/s lower than the mSWiM values, and the dynamic pressure values are slightly lower as well. We find few of the lower Pd values predicted by mSWiM, probably because Cassini would have been inside the expanded magnetosphere under such conditions. Systematic temporal variations such as interplanetary shocks do seem to be captured well, with arrival times within several days of the MHD prediction. Compared to dynamic pressures estimated from boundary crossings with well-known magnetopause and bow shock models, the magnetosheath-inferred dynamic pressure tends to be somewhat lower, but within the uncertainties of the analytical derivation. Comparison of the inferred dynamic pressure with observed Saturn's kilometric radiation (SKR) activity reveals several episodes of very good temporal tracking between dynamic pressure and SKR intensity, with relatively short time delays (4–5 hr), suggesting rather direct driving. Such good tracking intervals occur almost exclusively on the dawnside of the magnetosphere, where the dominant SKR source is visible. When the tracking is good, the SKR fluxes vary roughly as the square of the dynamic pressure.

kilometric radiation, magnetosheath, Saturn, solar wind dynamic pressure
2169-9380
7799-7819
Thomsen, M. F.
bc09abeb-5d20-449f-9f54-568fff6d220c
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Lamy, L.
aad11182-ba51-4937-99f3-cf983891abdd
Thomsen, M. F.
bc09abeb-5d20-449f-9f54-568fff6d220c
Jackman, C. M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Lamy, L.
aad11182-ba51-4937-99f3-cf983891abdd

Thomsen, M. F., Jackman, C. M. and Lamy, L. (2019) Solar wind dynamic pressure upstream from Saturn: Estimation from magnetosheath properties and comparison with SKR. Journal of Geophysical Research: Space Physics, 124 (10), 7799-7819. (doi:10.1029/2019JA026819).

Record type: Article

Abstract

An analytical method is developed by which measurements made by the Cassini spacecraft in Saturn's magnetosheath can be used to infer the upstream solar wind parameters, specifically the solar wind speed (Vsw) and the dynamic pressure (Pd). The method is validated by comparing the results with other estimates of these parameters, including the mSWiM MHD model and magnetopause and bow shock models applied to observed boundary crossings. The comparisons suggest that the new inferred Vsw are on average ~40 km/s lower than the mSWiM values, and the dynamic pressure values are slightly lower as well. We find few of the lower Pd values predicted by mSWiM, probably because Cassini would have been inside the expanded magnetosphere under such conditions. Systematic temporal variations such as interplanetary shocks do seem to be captured well, with arrival times within several days of the MHD prediction. Compared to dynamic pressures estimated from boundary crossings with well-known magnetopause and bow shock models, the magnetosheath-inferred dynamic pressure tends to be somewhat lower, but within the uncertainties of the analytical derivation. Comparison of the inferred dynamic pressure with observed Saturn's kilometric radiation (SKR) activity reveals several episodes of very good temporal tracking between dynamic pressure and SKR intensity, with relatively short time delays (4–5 hr), suggesting rather direct driving. Such good tracking intervals occur almost exclusively on the dawnside of the magnetosphere, where the dominant SKR source is visible. When the tracking is good, the SKR fluxes vary roughly as the square of the dynamic pressure.

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Thomsen_et_al-2019-Journal_of_Geophysical_Research__Space_Physics - Version of Record
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Accepted/In Press date: 7 June 2019
e-pub ahead of print date: 17 October 2019
Keywords: kilometric radiation, magnetosheath, Saturn, solar wind dynamic pressure

Identifiers

Local EPrints ID: 436536
URI: http://eprints.soton.ac.uk/id/eprint/436536
ISSN: 2169-9380
PURE UUID: 8ec83322-5c9d-4717-8c28-473a9d9e4a63
ORCID for C. M. Jackman: ORCID iD orcid.org/0000-0003-0635-7361

Catalogue record

Date deposited: 12 Dec 2019 17:30
Last modified: 22 Nov 2021 07:53

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Contributors

Author: M. F. Thomsen
Author: C. M. Jackman ORCID iD
Author: L. Lamy

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