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Large Scale Structure of the Solar Wind, Poynting Flux, and Ion Energy Flow between 35 and 130 Solar Radii.

Abstract : Measurements from the FIELDS and SWEAP instrument suites on Parker Solar Probe (PSP) are presented in order to investigate disparate aspects of the large scale structure of the solar wind and its associated Poynting and ion energy flux. The observations are obtained during a 30 day period beginning 10/31/2018 over radial distances from 36 to 130 Rs . We focus primarily on phenomena over time scales of >1 minutes, although, we do include some discussion of the contribution of short duration magnetic field, velocity, and Poynting flux spikes (switchbacks) (Bale et al., 2019, Mozer et al. this session) to longer term averages of ion energy flux and Poynting flux. Some of the observations include 1) PSP observed three fast solar wind streams with enhanced ion energy flux and Poynting flux falling with distance between 35 and 130 Rs over the 30 day period. These same streams were observed at 1 AU providing one of the largest baseline measurements of high-speed streams. 2) In a different study near perihelion, because of shifts between retrograde and prograde motion of the spacecraft relative to the solar surface, PSP explored features on the sun at the same Carrington longitude as many as three times. This leads to the observation that the reported CMEs observation on 10/31 and 11/11 occur at the same longitude of 327o and are arguably manifestations of the same long-term " evolving structure'. 3) Finally, with regard to energy flow, PSP also has phases of its trajectory lasting ~2 days when it moves ~6 Rs (38 to 46 Rs) in radial distance while moving less than 10 in longitude. These orbital configurations have been exploited to provide estimates of the average Poynting flux and ion energy flux over radial distance. When the Poynting flux (Sr) from 1 Hz to >30 minutes is averaged over 0.5 hours, the radial Poynting flux (~<1 mW/m2) is ~ an order of magnitude smaller than the steady state ion energy flux (8 mW/m2) and it's associated spatial or temporal variations. Evaluating the entire data base, the observed energy fluxes decrease strongly with radial distance with a major effect being the radial expansion of the solar wind. To model this expansion, we normalize Poynting flux as Sr(R/Rs)2 and also Sr(Br(Rs/Br(R) (analogous to cross helicity) and similarly normalize ion energy flux, and (as yet) find no obvious systematic dependence on radial distance.
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https://hal-insu.archives-ouvertes.fr/insu-03562460
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Submitted on : Wednesday, February 9, 2022 - 7:26:31 AM
Last modification on : Tuesday, May 10, 2022 - 3:24:57 PM

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J. R. Wygant, F. Mozer, S. D. Bale, M. Pulupa, S. T. Badman, et al.. Large Scale Structure of the Solar Wind, Poynting Flux, and Ion Energy Flow between 35 and 130 Solar Radii.. American Geophysical Union, 2019, San Francisco, United States. 15 pp. ⟨insu-03562460⟩

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