Publication:
Measures of Scale-dependent Alfvénicity in the First PSP Solar Encounter

Issued Date

2020-02-01

Resource Type

Article

ISSN

00670049

DOI

10.3847/1538-4365/ab64e6

Other identifier(s)

2-s2.0-85087211243

Rights

Mahidol University

Rights Holder(s)

SCOPUS

Bibliographic Citation

Astrophysical Journal, Supplement Series. Vol.246, No.2 (2020)

Suggested Citation

T. N. Parashar, M. L. Goldstein, M. L. Goldstein, B. A. Maruca, W. H. Matthaeus, D. Ruffolo, R. Bandyopadhyay, R. Chhiber, R. Chhiber, A. Chasapis, R. Qudsi, D. Vech, D. Vech, D. A. Roberts, S. D. Bale, S. D. Bale, S. D. Bale, J. W. Bonnell, T. Dudok De Wit, K. Goetz, P. R. Harvey, R. J. MacDowall, D. Malaspina, M. Pulupa, J. C. Kasper, J. C. Kasper, K. E. Korreck, A. W. Case, M. Stevens, P. Whittlesey, D. Larson, R. Livi, M. Velli, N. Raouafi Measures of Scale-dependent Alfvénicity in the First PSP Solar Encounter. Astrophysical Journal, Supplement Series. Vol.246, No.2 (2020). doi:10.3847/1538-4365/ab64e6 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/57865

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Title

Measures of Scale-dependent Alfvénicity in the First PSP Solar Encounter

Author(s)

T. N. Parashar
 M. L. Goldstein
 M. L. Goldstein
 B. A. Maruca
 W. H. Matthaeus
 D. Ruffolo
 R. Bandyopadhyay
 R. Chhiber
 R. Chhiber
 A. Chasapis
 R. Qudsi
 D. Vech
 D. Vech
 D. A. Roberts
 S. D. Bale
 S. D. Bale
 S. D. Bale
 J. W. Bonnell
 T. Dudok De Wit
 K. Goetz
 P. R. Harvey
 R. J. MacDowall
 D. Malaspina
 M. Pulupa
 J. C. Kasper
 J. C. Kasper
 K. E. Korreck
 A. W. Case
 M. Stevens
 P. Whittlesey
 D. Larson
 R. Livi
 M. Velli
 N. Raouafi

Other Contributor(s)

Universite d'Orleans
 University of Minnesota Twin Cities
 Space Sciences Laboratory at UC Berkeley
 University of California, Los Angeles
 University of Michigan, Ann Arbor
 University of California, Berkeley
 University of Maryland, Baltimore County
 Imperial College London
 Mahidol University
 Smithsonian Astrophysical Observatory
 NASA Goddard Space Flight Center
 Johns Hopkins University
 The Bartol Research Institute
 University of Colorado Boulder

Abstract

© 2020. The American Astronomical Society. All rights reserved.. The solar wind shows periods of highly Alfvénic activity, where velocity fluctuations and magnetic fluctuations are aligned or antialigned with each other. It is generally agreed that solar wind plasma velocity and magnetic field fluctuations observed by the Parker Solar Probe (PSP) during the first encounter are mostly highly Alfvénic. However, quantitative measures of Alfvénicity are needed to understand how the characterization of these fluctuations compares with standard measures from prior missions in the inner and outer heliosphere, in fast wind and slow wind, and at high and low latitudes. To investigate this issue, we employ several measures to quantify the extent of Alfvénicity - the Alfvén ratio r A, the normalized cross helicity σ c , the normalized residual energy σ r , and the cosine of angle between velocity and magnetic fluctuations . We show that despite the overall impression that the Alfvénicity is large in the solar wind sampled by PSP during the first encounter, during some intervals the cross helicity starts decreasing at very large scales. These length scales (often >1000d i ) are well inside inertial range, and therefore, the suppression of cross helicity at these scales cannot be attributed to kinetic physics. This drop at large scales could potentially be explained by large scale shears present in the inner heliosphere sampled by PSP. In some cases, despite the cross helicity being constant down to the noise floor, the residual energy decreases with scale in the inertial range. These results suggest that it is important to consider all these measures to quantify Alfvénicity.

Keyword(s)

Earth and Planetary Sciences
 Physics and Astronomy

Availability

URI

https://repository.li.mahidol.ac.th/handle/20.500.14594/57865

Collections

Scopus 2020