MMS Observations of Reconnection at Dayside Magnetopause Crossings During Transitions of the Solar Wind to Sub-Alfvénic Flow

Authors

Charlie J. Farrugia, University of New HampshireFollow
Noe Lugaz, University of New HampshireFollow
L. Alm, Swedish Institute of Space Physics
Bernard J. Vasquez, University of New HampshireFollow
Matthew Argall, University of New HampshireFollow
Harald Kucharek, University of New HampshireFollow
Hiroshi Matsui, University of New HampshireFollow
Roy B. Torbert, University of New HampshireFollow
Benoit Lavraud, Universite de Toulouse
O. Le Contel, University Paris
C. M. S. Cohen, California Institute of Technology
J. L. Burch, Southwest Research Institute
C. T. Russell, University of California
R. J. Strangeway, University of California
J. Shuster, NASA Goddard Space Flight Center
J. C. Dorelli, NASA Goddard Space Flight Center
J. P. Eastwood, Imperial College London
R. E. Ergun, University of Colorado
S. A. Fuselier, Southwest Research Institute
D. J. Gershman, NASA Goddard Space Flight Center
B. L. Giles, NASA Goddard Space Flight Center
Y. V. Khotyaintsev, Swedish Institute of Space Physics
P. A. Lindqvist, Swedish Institute of Space Physics
G. T. Marklund, Swedish Institute of Space Physics
K. W. Paulson, University of New Hampshire, Durham
S. M. Petrinec, Lockheed Martin Advanced Technology Center
T. D. Phan, Space Sciences Laboratory
C. J. Pollock, NASA Goddard Space Flight Center

Abstract

We present MMS observations during two dayside magnetopause crossings under hitherto unexamined conditions: (i) when the bow shock is weakening and the solar wind transitioning to sub-Alfvénic flow and (ii) when it is reforming. Interplanetary conditions consist of a magnetic cloud with (i) a strong B (∼20 nT) pointing south and (ii) a density profile with episodic decreases to values of ∼0.3 cm−3 followed by moderate recovery. During the crossings the magnetosheath magnetic field is stronger than the magnetosphere field by a factor of ∼2.2. As a result, during the outbound crossing through the ion diffusion region, MMS observed an inversion of the relative positions of the X and stagnation (S) lines from that typically the case: the S line was closer to the magnetosheath side. The S line appears in the form of a slow expansion fan near which most of the energy dissipation is taking place. While in the magnetosphere between the crossings, MMS observed strong field and flow perturbations, which we argue to be due to kinetic Alfvén waves. During the reconnection interval, whistler mode waves generated by an electron temperature anisotropy (Te⊥>Te∥) were observed. Another aim of the paper is to distinguish bow shock-induced field and flow perturbations from reconnection-related signatures. The high-resolution MMS data together with 2-D hybrid simulations of bow shock dynamics helped us to distinguish between the two sources. We show examples of bow shock-related effects (such as heating) and reconnection effects such as accelerated flows satisfying the Walén relation.

Publication Date

9-18-2017

Journal Title

JGR: Space Physics

Publisher

AGU

Digital Object Identifier (DOI)

https://dx.doi.org/10.1002/2017JA024563

Document Type

Article

Recommended Citation

C. J. Farrugia, N. Lugaz, L. Alm, B. Vasquez, M. R. Argall, H. Kucharek, H. Matsui, R. B. Torbert, B. Lavraud, O. Le Contel, I. J. Cohen, J. L. Burch, C. T. Russell, R. J. Strangeway, J. Shuster, J. C. Dorelli, J. P. Eastwood, R. E. Ergun, S. A. Fuselier, D. J. Gershman, B. L. Giles, Y. V. Khotyaintsev, P. A. Lindqvist, G. T. Marklund, K. W. Paulson, S. M. Petrinec, T. D. Phan, C. J. Pollock. MMS Observations of Reconnection at Dayside Magnetopause Crossings During Transitions of the Solar Wind to Sub-Alfvenic Flow. Journal of Geophysical Research. 122:9934-9951. 2017