MMS Observations of Reconnection at Dayside Magnetopause Crossings During Transitions of the Solar Wind to Sub-Alfvénic Flow
File(s)
Author(s)
Type
Journal Article
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 (
T
e
⟂
>
T
e
∥
) 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.
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 (
T
e
⟂
>
T
e
∥
) 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.
Date Issued
2017-10-09
Date Acceptance
2017-09-12
Citation
Journal of Geophysical Research: Space Physics, 2017, 122 (10), pp.9934-9951
ISSN
2169-9380
Publisher
American Geophysical Union
Start Page
9934
End Page
9951
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
122
Issue
10
Copyright Statement
©2017. American Geophysical Union. All Rights Reserved. Farrugia, C. J., Lugaz, N., Alm, L., Vasquez, B., Argall, M. R., Kucharek, H., … Pollock, C. J. (2017). MMS observations of reconnection at dayside magnetopause crossings during transitions of the solar wind to sub-Alfvénic flow. Journal of Geophysical Research: Space Physics, 122, 9934–9951. https://doi.org/10.1002/2017JA024563
Sponsor
Science and Technology Facilities Council (STFC)
Grant Number
ST/N000692/1
Publication Status
Published
Date Publish Online
2017-10-09