Event
Plasma Physics Seminar| Kevin Genestreti, Southwest Research Institute
Wednesday, January 27, 2021
3:30 p.m.
via ZOOM
Taylor Prendergast
301 405 4951
tprender@umd.edu
Title: "The onset of reconnection in Earth's magnetotail"
Abstract: The elongated tail of our nightside magnetosphere stores energy from the
solar wind. The oppositely-directed magnetic fields in the northern and
southern tail are separated by a current sheet, which periodically becomes
very thin then "short circuits". Understanding the causes of magnetic
reconnection - the "short circuit" mechanism - is an important yet elusive
problem in space physics. We have learned a tremendous amount about
reconnection by observing it while it is occurring in space, yet it is
still debated how reconnection starts in the first place. Ambiguity stems
from the difficulty of determining the accurate time history of a
reconnection event over the vast range of relevant spatial scales. The
standard picture is that reconnection of the solar wind and Earth's dayside
magnetic fields drives global (~1015 km3) magnetospheric convection, which
can thin the current sheet by compressing it or depleting its internal
pressure. However, tail reconnection does not necessarily follow dayside
reconnection and some thin current sheets remain stable. Microscopic (~107
km3) magnetic reconnection sites are formed after one of several proposed
instabilities is triggered. While several instabilities accompany
reconnection, causal relationships have been difficult to verify.
We start the seminar by summarizing the basic concepts of magnetospheric
reconnection and the wide-ranging impacts of reconnection on near-Earth
space. We then report a case study where many space and ground-based
observatories witnessed magnetotail reconnection being initiated. We find
that the tail current sheet became thin by evacuating its internal thermal
pressure without significant dayside reconnection. The solar wind prompted
the pressure evacuation and, eventually, initiated reconnection by
momentarily compressing the tail. Reconnection was initiated in multiple
locations once the current sheet surpassed the threshold for the
electron-tearing instability, which requires a sufficiently thin current
sheet with a weak magnetic field and a low ion-to-electron temperature
ratio. One reconnection site quickly engulfed the others, becoming the
dominant region that shredded the tail's magnetic field, fitting with
simple models.
POC: Dr. Marc Swisdak (swisdak@umd.edu)
Please contact Dr. Swisdak for ZOOM details
The full schedule for this semester can be found here:
https://terpconnect.umd.edu/~swisdak/PPS/plasma_seminar.html
