Transient Phenomena at the
Magnetopause and Bow Shock
and Their Ground Signatures
Christina Chu
University of Alaska Fairbanks
Geophysical Institute
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
Picture courtesy J. Ahrns
GEM Student Tutorial
12 June 2012
What Kinds of Phenomena?
 Hot Flow Anomalies
 Foreshock Bubbles, Cavities, Cavitons, Compressional
Boundaries
 Density Holes
 Magnetopause Reconnection
 Plasma Entry to Mantle
 Flux Transfer Events
Why should we care?
Disruptions can be carried through bow shock causing changes in
magnetosheath which can lead to surface waves in the magnetopause
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
2
 Occur at the bow shock
 Characterized by
 Flow deflection
Schwartz et al. [1985]
Hot Flow Anomalies (HFAs)
 Temperature increase
HFA Simulation from N. Omidi
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
3
Hot Flow Anomaly Formation Theory
 Discontinuity in solar wind
hits bow shock
 Coupling between
incoming solar wind
beam and reflected ion
beam = heating
 HFA expands causing the
signatures seen
Ni
and
B
vx
vy
vz
Ti
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
4
Identifying HFAs
Zhang et al. [2010]
Young/proto HFA
Mature HFA
Bx, By, Bz
B
n
vx, vy, vz
Ion E
e- E
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
5
Extraterresterial HFAs
 Earth (intrinsic magnetic field)
 Venus (no intrinsic magnetic field)
 Mars (weak to no intrinsic magnetic field)
 Saturn (intrinsic magnetic field)
 Heliopause
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
6
Venus HFA
 Slavin et al. [2009],
Messenger
 Collinson et al. [2012], Venus
Express
 Centered on IMF
discontinuity
 Inward convective motional
electric fields
 Decreased core magnetic
field
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
7
Mars HFA
 Øieroset et al. [2001],
Mars Global Surveyor
 Mars has no
magnetopause – this
eliminates HFA generation
at planetary
magnetopauses.
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
8
Saturn HFA
 Masters et al. [2009],
Cassini
 17 HFAs identified
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
9
HFA Simulated at Termination Shock
 Giacalone and Burgess [2010]
 2D hybrid simulation of heliospheric current sheet and
termination shock
 θCN = inclination of current
sheet to shock normal
 HFA formation θCN < 60°
Original density = blue
4 x original density = red
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
10
Ionospheric Observations of HFAs
 Deformation of the magnetopause generates
field-aligned currents (FACs) into the auroral
ionosphere
 FAC signatures are measured on the ground as
magnetic impulse events (MIEs) or traveling
convection vortices (TCVs) [Glassmeier et al.,
1989; Sitar et al., 1998]
 Sometimes, brightening of dayside aurora is
observed coincident with HFA/TCV signatures
Wong, C.Y.J. and Fillingim, M.O. [2011]
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
11
HFAs: Some Open Questions
 How are electrons being heated?
 How do HFA structures evolve with time?
 How do HFAs form?
 Are they related to the quasi-parallel or to the quasiperpendicular shock?
 How do HFAs impact the magnetosphere and
ionosphere?
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
12
Foreshock Region
 Property of
collisionless plasma
shocks
 Contains particles
and waves
associated with shock
foreshock
magnetosphere
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
13
Foreshock Region
Le and Russell [1994]
E
ExB
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
14
Foreshock Cavities
 Bulk flow nearly identical to the solar wind.
 Decrease in magnetic field and density
 Temperature and pressure inside are slightly greater than
that in the solar wind.
Foreshock Caviton
 Like foreshock cavity but is immersed in sea of ULF waves
Blanco-Cano et al. [2011]
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
15
Foreshock Compressional Boundaries
 Simulations showing
the foreshock
compressional
boundary at different
Alfven mach numbers.
 Formation: expansion
of foreshock with
strong wave particle
interactions.
 Associated with
density and magnetic
field decrease below
solar wind levels.
Omidi et al. [2009]
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
16
Foreshock Bubbles
Omidi et al. [2010]
Christina Chu
University of Alaska Fairbanks
Turner et al. [2011]
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
17
Density Holes
 Regions of space where the density suddenly falls by ten
times but the temperature of the remaining gas leaps
from 1e5 ºC to 1e7 ºC.
 Are different from hot flow anomalies
 Density holes are shorter in duration than HFAs
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
18
Magnetopause Reconnection
 Large-scale properties of reconnection at the
magnetopause
 The physics of magnetic reconnection at the dayside
magnetopause
 Quasi-steady versus time dependent reconnection at the
dayside magnetopause
 Plasma transport including particle entry and
energization through reconnection and diffusive
processes at the dayside magnetospheric boundary
 Impacts of the bow shock/magnetosheath and the
cusp/ionosphere systems on dayside magnetopause
reconnection
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
19
Magnetopause Reconnection
NIMF
Christina Chu
University of Alaska Fairbanks
SIMF
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
20
Flux Transfer Events
 ISEE 1 and 2 saw signatures
that looked like multiple
magnetopause crossings
 It was determined that those
signatures were magnetic
ropes on the
magnetosphere boundary
 Plasma within
magnetosheath FTE's flows
at or above the surrounding
magnetosheath flow
velocity
 Mixture of magnetospheric
and magnetosheath
plasma.
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
21
Flux Transfer Events
From http://www.spaceplasma.unh.edu/wiki/images/2/25/Zhang_UNH_themis-cluster_FTE.pdf
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
22
Again, why should we care?
Solar wind disruptions (ie in density, magnetic field, etc.) can be
carried through bow shock causing changes in magnetosheath
which can lead to surface waves in the magnetopause
Questions?
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
23
Extra Slides
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
24
Identifying HFAs
Zhang et al. [2010]
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
25
Flux Ropes in HFAs
 Flux Ropes
 Helical field structures with core fields
 Often have current sheets at edges (to separate it from the
surrounding plasma)
 Guide field is often present – creates twisted flux rope, with
twist field wrapped around an axis of guide field
Mulligan, Russell, Luhmann [2000]
Russell and Elphic
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
26
Plasma Entry to Mantle
Mantle
 de-energized magnetosheath plasma densities: few times
0.01 - 1 cm-3
 temperatures: ~100 eV
 tailward flow velocities: 100-200 km/s
 Velocity Filter Effect
 Low-energy ions (blue) take longer to mirror from the
ionosphere than higher energy ions (red),
 Low-energy ions are convected further across field lines,
 As one moves towards the magnetosphere, have
decreasing energy and density
(with deeper penetration into the mantle).
Christina Chu
University of Alaska Fairbanks
GEM 2012 Student Tutorial – Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures
27