Intro to magnetosphere (Chap. 8)
Magnetopause for IMF south: rotational discontinuity
Homework #3 posted
Reading: Finish Chap. 8 of Kallenrode
Bn!0, [un]=0, un!0
"[#]= 0 un=(Bn/#µ0)1/2
[ut]=([Bt]/#µ0)1/2
and
Interaction with solar wind
a. Finish magnetopause
b. Convection
c. Magnetospheric regions
Hodogram showing constant Bn,
rotation of tangential B
Consistency with tangential momentum balance; checking Whalen relation
Multi-spacecraft observations: stability
Required use of measured anisotropic pressure
Magnetic field from 4 Cluster
satellites
Density, temperature, anisotropy
from 3 Cluster satellites
Ion velocity from 3 Cluster
satellites
Quasi-steady reconnection for southward IMF
Northward IMF- Can reconnection occur?
Cluster 1, 3&4 see ion jetting (no
measurement on C2).
Cluster 1 observes consistency with Whalen
relation for more than 1 hour
Wind IMF N
Bi-directional streaming of electronsindicative of reconnection in both
hemispheres
Electrons at 180 degree pitch angle
Electrons at 0 degree pitch angle
Ions at 180 degree pitch angle
Ions at 90 degree pitch angle
Ions at 0 degree pitch angle
Long-lived proton auroral spot at footpoint of reconnection during IMF N
McFadden et al., 2009
Is reconnection always quasi-steady?
‘Flux transfer events’
Interpreted as due to intrinsic time-scale for variability
Russell&Le, http://www-ssc.igpp.ucla.edu/~guan/image/
FTEs due to multiple
reconnection locations
http://www.igpp.ucla.edu/public/THEMIS/SCI/Pubs/Nuggets/2010_nuggets/hasegawa/hasegawa_10.html
http://www.igpp.ucla.edu/public/THEMIS/SCI/Pubs/Nuggets/2010_nuggets/hasegawa/hasegawa_10.html
Where do currents flow?
Sketch the directions and locations where currents should occur.
Also think about the direction of the convection electric field.
Where is j•E<0; where is j•E>0?
From C.J. Owen
From Russell. C. T.
Describing global convection
For steady - state magnetosphere;
r
E = -!"
r r
r
r
Cold plasma drifts with v = (E # B)/B2 = (-!" # B)/B2
Velocity is perpendicular to the gradient in the potential and so the flow is
along lines of constant potential.
Describing global convection
For steady - state magnetosphere;
r
E = -!"
r r
r
r
Cold plasma drifts with v = (E # B)/B2 = (-!" # B)/B2
What is the flow pattern (equipotentials) for the constant Ey (as in solar
wind)?
So we can equivalently plot flow or potential.
Ey
Describing global convection
In the equatorial plane, imposed constant Ey from solar wind would give:
! sw = " E sw r sin #
Using definition of L,
! sw = " E sw LRE sin #
B
Describing global convection
Close to the earth, the plasma will co-rotate with the earth.
r
r r
Vcr = ! r
r
r
So Vcr = ( E cr
r
r
r
B)/B2 and E cr = #(!
r
Using our expression for B,
r
"B R 3
E cr = ! E2 E
r
$ 2 ˆ
ˆ'
& sin # r ! 2sin # cos ## )
%
(
"BE RE3 sin 2 #
r
where # is the co - latitude
* cr = !
Using r = LRE sin 2 !
" cr = #
r r
r) B
$BE RE2 sin 2 !
L
What is the flow pattern (equipotentials) for the combined co-rotation and
solar wind-imposed electric field?
!T = ! sw + ! cr
!T = " E sw LRE sin # "
!T = " E sw LRE sin # "
$BE R sin %
L
2
E
2
$BE RE2 sin 2 %
L
From Lysak, 2009
Is this realistic?
Plasmasphere
For low energy particles, it is not bad for quiet solar wind conditions.
Cold (<~1 eV) dense plasma from the ionosphere
Three things to look at:
High O+/H+
(1) The cold dense plasmasphere
Co-rotating with the earth
(2) Where does the ‘imposed solar wind electric field’ that we assumed was
constant come from? How does it vary?
(3) What about energetic particles?
Asymmetric
Plasmasphere: dependence on magnetic activity
How do we know about plasmasphere/plasmapause?
•
Initially studied ‘whistler’ waves from the ground
•
Satellite measurements in situ (slices)
•
Satellite remote imaging using UV
http://www.windows2universe.org/teacher_resources/main/asp_2010_magnetism_workshop.html
Kallenrode
Whistlers&plasmasphere
Propagation of whistlers depends on density
Carpenter in 1963 discovered plasmapause
http://vlf.stanford.edu/research/introduction-whistler-waves-magnetosphere
EUV imaging of plasmasphere
IMAGE Extreme Ultraviolet
Imager (EUV) image of the
plasmasphere on 24 May
2000. Several commonly
observed features of the
images are noted, including
the drainage plume and
shoulder. Figure and
caption from Sandel et al.
[2003
Burch, J. L. (2005), Magnetospheric imaging: Promise to
reality, Rev. Geophys., 43, RG3001,
doi:10.1029/2004RG000160.
Plasmapause and model boundaries
•
Four snapshots of the 2 June 2001 plasmaspheric erosion showing the
EUV equatorial He+ abundance: (a) 0001, (b) 0143, (c) 0305, and (d)
0437 UT. Bright patch “C” in Figure 11a is sunlight contamination. The
Sun is to the right. The X and Y axes and geosynchronous orbit are
drawn as dotted lines. The solid white curves represent the
plasmapause (major plasma gradients) determined by a test particle
simulation in the Volland-Stern electric field model. “N” denotes a
notch; “H” denotes the bulge. (e) Plasmapause position in MLT and
radial distance derived from the EUV image (solid green curve) and the
simulation (dash-dotted blue curve) for the time plotted in Figure 11d.
Figure and caption from Goldstein et al. [2003c]
Burch, J. L. (2005), Magnetospheric imaging: Promise to
reality, Rev. Geophys., 43, RG3001,
doi:10.1029/2004RG000160.
Activity
dependence
•
An example of the dramatic erosion of the plasmasphere observed by the
IMAGE EUV instrument. In a 14-hr period, nearly 80 metric tons of plasma were
removed from the inner magnetosphere as a result of the solar wind driven
convection. Ongoing research strives to quantify these losses as a function of
solar wind driving as well as to understand the implications of this mass
redistribution on various magnetospheric coupling processes.
http://vlf.stanford.edu/research/extreme-ultraviolet-imaging-plasmasphere
Measurement of rotation of plasmasphere plasma
Example of a measurement of the
angular velocity of plasmaspheric
plasma. (a) EUV image for 2348 UT on 7
April 2001, showing two notches
separated by about 180° in azimuth. (b)
Mapping of prominent brightness
gradients to the plane of the magnetic
equator in [L, MLT] coordinates. (c)
Magnetic longitude of the notch near
0730 MLT in Figure 14b as a function of
time. Over this period of 60 hours the
notch drifted in longitude at a nearly
constant rate. The dashed line
corresponds to an angular velocity that is
90% of the corotation velocity. Figure
and caption from Sandel et al. [2003,
Figure 7].
Burch, J. L. (2005), Magnetospheric imaging: Promise to
reality, Rev. Geophys., 43, RG3001,
doi:10.1029/2004RG000160.
Modeling convection patterns
(left) Model potential
contours at the magnetic
equator at 0800 UT on 12
August 2000 for (a)
Weimer and (c)
comprehensive ring current
model (CRCM) models.
Contours are drawn at
every 8 kV. (right) Drift
paths (solid lines) of
equatorially mirroring ions
with constant magnetic
moment calculated with (b)
Weimer and (d) CRCM
models. Dashed lines are
energy contours in keV.
The energy of these ions is
32 keV at 3.9 RE and 0600
MLT. Caption adapted from
and Figure from Fok et al.
[2003, Figure 9]
Measuring viscous contribution
What about convection during northward IMF?
Expected pattern due to viscous interaction
What is electric potential drop across the boundary region?
Usually less than 20 kV
Mozer, 1984