The tribulations and exaltations in
coupling models of the
magnetosphere with ionospherethermosphere models
Aaron Ridley
Department of Atmospheric, Oceanic and Space Sciences
Ionosphere Thermosphere
Modeling and coupling
 A quick review.
 The ionosphere and thermosphere.
 High latitude electrodynamics.
 Coupling the neutral winds to the
magnetosphere
 Ion outflow
 Other couplings
 Some that work
 Some that may not be on the horizon, but should be.
 Pontification time
GEM/CEDAR Workshop
July 1, 2005
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[e-] and Tn
Many Thermosphere/Ionosphere plots “stolen” from my student Yue Deng!
All T/I results from the global ionosphere thermosphere model (GITM)
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Temperature Altitude
Distribution
noon
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midnight
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Low Altitude Temperature
Distribution
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High Altitude Temperature
Distribution
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Electron Density Altitude
Distribution
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Low Altitude Electron
Distribution
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High Altitude Electron
Distribution
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High Altitude Electron
Distribution
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Vi and Vn with Bz = -1 nT
Ion flows driven primarily by potential
Neutral winds driven by (a) Gradient in
pressure; (b) Corriolis; (c) ion drag.
Note dawn/dusk differences
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July 1, 2005
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Vi and Vn with Bz = -10 nT
Ion flows driven primarily by potential
Neutral winds driven by (a) Gradient in
pressure; (b) Corriolis; (c) ion drag.
Note dawn/dusk differences
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July 1, 2005
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[e-] and Vn with HPI = 100 GW
Significant increase in the electron density
causes much larger ion drag effect
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Dawn cell “much” more defined.
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Vi, Vn, and how well they are
coupled
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Vi in F-region and E-region
 Rotation of Vectors
 Shortening of Vectors
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Would the real Vi please step forward?
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As the collision frequency becomes large, most people think of the
ion velocity rotating away from ExB to E.
That is not really true. Since there is a neutral wind, the ion
velocity rotates towards a combination of E and Un.
We can then think of this in a couple of different ways:
 The current caused by E is divergenceless, but the current caused by U n is
not, so we have to force the total current to be:
 So, calculate the divergence of the neutral wind driven current
(perpendicular to the magnetic field).
 Integrate this current, to come up with a total wind driven current.
 Solve a Poisson equation to find a potential that would cancel this
current out.
 The push the ions with the solved E-field.
 This the methodology used by all modeling groups for solving for
equatorial electrojet and coupling to magnetospheric codes.
 Pushing ions with Un will cause a polarization electric field. We could
map this polarization electric field along field lines to higher altitudes.
 Should be equivalent.
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Also applies to things like gravity and gradient pressure.
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July 1, 2005
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 Test run of the Space
Weather Modeling
Framework.
 IMF inputs shown.
 Look at potential.
 Look at currents caused
by neutral winds.
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Potential
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NW driven
current
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Ionospheric outflow
 Outflow is also very important in MI coupling.
 Can control the density in the plasma sheet.
 Oxygen outflow can significantly change the
mass density in the magnetosphere.
 Lowers the Alfven velocity.
 Adds to the ring current.
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July 1, 2005
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What controls Outflow?
 It seems like
outflow is a two
step process:
 Raise the
ionospheric
plasma up.
 Suck it out into
magnetosphere
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
 Joule heating is
one of the primary
mechanisms
thought to
control the raising
of the ionosphere.
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July 1, 2005
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Effect of heating on electron density
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
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Outflow Experiments
 Examine what the influence of the ion outflow
is on the magnetosphere
 Use simple constant boundary conditions at
the inner boundary of the magnetosphere
 diffusion lifts the density off the boundary a few
cells
 Gradient in pressure brings the plasma out into the
magnetosphere
 These experiments are meant to show what the
most simple thing possible will do to the
magnetosphere
 Run to steady-state Northward IMF, flip to
Southward IMF at t=0, and see what happens.
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N=1000; Grid 4; No RCM
QuickTime™ and a
PNG decompressor
are needed to see this picture.
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CPCP variations for 3 runs
N=10
N=100
Changing the density seems to:
• Increase the cross polar cap
potential
• Make the transition take longer
N=1000
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July 1, 2005
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But……
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The cross polar cap increasing doesn’t make much sense. Why
does it do this???? After thinking a bit…
Our numerical solver has to add diffusion for stability.
That diffusion is controlled by the fastest wave speed in the
cell… roughly the Alfven speed.
Which is controlled by the density.
So, turning the density up means turning the diffusion down.
Turning the diffusion down allows more current to make it to
the inner boundary, and hence to the ionosphere.
The cross polar cap potential goes up.
Purely numerical.
Crap.
The funny thing is that this is true for (a) grid resolution, (b)
where you put the boundary, and (c) Artificially reducing the
speed of light (Boris) also.
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July 1, 2005
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What Coupling Should Be
Solar Inputs
Magnetosphere Model
Field-aligned
Currents
Heat Flux
Electron & Ion
Precipitation
Electrodynamics Model
Plasmasphere
Density
Photoelectron Flux
Conductances
Potential
Upward Ion Fluxes
Neutral wind FACs
Ionosphere-Thermosphere Model
Tides
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July 1, 2005
Gravity Waves
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What we have discussed so far
Magnetosphere Model
Field-aligned
Currents
Electrodynamics Model
Potential
Upward Ion Fluxes
Neutral wind FACs
Ionosphere-Thermosphere Model
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Electron and Ion Precipitation
Magnetosphere Model
This is the hardest part of
the coupling
Electron & Ion
Precipitation
Electrodynamics Model
Need to have both ion and
neutral densities correct to
get conductances
Conductances
T-I models use energy
deposition codes to determine
ionization and heating rates as a
function of altitude, given input
(ion and electron) spectra at the
top of the model. This is sort of
a major weakness if not done
well, or if distributions are
assumed to be Maxwellian and
are not.
Ionosphere-Thermosphere Model
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July 1, 2005
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Photoelectrons
Magnetosphere Model
Photoelectron are created by
sunlight. These electrons flow
along field lines from the sunlit
hemisphere to the dark
hemisphere, causing soft
electron precipitation. This can
effect the F-region density in
the winter hemisphere.
Photoelectron flux
could be
parameterized with a
transmission
coefficient through
the plasmasphere.
Photoelectron Flux
Photoelectron codes are
relatively “expensive” to run,
so they are typically ignored.
Ionosphere-Thermosphere Model
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July 1, 2005
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Plasmaspheric Density
Magnetosphere Model
Many global circulation models
have a hard time getting the Fregion densities correct, because
the pressure gradient at the top of
the model is unknown. With an
accurate plasmaspheric model,
the gradient could be determined
and an inflow or outflow would be
self-consistently derived.
Plasmasphere
Density
Ionosphere-Thermosphere Model
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July 1, 2005
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Electron Heat Flux
Magnetosphere Model
Magnetospheric electron
heat flux causes the electron
to heat up in the ionosphere.
This changes the height
distribution of the electron
pressure, which causes the
ions to lift.
Heat Flux
Ionosphere-Thermosphere Model
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Electron Heat Flux
Magnetosphere Model
Wait. Did you say lift?
Heat Flux
Ionosphere-Thermosphere Model
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July 1, 2005
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Electron Heat Flux
Magnetosphere Model
The electron energy heat flux
may cause changes in the
amount of ion outflow.
Heat Flux
Upward Ion Fluxes
Therefore, passing the heat flux
from magnetospheric codes
(that are capable of computing it
- like RAM) to the IT models may
be crucial for accurately
specifying outflow regions
GEM/CEDAR Workshop
July 1, 2005
Ionosphere-Thermosphere Model
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Electron heat flux experiment
 Simulations done by Alex
Glocer, a graduate
student at UM.
 Using updated version of
the Gombosi et al. [1645, I
think] polar wind code.
 Do two ion outflow runs
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80o latitude
noon
Summer conditions
low f10.7
Run 1 nominal heat flux
Run 2 double heat flux
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Electron heat flux experiment
 By changing the electron
heat flux by a factor of
two:
 increase H+ outflow by a
little bit.
 Increase O+ by a factor of
two.
 While the polar wind code
is still being developed and
validated, the results are
intriguing.
GEM/CEDAR Workshop
July 1, 2005
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What Coupling Should Be
Solar Inputs
Magnetosphere Model
Field-aligned
Currents
Heat Flux
Electron & Ion
Precipitation
Electrodynamics Model
Plasmasphere
Density
Photoelectron Flux
Conductances
Potential
Upward Ion Fluxes
Neutral wind FACs
Ionosphere-Thermosphere Model
Tides
GEM/CEDAR Workshop
July 1, 2005
Gravity Waves
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Summary
 The thermosphere and ionosphere are overlapping,
tightly coupled regions of space that do influence the
magnetosphere. And Vise-versa.
 We sort of understand the neutral wind coupling to the
ion flows.
 We sort of understand what happens to electrons and
ions from the magnetosphere (if the magnetosphere
could specify them correctly…)
 We really don’t understand outflow
 Joule heating effects can last a LONG time.
 Electron energy flux could play a role - no one has
coupled this yet.
 Plasmasphere?
 Photoelectrons?
 Wouldn’t it be great is we could model the system
without the numerics getting in the way?
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July 1, 2005
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Thank You!
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July 1, 2005
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