The tribulations and exaltations in coupling models of the magnetosphere with ionosphere-thermosphere models

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The tribulations and exaltations in coupling
models of the magnetosphere with
ionosphere-thermosphere models

• Aaron Ridley
• Department of Atmospheric, Oceanic and Space
  Sciences

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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

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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
midnight
noon
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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
Neutral winds driven by (a) Gradient in pressure
(b) Corriolis (c) ion drag. Note dawn/dusk
differences
Ion flows driven primarily by potential
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Vi and Vn with Bz -10 nT
Neutral winds driven by (a) Gradient in pressure
(b) Corriolis (c) ion drag. Note dawn/dusk
differences
Ion flows driven primarily by potential
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e- and Vn with HPI 100 GW
Dawn cell much more defined.
Significant increase in the electron density
causes much larger ion drag effect
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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?

• 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 Un 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.
• Also applies to things like gravity and gradient
  pressure.

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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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What controls Outflow?

• It seems like outflow is a two step process
• Raise the ionospheric plasma up.
• Suck it out into magnetosphere
• Joule heating is one of the primary mechanisms
  thought to control the raising of the ionosphere.

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Effect of heating on electron density
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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 t0, and see what happens.

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N1000 Grid 4 No RCM
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CPCP variations for 3 runs
N10
N100

• Changing the density seems to
• Increase the cross polar cap potential
• Make the transition take longer

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But

• The cross polar cap increasing doesnt 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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What Coupling Should Be
Solar Inputs
Magnetosphere Model
Heat Flux
Field-aligned Currents
Electron Ion Precipitation
Plasmasphere Density
Electrodynamics Model
Photoelectron
Flux
Conductances
Potential
Upward Ion Fluxes
Neutral wind FACs
Ionosphere-Thermosphere Model
Tides
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
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.
Electrodynamics Model
Need to have both ion and neutral densities
correct to get conductances
Conductances
Ionosphere-Thermosphere Model
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Photoelectrons
Magnetosphere Model
Photoelectron flux could be parameterized with a
transmission coefficient through the plasmasphere.
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. Photoe
lectron codes are relatively expensive to run,
so they are typically ignored.
Photoelectron
Flux
Ionosphere-Thermosphere Model
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Plasmaspheric Density
Magnetosphere Model
Many global circulation models have a hard time
getting the F-region 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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Electron Heat Flux
Magnetosphere Model
Heat Flux
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.
Ionosphere-Thermosphere Model
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Electron Heat Flux
Magnetosphere Model
Heat Flux
Wait. Did you say lift?
Ionosphere-Thermosphere Model
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Electron Heat Flux
Magnetosphere Model
Heat Flux
The electron energy heat flux may cause changes
in the amount of ion outflow.
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
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
• 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.

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What Coupling Should Be
Solar Inputs
Magnetosphere Model
Heat Flux
Field-aligned Currents
Electron Ion Precipitation
Plasmasphere Density
Electrodynamics Model
Photoelectron
Flux
Conductances
Potential
Upward Ion Fluxes
Neutral wind FACs
Ionosphere-Thermosphere Model
Tides
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 dont 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?
• Wouldnt it be great is we could model the system
  without the numerics getting in the way?

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Thank You!
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