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

The tribulations and exaltations in coupling models of the

magnetosphere with ionosphere-thermosphere models

Aaron RidleyDepartment of Atmospheric, Oceanic and Space Sciences

Aaron RidleyDepartment of Atmospheric, Oceanic and Space Sciences

GEM/CEDAR WorkshopJuly 1, 2005

Slide 2 of

Ionosphere Thermosphere Modeling and coupling

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

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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Slide 3 of

[e-] and Tn[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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Slide 4 of

Temperature Altitude Distribution

Temperature Altitude Distribution

noon midnight

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Slide 5 of

Low Altitude Temperature Distribution

Low Altitude Temperature Distribution

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Slide 6 of

High Altitude Temperature Distribution

High Altitude Temperature Distribution

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Slide 7 of

Electron Density Altitude Distribution

Electron Density Altitude Distribution

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Slide 8 of

Low Altitude Electron Distribution

Low Altitude Electron Distribution

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Slide 9 of

High Altitude Electron Distribution


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Slide 10 of



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Slide 11 of

Vi and Vn with Bz = -1 nTVi 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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Slide 12 of

Vi and Vn with Bz = -10 nTVi 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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Slide 13 of

[e-] and Vn with HPI = 100 GW[e-] and Vn with HPI = 100 GW

Significant increase in the electron density causes much larger ion drag effect

Dawn cell “much” more defined.

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Slide 14 of

Vi, Vn, and how well they are coupled

Vi, Vn, and how well they are coupled

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Slide 15 of

Vi in F-region and E-regionVi in F-region and E-region

Rotation of Vectors Shortening of Vectors

Rotation of Vectors Shortening of Vectors

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Slide 16 of

Would the real Vi please step forward?

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.

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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Slide 17 of

Test run of the Space Weather Modeling Framework.

IMF inputs shown. Look at potential. Look at currents caused

by neutral winds.

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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Slide 18 of

PotentialPotential

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Slide 19 of

NW driven current

NW driven current

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Slide 20 of

Ionospheric outflowIonospheric 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.

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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Slide 21 of

What controls Outflow?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.

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.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

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Slide 22 of

Effect of heating on electron density

Effect of heating on electron density

QuickTime™ and aPhoto - JPEG decompressor


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Slide 23 of

Outflow ExperimentsOutflow 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.

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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Slide 24 of

N=1000; Grid 4; No RCMN=1000; Grid 4; No RCM

QuickTime™ and aPNG decompressor



Slide 25 of

CPCP variations for 3 runsCPCP variations for 3 runs

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

N=10 N=100

N=1000


Slide 26 of

But……But……

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.

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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Slide 27 of

What Coupling Should BeWhat Coupling Should Be

Magnetosphere Model

Field-aligned Currents

Heat FluxElectron & Ion Precipitation

Plasmasphere Density

Potential

Electrodynamics Model

Ionosphere-Thermosphere Model

Neutral wind FACs

Conductances

Upward Ion Fluxes

Tides Gravity Waves

Solar Inputs

Photoelectron Flux

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Slide 28 of

What we have discussed so farWhat we have discussed so far

Magnetosphere Model


Potential



Neutral wind FACsUpward Ion Fluxes

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Slide 29 of

Electron and Ion PrecipitationElectron and Ion Precipitation

Magnetosphere Model

Electron & Ion Precipitation



Conductances

This is the hardest part of the coupling

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.

Need to have both ion and neutral densities correct to get conductances

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Slide 30 of

PhotoelectronsPhotoelectrons

Magnetosphere Model


Photoelectron Flux

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 codes are relatively “expensive” to run, so they are typically ignored.

Photoelectron flux could be parameterized with a transmission coefficient through the plasmasphere.

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Slide 31 of

Plasmaspheric DensityPlasmaspheric 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.

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Slide 32 of

Electron Heat FluxElectron 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.

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Slide 33 of


Magnetosphere Model

Heat Flux


Wait. Did you say lift?

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Slide 34 of


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

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Slide 35 of

Electron heat flux experimentElectron 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

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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Slide 36 of

Electron heat flux experimentElectron 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.

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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Slide 37 of

What Coupling Should BeWhat Coupling Should Be

Magnetosphere Model


Heat FluxElectron & Ion Precipitation


Potential



Neutral wind FACs

Conductances

Upward Ion Fluxes

Tides Gravity Waves

Solar Inputs

Photoelectron Flux

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Slide 38 of

SummarySummary

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?

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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Slide 39 of

Thank You!Thank You!

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