Aaron Ridley Department of Atmospheric, Oceanic and Space Sciences

1. The tribulations and exaltations in coupling models of the magnetosphere with ionosphere-thermosphere models Aaron Ridley Department of Atmospheric, Oceanic and Space Sciences

2. 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 39

3. [e-] and Tn Many Thermosphere/Ionosphere plots “stolen” from my student Yue Deng! All T/I results from the global ionosphere thermosphere model (GITM) 309

4. Temperature Altitude Distribution midnight noon 465

5. Low Altitude Temperature Distribution 739

6. High Altitude Temperature Distribution 1001

7. Electron Density Altitude Distribution 1304

8. Low Altitude Electron Distribution 1573

9. High Altitude Electron Distribution 1846

10. High Altitude Electron Distribution 2149

11. 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 2638

12. 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 3067

13. [e-] and Vn with HPI = 100 GW Dawn cell “much” more defined. Significant increase in the electron density causes much larger ion drag effect 3471

14. Vi, Vn, and how well they are coupled 4132

15. Vi in F-region and E-region • Rotation of Vectors • Shortening of Vectors 4578

16. 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. 4931

17. Test run of the Space Weather Modeling Framework. • IMF inputs shown. • Look at potential. • Look at currents caused by neutral winds. 5577

18. Potential 6300

19. NW driven current 39

20. 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. 5238

21. 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. 4872

22. Effect of heating on electron density 4321

23. 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. 3965

24. N=1000; Grid 4; No RCM

25. 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

26. 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. 3180

27. 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 2713

28. What we have discussed so far Magnetosphere Model Field-aligned Currents Electrodynamics Model Potential Upward Ion Fluxes Neutral wind FACs Ionosphere-Thermosphere Model 2525

29. 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 2189

30. 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. Photoelectron codes are relatively “expensive” to run, so they are typically ignored. Photoelectron Flux Ionosphere-Thermosphere Model 1939

31. 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 1776

32. 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 1492

33. Electron Heat Flux Magnetosphere Model Heat Flux Wait. Did you say lift? Ionosphere-Thermosphere Model 1100

34. 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 999

35. 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 675

36. 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. 472

37. 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 281

38. 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? 78

39. Thank You! 39