Modelling the Magnetosphere-Ionosphere Coupling

Mihail Codrescu1 and Joachim Raeder2

1CIRES, University of Colorado, Boulder, CO2Space Science Center, University of New Hampshire, Durham, NH

Solar - Terrestrial Interactions from Microscale to Global Models Sinaia, September 6-10, 2005

Global modeling of the geospace environment began about 20 years ago with the first simple magnetohydrodynamic (MHD) models of the solar wind - magnetosphere interaction. It is thus a relatively young discipline compared to, for example, the modeling of the atmosphere. However, over this comparatively short period enormous progress has been made. Recently the inclusion of electrodynamic ionosphere models that provide the closure of field-aligned currents (FACs) and the connection between magnetospheric and ionospheric convection has been achieved. The coupling to the ionosphere followed the realization that the ionosphere might, at least in part, control magnetospheric convection, and thus the magnetospheric dynamics in general. In this paper we'll discuss the status of magnetosphere-ionosphere coupling with examples of ionosphere coupling to the inner magnetosphere as described by the Rice Convection Model and to a full magnetosphere MHD code, the OpenGGCM.

Current Systems in the Magnetosphere

The Thermosphere Ionosphere System

CTIPe and Rice Convection Model coupling

MI Coupling

MHD Magnetosphere + Rice Convection Model

Outline

Current Systems in the Magnetosphere

• Magnetopause current at equator and above polar cusp

• Region 1 field-aligned current

• Region 2 field-aligned current

• The symmetric ring current

• The partial ring current

• The plasma sheet current

• The substorm current wedge

• Currents NOT SHOWN:

– Closure of plasma sheet current

– Currents in the polar cusp

– Closure of boundary layer current

McPherron, R.L., Physical Processes Producing Magnetospheric Substorms and Magnetic Storms, in Geomagnetism, edited by J. Jacobs, pp. 593-739, Academic Press, London, 1991.

The Currents Produced by M-I Coupling• On the dawn side Region 1 current

flows downward from the inner edge of the low latitude boundary region

• R1 current splits with some flowing over the polar cap and the rest equatorward

• At the shielding layer current flows upward as Region 2 current

• This current flows westward in the equatorial plane through gradient and curvature drift

• On the dusk side the current flows downward as R1 current

• It then flows poleward meeting current flowing over the polar cap

• The currents combine and flow outward to the inner edge of the dusk boundary layer

• Closure from the outer edges of the boundary layers is unknown, but could be through the polar cusp or through the solar wind McPherron, R.L., Physical Processes Producing Magnetospheric Substorms

and Magnetic Storms, in Geomagnetism, edited by J. Jacobs, pp. 593-739, Academic Press, London, 1991.

Weimer pattern

T. Matsuo Private Communication, 2004

January 9 -10, 1997

http://www.sec.noaa.gov/pmap/

Fejer and Scherliess, 2001

Large Variability

What is the source of the vertical drifts?

Two Processes: -Prompt Penetration [e.g., Jaggi and Wolf, 1973]

-Disturbance dynamo [e.g., Blanc and Richmond, 1980]

[Scherliess and Fejer, 1997]

Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model is used.

Maruyama, private communication, 2005

RCM Input:--polar cap potential drop

--Tsyganenko 2003 storm magnetic field

--plasma sheet density and temperature on the high-latitude boundary

RCM run

50

-50

Penetration Electric fields

CTIPe Input

RCM - CTIPe Coupling Experiment

[Sazykin et al., 2004]

5UT

5UT Maruyama, private communication, 2005

LON=289

LON=127

03/31/01

-----: Quiet time

___: Disturbance Dynamo only (Weimer)

___: Penetration only (RCM)

___: both Disturbance Dynamo (Weimer) & Penetration (RCM)

-- Very Dynamic!

-- Very Complicated!

-- Hard to distinguish the effects!

Response of Vertical ExB Drift

4 CTIPe Runs:

0UT 24UT

(Maruyama, 2005)

Day

Night

Night

Day

MI Coupling

MHD model provides FAC, e- precipitation.

Potential solver uses FAC, conductances to compute 2d ionosphere potential

CTIM receives potential, e- precipitation, provides conductances and dynamo currents

OpenGGCM Structure

• Sunward of bow shock to distant tail

• +-40 RE in Y/Z• R = 3 RE inner

boundary with coupling to CTIM (Coupled Thermosphere Ionosphere Model)

• Driven by SW B,V,N,T, and F10.7

• Model is available for community use at CCMC: http://ccmc.gsfc.nasa.gov

Typical Numerical GridVariable, static grid spacing.Can be as small as 100 km near magnetopause, but for storm simulations usually 0.2-0.3 RE at subsolar MP, larger elsewhere.Parallelized using domain decomposition, 4 - 800 processors, various architectures.

ComputationFinite difference solution.

2. order explicit time integration.

2./4. order, flux-limited spatial differences.

Yee grid / constrained transport algorithm guarantees div(B)=0.

For space weather speed is of essence: ~ real time with 4M cells on ~60 Opteron CPUs.

I/O can be a bottleneck.

Model provides 3d magnetosphere B, V, N, T; ionosphere FAC, Pot, e- prec, Sig_P, Sig_H, J,…;

CTIM provides 3d Vp, Ti, Ne, Nmf2, H+/O+ Tn, N, O/N, ….;

Storms in different shapes

and sizes

Bastille Day storm stands out among 1998-2001 storms.

IMF Bz as large as -60 nT, IEF Ey as large as 70 mV/m

Dst ~ -300 nT

Bastille Day storm:

Geomagnetic activity

IMF Bz driverPolar Cap potential.

Black: AMIE (G. Lu, NCAR/HAO), green: model.

A indices from 60+ stations, model results in red.

Bastille Day storm simulation

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Reality check: GOES magnetopause crossings

Blue: typical quiet day at GOES.

Red: GOES data.

Black: model

Polar Cap Potential

saturation

Predicted versus observed PCP.Empirical models severely overpredict PCP.

OpenGGCM is close but on the high side versus AMIE.

Polar Cap Potential

saturation

IEF Ey is main driver for empirical models.

During Bastille Day storm PCP is so saturated there is virtually no Ey dependence.

Saturation mechanism

Shortened X-line due to MP erosion explains much of the effect.

Equivalent to Siscoe-Hill model: limited R1 system.

Scaled empirical models

Empirical models scaled by X-line size fit much better, but still high CPCP.

Simple linear model (green) is not adequate.

Limits of predictability

• With strong SW forcing tail PS is turbulent.

• How can turbulence be characterized?

• Is the turbulence in the model the “right” turbulence?

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

The future: RC and RB coupling• One of the biggest model

deficiencies is the lack of proper “inner magnetosphere” physics.

• Coupling with RC/RB models is in the works (RCM, Jordanova, Fok models).

• Coupling must be both to the magnetosphere (pressure feedback) and ionosphere (e- precipitation, R2 currents).

• Replacing CTIM with CTIPe may also be helpful (plasmasphere).

0 100 200 300 400 500 600 700 800 900 10001100 1200106

107

108

109

1010

1011

SolMax Flare SolMin

Photon Flux (Photons/cm

2sec)

Wavelength(A)

NRLEUV Spectra

From Rodney Viereck, SEC

Energy Deposition

100

150

200

250

300

350

400

450

500

1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4

Energy Deposition (W/m3)

Altitude (km)

105 to 135 nm 65 to 105 nm 55 to 65 nm 35 to 55 nm 25 to 35 nm 5 to 25 nm 1 to 5 nm 0 to 1 nm Total

Viereck, Private communication, 2004

Magnetosphere - Ionosphere Coupling

E

MHD Model

Magnetosphere -Ionosphere Coupler

T/I Model

Jll, np,Tp

Conductivities:ph

Electric potential:

P

Jll

Particle precipitation: Fe, E0

One Way Coupling Two Way Coupling

Adapted from Solomon 2004 (www.bu.edu/cism/AG/ppt/SolomonV2.ppt)

MHD magnetosphere model

Model region [-400,20]x[-50,50]x[-50,50] RE box

Solve MHD equationsAnomalous resistivity Numerics: explicit finite differenceOuter boundary conditions: solar wind upstream, open ol all other sidesInner boundary conditions: E, v from ionosphreComputing: Parallelized using message passing interface (MPI) 8-64 nodes, but scales well up to 256 nodes