Presentation on theme: "Inner Magnetospheric Modeling with the Rice Convection Model"— Presentation transcript:
1Inner Magnetospheric Modeling with the Rice Convection Model Frank Toffoletto, Rice University(with thanks to: Stan Sazykin, Dick Wolf, Bob Spiro, Tom Hill, John Lyon, Mike Wiltberger and Slava Merkin)
2Outline Motivation Code Descriptions Physics Examples Issues Importance of the inner magnetosphereThe tool of choice is the Rice Convection Model (RCM)Code DescriptionsRCMCoupled LFM RCMPhysics ExamplesIssuesDiscussion and Conclusion
3Why is the Inner Magnetosphere so important? Basic Physical understanding of plasmaspheric and ring-current dynamics.We won’t understand ring current injection until we understand the associated electric and magnetic fields self consistently.Space Weather:Many Earth orbiting spacecraft are inner magnetosphere.Radiation belts: Many space weather effects are related to to understanding and predicting highly energetic particles.For that we need a model of the electric and magnetic fields.The low- and mid-latitude ionosphere: Disruptions of the mid- and low-latitude ionosphere seem to be the most important aspects of space weather at present, particularly for the military.Inner magnetospheric electric fields appear to be the most unknown element in ionospheric modeling of the subauroral ionosphere.
4What can an Inner magnetospheric model (such as the RCM) provide? Missing physics: Global MHD does not include energy dependent particle drifts, which become important in the Inner Magnetosphere.An accurate and reasonable representation of the Inner Magnetosphere should be able to compute both Electric and Magnetic fields.Inputs to ionosphere/thermosphere models, such as electric fields and particle information.
5RCM Modeling RegionIn the ionosphere, the modeling region includes the diffuse auroral oval (the boundary lies in the middle of the auroral oval, shifted somewhat equatorward from the open-closed field line boundary).The modeling region includes the inner/central plasma sheet, the ring current, and the plasmasphere.Region-2 Field-Aligned currents (FAC) connect magnetosphere and ionosphere.
6RCM Physics Model Three pieces: Drift physics: Inner magnetospheric hot plasma population on closed magnetic field with flow speeds much slower than thermal and sonic speeds while maintaining isotropic pitch-angle distribution function.Ionospheric coupling: perpendicular electrical currents and electric fields in the current-conservation approximation.Field-aligned currents connecting the magnetosphere and ionosphere assuming charge neutrality.Plasma population and magnetic fields are in quasi-static equilibrium
7RCM Transport Equations Take a distribution function and “slice” it into “invariant energy” channels:For each “channel”, transport is via an advection equation:where the equations are in non-conservative form, and in the (,) parameter space these “fluids” are incompressibleIonospheric grid, where B-field is assumed dipolar, Euler potentials can be easily defined that are (essentially) colatitude and local-time angle.(Equations are solved using the CLAWPAK package)
8Equation of Magnetosphere-Ionosphere coupling Current conservation equation at ionospheric hemispheric shell (assumes Bis=Bin):Vasyliunas Equation (assumes Bis=Bin):Combine two together:High-latitude boundary condition: DirichletLow-latitude boundary condition: mixed with 2nd-order spatial derivatives (simple model of equatorial. electrojet)Equatorial plane mapping changes in time, grid there is non-orthogonal.Equatorial boundary is a circle of constant MLT. Polar boundary does not coincide with a grid line and moves in time.
10Basic RCM PhysicsElectronsIonsFor each species and invariant energy l, h is conserved along a drift path.Specific Entropy
11Basic RCM Physics- Electric Fields Inner magnetosphericelectric field shieldingFormation of region-2field-aligned currents
12Limitations to the Conventional RCM Approach to Calculating Inner-Magnetospheric Electric Field The change in magnetic field configuration due to a northward or southward turning has a large effect on the inner magnetospheric electric field.Hilmer-Voigt or Tsyganenko magnetic field models can’t give a good picture of the time response to a turning of the IMF.The potential distribution around the RCM’s high-L boundary must evolve in a complicated way just after a northward or southward turning hits the dayside magnetopause.The time changes in the polar-cap potential distribution occur simultaneously with the changes in magnetic configuration.Magnetic field model is input and not in MHD force balance with the RCM computed pressures.A fully coupled MHD/RCM code is an obvious choice to address these limitations.
13Coupled Modeling Scheme Solar CoronaSAICIonosphereT*GCMSolar Wind ENLILMagnetosphereLFMSEPMI CouplingActive RegionsRing Current RCMGeocorona and ExosphereRadiation BeltsInnerMagnetospherePlasmasphere
14Coupled Modeling Scheme MagnetosphereLFMIonosphereT*GCMRing Current RCMGeocorona and ExosphereInnerMagnetospherePlasmasphere
16Coupling Scheme LFM RCM Coupling exchange time is 1 minute LFM is nudged by the RCM
17Aside:Coupling approach In order to minimize code changes, we plan to use the InterComm library coupling software developed by Alan Sussman at the University of MarylandInterComm allows codes to exchange data using ‘MPI-like’ callsIt can also handle data exchanges between parallel codesFor now, the data exchange is done with data and lock filesThe plan is to replace the read/write statements with InterComm callsData is exchanged via a rectilinear intermediate grid - this allows for relatively fast and simple field line tracing
18Inner Magnetospheric Shielding The inner edge of the plasma sheet tends to shield the inner magnetosphere from the main Electric convection field.This is accomplished by the inner edge of the plasma sheet coming closer to Earth on the night side than on the day side.Causes region-2 currents, which generate a dusk-to-dawn E field in the inner magnetosphere.When convection changes suddenly, there is a temporary imbalance.For a southward turning, part of the convection field penetrates to the inner magnetosphere, until the nightside inner edge moves earthward enough to re-establish shielding.
19Example of shielding - Standalone RCM (RCM Runs courtesy of Stan Sazykin)
20RCM LFM: Run SetupSteady solar wind speed of 400 m/s, particle density of 5 /ccUniform Pederson conductance of 5 Siemens (0 Hall conductance)LFM run for 50 minutes without an IMF (from 3:10 - 4:00)IMF turns southward at t = 4:00 hours and coupling is started
21IMF and Cross polar cap potential for RCM LFM run
22Example of shielding - RCM-LFM run Region 2 currentsHigh pVg ‘Blob’
23Example of shielding - RCM-LFM run Low pVg Channels
28Electric fields and pVg RCM -LFM exhibits many of the same characteristics as the standalone RCM, albeit much noisierCaveat: In order achieve reasonable shielding, the density coming from the LFM was floored. Otherwise the LFM plasma temperature in the run becomes very high as the run progresses, which effectively destroys shielding.LFM ionospheric electric field is not the same as the RCM’s, this could be corrected by using a unified potential solver.However, the LFM is missing the corotation electric fieldInitially, the LFM’s pVg is typically lower than empirical estimates, later it becomes higher as the x-line moves tailward.
29Comparisons of Log10(pVg) LFMEmpiricalFigure courtesy of Xiaoyan Xing and Dick Wolf, based on Tsyganenko 1996 magnetic field model and Tsyganenko and Mukai 2003 plasma sheet model. (IMF Bx=By=5 nT, Bz = -5nT, vsw = 400 km/s, nsw=5 /cc)
30Comparisons of Log10(pVg) LFMEmpiricalFigure courtesy of Xiaoyan Xing and Dick Wolf, based on Tsyganenko 1996 magnetic field model and Tsyganenko and Mukai 2003 plasma sheet model. (IMF Bx=By=5 nT, Bz = -5nT, vsw = 400 km/s, nsw=5 /cc)
31Comparisons of Log10(pVg) LFMEmpiricalFigure courtesy of Xiaoyan Xing and Dick Wolf, based on Tsyganenko 1996 magnetic field model and Tsyganenko and Mukai 2003 plasma sheet model. (IMF Bx=By=5 nT, Bz = -5nT, vsw = 400 km/s, nsw=5 /cc)
32Ring Current Injection: The effect of the magnetic field Lemon et al (2004 GRL) used a coupled RCM equilibrium code (RCM-E) to model a ring current injection.A long period of adiabatic convection causes a flow-choking, in which the inner plasma sheet contains high-pV, highly stretched flux tubes.Nothing like an expansion phase or ring-current injection occurs.In order to study the inner-magnetospheric consequences of a non-adiabatic process, Lemon did an RCM-E run which started from a stretched configuration, but then moved the nightside RCM model boundary in to 10 RE and reduced the boundary-condition value of pV5/3 along this boundary within ±2 hr of local midnight.The result was rapid injection of a very strong ring current. Low content flux tubes filled a large part of the inner magnetosphere, forming a new ring current.
37What about the LFM?Should produce a more reasonable representation of the inner magnetospheric pressures, densities and (hopefully) the magnetic field.Trapped Ring CurrentThe presence of a ring current should encourage the formation of Region-2 currentsIdeal MHD should produce region-2 currents.It is not clear why the global MHD models do not.(Actually, higher resolution LFM runs show the beginnings of region-2 currents.)
38Pressure comparisons at ~midnight (RCM values computed along a constant LT in the ionosphere and then mapped to the equatorial plane.)
45Resolution seems to help - but need longer runs Low resolutionHigh resolution(but with no density ‘fix’)
46Summary Coupled code ‘runs’ From an RCM viewpoint, results don’t look unreasonableInner magnetospheric shieldingInner magnetospheric pressuresRing current injectionAlthough LFM computed pVg are low compared to empirically computed values
47Summary - 2 From an LFM viewpoint Magnetic field responds, to first order, as one would expectGet weak region-2 currentsBut get spectacular outflows from the inner magnetosphereDecoupled from the ionosphereMay be a resolution issue, for a given resolution, perhaps the code is unable to find equilibrium solutions that match computed pressuresTurning off the coupling results in disappearance of the ring current in ~15 minutesHigh speed flows seem to be associated with high plasma betasIt seems we are pushing the MHD in a way that it was not designed for
48Outlook Ultimately we hope to couple to TING/TIEGCM in a 3-way mode Ionospheric outflow could also be incorporatedA version of the RCM that includes a non-spin aligned non-dipolar field is in testing phase
50RCM: Inputs and Assumptions Magnetic field modelUsually an empirical modelInitial condition and boundary particle fluxesLoss rates and ionospheric conductivitiesParameterized empirically-based modelsElectric field model is computed self-consistentlyIonosphere is a “thin” conducting (anisotropic) shellElectric field in the ionosphere is potentialAssumptionsPlasma flows are adiabatic and slow compared to thermal speeds.Inertial currents are neglectedMagnetic field lines are equipotentialsPitch-angle distribution of magnetospheric particles is isotropicThe formalism allows the main calculations to be done on an 2D ionospheric grid.