Jan 17 Notes

CISM MIC WG (seminal) Meeting

Date: Friday, Jan 17, 2003

Time: 1:00 - 2:30 PM EST

Place: Access Grid

Participating Nodes: BU, Dartmouth, NCAR

Agenda:

1) Long-range strategy for advancing numerical modeling of MI coupling,

2) Realistic short-term goals for advancing MI coupling capabilities in CISM codes and the science resulting from CISM codes,

3) Reports of work in progress,

4) Future WG meetings,

5) Other issues?

For reference, four paragraphs from the CISM draft strategic plan pertaining to various aspects of MI coupling are appended.

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Notes from the 1/17/03 Meeting

Participants: BU (C Goodrich, J Hughes, J Lyon), Dartmouth (W Lotko, A Streltsov, M Wiltberger), NCAR (A Burns, L Qian, S Solomon, W Wang), NOAA (N Maruyama, T Fuller-Rowell)

Next Meeting: Friday, Feb 14, 1:00-2:30 EST

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WORK-IN-PROGRESS REPORTS:

LFM-RCM COUPLING: One-way coupling is basically complete (Lyon, Toffoletto). In this scheme, RCM uses the dynamic LFM magnetic field and potential distribution and returns a modified potential distribution. The LFM magnetic field enters RCM via calculation of flux tube volume and the mapping of FACs and convection between the ionosphere and equatorial magnetosphere (?). RCM uses the LFM potential distribution for the high-latitude boundary condition in its poisson solver for the ionospheric potential distribution in the (closed geomagnetic field) RCM domain. A first cut at two-way LFM-RCM coupling will require about 6 months effort and will involve modifying the LFM pressure distribution to be consistent with the RCM drift-kinetic distributions. A measure of (non) self-consistency in the two-way coupling scheme will be the difference in the FAC distributions calculated by the two codes. Fully self-consistent two-way coupling is likely to be a long-term project.

LFM-TING COUPLING: Generation 1 two-way coupling is basically complete (Burns, Wang, Wiltberger), with an extensive validation effort lying ahead. LFM provides TING with a distribution of the precipitating electron energy flux and characteristic electron energy (from "Knight physics" in upward FAC region) and the high-latitude potential distribution, obtained from the simple ionospheric model currently embedded within LFM. From these LFM inputs, TING calculates modifications to the ionospheric conductivity and recalculates the high-latitude potential distribution, which is then used as the low-altitude boundary condition at each time step for LFM. LFM-TING is currently able to run at 100-km horizontal resolution.

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ISSUES AND DIRECTIONS:

(We did not identify who would be responsible for some of these tasks or the time scale for completion; we should probably return to them at the next meeting.):

1) An analysis of the FACs predicted by the LFM and RCM for various conditions in the one-way coupling scheme may be scientifically useful because it would indicate the regions and conditions where the FACs and convection are regulated by MHD and where and when drift-kinetics and the ring current significantly affect the solution. Comparisons of the FACs from Iridium and those predicted by each model would also be useful.

2) Analysis of the electrojet w/ and w/o coupled codes would be scientifically useful, particularly for metric evaluation. The ground magnetic perturbations resulting from the simulated ionospheric currents can be compared with ground magnetometer data (Shepherd?). LFM-TING ionospheric currents and flows might also be compared with SuperDarn and Iridium data.

3) Analysis of the flywheel effect on the magnetosphere would be of considerable interest. One way of evaluating the effect would be to run LFM-TING w/ and w/o the neutral wind term in the ionospheric Ohm's law.

4) Can TING use the diffuse electron and ion precipitation (energy flux and characteristic energy) predicted by the coupled LFM-RCM model? These quantities can be derived directly from RCM distribution functions.

5) LFM, RCM and TING are all solving the same elliptic equation for the ionospheric potential distribution. A single poisson solver used by all 3 codes would be more efficient and may serve as the primary communication channel for MI coupling between the 3 codes.

6) TING uses a free BC on the normal flow at its upper boundary. LFM currently specifies zero normal flow at its lower boundary (?). Inertial coupling of LFM-TING might be enabled by matching the distributions of mass flux at the two boundaries, e.g. LFM to use TING mass flux as its lower BC at each time step.

7) The ionospheric mass outflow problem is actually much more complicated than simply matching BCs at the LFM-TING interface and has different physical origins in different regions. In the polar cap, the polar wind is dominant. In the plasmasphere, the closed flux tube variant of the polar wind gives rise to plasmaspheric refilling and interhemispheric flows. At present, modeling of the polar wind and plasmaspheric flows is not a CISM activity (Should it be initiated? by who?). In the auroral zone, the outflow is supercharged by collisionless heating and acceleration of upwelling ions in the topside ionosphere and low-altitude magnetosphere, especially during active periods near the polar cap boundary. Although understanding of collisionless auroral plasma energization has not matured to the point of a concise physical formulation, e.g. for embedding in LFM-TING, empirical studies can provide a good starting point. Recent observational work indicates that outflow near the PC boundary is causally regulated by Alfvénic Poynting fluxes. One approach under investigation (Lotko) is to key the ionospheric mass outflow rate to the Alfvénic Poynting flux (e.g., high-pass filtered LFM EM power) at the low-altitude LFM boundary. Self-consistency would require the upper TING BC to be adjusted to match this outflow rate. With coupled models, TING should specify the mass density at the boundary, LFM would specify the Alfvénic EM power input, and an empirical model would adjust the mass flux based on the TING density and LFM EM power flux. A first attempt at such coupling may be expected within 6-8 months.

8) Science study using LFM (and/or LFM-TING) fields: Follow the phase-space motion of representative outflowing "test" ions of various energies and pitch angles entering the LFM domain at its lower boundary. The Lorentz solver being developed for the rad-belt problem could be readily adapted for this study (Cress?).

9) Improvements in the Knight relation, representing effects of collisionless energy dissipation are needed (Lotko). The Knight relation does not treat regions of downward current where upflowing energized electrons are created in the lower magnetosphere (re: FAST results). While Knight physics is known to represent the observed current-voltage relation accurately in some inverted V precipitation structures, the Knight-predicted voltage is several times larger than observed in intense upward FAC channels containing intense microturbulence.

10) Science question: Do conductivity depletions (and corresponding convection enhancements) at horizontal scales ~100 km arise in regions of downward field-aligned current in the coupled LFM-TING model? [cf. attached excerpt by Opgenoorth from the ISSI monograph, "Auroral Plasma Physics", ed. by Paschmann et al., in press, 2003]. If not, what additional physics is needed to capture the effect?

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M-I Coupling Paragraphs from the Strategic Plan

Outer-Inner Magnetosphere Coupling: Important new science goals can be accomplished when the physics of the inner magnetosphere, as represented by the drift physics in the RCM, becomes embedded in the global MHD magnetospheric code (LFM+RCM). Then the magnetospheric component of the CISM physics-based code will be able to generate ring current and region 2 currents and associated shielding of the low-latitude ionosphere from high-latitude convection electric fields. This code will be able to resolve long-standing issues in magnetospheric physics by examining the time-dependent response and topology of the region 1 and region 2 current systems and its dependence on the interplanetary magnetic field.

Magnetosphere/Ionosphere Coupling: The first order goal is to determine the role and impact of MI coupling on the establishment and maintenance of the basic state of the ionosphere and magnetosphere. Our studies will shed light on the causes of the variability seen and the limitations of predictability. Once the LFM code is coupled to the thermosphere-ionosphere general circulation model (TIEGCM), a host of important science studies will be undertaken. At high latitudes, the global thermospheric response to magnetospherically driven Joule heating and energetic electron precipitation will be determined, including changes in ion and neutral composition, convection, ionization, and neutral, ion and electron heating. The evolution and spatial distribution of the auroral electrojet during storms and substorms will be simulated. Inclusion of field-aligned plasma flows, initially via empirical parameterized models, and, ultimately, using physical transport models, will enable studies of dynamic density stratification in the ionosphere and low-altitude magnetosphere and the effects of ionospheric outflow on the global magnetospheric system. Precipitation-induced ionization and ionospheric outflows are significantly enhanced by collisionless ion and electron energization processes that occur in the lower magnetospheric region between the upper boundary of the TIEGCM and the lower boundary of the LFM. Empirical and physical transport models of these processes will be developed and included in the low-altitude LFM boundary conditions. The global electrodynamic interaction between the thermospheric winds and magnetospheric convection and, in particular, the “flywheel” feedback of thermospheric winds on magnetospheric convection will be characterized.

Thermosphere/Ionosphere Physics: The global interaction between ionization and heating induced by solar EUV and X-rays and the effects produced by M/I coupling will be determined. This interaction will have immediate applications to forecasting atmospheric drag on satellites, especially during storm-time conditions. The effects on ionospheric structuring, variations in ionospheric content along specified slant paths, and the evolution of geomagnetic induced currents affecting ground-based electrical transmission systems will be investigated. At low latitudes, where interhemispheric flows arise, studies of penetration electric fields on plasmaspheric structure and the role of light ions at and above the exobase will also be enabled when the RCM is coupled with the LFM and TIEGCM models as described above.

Magnetic Storms: Magnetic storms are the premier space weather events, and the cause of many catastrophic space weather incidents. Magnetospheric behavior during magnetic storms is not well understood both because it is poorly sampled since storms are relatively rare, and because the coupling between the solar wind, magnetosphere, and ionosphere is much stronger during storms. CISM models will let us explore this coupling under extreme conditions in ways that are just not possible presently. Determining the role of the convection electric field on the storm-time ring current is a problem of central importance to understanding magnetic storms. We will investigate the phenomenon of “undershielding” which happens when the solar wind electric field changes suddenly thereby exposing the low-latitude ionosphere to electric fields from high latitudes and modifying the ionosphere’s radio propagation properties. This is very important for understanding the erosion of the plasmasphere during storms and the location of the auroral electrojet. Reaching closure on these issues is important if CISM is to make substantive advances in treating storm conditions.