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1998 GEM Snowmass Workshop Reports
GGCM Campaign: GGCM Modules
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From:  Phil Pritchet (pritchet@physics.ucla.edu)

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I.  Joint Session: Inner Magnetosphere/Storms and GGCM (Modules)
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     This session featured 3 invited talks and a general discussion regarding
the inclusion of the inner magnetosphere in a GGCM.

     Margaret Chen reviewed the physical aspects of a realistic storm time
ring current.  She discussed the properties of the quiescent ring current
distribution, the nature of the particle drifts during a storm time varying
electric field, and the need for a realistic dynamic source distribution.

     Anthony Chan presented some thoughts on a radiation belt module for
the GGCM.  He stressed that the magnetic drifts dominate the particle
motion, the local effects on the electromagnetic fields are negligible
(thus the fields could be input from a MHD model), and that hence the
module should be highly parallelizable.  He identified 3 main time scales:
(1) quasi-static (months), (2) MeV electron enhancements (hours to days),
and (3) rapid flux enhancements (few minutes) and discussed the merits
of a "Liouville" vs. a "Fokker-Planck" approach to constructing a module.

     Xinlin Li reviewed the physics of dispersionless particle injections.
He showed that recent results indicate that particles are brought in by
a transient field; there is no need to invoke an injection boundary.  The
important questions are where are these transient fields initiated and
how do they propagate earthward.

     In the general discussion several issues were identified for
consideration:
     (1) An ionospheric source is necessary to feed the plasmasphere and
         impact the GGCM.
     (2) One could convceive of a hierarchy of GGCMs in the spirit of
         Michael Ghil's tutorial on climate modeling.  One example of
         a smaller scale GGCM would be a dynamic plasmasphere that might
         embed the Rice convection model in a larger MHD model.
     (3) A radiation belt/particle tracing module could be run in a 
         non-self-consistent mode.


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II.  GGCM Modules - I
=====================

     This session explored the physics of a number of regions that would
couple to a GGCM and heard a report of progress in combining the Rice convection
model with a friction code.

     Homa Karimabadi reviewed recent progress in 3-D hybrid simulations of
the magnetopause.  He stressed that the kinetic structure of the boundary 
layer does not match any of the usual MHD discontinuities, that the main
mechanism producing a component of the magnetic field along the current
("core field" generation) is the Hall term, and that the time dependence
in FTEs arises from ion kinetics in 3D shutting off and turning on
reconnection.

     Frank Toffoletto described recent progress in combining the Rice
Convection Model (RCM) with an MHD code using a magnetofriction technique.
The MHD code can supply the magnetic field model, plasma boundary
conditions, and electric potential distributions around the polar cap
to the RCM, while the RCM in turn can supply to the MHD code accurately
computed pressures and densities that can be used to override or adjust
the MHD code in the inner magnetosphere.

     Aaron Ridley described the TIME (Thermosphere, Ionosphere, Mesosphere,
Electrodynamics) GCM.  He reported on progress in porting the code to
a heterogeneous workstation environment and modifying the model to
run in a distributed parallel computing environment.

     Bob Lysak reviewed the important physics effects associated with M-I
coupling that should be included in ionospheric/auroral modules that are
connected to MHD models.  Among the approaches that have been used to
treat these effects are to assume an effective conductance along the auroral
field line and use an empirical model for the evolution of the height-
integrated ionospheric conductivity, to include additional terms in the
generalized Ohm's law to model parallel electric fields, and to construct
a full model of the interactions between the ionosphere and the neutral
atmosphere.