Scientific Theme: Advanced Modeling and Observing Systems

Theme report: Advanced Modeling and Observing Systems
The vertical extension of the model domain has required the incorporation of additional physical processes and
substantial changes in the dynamical core and in its interface with the model physics. As is well known in upperatmospheric
modeling, temporal and spatial variations of specific heat along air parcel trajectories have to be
explicitly accounted for in the energy equation to represent correctly the effects of a highly variable thermospheric
composition. These variations are commonly not accounted for in lower-atmospheric GCMs, and instead rely on the
approximation of ―virtual temperature‖ and assume that the composition deviations from the uniform ―dry air,‖
primarily caused by the presence of water vapor, are small. A new spectral model formulation has been developed
and implemented in the GFS, using specific enthalpy cpT, where cp is specific heat at constant pressure and T is
temperature, as a prognostic variable instead of the traditional virtual temperature.
Molecular dissipative processes such as viscosity, heat conduction, and diffusion become so fast in the upper
thermosphere that they can no longer be treated within the standard vertical-column interface. Horizontal molecular
transport of momentum, heat, and constituents along pressure surfaces have been incorporated into the model as
well. This physical dissipation eliminates the need for excessive numerical damping commonly used to stabilize
numerical models in vertically extended domains. Additional physical processes incorporated in the extended model
domain include UV and EUV radiative heating, infrared radiative cooling with the breakdown of local
thermodynamic equilibrium, and non-orographic gravity waves. In the normal fully-coupled configuration ion drag,
Joule and particle heating are calculated self-consistently within GIP. In a stand-alone WAM, these processes can be
parameterized using an empirical ionosphere model.
Global Ionosphere Plasmasphere (GIP) model and electrodynamics. The plasma processes required in IDEA are
provided by the Global Ionosphere
Plasmasphere (GIP) module, which includes
a self-consistent global electrodynamic
solver. GIP was developed by extracting the
plasma processes embedded in the Coupled
Thermosphere Ionosphere Plasmasphere
electrodynamics (CTIPe) model. In earlier
versions of CTIPe, the Earth‘s magnetic
field was assumed to be a tilted dipole. In
reality, however, the low-latitude
geomagnetic field departs from the dipole
equator by more than ten degrees over the
Atlantic Ocean and Africa. Furthermore,
ionospheric dynamo electric fields depend
on the strength of the magnetic field, since
the wind-driven currents depend on the
field-line integration of the ionospheric
conductivity and neutral wind.
Figure 2. Wavelet amplitude spectrum of zonal wavenumber 2
oscillation in the WAM zonal wind at 20 S and 110 km altitude as a
function of period and day number in March and April.
GIP now explicitly includes the International Geomagnetic Reference Field (IGRF), an accurate representation of
the Earth‘s magnetic field, in order to introduce true longitude dependence. The global ionospheric dynamics and
energetics are solved in the magnetic APEX coordinate system. GIP receives the neutral atmosphere fields from
WAM, computes the Joule heating, ion-drag, and auroral particle heating and passes these parameters back to
WAM. The neutral and plasma domains are completely self-consistent and interactive.
Self-consistent coupling between the WAM and GIP is completed by solving the global electrodynamics and by
feeding the electric fields back into GIP. The electric fields are computed using a global potential solver in the same
APEX coordinate system. The electrodynamics module receives the dynamics from WAM and the field-aligned
conductivities from GIP, computes the electric fields, and provides the information back to both modules. The
resultant ionospheric dynamo electric fields reflect the forcing from the lower atmosphere and realistic ionospheric
structure through the use of the IGRF.
Early results from WAM provide the first confirmation that the model is capable of realistically reproducing the
dynamics and variability in the upper atmosphere, and that terrestrial weather features can affect the thermosphere-
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