Geoscience Reference
In-Depth Information
Most global-scale modeling of the Earth's upper atmosphere environment makes
use of global input parameters of both solar and geomagnetic indices. This
work concerns both first-principle models like the UAM of this chapter, which
describe the complex interaction of the various geospace “spheres” from a full-
scale physical-theoretical point of view, as well as empirical models, which merely
generalize large observational data sets in terms of more or less sophisticated
parametrized simulation tools to obtain a best-fit description of observable physical
quantities such as density or neutral wind vector patterns. All these global-scale
models are, first of all, climatological in nature, that is, they reproduce the large-
scale general trends in dependence of a few parameters such as the planetary
3-h-range magnetic index
K
p
, the geomagnetic
A
p
, or the solar EUV radiation proxy
index
F
10.7
already mentioned.
Most global empirical models for the description of the Earth's upper atmosphere
environment such as the International Reference Ionosphere (IRI), the NRLMSISE-
00 empirical model of the atmosphere (Picone et al.
2002
), which is also used
here as boundary condition, and upper atmosphere neutral wind models such as
the HWM (Hedin et al.
1991
) or its recently renewed version HWM07 (Drob et al.
2008
), and its companion paper with the disturbance wind DWM07 model (Emmert
et al.
2008
), describe the average geospace storm-induced perturbations of the
upper thermospheric neutral wind. All these models make use of global-scale input
parameters to describe accordingly the actual solar and geomagnetic activity status
as climatological descriptions of the atmospheric and plasma environment state. The
empirical models are also used as initial or boundary conditions for simulation runs
of the first-principle models or are enquired for comparison purposes.
Such large-scale model designs are good for global studies of low- to mid-latitude
phenomena, but fail for the study of highly dynamic and mesoscale processes, which
are typical particularly at auroral and polar latitudes. There are no empirical high-
latitude upper atmosphere neutral wind models with input parameters that describe
typically high-latitude forcing such as the auroral electrojet index AE, solar wind
parameters, and the IMF magnitude and orientation.
Seeking for better representation of the high-latitude energy and momentum
input, we tried to find adequate formulations for Region-1 FAC and high-energy
precipitations at auroral and polar latitudes. We made use of the IMF-dependent
empirical model of FACs of Papitashvili et al. (
2002
), as shown in Fig.
4.5
for
Southern Hemisphere conditions and an average IMF magnitude of 5 nT. The
pattern shows the spiral structure of Region-0, Region-1, and Region-2 currents,
discovered first by the famous work of Iijima and Potemra in the 1970s, with current
sheet pairs of opposite direction at the dawn and dusk side. Further related input
(or boundary) conditions comprise the auroral high-energy particle precipitations,
including the cusp region as the most important and intense energy input and
mesoscale thermospheric upwelling region, which has recently been shown by
CHAMP observations as a regular mass density anomaly near noon at high latitudes
(cf., e.g., Rentz and Luhr
2008
). The precipitation pattern must be chosen in
accordance with the FAC input regions.
A complication of the physical model formulation consist also in an optimal
choice of temporal and spatial discretization steps. The usual spatial steps are
1-2
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