CEDAR:
Modeling Metastable Helium Emissions in the Terrestrial Thermosphere
Principal Investigator (SwRI):
Richard Link
Principal Investigator (CPI):
James Bishop |
Principal Investigator (SwRI):
Richard Link
Principal Investigator (CPI):
James Bishop |
This collaborative research, proposed by Computational Physics, Inc.
and Southwest Research Institute, will carry out modeling studies of
the magnitude of and spatial variation in the upper atmosphere's 1083
nm airglow emission. The project will build upon the investigators'
previous exploratory work in a two-year effort. The investigators will
include empirical and analytic descriptions of the attenuation of
photoelectron fluxes upon passage through the plasmasphere
in the iterative calculation for conjugate photoelectron fluxes. They will
also generate comprehensive maps (latitude vs. local time) of helium
distributions and resulting 1083 nm and 388.9 nm emission intensities
under a variety of geophysical conditions, both for revealing the
sensitivities of the airglow emissions to various inputs and for
supporting the analysis and interpretation of 1083 nm and 388.9 nm data
obtained by others. In the second year, they will assess line profile
features for remote sensing of thermospheric temperatures and motions.
Helium is a tracer of upper thermospheric dynamics, so that measured
line center displacements may offer a unique test of general
circulation models of the upper thermosphere. However, since the 1083
emission peak altitude is above 400 km, observed displacements will not
constitute a direct wind speed measurement, but rather will reflect the
magnitude of lateral (ballistic) fluxes governed by latitudinal and
longitudinal gradients in density and temperature as well as by wind
patterns.
Recent Results:
| This figure shows the contribution of interhemispheric (conjugate) photoelectron transport to excitation of He(23S). The calculation is for summer solstice in the southern hemisphere. The bright area in the northern hemisphere is due to the winter helium bulge. |
| This figure shows column excitation rates of He(23S) due to radiative recombination of He+. The IRI-95 reference ionosphere model is used for the electron and He+ densities. This model has abrupt changes in ion composition at the terminators, as seen in this figure. Noon is in the middle (-70o) of these figures. |
| Height-integrated electron densities (total electron content) corresponding to the above He+ densities. |
