Predicting the Global Average Temperature of the Thermosphere From an Empirical Model of the Polar Poynting Flux

Details Predicting the Global Average Temperature of the Thermosphere From an Empirical Model of the Polar Poynting Flux Predicting the Global Average Temperature of the Thermosphere From an Empirical Model of the Polar Poynting Flux

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa23a1782w&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SA23A-1782

Physics

[0358] Atmospheric Composition And Structure / Thermosphere: Energy Deposition, [7924] Space Weather / Forecasting, [7969] Space Weather / Satellite Drag

Scientific paper

The total Poynting flux flowing into both polar hemispheres as a function of time is compared with measurements of neutral densities in the thermosphere. An empirical model, based on satellite measurements, uses the solar wind and interplanetary magnetic field (IMF) to compute the total Poynting flux; this power flow is dissipated as heat in both polar ionospheres, which in turn heat the neutral thermosphere. The density measurements are obtained from satellite accelerometer drag measurements at two altitudes, from the CHAMP and GRACE missions. The Jacchia-Bowman 2008 empirical thermospheric density model (JB2008) is used to facilitate the comparison. This model calculates a background level for the ``global nighttime minimum exospheric temperature,'' Tc from solar indices. Corrections to this background level due to auroral heating, Δ Tc, are presently computed from the Dst index. A new technique is used whereby a proxy measurement of this temperature difference, Δ Tc, is obtained by matching the CHAMP and GRACE density measurements with the JB2008 model. The orbit-averaged Δ Tc measurements on the two satellites are in good agreement, even though their orbits are at different altitudes. Through the use of a differential equation that incorporates the total polar heating, as well as an exponential cooling, the Δ Tc correction can be predicted from IMF values. The resulting calculations agree very well with the orbit-averaged measurements of Δ Tc. Results indicate that the thermospheric cooling rate is faster just after time periods with significant ionospheric heating. The enhanced cooling is likely due to nitric oxide (NO) that is produced at a higher rate in proportion to the ionospheric heating. The Δ Tc predictions use a variable that represents the amount by which the relative concentration of NO grows and decays, which in turn controls the cooling rate of the thermosphere. The Δ Tc temperature correction from this model can be used as a direct substitute for the Dst-derived correction that is now used in JB2008; statistical comparisons show that it is more accurate, in addition to having the capability to be available in near real-time. The ability to predict the thermospheric temperature changes in advance could result in improved tracking of satellite debris.

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