Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm31a2070h&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM31A-2070
Other
[3369] Atmospheric Processes / Thermospheric Dynamics
Scientific paper
We use the latest version of the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model (TIEGCM) to investigate the height distribution of Joule heating and its effects on the temperature and density variations at 400km. Two sets of cases are run, one for solar minimum (F10.7=70 sfu) and the other for solar maximum (F10.7=200 sfu), with other parameters the same. For each set of cases, after running the TIEGCM for 20 days starting at day of year 80 to reach a steady state, we turn off the Joule heating below a specified pressure level, which is set progressively higher for each successive run in the set, and run for another 4 days. Results are analyzed in terms of values integrated or averaged over the globe. The results show that the Joule heating deposited at high altitude is more efficient than heat at low altitude in affecting the temperature and density at 400 km. Fifty percent of the temperature increase at 400 km due to Joule heating is caused by heating above 160 km, which only counts for about 12% of the total Joule heating deposited in the upper atmosphere. Similarly, fifty percent of the density increase at 400 km due to Joule heating results from Joule heating above 150 km, which comprises 18% of the total Joule heating. Most of the Joule heating is deposited under 150 km, and the largest Joule heating deposition per pressure level happens at pressure level -4.25, about 120 km. However, the temperature change at 400 km is largest for heat deposited in the scale height centered at pressure level -3.25 (~135 km) for solar minimum or level 0.25 (~275 km) for solar maximum. Similarly, the density variation at 400 km is largest for heat deposited in the scale height centered at pressure level -3.75 (~127 km) for solar minimum or -0.25 (~250 km) for solar maximum. We also found that, although the same amount of Joule heating deposition causes a larger temperature increase for solar minimum than solar maximum, it causes a larger density increase at 400 km for solar maximum than solar minimum. The time scale for the upper thermosphere to respond to changes in heating varies with the altitude of heating. The heating deposited at lower heights needs more time to be transferred upward, as expected, and it takes less time to reach steady state at solar maximum than at solar minimum, due to the combined effects of heat conduction and radiative cooling. For solar minimum, the Joule heating deposited below pressure level -2.75 (~145 km) needs more time to affect the temperature at 400 km than the density, while Joule heating deposited above pressure level -2.75 needs more time to influence the density at 400 km than temperature. It is similar for the solar maximum case, except that the transition height moves up to pressure level -1.75 (~185 km).
Deng Youjin
Huang Yong-Yi
Richmond Arthur D.
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