Statistics – Computation
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsa41b..05b&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SA41B-05
Statistics
Computation
0358 Thermosphere: Energy Deposition (3369), 3369 Thermospheric Dynamics (0358)
Scientific paper
The resultant infrared cooling from the greenhouse gases carbon-dioxide, nitric oxide and the upper atmospheric atomic oxygen has been estimated in the height range of 120 to 200 km for different solar activity and geomagnetic conditions at moderate latitude utilizing MSIS-E (1990) models. The simplified energy equation has been used for computation particularly during noontime and nighttime conditions when the temperature gradient with time can be ignored. It is shown that the cooling decreases with height above 120 km exponentially exp(-s(z- 120)), where s' is a parameter dependent on the temperature profile and the exospheric temperature, z the height and 120 the lower boundary in km. It is also shown that the cooling and hence the density of the gases increase with increase in the solar activity irrespective of the season by an average factor of about 1.6 at 120 km and about 1.9 at 200 km from the minimum to maximum solar activity. Some of the enhanced cooling, besides nitric oxide, may be result of a larger value of the relaxation rate coefficient between carbon-dioxide and the atomic oxygen. The seasonally average value of about 1.8*10-7 ergs cm-3 s-1 at 120 km for average solar activity agrees well with the heating rate values. However, the total cooling is found to decrease with increase in the geomagnetic activity by an average factor of about 1.9 at 120 km and by 0.8 at 200 km from the quiet period (Ap ~ 4) to storm conditions (Ap ~ 30). The present results signify substantial changes in the total densities of the greenhouse gases and atomic oxygen with the solar activity and the geomagnetic conditions. Since the predominant cooling in the lowest thermosphere is from nitric oxide and carbon-dioxide, such changes in cooling with solar and geomagnetic activity imply similar changes in their densities in the lower thermosphere. However during disturbed conditions when the nitric oxide density is enhanced in the thermosphere, such cooling could be predominantly from the changes in the nitric oxide density. The changes in the cooling and thus in the densities of the individual gases and their detailed dependence on the season and the latitude require further investigation.
Bhatnagar Vasudha
Tan Aihong
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