Editing Thermosphere (section)

===Energy budget===
The thermospheric temperature can be determined from density observations as well as from direct satellite measurements. The temperature vs. altitude z in Fig. 1 can be simulated by the so-called [[David Bates (physicist)|Bates]] profile:<ref>Rawer, K., Modelling of neutral and ionized atmospheres, in Flügge, S. (ed): Encycl. Phys., '''49/7''', Springer Verlag, Heidelberg, 223</ref>

(1) {{pad|4em}} <math>T = T_\infty - (T_\infty- T_0) e^{ -s(z - z_0)}</math>

with  T<sub>∞</sub> the exospheric temperature above about 400&nbsp;km altitude, 
T<sub>o</sub> = 355&nbsp;K, and z<sub>o</sub> = 120&nbsp;km reference temperature and height, and s an empirical parameter depending on T<sub>∞</sub> and decreasing with T<sub>∞</sub>. That formula is derived from a simple equation of heat conduction. One estimates a total heat input of q<sub>o</sub>≃ 0.8 to 1.6&nbsp;mW/m<sup>2</sup> above z<sub>o</sub> = 120&nbsp;km altitude. In order to obtain equilibrium conditions, that heat input q<sub>o</sub> above z<sub>o</sub> is lost to the lower atmospheric regions by heat conduction.

The exospheric temperature T<sub>∞</sub> is a fair measurement of the solar XUV radiation. Since solar radio emission F at 10.7&nbsp; cm wavelength is a good indicator of solar activity, one can apply the empirical formula for quiet magnetospheric conditions.<ref name="Hedin">Hedin, A.E., A revised thermospheric model based on the mass spectrometer and incoherent scatter data: MSIS-83 J. Geophys. Res., '''88''', 10170, 1983</ref>

(2) {{pad|4em}} <math>T_\infty \simeq 500 + 3.4 F_0</math>

with T<sub>∞</sub> in K, F<sub>o</sub> in 10<sup>−2</sup> W m<sup>−2</sup> Hz<sup>−1</sup> (the Covington index) a value of F averaged over several solar cycles.  The Covington index varies typically between 70 and 250 during a solar cycle, and never drops below about 50. Thus, T<sub>∞</sub> varies between about 740 and 1350&nbsp;K. During very quiet magnetospheric conditions, the still continuously flowing magnetospheric energy input contributes by about 250&nbsp; K to the residual temperature of 500&nbsp; K in eq.(2). The rest of 250&nbsp; K in eq.(2) can be attributed to atmospheric waves generated within the troposphere and dissipated within the lower thermosphere.