| Fe Boltzmann temperature lidar measurements at South Pole from December 1999 through October 2001, combined with balloon observations, are used to characterize for the first time the monthly mean temperature profiles from the surface to about 110 km. The summertime temperatures agree reasonably well with current model predictions. During midwinter, both the stratopause and mesopause regions are 20–30 K colder than the model. These differences are caused by weaker than expected compressional heating associated with subsidence over the polar cap. The mesopause temperature responds much more rapidly to sunlight changes than model predictions, which suggests that IR heating by CO2 absorption may also be important to the thermal balance in this region.; The 12-month oscillations, associated with solar UV absorption by ozone, dominate the seasonal variations of temperature throughout the stratosphere and lower mesosphere from 10 to 70 km. The coldest temperatures occur in midwinter, when they are as much as 20–30 K colder than the MSIS-00 model predictions. In the mesopause region between 70 and 100 km, 6-month temperature oscillations dominate the seasonal variations with the warmest temperatures occurring near the spring and fall equinoxes. During late February and early March, the temperature near 85 km is more than 35 K warmer than the MSIS-00 model. The spring and fall temperature maxima in the mesopause region appear to be associated with the combined effects of the annual variations in adiabatic heating and cooling and the annual variations in solar heating, which are 180° out of phase. The seasonal temperature variations are largest near 86.5 km altitude, where they are approximately 82 K peak-to-peak.; Similar to the Na observations at South Pole in 1995–1997, the seasonal variations in Fe column abundance, height, and width exhibit a strong annual cycle. The Fe and Na densities exhibit strong 12-month oscillations with the amplitudes comparable to the background level, resulting in extremely thin layers and very low abundances during summer. The bottom sides of the Fe and Na layers are governed by different temperature-dependent neutral chemistry. The Fe density is correlated more closely with the temperature than is the Na. Above 95 km, both species have a negative correlation with the temperatures due to their ionic chemistry and photoionization. |
