[1] Lidar observations, conducted at the South Pole by University of Illinois researchers, are used to characterize the seasonal variations of mesospheric Na and Fe above the site. The annual mean layer abundances are virtually identical to midlatitude values, and the mean centroid height is just 100 m higher for Na and 450 m higher for Fe compared with 40°N. The most striking feature of the metal profiles is the almost complete absence of Na and Fe below 90 km during midsummer. This leads to summertime layers with significantly higher peaks, narrower widths, and smaller abundances than are observed at lower latitudes. The measurements are compared with detailed chemical models of these species that were developed at the University of East Anglia. The models accurately reproduce most features of these observations and demonstrate the importance of rapid uptake of the metallic species on the surfaces of polar mesospheric clouds and meteoric smoke particles. The models show that vertical downwelling in winter, associated with the meridional circulation system, must be less than about 1 cm s À1 in the upper mesosphere in order to avoid displacing the minor constituents O, H, and the metal layers too far below 85 km. They also show that an additional source of gas-phase metallic species, that is comparable to the meteoric input, is required during winter to correctly model the Na and Fe abundances. This source appears to arise from the wintertime convergence of the meridional flow over the South Pole.
The design, development, and first measurements of a novel mesospheric temperature lidar are described. The lidar technique employs mesospheric Fe as a fluorescence tracer and relies on the temperature dependence of the population difference of two closely spaced Fe transitions. The principal advantage of this technique is that robust solid-state broadband laser source(s) can be used that enables the lidar to be deployed at remote locations and aboard research aircraft. We describe the system design and present a detailed analysis of the measurement errors. Correlative temperature observations, made with the Colorado State University Na lidar at Fort Collins, Colorado, are also discussed. Last, we present the initial range-resolved temperature measurements in the mesosphere and lower thermosphere over both the North and the South Poles obtained with this system.
[1] Fe/Rayleigh lidar measurements are combined with the high-altitude balloonsonde data and used to characterize the seasonal variations of atmospheric temperature at South Pole from the surface (2.835 km) to 110 km altitude. Twelve-month oscillations, associated with solar UV absorption by ozone, dominate the seasonal variations of temperature throughout the stratosphere and lower mesosphere from 10 to 60 km. In the mesopause region between 70 and 100 km, 12-and 6-month oscillations dominate the seasonal variations with the warmest temperatures occurring near the spring and fall equinoxes. During the month of March, temperature near 80 km is more than 25 K warmer than MSIS-00. 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. During the month of June, the stratopause and mesopause temperatures are about 20-30 K colder than the model predictions. The seasonal temperature variations are the largest near 85 km altitude, where they are approximately 85 K peak to peak.
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