Pole-to-pole: Lidar observations of middle and upper atmosphere temperature and polar mesospheric clouds over the North and South Poles

Global climate change resulting from greenhouse gas increase has extended into the middle and upper atmosphere. Modeling studies show that the effects are more significant at high latitudes. Thus, the observations at the poles may provide some of the first conclusive evidence of global changes in the middle and upper atmosphere, and also provide a convenient mean of calibrating general circulation models. However, the middle and upper atmosphere region is difficult to study. To help address the measurement needs, we developed a new robust lidar system using an Fe Boltzmann technique. The new lidar utilizes mesospheric iron as a fluorescence tracer and relies on the temperature dependence of the population difference of two closely spaced Fe transitions. We deployed this new lidar to the North and South Poles from 1999 through 2001 to measure the temperatures and polar mesospheric clouds in the middle and upper atmosphere for both day and nighttime. Important scientific results and issues have emerged from our observations at the poles, especially on the polar mesospheric clouds (PMC) and temperatures. Significant hemispheric differences in PMC altitudes were found during our pole-to-pole measurements. Interpretation of these results has led to a new insight into the solar radiative forcing on the Earth atmosphere and a baseline for calibrating the atmospheric general circulation models. We review the pole-to-pole observations and results in this paper.