[Seminar] Prof. Xinzhao Chu

First Lidar Observations of Vertical Transport of Heat and Meteoric Na by the Complete Temporal Spectrum of Gravity Waves in the Mesosphere and Lower Thermosphere (MLT) over McMurdo, Antarctica

The upper atmosphere is filled with waves that originate in the lower atmosphere from storm systems and airflow over mountainous terrain, and then propagate upward. These waves play key roles in establishing the composition and temperature structures by mixing the upper atmosphere and by perturbing chemical reactions of important reactive species like atomic oxygen and ozone. By using meteoric sodium (Na) that is injected between 78 and 110 km altitude by the vaporization of cosmic dust, as a tracer, and exciting the Na atoms to fluorescence using a lidar system located at McMurdo Station, Antarctica, we directly measured the vertical transport of heat and Na induced by the full spectrum of waves. The results in the lower thermosphere (97–106 km) show that wave-driven motions in this region are not purely adiabatic (heat does not enter or leave the perturbed air parcel for adiabatic motions), which contradicts conventional thinking. By comparing the measured Na transport with theory, we also show that many of the waves between 80 and 95 km are propagating downward, which we believe are generated in this region when upward propagating waves become unstable and break, much like ocean waves behave when breaking over a shoal. This seminar will also introduce the lidar campaigns and highlight science discoveries made by the University of Colorado lidar group during the last 10+ years in Antarctica.