MLT Science Enabled by Atmospheric Lidars

With the pioneering development and deployment of different types of narrowband sodium fluorescence lidars in Europe (1985) and North America (1990) along with subsequent potassium and iron lidars, temperature and wind profilers have been observed to investigate atmospheric dynamics in the mesosphere and lower thermosphere (MLT) in midlatitude, polar and equatorial regions. Their achieved resolution allows investigation ranging from small-scale gravity waves to long-term global change. This chapter highlights MLT science enabled by resonance fluorescence lidars in the past 30 years, divided into sections on climatology and long-term change of the atmospheric (background) state; MLT responses to external forcings that lead to atmospheric tides, the global-scale impacts of sudden stratospheric warming as well as geomagnetic storms; gravity wave dynamics and their fluxes; synergistic campaigns with lidars serving as a central instrument, and lidar observation of metal layers in the thermosphere at ever-higher altitudes. Recent advances in maintenance-free resonance lidars will increase the time and duration of lidar observation as well as their ease of operation. These should lead to more coherent multiple-day continuous observations of the MLT. Continued efforts to increase lidar signal/noise and to extend measurements from the main metal layers (80–110 km) into the lower thermosphere (up to 150 km) are ongoing. Further technology developments will also enable more lidar deployment on airplanes and in space to study the MLT over the oceans and other remote areas.