HAO Colloquium - Jorge Chau, Leibniz Instiute for Atmospheric Physics

Quantification of gravity waves and turbulence in the mesosphere with atmospheric radars

Fundamental dynamics of cascade processes in the atmosphere can be studied “easier” in the mesosphere and lower thermosphere (MLT), where atmospheric waves and turbulence present larger temperature and wind amplitudes than at lower altitudes. The major waves in the MLT, i.e., planetary waves, tides, gravity waves, are subject to dynamic instability, resulting in the cascade of macro-turbulence to small-scale gravity waves and in turn to small-scale turbulence. In the MLT, at horizontal scales below 300-500 km co-exist gravity waves and stratified macro turbulence processes, the transition between them and their power-laws are poorly understood. These scales are not resolved in current general circulation atmospheric models, and therefore their possible influences are parameterized. Parametrization of the forcing at these scales remains a major source of model uncertainty. We will present two approaches that aim to contribute to the understanding of these horizontal scales in the MLT using atmospheric radars. The first approach called MMARIA (20 to 400 km horizontal scales), is based on the observation of large area of the MLT with multi-static specular meteor radars, followed by the exploitation of second-order statistics of line-of sight velocities. These statistics allow a 4D estimation of the six Reynold-stress tensor quantities (e.g., momentum fluxes) either in their correlation, spectrum, as well as structure functions. Our second approach makes use of 4D radar imaging of polar mesospheric summer echoes with MAARSY. Here we go after horizontal scales between 1 and 20 km. We will present preliminary results from those approaches, including the full-characterization of Kelvin-Helmholtz Instability (KHI) event with MAARSY.

Date and time: 
Thursday, December 5, 2019 - 2:00pm to 3:00pm