Proceedings with Extended Abstracts (single PDF file) - Radio ...

Report on Session I.1 “Radar scattering processes in the neutralatmosphere”Conveners: H. Luce and A. MuschinskiAbstract of session: Unambiguous retrieval of atmospheric parameters related toturbulence, waves, hydrometeors, etc, from MST radar measurements is still challengingand sometimes impossible. This difficulty is in part due to the nature of the specificinversion problem, in part due to our still insufficient knowledge on the relevantbackscattering mechanisms and their relative importance. This session was thus devoted torecent approaches (sophisticated radar observations, intercomparisons with in situmeasurements and numerical simulation results) used for improving our understanding onthese processes.Eight papers were presented in the Session I.1 chaired by M. Petitdidier, W. Singer and H.Luce. The two first presentations were invited talks prepared by D. Fritts of ColoradoResearch Associates (USA) and F. Dalaudier of Service d’Aéronomie (CNRS, France).These talks emphasized the importance of numerical simulations and in situ observations,respectively, for the interpretation of MST radar echoes. D. Fritts presented results of 3DDNS of turbulence generation by KHI and gravity wave breaking. These simulationsclearly demonstrate the generation of thin structures at the edges of a mixing layer. Thesestructures are characterized by strong thermal and velocity gradients and are quite similar tothose shown by F. Dalaudier observed experimentally in the shear of a jet-stream usinghigh-resolution temperature measurements. The simulation results were strongly debated,in particular, the importance of the initial conditions used (very small Ri number) and ofestablishing energy budget and the interaction of the mixing layer with other possibleprocesses (such as waves) in its surroundings which could affect the mixing evolution. F.Dalaudier reviewed recent observations by balloon and radar techniques. After a presentionof the measurement techniques and results with the CIRES TLS (Tethered Lifting System)and MUTSI experiment, he mainly emphasized the constraints and interpretationdifficulties when comparing atmospheric parameters measured by radars and balloons.Finally, these two talks stressed the importance of MST radar experiments coordinated withnumerical simulations and in situ observations for a better understanding of the atmosphericdynamics at small scales. More thorough intercomparisons are needed and the creation of aworking group on this topic could help to the development of common projects.D. Hooper (with J. Arvelius, K. Stebel and E. Pavelin) gave two talks showing thepossibility to retrieve static stability from MST radar returns and an application of theproposed approach to tropopause erosion by mountain wave breaking. A thorough analysisshowed interesting potential of the method based on N 2 estimation from vertical echopower. The observed desagreements mainly resulted from important balloon drifts andhorizontal inhomogeneities of the temperature field due to mountain waves. N 2 radarestimates were then used for calculating Ri number from the sole radar measurements andthen analysing an event of moutain wave breaking around the tropopause level. The Rinumber is an important (but not sufficient) parameter for identifying the nature of the radarechoes. Another approach from MST radar data was presented by A. McDonald by usingstatistics of the I and Q components of the received signals.18