Séminaire LATMOS (Guyancourt, amphithéâtre G. Mégie) le jeudi 9 février à 11h. Colin Wilson (AOPP, University of Oxford): "Measuring wind at the surface of Mars" (seminar in English!).

Surface-atmosphere exchanges of heat, momentum, volatiles and dust are responsible for much of the variability of the Martian climate; however, these exchanges are governed by boundary-layer winds, which are currently very poorly known. Boundary layer winds cannot be measured from orbit and must be measured from landers. Fast (10 Hz or more) 3-D wind sensors can resolve turbulent eddies, permitting eddy covariance measurement of heat and momentum fluxes. When combined with a tunable laser spectrometer and in situ dust-measuring instrumentation, measurements of volatile and dust fluxes are also possible. A particular focus of these instruments is the understanding of dust lifting: while the principle method of dust lifting appears to be saltation (liberation of dust particles by heavier sand grains), other mechanisms proposed include convective vortices, electrostatic charging, and thermopheresis (local thermal gradients), but the relative importance of these mechanisms is still not understood.

In this talk I will review the wide variety of different types of wind sensor which have been developed for (or deployed on) Mars landers. Detailed presentation of two wind sensors will be given: Firstly, a very lightweight 2-D thermal sensor which was flown to Mars on Beagle 2 in 2003 and which is proposed for re-flight in 2016; Secondly, a full 3-D ultrasonic anemometer, similar to those used for study of meteorological turbulence on Earth. The ability of these sensors - in combination with other in situ sensors – to improve understanding of dust lifting processes will be discussed.