19. Continuous Middle-Atmospheric Wind Profile Observations by Doppler Microwave Radiometry

Observations of wind profiles in the upper stratosphere /lower mesosphere are challenging as the established measurement techniques based on in situ methods, radars or airglow spectrometers cannot cover this altitude range. Nevertheless, wind information from these altitudes is important for the assessment of middle-atmospheric dynamics in general and as basis for planetary wave or infrasound propagation estimates. Benefitting from recent developments in spectrometers and low-noise amplifiers, microwave radiometry now offers the opportunity to directly and continuously measure horizontal wind profiles at altitudes between 35 and 70 km. This is achieved by retrieving the wind-induced Doppler shifts from pressure broadened atmospheric emission spectra. The typical measurement uncertainties and vertical resolutions of daily average wind profiles lie between 10–20 m/s and 10–16 km, respectively. In this chapter, comparisons of the measured wind profiles to different ECMWF model versions and MERRA re-analysis data are shown. Moreover, the oscillatory behaviour of ECMWF winds is investigated. It appears that the longer period wave activities agree well with the observations, but that the model shows less variability on timescales shorter than 10 days.