Abstract
Abstract. WIRA is a ground-based microwave Doppler spectroradiometer specifically designed for the measurement of profiles of horizontal wind in the upper stratosphere and lower mesosphere region where no other continuously running measurement technique exists. A proof of principle has been delivered in a previous publication. A technical upgrade including a new high-frequency amplifier and sideband filter has improved the signal to noise ratio by a factor of 2.4. Since this upgrade the full horizontal wind field comprising zonal and meridional wind profiles is continuously measured. A completely new retrieval based on optimal estimation has been set up. Its characteristics are detailed in the present paper. Since the start of the routine operation of the first prototype in September 2010, WIRA has been measuring at four different locations at polar, mid- and tropical latitudes (67°22' N/26°38' E, 46°57' N/7°26' E, 43°56' N/5°43' E and 21°04' S/55°23' E) for time periods between 5.5 and 11 months. The data presented in this paper are daily average wind profiles with typical uncertainties and resolutions of 10 to 20 m s−1 and 10 to 16 km, respectively. A comparison between the data series from WIRA and European Centre for Medium-Range Weather Forecasts (ECMWF) model data revealed agreement within 10% in the stratospheric zonal wind. The meridional wind profiles agree within their error bars over the entire sensitive altitude range of WIRA. However, significant differences in the mesospheric zonal wind speed of up to 50% have been found.
Highlights
Wind is a key parameter for the characterisation of the atmosphere and its dynamics on every altitude level
The new retrieval algorithm based on an optimal estimation inversion of the atmospheric radiative transfer model allows a much better characterisation of the altitude dependence of the wind profile information and of the errors in general
The instrument’s signal to noise ratio has been strongly improved by an upgrade. Did this improve the precision of the wind measurements, but since half of the integration time on the sky can be used for the measurement of www.atmos-meas-tech.net/7/4491/2014/
Summary
Wind is a key parameter for the characterisation of the atmosphere and its dynamics on every altitude level. A more extended overview of the different wind measurement techniques with their key characteristics and their sensitive altitude range can be found in Rüfenacht et al (2012). In the routine operation the duration of one measurement cycle is 60 s Such a cycle contains the measurement of the signals from the two calibration targets (ambient temperature load and sky at zenith) as well as from two or four cardinal directions for the wind retrieval. A reassessment of the frequency stability was performed after the last upgrade by using a GPS signal as frequency reference Because of the relatively low signal to noise ratio, the meridional wind, which is generally small, had not been routinely measured until summer 2012 in order to save integration time to get a more accurate estimate of the zonal.
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