Observation of horizontal winds in the middle-atmosphere between 30° S and 55° N during the northern winter 2009–2010

Abstract

Abstract. Although the links between stratospheric dynamics, climate and weather have been demonstrated, direct observations of stratospheric winds are lacking, in particular at altitudes above 30 km. We report observations of winds between 8 and 0.01 hPa (~35–80 km) from October 2009 to April 2010 by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station. The altitude range covers the region between 35–60 km where previous space-borne wind instruments show a lack of sensitivity. Both zonal and meridional wind components were obtained, though not simultaneously, in the latitude range from 30° S to 55° N and with a single profile precision of 7–9 m s–1 between 8 and 0.6 hPa and better than 20 m s–1 at altitudes above. The vertical resolution is 5–7 km except in the upper part of the retrieval range (10 km at 0.01 hPa). In the region between 1–0.05 hPa, an absolute value of the mean difference < 2 m s–1 is found between SMILES profiles retrieved from different spectroscopic lines and instrumental settings. Good agreement (absolute value of the mean difference of ~2 m s–1) is also found with the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis in most of the stratosphere except for the zonal winds over the equator (difference > 5 m s−1). In the mesosphere, SMILES and ECMWF zonal winds exhibit large differences (> 20 m s–1), especially in the tropics. We illustrate our results by showing daily and monthly zonal wind variations, namely the semi-annual oscillation in the tropics and reversals of the flow direction between 50–55° N during sudden stratospheric warmings. The daily comparison with ECMWF winds reveals that in the beginning of February, a significantly stronger zonal westward flow is measured in the tropics at 2 hPa compared to the flow computed in the analysis (difference of ~20 m s–1). The results show that the comparison between SMILES and ECMWF winds is not only relevant for the quality assessment of the new SMILES winds, but it also provides insights on the quality of the ECMWF winds themselves. Although the instrument was not specifically designed for measuring winds, the results demonstrate that space-borne sub-mm wave radiometers have the potential to provide good quality data for improving the stratospheric winds in atmospheric models.

Driving of the SAO by gravity waves as observed from satellite

“…For this purpose, realistic background winds are required for the period and altitude range considered. Previous studies have shown that zonal winds in the tropics provided by ECMWF are in good agreement with observations (e.g., Baldwin and Gray, 2005;Dee et al, 2011;Baron et al, 2013). In particular, there is qualitatively good agreement between the QBO-related gravity wave drag variations derived from the ECMWF ERAInterim reanalysis and those derived from satellite observations .…”

“…Even though fewer and fewer data are assimilated in ERAInterim at increasing altitude, the SAO zonal winds should be quite reliable (e.g., Baldwin and Gray, 2005;Dee et al, 2011;Baron et al, 2013). Consequently, the zonal wind tendency ∂u/∂t, which is determined directly from u, should also be quite reliable.…”

Simulation study for measurement of horizontal wind profiles in the polar stratosphere and mesosphere using ground-based observations of ozone and carbon monoxide lines in the 230–250 GHz region

“…Satellite measurements of mesospheric winds down to 80 km were determined from Aura Microwave Limb Sounder (MLS) observations of Doppler-shifted, Zeeman-split O 2 σ − and σ + lines around 118.75 GHz . Winds at 35-80 km were observed for a limited time over the latitude range 30 • S to 55 • N using ozone (O 3 ) and hydrogen chloride emission line measurements in the 625-650 GHz range by the Submillimeter-Wave Limb-Emission Sounder (SMILES) (Baron et al, 2013). The Atmospheric Laser Doppler Instrument (ALADIN) on the forthcoming Atmospheric Dynamics Mission (ADM) Aeolus satellite will make UV lidar measurements of winds in the troposphere and lower stratosphere (Stoffelen et al, 2005).…”

SMILES-2 Mission for Temperature, Wind, and Composition in the Whole Atmosphere

“…However, a cross comparison with the retrievals from other lines should help us to significantly reduce this bias. The bias that does not change for a long time can also be mitigated by using the fact that the equatorial flow is predominantly zonal at these altitudes (Baron et al 2013a) or comparing the retrievals with mid-latitude winds from meteorological analyses and reanalyses.…”

“…Unlike the shorter wavelengths, SMM lines are not affected by nonlocal thermodynamic equilibrium. Also, their large potential for global wind measurements in the stratosphere, mesosphere, and lower thermosphere has been demonstrated using the Doppler shifts of the 118.75 GHz O 2 line measured by the Microwave Limb Sounder (MLS) ) and the O 3 and HCl lines near 625 GHz measured by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) (Baron et al 2013a). …”