Evaluation of wind profiles from the NERC MST radar, Aberystwyth, UK

This study quantifies the uncertainties in winds measured by the Aberystwyth Mesosphere–Stratosphere– Troposphere (MST) radar (52.4 N, 4.0 W), before and after its renovation in March 2011. A total of 127 radiosondes provide an independent measure of winds. Differences between radiosonde and radar-measured horizontal winds are correlated with long-term averages of vertical velocities, suggesting an influence from local mountain waves. These local influences are an important consideration when using radar winds as a measure of regional conditions, particularly for numerical weather prediction. For those applications, local effects represent a source of sampling error additional to the inherent uncertainties in the measurements themselves. The radar renovation improved the signal-tonoise ratio (SNR) of measurements, with a corresponding improvement in altitude coverage. It also corrected an underestimate of horizontal wind speeds attributed to beam formation problems, due to pre-renovation component failure. The root mean square error (RMSE) in radar-measured horizontal wind components, averaged over half an hour, increases with wind speed and altitude, and is 0.8–2.5 m s−1 (6–12 % of wind speed) for post-renovation winds. Pre-renovation values are typically 0.1 m s−1 larger. The RMSE in radial velocities is < 0.04 m s−1. Eight weeks of special radar operation are used to investigate the effects of echo power aspect sensitivity. Corrections for echo power aspect sensitivity remove an underestimate of horizontal wind speeds; however aspect sensitivity is azimuthally anisotropic at the scale of routine observations (≈ 1 h). This anisotropy introduces random error into wind profiles. For winds averaged over half an hour, the RMSE is around 3.5 % above 8 km, but as large as 4.5 % in the mid-troposphere.