Using Doppler lidar observations to verify wind profile forecasts from the ECMWF IFS model

Pyry Pentikäinen,Ewan O'Connor

doi:10.5194/ems2022-229

Abstract

&lt;p&gt;&lt;span&gt;Long-range scanning Doppler lidars can provide the vertical profile of the horizontal wind &lt;/span&gt;&lt;span&gt;within the boundary layer. We used Doppler lidar wind profiles from six locations around the&lt;/span&gt; &lt;span&gt;globe to verify the wind profile forecasts generated by ECMWF from the operational IFS &lt;/span&gt;&lt;span&gt;model. The six locations selected cover a variety of surface types (rural, marine,&lt;/span&gt; &lt;span&gt;mountainous urban, coastal urban). &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We first validated the Doppler lidar observations at four locations by comparison with &lt;/span&gt;&lt;span&gt;collocated radiosonde profiles to ensure that the Doppler lidar observations were of sufficient &lt;/span&gt;&lt;span&gt;quality. The two observation types agree well, with the mean absolute error (MAE) in wind &lt;/span&gt;&lt;span&gt;speed almost always less than 1 m s&lt;sup&gt;-1&lt;/sup&gt;. Large deviations in the wind direction were usually &lt;/span&gt;&lt;span&gt;seen only for low wind speeds. This is due to the ambiguity in wind direction at low wind &lt;/span&gt;&lt;span&gt;speed and that the relative uncertainty in the wind direction measurement increases as the &lt;/span&gt;&lt;span&gt;wind speeds decrease. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The Doppler lidar observations are at sufficient temporal resolution for us to generate &lt;/span&gt;&lt;span&gt;time-height composites of the wind verification with one-hour resolution so that we can &lt;/span&gt;&lt;span&gt;investigate the diurnal cycle. Verification of the model winds showed that the IFS model &lt;/span&gt;&lt;span&gt;performs best over marine (ocean) locations. Larger errors were seen in locations where the &lt;/span&gt;&lt;span&gt;surface was more complex, especially in the wind direction. For example, in Granada, which &lt;/span&gt;&lt;span&gt;is near a high mountain range, the IFS model failed to capture a commonly occurring &lt;/span&gt;&lt;span&gt;mountain breeze, a feature which is highly dependent on the orography at sub grid-scale.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;At one location, we conditionally performed the wind verification based on the presence or &lt;/span&gt;&lt;span&gt;absence of a low-level-jet diagnosed from the Doppler lidar observations. The IFS model&lt;/span&gt; &lt;span&gt;was able to reproduce the presence of the low-level-jet but the wind speed maximum was &lt;/span&gt;&lt;span&gt;about 2 m s&lt;sup&gt;-1&lt;/sup&gt; lower than observed. This is attributed to the effective vertical resolution of the &lt;/span&gt;&lt;span&gt;model being too coarse to create the strong gradients in wind speed observed.&lt;/span&gt;&lt;/p&gt;

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