Atmos. Chem. Phys. Discuss., 9, 20775-20817, 2009
www.atmos-chem-phys-discuss.net/9/20775/2009/
doi:10.5194/acpd-9-20775-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model
S. Kirkwood1, M. Mihalikova1, T. N. Rao2, and K. Satheesan1
1Swedish Institute of Space Physics, Box 812, 98128 Kiruna, Sweden
2National Atmospheric Research Laboratory, Gadanki, India

Abstract. We use measurements by the 52 MHz wind-profiling radar ESRAD, situated near Kiruna in Arctic Sweden, and simulations using the Advanced Research and Weather Forecasting model, WRF, to study vertical winds and turbulence in the troposphere in mountain-wave conditions on 23 , 24 and 25 January 2003. We find that WRF can accurately match the vertical wind signatures at the radar site when the spatial resolution for the simulations is 1 km. The horizontal and vertical wavelengths of the dominating mountain-waves are ∼10–20 km and the amplitudes in vertical wind 1–2 m/s. Turbulence below 5500 m height, is seen by ESRAD about 40% of the time. This is a much higher rate than WRF predictions for conditions of Richardson number (Ri) >1 but similar to WRF predictions of Ri>2. WRF predicts that air crossing the 100 km wide model domain centred on ESRAD has a ∼10% chance of encountering convective instabilities (Ri>0.) somewhere along the path. The cause of low Ri is a combination of wind-shear at synoptic upper-level fronts and perturbations in static stability due to the mountain-waves. Comparison with radiosondes suggests that WRF underestimates wind-shear and the occurrence of thin layers with very low static stability, so that vertical mixing by turbulence associated with mountain waves may be significantly more than suggested by the model.

Citation: Kirkwood, S., Mihalikova, M., Rao, T. N., and Satheesan, K.: Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model, Atmos. Chem. Phys. Discuss., 9, 20775-20817, doi:10.5194/acpd-9-20775-2009, 2009.
 
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