Using QuikSCAT in the added value assessment of dynamically downscaled wind speed

Abstract

Hindcasts with reanalysis-driven regional climate models (RCMs) are a common tool to assess weather statistics (i.e. climate) and recent changes and trends. A remote sensing-based method to investigate the added value of surface marine RCM wind speed is introduced. The capability of the dynamical downscaling approach (with spectral nudging applied) to add value to the reanalysis wind speed forcing is assessed by the comparison with QuikSCAT Level 2B 12.5 km (L2B12) swath data in European waters for 2000-2007. Co-location criteria are within 0.1° and 0.06° in longitudinal and latitudinal distance from RCM grid points and within 10 min. In the wind speed range, QuikSCAT L2B12 is reliably reproducing (3-20 m s-1), dynamically downscaled wind speed does not show an added value in open ocean areas. However, in coastal areas with complex topography, the regional models show an added value, especially around Iceland and the Iberian Peninsula and in the Mediterranean, Baltic and Irish Seas, validating the findings of previous in situ data-based studies on the added value. Strong interseasonal differences exist, in winter enhanced cyclonic and meso-cyclonic activity increases the potential of dynamical downscaling. In winter time, the added value is more pronounced around Iceland and Greenland, south of Iceland and within the Gulf of Lyon/Mistral region. Summarizing the presented method can be easily applied for other ocean areas, making QuikSCAT a valuable tool to identify marine regions where dynamical downscaling adds value to surface marine wind speed. A detailed comparison of 10 m winds from the National Centres of Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) and the newer NCEP/DOE-II reanalyses is presented in the annex, motivating the use of the NCEP/NCAR reanalysis in the added value assessment.