Numerical Modelling of the Extratropical Storm Delta Over Canary Islands: Importance of High Resolution: Fid-Bau Portal

Numerical Modelling of the Extratropical Storm Delta Over Canary Islands: Importance of High Resolution

Jorba, O. / Marrero, C. / Cuevas, E. / Baldasano, J.M.

The tropical storm “Delta” was formed on November 23, 2005 in a sea zone of the subtropical Atlantic south of the Azores. After days with an erratic movement, the day 27 the storm reinforced their intensity and accelerated its movement towards the Northeast in the direction of the Canary Islands. On 28 and 29, it made a transition to extratropical storm, affecting the Canary Islands with very strong sustained winds with maximum streak of 152 km/h at the airport of La Palma and close to 250 km/h in the Izaña observatory (2,360 m altitude), which caused significant property damage. The aim of this numerical modelling is to reproduce the local effects of Delta storm with high spatial resolution. The WRF-ARW model is applied from 9 to 3 km of horizontal resolution using ECMWF forecasts as IBC. The simulation reproduces the main features that contributed to the high wind speeds observed. Variations in the vertical static stability, vertical wind shear and intense synoptic winds from the southwest part of Delta with a warm core at 850 hPa were the main features that have contributed to the development and amplification of intense gravitational waves, while the large-scale flow interacted with the complex topography of the islands. Nonhydrostatic and hydrostatic experiments were designed taking into account the settings and domain factors. The results associated with changes relative to a controlled simulation showed that the boundary layer, the horizontal resolution, and the nonhydrostatic option have the greatest impact.