Environmental Engineering Reference
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Numerical Modelling of the Extratropical
Storm Delta Over Canary Islands:
Importance of High Resolution
O. Jorba, C. Marrero, E. Cuevas and J.M. Baldasano
Abstract
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 move-
ment, 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 152km/h at the airport of La Palma and
close to 250km/h in the Izaña observatory (2,360m altitude), which caused signifi-
cant property damage. The aim of this numerical modelling is to reproduce the local
effects of Delta storm with high spatial resolution. The WRF-ARWmodel is applied
from 9 to 3km of horizontal resolution using ECMWF forecasts as IBC. The simula-
tion 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 850hPa were the main
features that have contributed to the development and amplification of intense gravi-
tational 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.
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