Coastal low level jets are a low-tropospheric wind feature driven by the pressure gradient produced by a sharp contrast between high temperatures over land and lower temperatures over the sea. This contrast between the cold ocean and the warm land in the summer is intensified by the impact of the coast-parallel winds on the ocean generating upwelling currents, sharpening the temperature gradient close to the coast, and giving rise to strong baroclinic structures at the coast.
During summertime the Iberian Peninsula is often under the effect of the Azores High and a thermal low pressure system inland, leading to a seasonal wind, in the west coast, called the Nortada (northerly wind). This study presents climatology of the costal low level jet off the west coast of the Iberian Peninsula, based on a high resolution (9 km) downscaling data produced using the WRF mesoscale model, forced by 20 years of ERA-Interim reanalysis (1989-2008). The simulation results show that the jet hourly frequency of occurrence in summer is above 30%, and decreases for about 10% in spring and autumn. The monthly frequencies of occurrence can reach higher values, around 40% in summer months, and reveal large inter-annual variability in all the three seasons. In summer, on a daily basis, the low level jet is present in almost 70% of the days. The jet wind direction is mostly from north-northeasterly, and occurs more persistently in three areas, where the interaction of the jet flow with local capes and headlands are more pronounced. The jet occurs at heights between 300 and 400 m, and its speed has a median around 15 m s-1, reaching maximum speeds of 25 m s-1.
2014. Vol. 66, 22377- p.