Coastal Iberia Summertime Low‐Level Flow Assessed From Scatterometers

In summer, the prevailing northerly flow off west Iberia occasionally intensifies and weakens
with significant consequences for weather conditions and marine ecology. High‐resolution Advanced SCATterometer (ASCAT) wind products on a 6.25 km grid (ASCAT‐6.25) were used to characterize wind maxima downwind to the major Iberian capes. Wind intensifications downwind Cape Finisterre are large and detached from the coast. They are considered as the response to a large feature in the coastal morphology. Intensifications downwind Cape Roca and Cape São Vicente are smaller and closer to the coast. These are triggered by interaction of supercritical or transcritical flow with topography. ASCAT‐6.25 evening and morning passes show two distinct regimes during intensification events: a southern regime with
wind maximum moving toward the coast during the day and a northern regime in which this diurnal shift is
not so clear. Another aspect that distinguishes these regimes is the later occurrence of the wind maximum in the southern portion of the coast. Also, wind relaxation events can be identified in ASCAT data. These are followed by a poleward flow of warm water that interrupts the upwelling conditions over west Iberia south of 41°N. Synoptic conditions favorable for the occurrence of intensifications and relaxations were obtained from NWP models. This study was supplemented by RapidScat observations during the summers of 2015 and 2016 at different phases of the diurnal cycle. RapidScat and ASCAT wind fields in combination with NWP data confirm that wind intensifications are multiday events, clearly distinct from the sea breeze circulation.