engleski

ASAR vs SeaWinds vs WRF : A three-way look at a train of the Adriatic bora events

Bora – a gusty, cold, downslope, north-easterly air flow blowing over the sea from the lee side of the Dinaric Alps – is among better known Adriatic winter winds. Its onset, longevity and severity are determined by larger atmospheric flows, but ultimately controlled by local orographic features. Bora outbreaks exhibit lateral shearing and jets of higher wind speed that provoke vigorous response. Measurements and modelling studies concur that in the Adriatic Sea an episode of Bora wind provokes a transient multiple-gyre response (e.g. Kuzmić and Orlić, Annales Geophysicae, 5B, 103-112, 1987 ; Kuzmić et al., Journal of Geophysical Research, 112 (C3), 2007) imbedded in cyclonic general circulation. Powerful bora wind events leave surface imprints detectable throughout the electromagnetic spectrum (e.g. Kuzmić and Tomažić, EUMETSAT P.50, 2007). In this study we gauge our ability to discern the bora wind over the Adriatic Sea exploiting the synergy of SAR data, scatterometer data, and numerical model simulations. More specifically, we explore how well the location and shape of bora jets and wakes are captured in the Envisat ASAR scenes, Quikscat SeaWinds scatterometer wind-vector fields, and WRF atmospheric model simulations, focused on an eight-day period in December 2007 when several bora events of varying intensity took place. The Weather Research and Forecasting (WRF) model is used employing two-way coupling and three- or four-stage nested grids, with the lowest nest ensuring very-high resolution (≈1km) simulations. The data from the three sources are interpolated in space and time as necessary, to conform particular comparison grid. Looking at sensor-registered and model-derived sigma-nought and wind-vector fields we sought to cross-validate different sensor- and model-based responses, paying particular attention to the spatial extent and variability of the bora jets and wakes, spatial resolution of detected and modeled fields, as well as to the wind direction issue in SAR-derived wind vector fields.

SAR WRF Bora Adriatic

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