Experimental study of the surface marine atmospheric boundary layer over Aegean Greece

Abstract

Micrometeorological measurements within the surface Marine Atmospheric Boundary Layer (MABL) took place at the shoreline of island of Karpathos, at the South East end of the Aegean Sea (Karpathio Pelagos), during summer 2012. Α meteorological mast was installed at a distance less than 30m from the shoreline, instrumented with a sonic anemometer and a fast krypton hygrometer at 14.5m height with a sampling frequency of 10Hz, in order to measure the turbulent transport of mass and energy of the surface MABL. At the same mast slow response sensors (1Hz) were also installed providing vertical profiles of wind speed and direction, temperature and humidity at three levels (3, 8 and 12 m). Satellite sea surface temperature images were also obtained. The spacial and temporal scales of the Aegean Pelagos have not been studied in the past while it is expected to present differences compared with those measured over oceans or open seas. It is worth to mention that this study is a follow-up of a previous study which took place during summer 2011 at Skyros island, northern Aegean provided similar measurements but with different fetch. During Karpathos campaign, more than of 120 hours stationary surface MABL observations of near neutral wind flows were recorded. The vertical profiles of temperature reveal the presence of a coastal internal boundary layer, mostly below 8m height. Eddy correlation analysis is used to study the turbulent fluxes of mass and energy. According to first results on the stable MABL, momentum fluxes depend on stability and give increasing values with the wind speed. The estimated values are higher, almost by a factor of two, compared to typical values measured over the ocean. These increased values could be attributed to a developed sea state since wind stress is greater over young and developing wave fields. Sensible heat flux is found to be increased with stability and rather independent from wind speed while moisture flux seems to not be dependent neither to stability or wind speed. Some part of the records present upward heat fluxes under near neutral conditions and mostly for positive sea-air temperature differences, possibly associated with sea spray or mesoscale heterogeneity of the sea surface temperature. Ongoing investigation of the turbulent exchanges is expected to provide a more thorough insight on the coupling processes between the surface MABL and Aegean sea.