COBALT: A High Tower Experiment for Monitoring the Micrometeorology of a Coastal Area

Coastal Boundary Layer Transition Experiment (COBALT) started in 2015 with the deployment of a 140-m tower designed to provide micrometeorological observations with high vertical resolution and deep coverage of the lower portion of the atmospheric boundary layer. Operation is scheduled to start at the first months of 2016, when the acquired instrumentation will have been installed and tested. The purpose of this presentation is to provide a general description of the site, proposed observations, main objectives, as well as to present and describe the first observations available. The observations will be carried on at a coastal site in Espirito Santo state, southeastern Brazil. The tower has been deployed next to a natural gas power plant, at 3 km from the ocean. The terrain is generally flat for an area of 30 km from the tower, where moderate hills exist. Turbulence observations of the wind components and temperature are carried at 11 vertical levels: 1, 2, 5, 10, 20, 40, 60, 80, 100, 120 and 140 m from the surface. At the 20-m level, a gas analyzer also provides high-frequency observations of water vapor and carbon dioxide concentrations, allowing the determination of the turbulent fluxes of these scalars. Vertical profilers provide the mean values of these concentrations at 6 levels, from 1 to 20 m. The boundary layer thermal structure is also monitored by 10 thermohygrometers, located in between the levels where turbulence observations are performed. Soil humidity and temperature are measured at 5 levels, from the surface to 90-cm depth, while the soil heat flux is monitored at a 10-cm depth. The components of the radiative budget are measured at the 20-m height. The project aims at different scientific questions, both at applied and basic levels. It will provide a detailed microclimatology of the region, including the thermal and turbulent structure of the local boundary layer. Those data may feed modelling studies of the boundary layer flow and dispersion characteristics at the region. The observations will help understand the development of an internal boundary layer near the coast and its temporal evolution. The high vertical resolution near the surface may provide useful information on stable boundary layer processes and their dependence on external forcings. Furthermore, the heterogeneous terrain and contrast between marine and terrestrial surfaces will help understand how the different landscapes control the turbulent flow, especially in the nocturnal case. The effects of surface heterogeneities on low frequency boundary layer flow will be investigated, and their vertical structure will be identified over the depth of the tower