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- Author or Editor: Gilles Sommeria x
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Abstract
The numerical model used by Deardorff (1972) for studying the clear air boundary layer under neutral or unstable conditions has been extended to include most of the physical processes occurring in a moist boundary layer in the absence of precipitation. It now contains a water cycle with cloud formation and a revised treatment of the subgrid-scale turbulence which incorporates effects of thermal stratification; it takes Into account infrared radiative cooling in clear and cloudy conditions and the influence of large-scale vertical motions and horizontal gradients. Section 2 includes a description of the model with emphasis on its new features. Section 3 presents some results obtained in a simulation of the trade wind boundary layer with detailed treatment of cloud dynamics in the absence of precipitation. The simulation shows how the turbulent characteristics evolve with time toward a statistically steady state, with an example being given of the turbulent field in the presence of clouds. The relative importance of the various physical processes in the evolution of the mean field of variables is indicated.
Abstract
The numerical model used by Deardorff (1972) for studying the clear air boundary layer under neutral or unstable conditions has been extended to include most of the physical processes occurring in a moist boundary layer in the absence of precipitation. It now contains a water cycle with cloud formation and a revised treatment of the subgrid-scale turbulence which incorporates effects of thermal stratification; it takes Into account infrared radiative cooling in clear and cloudy conditions and the influence of large-scale vertical motions and horizontal gradients. Section 2 includes a description of the model with emphasis on its new features. Section 3 presents some results obtained in a simulation of the trade wind boundary layer with detailed treatment of cloud dynamics in the absence of precipitation. The simulation shows how the turbulent characteristics evolve with time toward a statistically steady state, with an example being given of the turbulent field in the presence of clouds. The relative importance of the various physical processes in the evolution of the mean field of variables is indicated.
Abstract
Results from a detailed three-dimensional model of the atmospheric boundary layer are compared with observational data in a case of nonprecipitating convection in a tropical boundary layer. The model is a slightly improved version of the one developed by Sommeria (1976) in collaboration with J.W. Deardorff. The experimental data come from the NCAR 1972 Puerto Rico experiment which provided a good set of aircraft turbulence measurements in the fair weather mixed layer over the tropical ocean. The comparison involves statistical properties of the turbulent field as well as some structural features in the presence of small clouds.
Abstract
Results from a detailed three-dimensional model of the atmospheric boundary layer are compared with observational data in a case of nonprecipitating convection in a tropical boundary layer. The model is a slightly improved version of the one developed by Sommeria (1976) in collaboration with J.W. Deardorff. The experimental data come from the NCAR 1972 Puerto Rico experiment which provided a good set of aircraft turbulence measurements in the fair weather mixed layer over the tropical ocean. The comparison involves statistical properties of the turbulent field as well as some structural features in the presence of small clouds.
During May and June 1981 several French research organizations, the University of Abidjan (Ivory Coast) and the Agency for Security of Aeronautical Navigation (ASECNA), participated in the observational field program called “Convection Profonde Tropicale 1981” (COPT 81). COPT 81 was directed toward developing a better understanding of the dynamical and electrical features of precipitating convection in continental tropical regions.
The observational network was designed to study the development and evolution of diurnal convection and squall lines over the northern part of the Ivory Coast, which is an example of a tropical savanna region at the southern edge of the Sahel. It consisted of two Doppler radars, a central meteorological station equipped for the reception of satellite data, rawin sounding and interrogation of remote targets, an acoustic sounder, a central electrical and electromagnetical station, and a set of remote ground meteorological and electrical stations.
Some experimental results are presented to characterize the main features of a tropical continental squall line. The evolution of the boundary layer during its passage, its precipitation pattern and associated dynamical field, its surface trace and the modification it produces on the thermodynamical state of the atmosphere, as well as some of its associated electrical features, are given.
During May and June 1981 several French research organizations, the University of Abidjan (Ivory Coast) and the Agency for Security of Aeronautical Navigation (ASECNA), participated in the observational field program called “Convection Profonde Tropicale 1981” (COPT 81). COPT 81 was directed toward developing a better understanding of the dynamical and electrical features of precipitating convection in continental tropical regions.
The observational network was designed to study the development and evolution of diurnal convection and squall lines over the northern part of the Ivory Coast, which is an example of a tropical savanna region at the southern edge of the Sahel. It consisted of two Doppler radars, a central meteorological station equipped for the reception of satellite data, rawin sounding and interrogation of remote targets, an acoustic sounder, a central electrical and electromagnetical station, and a set of remote ground meteorological and electrical stations.
Some experimental results are presented to characterize the main features of a tropical continental squall line. The evolution of the boundary layer during its passage, its precipitation pattern and associated dynamical field, its surface trace and the modification it produces on the thermodynamical state of the atmosphere, as well as some of its associated electrical features, are given.
