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Free Content Dry and moist convection in the boundary layer over the Black Forest - a combined analysis of in situ and remote sensing data

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During the COPS experiment performed in south-western Germany and eastern France in 2007, several insitu and remote sensing systems were operated at Hornisgrinde - the highest summit of the northern Black Forest mountains. For this case study, data from a surface flux station, radiosondes, cloud camera, cloud radar, wind lidar, water vapour differential absorption lidar, and microwave profiler were used to investigate turbulence characteristics in cloud-free and cloud-topped convective boundary layers (CBLs). Short time intervals were analysed, during which dry and moist convective cells occurred, in order to obtain insight of the processes that determine the turbulent characteristic in the CBL.

The frequently-used aerosol concentration was used to calculate the CBL height, zi . It was found that active CBL clouds penetrated deeper into the free troposphere than dry convective cells. In the cloud-free CBL the normalised variance of the vertical velocity, σw 2, decreased to zero approximately at zi , while σw 2 was nearly constant between 0.5 and 1 z/zi in the cloud-topped CBL. The higher normalised σw 2 values in the cloud layer could be attributed to the additional elevated heat source due to condensation. In the cloud-free CBL the latent heat flux showed a strong decrease between 0.7 and 1.1 z/zi , i.e., it considerably moistened the upper part of the CBL and entrainment zone. In the cloud-topped CBL the latent heat flux decreased significantly above the CBL top only and became zero at about 1.4 z/zi . CBL height calculations, which took measures of the turbulence into account, resulted in normalised σw 2 and E profiles, which became zero at the CBL top and appeared more appropriate for CBL height scaling over complex terrain.

The case studies demonstrated that only the combined use of different monitoring systems allowed for the recording of the entire structure of the convective cells and that synergetic measurements in cloud-topped CBLs were indispensable to capture the latters' turbulent characteristics. Also, significant differences between turbulent characteristics in cloud-free and cloud-topped CBLs became evident.

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Keywords: ACTIVE CLOUDS; COMPLEX TERRAIN; CONVECTIVE BOUNDARY LAYER; CONVECTIVE CELLS; LATENT HEAT FLUX

Document Type: Research Article

Publication date: 2013-08-01

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  • Meteorologische Zeitschrift (originally founded in 1866) is the joint periodical of the meteorological societies of Austria, Germany and Switzerland. It accepts high-quality peer-reviewed manuscripts on all aspects of observational, theoretical and computational research out of the entire field of meteorology, including climatology. Meteorologische Zeitschrift represents a natural forum for the meteorological community of Central Europe and worldwide.
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