Aircraft Observation of Convection Waves over Southern Germany—A Case Study

Abstract

A vertical cross section of 100 km ? 10 km through a daytime midlatitude troposphere is analyzed using aircraft turbulence data with 1.5-m spatial resolution. Convectively forced internal gravity waves, also referred to as ?convection waves,? were studied with an instrumented aircraft over southern Germany. This is the first quantitative observational study of convection waves over a central European region. Characteristics are found to be in good agreement with results of previous numerical simulations and measurements. Vertical wind amplitudes are +0.5?1 m s?1 and lower than those found over the Great Plains of North America. Convection waves were trapped in midtropospheric levels by a layer of reduced stability aloft. The waves were forced by shallow moist convection penetrating into an overlying shear layer centered around the boundary-layer top. Both speed shear with a value of about 6.5 m s?1 km?1 and directional shear of about 26° km?1 were present. The measurements support the hypothesis that convection waves represent a typical fluid-dynamical mode of a daytime troposphere. They can be observed whenever there is moderate to strong convection in the atmospheric boundary layer and shear aloft.