Lee Waves without Mountains - Extensive wave induced cloud streets over Germany on 14th April 2015

Abstract

In the afternoon of 14th April 2015 a series of cumuliform wave cloud streets were observed over Haag an der Amper, Germany. These cloud streets were up to 300 km long with an alignment of 80/260 degrees, and extended for 400 km up/down wind. Analysis of radiosonde data from the region revealed several layers of differing stability, with two significant inversions that enabled the downwind propagation of these cloud streets. This study also explores the atmospheric conditions, typically observed along the North Sea coasts, which initiated the formation of these extensive lee waves. The results indicate that they were created by a nocturnal offshore land breeze, which initiated these waves and determined their alignment and subsequent propagation downwind. Some hours later another set of wave cloud streets, having a slightly shorter wavelength, were created by a diurnal onshore sea breeze. The potential for soaring flights using these unusual waves is also discussed.