Dr. Klaassen’s major research interests are in wave dynamics, stratified shear flows, the transition to turbulence, cloud dynamics and mesoscale meteorology. A variety of theoretical and numerical models are being employed to study the evolution and stability of nonlinear disturbances in the atmosphere. The goal is to improve our understanding the evolution of complex small-scale flows, and their interactions with the larger scales associated and weather and climate systems. These issues will become increasingly important over the next few years as hydrostatic global and regional models are pushed to finer resolution, and will be especially important in the development of nonhydrostatic global circulation and weather prediction models. Small-scale processes also represent fascinating examples fundamental problems in fluid dynamics. Recently, Dr. Klaassen’s group has focused on gravity wave processes in the atmosphere, including gravity wave generation, propagation and breaking. We are also developing parameterization schemes for the representation of drag due to small-scale unresolved gravity waves, a process which is of crucial importance in determining the circulation of the middle atmosphere and its effect on ozone. This work is also relevant to other stably stratified geophysical flows, e.g., the ocean. Other areas of interest include moist convection, and the transition to turbulence in shear flows.
Noctilucent Polar Mesospheric Clouds reveal breaking gravity waves near an altitude of 83 km. The momentum deposition from such breaking waves plays a crucial role in shaping the circulation of the middle atmosphere.Photo by Pekka Paravainien, Turku, Finland 21/22 July 1989, 02:15 GMT.