The 2000 Vilhelm Bjerknes Medal is awarded to Sergej Zilitinkevich for his outstanding contribution to the creation of modern theory of turbulent boundary layers in the atmosphere.
Sergej Zilitinkevich is one of the creators of the modern theory of planetary boundary layers in the atmosphere and the ocean. His scientific papers and books are well known throughout the world and are often referred to in all major journals on atmospheric and oceanic sciences. It is already a trademark to use and quote the Zilitinkevich scale for the thickness of stably stratified boundary layers in rotating fluids, Zilitinkevich correction for the spin-up effect in turbulent entrainment at the outer edge of evolving turbulent layers, his bulk resistance and heat/mass transfer laws for non-steady stratified boundary layers, and his directional dimensional analysis for turbulence statistics in convective flows. These papers are included as an integral part of the background physics in modern textbooks on geophysical boundary layers. Moreover, they lay a cornerstone on theoretical modelling of turbulent transport and parameterization of turbulent fluxes at the air-sea/air-land interface in weather prediction, climate and other atmospheric models.
At present Sergej Zilitinkevich develops an advanced theory of non-local turbulent transport with due regard to semi-organised structures (overlooked in the classical theory). Here, he address the fluxes of energy and mass, including greenhouse gases, at the atmosphere-earth interface in shear-free convection (e.g., over equatorial Pacific Ocean) and in very strong static stability (e.g., over wide areas of northern Europe, Canada and Siberia in winter). In both regimes he discovered a much higher level of mixing than considered before, which is of crucial importance for modelling applications, especially as concerns climate, biosphere and global change. These results are being validated against experimental data, disseminated and implemented in operational models in a number of European research centres.