Zur Parametrisierung der stabilen atmosphärischen Grenzschicht über einem antarktischen Schelfeis = Parameterization of the stable atmospheric boundary layer over an Antarctic ice shelf

Abstract

The stalde atmospl~eric boundary layer has been investigated on the basis of two extencled bo~~ndary-layer xperiments, perforn~ed at the German Antarctic research station Neumayer. Almost all parameterizations of the turbulent exchange in atmospheric models (from boundary-layer models up to global circulation models) are based 011 hydrodynamic theories and empirical laws (universal functions), which are valicl above horizont,al homogeneous surfaces. The conditions a t the Neumayerstation allow the test of such theories as well as their further development. In this thesis empirical and theoretical invest,igations of parameterizations of the surface fluxes, t~he turbulent, fluxes in t,he whole boundary layer and of the height of the st,able boundary layer are performed. Until now only a few experimental investigations exist for moderately to strong stable stratification. The data measured at the Neumayer-station allow the determination of the universal functions for this stability range. The normally used linear dependence of the universal functions from the stability parameter z / L is confirmed even for this range, but only up to an upper limit of z / L = 1. z is the lleight above ground, L tlle Olmchov-length. With increasing stability the universal functions reach constant values. In addition, the turbulent surface fluxes have been calculated from profile ineasurements with methods of optimization theory. The results are in good agreement with directly measured turbulent fluxes. It is shown, that the height of the stable boundary layer a t the Neumayerstation is very low. The main reason for this phenomena is the stability of the free atmosphere above the boundary layer. Based on the equations of motion an ext.ended relation for the pa,rameterization of the height of the stable boundary layer is detern~ined, which takes into account the stability of the free atmosphere. This relation is verified with our mea,surements. Taking into account this paranieterization in a turbulente-closure-scheme of a one-dimensional boundary layer model, the best. agreement bet.ween simulated and measured boundary-layer development is achieved. The improved parameterizations, derived from the performed theoretical and experinient,al investigations, are used in a one-dimensional boundary layer model for the simulation of the stable atmospheric boundary layer. The stationary state as well as the influence of different external fact,ors on the development in time are investigated. The simulated development of the boundary layer is compared with observed results for selected case studies with the use of variable lower and upper bounclary ~ondit~ions and different turbulente-closure-schemes.