| Popis: |
An analysis of the katabatic flow structure is presented, based on data collected along a simple slope over a two-month period. Four meteorological stations were deployed along the nearly two-dimensional east slope of Mt. Hymettos in Greece. The study focuses on the momentum and energy budgets of the flows during carefully selected stationary periods with negligible ambient winds. In order to achieve a proper selection, the mean features of the observed flows are presented along with their response to external winds. The observed profiles are successfully compared with the theoretical Prandtl profiles. Bulk quantities of the katabatic layer are compared with proposed experimental values in order to check the representativity of the observed flows. These comparisons offer a further test of theoretical considerations and assist in discussions of processes affecting mean-flow features. The flows were similar to 20 m deep, with velocities 1-2 m s(-1). During steady-state periods the katabatic acceleration was mainly balanced by the surface friction, the contribution of advective terms being small. The estimated interfacial drag was less important than the surface drag, which proved large compared with usually suggested values. Within the experimental uncertainties, values of the drag coefficient of the order of 10(-2) seem appropriate. The steady-state energy balance showed that the downslope advection balanced the turbulent heat flux to the ground surface. |
