engleski

On the Bora near-ground velocity profile

Although the effects of the atmospheric boundary layer flow on engineering structures are mostly known, some local transient winds still create considerable difficulties to traffic, structures and other human activities. Hence, more work needs to be done in order to fully characterize flow characteristics of those particular local winds. In this study, vertical profile of wind velocity for the main wind direction is analyzed for the gusty Bora wind blowing on the eastern Adriatic coast. While the Bora wind is present all year around, this study focuses on the data acquired during one particular summer Bora episode. Applicability of the commonly used power-law and the logarithmic-law on 3-level high frequency Bora measurements up to 40 m height is tested. This is done partly because those two empirical approximations are still common in engineering community, while hardly ever used by geophysicists and meteorologists. Observed experimental data are generally i n good agreement with the power-law and the logarithmic- law approximations. Here, the power-law exponent is calculated by fitting the experimental data to the power-law, while friction velocity and aerodynamic surface length are calculated from the logarithmic-law by using two different approaches. Determined friction velocity is nearly the same as calculated using both approaches, while aerodynamic surface length slightly differs depending on the calculation method. However, the most exciting finding is an increase in the power- law exponent, friction velocity and aerodynamic surface length with decreasing Bora wind velocity that indicates an urban-like velocity profile for smaller wind velocities and a rural-like velocity profile for larger wind velocities.

Aerodynamic surface roughness length ; Friction velocity ; Logarithmic-law ; Power-law ; Field measurements

nije evidentirano