The relationship of surface wind to geostrophic wind and the empirical determination of the friction coefficient

The relationship between surface wind to geostrophic wind over land was investigated on the basis of Berlin wind data. The cross-isobar angle is shown to have a significant dependence on the geostrophic wind speed and is also shown to increase with increasing geostrophic wind speed, following fundamentally a logarithmic function. For the ratio of surface wind speed to geostrophic wind speed, a significant decrease with increasing geostrophic wind amount is found which can be described by a potential function. The decrease of the cross-isobar angle with increasing wind ratio also follows a potential function. The friction coefficient is thus established empirically by putting these relationships into the friction law.