ATPL Meteorology Practice Test

When calculating surface winds over the sea, the correct answer reflects the influence of friction and the overall balance of forces acting on the wind. At the surface, particularly over water, friction with the water surface reduces the speed of the wind compared to the geostrophic wind (which assumes a balance between the Coriolis and pressure gradient forces, with no friction). In this context, the calculation of wind speed as 70% of the geostrophic wind accounts for the effects of surface friction while still recognizing that the directional influences are slightly altered. The statement about the wind being deviated by 10 degrees indicates that this adjustment accounts for the Coriolis effect perpendicular to the direction of motion, which is particularly relevant over large water bodies. This option provides a more accurate estimate of the actual surface wind conditions experienced over the sea, as it takes into account the necessary adjustments for the effects of friction and the resulting shift in wind direction.