•We use the information of horizontal
divergence to infer the vertical velocity. However, for
midlatitude weather, the horizontal divergence is due
primarily to the small departures of the wind from geostrophic balance. A
10% error in evaluating one of the wind components can easily cause the estimated
divergence to be in error by 100%.
•For this reason, the continuity equation
method is not recommended for estimating the vertical
motion field from observed horizontal winds.