The angle of indraft is the angle that the actual wind direction makes with the isobars which depends on:
- Gradient force: this in turn depends on pressure gradient – the greater the pressure gradient, the greater the gradient force & vice-versa.
- Latitude: the greater the latitude, the greater the Coriolis force and vice versa.
- Friction: greater friction is experienced by wind when blowing over land surface that when blowing over sea surface.
A rough thumb rule whilst predicting the wind direction is to make the angle of indraft about 30 over land and about 10 over sea, the difference being due to differing values of friction over land and over sea. However this thumb rule should not be applied in the case of severe depressions or tropical revolving storms because of the appearance of new force called cyclo-strophic force or centrifugal force.