Drift and transport wander

[rudderrudderrat]

Hi Lars,

It's because of the shape of the Lines of Longitude as you approach the Poles.

At the Equator, Longitude lines are parallel to each other and at right angles to the Equator (Latitude Zero). So there is no transport wander.

Now imagine a flat map of the North Pole looking like a dart board (a Polar Projection, with the bull representing the N Pole). Keep your pencil pointing to some distant point and move N - S over the dart board. No change in heading apart from flipping due South as you cross the Pole. Now move E - W, you'll see big changes in heading (with ref to the Longitude Lines).