Page "Hodograph" Paragraph 8

* Temperature advection: change of temperature in a layer of air can be calculated by the direction of the wind at that level and the direction of the wind shear with the next level.

In the northern hemisphere, warm air is to the right of a wind shear between levels in the atmosphere.

The opposite is true in the southern one ( see thermal wind ).

So in the example hodograph, the wind from southwest meet the right side of the wind shear which means a warm advection and thus warming of the air at that level.