Thermal Wind Component
The thermal wind component is caused by a pressure gradient trying to move air from high temperature/high pressure towards low temperature/low pressure and any given altitude. This movement from high to low is affected by coriolis (geostrophic) force turning the flow of air to the right in the northern hemisphere and to the left in the southern hemisphere. The resultant flow of air parallel to isotherms (lines joining points of equal temperature) is refered to as the thermal wind component.
The ‘free-flow’ (approximately 2,000ft) wind blows parallel to isobars (lines of equal sea-level pressure) with low pressure on the left in the northern hemisphere.
The thermal wind component blows parallel to isotherms (lines of equal temperature) with low temperature on the left in the northern hemisphere.
The upper wind is the vector sum of the free-flow wind and the thermal wind component and blows parallel to isohypses (contours or lines joining equal height above msl for a given pressure) with low contour height on the left in the northern hemisphere.