There is no strong relationship between latitude and wind speed. By looking at the plot, most of the cities fall into 0 to 15 mph range. Differences of temperature cause differences in pressure and this drives the wind. Convected energy from the earth's surface rises upward and becomes wind as it begins to move horizontally. This movement is caused primarily by pressure gradient force, as high pressure air moves toward low pressure areas. Curvature of the wind is caused by the rotation of the earth. In the area from the equator to 30 degrees a large circular overturning of air occurs as warm low pressure air rises, moves poleward, cools, and returns to the surface. The cool surface air that moves back towards the equator and completes the circle (northeast and southeast, depending upon the hemisphere).