Remember it's relative temperature difference that generates high and low pressure areas. If the ground, or sea, is warmer than the air up above, the air is heated and pressure drops. If the ground is cooler, it cools the air and pressure rises. It's not surprising that the ground is hot at the equator, but at higher latitudes, there is an interaction between the air and ground/ sea. As it goes north, the air cools faster than the sea- water holds heat better than air does. Also, the ground takes time to cool after the summer, and to warm up again after the winter, so the pressure pattern over a large land mass will be alter depending on the season.