What is the actual cause of high or low atmospheric pressure?

Answer 1

There are a number of causes of atmospheric air pressure. The heating and cooling of the earth's surface causes a change in air pressure.

The coriolis effect, due to the rotation of the earth, creates differences in air pressure also.

remember that atmospheric air pressure is mainly due to air masses falling or rising. If the air is falling this is a high air pressure system, produces clearer skies as the air pushes things away from the centre of the high pressure.

Often high and low air pressures are due to large convection currents (air going up in one spot, going down in another)

Answer 2

It is mainly due to the sun's differential heating of the surfaces of two or more areas over land or between land and sea areas.In fact the heat from the sun is the root cause of all the weather over earth.