North Pacific High: an hypothesis

An hypothesis is offered for the cause and maintenance of the North Pacific High (NPH). Over a broad but well defined open ocean area, in the mid-latitude North Pacific, the ocean heats the atmosphere from below, and outside the boundaries of the heat source the ocean cools the air at the sea surface. Vertical thermal convection in the air over the heat source brings down relatively cool dry air, producing a horizontal contrast mainly in relative humidity inside and outside the heat source region. Consequently relatively high density air is produced over the heat source, and if the temperature is approximately constant, then the barometric pressure will be high over the heat source as well. Being unstable, due to a horizontal pressure gradient, the high density air will try to move radially outward from the heat source, and the Coriolis force will bend the outward flow into a clockwise circulation around the center of high pressure. The heat source is provided by a broad northeastward warm surface current, previously described, that crosses mid-latitudes on the eastern side of the North Pacific at all times of the year. Given the known characteristics of the warm current, the heat source mechanism can explain the observed seasonal variations of the NPH also. A more complete substantiation (or refutation) of the general hypothesis for the origin of the NPH must await the accumulation of additional oceanic and atmospheric data.