This is referring to the fact that when you go up in the atmosphere over high latitudes (e.g. poles), air pressure drops faster than over the equator. So when polar people talk about "physiological altitude" they usually mean what altitude at the equator has the same air pressure as the altitude you're at down south. It will be a few thousand feet higher. Also, barometric pressure changes with weather can increase the "equivalent altitude," which is why the above commenter is saying it can "sometimes" reach 14 thousand feet. Storm fronts are generally low pressure.