At the surface as latitude increases temperature decreases so density will increase as we move from the Equator towards the poles. At the Equator the surface temperatures are high so the rate of change of pressure with height is relatively low compared to the poles where temperatures are low and the change of pressure with height is relatively high. This means that at, say, 50 000 ft the pressure over the Equator will be relatively high compared to the pressure at 50 000 ft over the poles. The temperatures are lower at 50 000 ft at the Equator than at the poles which means that the density at 50 000 ft at the poles will be less than at 50 000 ft at the Equator. So we can summarize the change of density as follows:
• at the surface density increases as latitude increases
• at about 26 000 ft density remains constant with an increase in latitude.
• above 26 000 ft density decreases with an increase in latitude. (Maximum deviation from standard occurs at about 50 000 ft.)