As a storm approaches your locality, the air pressure tendency is usually upward. Radiational cooling of air causes air density to increase decrease. When air is heated within the atmosphere, air density increases. When air pressure readings at Denver are reduced to sea level, air pressure is adjusted upward downward. Earth's atmosphere has a well-defined top at the tropopause.
Air pressure varies with time.
An isobar joins localities reporting the same air pressure temperature humidity rainfall 15. After reducing barometer readings to sea level, air pressure varies with time because of changes in air temperature. The top of Earth's atmosphere is the tropopause is the stratopause is in the homosphere cannot be determined precisely 18. The standard atmosphere features an average sea-level air pressure of 1013.25 mb. The rate at which air pressure drops with altitude is fixed and constant.