In a mountain wave, what effect can be seen on altimeter readings?

In a mountain wave scenario, the altimeter can read incorrectly due to fluctuations in atmospheric pressure. This is primarily because mountain waves are associated with strong vertical air movements, which can lead to rapid changes in air density and pressure. When a pilot flies through a mountain wave, the altimeter, which measures pressure to determine altitude, may not accurately reflect the actual altitude above sea level because the pressure at which the aircraft is flying can vary widely.

The pressure changes induced by the wave action can lead to an altimeter that indicates a higher or lower altitude than the actual situation. For example, as the aircraft ascends or descends through different air layers affected by the wave, the local pressure might not conform to the standard atmospheric model, resulting in altimeter inaccuracies. Understanding this aspect is vital for pilots operating in mountainous regions, as altitude information derived from the altimeter may not be reliable and could lead to dangerous situations such as unintentional terrain collisions or improper flight path assessments.