What will be the effect on the reading of an aneroid altimeter of an aircraft parked on the ground during the period following the passage of an active cold front?

After the passage of an active cold front, the atmospheric pressure tends to rise. When an aircraft is parked on the ground, and the barometric pressure increases, the reading of an aneroid altimeter - which is calibrated to reflect changes in atmospheric pressure by indicating altitude - will respond accordingly.

In particular, since the aircraft is stationary and we are considering the altimeter's reading under the influence of rising pressure, it will indicate a lower altitude than the true altitude. This results in a decrease in the altimeter reading. Therefore, after the cold front passes and pressure increases, the aneroid altimeter will reflect this condition by showing a decreased altitude reading.

This phenomenon occurs because aneroid altimeters work by measuring the ambient air pressure, which directly correlates with altitude: higher pressure corresponds to a lower altitude reading and vice versa. Understanding how altimeters work in relation to pressure changes is essential for pilots in managing altitude awareness, especially during weather transitions like cold fronts.