At what rate does a rising water vapor molecule cool?

The correct rate at which a rising water vapor molecule cools is typically around 10°C for every kilometer of ascent in the atmosphere, especially within the context of the moist adiabatic lapse rate. When air rises, the pressure decreases, allowing the water vapor to expand and cool. As this cooling occurs, condensation may take place if the temperature drops to the dew point, leading to cloud formation and precipitation.

In saturated air, where water vapor is present, the process is slightly different from dry air cooling due to the release of latent heat during condensation. This phenomenon contributes to a rate of cooling around 6°C to 7°C per kilometer, but when considering saturated air that is rising and condensing, the effective rate of cooling can be approximated to 10°C per kilometer under typical atmospheric conditions. This is an important concept in meteorology as it helps in understanding weather patterns, cloud formation, and the behavior of air masses.

Understanding this lapse rate is crucial for students as it forms the backbone of many principles in aviation, such as weather forecasting and aircraft performance in different atmospheric conditions.