Earth Science · Atmosphere · Weather / Principles and Exploration
Rising air and clouds — principles and investigation
As air rises, the surrounding pressure decreases, causing it to expand and cool down. Vary the ground temperature, dew point, environmental lapse rate, and reaching height to find the point at which the air parcel becomes saturated. Clouds and their stability are examined by distinguishing between the cooling rate difference before and after condensation and the temperature difference with the surrounding air.
How does it work?
Before condensation, the model reduces air temperature by 10 °C per km and dew point by 2 °C per km. After condensation, it uses an air-temperature decrease of 5 °C per km.
Condensation altitude = (T−Td)/8 km
Try this investigation
- Set the target height of the air parcel by dragging it in the scene or using the height slider. When run, it rises from the ground and clouds form after the condensation altitude.
- Run and record 1.5 km and 3 km at ground temperature of 25℃ and dew point of 13℃. Check temperature and saturation.
- Maintain the target of 3 km and change the environmental temperature lapse rate to 3 and 12 ℃/km to compare air and environmental temperatures.
Interpreting your results
What is the temperature of the air parcel at the condensation altitude of 1.5 km?
(25−13)/(10−2)=1.5 km. Before condensation, it cools by 10 ℃/km, so 25−10×1.5=10 ℃.
Assumptions and limitations
It is an interval approximation that sets the dry, dew point, and wet lapse rates as constants of 10, 2, and 5 ℃/km, respectively. The lapse rate changes due to mixing, radiation, and atmospheric pressure are omitted. Stability/unstability is a buoyancy judgment that compares the surroundings and temperature at a given height, and is not the stability of the entire atmosphere or the actual cloud and precipitation forecast.