Assume that parcel of air at the surface has a temperature of 29 degree C and a relative humidity of 50%. If the parcel rises, at what altitude should clouds begin to form?
I can't find any kind of formula in the textbook to figure this out. All the figures in the book show the condensation point is 2000m, but that doesn't sound right with the humidity value already so high at the surface.
Clouds start forming when the temperature equals the dew point. Given the air temperature and relative humidity, the dew point can be calculated as:
Td = T - ((100-RH)/5) = 29 - ((100-50)/5) = 29 - 10 = 19 degree Celcius. (pls. check link 1 for this equation).
Using the adiabatic rate of rise as 6 deg C per 1000 m and using unitary method,
6 degree rise in 1000 m.
=> (29-19) deg C rise in = 1000 x (29-19) / 6 m = 1666.7 m above the surface.
Thus the cloud formation would start about 1666.7 m above the surface.