Originally Posted by
langleybaston
So what is a LAYER 1.5km UP?
A layer has a bottom and a top.
Temperature has a huge diurnal variation so is useless for a definition.
Far far apart.
Maybe the bottom of the layer is at the surface (or just above the boundary layer) I don't know what he actually said nor meant, although I would have thought it unwise to define the depth of the layer too closely.
I thought that air temperature has a huge diurnal variation only close to the surface of the earth and temperature combined with dew point give a measure of humidity, which, in the station circle, is only represented at the surface? As you imply surface observation could require several days observations and skill to identify the horizontal boundaries of an air mass and only with difficulty describe the depth of it. Perhaps the definition of and method of detection of air masses has changed since you retired.
Having described how you would find an air mass, how would you define an air mass?