How to interpret potential temperature versus height diagrams
A potential temperature versus height chart gives a simple means
for visually identifying vertical atmospheric structure. A
vertical line (no change of potential temperature with height)
indicates an adiabatic lapse rate; a line sloping to the left ( a
decrease of potential temperature with height) indicates a
super-adiabatic lapse rate; a line sloping to the right (an
increase of potential temperature with height) indicates a lapse
rate between adiabatic and diabatic, or an inversion.
A critical inversion to cap vertical mixing in the boundary layer was defined
by Heffter (1983) as:
1) dO/dz >= 0.005 degK/m
2) O(top) - O(base) >= 2 deg K
where dO/dz is the change of potential temperature (O)
with height (z) and O(top) and O(base)
are defined at the top and base of the inversion being considered.
We have colored the theta line orange for segments that meet the
above criteria to help the user discern the critical inversions.
In most cases we are only trying to define the top of the mixed
layer and therefore the critical inversion above 500 mb are
irrelevant.
