> What is the blue line ("Variable 10xKz") on the Stability Plot?

What is the blue line ("Variable 10xKz") on the Stability Plot?

Kz is the vertical mixing coefficient (times 10 hence 10x) at the top of
the surface layer (about 75 m). It has units of m2/s. When divided by
the turbulent length scale, which could be proportional to the depth of
the boundary layer in the daytime, the result is a turbulent mixing
velocity. For instance, if Kz were 100 and the PBL depth was 1000, then
the mixing velocity would be 0.1 m/s, suggesting that it would take
about 3 hours (1000 m / 0.1 m/s) for the PBL to become well mixed.