The PBL inversion (or 'turbulence inversion') is due to the stirring of air caused by surface roughness and moderate wind. The stirring leads to good mixing, and hence a lapse rate equal to the dry adiabatic rate. This adiabatic profile connects at the top of the PBL (Figure 1.11) with conditions determined by the wider region (Table 1.1), and there is an inversion at the discontinuity. It is typically 500-1,000 m high, depending on the degree of roughness which stirs the PBL. There is often a subsidence inversion coinciding with a PBL inversion, though the formation process is quite different.
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