A subsiding layer becomes compressed as it sinks to levels at higher pressures, so the top descends further than the bottom of the layer does (i.e. warms more), and consequently the lapse rate within the layer changes in a way that results in greater stability. This is the converse of the instability created within a rising layer (Section 7.4). More importantly, the inversion that commonly occurs above the lowest few hundred metres is due to the air against the ground being unable to descend further, whilst higher levels continue to warm by subsidence.
Subsidence inversions are associated with the air descending within a high-pressure system (Chapter 13). The ground-level high pressure causes surface air to spread out to low-pressure areas around, and that draws air down from above. The subsiding air's warming and the low water content of the original upper-level air (Section 6.6) lead to it having a characteristically low relative humidity at the surface.
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