Where does subsidence collide?

In atmospheric science, subsidence is the large-scale, gentle sinking of air, typically in regions of high pressure where air aloft converges and descends. As the air sinks it warms adiabatically and dries, suppressing cloud formation, which is why subsidence underlies the clear skies of the subtropical highs and the capping temperature inversions that trap pollution. Holton's An introduction to dynamic meteorology treats subsidence within large-scale vertical motion. The referent is downward air motion, measured as a vertical velocity, and it is a different construct from the sinking of the ground or an implant settling into bone, sharing only the meaning of settling.[1]

Unit

The downward vertical velocity of air (e.g. in pressure or height coordinates)

Recovery means

Not applicable

Measured by

Inferred from the large-scale vertical velocity (omega) and the associated adiabatic warming and drying

In geology and hydrogeology, land subsidence is the gradual sinking of the ground surface, most often where groundwater, oil, or gas is withdrawn faster than it is replenished and the drained, compacting sediments lose volume. It can also follow mining, the drainage of organic soils, or the dissolution of soluble rock, and it causes cracked foundations, failing drainage, and heightened flood risk. Galloway and Burbey's 2011 review Regional land subsidence accompanying groundwater extraction synthesises the mechanisms. The referent is the lowering of the land surface, measured in centimetres of settlement, and it shares only the word with sinking air or a settling orthopaedic implant.[2]

Unit

The vertical lowering of the ground surface (e.g. centimetres per year)

Recovery means

Largely irreversible once sediments compact, though some elastic rebound can occur if water levels recover

Measured by

Measured by levelling, GPS, borehole extensometers, and InSAR satellite interferometry

In orthopaedic surgery, subsidence is the sinking of an implant into the bone that supports it, classically a spinal interbody cage settling into the adjacent vertebral endplates after a fusion, but also prosthetic stems migrating into bone. Excessive subsidence can reduce the restored disc height, narrow the nerve openings, and compromise the fusion. Marchi and colleagues' 2013 study Radiographic and clinical evaluation of cage subsidence graded subsidence after lateral interbody fusion. The referent is the migration of a device into bone, measured as loss of height on imaging, and it is unrelated to sinking air or sinking ground beyond the shared meaning of settling.[3]

Unit

The distance an implant sinks into the supporting bone (e.g. millimetres of height loss)

Recovery means

Not applicable; managed surgically through implant sizing, endplate preservation, and fixation

Measured by

Graded on serial radiographs or CT as loss of disc or implant height relative to the immediate post-operative baseline