Stable Layers

Having considered instability, we turn to the subject of stable layers of the atmosphere, in which either (i) temperatures decrease with height but less rapidly than the relevant adiabatic lapse rate (i.e. the environmental lapse rate is sub-adiabatic), (ii) the layer is isothermal (with a unform temperature

Plate 7.1 A tornado in South Australia on 20 August 1971.

throughout), or (iii) there is an inversion, with an increase of temperature with height (Figure 7.5). If an inversion has a strength of 5 K/km, then a parcel of air lifted consequently has great buoyancy back up over 1 km finds itself within an environment towards the status quo. The result is that any that is 15 K warmer (since the parcel cools at stable layer, but especially an inversion, resists the DALR, 10 K/km), so that there is a par-vertical movement of any kind and therefore ticularly strong tendency for the parcel to sink separates the air above from that beneath. The back again. Likewise, a parcel pushed down in layer creates a stratification of the atmosphere the layer finds itself in particularly cold air, and into distinct layers.

A temperature profile of the troposphere usually has several kinks indicating various stable layers, which in the extreme are inversions, described in Table 7.3. These will now be discussed, regarding all stable layers as inversions, for brevity.

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