Now we turn to the case of the saturated air within a cloud. Here the test of stability or instability is a comparison of slopes of the observed temperature profile with the SALR, not the DALR. Both are included in Figure 7.5,
Figure 7.4 A comparison of the dry adiabatic lapse rate (DALR) with the environmental lapse rate (ELR) in each of two layers, showing, for example, that atmospheric local static stability corresponds to an ELR (in section be) more clockwise than the DALR.
where the SALR is different for hot and cold climates, respectively (Section 7.2). The lines for both extremes of SALR are more vertical than the line for the DALR.
Figure 7.5 also shows a pair of lapse rates labelled 'conditionally unstable'; this needs explaining. They are environmental lapse rates of a layer which is either stable, if the air is unsaturated (i.e. the line is more vertical than the DALR line), or unstable if there is saturation. In other words, instability depends on the condition of the atmosphere, whether or not it is saturated, when the ELR is like those indicated by the lines labelled 'conditionally unstable'. The lapse rate for a conditionally unstable layer lies between the DALR and the SALR. The lower of the two labelled lines in Figure 7.5 implies conditional instability at all latitudes, whilst conditional instability applies only near the equator for the upper one. Therefore, conditional instability is more likely at low latitudes. To distinguish conditional instability from instability in dry air, the latter is sometimes called absolute instability.
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