The Turner stability class or Turner stability index is a classification of atmospheric stability over an interval of time based on measurements of surface-level wind speed and net solar radiation. Classes range from 1 (most unstable) to 7 (most stable). The Turner stability class system was devised by D. B. Turner as a modification of the Pasquill stability class system.
The following table is used to determine the Turner stability class for a given wind speed and net solar radiation:
+ Turner Stability Class Wind speed (knots) Net radiation index 4 3 2 1 0 -1 -2 0, 1 1 1 2 3 4 6 7 2, 3 1 2 2 3 4 6 7 4, 5 1 2 3 4 4 5 6 6 2 2 3 4 4 5 6 7 2 2 3 4 4 4 5 8, 9 2 3 3 4 4 4 5 10 3 3 4 4 4 4 5 11 3 3 4 4 4 4 4 ≥ 12 3 4 4 4 4 4 4
The net radiation index is determined by following a procedure (see flowchart) that takes into account the cloud cover, ceiling height, and solar altitude.
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