ISENTROPIC THERMAL SHEAR IN METEOROLOGICAL NAVIGATION

Willibald Partl

Peer Reviewed

Abstract:	FLIGHT CREWS PRACTISING pressure pattern flight can make the observation that in general -especially at the 400-500 mb level-there is a close correlation between D-values and temperatures: rising D-values are associated with rising temperatures and vice versa. To meteorologists this fact is in no way surprising because there is a physical law for that. We can easily understand this correlation if we look at Figure 1 where we compare a column of cold air with one of warm air: assuming equal pressure (QNH) at the bottom of each column, we can see that the metric heights of the various pressure levels differ more and more with pressure altitude and that they are higher in the warm air than in the cold air. At an average difference of 10° C. between both columns, the difference in metric height (our well-known Dvalue change) amounts to 600 feet in 18,000 feet pressure altitude, and 1,200 feet in 36,000 feet pressure altitude.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 6, Number 6
Pages:	374 - 382
Cite this article:	Partl, Willibald, "ISENTROPIC THERMAL SHEAR IN METEOROLOGICAL NAVIGATION", NAVIGATION: Journal of The Institute of Navigation, Vol. 6, No. 6, 1959, pp. 374-382.
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