THE ISOTHERMAL REGION, OR STRATOSPHERE 53
But, AT2, winter to summer, is roughly 12° C., and h about 110 meters. Hence the change in the seasonal height of the stratosphere, if there is constancy in atmospheric composition, and other conditions, except temperature, is, roughly,
AH = 0.16 X 12 X 110 = 211.2 meters.
It must be distinctly noted, however, that many disturbing elements, such as quantity and distribution of water vapor, frequency and extent of cirrus clouds, and the like, so modify these simple relations that they apply only to average conditions, and to them but approximately.
STORM EFFECTS ON TEMPERATURE GRADIENTS
The average of a season's (winter or summer) vertical temperature gradients gives a fairly regular curve, and, of course, the same would be true of the average of these averages, or what might be called the annual gradient for any given locality. However, each particular flight yields its own temperature-altitude curve, which differs more or less from others of the same place and season, especially in the values of the gradients in the first 2 or 3 kilometers, in the absolute temperatures at other levels, and in the location of the upper inversion.
With the view of determining the causes of some of these flight-to-flight irregularities, both the summer and the winter records from which the corresponding seasonal gradients were determined (all'in Europe) were grouped, according to the heights of the barometer at the times and places of observation, into "highs," "neutrals," and "lows." Thus the "highs" belong to barometric readings of 5 mm. or more above, and the "lows" to readings of 5 mm. or more below, the seasonal normal, and the "neutrals" to the various intermediate values, all reduced to sea level.
Figure 17 shows the winter averages, respectively, of 54 highs, 72 neutrals, and 59 lows. Commonly, as the figure shows, a high barometer in the winter is accompanied by low surface temperatures, a slow decrease of temperature up to the height of about 3 kilometers, relatively warm air, in general, between the levels of 2 and 9 kilometers, a high upper inversion, a cold stratosphere, and a marked minimum temperature in its lower portion. A winter low, on the contrary, and in comparison with a high of the same season, is accompanied by warm surface temperatures, a more rapid decrease of temperature with increase of elevation through the first 3 kilometers, relatively cold air from, roughly, 2 to 9 kilometers height, a low upper inversion, and a warm stratosphere.
The normal barometer, as one would expect, is accompanied by intermediate values in all particulars.