The topographic features that indicate the cir-culation patterns at 500 millibars in the at-mosphere correspond in general to those at lower and higher levels. However, they may experience a shift in location as well as a change in intensity and shape. For example, a closed high on a sur-face synoptic chart may be reflected by a ridge aloft. In addition, upper air circulation patterns may take on a wavelike structure in contrast to the alternate closed lows, or closed high patterns at the surface level. The smoothing of the circula-tion pattern aloft is typical of atmospheric flow patterns.

A cold core high is one in which the temperatures on a horizontal plane decrease toward the center. Because the temperature in the center of a cold core high is less than toward the outside of the system, it follows that the vertical spacing of isobars in the center of this system is closer together than on the outside. Although the pressure at the center of these systems on the surface may be high, the pressure decreases rapidly with height. (See fig. 3-2-5.) Because these highs are often quite shallow, it is common for an upper level low to exist above a cold core high. NOTE: For the purpose of illustration, figures 3-2-5 through 3-2-8 are exaggerated with respect to actual atmospheric conditions.

If the cold core high becomes subjected to warming from below and to subsidence from aloft, as it moves southward from its source and spreads out, it diminishes rapidly in intensity with time (unless some dynamic effect sets in aloft over the high to compensate for the warming). Since these highs decrease in intensity with height, thicknesses are relatively low. In the vertical, cold core highs slope toward colder air aloft. Examples of cold core highs are the North American High and the Siberian High and the migratory highs that originate from these anticyclones.

A warm core high is one in which the tem-peratures on a horizontal level increase toward the center. Because the temperatures in the center of a warm core high are higher than on the outside of the system, it follows that the vertical spacing of isobars in the center is farther apart than toward the outside of the high. For this reason, a warm core high increases in intensity with altitude and has an anticyclonic circulation at all levels (see fig. 3-2-6). In the vertical, warm core highs slope toward warmer air aloft. 

Examples of warm core highs are the Azores or Bermuda High and the Pacific High.

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