Chapter 11 — WATCH ROUTINES (CONTINUED) 



weight of the atmosphere depends upon the 

 density. Cold air is denser than warm air. 

 Therefore, cold air must exert more pressure 

 at a given altitude. Assume that two columns 

 of air are exerting the same pressure at the 

 surface; the column containing the warmer air 

 has to extend to a greater altitude to exert 

 a pressure at the surface equal to that exerted 

 by a column of colder and denser air. Since the 

 height of the colder column is lass, it follows 

 that the pressure must decrease more rapidly 

 with altitude in the colder air, and the vertical 

 spacing of isobars is closer together. For this 

 reason, a pressure system on the surface does 

 not necessarily exist aloft. On the other hand, 

 under the proper temperature conditions, a pres- 

 sure system may intensify with height. 



High- and low-pressure systems are classi- 

 fied as either cold core or warm core systems. 



COLD CORE HIGH. — A cold core high is 

 one in which the temperatures on a horizontal 

 level decrease toward the center. 



Because the temperature in the center of 

 a cold core high is less than toward the out- 

 side 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 de- 

 creases rapidly with height. (See fig. 11-16.) 

 (For the purpose of illustration, figures 11-16 

 through 11-19 are exaggerated from the way 

 that they appear in actual atmospheric condi- 

 tions.) 



Examples of cold core highs are the North 

 American High and the Siberian High. 



WARM CORE HIGH. — A warm core high is 

 one in which the temperatures 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 inten- 

 sity with altitude. (See fig. 11-17.) 



Examples of warm core highs are the Azores 

 or Bermuda High and the Pacific High. 



COLD CORE LOW. — A cold core lo*/ is one 

 in which the temperatures decrease on a hori- 

 zontal level toward the center. 



Because the temperatures are colder in the 

 center of a cold core low, it follows that the 

 isobaric surfaces in a vertical plane are closer 

 together in the center. For this reason, cold 

 core lows increase in intensity with height. 

 (Sse fig. 11-18.) 



Examples of cold core lows are the Aleutian 

 Low and the Icelandic Low. 



WARM CORE LOW, — A warm core low is 

 one in which the temperatures increase toward 

 the center in a horizontal plane. 



Because the temperatures are greatest in 

 the center of a warm core low, it follows that 



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Figure 11-17. — Warm core high. 



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Figure 11-16. — Cold core high. 



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Figure 11-18. — Cold core low. 



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