AEROGRAPHER'S MATE 3 & 2 



the isobar ic surfaces in the center are farther 

 apart in the vertical than toward the outside 

 where the temperatures are lower. For this 

 reason, warm core lows disappear rapidly with 

 altitude. (See fig. 11-19.) 



Examples of warm core lows are the Equa- 

 torial Low and the thermal lows that form over 

 land areas during the summer. 



VERTICAL AXES. — The vertical axes of 

 pressure systems are seldom perpendicular. 

 Lows tend to slope toward colder air aloft 

 and highs toward warmer air. Thus, the posi- 

 tion of pressure centers in the upper air will 

 not necessarily coincide with their position on 

 the surface. (See fig. 11-20.) 



600 MB 

 700 MB 

 800 MB 

 900 M8 

 1000 MB 



600 MB 

 700 MB 

 800 MB 

 900 MB 

 1000 MB 



209.3i2 



Figure 11-19. — Warm core lov/. 



LEGEND: 



-UPPER AIR 

 -SURFACE 



Analysis Elements 



CONTOURS. — Contours or isoheights are 

 lines of equal height drawn on a constant pres- 

 sure chart. These contours show the height of 

 the constant pressure surface in question; they 

 are drawn for 30-meter, 60-meter, or 120- 

 meter intervals as appropriate. For constant 

 pressure charts up to the 300-mb level, con- 

 tours are drawn for 60-meter intervals. For 

 levels at and above the 300-mb level, 120- 

 meter intervals are used. In cases in which 

 the gradient is weak or in order to delineate 

 pressure centers, intermediate intervals (30- 

 moter or 60-meter) may be used. Contours 

 are the upper air equivalent of isobars. They 

 look about the same as isobars, but are usually 

 much smoother. They are drawn for meter in- 

 tervals rather than pressure intervals, as are 

 the isobars. Contours are labeled in accord- 

 ance with the specifications listed in table 11-2. 



The contours on the constant pressure charts 

 show smooth, sweeping orientations of troughs 

 and ridges instead of the confused pressure 

 distribution often found on surface charts. Nor- 

 mally, they parallel the wind direction and are 

 spaced inversely proportional to the wind speed. 

 Closed high- and low-pressure systems appear 

 less frequently on constant pressure charts 

 than on surface charts. 



High and low areas can be located by the 

 reported height values. Lows have a lower 

 height value than the surrounding reported 

 heights, and highs have higher reported heights 

 than the surrounding reported heights. High 

 and low systems on constant pressure charts 

 are labeled in the same manner as on sur- 

 face charts. An H in blue denotes a high, and 

 a red L denotes a low. 



FRONTS. — Fronts can normally be located 

 on the constant pressure charts up to and in- 

 cluding the 700-mb level by the wind direction, 

 temperature, and moisture distribution. Fronts 

 are either drawn on the charts in the same 

 manner as surface charts or are shown simply 

 by a trough line. 



ISOTHERMS. — Isotherms are lines of equal 

 temperature, which are drawn for every 5° 

 of temperature, beginning with any value divisible 

 by 5. The Navy standard color for isotherms 

 is red. 



209.313 

 Figure 11-20. — Comparison of pressure systems. 



ISODROSOTHERMS. — Lines of equal dew- 

 point are isodrosotherms. They are drawn in 



214 



