AEROGRAPHER'S MATE 3 & 2 



AIR MASS SYMBOLS COLOR OF ENTRY 



Arctic , continental cA Blue 



Arctic, maritime mA Blue 



Polar , continental cP Blue 



Polar, maritime mP Blue 



Tropical , continental cT Red 



Tropical , maritime mT Red 



Equatorial E Red 



Superior S Red 



The air masses are also defined thermally as follows: 



SYMBOL ENTRY THERMODYNAMIC STATE 



k Blue Air mass is colder than the surface over 



which it is passing. 



w Red Air mass is warmer than the surface over 



which it is passing. 



209.305.2 

 Figure 11-9, — Weather analysis symbols— Continued. 



4. Isobars must agree not only with the are found between two distinct low-pressure 



pressure, but also with the general windflow. areas. 

 Winds blow in a clockwise direction about a 



high-pressure area and counterclockwise about COL (OR SADDLE). — The col is a region 



a low-pressure area in the. Northern Hemi- between two highs and two lows. The col is one 



sphere. Because of the effect of surface fric- of the most treacherous types of barometric 



tion, winds blow across isobars at a slight distribution. Sometimes the col marks a lo- 



angle from high to low pressure. cality of fine weather, while at other times 



5. Isobars "kink" at fronts. 



severe thunderstorms are exparienced. 



TROUGH. — A trough is an elongated area of 

 Isobaric Patterns relatively low pressure and usually extends from 



a low-pressure area. The isobars of a trough 



Frequently, reference is made to various may be either U-shaped or V-shaped. U-shaped 



isobaric patterns. Some of the basic patterns troughs contain no fronts, while V-shaped troughs 



are described below and shown in figure 11-10. are associated with fronts. Unsettled or bad 



weather and a possibility of a formation of a 

 RIDGE (OR WEDGE). — A ridge is an elongated secondary front may be expected with U-shaped 

 area of relatively high pressure that extends from troughs. In V-shaped troughs the weather ele- 

 the center of an anticyclone or high. The wind ments vary sharply, 

 circulation is essentially anticyclonic in the 



Northern Hemisphere. Ridges of high pressure In drawing isobars in the vicinity of moun- 



are usually areas of fine fair weather. They tainous regions, special care must be taken. 



206 



