AEROGRAPHER'S MATE 3 & 2 



1008 



-1008 



BASIC ANALYSIS 



FINAL ANALYSIS 



209.300 

 Figure 1 1- 6 „ — Smoothing of isobars. 



first; then extend the isobars over adjacent 

 oceans. Other conditions being equal, it is eas- 

 ier to draw isobars in areas of strong wind 

 than where the winds are weak. Isobars should 

 be drawn so they agree logically with the pre- 

 ceding map. The previous map is the key to 

 the present chart. For example, suppose that the 

 preceding map shows a young, deepening cy- 

 clone. The present map should show that the 

 low has moved a reasonable distance and deep- 

 ened. The deepening is indicated by new and 

 closer isobars around the center. 



In drawing an isobar, keep in mind that the 

 higher pressures are on one side of the isobar 

 and the lower pressures are on the other side. 

 (See fig. 11-7.) If pressures are higher (or 



lower) on both sides of an isobar than the value 

 of the isobar itself, a mistake has been made. 

 The 2-station method of analysis is a very 

 good method by which to actually begin and 

 complete the basic analysis. 



The first step in the 2-station method of 

 analysis is to select the area of the chart over 

 a land surface where numerous reports are 

 available. Locate the area of highest and low- 

 est plotted pressure values. Select one region 

 and locate in this region the station having the 

 highest or lowest plotted pressure value. Note 

 this pressure value. Go in any direction from 

 this station to a station immediately adjacent. 

 Note the pressure at this station. Determine 

 what standard isobaric value, if any, fits be- 

 tween these two stations in a logical numerical 

 order. If a standard isobar can be drawn be- 

 tween these two stations, draw a short pencil 

 line between these two stations and more or 

 less parallel with the wind shafts at the two 

 stations. If a standard isobar does not fit be- 

 tween the two stations, continua in the* same 

 direction to the next adjacent station and re- 

 peat the entire process outlined above. 



Note the plotted pressure values at several 

 stations immediately downwind from the point 

 of origin. If it is found that the numerical value 

 of the isobar being drawn fits, in a logical 

 numerical order, between only two of these 

 stations, project the short line being drawn to 



\ WRONG 



(4) 



H 



209.302 



Figure 11-7.— A small pressure center between isobars. 



200 



