Chapter 11 — WATCH ROUTINES (CONTINUED) 



therefore most frequently received. It is ex- 

 tremely important that the sea surfaoe tem- 

 perature (SST) be obtained and plotted as 

 accurately as possible, since the SST analysis 

 may be used as a guide when analyzing charts 

 compiled of less frequently received data. Er- 

 roneous values and incorrect positioning of cor- 

 rect values can change the entire character 

 of the SST analysis and all of the resultant prod- 

 ucts. A single day's collection of reports is usu- 

 ally not sufficient for the preparation of a SST 

 regional analysis. It is usually necessary to plot 

 an accumulation of several days' data on the same 

 chart. The exact number of days to be used will 

 vary dependent upon the size of the area to be con- 

 sidered, the number of reports received daily, and 

 the characteristics of the forecast area. 



Although most temperatures are observed, 

 recorded and transmitted in degrees Celsius 

 they are analyzed in degrees Fahrenheit, and 

 must therefore be converted prior to plotting 

 them on the SST chart. 



Many errors in the transmitted messages 

 can be corrected by the plotter. Erroneous 

 values are generally the result of encoding 

 errors or transmission garbles. 



Plotting Mixed/Sonic 

 Layer Depth Charts 



The Mixed Layer Depth (MLD) refers to 

 the depth to which the surface layer of water 

 has been mixed through convective and/or me- 

 chanical mixing processes. Sonic Layer Depth 

 (SLD) refers to the depth of maximum sound 

 velocity in the upper 1500 feet of the ocean. 



A plus (+) sign following the plotted layer 

 depth value indicates the MLD may be at a 

 greater depth than the value plotted. This would 

 occur if no reported level had a temperature at 

 least 2°F colder than the reported sea sur- 

 face temperature and the maximum depth of 

 the sounding is plotted as the MLD. 



If the reported temperature at the layer 

 depth is warmer than the SST, a "P" is plotted 

 after the layer depth value to indicate a posi- 

 tive temperature gradient from the surface to 

 the layer depth. 



In some cases both a "P" and a "+" are 

 plotted. In this instance the P precedes the 

 +; for example 240P+. 



Plotting Gradients 



Although SST and LD charts present valuable 

 information for computing sonar ranges, etc., 



additional and/or more precise determinations 

 of value to the forecaster require knowledge 

 of the thermal gradients in the water column. 

 Analyzed plots of the temperature gradient (rate 

 of change) in the 100 feet of water imme- 

 diately below the MLD provide the forecaster 

 with an indication of the degree of stability of 

 the water column and the degree of persistence 

 of the MLD. 



Oceanographic Analysis 



By the time the Aerographer's Mate has 

 advanced to Aerographer's Mate 3 and is in 

 the process of advancing to Aerographer's Mate 

 2, he should realize that a correct analysis 

 is amoung the most important tools in fore- 

 casting. There are many different types of 

 analyses. Those presented in the following para- 

 graphs are designed to assist in the prepara- 

 tion for advancement to Aerographer's Mate 

 2. However, the Aerographer's Mate should 

 attempt to acquaint himself with as many of 

 the other types of analyses as he can, if he 

 is to acquire a more comprehensive under- 

 standing of the meteorological-oceanographic re- 

 lationship and its application towards the 

 problems he will eventually encounter in fore- 

 casting. 



Many of the same procedures discussed for 

 meteorological charts in this chapter also apply 

 when preparing the oceanographic analysis. 



SEA SURFACE TEMPERATURE (SST) ANAL- 

 YSIS. — The analysis of the sea surface tem- 

 perature (SST) chart, in the absence of computer 

 products, is usually accomplished by using a 

 synoptic approach similar to that used for mete- 

 orological charts. This method is subjective in 

 that different analysts will draw somewhat dif- 

 ferent conclusions from the same set of data. 

 However, as long as the same general rules 

 are adhered to the end product will be ap- 

 proximately the same. 



One of the more important rules that the 

 analyst of the SST data should keep in mind 

 is that warm currents generally move more 

 rapidly than cold currents. This is true be- 

 cause cold water will contract, causing the 

 surface to have a lower level than warm water. 

 This allows the warm water to flow down hill 

 as it moves northward. Also, since the mole- 

 cules in the warm water are farther apart due 

 to the higher temperature, the warm water 

 is lighter (less viscous) and therefore able 

 to move more rapidly. 



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