variations. T^'JO anomaly charts are required for optimal prediction: 

 one for surface anomalies over the entire North Atlantic and one for 

 uncorrelated anomalies at 400 feet. 



If areas of anomalies do not change too rapidly, weekly charts should 

 be sufficient for determining surface anomalies and uncorrelated anomalies 

 at 400 feet. Such charts covering periods of several years would yield 

 valuable data for further study of the possible periodicity and causes of 

 uncorrelated anomalies at UOO feet and most likely would also yield some 

 clues leading to a better understanding of surface anomalies. 



C. Prediction Example 



The following example Illustrates the prediction technique at 

 52°N,15°W on 3 August 1951. Surface temperature, based on 3 BT's, was 

 6l.0°F. Mean annual temperature taken from figure 2 is 54.1°F. Annual 

 temperature amplitude (a) taken from figure 11 is U.50F. The location, 

 according to figure 12, is in a region in which equation (lO) and figure 

 A-2 apply. Following the procedure outlined on page 26 by entering the 

 upper left of the nomogram with latitude 52° and time 3 August, K-, = 



0.22 is obtained. Entering the second graph with K-, = 0.22 and A = 



4.5, Ko = 1.0. Descending from this point to latitude 52° in the third 

 graph, Ko = -2.^5 on the left margin. From the K^ value and mean annual 



temperature at the surface, ^„ „ ~ 5^'1°F^ tiie mean temperature at 400 



o ' 



feet (^(inn^^ 51 •? ^^ is obtained in the lower left corner of the nomogram. 



Mean temperature interpolated from the mean monthly charts for July 

 and August (figures B-7 and B-8) is 59.1°F. Since the observed surface 

 temperature is 6l.0°F, the surface anomaly is 1.9°F. The anomaly ratio 

 from figure 8 is 0.75* The surface anomaly miiltiplied by the ratio yields 

 a i+OO-foot anomaly of 1.4 F. Addition of this anomaly to the mean tem- 

 perature at 400 feet, 51 •? F, gives the predicted temperature at 400 feet 

 ( ^iion)* 53.1°F. The observed temperature at 400 feet computed from the 

 3 BT*s was 51.9°F. The prediction error (E) is 1.2°F. 



As shown by this example, some of the mean temperatures at 400 feet 

 agreed closely with observed temperatures; however, anomaly corrections 

 generally reduced prediction errors, especially when the anomaly values 

 were negative. 



In warm seasons (spring, summer, and early autumn), it is better 

 to disregard large positive anomalies in the Worth Atlantic (except in 

 the Labrador Sea) . Instead, it is better to use the uncorrected mean 

 temperature at 400 feet obtained from the nomogram. About 95 percent 

 of test predictions diiring warm seasons were more accirrate without 

 anomaly correction when the surface temperatiire anomaly exceeded an 

 arbitrary value of 2.5°F. This rule does not apply during cold seasons 

 and does not apply at any time in the Labrador Sea. Any other value 



31 



