-400 



I I I I I I I I I I I 



I I I I 



Q(N)= Q(S)-Q{B)-Q(C)-Q{E) 



■ ■ ' ' ■ 



JFMAMJ JASONDJ FM 



Figure 3. —Relative nugnitude of the 1956-70 mean monthly compo- 

 nents of heat exchange across the sea surface at Ocean Weather 

 Station V (OWS-V) in calcm'^day'. Q(S)— radiation from sun and sky, 

 Q(B)— effective back radiation, Q(C)— conduction of sensible heat, Q(E) 

 —heat used for evaporation, and Q<N)— net heat exchange across the 

 sea surface. 



Seasonal Anomalies of Q(N) and Q(E) 



Large-scale climatic anomalies are illustrated in the bar 

 diagrams, Figures 7 and 8, in which Q(N) and Q(E) 

 anomalies of the 6-mo averages for the warming and 

 cooling portions of the annual cycle are shown. In these 

 figures adjustments for the change in location of the 

 weather ship were made. Differences in the 20-yr monthly 

 mean (1949-68) meteorological properties between mer- 

 chant vessel data collected in 2° quadrangles centered at 

 lat. 34°N, long. 164°E and lat. 31°N, long. 164°E (Table 2) 

 were added to the monthly mean meteorological properties 

 from September 1951 through March 1955. The adjusted 



mean properties were then used to calculate the adjusted 

 heat exchange processes and their 6-mo anomalies. 



The figures show that the anomalies in most years 

 persist for more than 6 mo. Often, an anomaly during the 

 cooling 6 mo is followed or preceded by an anomaly of the 

 same sign during the warming 6 mo. Pronounced cold 

 (negative) anomalies occurred during the fall and winter of 

 1956-57, 1959-60, and 1967-68. A pronounced warm 

 (positive) anomaly during the cooling portion of the annual 

 cycle occured in 1968-69 while lesser warm anomalies 

 occurred in 1958-59, 1962-63, and 1965-66. During the 

 cooling 6 mo the seasonal anomalies in Q(N) reflect those 

 of Q(E) (Fig. 8). 



Q(E) as a Function of (e. 



- e» 



and W 



Because of the important role played by the evaporative 

 process in the heat and water (salt) budgets of both the 

 ocean and atmosphere, we will examine the dependence of 

 evaporation on the wind speed, W, and the vapor pressure 

 difference, (e„ - e,). An "evaporation diagram" helps to 

 illustrate this dependence (Fig. 9). In this diagram the wind 

 speed is plotted along the abscissa and the vapor pressure 

 difference, Ae, along the ordinate. Contours indicate Q(E) 

 based on the bulk exchange formula with a Co of 0.0013. The 

 climatic mean value of W and Ae is plotted for each month and 

 designated by Roman numerals, solid lines connecting the 

 plotted points. This diagram allows one to determine whether 

 a change in the evaporation rate is caused by a change in the 

 wind speed and/or the vapor pressure difference. The 

 "evaporative climate" of a location can be characterized by 

 this diagram and, again one can determine whether an 

 anomaly is caused by an anomalous wind speed and/or an 

 anomalous vapor pressure difference. Qualitative interpreta- 

 tions based on this diagram are independent of the coefficient 

 used in the bulk exchange formula. 



The lowest evaporation rate at OWS-V occurs during 

 June and July (Fig. 9) and then increases until September 

 due to an increase in Ae with little change in W. During the 

 next 2 mo the evaporation rate increases primarily because 

 of the increase in the wind speed. From November through 

 February the evaporation rate is at its maximum and 

 changes little; the decrease in Ae is compensated for by an 

 increase in W. After February both Ae and W decrease 

 until the minimum evaporation rate is reached in June. The 

 seasonal rise in evaporation is initially caused by the rise in 

 Ae and then continues rising because of the increase in W. 

 The seasonal decline in evaporation is caused by a 

 simultaneous decline in both Ae and W. 



Table 2.— Differences between monthly mean meteorological properties (1949-68) in 

 2° quadrangles centered at 1) Ut. 34°N, long. 164°E and 2) lat. 31°N, long. 164°E. 

 Values are mean (1) - mean (2). A = Sea-surface temperature, °C', B = Air 

 temperature, °C; C = Wind speed, m sec '; D = Vapor pressure of the air, 

 millibars; and E = Total cloud cover, tenths. 



