Expressions that have been used in the Pacific 

 area for the cloud correction of the clear sky 

 radiation range from linear to cubic functions 

 of cloudiness: Tabata (1958) used the Angstrom 

 factor (1 - 0.71C). Roden (1959) used the Budyko 

 factor (1 - kC) where k ranges from 0.65 at the 

 Equator to 0,68 at lat. 35° N. Johnson, Flittner, 

 and Cline (1965) and Wyrtki (1966) used the quad- 

 ratic Beriland factor (1 - aC - 0.38C^). (John- 

 son et al. listed for the coefficient "a" the val- 

 ues 0.38, 0.40, 0.39, 0.37, 0.35, 0.36, 0.38, cor- 

 responding to lat. 0°, 5°, 10°, 15°, 20°, 25°, 30°, 

 and 35° N., respectively, and Wyrtki used "a" = 

 0.38.) Finally, Laevastu (1960, 1965) suggested 

 the use of a cubic cloud factor (1 — 0.6c'). 



In this paper I use the Beriland expression. 

 Qualitatively, the pyranometer records of the 

 TWZO cruises indicate that a linear decrease 

 of Q(S) with Increasing cloudiness is too rapid 

 and a cubic decrease is initially too slow. The 

 coefficient "a" = 0.3 has been chosen for the 

 Beriland expression and is based on pyranom- 

 eter records for 21 days of solid overcast which 

 gave an average cloud factor of 0.32. This fac- 

 tor compares with others for solid overcast as 

 follows: Tabata 0.29, Roden 0.32 to 0.35, Wyrt- 

 ki 0.24, Johnson etal. 0.22 to 0.27, and Laevastu 

 0.4. 



Table 1 .--Coefficients in the harmonic series for 

 the computation of Q at lat. 0°, 10°, 20°, 30°, 

 and 40° N. ° 



Q(B), Effective Back Radiation 



The seasonal and spatial variations in effec- 

 tive back radiation are relatively small com- 

 pared with those of the radiation received from 

 sun and sky. Wyrtki (1966) calculated a range 

 of 60 to 200 cal. cm:2 day-i for the North Pacific; 

 Tabata (1958) reported 85 to 130 cal. cmr^day"' 

 off the British Columbia coast; Roden (1959) 

 calculated 84 to 138 cal. cmr^day"' for the re- 

 gion off California and Baja California; and Sec- 

 kel (1962) estimated 115 to 150 cal. cmT^day"' 

 for the Hawaiian region. 



During the TWZO cruises, the net long wave 

 radiation was measured by means of a Suoml- 

 Kuhn net radiometer (Charnell, 1967). These 

 measurements indicate a range of 58 to 173 cal. 

 cmr^ day"'. 



Roden (1959), Johnson et al. (1965), and Wyrtki 

 (1966) used the Beriland expression for the com- 

 putation of the effective back radiation in which 

 the coefficient to correct for cloudiness ranges 

 from 0.5 at the Equator to 0.65 at lat. 35° N. 

 Charnell (1967) computed this coefficient for 

 solid overcast conditions to be, on the average, 

 0.6. In this report I have used the Beriland ex- 

 pression for Q(B) with cloud coefficient 0.6 and 

 have neglected the variation with latitude. 



Q(E), the Heat of Evaporation 



Together with the radiation from sun and sky, 

 the heat used for evaporation is the most impor- 

 tant term affecting the net heat exchange across 

 the sea surface. In the expressions used by all 

 of the workers cited above, the evaporation de- 

 pends on the difference between the saturation 

 vapor pressure over sea water at the sea sur- 

 face temperature and the actual vapor pressure 

 of the air above the sea surface (in this paper 

 termed sea-air vapor pressure difference'), the 

 wind speed, and a coefficient. The evaporation 

 coefficient is affected by the wind speed and the 

 stability of the air above the sea surface. The 

 height above the sea surface at which psychro- 

 metric and wind measurements are made can 

 also be important in the computation of evapor- 

 ation, depending on the vertical gradients of hu- 

 midity and wind speed near the height of mea- 

 surement. Laevastu (1960) and Malkus (1962) 

 have discussed the unresolved uncertainties 

 concerning the choice of the coefficient. 



The evaporation coefficient computed from 

 the expression discussed by Malkus (1962) de- 

 pends on the drag coefficient and varies with 

 the wind speed from 3 (winds below 4 m. sec."' ) 

 to 9 (winds above 12 m. sec."'). Most workers 

 use a constant coefficient for the computation 

 of climatic averages of the evaporation. Wyrtki 

 (1966) used a coefficient of 6 obtained from the 

 Malkus formula, which corresponds to a wind 

 speed of 8 m. sec."' at 10 m. height. Tabata 



Subsequently in this paper the difference be- 

 tween the saturation vapor pressure over sea 

 water at the sea surface temperature and the 

 actual vapor pressure of the air above the sea 

 surface is referred to as the sea-air vapor pres- 

 sure difference. 



