Figure 11.— Monthly components of resultant wind stress at Ocean 

 Weather SUtion V (OWS-V), 1952-70. Magnitudes of less than 0.28 

 dyne cm'' were not plotted. Distances between points are equivalent 

 to 2 dynes cm'' . The magnitude of stress components Urger than 2 

 dynes cm'' are labelled. 



months with anomalously high or low stress tend to be 

 months with anomalously high or low evaporation rates, for 

 example, February 1958, January and February 1963, and 

 February 1968. This association does not necessarily apply 

 generally because an anomalously high mean wind speed 

 used in the evaporation formula can occur during a month 

 with a low resultant wind stress. For example, the month 

 of November has, on the average, a wind speed 

 approximately as high as during December and March 

 (Appendix I) and, yet, the resultant stress for November is 

 much lower than that during December and March (Fig. 

 11). 



CONCLUSION 



Figure 1 shows that the highest net annual heat loss at 

 lat. 34°N lies more than 1,500 km to the west of OWS-V 

 (Ocean Weather Station V). It is therefore possible that the 

 air-sea interaction climatology at OWS-V will differ from 

 that of the high heat loss area to the west. During fall and 



winter the Asian high- and Aleutian low-pressure systems 

 pump cold, dry continental air over the warm waters of the 

 western Pacific causing high evaporative and sensible heat 

 losses. The seasonal variation in the net heat exchange 

 across the sea surface in the high heat loss area, there- 

 fore, is associated with the monsoon circulation of the 

 Asian continent. 



According to climatic sea-level pressure charts, during 

 fall and winter, OWS-V lies in the westerly wind sytem 

 associated with the Aleutian low and the subtropical high 

 pressures. In agreement with the pressure charts, the wind 

 stress during these seasons is predominantly zonal (Fig. 

 11). Evidence of the monsoon type of circulation is absent 

 in that small meridional components of the stress directed 

 northward or southward occur irregularly. 



Despite the differences in the wind regimes between 

 OWS-V and near the Asian continent, the importance of 

 the evaporative heat loss during fall and winter relative to 

 the other heat exchange processes is expected to be 

 similar. From November through March the sea-surface 

 temperature at OWS-V is 2°C or more warmer than the air 

 temperature and the average wind speed is more than 9 m 

 sec"'. High evaporation rates during fall and winter are 

 therefore expected and are the principal contribution to the 

 net annual heat loss at OWS-V (Fig. 3). 



Evaporation is also a major contributor to the seasonal 

 variation in the net heat exchange across the sea surface 

 with an annual range of 288 cal cm"^ day'' compared to the 

 annual range in radiation from sun and sky of 340 cal cm'^ 

 day"'. To the west, the evaporation becomes the dominant 

 process causing the seasonal variation in the net heat 

 exchange. Near Japan an annual range in the heat used for 

 evaporation of more than 500 cal cm"^ day"' is indicated by 

 Wyrtki (1966). 



The evaporation diagram. Figure 9, shows the relative 

 contributions of the vapor pressure difference and the wind 

 speed to the changes in the evaporative heat loss at 

 OWS-V. These factors are not entirely independent, since 

 both depend on the circulation associated with the 

 atmospheric pressure distribution. For example, anom- 

 alously high evaporation rates occurred during February of 

 1958 and 1968. These months also had anomalously high 

 wind speeds, vapor pressure differences, and air-sea 

 temperature differences, and Figure 11 shows that there 

 was a southward component in the resultant wind stresses. 

 Mean sea-level pressure chartsV for these months indicate 

 an eastward displacement of the Aleutian Low resulting in 

 northwesterly winds in the vicinity of OWS-V. Thus, 

 OWS-V, near the periphery of the net annual heat loss 

 area, can experience a wind and air-sea interaction regime 

 that is commonly found to the west. 



The uncertainties in the computation of the air-sea 

 interaction processes had little bearing on the foregoing 

 discussion. Interseason and interannual variations would be 

 evident regardless of the magnitude of the coefficients or 

 whether stability corrections are used. The processes listed 

 in Appendix II are therefore indices for quantitative 

 comparisons. Results obtained when the stability correc- 

 tions of Deardorff (1968) were used in the computations of 

 the turbulent exchange processes (Appendix III) indicate 

 that interseason and interyear differences based on 



'Northern Hemisphere charts of mean sea-level atmospheric 

 pressure, Long Range Prediction Group. NOAA, National Meteoro- 

 logical Center. 



17 



