latent heat flux are approximately 20 to 40 W/m : larger in southern 

 and offshore sections of the grid than in the northern and inshore 

 regions. Values range from about 30 to 60 W/m : north of lat. 40°N 

 to about 60 to 100 W/m 2 south of lat. 30°N. The observed spatial 

 distributions of Q E primarily result from systematic variations in 

 sea-air vapor pressure differences and to a lesser extent from hori- 

 zontal gradients in windspeed. Monthly mean winds are. at most, 

 only twice as large off the Pacific Northwest compared with values 

 off Baja California. However, mean sea-air vapor pressure differ- 

 ences are 2 to 4 times greater in the southern region than in the 

 northern section and 2 to 3 times larger offshore than near the coast. 

 The north-south contrast is particularly evident in winter (Charts 

 25-27) when the atmospheric circulation off the coast of southern 

 Baja California contributes to relatively large mean sea-air vapor 

 pressure differences (e„-e a > 10 mbars). During summer (Charts 

 30-32), east-west gradients in Q E are enhanced by the reduction in 

 latent heat flux near the coast due to the local effects of upwelling. 



Sensible heat flux between ocean and atmosphere is depicted in 

 Figure 19 by the difference between curve 3 and the heavy line 

 denoting Q v . The magnitude of Q c is virtually negligible over much 

 of the California Current region due to the small sea-air tempera- 

 ture differences (7" s — T„< 1 .0°C) over the area during most of year. 

 The sensible heat flux from ocean to atmosphere ranges from near 

 to 20 W/m : over most of the grid with the higher heat losses 

 (g r >30 W/m : ) during winter in the northern latitudes (Charts 37, 

 38. 47. 48). 



The largest Q c values occur during summer in the area adjacent 

 to Cape Mendocino and Cape Blanco, when upwelling of cold 

 water causes mean air-sea temperature differences to exceed 

 1.5°C: the ocean receives a sensible heat gain of up to 30 W/m : 

 (Charts 42-45). Sensible heat gains are < 5 W/m 2 during late spring 

 and summer along the coast of Baja California and values of 5 to 10 

 W/m 2 extend overbroad regions from Point Conception to Vancou- 

 ver Island during May. June. July, and August. In a region off the 

 coast of Washington, high vertical stability associated with the 

 Columbia River freshwater plume (Barnes et al. 1972) may con- 

 tribute to relatively warm sea surface temperatures and, conse- 

 quently, to sensible heat loss in this area (Charts 41-43). 



The net heat gain or loss across the sea surface, Q N , is indicated 

 by the heavy lines in Figure 19. The annual mean net heat exchange 

 is characterized by heat transfer to the ocean over the entire region, 

 a feature previously described by Wyrtki (1965). The annual net 

 heat gain is much larger near the coast than offshore as a result of 

 small heat losses by turbulent heat fluxes and the greater input of 

 solar radiation due to the lower relative cloud cover during summer. 

 The ocean loses heat to the atmosphere over the entire area only in 

 December (Chart 60). 



Over most of the California Current region the net heat exchange 

 is determined by a balance between the incident solar radiation and 

 the heat losses due to effective back radiation and latent heat flux. 

 In the offshore regions the largest heat loss term is the latent heat 

 flux, Q E , while along the coast the effective back radiation, Q B , is 

 the largest heat loss term. Seasonal variations in the components 

 contributing to oceanic heat loss are largest in the coastal upwelling 

 regions off northern California and Oregon and to a lesser extent 

 off the coasts of Baja California and Vancouver Island where the 

 presence of cold upwelled water in late spring and summer reduces 

 the turbulent flux of latent heat and causes sensible heat gain to the 

 ocean, thereby increasing the heat input to the ocean. 



The coastal upwelling zones along the west coast of the United 

 States and Baja California experience the largest net annual heat 

 gain as a result of the combined effects of the increase in incident 



solar radiation in regions of minimum cloudiness and the decrease 

 in heat losses by turbulent fluxes. The net annual heat gain is largest 

 off Cape Mendocino with a mean value of 124 W/m 2 . Seasonal var- 

 iations in the net heat exchange within the 1 ° squares adjacent to the 

 coast are graphically portrayed in the time series isogram displayed 

 in Figure 20. The coastal zone north of lat. 47°N is characterized 

 by net heat losses of more than 100 W/m 2 during December and 

 January and net heat gains of 200 W/m 2 during July. The coastal 

 upwelling zone between lat. 38°N and 44°N shows net heat gains 

 of 200 to 250 W/m 2 during July and relatively small heat losses of 

 20 to 40 W/m 2 during winter. The coastal square at lat. 34°N, 

 southeast of Point Conception, experiences net heat gain during 

 nearly the entire year with maximum heat gain > 180 W/m 2 during 

 May, June, and July. 



There are considerable latitudinal differences in the annual 

 cycles of net heat exchange along the coast of Baja California. The 

 region near Punta Baja (lat. 30°N) is characterized by a relatively 

 small maximum net heat gain during summer of about 150 W/m 2 

 due to high cloud cover (0.8) during June and July. The area south 

 of Punta Eugenia (lat. 27°N) is influenced by a less extensive cloud 

 deck and shows much higher net heat gain, >200 W/m 2 , during 

 spring and summer (Charts 53-56), which may mask the effects of 

 coastal upwelling on sea surface temperatures in this area (Bakun 

 and Nelson 1977). 



Spectral Characteristics of Heat Exchange Processes 



The monthly mean data described in this report resolve the 

 annual cycle. However, marine biological communities must 

 respond to a wider spectrum of atmosphere-ocean variations on 

 time scales ranging from a few days to several years. Relatively 

 rapid diurnal and "event scale" fluctuations (i.e., periods of 1-10 

 d) contribute to turbulent mixing and dispersion of biological 

 microstructure. Lower frequency "climatic" variations, which 

 appear as long-term trends or periodicities, or as interyear differ- 

 ences, affect fisheries over much broader space and time scales. 

 Year-to-year fluctuations in the timing, amplitude, and spread of 

 the seasonal production cycle in major spawning regions may 

 induce significant changes in recruitment of year classes to the fish- 

 eries (Cushing 1975). Annual differences in the character of the 

 production cycle are environmentally controlled and related to 

 changes in the stability of the upper water column which is 

 enhanced by an increase in solar radiation and a decrease in wind 

 strength. 



Available ship reports are unevenly distributed in space and time. 

 Therefore, it is generally not possible to construct consistent time 

 series of air-sea interaction processes for large regions and preserve 

 fine spatial resolution, by applying the simple space and time aver- 

 aging methods which were used to assemble the long-term monthly 

 means. Where the density of reports is large, e.g.. within 300 km of 

 the coast south of Point Conception, statistically significant 

 monthly mean values might be computed over fairly long periods. 

 A few time series of air-sea interaction processes have been pro- 

 duced, either by compositing ship reports in 5° square blocks 

 (Clark et al. 1974) or by making use of objectively analyzed mete- 

 orological products (Bakun 1973) which have a spatial resolution of 

 approximately 3°. Analyses of these data show wide variations in 

 space and time. However, the errors associated with the low fre- 

 quency, nonseasonal fluctuations are generally unknown, and there 

 is little coherence or persistence in the monthly anomaly patterns of 

 the heat exchange processes (Clark et al. 1974). 



Seasonal and nonseasonal fluctuations in net heat exchange. Q s . 

 were investigated at a few selected locations in the Southern Cali- 



27 



