AVERAGE A^o STRUCTURE 111 



4.3.3. Average N„ Structure 



The first series of charts presented in this analysis are those showing 

 the time variation of A^'o both vertically above each station as well as at 

 the standard ground-observing level. A slight dichotomy in data sample 

 exists since the vertical data are monthly averages of radiosonde observa- 

 tions taken twice a day, corresponding in time to the hours 0300 and 1500 

 GMT, while the surface data are 8-year means for the even hours of the 

 day local time [29]. This climatic variation at each station is represented 

 by a two-part chart prepared for each station, the first part depicting 

 seasonal changes in the mean value of No throughout the first 3.5 km 

 above the station and the second showing the seasonal and diurnal changes 

 of No at station elevation. These two presentations give a more complete 

 climatic picture of a location than do the usual unidimensional annual 

 cycle graphs. 



Tatoosh Island (TTI), figure 4.16, off the coast of Washington State, 

 illustrates typical features of a marine west coast climate. The seasonal 

 profile changes indicate moderate gradients the year around with a small 

 summer maximum in the No gradients in keeping with the cool tempera- 

 ture regime and small diurnal temperature range of this maritime- 

 dominated climate. This consistency of weather conditions is further 

 emphasized by the almost complete lack of diurnal pattern in the surface 

 data throughout the year and small seasonal change in No for any hour 

 of the day. 



The seasonal profile chart of Oakland (OAK), figure 4.17, indicates less 

 maritime effect than at Tatoosh Island and shows clearly the influence of 

 the summer subsidence inversion on the northeastern edge of the Pacific 

 high-pressure area by both the low values of No and increased gradients 

 at about 1.0 km. The surface data show the moderate seasonal and 

 diural cycles for all months of the year expected in a Mediterranean 

 climate. 



The effects of the Pacific High are more pronounced further south along 

 the California coast. The vertical profile data for San Diego (SAN), 

 figure 4.18, show clearly that during the winter months the strongest 

 gradients of A^o are near the surface as one would expect in a maritime 

 dominated climate while, by contrast, in the summer the well-known 

 Southern California elevated inversion produces strong gradients aloft. 

 The subsiding air above the inversion is reflected by a characteristic in- 

 crease of No with height. The maritime effect is also evident at the 

 surface in the low diurnal range of about 10 N units. It is significant 

 that the presence of the elevated layer produces a smaller diurnal range 

 in the summer than in the winter. 



The semitropical nature of the humid periphery of the Gulf of Mexico 

 is reflected by the data for Brownsville, Tex. (BRO), figure 4.19, which 

 show a strong seasonal cycle and pronounced diurnal range in the summer 



