130 



N CLIMATOLOGY 



Figure 4.33. Comparison of mean seasonal to mean diurnal ratio of No at the earth's 



surface. 



The more southerly and humid stations have relatively high mean AA^ 

 values in excess of 55 A'^ units/km. The single European station, Wies- 

 baden, shows both low average value of AA'^ arising from the low average 

 temperatures and small seasonal variation associated with the continuous 

 onshore advection of cool, moist air from the Atlantic Ocean. The values 

 R{AN) < 1.0 for the Canadian stations of Churchill and Isachsen reflect 

 the steep gradients associated with the intense stratification during the 

 long winter night. The high, dry climate of Denver produces low 

 mean values of AA^ but a high seasonal range. The interplay of conti- 

 nental and maritime effects along the east coast produces relatively high 

 values of R{AN) while the presence of the Pacific high inversion layer 

 below 1 km accounts for similar values along the west coast. The ex- 

 tremely high value of R{AN) of 1.8 for Tripoli (TPI) arises principally 

 from the intense summertime A^ gradients that exist near the surface in 



