ATi.AN-1. DEEP-SEA EXPED. 1910. VOL. i| PHYSICAL OCEANOGRAPHY AND METEOROLOGY 



45 



Fig. o. \';uiatioiis in the vertical gradient ol temperature, tlie 

 teniperaliire decreasing downwards. 



This case is very common in the upper water-layers 

 especially in spring and summer. If r is constant in 



vertical direction 



(^J = °) 



the temperature obviously 



decreases. We may, however, presume that in many, or 

 probably most, cases with the supposed distribution of 

 temperature the velocity of the current decreases with the 

 depth, while the stability increases. Under these circum- 

 stances we must expect that r decreases, so that the pro- 

 ■> -^ 



duct • — becomes positive. Then the temperature 



5z Sz 



rises, remains constant or falls according as 



dz^ 



Sz Sz 



The temperature sinks when 



c'Z 



, which may 



probably happen if 



Su 



dZ 



ind '^ (or, practically, -— | :^ 0. 

 $z \ 2z-'l ' 



II. 



S2_ 



dz^ 



= 0. 



A vertical distribution of temperature with practically 

 constant variations with depth is often met with, especially 

 in intermediate water-layers. If r is constant no rise or 

 fall of temperature takes place. If r varies, the sign of 

 2r 



ez 



Tiie temperature rises if r decreases with depth, and vice 



versa. 



111. ^— ^ ^ 0. 



Such a distribution of temperature is found at the 

 upper limit of the deep water, and in summer also at 

 high levels below the heated surface-wafers. The analysis 

 lead to results opposite to those deduced above in 

 e.xample I. 



The conditions in quasi-discontinuity layers may be 

 worthy of a special mentioning. Fig. 7 demonstrates the 

 vertical distribution of temperature at two stations SW 

 of Ireland, viz. the ''Michael Sars" station 92 from July 

 23rd, 1910, and the "Thor" station 280 from September 

 3rd, 1906. The latter station was situated 10 naut. miles 

 to the south of the former. The distribution of tempera- 

 ture is represented by isotherms for every degree centi- 

 grade from the surface to 400 metres. Allowing for local 



TTI 

 



100 



200 



300 



^00 



23Yiri9IO 



3 IX: 1906 

 /7-52— 



16' 



iz' 



/?' 



//' 



//• 



-lors"- 



1034 



determines which way the temperature variations go. | 



ig. 7. Tile vertical distribution of teniperaliire at the "Michael Sars" 



station 91 (23. VII. 1910) and the "Thor" station 18(1 (3. IX. I'.HHi), 



Isotherms are drawn for each whole degree centigiade between tlie 



surface and 400 metres. 



