l-'Ki] McEici II : Ili/(Jnt(jrapliic Obscrrntions (if Scripps liisliiulion 271 



3. Diurnal Variation 



In the same regiou (eight miles west of the Coronado Islands) the 

 diurnal range in surface tempei-ature is about 1?0 C. The minimum 

 temperature occurs between 1 and 2 in the morning and the maximum 

 between 5 and 7 in the afternoon. Between 10 and 11 in the morning 

 and 10 and 11 at night the temperature is approximately the same as 

 the average for a twenty-four hour interval. The maximum occurs 

 about sixteen hours after the preceding minimum and about eight 

 hours before the following minimum. 



An empirical law of diurnal variation in surface temperature based 

 on a large number of observations may be used for correcting a tem- 

 perature observed at any hour approximately to its value correspond- 

 ing to any other hour. For example, adding to an observed temper- 

 ature the correction entered in the following table gives its most prob- 

 able value at 10 a.m. 



TABLE I 



corkections to surface temperature observations to give their most 

 Probable Values at 10 a.m. 



Time of observation 



A.M. P.M. 



0-3 3-6 6-9 9-12 



Correction -|-0?4.5 -|-0?40 -F0?.30 0?00 



Diurnal variation decreases in magnitude as the depth increases; 

 and at depths exceeding twenty-five meters it is not indicated at all 

 by our data. Furthermore, the observations we have made do not 

 justify computing a table of corrections for any level but the surface. 



While a small diurnal variation (about 0.05"/o„) in surface salinity 

 is indicated by our data, it is apparently more complicated than that 

 of the temperature, and our observations are not adapted to deter- 

 mining its law. 



