gQ INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 



Total amount of all clouds (N). — In coding total amount of clouds 

 for the radio message, use the code figure (see table below) which 

 corresponds to the entry in the column for total amount of cloud on 

 Form 1210A; instructions for this entry appear on page 52. 



Symbol N — Total amount of all clouds 

 [Ktgardless of kinJ of cloucis] 



Code 

 figures 



Proportion of sky covered (in tenths) 



0. 



Less than 0.1. 



1. 



0.2 to 0.3 



0.4 to 0.6. 



0.7 to OS. 



0.9. 



More than 0.9 but with openings. 



Sky completely covered with clouds. 



Sky obscured by fog, duststorm, or other phenomenon. 



Code figure is to be used onl}' when the sky is completely free 

 from clouds. 



Code figure 8 is to be used only when the sky is completely covered 

 Avitli cloucis, so that no blue sky is visible. 



Code figure 9 should be reported only if the sky is invisible, owing 

 to fog. 



Amount of loicer clouds (Nh). — The total amount of lower clouds 

 is coded according to the scale and table used in reporting the total 

 amount of all clouds (N). 



Temperature difference hetween air and water (Td). — This quan- 

 tity is the decisive factor in the stratification of temperature and 

 liumidity in the lower layers of the atmosphere over the sea, and 

 hence, to a large degree, for the state of the weather and the visi- 

 bility. Since the difference between air and sea temperatures rarely 

 amounts to more than 10° F. over the open ocean, the utmost care 

 must, therefore, be taken to obtain accurate values of these quantities, 

 from which '"T,," is calculated. This is especially important when 

 the air and sea have nearly the same temperature. 



The table below gives the code numbers to be used in reporting 

 various values of "Td." 



Symbol Td — Temperature difference {air aud vatvr) 

 [DilTerence between temperature of sir and temperature of water at or near surfaccl 



