72 MANUAL OF MARINE METEOROLOGICAL OBSERVATIONS 



guides in estimating the height of clouds. Some indication of the height of 

 the clouds may be obtained from the detail with which the small indentations 

 on the bottom surface can be observed. At night it may be possible to use a 

 ship's searchlight to observe the cloud base, 



8220. There is no reliable way to determine exact cloud height by 

 estimation. However, when an observer is required to give his best esti- 

 mate without the aid of cloud measuring devices, he may resort to one or 

 more methods mentioned in J8201. For clouds caused by convection, such 

 as cumulus, and stratocumulus during high winds, the temperature and dew- 

 point formula may be used to obtain an indication of the level where conden- 

 sation takes place, 



8230, The approximate cloud height formula is: Height of clouds = 

 (temperature-dew point) x 396 feet. Air temperature and dew point are in de- 

 grees Celsius, For example, when the air temperature is 14.6°C and the 

 dew point is 9A°C, the difference of 5.2 multiplied by the constant gives the 

 approximate height of the convective cloud base, e,g., 5,2 x 396 = 2,000 

 (to the nearest thousand feet), 



8300, CODING AND ENTRIES OF CLOUD DATA 

 ON FORM 615-5 



8310. TOTAL CLOUD AMOUNT (N). Select the approximate code figure 

 from Code Table 3 corresponding to the total amount of sky covered by all 

 types of clouds, and enter the figure in column 7 of Form 615-5, A few 

 clouds or fragments of clouds are entered as "l," If the sky is completely 

 covered (overcast), N is entered as 8; however, if a few patches of blue sky 

 are visible, N is entered as 7. 



8320, FRACTION OF THE CELESTIAL DOME COVERED Kf SPECIFIED 

 Cl or Cm cloud - (Nh). Select the code figure from Code Table 3 cor- 

 responding to the amount of sky covered by the type or types of cloud reported 

 by Cl (not necessarily the amount of allC]_, clouds present), or by Cm clouds 

 when no C^ clouds are present (see J8340 and 8350), Code figure "O" is 

 entered for Nj^ when there are no Cl or Cm clouds present. Less than one- 

 eighth but more than none (i,e., "fragments") is coded as 1, "Overcast but 

 with openings" (less than eight-eighths but more than seven- eighths) is 

 coded as 7, Code figure 9 is used to report "Sky obscured by fog, rain, snow, 

 smoke or other phenomena or obstruction except clouds," 



19. 



8321. The coded valujs for Nj^ is entered on WB Form 615-5 in column 



