CHAPTER B 



METEOROLOGICAL, SEA AND SWELL, AND SPECIAL OBSERVATIONS 



B-1 General. — The interaction of sea and air 



is extremely important in the studies of various 

 oceanographic problems. Almost all oceano- 

 graphic observations must be accompanied with 

 simultaneous meteorological and sea surface 

 observations. Spaces for such obsen'ations 

 usually are provided on oceanographic log 

 slieets, and codes and tables to assist in record- 

 ing these observations are included in this 

 chapter. 



An oceanographic observer must be able to 

 take and record marine meteorological observa- 

 tions that are called for by the \'arious log 

 sheets. The tables and methods used in this chap- 

 ter are adapted from manuals used by the U.S. 

 Weather Bureau for recording marine meteor- 

 ological observations. 



B-2 Types of Meteorological and Sea and 

 Swell Observations. — The types of meteoro- 

 logical and sea and swell observations required 

 with the oceanograjDhic log slieets include: 

 Weather, cloud type and amount, visibility, 

 wind speed and direction, dry- and wet-bulb 

 air temperatures, barometric pressure, and wind 

 wave (sea) and swell. On certain surveys, other 

 meteorological and/or sea surface measure- 

 ments are required, and these are obtained with 

 special instruments. For example, solar radia- 

 tion studies are made with data recorded by 

 the pyrheliometer. Also, precise temperature 

 measurements taken and recorded simultane- 

 ously at different levels on the ship are made 

 with a temperature-laiDse-rate indicator. Such 

 measurements are valuable in explaining vary- 

 ing conditions in the upper layers of the ocean. 

 Much of the information that follows has been 

 extracted from the U.S. Weather Bureau's 

 Manual of Marine Meteorological Observations, 

 Circular M, and Manual of Cloud Forms and 

 Codes for States of tlie Sky, Circular S. For 

 more complete instructions, reference should be 

 made to the above manuals. 



B-3 Weather. — Table B-1 is used to indicate 

 and record on the A-Sheet (see ch. E) the state 

 of the weather at the time of observation. The 



100 descriptive terms include most weather 

 phenomena that will be encountered. Code fig- 

 ures shmdd not he used to record weather on 

 the A-Sheet. If a code figure is used to describe 

 a weather condition in reporting or recording 

 any observation, the code designation must be 

 plainly indicated on all log sheets and rigor- 

 ously adhered to; otherwise, the data are of no 

 value. Terms selected should describe the 

 weather at the time of observation or during 

 the preceding hour. Neither when selecting the 

 general description nor in determining the com- 

 plete description of the weather must account 

 be taken of weather phenomena which occurred 

 more than 1 hour preceding the observation 

 time. 



B-4 Clouds. — The type of the significant 

 cloud layer should be recorded on the A-Sheet 

 using the descriptions given in table B-2 and 

 figures B-1 through B-26. If fragments of a 

 cloud layer (i.e., covering less than Vjq of the 

 sky) are observed under a cloud layer covering 

 i/io or more of the sky with bases below 8000 

 feet, the fragments will be disregarded. The 

 height of the cloud is the distance from sea 

 level to the base of the cloud. The amount of 

 total cloud cover should be recorded on the 

 form in tenths of sky covered. In the thin types 

 of mackerel sky there are almost always gaps or 

 spaces through which clear sky can be seen. 

 When these conditions prevail, the amount of 

 cloud should never be recorded as greater than 

 %o ^ven though such clouds are spread over 

 the entire sky. 



B-5 Visibility. — Horizontal visibility often 

 is very useful as an indicator of the condition of 

 the lower atmosphere, which in turn has effects 

 on the sea surface. As a general rule, the visi- 

 bility is good when the air temperature is lower 

 than the sea temperature and very poor when 

 higher. The reason for this is that, in the former 

 condition, the lowest layers of the atmosphere 

 are being heated by the sea. This tends to make 

 the atmosphere thermally unstable and favors 



B-1 



