CHAPTER 11 



METEOROLOGICAL OBSERVATIONS 



11-1 GENERAL REMARKS.— As men- 

 tioned in chapter 1, the interaction of sea and 

 air is extremely important in the studies of 

 various oceanographic problems. Almost all 

 oceanographic observations must be accompa- 

 nied with simultaneous meteorological observa- 

 tions. Spaces for such observations are pro- 

 vided on oceanographic log sheets A, B, and E. 

 Codes and tables required to record these ob- 

 servations are included in part II of this manual, 

 and instructions for the proper use of these 

 tables and log sheets are given in chapter 14. 

 An oceanographic observer must be able to take 

 and record marine meteorological observations 

 that are called for by the various log sheets. 

 These codes are adapted from the new inter- 

 national code, b_\ the U. S. Weather Bureau, 

 for recording marine meteorological observa- 

 tions. 



11-2 TYPES OF OBSERVATIONS.— The 

 types of meteorological observations required 

 with the oceanographic log sheets include: 

 weather, cloud t.ype and amount, visibility, 

 wind wave (sea) and swell, wind direction and 

 speed, air and wet-bulb temperatures, relative 

 humidity, and barometric pressure. On certain 

 special surveys, other measurements are some- 

 times required. Often these are obtained with 

 special recording instruments. For example, 

 incoming solar radiation studies are made with 

 data recorded by the pyrheliometer. Also, 

 precise temperature measurements taken and 

 recorded simultaneously at different levels on 

 the ship are made with the temperature-lapse- 

 rate indicator. Such measurements are valu- 

 able in explaining varying conditions in the 

 upper layers of the ocean. The following infor- 

 mation has been extracted from the U. S. 

 Weather Bureau's Instructions for Recording 

 and Coding Marine Meteorological Observa- 

 tions in the New International Code, and they 

 are intended as guides. For more complete 

 instructions reference should be made to the 

 above manual, also the U. S. Weather Bureau's 

 Circular M, Instructions to Marine Meteoro- 



logical Observers and Circular S, Manual of 

 Cloud Forms and Codes for States of Sky. 



11-3 Weather. — Table 1 contains the code 

 used in indicating the state of the weather at 

 the time of observation. (See pt. II.) The 

 table is divided into 10 decades, each of which 

 contains 10 numbers. These decades corre- 

 spond to the 10 main types of weather. The 

 first digit of any number in the table indicates 

 the decade to which that particular number 

 belongs. After the observer lias selected the 

 decade which best applies to tlie prevailing 

 weather condition, he should pick out from that 

 particular decade the number which most cor- 

 rectly describes the weather at the time of 

 observation or during the hour preceding. 

 Neither when selecting the decade nor in the 

 determination of the complete number must 

 account be taken of weather phenomena which 

 occurred more than 1 hour preceding. 



11-4 Clouds. — The form of the significant 

 cloud layer should be recorded using the code 

 given in table 2. If the skj- is cloudless at the 

 time of observation, a dash should be entered. 

 If fragments of a cloud layer (i. e., covering less 

 than 1/10 of the sky) are observed under a 

 cloud layer covering 1/10 or more of the sky 

 witli bases below 8,000 feet, the fragments will 

 be disregarded and the code figure selected to 

 indicate amount of the next higher cloud type. 

 The height of the cloud is the distance from sea 

 level to the base of the cloud. The amount of 

 total cloud cover is indicated in tenths of sky 

 covered and is recorded using the code in 

 table 3. 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 

 recordeti as greater than 9/10 even though such 

 clouds are spread over the entire sky. 



11-5 Visibility. — Observations of visibility 

 should be made using the code in table 4. 

 Horizontal visibility is often very useful as an 

 indicator of the condition of the lower atmos- 

 phere, which in turn lias effects on the sea 

 surface. As a general rule, the visibility is good 



110 



H. O. 607 



