OCEAN AND SEA-LEVEL PRESSURES 



NOTES 



The problem of obtaining reliable meteorological data over the oceans 

 of the earth is a difficult one, and yet such data are highly important for 

 studying world-wide weather conditions. Aside from widely separated 

 island stations, the observations on ships present the only available data. 



In order to obtain monthly and annual means of such observations it 

 has been customary to average the observations taken within certain limits, 

 as for example within each 5-degree square of latitude and longitude. 

 This method requires a great many observations for even approximate 

 accuracy where the mean is supposed to apply to the center of the square, 

 and the mean may even then be in error, owing to the observations being 

 clustered in one portion of the square. A better method is to estimate 

 values between isobars from daily synoptic charts at the crossing of lines 

 of latitude and longitude, which thus remain fixed points on the map. 



The Japanese Imperial Observatory publishes daily charts of the North 

 Pacific, and the British Meteorological Office publishes maps of the North 

 Atlantic. These maps were supplemented by maps prepared by the Marine 

 Division of the United States Weather Bureau and by Norwegian daily 

 weather maps. These maps combined furnished excellent material for daily 

 estimates of pressure at fixed points on the oceans. 



After consultation with Dr. G. C. Simpson and Dr. C. G. Abbot, it 

 was decided that such readings for the 10 years 1921 to 1930 would be 

 valuable material to accompany the readings from land stations to be 

 published in World Weather Records. A grant was made by the Secretary 

 of the Smithsonian Institution from the Roebling Fund for this purpose, 

 and Jerome Namias was employed to make readings. A desk and the use 

 of the charts and maps at the office of the United States Weather Bureau 

 were kindly put at his disposal by the Chief of the Weather Bureau, and 

 Mr. Namias entered on his task with zeal and intelligence. Mr. McDonald, 

 Chief of the Marine Division, assisted in every way possible and thus 

 contributed to the success of the undertaking. The work was begun about 

 July 1, 1932, and ended in the latter part of December. 



At first it was decided to make readings at the intersection of each io° 

 line of latitude and longitude, but this was considered too great a task to 

 be accomplished in a reasonable time, and the work was confined to read- 

 ings at intersections of each 20 of longitude and io° of latitude, except 

 in the North Atlantic, where the readings were made somewhat closer. 



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