344 transactions op section a. 



Department of Meteorology. 



Th3 following Papers and Report were read : — 



1. The Effect of the Labrador Current upon the Surface Temperature of the 

 North Atlantic ; and of the latter upon Air Temperature and Barometric 

 Pressure over the British Islands. By Commander M. W. C. Hep- 

 worth, C.B., R.N.R. 



In a paper contributed to this Association by myself, in 1908, on 'A Com- 

 parison of the Changes in the Temperature of the Waters of the North Atlantic, 

 and the Strength of the Trade Winds,' it was pointed out that evidence was not 

 wanting to prove that deviations from the normal in the average distribution of 

 surface temperature in the North Atlantic, during a series of months, are related, 

 through the agency of the Gulf Stream, to departures from the average strength 

 of the Trade Winds of the North and South Atlantic in the corresponding series 

 of months of the previous year; notwithstanding the many causes affecting the 

 temperature of the surface water, which tend to mask the appearance of such a 

 connection. 



The purpose of the present paper is to show by diagrams the effect of the 

 Labrador Current, one of the most potential of the causes referred to, in modify- 

 ing the Gulf Stream influence in the North Atlantic. 



During the five years, 1903-07, increased activity of this current, evinced by 

 an increase of ice in the North- Western Atlantic, was generally followed by a 

 decline in the surface temperature of a part of the ocean represented by a zone 

 between Florida Strait and Valencia. 



Moreover, from a comparison of the surface temperature in that zone with 

 air temperature and barometrical pressure at three stations in these Islands — 

 Valencia, Sumburgh Head, and North Shields — it appears that a decline in sea 

 temperature is frequently associated with a corresponding decline in air tempera- 

 ture at the stations named ; and, to some extent, with an increase of pressure also, 

 and vice versd. 



As regards ice frequency it should be understood from the outset that it is 

 the cold ice- bearing current, not the ice it brings, that lowers the surface tem- 

 perature of the ocean. 



As best illustrating the correlations referred to above, the years 1903 and 

 1906 may be taken. In 1903 the abnormal quantity of ice brought south was 

 associated with an almost persistent defect in sea temperature from May to 

 December ; a corresponding defect in air temperature, and, partially, an increase 

 in pressure. 



In 1906 the association of ice frequency with sea temperature and air tem- 

 perature at the three stations was no less marked. With the failing activity of 

 the Labrador Current in September and October, shown by declining ice fre- 

 quency, sea temperature rose ; and air temperature at the three stations, rising 

 in August, remained about the normal during those months. The increase and 

 diminution of pressure corresponding to the fall and rise of air temperature 

 could also be traced except in May and September. In the latter month, how- 

 ever, an anti-cyclone became the dominating factor. 



This year (1911) the quantity of ice increased rapidly from January to April 

 and decreased as rapidly after May. The surface temperature of the North 

 Atlantic, mainly in defect until April has been above the average since that 

 month. Air temperature somewhat above the normal at the three stations in 

 January and February declined in March, recovered in April, and has since been 

 above the normal, considerably above in May, and since June. 



2. The Amount and Vertical Distribution of Water Vapour on Clear Days. 

 By Professor W. J. Humphreys. 



It is of especial importance to anyone using a bolometer, or a pyrheliometer, 

 to know the approximate amount of water-vapour through which the radiation 

 reaching his instrument has passed. 



