112 MR ROBERT C. MOBSMAN ON THE METEOROLOGY OF 



felt at Snow Hill, where the continental effect is most pronounced ; the South Orkneys 

 also come well within the sphere of this influence. The lowest isotherm, viz. that of 

 — 10°, is indicated to the east of Graham's Land in about 66° S., the relative mildness 

 od the same parallel 10 degrees to the west on the Pacific side being a noticeable feature. 

 The thermal gradient continues very steep in sub-Antarctic and Antarctic regions. 



The cloudiest zone is indicated in from 57° to 60° S. by the isoneph of 80, the 

 lowest values being 50 over the coast of Graham's Land, and 60 in Tierra del Fuego. 



On the Pacific side of the Straits of Magellan rainfall is at its annual minimum. 



In August, cyclonic conditions prevail very generally, pressure having fallen except 

 over the extreme south of South America. The fall is greatest — about a tenth of an 

 inch — over Graham's Land and to the west. The isobaric chart shows a well-marked 

 cyclonic area over Graham's Land, and steep gradients to the south and west of Cape 

 Horn. Associated with this is a decided increase in storm frequency. North-east 

 gales blow with great persistence and strength to the south of the South Shetlands. A 

 small area of relatively high pressure is shown in the Bellingshausen Sea, and in this 

 region, west of about 85° W. and south of 65° S., winds from all quarters blow with 

 average strength, thus showing no indication of steep gradients. Temperature south of 

 60° S. has risen decidedly, but in strictly oceanic situations in lower latitudes the rise is 

 small. The isotherms present much the same aspect as in July, but very clearly 

 indicate the greater rise of temperature in the south. 



Cloud shows a marked increase in high southern latitudes, especially to the east of 

 Graham's Land, this being explained by the greater condensation accompanying the 

 increased prevalence and strength of warm winds from lower latitudes. In Tierra del 

 Fuego, in places removed from oceanic influence, the least amount of cloud for the year 

 is recorded. 



In September, the first spring month of the southern hemisphere, the changes in 

 pressure are somewhat irregular. There is a noticeable fall at the South Orkneys, and 

 a slight increase, extending from 55° to 65° S., between the meridians of 67° and 55° W. 

 The most interesting feature of the isobaric chart is the total absence of any indication 

 of the Antarctic high, there being two large low-pressure areas, one over the Weddell 

 Sea, the other to the west of and partially covering Graham's Land. Gradients over 

 the larger part of the area south of 50° S. are comparatively uniform, except in the 

 Cape Horn region, where they are steep. 



Temperature has risen everywhere. The rise is greatest south of 60° S., amounting 

 to 5° or 6°, but elsewhere (with the exception of Ushuaia and Sandy Point) it does not 

 reach half this amount. The isotherms north of from 63° S. on the 80th meridian of 

 W. long, to 57° S. on the 40th meridian have opened out considerably, thereby show- 

 ing that the continental influence of the frozen sea is becoming restricted. The 

 thermal gradient is still very steep between the Pacific and the Weddell Sea side of 

 Graham's Land. 



Cloud shows a comparatively uniform distribution, but has increased in the far 



