212 PRESSURE, WINDS AND WEATHER. 



only at 8 a.m., 2 P.M. and 8 p.m., these hours fixed the times for which maps are possible. 

 The obfservations at corresponding times at Cape Evans and Cape Adare were extracted from 

 the registers and the data for all three places were entered on to outline maps. Whenever 

 sledging parties were making observations their results have also been used. As a rule 

 observations during sledging journeys are taken at irregular hours, curves of temperature and 

 barometer were therefore plotted from the observations and the values at the exact time required 

 read off from them. The wind at the nearest time of observations has been used. During the gi'eater 

 part of the year, however, there are only the observations from the three base stations available, and 

 It appeared at first hopeless to construct isobars over such a large area from such scanty 

 information, especially as the wind directions at both Cape Adare and Cape Evans are so 

 largely afiacted by the configuration of the surrounding land masses. But after attempting 

 many maps and getting an idea of the general pressure distribution, it was found possible to 

 draw isobars to fit the pressure values and to arrange them so that the gradient was in 

 fair agreement with the wind direction and wind force at all three stations. No claim is 

 made for the accuracy of the charts in detail, and in some cases other arrangements of 

 isobars would no doubt fit the observations equally well ; still the whole series of charts 

 must give a fairly accurate idea of the pressure distribution in the Ross Sea area. In Volume II 

 two maps for each day are shown: those for 8 a.m. and 8 p.m. Framhoim time, which 

 corresponds to 6 a.m. and 6 p.m. Cape Adare time and 7 a.m. and 7 p.m. 180 meridian 

 time used at Cape Evans.* 



We will first examine the maps during periods when large pressure waves are showni 

 on the plates in order to see if they are connected with moving pressure systems. The 

 first example will be the large wave, the trough of which passed Framheim on 24th May, 

 1911. Plate 5 should therefore be unfolded and the maps opened at May 24th. 



If this deep pressure trough were due to a cyclone we should expect the central area 

 of the depression to pass over Framheim between 8 a.m. and 8 p.m. The map for 8 a.m. 

 of the 24th show.s high pressure over Cape Adare and low pressure to the south-east of Framheim. 

 The wind at Framheim is much too light for the central area of a deep cyclone to be just 

 about to pass over the station. At 8 p.m., when the centre of the cyclone should be passing 

 Cape Evans, we find that that station is still under the influence of the high pressure area 

 near to Cape Adare. There are no indications of a cyclone on this map, as it is impossible 

 to dignify the low pressure area near Framheim by such a name. 



During the next twelve hours the pressure trough has passed beyond Cape Adare and 

 the pressure is rising over the whole area. A comparison of the 8 p.m. map for the 24th 

 with that for 8 a.m. on the 25th makes it quite clear that no cyclone passed Cape Adare 

 at midnight, for in spite of the large absolute pressure changes at all stations, the relative 

 pressure is little different and the pressure distribution is practically unchanged. Throughout 

 the whole period that the low pressure wave was passing over the area, from 8 a.m. on the 

 23rd to 8 p.m. on the 25th, Cape Adare has been under anticyclonic conditions with calm 

 or light wind and only a little cloud. 



We wiU pass on to the consideration of the passage of the crest of the same wave 

 which arrived at Framheim at midday on the 27th, leaving for future consideration the 

 blizzard at Cape Evans on the afternoon of the 25th. 



The hours for which the wind directions are shown on the plates for Cape Evans and Cape Adare do not 

 happen to be those for which the maps are shown. Generally this leads to no confusion when comparing the 

 maps and the plates, but sometimes the wind show on the map appears not to agree with the %^ind shown on 

 the plate. This is because at the time the wind was changing du-ection and the direction shown on the map 

 was recorded during the interval between the wind observation entered on the plates. 



