'54 



nature; 



[Dec. I 



888 



THE MOVEMENTS OF CYCLONIC AREAS} 



THE Meteorological Council having undertaken a 

 special discission of the weather over the North 

 Atlantic and adjacent continents for the thirteen months 

 ending with August 1883, the period agreed upon for the 

 international circumpolar observations, the preparation 

 , of the synoptic charts for the same area originally com- 

 menced by Captain Hoffmeyer, and since his death 

 carried on conjointly by the Institute at Copenhagen and 

 the Seewarte at Hamburg, was suspended for the time, 

 and a new series was started from September i, 18S3. 

 The charts are issued in quarterly volumes, and the 

 " Vierteljahrs-Wetter-Rundschau " is a carefully-prepared 

 summary of the principal meteorological features in each 

 volume, to which is added a critical examination of the 

 routes followed by sailing-ships from Europe to and from 

 America, and to and from the equator, with tables showing 

 the time occupied by each ship in sailing between certain 

 latitudes and longitudes. Passage tables have always been 

 a favourite study with mariners. Here there are hundreds 

 of voyages tabulated in order of date, so that the sailing 

 qualities of several ships are comparable from being under 

 the same conditions of weather, and the value of the 

 tables is therefore greatly enhanced. 



The novel point in the work, however, is the introduc- 

 tion by Dr. Koppen of a new system of discussing the 

 paths of storms. For some years past, meteorologists 

 have been slowly coming round to the opinion that anti- 

 C3'clonic areas exercise a very important influence on the 

 movements of cyclones ; indeed, it may be safely asserted 

 that the latter are almost entirely dependent upon the 

 former for every stage of their progress. But although 

 this is daily becoming more manifest, little has been done 

 in the way of improving our mode of tracking cyclones. 

 Ordinary track-charts represent the paths of storms 

 during fi.xed periods of a calendar month, as if those 

 of the early days were comparable with those of the end 

 of the month— that the tracks, in fact, were regulated by 

 time rather than by changing circumstances. A month's 

 storm-tracks are so numerous, the direction of translation 

 so varied, disturbances travelling in every conceivable 

 direction— north, south, east, and west — and twisting 

 round and round within a small radius, that to trace an 

 individual disturbance is a work of no small difficulty. 

 Even when the tangle is unravelled, there is nothing on 

 the chart to show why one storm travels direct across the 

 Atlantic to Europe in two or three days, another takes 

 ten or eleven days, while others dart off through Davis 

 Strait or by the east coast of Greenland to the Arctic 

 regions ; and the consequence is that we are left entirely 

 to theorizing to explain the different movements, and 

 theory has generally sought for the cause within the 

 cyclones themselves. The more we examine synchronous 

 weather-charts the more patent is it that cyclonic areas 

 are strictly limited in their movements, both in rate and 

 direction, by the surrounding conditions. 



In Nature, vol. xxxiii. p. 206, a diagram is given 

 ghowing the track of a low-pressure system and its 

 influencing anticyclone, the position of the lowest and of 

 the highest barometer being indicated for each day. In 

 the vohmie for 1880 of " Aus dem Archiv der Seewarte," 

 the daily positions' of the cyclonic centres for the first 

 three months of 1878 are given, but the movement of 

 maximum pressure is shown by a simple line without any 

 indication of the position every twenty-four hours. Dr. 

 Koppen has considerably improved on these plans. He 

 has before him the daily charts for several weeks, and finds 

 that for a number of consecutive days there is a general 

 resemblance in the distribution of high and low pressure 



' " Vierteljahrs-Wetter-Rundschau an der Hr.nd der taglichen synoptischen 

 Wetterkarten fiir den Nordatlantischen Ocean des D.anischen Meleo'O- 

 iqgischen Instituts und der Deutschen Seewarte." Parts i to 5, September 

 1S83 to November 18P4, with 41 Chans. (Berlin : Mittler und Sohn, 

 1887-3?.) 



areas, the former almost stationary, the latter travelling 

 along on the edges of the anticyclones. He selects the 

 ruling type for the whole area of the charts, and then 

 proceeds to represent the period of the type on one 

 chart, the number of such periods in the twelve months 

 ending with August 1884 being fifty-seven, ranging from 

 three to eleven days each. The movements of the 

 cyclones during the type are represented by lines joining 

 the ascertained jpositions each day, and by a simple 

 arrangement the lowest pressure and the force of the 

 wind are represented daily. The anticyclones are treated 

 differently, they are considered as practically stationary,, 

 and the isobar of 765 mm. (30' 12 inches) be ng found on the 

 charts every day, it has been adopted as the representa- 

 tive of the high-pressure systems. This isobar for the 

 several days of the type produces a mean line which 

 shows the average position of the anticyclone during the 

 period. The maximum barometric values are shown near 

 the centre, and also the direction in which the highest 

 pressures moved, as in the volume already alluded to. 



An examination of the results as shown by this method 

 indicate? that the question of storm tracking has been 

 greatly simplified. Instead of twelve monthly charts full 

 of tangled curves exhausting our patience to unravel them, 

 we have about five for each month, the paths of disturb- 

 ances during the prevalence of a type not varying greatly^ 

 and individual cases are followed without difficulty. The 

 question of expense in lithographing the charts has ap-^ 

 parently compelled Dr. Koppen to represent two, and 

 even three, types on one chart, which tends to confusion ; 

 and if more of this kind of work is to be done, it will be 

 well to strain a point to give each period by itself, so as 

 not to perplex those who only occasionally deal with such 

 charts. There are, however, several single periods to 

 which a chart has been devoted, and a study of these only 

 will suffice to convince us that an advance in the right 

 direction has been made. Take the sixth and seventh 

 charts representing the conditions between October 26 

 and November i, and November 2 to 10, 1883, and the 

 importance of the work is at once apparent. In the 

 former the permanent anticyclone over the ocean is well 

 south, while the European anticyclone covers all but the 

 most northern parts of Scandinavia and Russia. The 

 cyclones follow a well-marked path from America 

 to Iceland and the White Sea. In the second case the 

 Atlantic anticyclone is further north, and the European 

 area has moved away to the eastward, and in keeping with 

 these changes, the disturbances have also modified their 

 directions. Speaking very generally, storm areas run 

 parallel with the edge of the anticyclone. According to 

 the position of the latter so do the cyclones advance, 

 recede, or stand still. We see that land does not seem to 

 offer any resistance to the advance of a storm area, the 

 changes of direction in mid-ocean being quite as frequent 

 as near the land. Tropical storms may either march due 

 north, curve round by the American coast, or proceed to 

 the western side of the Gulf of Mexico, and then cross the 

 American continent to the Atlantic ; but in each case we 

 t^.nd the position of the anticyclone to govern the course 

 followed. From a similar cause the rate of movement is 

 also affected, varying quite as much on the level surface 

 of the sea as in the midst of mountainous continents. In 

 the chart for March 30 to April ii, 1884, the anticyclones 

 over Europe, the Atlantic, Greenland, and America form 

 a barrier allowing no means of escape for the disturbance 

 which is seen to wind about from Davis Strait to the 

 coast of Ireland and back again to the neighbourhood of 

 its starting-point. The question of direction and rate,, 

 therefore, depends largely upon the position and stability 

 of the anticyclones ; and if we can in any way discover 

 the resisting power of the latter we should no doubt 

 greatly increase our ability to forecast changes. For the 

 purposes of storm-warnings, it seems to be quite as neces- 

 sary to know the conditions over Eastern as over Western 



