128 



NATURE 



[December 6, 1900 



ON SOLAR CHANGES OF TEMPERATURE 

 AND VARIATIONS IN RAINFALL IN THE 

 REGION SURROUNDING TfiE INDIAN 

 OCEAN> 



II. 



Indian Rainfall. S.W. Monsoon, 1877-1884 



IT will be clear from what has been stated that our pbject 

 in studying rainfall was to endeavour to ascertain 

 if the + and - temperature pulses in the sun were 

 echoed by + and - pulses of rainfall. The Indian rain- 

 fall was taken first, not only because in the tropics we 

 may expect the phenomena to be the simplest, but be- 

 cause the regularity of the Indian rains had broken 

 down precisely when the widened line observations 

 showed a most remarkable departure from the normal. 



It was also important for us to deal with the indi- 

 vidual observations as far as possible, because it was of 

 the essence of the inquiry to trace the individual pulses 

 if they were found. Hence the S.W. monsoon was, in 

 the first instance, considered by itself, because although 

 Eliot holds that the winter rains (N.E. monsoon) are due 

 to moisture brought by an upper S W. current,^ their 

 incidence is very different and their inclusion might mask 

 the events it was most important to study. 



The first investigation undertaken was the study of 

 the rainfall tables published by the Meteorological De- 

 partment of the Government of India. These were 

 brought together by Blandford down to the year 1886.^ 

 As the widened line observations were not begun at 

 Kensington till 1879, the discussion was limited in the 

 first instance to the period 1877-1886 inclusive, em- 

 bracing the following changes in solar temperature, oc- 

 curring, as will be seen, between two conditions of mean 

 solar temperature : — 



Bearing in mind that the intensity of the -f pulse may 

 in some measure be determined by the solar disturb- 

 ances, which for the present are registered by spotted 

 area, it is important to point out that the preceding 

 maximum in 1870 was remarkable for obvious indications 

 of great solar activity.* 



It soon became evident that in many parts of India 

 the -f and — conditions of solar temperature were 

 accompanied by -|- and - pulses producing pressure 

 changes and heavy rains in the Indian Ocean and the 

 J surrounding land. These occurred generally in the first 

 year following the mean condition, that is, in 1877-8 and 

 1882-3, dates approximating to, but followed by, the 

 minimum and maximum periods of sun-spots. 



Meldrum, as far back as 1881,^ referred to " the extreme 



1 By Sir Norman Lockyer, K.C.B., F.R.S.. and W. J. S. Lockyer, M.A. 

 (Camb.), Ph.D. (Gott.) Paper read before the Royal Society on 

 November 22. Continued from p. 109. 



2 Report, 1877, p. 125. 



3 " Indian Meteorological Memoirs," vol. iii. 



4_ " The year 1870 was characterised by an exuberance of solar energy, 

 which is without parallel since the beginning of systematic observations 

 (i.e. since 1825). The number of observed groups far exceeds that of any 

 previous year, and it appears also from a cursory comparison with the 

 maximum year's observations, as recorded by Hofrath Schwabe, that the 

 magnitude of the different groups, as well as the average amount of spotted 

 surface during any period of the year, is unprecedented." {Monthly Notices, 

 vol xxxi. p. 79, Warren de la Rue, B. Stewart, B. Loewy.) 



The table which the authors of this paper give shows that during the 

 year, although observ.itions of the sun were made on 213 days out of the 

 364, there was no day without spots recorded. In fact, during the whole 

 year no less than 403 new groups of spots were noted, thus showing us that 

 on I he average there was more than one new group per diem. 



The authors further remark, " A very remarkable feature of the groups 

 observed during the year appears to be their extraordinary lifetime. . . an 

 exceedingly large number of groups completed 3, 4, and even more revolu- 

 tions before finally collapsing." 



5 " On the Relations of Weather to Mortality, and on the Climatic Effect 

 of Forests." 



oscillations of weather changes in different places, at the 

 turning-points of the curves representing the increase 

 and decrease of solar activity." 



It was especially in regions such as Malabar and the 

 Konkan when the monsoon strikes the west coast of 

 India, that the sharpness and individuality of these 

 pulses was the most obvious. 



Orie method of study employed has depended upon 

 Cl\ambers's view {Indian Meteorological Memoii^s., vol. iv. 

 Part 5, p. 271) that the S.W. monsoon depends upon the 

 oscillations of the equatorial belt of low pressure up to 

 31° N. lat. at the summer solstice. The months of rain- 

 receipt on the upward and downward swing will therefore 

 depend on the latitude, and these months alone have 

 been considered. 



We began by taking elevated stations in high and low 

 latitudes. 



J , ^ The 1881 pulse (in July) was the heaviest recorded 

 T t I ° N ' '<^'^^ inches) save one in 1882 ; the rainfall was 



rn ( f f nearly as high. 

 1 1,500 leet j .pjjg p^jgg ^gj^ j^ jg^g ^^g jj^g highest of all. 



Murree \ The 1881 pulse (Aug.) is high, but is followed by 

 Lat. 33° N. >- a higher next year. 

 6344 feet J The 1878 pulse (Aug.) is highest of all. 



^Fi*^'^^ 1 Taking the fall in July and Aug. The 1881 pulse 

 iMiya I occurs in 1882, and is highest. Next comes the 

 Lat. 7 N. pulse ini 878. 

 6150 feet J *^ 



It must also be stated that if we take the sun-spot 

 maximum, including the period we have chiefly dis- 

 cussed (1877- 1 886), as normal, it is found that there 

 are variations in rainfall accompanying the preceding 

 and succeeding maxima of 1870 and 1893. This varia- 

 tion indicates the existence of a higher law, but there 

 has not been time to discuss them thoroughly enough 

 to justify any definite statements about them. 



The Rainfall of " Whole India." 

 The next step was to work on a longer base, and for 

 this purpose Eliot's whole India table of rainfall, 1875- 

 1896 (Nature, vol. Ivi. p. 110), embracing both the 

 S.W. and N.E. monsoons, being at our disposal, was 

 studied. 



It was anticipated that such a table, built up of means 

 observed over such a large area and during both mon-i 

 soons, would more or less conceal the meaning of the 

 separate pulses observed in separate localities ; this we 

 found to be the case. But, nevertheless, the table helped 

 us greatly, because it included the summation of results 

 9 years later than those included in Blandford's masterly 

 memoir. Predominant pulses were found in 1889 and 

 1893, following those °f 1877-8 and 1882-3. So that it 

 enabled us to follow the working of the same law through 

 another sun-spot cycle, the law, that is, of the mean solar 

 temperature being followed by a pulse of rainfall. 



Mean sun Rain pulse 



1876 - 1878 



1881 + 1882 



1886-7 - 1889 ■ 



1892 -f- 1893 



The main feature of this table is the proof of a tremen- 

 dous excess of rainfall in 1893— by ^^.r the greatest excess 

 of all (percentage variation, -h 22). This was far greater 

 than the excess in 1882. 



The next remarkable excess occurs in 1878 (percentage 

 variation, -I- 15). 



The pulses in the period stand as follows : — 



Percentage Heat 

 pulse 



Min. 1878 

 Max. 1882 



Min. i{ 



variation 

 + 15 



+ 6 

 + 6 



Years after 

 rise of 



Years after 

 rise of 

 iron 

 lines. 



NO. 1623, VOL. 63] 



— Max. 1S93 +22 -I 



unknown 

 lines. 



