596 MONTHLY WEA
The 7-year variation in pressure is shown by curves 8 and 9, representing the Toronto and St. Louis series of observations. It has been found that the hases of the 7-year period in pressure are nearly sync L onous over very extensive regions embracing areas as large as the United States. St. Louis well illustrates the character of this fluctuation for the interior of the country. The Toronto series carries the variation back to 1840. Ob- servations at Providence estend the record back to 1832.
This record shows pressure niasima in 1835 and 1840 and minima in 1537 and 1844. A tendency for high pressure slightly to precede low ten1 erature, and vice versa, is
Curves 10 and 11 show fluctuations in tlie mean annual stage of the river at Cincinnati and Little Rock. The variations in the yearly amounts of preci itation oyer the
these river- w e readings. The regularit of the 7-year cycle in the%%tle Rock record is remarka i! le and it is not surprising that this cycle has been observed in tlie fluctu- ation of this river at Fort Smith, as stated above. The curves show that low temperatures are associated with eriods of maximum precipitation and high pressure. !he curves of the latter are inverted with reference to the curve of temperature. Records of high waters at Natchez, Miss., yield maxima aa follows: 1814, 1823, 1831, 183G, 1843, 1S49, and 185S,
and minima in 1519, 1S2S, 1834, 1539, 1845, and 1855.
The high stages of 1858-59 were general over the entire Mississippi watershed. At Cairo and St. Louis the 1858
sta e exceeded the 1859 stage. In the upper Mississippi Va fi ey, as shown by the record at Davenport and St. Louis,
a pronounced maximum stage occurred in lSG2 and a *
mmimum in 18G4, followed by a niasimum in 1867.
These fluctuations accord closely with those of temper- ature as shown by the Schott curve and with pressure as shown by the Toronto curve and the Providence obser- va tions.
clear from an inspection of t K e curves.
watershed above these stations are we1 f represented %y
A 7-YEAR PERIOD IN CROP YIELDS.
The yield of corn for the whole United States varies in a 7-year period. Masimum yields occurred about 1871,
1877, 1884, 1889, 1897, 1905, 1914, and 1920. These dates occurred at or shortly after the epochs of maximum precipitation. The importance from an economic point of viqw of cyclical relationship between weather and crops can not be overestimated. Far-reaching effects re- sulting from this close relationship can also be traced in a 7 or 8 year period in industrial and business actiyity.
THE 7-IEAR PERIOD IN OTHER REGION8 OF TIIE GLOBE.
The 7-year yeriod has been traced in European records of pressure. lhe dates of high and low winter pressure found by Maurer have been given above. The variations
based on yearly means according to the researches of the writer are: Maxima, 1746, 1753, 1760, 1767, 1774, 1779,
1787, 1796, 1803, 1808, 1513, 1821, 1826, 1834, 1841,
1850,1858,1863,1868,1874,1882,1S90,1898, 1905,1914.
The dates of minima are: 1742, 1750, 1757, 1764, 1771,
1777,1783,1791,1800,1806,1811,1817,1823,1829,1838,
1845,1853,1861,1865,1871,1878,1186,1894,1903,1910.
These epochs synchronize closely with tli-ose of the United States. On the other hand, the Iceland pressure varies oppositely, as follows: Maxinia, 1844, 1854, 1859, 1866,
1871, 1878, 1887, 1894, 1901, 1909, 1916; minima, 1847,
1857, 1863, 1868, 1874, 1883, 1890, 1898, 1004, 1913..
The temperature in Europe varies generally o posltf to that of the United States east of the Rocky J ountam.
THER REVIEW. OCTOBER, 1920
The records at Greenwich and Paris show maxima 1852,
1858, 1663, 1868, 1875, 1S84, 1893, 1899, 1905, 1912;
minima, 1854, 1860, 1865, 1571, 1879, 1888, 1895, 1902,
1909, 191 7. This opposition between the temperatures of the United States and Western Euro e is probably due to the periodical variation of the Icelan B pressure. m e n the Iceland low is strongly developed, the winds over the eastern United States have a strong northerly component, while those of western Europe show an increase in the southerly component of the winds. On the other hand, when the Iceland presHure is high there is an increased fre uency of cold, continental winds over western Europe
have an increased southerly component. The resultant, direction d the wind at Providence, R.I., from 1830 to 1876 has varied in an a proximately 7-year
These years correspond closely to vears of low tempera- ture and low Iceland pressure. The years of extreme southerly deviation are 1S34,1839-1840,1845,1853,1S60,
1865, and 1S70. The resultant direction of the wind at Portland, Me., has varied between extreme northerly points in 1S76, 1883, 1S91, and 1898, and estreme south-
wlii (3 e, at the same time, the winds over the United States
period. The years of extreme nort ?l erly deviation are
1831, 1837, 1843, 1847-1848, 1Y57, 1863, 1867, 1875.
about 21 or 32
A MECHANISM OF CLIMATIC CYCLES.
[Re\iew 9 reprinted from thc Meteorological Magazinr, Octohr, 10zO,5S:2oszoa.]
One of the main lines of research followed in the at- t.empt to forecast t,he eneral character of a season several
\n-ent>her c.ycles. The cycles which we have been asked at one time or another to accept vary in period indehitely, but t.he favoiites are t.he suns ot cycle of 11.2 years and
cycle, in spite of a sufficient solar beis, has proved $is- , its nieteorolo ical effects being always s m d appointin? and usualy debatable. ft is well deyelopecl ody where t,he response of climatic to solar conditions is of the simplest, as,. for example, on the west coast of Africa; where the rainfall, e. g., at Bathurst, shows three periodic- ities of 11 years, amplit,udeS 193 mm.; 3.2 years, ampli- tude 180 min., and 2.1 years, amplitude 102 mm., to- gether with a secular variation corres ondin to that observable in sun spots since 1S70. Even %ere the amlilitude of t,he short period nearly equals tllat of the sunspot cycle. On the other hand, the three ear period
cause-the solar prominence cycle-seems iiisu8cient. To meet this difficulty in the case of Java rainfall, C. Bra& has )ut fonvFrd in this memoir a resonance
there hypothesis.  Accordmg to this hypothesis, be a purely terrestrial cycle of cause and effect, whic completes itself and returns to its starting point in about
months or a year in a % vaiice has been the investigation of
a shorter one of a.pprodmatey 3 3 years. The suns ot
is often very obvious17 developed, and its o n? y ap arent
1 Csswell. Results of hleteorological Observations made at Provideme, R. I. Smith-
sonlsn Contrih. 443. 1882.
1 Batavin, K. Ms9. en Alefeor. OtW?r\3tOri~. Verh. No. 5. Atmogpheric variations of short and long diustion.in the Malay Arclupln&w, nnd the possilnlity to foreeast them, by C. Br:+ Bst~vm. 1919.
2 h e another review, 310. WEATHER R~v,.luly, 19?0,48:314-415.
a I. c., the ooeificlemt a in the formula R--R+a sin t .
k r o B E R , 195%. MONTHLY WEATHER REVIEW. 597
the same time as the solar prominence cycle. When t.his
happens, the latter fixes the period of the former and eatJy increases the range of its phenomena. The best
gown effect of "resonance" is the semidiurnal variation of ressure. fn the case of Java rainfall the chain of events is briefly aa follows: Pressure variat.ions at Batavia coincide with those a t Port. Darwin in Australia, but the latt.er have double the amplitude of the former. Consequently, re-
membering that we are dealing with the Southern Heniis- phere, high pressure increases the strength of the emt monsoon (November to April) and decreases that of the west monsoon (Ma to October). It happens that dur- ing the former hig E pressure causes low temperature and is self-sustaining, but during the latt,er high pressure causes high tem erature. This in t,he course of two gears enetrates to t. f l e upper. air and reduces t,he pressure h o w normal. Consequently tbere is a t.hree-yearl7 variation of pressure o a Lisaw-toothll type, tlie curve rising slowly for two years and then sinking rapidly for
one year. Note t,hat the changes from low to high, or mce versa, can take place only in the west nioiisooii a d
the period is thus limited to exactly three years.
It is obvious that a similar sequence of events must take place at many localities near the Equator where conditions are suitable. An esnmple is La os, Nigeria,
Although pressure data are lacking! we may infw t,list this is analogous to the c ~e of Batavia, t.he Salia.ra taking the place of northern Australia. A self-regulatin system of a different. type has been
ice la s a part. A weak Atltmtic circulation means ice
pressure to the east of Greenland and lowers it to tlie west, causing northerly mincls over Baffins Bay and
southerly winds at Icelaiicl, so increasing the strengt.h of the Atlantic circulation and reversing t,lie ice conclitions. The winter weather in western Euro e is known t.o be
su pose the latter to be affected to some est.ent, by t,he
seasons of the year. Hence there are indications of a
forced eriodicity of three years in the weat.her of
And here, it seems, we have the esplanation of why these periodicities so frequent,ly persist for a tinie, and
where there is a marked three-year rairifa f periodicit.)-.
described by W. 9 einardus in the n0rt.h Athnt.ic.' Here
at Pe9 c and and little off Newfoundland: this raises the
influenced by the strengt,h of the Gul P drift, and we iiia:~
so P ar prominence period, acting perhaps only at &ert.sin
western E ur0'0pe.~
4 Ann. IIydrogr Berlin 1wW p. 353. See further discussion of this and later con-
6 See MONTHLY WEATHER REVIEW, August, 1920,48:465-4ii. tributions in MON~HLY 1VvhATHk.R REVIEW, November. 191'1 46510-5E.
then break down. For the solar prominence period is not exactly three years, but a few mont,hs longer, so that it. will gradudy outstrip the terrestrial period. After aiding the latter for a few cycles it w i l l gradually come will die out, or perhaps skip at t,he wrong dates, when t,he This has hitherto been ascribed to a failure of the cycle, but, bearing in mind the new principle, it. may be possible in t,he future to forecast these vagaries. Rainfall forecasts based on the modifi- cations of the three-vear period are in fact dready being issued in Java, and there seems no reason why they should not be e uallv practicable in other tropical regions.-0. E. P. %moji'8.
to oppose it, the
EFFECTS OF HEAVY RAINFALL ON PANAMA-CANAL SLIDES.
-4mong the engineering surprises attending the con- struction and operation of the Panama Canal may be mentioned the effects of the heavy isthmian rainfall on the troublesome slides that developed in the banks of the canal as escavation work progressed. It was generally believed by engineers, as well as by the public, that these slides would be most active and troublesome during the season of heavy rainfall. As a matter of fact, the opposite proved to be the case. Prac- tically all of the estensive deep-peatecl troublesome slides displavecl greater activity in the dry season than during the rainy season. The esplanation offered by geologists was that the cohesiveness of the material in the canal banks is greatest when the material is saturated by the heavy rains, enabling it to stand up better than it does during the dry season, when it dries out, tending to lose its cohesiveness and crumble under the weight superim- posed upon it.
A type of superficial slide of small extent has hen more prevalent during the rainy season-loose surface.materia1 sliding into the canal under the influence of heavy rain- fall, but the mass of material involved has been too small to make the handling of these slides a serious problem. For example, the troublesome Lktmzchn dido pushed out across the canal channel during the construction period, with a slow, ponderous, glacierlike movement. This slicle has been intermittently active from the early construction days down to the present time, but generally more active in the dry season. It gradually spread until it involved an area of more than 50 acres.-H. G. C'or let hwa,i.te.