Surface Signs of the Biennial Atmospheric Pulse

MONTHLY WEATHER REVIEW 549

SURFACE SIGNS OF THE BIENNIAL ATMOSPHERIC PULSE

H. E. LANDSBERG, J. M. MITCHELL, JR. US. Weather Bureau, Washmg!on, D.C. and H. L. CRUTCHER, F. T. QUINLAN

National Weather Records Center, US. Weather Bureau, Asheville, N.C. [Manuscript received July 1, 19631 ABSTRACT Further e\ idelice is prcseiited for the prcsericc of a persistent pcriodicity somewhat in excess of 2 years duration. Its existence can be shown in the surface temperature at widely separated stations along two ineridiaiis from Norway to South Africa and from Canada to Cape Horn. Time series analysis by means of a narrow band-pass filter indicates phase relations among the stations, the most iinportant of theae being that the intertropical rcgions appear to be mutually in phase and that the higher-latitude statioiis are out of phase with the tropical stations. In the Northern Hemisphere, at extratropical stations, the amplitudes of thc pulse arc largest when the pulsc extremes coincide with the winter months.

1. INTRODUCTION found in surface data. This was first discorcrcci by Clayton [6] in the 1880s. We noted it again in our Search for rhythmical phcnoniena in the atmosphere detailed analysis of the carefully scrutinized IVoocls tock, has fallen into sonic state of disrepute among metcorolo- Md., data [ll]. In the temperature series, covering the gists during the past two clecades. This has been a natural interval from 1570 to 1956, the 2.1 ycar pulsc stood out reaction to the niany spurious cycles which were claimed among all others in the power spectrum. As a matter of to exist in atmospheric phenomena. Some of these continuity part of this spcctrum is shown again in figwe 1. rhythms appeared and then vanished again and without -4 fairly exhaustive survey of the literature [IO] revealed reasonable physical explanations they mere rarely more that periods from 2 to 2.5 yr. have been found b;- a score than some statistical will-o’-the-wisp. Especially, the of investigators in a variety of series of surface obserrations. search for solar cycles was disappointing in observations including temperaturc, precipitation, and pressure data. from the lower atmosphere although their existence in In most cases this was only one cycle among others. ionospheric data could hardly be disputed. Although its statistical significance appeared dlsecured. It was, therefore, quite intriguing when a remarkable none of the earlier investigators attcnipted to at tribute cyclical phenoinenon was discovered in 1961 in the wind causes to it. A connection to the Southern Oscillation and temperature field of the equatorial stratosphere already suggested the worldwide aspect of the phenoinenon [13, 14, 17, 181. The period of these phenomena was in But it is evidently also present in polar reg tlie range Iroiii 23 to 29 months. The observations [4]. spite of the fact that this pulse is deeply en sufficed only to trace this back €or about three full oscil- In in general atmospheric “noise” in the surface data it lations but evidence for a similar fluctuation reaching seemed worthwhile to pursue it further in such inaterial. into the moderate and higher latitudes made it appear One could not expect to get such well-dcvclopcd and that this seemed indeed to be a widespread feature of the high-level circulation [I, 21. isolated cycles as were found in the tropical stratosphere. Quite indcpendcntly a similar periodicity was discovered In fact, at the surface, this fluctuation which we called in the concentration of atmospheric ozone in tlie Southern the biennial pulse contributes only a few percent, of the Hemisphere. This not only widens the geographical variance in the monthly-averaged data. On tlic othei horizon but may also extend the influence of this oscil- hand, there is a much larger amount of surface milterid lation to very high levels [7]. available and the series are much longcr. If any significance is to be attached to this pulse at all then its 2. DISCOVERY OF THE PULSE persistence through a long history and its geographical By the same token it had long been linon-n that pulses distribution might lead us to Iurther interpretsd t’lolls. ol’ the length around or slightly above 2 years could k)c ‘The existence of a pulse of similar length in lakc levels.

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PERIOD IN MONTHS PERIOD IN MONTHS 120 60 48 36 30 24 21 18 15 12 120 6048 36 30 24 21 I6 15 12 9 o7 -, ,, ,, 07 ITIII II I I I TORONTO, CANADA UPPSALA, SWEDEN 1841- 1950 1855- I950 .os

.05

.04

u = .25 UM (f = .94)+ .75 U.(p= .13) .03

.o2

01 - .01

.oo I‘ I I I I J .oo I I -> 07 I IIII II I 1 I- 4 4 WOODSTOCK, U.S. A. QUITO, ECUADOR Y 1870 - 1956 1901-1950 - Ly .06

.OS

.04

.03 03 -

.02. 02 -

.01

.oo I , I I I I 5 ‘0~ 15 20 25 30 HARMONIC HARMONIC

FIGURE1.-Power spectra of monthly mean temperature at selected stations, showing first 30 harmonics from- analyses with maximum lag of 132 months. Data were “prewhitened” Lo remove annual march by the formula T’= T-T+T, where is the record-mean temperature in the same month as T,and 7 is the record-mean annual temperature. Fittea “red noise” continua, and their 95 percent confidence limits in the neighborhood of the biennial pulse, are shown by the smooth curves (see text).

varves, and, perhaps, tree rings suggests that we are tures of 13 Midwestern and Great Plains stations. An concerned with a very long-lived [IO] element of the analysis of the long combined temperature series (for atmospheric circulation. Vienna, Berlin, deBilt) of Baur [3] also showed this as the most prominent cyclical feature for the interval 1761 3. POWER SPECTRA OF TEMPERATURE SERIES to 1953 [lo]. Through power spectrum analysis, evidence for the In figure 1, added to the Woodstock spectrum already presence of this pulse has been found in various other data mentioned, are further series of spectra in which this series. Thus we found it as the most prominent peak of pulse is evident. These cover extended time intervals at an otherwise “white” spectrum of the combined tempera- Toronto, Ontario, Canada; Uppsala, Sweden; and Quito,

Unauthenticated | Downloaded 09/28/21 11:19 AM UTC OCTOBEK-DECEMBER1963 MONTHLY WEATHER REVIEW 551 Ecuador. In each of these spectra, the biennial peak, centered near harmonics 10 and 11, is found to be signifi- cant at the 95 percent level when referred to a null-hypoth- esis continuum of red noise [8] shown by the smooth curve.’ A further argument in favor of the reality of this 0 (Central weight) ,0602 -14,14 -. 0334 - 1.1 .0577 -15,15 - ,0253 oscillation is the fact that it is common to locations sepa- - 2.2 ,0512 -16,16 -. 0165 - 3.3 .0410 -17, 1i - ,0079 rated far beyond the limits of the usual high spatial - 4.4 .mi9 -lX,18 . 0000 - 5,5 ,0133 -19,19 ,0065 correlation. Thus one might have attributed to spatial - 6.6 -. 0017 -20,20 ,0115 - 7, 7 -. 0158 --21,21 .0147 correlation the effects in Sweden and central Europe, or - -.88 - -. 0279 -22,22 ,0163 - 9,Q -. 03i2 -23,23 ,0165 those in Canada, the Midwest, and the Middle Atlantic -10,lO -_0431 -24,24 .0156 -11,ll -_0454 --Y5,25 ,0140 area, but the prevalence of the pulse in data from three -12,12 -. 0442 --26,26 .om -13,13 -. 0400 -27,27 .0100 continents stamps this as a feature of the general circulation at large. 4. FILTERED SERIES perature. This is because the biennial peak in the spectra Rather than to analyze further series as power spectra of pressure at most, of the stations was found not to be as it seemed more interesting to relate phases and amplitudes marked as that of temperature. Inasmuch as the filtering of the biennial pulse at various localities. For this purpose procedure produces of necessity a rather regularly periodic several long series were subjected to a band-pass filtering output even for purely random series, it was felt that the technique suggested by Brier [5]. By this technique, it is results for pressure might be dominated by irrelevant possible to filter out all frequencies of variation in a time random noise effeck3 series except those near a preselected frequency of interest, Tnterpretation of the results for temperature must and at the same time to preserve amplitude and phase properly allow for randoni noise effects also. The spectra information concerning the latter with a very high degree in figure 1 indicate that roughly half of the variance of of fidelity. temperature derived from periods ncar 2 yr. is associated In particular, we used a 55-term weighted moving- with background “red noise”. Some distortion of the average filter with the weight values shown in table 1. biennial pulse in the filtered series is therefore to be antici- The response of this filter (applied to monthly data) is pated, especially at times when the pulse itself is compara- unity at a period of 24 months, and falls gradually to tively weak. zero at periods of 13fS on the high-frequcncy side and of The filtered temperatture series are shown in figure 2 about 60 months on the low-frequency side, remaining for a selected 40-pr. period of record 1908-1947. They virtually zero outside these limits. In other words, the me arranged in geographical order of latitude along each filter in table 1 passes with negligible distortion of phase of the two meridians, md dl are scaled in units of “C. and amplitude all fluctuations with a period near 24 Ss a measure of the practical significance of the biennial months, and also passes (with more or less reduced ampli- pulse in surface temperature, the median and maximum tude) all fluctuations with periods not exceptionally double amplitudes of the pulse in the period 1908-1947 longer or shorter than 24 months. In this way, irregular are compared in table 2 with the mean 10-yr. range of variations of phase, exact period, and amplitude of a annual mean temperature in the same peri~d.~Table 2 “biennial pulse” can be followed through the full length of shows that the median amplitude to each location approxi- the time series subjected to the mates to half of the IO-yr. range, and that the rnax4muni The data chosen for band-pass filter analysis are from amplitude tends to exceed the range somewhat. However, stations along two meridans, 70”-80” W. and 1Oo-2O0 E. since about half of the variance in the filtered series It was hoped in this way to sample the dependence of derives from noise the importance of the real pulse is phase and amplitude of the biennia1 pulse on both latitude about one-third less than that suggested in table 2. and intercontinental differences of longitude. Although the series of pressure values have been analyzed along with those of temperature at the selected stations, the 5. PHASE RELATIONS results reported here pertain almost exclusively to tem- Inspection of the data in figure 2 leads one to the 1 In each spectrum in figure 1 (except that for Quito), the continuum is given by the sum of two appropriately weighted Markov red-noise spectra with parameters estimated following conclusions. from the shape of the corresponding autocorrelation function (see [SI footnote 3). The (a) Western Meridian (70°-800 W.). The pulses at spectrum for Quito is unusual in that only pait of its variance could be attributed to Quito (on the equator) and Col6n (9’ N.) are consistent,ly Markovian Dersistence; hence its continuum is shown as B fractional part of a single Markov component. 2 If the last 27 values of a time series are averaged, and the series is extended 27 additional 3 It should he remarked that a study of meridional pressure gradients may be more months by entering this average 27 times, application of the filter in table 1 to the aug- pertinent to a physical understanding of the biennial pulse. Such a study is being mented time series will preserve phase (but not amplitude) information about the biennial planned by the nrriters. pulse right up to the ending date of the series. The beginning of a series may be similarly 4 The mean 10-yr. range was chosen in lieu of the total 40-yr. range to decmpliasizc extended if desired. the effect of secular trends in the series.

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Month - I.

Double anii,litudc of hqean 10-pr. biennial pulsc range or Station ___ annual temper- Meclian 1 &taxiinurn ature

Upgsala, Smcdcn...... 1.4 4.2 2.9 Vienm, Austria...... 1.4 3.0 2.2 Toronto, Canada ...... 1.4 4.0 2. i ...... 1.0 2. 4 1. 6 ...... 0. 4 0.8 1.1 CoMn, C.Z ...... 0.4 1. 0 1.3 Quito, Ecuador.-...... 0.4 1.2 1.1 Cape 'Town. So. Africa...... I. 2 1.0 Punta Arenas. Chilc...... 1.4 1.2

in phase. The pulse at Port-au-Prince (19' N.) is also longitudes in the Tropics [14]. Our result would imply in phase with these during the first half of the 40-5-r. that this may not be true at dl times. record, but varies independently thereafter. The pulses To summarize the conclusions concerning phase, a ut Charleston (33' N.) and at Toronto (44" N.) are mutu- rather abrupt reversal of phase appears to exist along ally in phase, and both arc consistently about 180' out both meridians between the Tropics and extratropical of phase with those at Quito arid Col6n. The pulse at latitudes, particularly in the h-orthern Hemisphere. The Punta Arenas (53' S.) has some tendency also to be out latitude of this phase reversal is eridentlj- near the axis of of phase with those at Quito and Co16i1, and in phase the subtropical high-pressure belts, delimiting the Hadley with those at Charlestown and Toronto; however this lust cell of the general circulation. This is in line with phase relationship is quite vague. changes found in stratospheric tcmperature, at about the (b) Eustern Meridian (10"-20" E.). The pulse at same latitudes, by Angel1 and Tiorshover [2). In the Livingstone (18' S.), the only station on this meridian tropical zone along both meridians, thc pulse is in mutual located rather near the equator, has some tencleric\- to phase for part but not all of the 40-yr. period of the remain out of phase with those at TTienna (48' N.), analysis. In the higher southern latitudes, the pulsc is Uppsala (60' N.), and Gjesvar (71' N.). The latter uniforruly out of phase between the two meridians, but 110 thrce are all consistently in phase with one another. corresponding relation is obvious in the higher northern Based on the short available record at Biskra (35' N.), latitudes. the pulse in North Africa is not clearlv related in phase Amplitude variations of the pulse, appear not to havc to the pulses elsewhere except perhaps at Cape Town any systematic relationship at the different stations. Tt (34' S.). The pulse at Cape Town tends onlj- loosely to may tentatively be concluded that the spatial correlation be out of phase with the pulses at Livingstone and Bislaa. of pulse amplitude decays with distance at, a rate compa- (el Comparison between meridianb. On examination of rable to that of climatic tcmperature in general. At most the phase relationships between stations along diff went of the stations, there is some tcndenc)- for the amplitude meridians, some conclusions are the following. Among of the pulse to oscillate with periods belween about 7 and the higher northern-latitude stations, the phase relation- 9 yr. ship between meridians is not systematic. In the high An especially noteworthy aspect of the biennial pulse is southern latitudes, however, the pulses at Cape Town and its tendency to become locked in phase with the seasoxi of Puntn A4renas are found to be quite consistently and the year. This is evident from table 3, which shows for almost exactly 180' out of phase during the full 40-JT. each full-record station in figure 2 thc number of times the period. pulse reached a maximum in each month of the year In the Tropics, a conclusive evaluation of the phase between 1908 and 1947. At all the Northern Hemispheric relationship between meridians is complicated by the stations, there is some preference for the maxima to rathcr dissimilar station latitudes. The most logical occur in winter (especially January-, Februarj-, and March). Quito, on the equator, appears to be in step with the North- comparison would appear to be one between Quito and ern Hemisphere in this respect. On the other hand, the Livingstone. The pulses at these locations are consistent- phase of the pulse at the Southern Hemispheric stations ly in phase with one another between tbe beginning date shows a much weaker seasonal locking, tending merely to of the Livingstone record (1918) and 1934, but bear a avoid the high-summer months (December and January). shifting relationship thereafter (1934 to 1948). This To clarify further the iuatter of phase locking with result is particularly interesting in view of the fact that, season, the entir niperature series at two of the longest since 1954 at least, the phase of the biennial stratospheric record stations in this study (Uppsala and Charleston) wind oscillation has been very similar at widely separated were filtered in the same way as before. The results,

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TABLE$.-Number of maxima and minima in biennial pulse occurring each month of the year, and mean double amplitude ("C.), based on full period of record at two stations -0 I Month D

"l *0. Uppsala, Sweden, 1855-1950 (96 yr.) ...... :. -

:.:I.

0 If

Charleston, U.S.A., 18234950 (128 yr.) I?"l 0. NumberNumberminima~~~~l3 maxima.. .. 11 Meanamplitude-._ 1.3 1.5 1.0 1.0 0.9 0.8 0.4 0.5 0.1 0.9 1.2 1.2 ? ? ;i :.I. 1;: 1;: 1 1: I I I 1 1 i I I?0 0

NY) su~nmarizedin table 4, indicate that the pulse phase at 0. both stations leans strongly toward inter.^ This is shown not only by a higher frequency of maxima and 0N minima reached during winter, but also by a larger mean D amplitude of the pulse at' times when its extremes coin- 2 cide with winter. If the fundamental period of t'he 0 biennial pulse is not precisely 2 yr., then such behavior not only implies some sort of modulation of pulse ampli- z tude by the annual inarch of relevant climatic variables, 0. but also a tendency for the shape of the pulse to be dis-

torted when the maxima and minima occur other than in 0Y) winter. 0 The 7- to 9-yr. oscillation of pdse amplitude at many stations, mentioned earlier may be a different manifesta- 0 tion of the same modulation phenomenon, inasmuch as a 0 pulse whose fundamental period is 27-28 months would ... VI0. pass through 3 cycles in just about 7 yr., 3% cycles in 8 . , . .:. .I...... m yr., and 4 cycles in 9 yr.6 ..I. . .'

0 2 6. LONG SERIES mVI The filtered temperature series for the full length of m available records at Uppsala and Toronto are shown ...... 1,. :. ' ::* 0 respectively in figures 3 and 4. The similarly filtered m series of sea level pressures at Toronto is also shown in ...... :' - .. figure 4. These series raise some interesting questions...... VI First, some of the earliest known references to the bi- m-h ennial pulse in temperature, made around the turn of the century by Clayton [6], Woeikof [20, 211, and 'cva11Bn .. h0 [19], followed an epoch in which the pulse sometimes m reached exceptionally large amplitudes. The pulse may -.. ,::.. -,: :; '_' ' . . therefore have seemed a rather natural subject for investi- ,I. VI0 ...... " gation at that time. Second, the biennial pulse in Toronto 2 pressure is typical of the situation at the other stations 0

8 Nonetheless, some investigators have noted the oscillation in indices of summer heat, m such as Sutton [16] for London and Schindler [I51 for Frankfurt am Main. 8 It may bo added that a 27-28-month cyclr would again be in phase with the (winter) seeson after from 6 to 8 cycles. ox at intervals of from about 14 to 17 yr. This is comparable to the intervals between the spells of outstandingly large-amplitude pulsrs at Toronto and Uppsala. for example.

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0 P

vVI 11

0 P

VICI 0

0 P

n“l :

0n z

-“l z

z 0’

VI 0.-0

0 c. -c. 0

VIP m

0 m

mVI m

0 m

hVI m

0 -mh

-amVI

0 m

n -nm

0VI m

tVI m

I 0 0 0 0 0

Unauthenticated | Downloaded 09/28/21 11:19 AM UTC 556 MONTHLY WEATHER REVIEW OCTOBER-DECEMBER1963 we studied in showing no systematic phase or amplitude 10th General Assembly, Rome 1954, Scienti$c Proceedings rela tionship with the corresponding temper ature pulse. International Association of Meteorology, London, 1956, pp. On the other hand, the Toronto pressure pulse is unique 336-345. 5. G. W. Brier, “Some Statistical Aspects of Long-Term Fluctua- in showing a rather striking variation of amplitude at tioris in Solar and Atmospheric Phenoniena?” Annals of the intervals of about 19 or 20 >7r. (since 1887). Although New York Academy sf Sciences, vol. 95, Art I, Oct. 1961, possibly only spurious, this phenomenon is the inore pp. 173-187. intriguing because it coincides with a siiiiilarly regular re- 6. H. H. Clayton, “A Lately Discovered Rleteorological Cycle,” currence of wet and dry periods in the Central Plains of American Meteorological Journal, vol. 1, 1885, pp. 130, 528. 7. J. 1’. Funk and G. L. Garnham, “Australian Ozone Observa- the United States [12]. The periods of large pulse ampli- tions and a Suggested 24 Month Cycle,” Tellus, vol. 14, tude in ‘roronto pressure coincided with wet periods in NO. 4, NOV.1962, pp. 378-382. the Plains, and those of small pulse amplitude with dry 8. D. L. Gilinan, F. .J. Fuglister and ,J. M.Mitchell, .Jr., “On the periods. Power Spectrum of ‘Red Noise’,’’ Journal of Ihe Atmospheric 7. CONCLUSIONS Sciences, vol. 20, No. 2, Mar. 1963, pp. 182-184. 9. H. H. Lamb, J. R. Probert-Jones, and J. W. Sheard, “A New Our data leave no doubt that the pulse, slightly in ex- Advaiice of the Jan Mayen Glaciers and a Remarkable cess of‘ 2 years in period, is a worldwide phenomenon. They Increase of Precipitation,” Journal oj Glaczology, vol. 4, KO. 33, Oct. 1962, pp. 355-365. also show that this has been hirly persistent featme 10, H. E. ~~~d~b~~~,“Biennial pulses in the Atmosphere,” Beitrijge during the past century. Although there is no definite zur Physzk der Atmosphare, vol. 35, hTo. 3/4, 1962, pp. 184-194. proof of this as yet, it appears reasonable to suppose that 11. H. E. Landsberg, J. M. Mitchell, Jr., and H. L. Crutcher, the intertropical region may be the seat of the per- “Power Spectrum Analysis of Climatological Data for Wood- turbation. This we hope to explore further in studies oE stock College, Maryland,” Monthly Wezther Review, vol. 87, NO. 8, Aug. 1959, pp. 283-298. time series of pressure gradients. 12. W. C. Palmer, “Meteorological Ilrought: Its Measurement and ACKNOWLEDGMENTS Classification,” U.S. We-ather Bureau Manuscript, 1961 (to be published in Weather Bureau Research Paper Series). The writers are grateful to Messrs. Glenn W. Brier and 13. R. J. Reed, W.J. Campbell, L. A. Rasmusseii, and D. G. Rogers, Thoinas H. Carpenter, U.S. Weather Bureau, for their “Evidence of a llownward-Propagating, Aniiual Wind Re- versal in the Equatorial Stratosphere,” Journal of Geophysical assistance in designing the band-pass filter used in this Research, vol. 66, No. 3 Mar. 1981, pp: 813-818. paper. They acknowledge also the invaluable help of 14. R. J. Reed and ‘D. G. Rogers, “The Circulation of the Tropical Messrs. Grady McKay and M. Larry Snelson, of‘ the Stratosphere in the Years 1954-1960,” Journal of the Atmos- National Weather Records Center, in preparing the COM- pheric Sciences, vol. 19, No. 2, Mar. 1962, pp. 127-135. puter progra,ms for the spectrum and filter analysis. 15. G. Schiiidler, “Eigenartiges Thermisches Verhalten der Soni,mer im Frankfurter Rauni,” Meteorologische Ricndschau, vol. 1’2, REFERENCES 1959, pp. 189-190. 16. 0. G. Sutton, “Summers in London,” Weather, vol. 17, No. 12, 1. J. K. Angell and J. Korshover, “The Biennial Wind and Tem- Dec. 1962, p. 408. perature Oscillations of the Equatorial Stratosphere and 17. R. G. Veryird and R. A. Ebdon, “Fliictuations in Equatorial Their Possible Extension to Higher Latitudes.” Monthly Stratospheric Winds,” Nature, vol. 189, 1961, pp. 791-793. Weather Review, vol. 90, No. 4, Apr. 1962, pp. 127-132. 18. R. G. Veryard arid. R. A. Ebdon, “Fluctuations in Tropical 2. J. I<. Angell and J. Korshover, “Harmonic Analysis of the Stratospheric Winds,” Meteorological Magazine, vol. 90, No. Biennial Zonal-Wind and Temperature Regimes,” Monthly 1066, May 1961, pp. 125-143. Weather Reozew, vol. 91, Nos. 10-12, @ct.-Dec. 1963, pp. 19. A. WallBn, “Temperatur-, Nederschlag- und Wasserstands- 537-548 schwankungen in. Nordeuropa,” Meteorologische Zeitschrijt, 3. F. Baur, “Langjahrise Beobachtungsreihen,” Linke’s Meteor- VO~.31, 1914, pp. 209-220. ologzsches Taschenbuch, Neue Ausgsbe, vol. 11, 1953, pp. 20. A. I. Woeikof, “Perioden in der Temperatur von Stockholm,” 6 10-614. Meteorologische Zeitschrift, vol. 23, 1906, pp. 433-436. 4. H. P. Berlage, “The Southern Oscillation, a 2-3 Year Funda- 21. A. I. Woeikof, “Die Schneedecke in ‘paaren’ und ‘unpaaren’ mental Oscillation of World-Wide Significance,” I. U. G. G. Wintern,” Meteorologische Zeitschrijt, vol. 12, 1895, pp. 77-78.

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