quasi-biennial and quasi-triennial oscillations in some atmospheric parameters

PAGEOPH, Vol. 147, No. 3 ( 1 9 9 6 ) 0033-4553/96/030567-1751.50 + 0.20/0 �9 1996 Birkh~iuser Verlag, Basel

Quasi-biennial and Quasi-triennial Oscillations in Some Atmospheric Parameters

R. P. KANE ~

Abstract--A spectral analysis of the 12-month running averages of several atmospheric parameters for 40 years (1951 1990) indicated prominent QBO (Quasi-Biennial Oscillations) and QTO (Quasi-Tri- ennial Oscillations). The 50 mb tropical wind has a very prominent QBO peak at T = 2.33 years, which was well reflected in N. Pole 30 mb temperature but not in average surface air temperatures of Northern and Southern Hemispheres. The 50 mb wind had no prominent QTO; but sea-surface temperatures showed prominent QTO at ~3.6 years as well as peaks at ~4.8 years (also shown by N. Pole 30 mb temperature) which matched very well with similar peaks in the Pacific SST and SO (Southern Oscillation) index. Specific humidity in the lower troposphere (1000 and 700 mb) and temperature at 300rob obtained by radiosondes in the western Pacific for 15 years (1974-1988) showed mainly a biennial oscillation.

Key words: Quasi-biennial oscillation.

1. Introduct ion

The wind and temperature variations in the tropical stratosphere display a

strong QBO (Quasi-Biennial Oscillation), first observed three decades ago (e.g.,

REED et al., 1961). Several details have been studied since then, indicating system-

atic phase changes o f the QBO with latitude and height (e.g., NEWELL et al., 1974;

DUNKERTON and DEHSI, 1985; ANOELL, 1986; NAUJOKAT, 1986). The westerly

accelerations appear first at the equator, spread with time to higher latitudes and

are, in general, more intense than the easterly accelerations. Also, the max imum

occurs later at lower altitudes, by as much as 10 -12 months, f rom 10 mb to 50 mb.

Similar QBO-like oscillations also occur in the troposphere. However, the relation-

ship between stratospheric and tropospheric QBOs seems to be controversial.

TRENBERTH (1980) feels that the two QBOs are unrelated (see also KANE, 1992).

YASUNARI (1989) indicated a possible link between the two as well as with SST (Sea-Surface Temperature). In the case o f SST, there is the well-known phe- nomenon E N S O (El Nif io-Southern Oscillation) which is characterized by two

lnstituto Nacional de Pesquisas Espaciais--INPE, C. Postal 515, 12201-970-S~o Jos6 dos Cam- pos, SP, Brasil.

568 R.P. Kane PAGEOPH,

prominent modes viz. 4-5 years and a QBO. RASMUSSON et al. (1990) specify this QBO as a precisely biennial mode (24 months) and suggest that these may not be related to the stratospheric QBO which has an average 28-month period. On the other hand, BARNETT (1989) wonders whether E1 Nifio and stratospheric QBO are "the same creatures" and ANGELL (1992) presents evidence for a pattern in the relationship between E1 Nifio and stratospheric QBO.

The SST used in the above analyses is that of equatorial Pacific. Using data from the region 6~176 180~176 WRIGHT (1984) prepared an SST index which is highly correlated with the SO (Southern Oscillation) index as represented by the Tahiti minus Darwin sea-level atmospheric pressure difference. What are the characteristics of temperature in other latitudes and altitudes? What are the characteristics of humidity? Do these show a QBO and if so, how does it relate to the QBO in equatorial Pacific SST and tropical stratospheric wind? CESS (1990) and ARDANUY et al. (1992) showed that global averages of outgoing long-wave radiation observed by Nimbus-7 satellite correlated well with global surface temperature and both indicated 2-2.5 year periodicity during 1979-1984. Recently, GUTZLER (1992) used the data from four radiosonde stations viz. Koror (7.3~ 134.5~ Truk (7.4~ 151.8~ Pohnpei (6.9~ 158.3~ and Majuro (7.1~ 171.4~ to define indices of temperature and humidity over the tropical western Pacific, and presented monthly mean time series for specific humidity (Q) and temperature (T) at three levels (1000, 700 and 300 mb). (This average from only 4 stations may or may not be fully representative of the entire western Pacific.) A periodic seasonal cycle was seen in each of the time series. Gutzler calculated long-term (fifteen-year, 1974-88) linear trends and showed that both Q and T have increased throughout the troposphere since the mid-1970s and studied the vertical structure of these decadal-scale trends. Regarding the interannual variability, Gutzler only mentioned that it was associated with the E1 Nifio-Southern Oscilla- tion cycle. In this note, we examine the presence of a QBO and QTO (Quasi- Biennial Oscillation and Quasi-Triennial Oscillation) in the time series presented in GUTZLER (1992) as well as in other temperature series.

2. Data

The data used are for 1951-1990 (40 years) for the Northern Hemisphere (JONES et al., 1986a) and Southern Hemisphere (JONES et al., 1986b) average surface air temperatures, based on land-based meteorological station data and fixed-position weather ship data. Further data were obtained from JONES (1988) and were also sent to us privately by Dr. Jones. Radiosonde data were read from GVTZLER (1992) and refer to once daily daytime soundings, averaged to reflect monthly means. Data were obtained at 50 mb pressure increments (from 1000 mb to 300 mb) for only 15 years, during January 1974 to December 1988. Instrumental

Vol. 147, I996 Quasi-biennial and Quasi-triennial Oscillations 569

accuracy and biases have been discussed in PRATT (1985) and ELLIOTT and GAFFEN (1991). Southern Oscillation data are Tahiti (18~ 150~ minus Darwin (12~ 131~ atmospheric pressure given in PARKER (1983) and updated from Meteorological Data reports. The (50mb) stratospheric zonal wind data were obtained from VENNE and DARTT (1990) as a four-station average viz. Gan (0.7~ 73.2~ Balboa (8.9~ 79.6~ Singapore (1.4~ 103.9~ and Canton (2.8~ 171.7~ For higher altitudes we used the 30 mb and 50mb temperature data given in LABITZKE and VAN LOON (1991) as additional kindly supplied to us privately by Dr. Labitzke. These data were area-weighted for (10~176 as well as for the North Pole alone. The equatorial Pacific SST index was obtained from WkIGHT (1984) while SST at 90~ and at Puerto Chicama, Peru were read from RASMUSSON et al. (1990). For comparison, average total ozone values for Northern Hemisphere temperature latitudes were used, supplied to us privately by Dr. Angell. Also, carbon dioxide measurements at Mauna Loa, Hawaii were used from KEELING et al. (1989).

3. Isolating Quasi-biennial and Quasi-triennial Oscillations

Most of the parameters have large seasonal variations, which must be eliminated for studying larger periods. Usually, this is achieved by evaluating average values for Jan., F e b . , . . . , Dec., for several years and subtracting these from the individual yearly values. We consider this procedure unsatisfactory; because the nature of the seasonal wave (mainly amplitudes) changes from year to year. Hence, no average is adequate and subtraction may leave undesirable residues. Instead, we prefer the method of 12-month running means. This reduces the amplitudes of nearby periodicities. Thus, the amplitude of 2-year (biennial) wave is reduced to 65% and that of a 3-year (triennial) wave to 85%. In compensation, the resulting curves are smooth.

The 12-month running means show all larger periodicities, including QBO and QTO. To isolate the QBO and QTO, larger periodicities must be eliminated. For a rough visual inspection, we estimated their combined effect by evaluating 3-year running averages. When these are substracted from the 12-month running means, what remains is mostly the QBO and QTO. The running mean is rather a poor filter and some sidelobes are probably still present in the data. However, the positioning of the various peaks seems to remain essentially unaltered. Some alternate methods were also tried to confirm this. For example, further 4-year running averages were calculated and subtracted. The peak positions did not alter. Also, the peaks in the original data (12-month running means) were in the same position as those for the filtered series (12-month running means minus 3-year average) as will be seen in the diagram that follows. Thus, the probable inadequacy of the 3-year averages as a proper filter causes no serious distortions, at least for visual inspection.

570 R.P . Kane PAGEOPH,

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-'.,,:1"-o' "'.o'" i "'~176 "o" "o'" I " e - i "o'" ".o' _TROPICAL(50) MB WIND I - - 90..=. 19 \ 24,

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Vol. 147, 1996 Quasi-biennial and Quasi-triennial Oscillations 571

4. Results from Visual Inspection

A. Data for 1951-1990

Figure 1 shows the results for the longer (40 years) temperature data. In Figure l(a), the thin lines delineate the 12-month running means of average surface-air temperatures in the Northern and Southern Hemispheres (JONES et al., 1986a,b). The thick lines depict 3-year running averages. The crosses show Southern Oscilla- tion (SO) index obtained as Tahiti minus Darwin atmospheric pressure. The rectangles indicate occurrences of E1 Nifio, full, strong; hatched, moderate; open, weak, as defined by QUINN et al. (1987), based on the ranges of temperature increase in the Ecuador-Peru coast. The E1 Nifios usually coincide with the minima in the SO plot, as expected. The long-term variation of temperature is similar in the Northern and Southern Hemispheres, with temperature maxima during sunspot maximum years 1958-59, 1969-72, 1979-82 for the Southern Hemisphere but only during 1958-59 and 1979-82 for the Northern Hemisphere. When the thick curve is subtracted from the thin curve the difference is as illustrated in Figure l(b). The QBO and QTO are now seen clearly. The numbers indicate spacing (in months) of successive QBO maxima. As can be seen, the spacing is variable, ranging from 18-44 months, indicating the presence of QBO and some QTO also. Also, in a rough way, the peaks for the Northern and Southern Hemispheres average temperatures match. The dotted curve is for 50 mb tropical zonal wind (VENNE and DARTT, 1990) showing a strong QBO and the vertical lines mark the maxima (westerly). The temperature maxima seem to have no fixed lag or lead with respect to the wind QBO.

The other plots in Figure l(b) are for 50 mb and 30 mb temperatures, area- weighted for 10~176 and 30 mb temperatures for the North Pole alone (LABITZKE, 1987; LABITZKE and VAN LOON, 1991, and also private communication from Dr. LABITZKE). All these show prominent peaks. The 30 mb and 50 mb QBO peaks for 10~176 temperature match between themselves but do not match (even with lags or leads) with the peaks of surface temperature, nor with the

Figure 1 (a) 12-month running means (thin lines) of the surface-air temperatures in the Northern and Southern Hemispheres. Thick lines are 3-year running averages. Crosses represent Southern Oscillation index obtained as Tahiti minus Darwin atmospheric pressure. Rectangles illustrate E1 Nifios (full, strong; hatched, moderate; open, weak). (b) QBO and QTO (obtained as 12-month running means minus 3-year running means) for the surface-air temperatures, temperatures at 30 mb and 50 mb for 10~176 and temperature at 30 mb for North Pole. The dotted curve shows 50 mb tropical zonal wind, for which the westerly maxima are indicated by vertical lines. For all plots, maxima are marked by full circles and minima by open circles. Numbers represent spacing (in months) of successive peaks. (c) QBO and QTO of SST index, SST at 90~ SST for Puerto Chicama (Peru), 50 mb wind (dots) and SO index (crosses).

(d) QBO of Northern Hemisphere temperature latitude total ozone and QTO of Mauna Loa CO 2.


QBO of 50 mb equatorial wind. The latitude range 10~176 is very large; but we were unable to obtain data for smaller latitude bands. The QBO of 30 mb North Pole temperature seems to match with the QBO of 50 mb wind, with temperature minima occurring roughly at westerly wind maxima.

Figure l(c) shows results for SST index (WRIGHT, 1984). The longer periodicities are eliminated and hence, this is QBO and QTO only of SST. The SST maxima are associated with E1 Nifio events but in no way match with wind QBO, with any lag or lead. Some of the SST index peaks match with peaks of the Northern and Southern Hemispheres surface-air temperatures (Fig. lb), indicating the well- known impact of equatorial SST on tropical air temperature. The other plots in Figure l(c) are for SST at 90~ and SST at Puerto Chicama (Peru coast at 7.7~ (RASMUSSON et al., 1990) which seem similar to the SST index plot.

The 50 mb wind only has a strong QBO. To check whether our procedure of subtracting 3-year averages causes any distortions, the 50 mb wind 12-month mean series of Figure l(b) (dots) was subjected to further 3-year running averages and these averages were subtracted from the original series. The difference is shown as the dotted series in Figure l(c). As can be seen, amplitudes have slightly changed; but the positions of the maxima have remained unchanged and coincide with the vertical lines, indicating that our procedure of subtracting 3-year averages does not distort (displace) the positions of the maxima and minima. In Figure l(c), the crosses show the SO index, obtained by subtracting 3-year averages from the original plot (crosses, Fig. la) of SO index. As can be seen, there is little relation between the 50 mb wind QBO and SO index peaks, the latter combining both QBO and QTO.

Figure l(d) illustrates the Northern Hemisphere temperature latitude total ozone (Dr. ANGELL, private communication) and Mauna Loa CO2 (KEELING et aL, 1989). Ozone shows QBO, with ozone minima occurring about 2-3 seasons earlier than 50 mb west-wind maxima. For Mauna Loa CO2, the peaks are irregularly spaced, with longer spacings, indicating a larger contribution from QTO than from QBO.

B. Data for 1974-1988

Figure 2 (left half) shows a plot of monthly mean values of the specific humidity Q and temperature T at three selected levels 1000, 700 and 300 rob, for 1974-88, for which Dr. Gutzler kindly supplied us the data. A large seasonal variation is evident in all plots. To eliminate the same, running averages over 12 months were calculated. These are shown as thin lines in Figure 2 (right half). Short-term (2-3 year) fluctuations (QBO) are seen in all plots, superposed on a longer term variation, represented by the thick (smoother) lines, obtained as 3-year running averages. To isolate the 2-3 year fluctuations, the thick line values were subtracted from the thin line values. The resulting residues are shown in Figure 3. The peaks

Vol. L47, 1996 Quasi-biennial and Quasi-triennial Oscillations 573

74 76 78 80 82 84 86 88 I t I I I 1 I I I I I I I

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Left half: Monthly mean time series of specific humidity Q (gm/kg) and temperature T(~ at 1000, 700 and 300 mb. Right half: 12-month running averages (thin lines) and 3-year running averages (thick

smoother lines) of Q and T. Bottom plot displays 3-year running averages of sunspots.

are indicated by full circles and ,the spacings between them are indicated by

numbers (in months). For specific humidity Q, the spacing ranges from 20 to 28 months (QBO), though an occasional 16 and 18 is also seen. However, the running

mean or "box-car" filter applied by us cannot produce good resolution in the high-frequency end. For temperature T, the spacing is considerably larger, from 20 to 46 months, indicating that the QBO of Q and T is not alike.

To check whether the various series were mutually correlated with any lags or leads, cross-spectra were determined for some pairs. However, the correlations always became low (0.5 or less) for any lags for all series, except for 50 mb wind with N. Pole 30 mb temperature and SO index with Pacific SST, which showed correlations exceeding 0.6. A possibilty remained that the various series included more than one common peak but in different proportions of amplitudes. Hence, all the series were spectrally analyzed as discussed in the next section.


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Figure 3 12-month running averages minus 3-year running averages, for specific humidity Q and temperature T at 1000, 700 and 300 mb. The bottom part shows the Southern Oscillation Index (SOI) obtained as Tahiti minus Darwin sea-level atmospheric pressure, El Nifios (blank, weak; hatched, moderate; full, strong) and 50 mb tropical zonal wind. Numbers indicate spacing (in months) between successive peaks.

In the center, the crosses show 90~ SST (RASMUSSON et al., 1990).

5. Power Spectrum Analysis

I f bo th QBO and QT O are present, there is no simple method to separate the

two by filtering. However, a power spectrum analysis o f the original 12-month running mean data can resolve the two adequately. To obtain quantitative estimates

and the significance o f the periodicities involved, the 12-month running averages (without subtracting 3-year averages) were subjected to Max imum Ent ropy Spectral

Analysis (ULRYCH and BISHOP, 1975) and Multiple Regression Analysis (BEVING- TON, 1969). The methodology was used in KANE and TEIXEIRA (1990) in which

Vol. 147, 1996 Quasi-biennial and Quasi-triennial Oscillations

MAXIMUM ENTROPY SPECTRA (LPEF=33% OF DATA LENGTH)

575

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Figure 4 Upper half: Maximum Entropy Spectra (Power versus Periodicity), for 50 mb wind Northern and Southern Hemisphere surface temperatures, North Pole 30 mb temperature and SO index (Tahiti minus Darwin atmospheric pressure). Lower half: Multiple Regression Analysis estimates of the amplitudes for the various periodicities observed in the Maximum Entropy Spectra. The numbers indicate periodicities

T in years. Note that the abscissa scale is logarithm of T.


power spectra of the annual mean surface temperature (JONES et al., 1986a,b) were obtained for 1851-1984. Maximum Entropy Spectral Analysis (MESA) is superior to the conventional BLACKMAN and TUKEY (1958) method and locates peaks very accurately (for example, in the QBO region, 2.10 can be easily distinguished from 2.30). However, the amplitude estimation in MESA is unreliable (KANE and TRIVEDI, 1982). Hence we only used MESA for detecting the possible periodicities T k (k = 1 to n) where n is the number of peaks indicated in the MESA specta. To be on the safe side, we chose all peaks, small and big. The peaks T~ were used in the expression:

k = 1 ~k + b~, cos 27c + E

~ + r + E (1)

where f ( t ) = t h e observed time-series and E =Error Factor. The parameters A0, (ak, bk) and their standard errors are then estimated by a Multiple Regression Analysis (MRA), using a least-square fit. From these, (r~, ~b~) and the standard error ~rr k can be calculated. Amplitudes rk exceeding 2ark can be considered as significant at a 95% a priori confidence level. As an example, the Maximum Entropy Spectra for some temperature is shown in the upper half of Figure 4. Since 3-year averages are not subtracted, there is no distortion on this account and all possible periodicities (QBO, QTO and higher periodicities) are revealed. The top plot shows spectra (for 1951-1990) for the 50 mb wind, Northern and Southern Hemispheres average surface temperatures, North Pole 30 mb temperature (for 1957-1990 only), the SO (Southern Oscillation) index represented by Tahiti minus Darwin atmospheric pressure and equatorial Pacific SST. As can be seen, various QBO and QTO peaks are resolved clearly. In particular, peaks in the QBO region (2-3 years) are resolved with great accuracy and 2.10, 2.20, 2.30 etc. can be easily distinguished. A BLACKMAN and TUKEY (1958) spectral plot using Jenkins and Watts smoothing techniques manifested only a broad maximum in this region. Thus, in MESA, the bandwidth is very small. The very high resolution capacity of MESA has been demonstrated by using artificial samples by many workers (e.g., KANE, 1977, 1979). The numbers represent periodicity T peaks (in years). Note that the abscissa scale is logarithm of periodicity (T), instead of the usual frequency ( f ) . Also, the ordinate scale is logarithmic. Normally, meteorological variables show a red spectral character i.e., larger power for lower frequencies (higher periodicities). In our case, the surface temperatures do show this. But the 50 mb wind has largest power in the QBO region and SO index and equatorial east Pacific SST in the 3-6 year region.

Similar spectra were obtained for the radiosonde data presented in Figure 2 (right half, 12-month running means).


A. Spectra for 1951-90

When the periodicities were used in equation (1) and a Multiple Regression Analysis was carried out, the amplitudes obtained for the long temperature data series were as shown in the lower half of Figure 4. The hatched portion repesents the 2 sigma level. Thus, all amplitudes exceeding this level are significant at a 95% (a priori) confidence level.

From Figure 4 (lower half) the following may be noted: (i) The 50 mb wind has one prominent QBO peak at T = 2.33 and a subsidiary

peak at T = 2.68 years. The prominent peak at T = 2.33 years is not reflected in the N. and S. Hemispheres average surface temperatures, which have only small QBO peaks near T--2.60 years, roughly matching only with the subsidiary peak at T = 2.68 years of the wind but also matching with similar small peaks (T = 2.4-2.8 years) in the equatorial Pacific SST and SO index (Tahiti minus Darwin). On the other hand, surface temperatures have prominent QTO (T = about 3.6 years) which match with similar prominent peaks for the SO index and SST. Thus, surface temperature QBO is rather small and only partially related to wind QBO, while surface temperature QTO is prominent and seems to be related to the SO index (which, in turn, is well related to equatorial Pacific SST and to E1 Nifio phe- nomenon, hence called ENSO).

(ii) The North Pole 30rob temperature shows QBOs at T =2.31 years and T = 2.77 years which match with the 50 mb wind QBO (T = 2.33 and 2.68 years). Thus, the QBO of N. Pole 30 mb temperature may be related to the stratospheric wind QBO. Note, however, that the N. Pole series was from 1957 onwards only while 50 mb wind series was from 1951 onwards.

(iii) All the parameters (except SST) show a peak near T = 4.6-5.0 years. However, this peak is very weak in the 50 mb wind and strongest in the SO index. Hence, again a ENSO relationship is indicated.

(iv) The peaks near T = 9-10 years in the temperature have no correspondence with peaks in the SO index or in the 50 mb wind. Hence, these peaks seem to have some other origin, probably a solar cycle effect or a long-term trend.

B. Spectra for 1974-1988

For the shorter (15 years) radiosonde data, the results are presented separately. The periodicities and their amplitudes are given in Table 1. The most prominent periodicity is underlined and, as can be seen, is significant at a level better than 5or a priori except for Q(300) where the significance is between 2or and 30. For Q(1000) and Q(700), the most prominent periodicity is 24 m (2 years), while for (2(300), 24 m (2 years) and 40 m (3.3 years) are similarly significant. For T(1000) and T(700), larger periodicities (41 m, 56 m i.e., 3.4 and 6.8 years) are prominent while for T(300), 25 m, 40 m and 87 m (i.e., 2.1, 3.3 and 7.3 years) are similarly


Table 1

(a) Periodicities significant at a 2~ level (a priori) and their amplitudes, (b) decadal trends and solar cycle effects, for the various parameters

(a) (b)

Solar cycle effect Parameter Periodicity Amplitudes Decadal trend ( 150 sunspots)

(Months) (Years) Q(1000) 24 2.0 .176 • .033 +.97 • .12 +.28 • .17 (gm/kg) 38 3.2 .113 • .033 (.98)

70 5.8 .103 • .033

Q(700) 24 2.0 .207 • .027 + .36 • .12 + .14 • .17 (gm/kg) 81 6.7 .088 • .027 (.43)

Q(300) 24 2.0 .0046 • .0023 +0.36 • .005 -.001 • .007 (gm/kg) 40 3.3 .0054 _+ .0023 (.04)

26 2.2 .051 • .009 +.11 • .05 +.34• .07 T(1000) 41 3.4 .098 • .009 (. 11) (~ 81 6.8 .043 • .009

T(700) 27 2.3 .084 • .026 + .40 • .08 + .61 • 11 (~ 56 4.7 .136 • .026 (.43)

T(300) 25 2.1 .150 • .026 +.57 • .08 +.61 • .11 (~ 40 3.3 .132 • .026 (.54)

87 7.3 .102 • .026

50 mb wind 30 2.5 11.5 • 0.5 - - - - (m/s)

(Tahiti minus Darwin) 31 2.6 .30 • .13 (mb) 43 3.6 .48 • .13 - -

63 5.3 .27 _+ .13

a lmos t p rominen t . Thus, Q has a decidedly definitely shor ter per iod ic i ty ( ~, 24 m, 2

years) as c o m p a r e d to T ( ~ 4 0 m, ' 3.3 years) for the lower t roposphere (1000 and

700 rob) while for 300 mb, Q tends to have longer per iodici t ies (40 m, 3.3 years)

while T tends to have shor ter per iodici t ies (25 m, 2.1 years). F o r the 50 m b wind,

a s imilar analysis for this shor t (15 years) pe r iod manifes ted only one p rominen t

per iodic i ty (30 m, 2.5 years) as ind ica ted in Table la . The longer d a t a (1951-1990 ,

40 years) for the 50 m b wind had shown a s t rong peak at T = 2.33 years and a

subs id iary peak at T = 2.68 years (Fig. 4, lower half).

The lower ha l f o f F igure 3 depicts the Southern Osci l la t ion Index (SOI) ,

represented by the mean sea-level pressure difference Tahi t i (18~ 150~ minus

Darwin (12~ 131~ The rectangles exhibi t occurences o f E1 Nifios (open, weak;

hatched, modera te ; full, s trong, as defined by QUINN et al., 1987). The min ima o f

SOI general ly ta l ly with E1 Nifios, as is wel l -known. (Hence the te rm ENSO) .

However , the only resemblance between the E1 Nif io occurrence and f luctuat ions o f


Q and T appears to be during the strong E1 Nifio of 1982-83 when Q at 1000 mb and 700 mb displayed large reductions, indicating extreme dryness. However, for Q(300), this effect is either not seen or is seen delayed by approximately a year. It would thus seem that for humidity, there is a transition from the 700 to the 300 mb region. The results for temperature T are intriguing. WRIGHT (1984) prepared an SST index using data from the region 6~176 180~176 and demonstrated that this SST index matched very well with the SOI with increased temperature coincid- ing with SOI minima. In the present case, T(1000) expresses large decreases of temperature during 1982-83. However, at upper levels, T(700) and T(300) reveal increases. Since these temperatures refer to roughly 7~ and 135~176 the implication would be that, at the sea surface level (1000 mb), the 180~176 region (East Pacific) and the 135~176 region (West Pacific) display opposite temperature variations. At higher altitudes (700 mb and 300 mb), the temperatures are reverse to those at 1000 rob, indicating a transition from the 1000 to 700 mb level. A similar behavior is seen during the moderate E1 Nifios of 1986-87. During the moderate E1 Nifio of 1977 also, T(1000) shows a steady level, while T(700) and T(300) show decreasing tendencies. However, during the weak E1 Nifio of 1975, all levels showed temperature decreases. Thus, during strong and moderate E1 Nifios, there seems to be a reversal of temperature variation characteristics somewhere between 700 mb and 1000 mb for the east Pacific. For 90~ RASMUSSON et al.

(1990) show a biennial mode for SST, which is illustrated by crosses in our Figure 3 (middle part). The variation seems to be similar to T(700) for 1982 but similar to T(1000) for 1981.

The thick lines in Figure 2 (right half) indicate long-term trends. But these are not uniformly upwards. A comparison with sunspots (bottom plot), evidences possible increases of Q and T associated with sunspot maximum (1980). We carried out a bivariate regression analysis where Q and T values were correlated simulta- neously with sunspot numbers and time. For example, Q = a + b t + c S where b is the linear trend and c is the coefficient relating Q with sunspots S. The results are shown in Table l(b). Temperatures at all levels show possible solar cycle associations while only Q(1000) evidences some solar cycle association of marginal significance. The decadal trends are all significant at more than 3 sigma a priori

level and are similar to those reported by Gutzler whose values are shown in parentheses. However, since only one solar cycle is involved, the solar cycle associations need further confirmation in later years.

6. Conclusion and Discussion

It would thus seem that many of these temperature series have small QBOs and large QTOs, some only partially related to the 50 mb equatorial zonal wind QBO but well related to SO index QBO and QTO, indicating a consfderable impact of


equatorial SST on air temperature. The peaks in specific humidity at 1000 and 700 mb and temperature at 300 mb in the West Pacific are mostly near T = 2 years, indicating some connection with an annual cycle (MEEI-IL, 1987). ANGELL (1992) presented evidence of a relationship between E1 Nifio and wind QBO but, as pointed out by him, the two have very different periods (average 2.3 years for QBO and 4.3 years for E1 Nifio) and during 1954-91 there were 9 E1 Nifios and 16 wind QBO waves, consequently there cannot be an E1 Nifio associated with every wind QBO wave and the relationship has "to skip a beat" on occasion. Angell presented evidence for a pattern in this "skip," but desisted from giving a physical explana- tion. YASUNARI (1989) presented evidence of a "coupling" of the stratospheric wind QBO with tropospheric wind QBO which, in turn was coupled to the QBO of SST anomalies in the equatorial Pacific. However, to see phase relatioships, Yasunari used filtered zonal wind anomalies; and the Butterworth recursive filter he used maintained a maximum response for 22 to 32 months, centered at 27 months. We suspect that this procedure results in a bias for the spacings of 27 months and hence creates an artificial regularity, which would result in fixed lags or leads. We feel that the wind QBO and the other QBOs, especially the SO index QBO, are independent phenomena, though they may influence each other. Also, the SO index has a significant QTO. GELLEI~ and ZHAN6 (1991) explored a mechanism by which SST variations can modulate tropical wave activity such that warm SST favors, Rossby gravity waves in the western tropical Pacific and Kelvin waves in the eastern tropical Pacific at the tropopause level, which may tend to force a stratospheric zonal flow oscillation with the same period as the SST-QBO. It may be noted, however, that the QBOs of SST and stratospheric wind do not most often have the same period. Inversely, GRAY et al. (1992) described a hypothetical mechanism whereby QBO of lower tropical stratospheric zonal winds alters the distribution of intense deep convective activity throughout the tropical West Pacific.

At stratospheric heights, several studies link the equatorial QBO with extratropical stratosphere in winter (e.g., HOLTON and TAN, 1980, 1982; VAN LOON and LABITZKE, 1987; DUNKERTON and BALDWIN, 1991) and demonstrate that the polar vortex on an average tends to be colder and more intense in the west phase of equatorial wind QBO. Our Figure l(b) seems to confirm this result. However, recently, LABITZKE and VAN LOON (1992) mention that their earlier results are not statistically significant. In our Figure l(b), the peaks for 30 mb and 50 mb temperatures for 10~176 match between themselves but do not match well with 50 mb tropical wind QBO. Obviously, the tropical wind QBO influence on extratropical regions is very complicated. The mismatch could be partly because 10~ ~ is a large latitude range.

In this note we are comparing the spectra of the various parameters and assuming that similar spectra imply close relationships. However, atmospheric phenomena are highly nonlinear and considerable distortions could occur as phenomena move from one region to another. Hence, relationships between pheno-


mena showing dissimilar spectra cannot be completely ruled out. Also, we are comparing average spectra over certain periods. However, the spectra may vary from time to time. The 50 mb wind itself displays such variations. This would be an additional limitation on the method of comparing spectra. Naturally, our conclu- sions should be considered with these limitations.

For most trace gases, ocean is an important source or sink, depending on temperature. Convective activity associated with SST could modulate the Hadley cell circulation as well as interaction between equatorial wind QBO and extratropical planetary waves. Recently, GRAY and CHIPPERFIELD (1990) and CroPPER- FIELD and GRAY (1992) produced an interactive radiative-dynamical-chemical model of the atmosphere which predicts QBO in temperatures and quantities of chemical species in the troposphere and stratosphere. Our results do present such QBOs but the phase matching and spacings are unsatisfactory. Our QBO in some Q and T has a periodicity near T = 2 years which suggests some linking with the annual (seasonal) cycle (MEEHL, 1987).

Results pertaining to water vapour content of the atmosphere have also been reported earlier. HENSE et al. (1988) reported trend results for tropics for the 500-700mb level and FLOHN and KAPALA (1989) for tropical oceanic surface region, while ELLIOTT et al. (1991) reported results for surface to 500rob for 8 selected stations. However, all these presented only annual values, which are not suitable for a finer study of QBO. GAFFEN et al. (1991) applied data from 1973-85 for 1000, 850, 700 and 500mb for tropics, North America and on a global scale, and conducted an empirical orthogonal function analysis. They found modes 1 and 2 statistically significant and mode 2 presenting an appear- ance similiar to SO index, especially during the E1 Nifio of 1982-83. However, the correlation coefficient was only about + 0.5. Their orthogonal function analysis is different from our power spectrum analysis and their results cannot be compared directly with ours. In general, their similarities and dissimilarities with the SO index are similar to what we have reported in the present study. During 1982-83 they report dry air in the western Pacific and moist air in the eastern Pacific.

The uptrend in temperature in Figure 2 is compatible with the Northern Hemisphere surface air temperature variation (JONES, 1988 and further update).

Acknowledgements

Thanks are expressed to Dr. Jones, Dr. Wright, Dr. Angell and Dr. Labitzke for privately supplying temperature and other data. Thanks are extended to Dr. Gutzler for kindly providing us with the humidity and temperature data. This work was partially supported by FNDCT, Brazil, under contract FINEP- 537/CT.

582 R.P . Kane PAGEOPH,

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(Received July 24, 1995, accepted January 23, 1996)

quasi-biennial and quasi-triennial oscillations in some atmospheric parameters

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