Anomalously Short Duration of the Easterly Wind Phase of the QBO at 50hPa in 1987 and Its Relationship to an El Nino Event

Maruyama, Taketo; Tsuneoka, Yoshie

doi:10.2151/jmsj1965.66.4_629

Cited by 36 publications

(24 citation statements)

References 7 publications

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“…The seasonal cycle affects the QBO in the lower stratosphere [Dunkerton, 1990;Kinnersley and Pawson, 1996] in a manner distinct from its effect in the middle stratosphere. Long-term variations of QBO forcing are also possible, e.g., due to E1 Nifio-Southern Oscillation [Maruyama and Tsuneoka, 1988]. Synchronization in the middle stratosphere constrains the timing of QBO phases and onsets in this region but does little to determine whether the next onset will occur two, two and a half, or three years later.…”

Section: Resultsmentioning

confidence: 99%

Interaction of the quasi‐biennial oscillation and stratopause semiannual oscillation

Dunkerton¹,

Delisi²

1997

J. Geophys. Res.

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Abstract. Analysis of rawinsonde and rocketsonde data at Ascension Island (7.6øS, 14.4øW) and Kwajalein (8.7øN, 167øE) in 1962-1991 suggests that the quasi-biennial oscillation (QBO) in the middle stratosphere is synchronized with the seasonal cycle and that descending westerly phases of the stratopause semiannual oscillation (SAO) are strongly influenced by the underlying QBO. The effect of the seasonal cycle on the QBO in the middle stratosphere is revealed in two, perhaps unrelated, observations: first, a tendency for deseasonalized QBO westerly maxima to occur in local winter (or to avoid local summer); second, a smooth, uninterrupted connection between descending SAO westerly shear zones and the formation of a new QBO westerly shear zone aloft. The timing of deseasonalized QBO westerly maxima in the middle stratosphere allows a simple composite of 2-and 3-year cycles to be constructed from the data, illustrating the effect of the QBO on descending westerly phases of the stratopause SAO. IntroductionThe quasi-biennial oscillation (QBO) of the equatorial stratosphere is so named because the average period of the oscillation is slightly longer than 2 years. Almost 20 cycles have been observed since rawinsonde data first became available in the early 1950s; the average period is now 28.4 months. Individual cycles range from ---22 to 36 months, i.e., from about 2 to 3 years.The prefix "quasi" would apply equally well to an oscillation with continuously variable period, or an oscillation consisting of discrete periods (e.g., 24 months, with a few 30-or 36-month cycles) strung together in some regular or irregular fashion. The period of the QBO is customarily measured at mandatory rawinsonde pressure levels, e.g., 50, 30, or 10 mbar [Dunkerton and Delisi, 1985;Angell, 1986;Naujokat, 1986;Dunkerton, 1990]. This approach, based on one-dimensional time series, leads to the conclusion that the QBO period is variable, tending to form a continuous distribution as time progresses. Exact synchronization with the seasonal cycle is not observed, although as noted by Dunkerton [1990], the deseasonalized mean flow acceleration, distribution of phase onsets, and period of the QBO evidently depend on the time of year. This dependence on the seasonal cycle is due, in part, to a pronounced tendency for descending QBO easterlies to "stall" near 30 mbar between July and February [Naujokat, 1986]. Modulation of the QBO by the seasonal cycle can be distinguished from exact synchronization, which would produce one or more delta functions in the distribution of onset times. Both types of behavior were simulated in a QBO model [Dunkerton, 1990] Data AnalysisData from the historical rocketsonde network were obtained from a variety of sources and processed to form monthly means 26,107

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Section: Resultsmentioning

confidence: 99%

Interaction of the quasi‐biennial oscillation and stratopause semiannual oscillation

Dunkerton¹,

Delisi²

1997

J. Geophys. Res.

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“…Results of the present study show that mixed Rossby-gravity wave activity has a dominant annual variation at the 70hPa and 50hPa levels and the half-QBO cycle appears quite weak. Maruyama and Tsuneoka (1988) showed that a rapid descent of the westerly regime occurred during an El Nino event. The present analysis of Kelvin wave activity shows that its enhancement was associated with the descent of the westerly regime.…”

Section: Discussionmentioning

confidence: 99%

Annual and QBO-Synchronized Variations of Lower-Stratospheric Equatorial Wave Activity over Singapore during 1961-1989

Maruyama¹

1991

Journal of the Meteorological Society of Japan

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Annual and QBO-synchronized variations (variations synchronized with the QBO cycle of the zonal wind) of lower-stratospheric equatorial wave activity were investigated by spectrally analyzing the upper-air data at Singapore (1.4N, 104.OE) for the period January 1961 to February 1990. To measure the equatorial wave activity, the quadrature spectra between the zonal wind component and temperature integrated over the period range 7.4-32 days were used for Kelvin waves, and the power spectra of the meridional wind component integrated over the period range 3.3-5.1 days for mixed Rossby-gravity waves.Annual variations in the mixed Rossby-gravity wave activity were found at the 30, 50 and 70hPa levels with a maximum around March. The amplitude was largest at the 70hPa level. For the Kelvin wave, a weak annual variation was found at 70hPa. QBO-synchronized variations were found in the Kelvin wave activity at the 30, 50 and 70hPa levels. A QBO-synchronized variation of mixed Rossbygravity wave activity was found at 30hPa, but was unclear at the 50 and 70hPa levels. Annual variations of mixed Rossby-gravity wave activity in the 50-70hPa layer appear to be related to a rapid descent of the easterly wind regime during March-June and a slow descent in July-February during the layer 30-50hPa layer.

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“…Second, it is known that the tropical troposphere has a quasi-biennial oscillation of On the other hand, a more subtle relationship (either nonlinear or multivariate) might exist between these phenomena. There is evidence that ENSO warm events enhance the rate of QBO westerly descent [Maruyama and Tsuneoka, 1988]. This effect is dynamically plausible [Dunkerton, 1990; Geller et al, 1997] but would not result in any linear correlation.…”

Section: Effects Of the Qbo On The Tropical Tropospherementioning

confidence: 99%

The quasi‐biennial oscillation

Baldwin¹,

Gray²,

Dunkerton³

et al. 2001

Reviews of Geophysics

1,838

117

1,674

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Abstract. The quasi-biennial oscillation (QBO) dominates the variability of the equatorial stratosphere (---16-50 km) and is easily seen as downward propagating easterly and westerly wind regimes, with a variable period averaging approximately 28 months. From a fluid dynamical perspective, the QBO is a fascinating example of a coherent, oscillating mean flow that is driven by propagating waves with periods unrelated to that of the resulting oscillation. Although the QBO is a tropical phenomenon, it affects the stratospheric flow from pole to pole by modulating the effects of extratropical waves. Indeed, study of the QBO is inseparable from the study of atmospheric wave motions that drive it and are modulated by it. The QBO affects variability in the mesosphere near 85 km by selectively filtering waves that propagate upward through the equatorial stratosphere, and may also affect the strength of Atlantic hurricanes.

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Anomalously Short Duration of the Easterly Wind Phase of the QBO at 50hPa in 1987 and Its Relationship to an El Nino Event

Cited by 36 publications

References 7 publications

Interaction of the quasi‐biennial oscillation and stratopause semiannual oscillation

Interaction of the quasi‐biennial oscillation and stratopause semiannual oscillation

Annual and QBO-Synchronized Variations of Lower-Stratospheric Equatorial Wave Activity over Singapore during 1961-1989

The quasi‐biennial oscillation

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