Zonal Wind Quasi-biennial Oscillation Research Articles

Characteristics of tropospheric biennial oscillation and its possible association with the stratospheric QBO

Signals of oscillation with periods ranging from 20 to 32 months are found in the tropospheric temperature over the near‐equatorial Indian station, Thumba (8° 23′ N, 76° 52′ E). The phase of this Tropospheric Biennial Oscillation (TBO) in temperature does not vary with height from surface to the level of tropopause and is associated with the intensity of the Indian monsoon rainfall. A quasi‐biennial oscillation (QBO) signal is seen in the lower stratosphere. Marked differences in amplitude of QBO and TBO are noticed between the two decades 1971–81 and 1982–92. During the first decade the downward propagating phase of QBO is disturbed in the 18–23 km altitudes. The QBO in zonal wind, however, has neither inter decadal variability nor disturbances.

The Influence of Wave– and Zonal Mean–Ozone Feedbacks on the Quasi-biennial Oscillation

The effects of wave and zonal mean ozone heating on the evolution of the quasi-biennial oscillation (QBO) are examined using a two-dimensional mechanistic model of the equatorial stratosphere. The model atmosphere is governed by coupled equations for the zonal mean and (linear) wave fields of ozone, temperature, and wind, and is driven by specifying the amplitudes of a Kelvin wave and a Rossby‐gravity wave at the lower boundary. Wave‐mean flow interactions are accounted for in the model, but not wave‐wave interactions. A reference simulation (RS) of the QBO, in which ozone feedbacks are neglected, is carried out and the results compared with Upper Atmosphere Research Satelliteobservations. The RS is then compared with three model experiments, which examine separately and in combination the effects of wave ozone and zonal mean ozone feedbacks. Wave‐ozone feedbacks alone increase the driving by the Kelvin and Rossby‐gravity waves by up to 10%, producing stronger zonal wind shear zones and a stronger meridional circulation. Zonal mean‐ ozone feedbacks (ozone QBO) alone decrease the magnitude of the temperature QBO by up to 15%, which in turn affects the momentum deposition by the wave fields. Overall, the zonal mean‐ozone feedbacks increase the magnitude of the meridional circulation by up to 30%. The combined effects of wave‐ozone and ozone QBO feedbacks generally produce a larger response then either process alone. Moreover, these combined ozone feedbacks produce a temperature QBO amplitude that is up to 30% larger than simulations without the feedbacks. Correspondingly, significant changes are also observed in the zonal wind and ozone QBOs. When ozone feedbacks are included in the model, the Kelvin and Rossby‐gravity wave amplitudes can be reduced by ;10% and still produce a QBO similar to simulations without ozone.

Global QBO Circulation Derived from UKMO Stratospheric Analyses

Global circulation anomalies associated with the stratospheric quasi-biennial oscillation (QBO) are analyzed based on U.K. Meteorological Office (UKMO) assimilated wind and temperature fields. Zonal winds and temperatures from the assimilation are compared with Singapore rawinsonde data (the standard QBO reference time series), showing reasonable agreement but an underestimate of maxima in the UKMO analyses. Global structure of the QBO in zonal wind, temperature, and residual mean meridional circulation (derived from thermodynamic balance and mass continuity) is isolated, showing coherent tropical and midlatitude components. Important aspects of the QBO revealed in these data include 1) out of phase maxima in temperature (and vertical velocity) between the lower and upper stratosphere, and 2) strong seasonal synchronization of midlatitude anomalies. These characteristics are also evident in long records of satellite radiance measurements.

The first simulation of an ozone QBO in a general circulation model

The quasi‐biennial oscillation (QBO) of ozone has been simulated for the first time in a general circulation model (GCM). The model employed is the first version GCM developed at the Center for Climate System Research / National Institute for Environmental Studies (CCSR/NIES). The model has a horizontal resolution of T21 and 60 layers in the vertical. Modified Chapman reactions of ozone photochemistry are included in the model, allowing the ozone to be fully interactive with the radiative and dynamical fields. The simulation is, for the most part, successful except that a deficiency of about 40 DU exists in the total ozone in comparison with observations. The simulated zonal wind QBO has a rather short period (about 1.5 years) and somewhat weak easterlies. The lower stratospheric ozone QBO over the equator is qualitatively similar to that observed, although the simulated amplitude of about 0.3 ppmv is somewhat less than that observed. The phase relationship between the equatorial upper and lower stratospheric ozone QBOs is successfully reproduced, although the phase of the modeled ozone QBO slightly precedes the observed phase in the upper stratosphere. The mid‐latitude ozone QBO is out of phase with the equatorial ozone QBO. The phase propagation of planetary‐scale structure in ozone from the mid‐latitudes to equatorial regions is more pronounced during the westerly than in the easterly phase of the stratospheric QBO, especially in the Northern Hemisphere winter.

An Analytical Study of Ozone Feedbacks on Kelvin and Rossby–Gravity Waves: Effects on the QBO

An equatorial beta-plane model of the middle atmosphere is used to analytically examine the effects of radiative cooling and ozone heating on the spatial and temporal evolution of the quasi-biennial oscillation (QBO). Under the assumption that the diabatic heating is weak and the background fields of wind, temperature, and ozone are slowly varying, a perturbation analysis yields expressions describing the vertical spatial modulation of Kelvin and Rossby–gravity waves in the presence of ozone. These expressions show that wave-induced changes in the diabatic heating arising from the advection of basic-state ozone reduce the local radiative damping rate by up to 15% below 35 km. In a one-dimensional model of the QBO, eddy ozone heating increases the amplitude of the zonal wind QBO by 1–2 m s−1 and increases the oscillation period by about two months. The significance of these results to the observed QBO is discussed.

Vertical structure of the extratropical quasi‐biennial oscillation in ozone, temperature, and wind derived from ozonesonde data

An analysis of the extratropical ozone sounding data shows that ozone, temperature, and wind as well as tropopause height reveal interannual variability with timescales in the range 24–30 months. This quasi‐biennial variability is noticed, as a rule, in a whole range of ozone sounding heights (0–35 km) and connected with the equatorial quasi‐biennial oscillation (QBO). The QBOs in ozone and temperature are revealed differently in the middle and lower stratosphere as well as in the troposphere. In the middle stratosphere a downward phase progression of the ozone QBO is noticed similar to that of the equatorial dynamical QBOs. The rate of the phase descent of the QBO depends on the geographical region and varies from 0.5 km/month to 1 km/month. In the northern hemisphere the rate is greatest in the polar region but lowest in the subtropics. Local maxima are noticed in the vertical structures of the ozone QBOs. In the northern midlatitudes these maxima are centered at heights of about 12, 20, and 30 km. In the lower stratosphere the QBO in ozone is in phase with that in temperature. Mean amplitudes of the temperature QBO in the troposphere are close to those in the stratosphere. The downward phase progression of the temperature QBO is noticed in the northern midlatitude stratosphere. There is an abrupt phase shift between the QBOs in ozone and temperature in the lower stratosphere and those in the middle troposphere. Over the North American stations the phase shift is that the temperature QBOs in the troposphere are in opposite phase with those in the stratosphere. In zonal and meridional winds the QBO are revealed in the northern midlatitudes. In contrast with the QBOs in ozone and temperature, the wind QBOs reveal the small rate of the phase changing with height. There are no significant phase shifts between the wind QBO in the lower stratosphere and that in the troposphere. The maximum amplitudes of the wind QBO are noticed in the vicinity of the tropopause position and at heights of 25–30 km. Amplitudes of the QBO in zonal wind are close to those in meridional wind. The QBO of tropopause height exposed in the northern hemisphere has the greatest amplitude over Japan. The tropopause height QBO is in opposite phase (in phase) with the QBOs in ozone and temperature in the lower stratosphere (troposphere). Vertical structures of the QBOs obtained for ozone, temperature, and wind in the stratosphere as well as the corresponding QBO of tropopause height support a hypothesis that the extratropical QBO is caused by quasi‐biennial forcing of the mean diabatic meridional circulation by planetary‐scale waves with the resulting modulation of vertical advection.

On the phase propagation of extratropical ozone quasi‐biennial oscillation in observational data

Global column ozone data from total ozone mapping spectrometer (TOMS), backscattered ultraviolet (BUV) and Dobson stations are analyzed to determine the pattern and phase property of the ozone quasi‐biennial oscillation (QBO) signal. It is found that the ozone QBO signal is strongest in middle and high latitudes and is present mainly in the winter‐spring season in both hemispheres. The extratropical ozone QBO signal is out of phase with the equatorial ozone QBO, which is itself in phase with the QBO in equatorial zonal wind. There are three distinctive regions, namely tropical, midlatitudinal, and polar regions, in each of which the ozone QBO signal has a fairly constant phase with respect to latitude. There is a phase reversal (sign change) between the equatorial and the extratropical regions associated with the return branch of the equatorial QBO secondary circulation, and this sign reversal occurs at ±12° of latitude symmetric about the equator. In the northern hemisphere between the midlatitudinal and polar regions, there is another possible phase reversal in some (but not all) years possibly in connection with the presence or absence of midwinter sudden warming, which creates a positive or negative anomaly relative to the region outside the polar vortex. In the southern hemisphere polar latitudes, the ozone QBO signal is usually delayed until spring in connection with the final warming. These properties are found in all data sets analyzed by the same method. Evidence does not support a gradual phase propagation from the subtropical region to the high‐latitude region. Previous reported evidence for phase propagation is reexamined and is found to be artifacts of data processing.

Stratospheric ozone variations in the equatorial region as seen in Stratospheric Aerosol and Gas Experiment data

An analysis is made of equatorial ozone variations for 5 years, 1984–1989, using the ozone profile data derived from the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument. Attention is focused on the annual cycle and also on interannual variability, particularly the quasi‐biennial oscillation (QBO) and El Niño‐Southern Oscillation (ENSO) variations in the lower stratosphere, where the largest contribution to total column ozone takes place. The annual variation in zonal mean total ozone around the equator is composed of symmetric and asymmetric modes with respect to the equator, with maximum contributions being around 19 km for the symmetric mode and around 25 km for the asymmetric mode. The persistent zonal wavenumber 1 structure observed by the total ozone mapping spectrometer over the equator is almost missing in the SAGE‐derived column amounts integrated in the stratosphere, suggesting a significant contribution from tropospheric ozone. Interannual variations in the equatorial ozone are dominated by the QBO above 20 km and the ENSO‐related variation below 20 km. The ozone QBO is characterized by zonally uniform phase changes in association with the zonal wind QBO in the equatorial lower stratosphere. The ENSO‐related ozone variation consists of both the east‐west vacillation and the zonally uniform phase variation. During the El Niño event, the east‐west contrast with positive (negative) deviations in the eastern (western) hemisphere is conspicuous, while the decreasing tendency of the zonal mean values is maximum at the same time.

Quasi-Biennial Oscillations of Ozone and Diabatic Circulation in the Equatorial Stratosphere

The quasi-biennial oscillation (QBO) in ozone in the equatorial stratosphere is obtained by analyzing the Stratospheric Aerosol and Gas Experiment (SAGE) data from 1984 to 1989. The phase of the ozone QBO in the lower stratosphere is found to precede the zonal wind QBO by several months as opposed to the theoretically expected in-phase relationship between the two. A mechanistic model is developed to explore possible reasons for this disagreement. The model is capable of simulating the actual time evolution of the ozone QBO by introducing the observed zonal wind profile as input. The modeled results confirm the conventional view that the ozone QBO is generated by the vertical ozone advection that is driven to maintain the temperature structure against radiative damping. However, a series of experiments emphasizes the importance of the feedback of the ozone QBO to the diabatic heating through the absorption of solar radiation. Due to this effect, the phase of the ozone QBO shifts up to a quarter cycle ahead and approaches that of the temperature QBO. Because of this inphase relationship, the feedback of the ozone QBO to the diabatic heating acts to compensate for the radiative damping of the temperature structure, thus reducing the magnitude of the induced diabatic circulation. Because the reduction of the magnitude of the vertical motion facilitates downward transport of easterly momentum by the mean flow, this feedback process can help to resolve the insufficiency of the easterly momentum in driving the dynamical QBO in general circulation models (GCMs). It should be emphasized that more sophisticated models that allow for full interaction between the chemical species and radiative and dynamical processes should be developed to improve our understanding of both dynamical and ozone QBOs.

Relationship between QBOs of stratospheric winds, ENSO variability and other atmospheric parameters

AbstractThe 50‐mbar tropical zonal wind has a predominent quasi‐biennial oscillation (QBO) mode of an average period of ca. 28 months, with variation in the range 21–33 months and amplitudes varying within ± 20 per cent. For the Southern Oscillation, Tahiti minus Darwin (T‐D), sea‐surface temperature (SST) and equatorial rainfall indices, QBO is not the strongest mode. Periods of 3.6 and ca. 6 years are stronger. The QBO modes for these and other parameters (e.g. surface winds and winds in upper and lower troposphere and stratospheric winter temperature at the North Pole) are very irregular, with amplitudes, phases, and sometimes even period having large changes with time. It seems that these have little relationship with the 50‐mbar zonal wind QBO and may have altogether different origins.

A study of quasi-biennial oscillation in the tropical stratosphere

The characteristics of the quasi-biennial oscillation in zonal wind and temperature at Trivandrum (8.5°N, 77°E) have been studied using data covering 16 years. Similar study has been carried out for zonal wind at Balasore (21.5°N, 87°E) using data covering 9 years. The cycle to cycle variation of amplitudes, their altitude variation, periods and descent rates of the westerly and easterly regimes have been studied.

The Quasi-biennial Oscillation of Ozone in the Tropical Middle Stratosphere: A One-Dimensional Model

A one-dimensional model of the quasi-biennial oscillation (QBO) of ozone in the tropical middle stratosphere is derived based on assumed (observed) zonal wind QBO in a coupled dynamic, radiative/photochemical system. It is found that the derived vertical variation of the ozone QBO amplitude has two maxima, one at 32 km and the other at 22 km, and a minimum at 28 km. These are in qualitative agreement with observations. In the height interval 30-35 km, the ozone QBO is closely related to temperature dependent photochemistry, and the ozone and temperature variations are out of phase. Below 28 km, where vertical ozone and thermal transports are important, ozone and temperature oscillations are in phase, but both are approximately 270 deg out of phase with the vertical wind variation.

NOTE CONCERNING THE PERIOD OF THE QUASI-BIENNIAL OSCILLATION

Abstract The period of the quasi-biennial oscillation is examined through the use of a harmonic procedure which allows one to examine periods of interest without omission of any data. On the basis of 8, and 5½ years, of mean-monthly zonal-wind and temperature data in the Northern and Southern Hemispheres, respectively, it is found that: (1) A quasi-biennial oscillation in zonal-wind exists in the troposphere of the Tropics and subtropics; (2) The temperate-latitude stratosphere is the seat of a surprisingly strong temperature oscillation of approximately 24-mon. period, with some stations in the western Pacific exhibiting a biennial oscillation larger than the annual oscillation; (3) In temperate and low-polar latitudes of the Northern Hemisphere stratosphere the predominant period of zonal-wind oscillation exceeds 30 mon., while in the Southern Hemisphere there is more evidence for a 26–28-mon. periodicity, thus suggesting an asymmetry between hemispheres. Inasmuch as these results imply that at some lat...