Westerly Phase Of Quasi-biennial Oscillation Research Articles

Modifications of the quasi‐biennial oscillation by a geoengineering perturbation of the stratospheric aerosol layer

AbstractThis paper examines the impact of geoengineering via stratospheric sulfate aerosol on the quasi‐biennial oscillation (QBO) using the NASA Goddard Earth Observing System version 5 Chemistry Climate Model. We performed four 30 year simulations with a continuous injection of sulfur dioxide on the equator at 0° longitude. The four simulations differ by the amount of sulfur dioxide injected (5 Tg/yr and 2.5 Tg/yr) and the altitude of the injection (16 km–25 km and 22 km–25 km). We find that such an injection dramatically alters the quasi‐biennial oscillation, prolonging the phase of easterly shear with respect to the control simulation. This is caused by the increased aerosol heating and associated warming in the tropical lower stratosphere and higher residual vertical velocity. In the case of maximum perturbation, i.e., highest stratospheric aerosol burden, the lower tropical stratosphere is locked into a permanent westerly QBO phase.

Global climatological variability of quasi-two-day waves revealed by TIMED/SABER observations

Abstract. This paper presents characteristics of quasi-two-day waves (QTDWs) in the mesosphere and lower thermosphere (MLT) between 52° S and 52° N from 2002 to 2011 using TIMED/SABER temperature data. Spectral analysis suggests that dominant QTDW components at mid-high latitudes of the Southern Hemisphere (SH) and the Northern Hemisphere (NH) are (2.13, W3) and (2.04, W4), respectively. The most remarkable QTDW is (2.13, W3), which happened in the southern summer of 2002–2003 at 32° S from 60 to 90 km in altitude. Its downward phase propagation indicates upward propagation of the wave energy and a potential source region below 60 km. Analysis of horizontal wind fields in the same period shows the westward and southward propagation of (2.13, W3) and a possible reflection region above 90 km. Fundamental parameters of QTDWs present significant interhemispheric differences and interannual variations in statistical analysis. Amplitudes in the SH are twice larger than that in the NH, and vertical wavelengths are a little longer in the SH. QTDWs may endure stronger dissipation in southern summer because of shorter durations of their attenuation stages. Impact of the equatorial quasi-biennial-oscillation (QBO) on QTDWs can extend to mid-high latitudes of both hemispheres. It seems easier for QTDWs to propagate upward in the equatorial QBO's westerly phase in the lower stratosphere and easterly phase in the middle stratosphere. Interannual variations of QTDW strength may be influenced by solar activity as well. Strengths of QTDWs appear to be stronger (weaker) in the solar maximum (minimum).

Meteor‐radar observed mesospheric semi‐annual oscillation (SAO) and quasi‐biennial oscillation (QBO) over Maui, Hawaii

We observed the variations of the semi‐annual oscillation (SAO) in the mesopause region of northern subtropics, and we describe its origin and forcing implications. Using the measurements of horizontal wind profiles made by the University of Illinois meteor radar in Maui, Hawaii (20.7°N, 156.3°W) from May 2002 to June 2007 and the European Centre for Medium‐Range Weather Forecasts (ECMWF) interim data set, we find that the mesospheric SAO, with the winter westerly near 80–90 km clearly stronger than the summer westerly, is out of phase with the stratospheric SAO near 1 hPa (∼50 km). The mesospheric SAO easterly is strong during the easterly phase and weak during the westerly phase of the stratospheric quasi‐biennial oscillation (QBO) near 10 hPa (∼30 km), suggesting the modulation of the mesospheric SAO by the stratospheric QBO. The mesospheric QBO has an amplitude of approximately 5 m/s near 80 km. It is in phase with the stratospheric QBO near 10 hPa and out of phase with the QBO‐like oscillation near 1 hPa. The correlation of the gravity wave (GW) and the quasi‐two‐day wave (QTDW) activities with the mesospheric SAO and QBO suggests that the GW drags and the QTDW Eliassen‐Palm flux divergences likely contribute to the QBO modulation of the mesospheric SAO. The winter easterly wind in the tropical upper stratosphere pushes further into the northern subtropics during the QBO westerly phase than during the easterly phase. This may have impacts on the upward propagation of westward‐propagating GWs originated from the middle latitudes, and thus the westward GW forcing in the upper mesosphere of northern subtropics.

On the relationship between QBO and distribution of tropical deep convection

There have been several observational and modeling analyses that have indicated that the stratospheric quasi‐biennial oscillation (QBO) significantly affects the tropical troposphere. This article aims to identify the QBO signal in tropical deep convection. Some difficulties in previous studies were ambiguities in the identification of tropical deep convection in observations, and also in separating the El Niño/Southern Oscillation (ENSO) and other tropospheric signals from QBO influences. We use a recent cluster analysis of 21.5 years of International Satellite Cloud Climatology Project tropical weather states to identify tropical deep convection and cirrus clouds, as well as 32.25 years of precipitation data as proxies for deep convection. Correlations between the QBO, ENSO, and other tropospheric patterns such as the tropospheric biennial oscillation and Pacific decadal oscillation are taken into account to isolate the influence of the QBO. Whereas tropical deep convection is mostly related to ENSO and the annual cycle, the QBO westerly phase, independent of the annual cycle as well as linear and nonlinear impacts of ENSO, leads to an eastward shift in the strength of meridional overturning contributions to the Hadley circulation over the Pacific and thus also affects the subtropical circulation. For deep convective clouds, relative differences in convective cloud cover between the QBO easterly and QBO westerly phases can be as large as 51% ± 7% of the annual average over isolated regions in the tropical west Pacific and 103% ± 35% over the east Pacific, where the absolute values are lower and where notable deviations occur during the QBO westerly phase.

Biennial variability in aerosol optical depth associated with QBO modulated tropical tropopause

AbstractThe role of quasi‐biennial oscillation (QBO) in determining the distribution of atmospheric aerosols over the north Indian region has been investigated. The results reveal that aerosol optical depth (AOD) undergoes a biennial variability in response to positive and negative phases of QBO. Large aerosol loading occurring in the pre‐monsoon season during westerly phase (positive phase) of QBO is concurrent with a quasi‐horizontal advection, diffusion and gravitational sedimentation. Further analysis of tropopause anomalies confirm that warming (cooling) of the tropical tropopause during the positive (negative) phase of QBO is accompanied by an increase (decrease) in AOD over the study region. Copyright © 2011 Royal Meteorological Society

Variability of sunspot cycle QBO and total ozone over high altitude western Himalayan regions

Long-term trend of total column ozone at high altitude region in Ladakh is studied, using a total ozone mapping spectrometer and an ozone monitoring instrument during 1979–2008. In the region, total ozone exhibits seasonality with maximum in spring and minimum in autumn. The decreasing trend of total ozone was found as −2.51±0.45% per decade with 95% confidence level in the region. Ozone deficiency in the Ladakh region is strongest (−33.9 DU at Hanle) in May and weakest (−11.5 DU at Hanle) in January–February. In the study, the solar maximum in 1990 is in phase with ozone maximum, while ozone variation lags in phase with the 1980 and 2000 solar maxima. However, a significant correlation between total ozone and sunspot number is achieved in the westerly phase of quasi-biennial oscillation during spring season. Decreasing trend of ozone in the region is correlating well with the cooling rate in the lower stratosphere.

Equatorial Waves in Opposite QBO Phases

Abstract A methodology for identifying equatorial waves is used to analyze the multilevel 40-yr ECMWF Re-Analysis (ERA-40) data for two different years (1992 and 1993) to investigate the behavior of the equatorial waves under opposite phases of the quasi-biennial oscillation (QBO). A comprehensive view of 3D structures and of zonal and vertical propagation of equatorial Kelvin, westward-moving mixed Rossby–gravity (WMRG), and n = 1 Rossby (R1) waves in different QBO phases is presented. Consistent with expectation based on theory, upward-propagating Kelvin waves occur more frequently during the easterly QBO phase than during the westerly QBO phase. However, the westward-moving WMRG and R1 waves show the opposite behavior. The presence of vertically propagating equatorial waves in the stratosphere also depends on the upper tropospheric winds and tropospheric forcing. Typical propagation parameters such as the zonal wavenumber, zonal phase speed, period, vertical wavelength, and vertical group velocity are found. In general, waves in the lower stratosphere have a smaller zonal wavenumber, shorter period, faster phase speed, and shorter vertical wavelength than those in the upper troposphere. All of the waves in the lower stratosphere show an upward group velocity and downward phase speed. When the phase of the QBO is not favorable for waves to propagate, their phase speed in the lower stratosphere is larger and their period is shorter than in the favorable phase, suggesting Doppler shifting by the ambient flow and a filtering of the slow waves. Tropospheric WMRG and R1 waves in the Western Hemisphere also show upward phase speed and downward group velocity, with an indication of their forcing from middle latitudes. Although the waves observed in the lower stratosphere are dominated by “free” waves, there is evidence of some connection with previous tropical convection in the favorable year for the Kelvin waves in the warm water hemisphere and WMRG and R1 waves in the Western Hemisphere, which is suggestive of the importance of convective forcing for the existence of propagating coupled Kelvin waves and midlatitude forcing for the existence of coupled WMRG and R1 waves.

Nonlinear relation of the Arctic oscillation with the quasi-biennial oscillation

A nonlinear principal component analysis (NLPCA) is applied to a set of monthly mean time series from January 1956 to December 2007 consisting of the Arctic oscillation (AO) index derived from 1,000-hPa geopotential height anomalies poleward of 20°N latitude and the zonal winds observed at seven pressure levels between 10 and 70 hPa in the equatorial stratosphere to investigate the relation of the AO with the quasi-biennial oscillation (QBO). The NLPCA is conducted using a new, compact neural network model. The NLPCA modeling of the dataset of the AO index and QBO winds offers a clear picture of the relation between the two oscillations. In particular, the phase of covariation of the oscillations defined by the two nonlinear principal components of the dataset progresses with a predominant 28.4-month periodicity. This predominant cycle is modulated by an 11-year cycle. The variation of the AO index with the QBO phase also shows that the average AO index is positive when the westerly QBO phase descends past 30 hPa and, conversely, the average AO index is negative when the easterly QBO phase descends past 30 hPa. This relationship is evident during the boreal cold season from November to April but non-existent during the boreal warm season from May to October.

成層圏ＱＢＯとアジア域降水活動との関係

The influence of stratospheric quasi-biennial oscillation (QBO) on global precipitation features was studied over a 25-year period. The years from 1980 to 2004 are classified into easterly and westerly phases of QBO. Composite analyses in Asia reveal noteworthy pluvial anomalies near the Philippines, and inactive front activity and typical drought events due to adiabatic descent over Japan during the easterly phase of QBO. Cool summers and extreme rainfall events in Japan tend to prevail in the westerly phase. In particular, ten Typhoons struck Japan in 2004 accompanied by the westerly phase of QBO.

Nonlinearity of the combined warm ENSO and QBO effects on the Northern Hemisphere polar vortex in MAECHAM5 simulations

The influence of the quasi‐biennial oscillation (QBO) on the Northern Hemisphere (NH) polar vortex response to warm El Niño–Southern Oscillation (ENSO) events and the impact of the warm ENSO events on the QBO signal in the NH polar stratosphere have been analyzed using the Middle Atmosphere ECHAM5 model. The experiment setup was designed to include simulations of extended NH winter seasons for either strong easterly or strong westerly phases of the tropical QBO, forced with either sea surface temperatures (SSTs) from the strong ENSO event that occurred in 1997/1998 or with climatological SSTs. It has been found that the weakening and warming of the polar vortex associated with a warm ENSO are intensified at the end of the winter during both QBO phases. In addition, the westerly QBO phase delays the onset of the warm ENSO signal, while the easterly QBO phase advances it. Warm ENSO events also impact the extratropical signal of the QBO by intensifying (weakening) the QBO effects in early (late) winter. Therefore, it appears that during warm ENSO events the duration of QBO signal in the northern extratropics is shortened while its downward propagation accelerated. Our dynamical analysis has revealed that these results are due to changes in the background flow caused by the QBO combined with changes in the anomalous propagation and dissipation of extratropical waves generated by warm ENSO. In both cases, a nonlinear behavior in the response of the polar vortex is observed when both warm ENSO and the easterly phase of the QBO operate together. These results suggest that the Arctic polar vortex response to combined forcing factors, in our case warm ENSO and the QBO phenomena, is expected to be nonlinear also for other coexistent forcing factors able to affect the variability of the vortex in the stratosphere.

Quantification of gravity wave forcing in driving the stratospheric Quasi‐Biennial Oscillation

Using long‐term Rayleigh lidar temperature observations during April 1998–April 2005 in the lower stratospheric region, momentum flux divergence of the gravity waves of periods 0.5–1 and 2–4 hours are estimated over Gadanki (13.5°N, 79.2°E), India. Monthly mean zonal winds from NCEP/NCAR reanalysis data over Gadanki at two pressure levels 10 and 20 hPa are used to study the characteristics of the Quasi‐Biennial Oscillation (QBO) and its month‐to‐month acceleration. This observed mean flow acceleration is compared with that estimated from the momentum flux divergence of gravity waves, which led to a better insight into the role of gravity waves in driving the QBO. The present analysis reveals that the contribution of gravity waves towards the westerly phase of QBO varies from ∼10–60% while that during easterly phase from ∼10–30%. The present study thus quantifies the role of gravity waves in driving the easterly and westerly phases of QBO.

Equatorial wave analysis from SABER and ECMWF temperatures

Abstract. Equatorial planetary scale wave modes such as Kelvin waves or Rossby-gravity waves are excited by convective processes in the troposphere. In this paper an analysis for these and other equatorial wave modes is carried out with special focus on the stratosphere using temperature data from the SABER satellite instrument as well as ECMWF temperatures. Space-time spectra of symmetric and antisymmetric spectral power are derived to separate the different equatorial wave types and the contribution of gravity waves is determined from the spectral background of the space-time spectra. Both gravity waves and equatorial planetary scale wave modes are main drivers of the quasi-biennial oscillation (QBO) in the stratosphere. Temperature variances attributed to the different wave types are calculated for the period from February 2002 until March 2006 and compared to previous findings. A comparison between SABER and ECMWF wave analyses shows that in the lower stratosphere SABER and ECMWF spectra and temperature variances agree remarkably well while in the upper stratosphere ECMWF tends to overestimate Kelvin wave components. Gravity wave variances are partly reproduced by ECMWF but have a significant low-bias. For the examples of a QBO westerly phase (October–December 2004) and a QBO easterly phase (November/December 2005, period of the SCOUT-O3 tropical aircraft campaign in Darwin/Australia) in the lower stratosphere we find qualitatively good agreement between SABER and ECMWF in the longitude-time distribution of Kelvin, Rossby (n=1), and Rossby-gravity waves.

Analysis of the Characteristics of the Stratospheric Quasi-zero Wind Layer Over China

利用ECMWF提供的ERA-40再分析风场资料首次分析了中国上空平流层准零风层的特点及其随季节和地理位置的变化特征.结果表明,准零风层一般处于18～25 km高度范围内,零风线所在的高度随时间和地理位置的不同稍有变化.根据准零风层随纬度的变化特征,中国上空可以分成三个区域:低纬地区(5°N～20°N)、中低纬过渡区域(20°N～32.5°N)和中高纬地区(32.5°N～55°N).低纬地区一般在冬季和初春有准零风层结构存在;中高纬地区一般在春末和夏季存在准零风层结构;而中低纬过渡区域是否有准零风层结构存在还与准两年震荡(QBO)有关,在QBO东风相位时,过渡区域呈现的特性偏向于中纬特性,在QBO西风相位时,过渡区域呈现的特性偏向于低纬特性.准零风层随经度变化非常小,零风线所在高度随经度的变化幅度一般不超过2 km,过渡区域的变化幅度相对大些.

Modulation of northern hemisphere wintertime stationary planetary wave activity: East Asian climate relationships by the Quasi‐Biennial Oscillation

The modulation of the relationship between the tropospheric stationary planetary wave activity and the East Asian winter climate by the tropical quasi‐biennial oscillation (QBO) wind in the stratosphere is investigated. In the QBO easterly phase, a significant warming appears in northeastern Asia in the presence of high wave activities. This corresponds to a weakened East Asian trough at 500‐hPa, which determines the extent to which cold waves penetrate into East Asia. However, in the QBO westerly phase, both the surface warming and the weakening of the East Asian trough become insignificant in response to high wave activities. The possible mechanism for this QBO modulation on the tropospheric wave activities may be attributed to the indirect influence of the QBO induced polar and extratropical stratospheric circulation changes. Under the QBO easterly phase conditions, the tropospheric wave activity flux divergence in the higher‐latitude region is enhanced due to enhanced upward Eliassen‐Palm (EP) flux into the stratosphere, while the wave flux convergence in the subtropical troposphere is increased due to the decrease in the equatorward flux. This leads to an enhanced wave activity difference and thus the associated East Asian climate anomalies become larger and robust. An opposite effect (i.e., reduced wave activity difference) appears in the QBO westerly phase. Further analyses reveal that the QBO significantly modulates both the zonal wave number 1 and 2 in the sea level pressure field but not for wave number 3. The combination of wave number 1 and 2 patterns leads to the strongest surface temperature anomalies in northern Asia.

Solar‐QBO interaction and its impact on stratospheric ozone in a zonally averaged photochemical transport model of the middle atmosphere

We investigate the solar cycle modulation of the quasi‐biennial oscillation (QBO) in stratospheric zonal winds and its impact on stratospheric ozone with an updated version of the zonally averaged CHEM2D middle atmosphere model. We find that the duration of the westerly QBO phase at solar maximum is 3 months shorter than at solar minimum, a more robust result than in an earlier CHEM2D study due to reduced Rayleigh friction drag in the present version of the model. The modeled solar cycle ozone response, determined via multiple linear regression, is compared with observational estimates from the combined Solar Backscattered Ultraviolet (SBUV/2) data set for the period 1979–2003. We find that a model simulation including imposed solar UV variations, the zonal wind QBO, and an imposed 11‐year variation in planetary wave 1 amplitude produces a lower stratospheric ozone response of ∼2.5% between 0 and 20°S and an upper stratospheric ozone response of ∼1% between 45 and 55 km, in good agreement with the SBUV‐derived ozone response. This simulation also produces an (enhancement/reduction) in the (lower/upper) stratospheric temperature response at low latitudes compared to the effects of solar UV variations alone, which are consistent with model vertical velocity anomalies produced by the solar‐modulated QBO and imposed changes in planetary wave forcing.

Sensitivity of the boreal winter circulation in the middle atmosphere to the quasi‐biennial oscillation in MAECHAM5 simulations

The polar vortex in the Northern Hemisphere exhibits high intraseasonal and interannual variability which, to some degree, may be controlled by the quasi‐biennial oscillation (QBO) in the tropical stratosphere. Here we analyze the QBO signal in the Northern Hemisphere polar vortex in a model simulation using the general circulation model MAECHAM5 (Middle Atmosphere European Center Hamburg Model), which simulates the QBO as an internal mode of variability. Composites have been computed for the westerly and easterly QBO phases from early winter to late winter (November–December, December–January and January–February) of a 50‐year experiment containing 20 complete QBO cycles. This method identifies tropical and midlatitude patterns in wind and temperature that are related to the secondary meridional circulation of the QBO extending towards the winter pole. In the tropics, significant QBO signature is observed in the mesosphere up to 0.05 hPa only in early winter and mainly in the easterly QBO phase forced by the parameterized gravity waves‐mean flow interaction. At high latitudes, MAECHAM5 shows a significantly warmer (colder) polar stratosphere in the easterly (westerly) QBO phase at 30 hPa accompanied by a weaker (stronger) polar vortex in the late winter months, from December to February (December to January) in the easterly (westerly) phase of the QBO. In early winter there is no significant change in temperature and zonal mean zonal wind in the polar stratosphere. The analysis of EP fluxes shows a different behavior between QBO phases, with changes in the waveguide. Wave propagation occurs upwards and polewards in the easterly QBO phase at 30 hPa, while waves are refracted equatorward in the westerly phase. No relationship has been found between the tropical QBO and the final warming at the end of the boreal winter.

Revisiting the Possible Links between the Quasi-Biennial Oscillation and the Indian Summer Monsoon Using NCEP R-2 and CMAP Fields

AbstractIn the past the stratospheric quasi-biennial oscillation (QBO) has sometimes been proposed to explain the tendency for the Indian summer monsoon (ISM) to alternate between strong and weak years. In this study, NCEP Reanalysis-2 (R-2) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) fields are statistically analyzed to assess the relationship between equatorial zonal winds in the stratosphere and ISM. In a first step, it is shown that zonal winds at 15 hPa during the preceding winter (January–February) are the best stratospheric predictor of the summer rainfall over the Indian subcontinent as a whole. This relationship mainly holds for August and September, or the late ISM. Surprisingly, the QBO pattern is not significantly associated with the rainfall variability during June–July or the early ISM. CMAP and NCEP R-2 fields corroborate these findings and show that westerly QBO years are associated with a deepening of the monsoon trough over the Gangetic plains and decreased convective activity in the eastern equatorial Indian region. However, further statistical analysis shows that the QBO–ISM link is complex since a westerly QBO phase at 15 hPa in boreal winter leads to a weaker monsoon surface circulation with, in particular, a weakening of the Somali jet at the beginning of the monsoon, but a much stronger circulation in September. At that time, the Tibetan high is reinforced, the tropical easterly jet at 200 hPa is stronger over India, and the local reversed Hadley circulation is also strengthened north of the equator. The mechanisms by which the QBO may affect ISM have been explored through, in particular, correlations between stratospheric winds and tropopause temperature and pressure fields. The results provide support for an out-of-phase behavior of convective activity between the Indian subcontinent and the equatorial Indian Ocean induced by the QBO phase, especially during the late ISM. During a westerly QBO phase, convective activity is, in September, enhanced over India, which brings higher precipitation, compared to the east phase. This work also suggests that the winter QBO at 15 hPa could have some skill in foreshadowing the late ISM.

Modeling the atmospheric response to solar irradiance changes using a GCM with a realistic QBO

The impact of solar irradiance changes on the winter polar stratosphere is investigated using a general circulation model in which the equatorial Quasi‐Biennial Oscillation (QBO) is internally generated and self‐sustaining. The model results compare favorably with observations, supporting previous findings that the equatorial zonal wind modulates the polar stratospheric response to solar irradiance changes. In the QBO easterly phase, Northern Hemisphere sudden stratospheric warmings are found to be more prevalent under solar minimum conditions than under solar maximum conditions. However, in the QBO westerly phase the reverse is true. The possible solar‐modulation of the QBO period is also investigated. Although small changes are evident in the same sense as those observed, i.e. a lengthening of the period during solar minimum conditions, longer simulations would be required to verify the statistical significance of this result.

Kelvin waves and ozone Kelvin waves in the quasi‐biennial oscillation and semiannual oscillation: A simulation by a high‐resolution chemistry‐coupled general circulation model

Equatorial Kelvin waves and ozone Kelvin waves were simulated by a T63L250 chemistry‐coupled general circulation model with a high vertical resolution (300 m). The model produces a realistic quasi‐biennial oscillation (QBO) and a semiannual oscillation (SAO) in the equatorial stratosphere. The QBO has a period slightly longer than 2 years, and the SAO shows rapid reversals from westerly to easterly regimes and gradual descents of westerlies. Results for the zonal wave number 1 slow and fast Kelvin waves are discussed. Structure of the waves and phase relationships between temperature and ozone perturbations coincide well with satellite observations made by LIMS, CLAES, and MLS. They are generally in phase (antiphase) in the lower (upper) stratosphere as theoretically expected. The fast Kelvin waves in the temperature and ozone are dominant in the upper stratosphere because the slow Kelvin waves are effectively filtered by the QBO westerly. In this simulation, the fast Kelvin waves encounter their critical levels in the upper stratosphere when zonal asymmetry of the SAO westerly is enhanced by an intrusion of the extratropical planetary waves. In addition to the critical level filtering effect, modulations of wave properties by background winds are evident near easterly and westerly shears associated with the QBO and SAO. Enhancement of wave amplitude in the QBO westerly shear is well coincident with radiosonde observations. Increase/decrease of vertical wavelength in the QBO easterly/westerly is obvious in this simulation, which is consistent with the linear wave theory. Shortening of wave period due to the descending QBO westerly shear zone is demonstrated for the first time. Moreover, dominant periods during the QBO westerly phase are longer than those during the QBO easterly phase for both the slow and fast Kelvin waves.

Arctic oscillation response to the 1991 Pinatubo eruption in the SKYHI general circulation model with a realistic quasi‐biennial oscillation

Stratospheric aerosol clouds from large tropical volcanic eruptions can be expected to alter the atmospheric radiative balance for a period of up to several years. Observations following several previous major eruptions suggest that one effect of the radiative perturbations is to cause anomalies in the Northern Hemisphere extratropical winter tropospheric circulation that can be broadly characterized as positive excursions of the Arctic Oscillation (AO). We report on a modeling investigation of the radiative and dynamical mechanisms that may account for the observed AO anomalies following eruptions. We focus on the best observed and strongest 20th century eruption, that of Mt. Pinatubo on 15 June 1991. The impact of the Pinatubo eruption on the climate has been the focus of a number of earlier modeling studies, but all of these previous studies used models with no quasi‐biennial oscillation (QBO) in the tropical stratosphere. The QBO is a very prominent feature of interannual variability of tropical stratospheric circulation and could have a profound effect on the global atmospheric response to volcanic radiative forcing. Thus a complete study of the atmospheric variability following volcanic eruptions should include a realistic representation of the tropical QBO. Here we address, for the first time, this important issue. We employed a version of the SKYHI troposphere‐stratosphere‐mesosphere model that effectively assimilates observed zonal mean winds in the tropical stratosphere to simulate a very realistic QBO. We performed an ensemble of 24 simulations for the period 1 June 1991 to 31 May 1993. These simulations included a realistic prescription of the stratospheric aerosol layer based on satellite observations. These integrations are compared to control integrations with no volcanic aerosol. The model produced a reasonably realistic representation of the positive AO response in boreal winter that is usually observed after major eruptions. Detailed analysis shows that the aerosol perturbations to the tropospheric winter circulation are affected significantly by the phase of the QBO, with a westerly QBO phase in the lower stratosphere resulting in an enhancement of the aerosol effect on the AO. Improved quantification of the QBO effect on climate sensitivity helps to better understand mechanisms of the stratospheric contribution to natural and externally forced climate variability.