The Influence of the Equatorial QBO on the Northern Hemisphere Winter Circulation of a GCM

Niwano, Mototaka; Takahashi, Masaaki

doi:10.2151/jmsj1965.76.3_453

Cited by 36 publications

(28 citation statements)

References 19 publications

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“…2a) during the first winter occurs during the October-November-December months, rather than December-January-February months. Also, it has to be noted that here we try to simulate one event rather than calculate the composites of several cases as is carried out in the previous modeling/observational studies (Holton and Tan, 1980;Niwano and Takahashi, 1998;Calvo et al, 2007). Hence, the vortex is highly sensitive to the winter months selected and the dynamics of the vortex is non-linear.…”

Section: Hpa Geopotential Height Response In Boreal Wintermentioning

confidence: 99%

“…Hamilton (1998) reproduced the Holton-Tan effect making use of a general circulation model run for a continuous 48-year period with a time varying tropical momentum forcing that produced a 27-month QBO in the equatorial zonal wind with realistic QBO features. Niwano and Takahashi (1998) investigated this feature using their model that spontaneously produces a QBO-like oscillation in the tropics with a period of about 1.4 years and revealed that the NH polar vortex was weaker in the easterly QBO phase based on the January-March composites of the equatorial wind averaged between 7 and 50 hPa. Calvo et al (2007) using the middle atmosphere version of ECHAM5, which has an internally generated QBO pointed out a significantly warm polar vortex in the easterly QBO phase in January-February months and a cold, strong polar vortex in the westerly QBO phase in the December-January months.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 2: Sensitivity to the phase of the QBO and ENSO

et al. 2009

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Abstract.The sensitivity of the climate impact of Mt. Pinatubo eruption in the tropics and extratropics to different QBO phases is investigated. Mt. Pinatubo erupted in June 1991 during the easterly phase of the QBO at 30 hPa and the phase change to westerly took place in August 1992. Here, the consequences are analyzed if the QBO phase had been in the opposite phase during the eruption of Mt. Pinatubo. Hence, in this study, simulations are carried out using the middle atmosphere configuration of ECHAM5 general circulation model for two cases -one with the observed QBO phase and the other with the opposite QBO phase. The response of temperature and geopotential height in the lower stratosphere is evaluated for the following cases -(1) when only the effects of the QBO are included and (2) when the effects of aerosols, QBO and SSTs (combined response) are included. The tropical QBO signature in the lower stratospheric temperature is well captured in the pure QBO responses and in the combined (aerosol + ocean + QBO) responses. The response of the extratropical atmosphere to the QBO during the second winter after the eruption is captured realistically in the case of the combined forcing showing a strengthening of the polar vortex when the QBO is in its westerly phase and a warm, weak polar vortex in the easterly QBO phase. The vortex is disturbed during the first winter irrespective of the QBO phases in the combined responses and this may be due to the strong influences of El Niño during the first winters after eruption. However, the pure QBO experiments do not realistically reproduce a strengthening of the polar vortex in the westerly QBO phase, even though below normal temperatures in the high latitudes are seen in OctoberNovember-December months when the opposite QBO phase is prescribed instead of the December-January-February winter months used here for averaging.

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Section: Hpa Geopotential Height Response In Boreal Wintermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 2: Sensitivity to the phase of the QBO and ENSO

et al. 2009

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“…Niwano and Takahashi (1998) investigated the influence of the equatorial QBO that was simulated in their GCM on the NH winter circulation, while Hamilton (1998) investigated the effects of an imposed QBO using the GFDL SKIHI GCM. Both studies confirmed the Holton-Tan relationship and showed modest effects of the QBO to the winter troposphere.…”

Section: Troposphere-stratosphere Coupled Variationmentioning

confidence: 99%

Numerical Studies on Time Variations of the Troposphere-Stratosphere Coupled System.

Yoden

Taguchi

Naito

2002

Journal of the Meteorological Society of Japan

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Interannual variation is a year-to-year variation which is defined as a deviation from the climatolog-ical annual cycle of a meteorological quantity. It can be caused by a variation of an external forcing of the atmospheric circulation system, or can be generated internally within the system. On the other hand, intraseasonal variation is a low-frequency variation within a season, and it is basically considered to be a result of internal processes which may exist even under constant external conditions. In this article, some observational facts on the intraseasonal and interannual variations of the polar stratosphere are presented, and the use of a hierarchy of numerical models to understand the strato-spheric variations is reviewed systematically. Numerical models can be roughly divided into three classes based on their complexity; simple low-order models, medium mechanistic circulation models, and complex general circulation models. In order to understand the stratospheric variations, a hierarchy of stratosphere-only models have been used under an assumption of ''slave stratospheric-variations'' or ''independent stratospheric-variations''. Parameter sweep experiment, in which many trials of computations in parameter space are done by sweeping the value of a control parameter, is a powerful method to understand complex behavior in the models. Recently, however, the importance of the coupled variability of the troposphere and the stratosphere was pointed out for the intraseasonal and interannual variations. In addition to numerical studies with simple or complex models, we have done some parameter sweep experiments with three-dimensional mechanistic circulation models to understand the troposphere-stratosphere coupled variability. All the effects of external forcings that might cause interannual variations can be excluded in the numerical experiments to focus only on internally generated variations within the coupled system. The obtained intraseasonal and interannual variations have some similar characteristics of the real atmosphere in some realistic parameter ranges. Roles of the interannual variations of the external forcings are discussed , which might be significant even if the amplitude is small.

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“…They suggested that sudden stratospheric warmings are less likely during QBO W, when the zero wind line lies in the summer subtropics. The QBO modulates the position of critical surfaces and thus the propagation and absorption of extratropical planetary Rossby waves (e.g., Holton and Austin 1991;Haynes et al 1991;O'Sullivan and Young 1992;O'Sullivan and Chen 1996;Kinnersley and Pawson 1996;Hamilton 1998;Niwano and Takahashi 1998;Gray et al 2001). When QBO easterlies (E) are in the tropical stratosphere, the zero wind line lies in the winter subtropics, and planetary Rossby wave breaking (RWB) is more likely to occur in the northern winter (McIntyre and Palmer 1983).…”

Section: Introductionmentioning

confidence: 99%

Seasonal Influence of the Quasi-Biennial Oscillation on Stratospheric Jets and Rossby Wave Breaking

Hitchman

Huesmann

2009

Journal of the Atmospheric Sciences

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The influence of the stratospheric quasi-biennial oscillation (QBO) on the polar night jets (PNJs), subtropical easterly jets (SEJs), and associated Rossby wave breaking (RWB) is investigated using global meteorological analyses spanning 10 recent QBO cycles. The seasonal dependence of the descent of the QBO is shown by using five layered shear indices. It is found that the influence of the QBO is distinctive for each combination of QBO phase, season, and hemisphere (NH or SH). The following QBO westerly (W) minus easterly (E) differences in the PNJs were found to be significant at the 97% level: When a QBO W (E) maximum is in the lower stratosphere (;500 K or ;50 hPa), the NH winter PNJ is stronger (weaker), in agreement with previous results (mode A). Mode A does not appear to operate in other seasons in the NH besides DJF or in the SH in any season. When a QBO W (E) maximum is in the middle stratosphere (;700-800 K or ;10-20 hPa), the PNJ in the SH spring is stronger (weaker), also in agreement with previous results (mode B). It is found that mode B also operates in the NH spring. A third distinctive mode is found during autumn in both hemispheres: a QBO W (E) maximum in the middle stratosphere coincides with a weaker (stronger) PNJ (mode C). The signs of wind anomalies are the same at low and high latitudes for modes A and B, but are opposite for mode C. This sensitive dependence on QBO phase and season is consistent with the nonlinear nature of the interaction between planetary waves and the shape of the seasonal wind structures.During the solstices the meridional circulation associated with QBO connects primarily with the winter hemisphere, whereas during the equinoxes it is more symmetric about the equator. QBO W enhance the equatorial potential vorticity (PV) gradient maximum, but the time-mean maximum may be related to chronic instabilities in the subtropics. The equatorial PV gradient maximum and flanking RWB tend to be more pronounced in the Eastern Hemisphere in stratospheric analyses.When QBO W are in the middle stratosphere, the flanking PV gradient minima (SEJs) are enhanced and RWB is more frequent and symmetric about the equator. When QBO W are in the upper stratosphere, a strong seasonal asymmetry is seen, with enhanced RWB in the summer SEJ, primarily during boreal winter. This is consistent with an upward increase of summer to winter flow and modulation by a strong ''first'' and weak ''second'' semiannual oscillation.

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The Influence of the Equatorial QBO on the Northern Hemisphere Winter Circulation of a GCM

Cited by 36 publications

References 19 publications

Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 2: Sensitivity to the phase of the QBO and ENSO

Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 2: Sensitivity to the phase of the QBO and ENSO

Numerical Studies on Time Variations of the Troposphere-Stratosphere Coupled System.

Seasonal Influence of the Quasi-Biennial Oscillation on Stratospheric Jets and Rossby Wave Breaking

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