scholarly journals A Possible Influence of Equatorial Winds on the September 2002 Southern Hemisphere Sudden Warming Event

2005 ◽  
Vol 62 (3) ◽  
pp. 651-667 ◽  
Author(s):  
Lesley Gray ◽  
Warwick Norton ◽  
Charlotte Pascoe ◽  
Andrew Charlton
Keyword(s):  
Southern Hemisphere ◽  
Planetary Wave ◽  
Polar Vortex ◽  
Contributory Factor ◽  
Quasi Biennial Oscillation ◽  
Model Studies ◽  
Wave Forcing ◽  
Zonal Winds ◽  
Speed Up ◽  
Biennial Oscillation

Abstract The stratospheric sudden warming in the Southern Hemisphere (SH) in September 2002 was unexpected for two reasons. First, planetary wave activity in the Southern Hemisphere is very weak, and midwinter warmings have never been observed, at least not since observations of the upper stratosphere became regularly available. Second, the warming occurred in a west phase of the quasi-biennial oscillation (QBO) in the lower stratosphere. This is unexpected because warmings are usually considered to be more likely in the east phase of the QBO, when a zero wind line is present in the winter subtropics and hence confines planetary wave propagation to higher latitudes closer to the polar vortex. At first, this evidence suggests that the sudden warming must therefore be simply a result of anomalously strong planetary wave forcing from the troposphere. However, recent model studies have suggested that the midwinter polar vortex may also be sensitive to the equatorial winds in the upper stratosphere, the region dominated by the semiannual oscillation. In this paper, the time series of equatorial zonal winds from two different data sources, the 40-yr ECMWF Re-Analysis (ERA) and the Met Office assimilated dataset, are reviewed. Both suggest that the equatorial winds in the upper stratosphere above 10 hPa were anomalously easterly in 2002. Idealized model experiments are described in which the modeled equatorial winds were relaxed toward these observations for various years to examine whether the anomalous easterlies in 2002 could influence the timing of a warming event. It is found that the 2002 equatorial winds speed up the evolution of a warming event in the model. Therefore, this study suggests that the anomalous easterlies in the 1–10-hPa region may have been a contributory factor in the development of the observed SH warming. However, it is concluded that it is unlikely that the anomalous equatorial winds alone can explain the 2002 warming event.

scholarly journals On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/2016

2018 ◽  
Vol 18 (7) ◽  
pp. 4803-4815 ◽  
Author(s):  
Vivien Matthias ◽  
Manfred Ern
Keyword(s):  
Planetary Wave ◽  
Polar Night ◽  
Quasi Biennial Oscillation ◽  
Model Studies ◽  
Broadband Emission ◽  
Variable Gravity ◽  
Stationary Planetary Wave ◽  
Second Period ◽  
Biennial Oscillation

Abstract. The midwinter 2015/2016 was characterized by an unusually strong polar night jet (PNJ) and extraordinarily large stationary planetary wave (SPW) amplitudes in the subtropical mesosphere. The aim of this study is, therefore, to find the origin of these mesospheric SPWs in the midwinter 2015/2016 study period. The study duration is split into two periods: the first period runs from late December 2015 until early January 2016 (Period I), and the second period from early January until mid-January 2016 (Period II). While the SPW 1 dominates in the subtropical mesosphere in Period I, it is the SPW 2 that dominates in Period II. There are three possibilities explaining how SPWs can occur in the mesosphere: (1) they propagate upward from the stratosphere, (2) they are generated in situ by longitudinally variable gravity wave (GW) drag, or (3) they are generated in situ by barotropic and/or baroclinic instabilities. Using global satellite observations from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) the origin of the mesospheric SPWs is investigated for both time periods. We find that due to the strong PNJ the SPWs were not able to propagate upward into the mesosphere northward of 50∘ N but were deflected upward and equatorward into the subtropical mesosphere. We show that the SPWs observed in the subtropical mesosphere are the same SPWs as in the mid-latitudinal stratosphere. Simultaneously, we find evidence that the mesospheric SPWs in polar latitudes were generated in situ by longitudinally variable GW drag and that there is a mixture of in situ generation by longitudinally variable GW drag and by instabilities at mid-latitudes. Our results, based on observations, show that the abovementioned three mechanisms can act at the same time which confirms earlier model studies. Additionally, the possible contribution from, or impact of, unusually strong SPWs in the subtropical mesosphere to the disruption of the quasi-biennial oscillation (QBO) in the same winter is discussed.

scholarly journals Does the Holton–Tan Mechanism Explain How the Quasi-Biennial Oscillation Modulates the Arctic Polar Vortex?

2012 ◽  
Vol 69 (5) ◽  
pp. 1713-1733 ◽  
Author(s):  
Chaim I. Garfinkel ◽  
Tiffany A. Shaw ◽  
Dennis L. Hartmann ◽  
Darryn W. Waugh
Keyword(s):  
Zonal Wind ◽  
Planetary Wave ◽  
Lower Stratosphere ◽  
Critical Line ◽  
Polar Vortex ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Mean Meridional Circulation ◽  
The Mean ◽  
Biennial Oscillation

Abstract Idealized experiments with the Whole Atmosphere Community Climate Model (WACCM) are used to explore the mechanism(s) whereby the stratospheric quasi-biennial oscillation (QBO) modulates the Northern Hemisphere wintertime stratospheric polar vortex. Overall, the effect of the critical line emphasized in the Holton–Tan mechanism is less important than the effect of the mean meridional circulation associated with QBO winds for the polar response to the QBO. More specifically, the introduction of easterly winds at the equator near 50 hPa 1) causes enhanced synoptic-scale Eliassen–Palm flux (EPF) convergence in the subtropics from 150 to 50 hPa, which leads to the subtropical critical line moving poleward in the lower stratosphere, and 2) creates a barrier to planetary wave propagation from subpolar latitudes to midlatitudes in the middle and upper stratosphere (e.g., less equatorward EPF near 50°N), which leads to enhanced planetary wave convergence in the polar vortex region. These two effects are mechanistically distinct; while the former is related to the subtropical critical line, the latter is due to the mean meridional circulation of the QBO. All of these effects are consistent with linear theory, although the evolution of the entire wind distribution is only quasi-linear because induced zonal wind changes cause the wave driving to shift and thereby positively feed back on the zonal wind changes. Finally, downward propagation of the QBO in the equatorial stratosphere, upper stratospheric equatorial zonal wind, and changes in the tropospheric circulation appear to be less important than lower stratospheric easterlies for the polar stratospheric response. Overall, an easterly QBO wind anomaly in the lower stratosphere leads to a weakened stratospheric polar vortex, in agreement with previous studies, although not because of changes in the subtropical critical line.

scholarly journals Solar and QBO Influences on the Timing of Stratospheric Sudden Warmings

2004 ◽  
Vol 61 (23) ◽  
pp. 2777-2796 ◽  
Author(s):  
Lesley J. Gray ◽  
Simon Crooks ◽  
Charlotte Pascoe ◽  
Sarah Sparrow ◽  
Michael Palmer
Keyword(s):  
Northern Hemisphere ◽  
Zonal Wind ◽  
Polar Vortex ◽  
Quasi Biennial Oscillation ◽  
Model Experiments ◽  
Zonal Winds ◽  
Stratospheric Sudden Warmings ◽  
Hemisphere Winter ◽  
Biennial Oscillation ◽  
Northern Hemisphere Winter

Abstract The interaction of the 11-yr solar cycle (SC) and the quasi-biennial oscillation (QBO) and their influence on the Northern Hemisphere (NH) polar vortex are studied using idealized model experiments and ECMWF Re-Analysis (ERA-40). In the model experiments, the sensitivity of the NH polar vortex to imposed easterlies at equatorial/subtropical latitudes over various height ranges is tested to explore the possible influence from zonal wind anomalies associated with the QBO and the 11-yr SC in those regions. The experiments show that the timing of the modeled stratospheric sudden warmings (SSWs) is sensitive to the imposed easterlies at the equator/subtropics. When easterlies are imposed in the equatorial or subtropical upper stratosphere, the onset of the SSWs is earlier. A mechanism is proposed in which zonal wind anomalies in the equatorial/subtropical upper stratosphere associated with the QBO and 11-yr SC either reinforce each other or cancel each other out. When they reinforce, as in Smin–QBO-east (Smin/E) and Smax–QBO-west (Smax/W), it is suggested that the resulting anomaly is large enough to influence the development of the Aleutian high and hence the time of onset of the SSWs. Although highly speculative, this mechanism may help to understand the puzzling observations that major warmings often occur in Smax/W years even though there is no strong waveguide provided by the QBO winds in the lower equatorial stratosphere. The ERA-40 data are used to investigate the QBO and solar signals and to determine whether the observations support the proposed mechanism. Composites of ERA-40 zonally averaged zonal winds based on the QBO (E/W), the SC (min/max), and both (Smin/E, Smin/W, Smax/E, Smax/W) are examined, with emphasis on the Northern Hemisphere winter vortex evolution. The major findings are that QBO/E years are more disturbed than QBO/W years, primarily during early winter. Sudden warmings in Smax years tend to occur later than in Smin years. Midwinter warmings are more likely during Smin/E and Smax/W years, although the latter result is only barely statistically significant at the 75% level. The data show some support for the proposed mechanism, but many more years are required before it can be fully tested.

scholarly journals Surface impacts of the Quasi Biennial Oscillation

2018 ◽  
Vol 18 (11) ◽  
pp. 8227-8247 ◽  
Author(s):  
Lesley J. Gray ◽  
James A. Anstey ◽  
Yoshio Kawatani ◽  
Hua Lu ◽  
Scott Osprey ◽  
...  
Keyword(s):  
Polar Vortex ◽  
Late Winter ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Zonal Winds ◽  
Orthogonal Function ◽  
The North ◽  
The Pacific ◽  
Biennial Oscillation ◽  
The North Pacific

Abstract. Teleconnections between the Quasi Biennial Oscillation (QBO) and the Northern Hemisphere zonally averaged zonal winds, mean sea level pressure (mslp) and tropical precipitation are explored. The standard approach that defines the QBO using the equatorial zonal winds at a single pressure level is compared with the empirical orthogonal function approach that characterizes the vertical profile of the equatorial winds. Results are interpreted in terms of three potential routes of influence, referred to as the tropical, subtropical and polar routes. A novel technique is introduced to separate responses via the polar route that are associated with the stratospheric polar vortex, from the other two routes. A previously reported mslp response in January, with a pattern that resembles the positive phase of the North Atlantic Oscillation under QBO westerly conditions, is confirmed and found to be primarily associated with a QBO modulation of the stratospheric polar vortex. This mid-winter response is relatively insensitive to the exact height of the maximum QBO westerlies and a maximum positive response occurs with westerlies over a relatively deep range between 10 and 70 hPa. Two additional mslp responses are reported, in early winter (December) and late winter (February/March). In contrast to the January response the early and late winter responses show maximum sensitivity to the QBO winds at ∼ 20 and ∼ 70 hPa respectively, but are relatively insensitive to the QBO winds in between (∼ 50 hPa). The late winter response is centred over the North Pacific and is associated with QBO influence from the lowermost stratosphere at tropical/subtropical latitudes in the Pacific sector. The early winter response consists of anomalies over both the North Pacific and Europe, but the mechanism for this response is unclear. Increased precipitation occurs over the tropical western Pacific under westerly QBO conditions, particularly during boreal summer, with maximum sensitivity to the QBO winds at 70 hPa. The band of precipitation across the Pacific associated with the Inter-tropical Convergence Zone (ITCZ) shifts southward under QBO westerly conditions. The empirical orthogonal function (EOF)-based analysis suggests that this ITCZ precipitation response may be particularly sensitive to the vertical wind shear in the vicinity of 70 hPa and hence the tropical tropopause temperatures.

scholarly journals Does the coupling of the semiannual oscillation with the quasi-biennial oscillation provide predictability of Antarctic sudden stratospheric warmings?

2021 ◽  
Vol 21 (17) ◽  
pp. 12835-12853
Author(s):  
Viktoria J. Nordström ◽  
Annika Seppälä
Keyword(s):  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Winter ◽  
Flux Divergence ◽  
Quasi Biennial Oscillation ◽  
Easterly Wind ◽  
Wave Forcing ◽  
A Minor ◽  
Biennial Oscillation ◽  
Semiannual Oscillation

Abstract. During September 2019 a minor sudden stratospheric warming took place over the Southern Hemisphere (SH), bringing disruption to the usually stable winter vortex. The mesospheric winds reversed and temperatures in the stratosphere rose by over 50 K. Whilst sudden stratospheric warmings (SSWs) in the SH are rare, with the only major SSW having occurred in 2002, the Northern Hemisphere experiences about six per decade. Amplification of atmospheric waves during winter is thought to be one of the possible triggers for SSWs, although other mechanisms are also possible. Our understanding, however, remains incomplete, especially with regards to SSW occurrence in the SH. Here, we investigate the effect of two equatorial atmospheric modes, the quasi-biennial oscillation (QBO) at 10 hPa and the semiannual oscillation (SAO) at 1 hPa during the SH winters of 2019 and 2002. Using MERRA-2 reanalysis data we find that the easterly wind patterns resembling the two modes merge at low latitudes in the early winter, forming a zero-wind line that stretches from the lower stratosphere into the mesosphere. This influences the meridional wave guide, resulting in easterly momentum being deposited in the polar atmosphere throughout the polar winter, decelerating the westerly winds in the equatorward side of the polar vortex. As the winter progresses, the momentum deposition and wind anomalies descend further down into the stratosphere. We find similar behaviour in other years with early onset SH vortex weakening events. The magnitude of the SAO and the timing of the upper stratospheric (10 hPa) easterly QBO signal was found to be unique in these years when compared to the years with a similar QBO phase. We were able to identify the SSW and weak vortex years from the early winter location of the zero-wind line at 1 hPa together with Eliassen–Palm flux divergence in the upper stratosphere at 40–50∘ S. We propose that this early winter behaviour resulting in deceleration of the polar winds may precondition the southern atmosphere for a later enhanced wave forcing from the troposphere, resulting in an SSW or vortex weakening event. Thus, the early winter equatorial upper stratosphere–mesosphere, together with the polar upper atmosphere, may provide early clues to an imminent SH SSW.

scholarly journals The Arctic vortex in March 2011: a dynamical perspective

2011 ◽  
Vol 11 (22) ◽  
pp. 11447-11453 ◽  
Author(s):  
M. M. Hurwitz ◽  
P. A. Newman ◽  
C. I. Garfinkel
Keyword(s):  
Planetary Wave ◽  
La Niña ◽  
The Arctic ◽  
Late Winter ◽  
Quasi Biennial Oscillation ◽  
The North ◽  
La Nina ◽  
Sea Surface Temperature Anomalies ◽  
Biennial Oscillation ◽  
The North Pacific

Abstract. Despite the record ozone loss observed in March 2011, dynamical conditions in the Arctic stratosphere were unusual but not unprecedented. Weak planetary wave driving in February preceded cold anomalies in the polar lower stratosphere in March and a relatively late breakup of the Arctic vortex in April. La Niña conditions and the westerly phase of the quasi-biennial oscillation (QBO) were observed in March 2011. Though these conditions are generally associated with a stronger vortex in mid-winter, the respective cold anomalies do not persist through March. Therefore, the La Niña and QBO-westerly conditions cannot explain the observed cold anomalies in March 2011. In contrast, positive sea surface temperature anomalies in the North Pacific may have contributed to the unusually weak tropospheric wave driving and strong Arctic vortex in late winter 2011.

scholarly journals Analysis of Arctic Spring Ozone Anomaly in the Phases of QBO and 11-year Solar Cycle for 1979–2011

2021 ◽  
Author(s):  
Yousuke Yamashita ◽  
Hideharu Akiyoshi ◽  
Masaaki Takahashi
Keyword(s):  
Solar Cycle ◽  
Climate Model ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Spring ◽  
The Arctic ◽  
Negative Anomaly ◽  
Late Winter ◽  
Quasi Biennial Oscillation ◽  
Biennial Oscillation

Arctic ozone amount in winter to spring shows large year-to-year variation. This study investigates Arctic spring ozone in relation to the phase of quasi-biennial oscillation (QBO)/the 11-year solar cycle, using satellite observations, reanalysis data, and outputs of a chemistry climate model (CCM) during the period of 1979–2011. For this duration, we found that the composite mean of the Northern Hemisphere high-latitude total ozone in the QBO-westerly (QBO-W)/solar minimum (Smin) phase is slightly smaller than those averaged for the QBO-W/Smax and QBO-E/Smax years in March. An analysis of a passive ozone tracer in the CCM simulation indicates that this negative anomaly is primarily caused by transport. The negative anomaly is consistent with a weakening of the residual mean downward motion in the polar lower stratosphere. The contribution of chemical processes estimated using the column amount difference between ozone and the passive ozone tracer is between 10–20% of the total anomaly in March. The lower ozone levels in the Arctic spring during the QBO-W/Smin years are associated with a stronger Arctic polar vortex from late winter to early spring, which is linked to the reduced occurrence of sudden stratospheric warming in the winter during the QBO-W/Smin years.

The Influence of the Quasi-Biennial Oscillation on the Troposphere in Winter in a Hierarchy of Models. Part I: Simplified Dry GCMs

2011 ◽  
Vol 68 (6) ◽  
pp. 1273-1289 ◽  
Author(s):  
Chaim I. Garfinkel ◽  
Dennis L. Hartmann
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Polar Vortex ◽  
Equation Model ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
Subtropical Jet ◽  
Long Time ◽  
Biennial Oscillation

Abstract A dry primitive equation model is used to explain how the quasi-biennial oscillation (QBO) of the tropical stratosphere can influence the troposphere, even in the absence of tropical convection anomalies and a variable stratospheric polar vortex. QBO momentum anomalies induce a meridional circulation to maintain thermal wind balance. This circulation includes zonal wind anomalies that extend from the equatorial stratosphere into the subtropical troposphere. In the presence of extratropical eddies, the zonal wind anomalies are intensified and extend downward to the surface. The tropospheric response differs qualitatively between integrations in which the subtropical jet is strong and integrations in which the subtropical jet is weak. While fluctuation–dissipation theory provides a guide to predicting the response in some cases, significant nonlinearity in others, particularly those designed to model the midwinter subtropical jet of the North Pacific, prevents its universal application. When the extratropical circulation is made zonally asymmetric, the response to the QBO is greatest in the exit region of the subtropical jet. The dry model is able to simulate much of the Northern Hemisphere wintertime tropospheric response to the QBO observed in reanalysis datasets and in long time integrations of the Whole Atmosphere Community Climate Model (WACCM).

Quasi-biennial oscillation disrupted by abnormal Southern Hemisphere stratosphere

2020 ◽  
Author(s):  
James Anstey ◽  
Tim Banyard ◽  
Neal Butchart ◽  
Lawrence Coy ◽  
Paul Newman ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Boreal Winter ◽  
Lead Times ◽  
Climate Projections ◽  
Intergovernmental Panel ◽  
Quasi Biennial Oscillation ◽  
Reliable Source ◽  
Biennial Oscillation ◽  
Wave Momentum

Abstract The quasi-biennial oscillation (QBO) is a repeating cycle of tropical stratosphere winds reversing direction from eastward to westward roughly every 14 months. Discovered independently by British and American scientists the QBO continued uninterrupted for 27 cycles from 1953 until February 2016 when a westward jet unexpectedly formed in the lower stratosphere during the eastward phase. This disruption is attributed to unusually high wave-momentum fluxes from the Northern Hemisphere. A second, similar, QBO disruption occurred during the 2019/2020 northern winter though wave fluxes from the Northern Hemisphere were weak. Here we show that this latest disruption to the regular QBO cycling was stronger than that seen in 2016 and resulted from horizontal momentum transport from the Southern Hemisphere during abnormal winter conditions. In both disruptions the normal downward progression of the QBO halts and the eastward shear zone above the disruption moves upward assisted by stronger tropical upwelling during the boreal winter. The predictable signal associated with the QBO's quasi-regular phase progression is permanently lost during disruptions and the oscillation reemerges after a few months significantly shifted in phase from what would be expected if the phase had progressed uninterrupted. We infer from an increased wave-momentum flux into equatorial latitudes seen in model climate projections supporting the latest Intergovernmental Panel on Climate Change (IPCC) assessment that disruptions to the QBO are likely to be more common in future. Consequently, we anticipate that in future the QBO will be a less reliable source of predictability on lead times extending out to several years than it currently is.

scholarly journals Stratospheric semi-decadal oscillations in NCEP data

2008 ◽  
Vol 26 (8) ◽  
pp. 2143-2157 ◽  
Author(s):  
H. G. Mayr ◽  
J. G. Mengel ◽  
F. T. Huang ◽  
E. R. Talaat ◽  
E. R. Nash ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Data Analysis ◽  
Temperature Data ◽  
Spectral Features ◽  
Altitude Range ◽  
Quasi Biennial Oscillation ◽  
Atmospheric Research ◽  
Zonal Winds ◽  
Environmental Prediction ◽  
Biennial Oscillation

Abstract. An analysis of the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) data is presented to provide a more complete description of the stratospheric 5-year semi-decadal (SD) oscillation (Mayr et al., 2007). The zonal-mean temperature and zonal wind data from the Atmospheric Research R-1 analysis are employed, covering the years from 1962 to 2002 in the altitude range from 10 to 30 km. For diagnostic purposes, the data are separated into the hemispherically symmetric and anti-symmetric components, and spectral analysis is applied to identify the signatures of the SD oscillations. Through the synthesis or filtering of spectral features, the SD modulations of the annual oscillation (AO) and quasi-biennial oscillation (QBO) are delineated. In agreement with the earlier findings, the magnitude of the SD oscillation is more pronounced when the 30-month QBO dominates during the years from 1975 to 1995. This is consistent with results from a numerical model, which shows that such a QBO generates the SD oscillation through interaction with the 12-month AO. In the zonal winds, the SD oscillation in the NCEP data is confined to equatorial latitudes, where it modulates the symmetric AO and QBO by about 5 m/s below 30 km. In the temperature data, the effect is also seen around the equator, but it is much larger at polar latitudes where the SD oscillation produces variations as large as 2 K. Our data analysis indicates that the SD oscillation is mainly hemispherically symmetric, and it appears to originate at equatorial latitudes where most of the energy resides.

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