Has the stratospheric HCl in the Northern Hemisphere been increasing since 2005

Author(s):  
Yuanyuan Han ◽  
Wenshou Tian ◽  
Fei Xie

<p>Stratospheric hydrogen chloride (HCl) is the main stratospheric reservoir of chlorine, deriving from the decomposition of chlorine-containing source gases. Its trend has been used as a metrics of ozone depletion or recovery. Using the latest satellite observations, the authors find that a significant increase of Northern Hemisphere stratospheric HCl during 2010–2011 can mislead trends of HCl in recent decades. Agree with previous studies, HCl increased from 2005 to 2011; while when removing the large increase of stratospheric HCl during 2010–2011, the increasing linear trend from 2005 to 2011 becomes weak and insignificant, in addition, the linear trend of Northern Hemisphere stratospheric HCl from 2005 to 2016 also shows weak and insignificant. The significant increase of HCl during 2010–2011 is attributed to a super strong north polar vortex and a reduced residual circulation during 2010–2011, which slowed down the transport of HCl from the low–mid latitudes to the high latitudes, leading to accumulation of HCl in the middle latitudes of the stratosphere during 2010–2011. Further analysis suggests that the strong polar vortex and the reduced residual circulation were caused by the joint effect of a La Niña event and the west phase of the quasi-biennial oscillation.</p>

2020 ◽  
Vol 8 ◽  
Author(s):  
Yuanyuan Han ◽  
Fei Xie ◽  
Jiankai Zhang

Stratospheric hydrogen chloride (HCl) is the main stratospheric reservoir of chlorine, deriving from the decomposition of chlorine-containing source gases. Its trend has been used as a metric of ozone depletion or recovery. Using the latest satellite observations, it is found that the significant increase of Northern Hemisphere stratospheric HCl during 2010–2011 can mislead the trend of HCl in recent decades. In agreement with previous studies, HCl increased from 2005 to 2011; however, when the large increase of stratospheric HCl during 2010–2011 is removed, the increasing linear trend from 2005 to 2011 becomes weak and insignificant. In addition, the linear trend of Northern Hemisphere stratospheric HCl from 2005 to 2016 is also weak and insignificant. The significant increase of HCl during 2010–2011 is attributed to a strong northern polar vortex and a weakened residual circulation, which slowed down the transport of HCl between the low-mid latitudes and the high latitudes, leading to an accumulation of HCl in the middle latitudes of the stratosphere. In addition, a weakened residual circulation leads to enhance conversion of chlorine-containing source gases of different lifetimes to HCl, thus increasing the levels of HCl. Simulations by both chemistry transport and chemistry-climate models support the result. It is further found that the joint effect of a La Niña event, the west phase of the quasi-biennial oscillation and positive anomalies of sea surface temperature in the North Pacific is responsible for the strong northern polar vortex and a weakened residual circulation.


2004 ◽  
Vol 61 (23) ◽  
pp. 2777-2796 ◽  
Author(s):  
Lesley J. Gray ◽  
Simon Crooks ◽  
Charlotte Pascoe ◽  
Sarah Sparrow ◽  
Michael Palmer

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.


2019 ◽  
Vol 124 (23) ◽  
pp. 12568-12586 ◽  
Author(s):  
Jiankai Zhang ◽  
Fei Xie ◽  
Zhichao Ma ◽  
Chongyang Zhang ◽  
Mian Xu ◽  
...  

Author(s):  
Yousuke Yamashita ◽  
Hideharu Akiyoshi ◽  
Masaaki Takahashi

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.


2011 ◽  
Vol 68 (6) ◽  
pp. 1273-1289 ◽  
Author(s):  
Chaim I. Garfinkel ◽  
Dennis L. Hartmann

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).


2020 ◽  
Author(s):  
James Anstey ◽  
Tim Banyard ◽  
Neal Butchart ◽  
Lawrence Coy ◽  
Paul Newman ◽  
...  

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.


2010 ◽  
Vol 67 (5) ◽  
pp. 1402-1419 ◽  
Author(s):  
James A. Anstey ◽  
Theodore G. Shepherd ◽  
John F. Scinocca

Abstract The interannual variability of the stratospheric polar vortex during winter in both hemispheres is observed to correlate strongly with the phase of the quasi-biennial oscillation (QBO) in tropical stratospheric winds. It follows that the lack of a spontaneously generated QBO in most atmospheric general circulation models (AGCMs) adversely affects the nature of polar variability in such models. This study examines QBO–vortex coupling in an AGCM in which a QBO is spontaneously induced by resolved and parameterized waves. The QBO–vortex coupling in the AGCM compares favorably to that seen in reanalysis data [from the 40-yr ECMWF Re-Analysis (ERA-40)], provided that careful attention is given to the definition of QBO phase. A phase angle representation of the QBO is employed that is based on the two leading empirical orthogonal functions of equatorial zonal wind vertical profiles. This yields a QBO phase that serves as a proxy for the vertical structure of equatorial winds over the whole depth of the stratosphere and thus provides a means of subsampling the data to select QBO phases with similar vertical profiles of equatorial zonal wind. Using this subsampling, it is found that the QBO phase that induces the strongest polar vortex response in early winter differs from that which induces the strongest late-winter vortex response. This is true in both hemispheres and for both the AGCM and ERA-40. It follows that the strength and timing of QBO influence on the vortex may be affected by the partial seasonal synchronization of QBO phase transitions that occurs both in observations and in the model. This provides a mechanism by which changes in the strength of QBO–vortex correlations may exhibit variability on decadal time scales. In the model, such behavior occurs in the absence of external forcings or interannual variations in sea surface temperatures.


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