Abstract
Abstract. Statistical relationships between the variability of the area covered by double tropopause events (DTs), the strength of the tropical upwelling, the total column ozone and of the lower stratospheric water vapour are analyzed. The QBO and ENSO signals in the double tropopause and tropical upwelling as well as their influence on the statistical relationships are also presented. The analysis is based on both reanalysed data (ERA-Interim) and satellite data. Significant anticorrelations were found between the area covered by DTs and the total column ozone in the midlatitudes of the Northern Hemisphere. This relationship is confirmed by a large positive correlation between the areas covered by ozone laminae and double tropopause events as found in the HIRDLS satellite dataset. Significant anticorrelations were also found between the global area of double tropopause events and the near global (50° S–50° N) water vapour in the lower stratosphere. The correlations of DT variables with total column ozone and ozone laminae are both consistent with the poleward displacement of tropical air with lower ozone mixing ratio and with tropospheric intrusions of tropical tropospheric air into the lower extratropical stratosphere. The association of DTs with the poleward displacements of the tropical air is also consistent with a strong positive correlation between the area covered by DTs and the wave activity in the lower most stratosphere, between the first and second lapse rate tropopauses, as found in the ERA-Interim reanalysis. Finally, a significant anticorrelation was found between the tropical upwelling and the near global lower stratospheric water vapour. Moreover, the step like decrease in the lower stratospheric water vapour after 2001 is mirrored by a step like increase in the tropical upwelling.
Highlights
Stratospheric ozone accounts for about 90 % of the total column ozone (TCO) and controls the amount of damaging UV radiation reaching the earth surface (Staehelin et al, 2001)
Significant anticorrelations were found between the area covered by double tropopause events (DTs) and the total column ozone in the midlatitudes of the Northern Hemisphere
The association of DTs with the poleward displacements of the tropical air is consistent with a strong positive correlation between the area covered by DTs and the wave activity in the lower most stratosphere, between the first and second lapse rate tropopauses, as found in the ERA-Interim reanalysis
Summary
Stratospheric ozone accounts for about 90 % of the total column ozone (TCO) and controls the amount of damaging UV radiation reaching the earth surface (Staehelin et al, 2001). Castanheira and Gimeno (2011) and Peevey et al (2012) showed that double tropopause events (DTs) are associated with Rossby waves in the subtropics and midlatitudes These waves can produce intrusions of tropical tropospheric air into the extratropical lower stratosphere (Randel et al, 2007; Pan et al, 2009). Changes in this subtropical wave activity may be associated with changes in the tropical upwelling (Holton et al, 1995) Considering such possible links, it is reasonable to expect that the variability of double tropopause events will be related with the variabilities of the BDC strength and the mixing ratios of ozone and stratospheric water vapour. Our main goal is to explain how horizontal advection and quasi-horizontal mixing associated with DTs can impact the variability of ozone and stratospheric water vapour, and the dynamical relationship between DTs and the ascending branch of the BDC at the tropical tropopause level
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