Observed Hemispheric Asymmetry in Stratospheric Transport Trends From 1994 to 2018

Strahan, S. E.; Smale, Dan; Douglass, Anne R.; Blumenstock, Thomas; Hannigan, J. W.; Hase, Frank; Jones, Nicholas; Mahieu, Emmanuel; Notholt, Justus; Oman, Luke D.; Ortega, Ivan; Palm, Mathias; Prignon, Maxime; Robinson, John; Schneider, Mat­thias; Sussmann, Ralf; Velazco, Voltaire A.

doi:10.1029/2020gl088567

Cited by 14 publications

(38 citation statements)

References 55 publications

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“…10 Since natural variability is high in polar regions and the observational period is relatively short, it is quite expected that a simple multiple regression will lead to trend estimates that are not statistically significant. Other methods for trend analysis in polar regions, such as considering seasonal trends (Solomon et al, 2016;Szeląg et al, 2020;Galytska et al, 2019) can be explored in future work. In addition, the relation of winter-spring trends with respect to the position of the polar vortex would be an interesting subject in future studies.…”

Section: Evaluation Of Regional Ozone Trendsmentioning

confidence: 99%

Measurement report: regional trends of stratospheric ozone evaluated using the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP)

et al. 2021

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Abstract. In this paper, we present the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP) in the stratosphere with a resolved longitudinal structure, which is derived from data from six limb and occultation satellite instruments: GOMOS, SCIAMACHY and MIPAS on Envisat, OSIRIS on Odin, OMPS on Suomi-NPP, and MLS on Aura. The merged dataset was generated as a contribution to the European Space Agency Climate Change Initiative Ozone project (Ozone_cci). The period of this merged time series of ozone profiles is from late 2001 until the end of 2018. The monthly mean gridded ozone profile dataset is provided in the altitude range from 10 to 50 km in bins of 10∘ latitude × 20∘ longitude. The merging is performed using deseasonalized anomalies. The created MEGRIDOP dataset can be used for analyses that probe our understanding of stratospheric chemistry and dynamics. To illustrate some possible applications, we created a climatology of ozone profiles with resolved longitudinal structure. We found zonal asymmetry in the climatological ozone profiles at middle and high latitudes associated with the polar vortex. At northern high latitudes, the amplitude of the seasonal cycle also has a longitudinal dependence. The MEGRIDOP dataset has also been used to evaluate regional vertically resolved ozone trends in the stratosphere, including the polar regions. It is found that stratospheric ozone trends exhibit longitudinal structures at Northern Hemisphere middle and high latitudes, with enhanced trends over Scandinavia and the Atlantic region. This agrees well with previous analyses and might be due to changes in dynamical processes related to the Brewer–Dobson circulation.

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Section: Evaluation Of Regional Ozone Trendsmentioning

confidence: 99%

Measurement report: regional trends of stratospheric ozone evaluated using the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP)

et al. 2021

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“…They further analyzed BDC diagnostics, that is, the position of the subtropical transport barriers (derived from observations and model outputs), the turnaround latitude, and the latitude of the meridional trace gas gradient genesis (from ERA-Interim), to conclude that a southward shift by about 5° of the tropical transport barriers could explain the observed and modeled hemispheric asymmetry in trends. Recently, Strahan et al (2020) reported on hemispheric asymmetry in trends of long-lived tracers and AoA through an analysis of longer NDACC (Network for the Detection of Atmospheric Composition Change; De Mazière et al, 2018; http://www.ndacc.org) FTIR time series of HCl and nitric acid (HNO 3 ). These results place the previously reported trends in a longer context where interhemispheric anomalies of long-lived tracers and AoA exhibit a 5-7-year period.…”

Section: Introductionmentioning

confidence: 99%

“…The reported hemispheric asymmetry in 2005-2012 in Mahieu et al (2014;HCl) and Stiller et al (2017;N 2 O and AoA) is, for example, located between a large positive interhemispheric anomaly (peaking around 2005) and a large negative one (peaking around 2011; Southern Hemisphere minus Northern Hemisphere). Finally, Strahan et al (2020) also indirectly derived AoA trends from NDACC FTIR HCl and HNO 3 interhemispheric anomalies using a CTM AoA simulation driven by MERRA-2 (National Aeronautics and Space Administration's Modern Era Retrospective-analysis for Research Applications version 2; Gelaro et al, 2017). They concluded that the Southern Hemisphere AoA is getting younger by 1 month per decade compared to that of the Northern Hemisphere for the period 1994-2018.…”

Section: Introductionmentioning

confidence: 99%

Stratospheric Fluorine as a Tracer of Circulation Changes: Comparison Between Infrared Remote‐Sensing Observations and Simulations With Five Modern Reanalyses

et al. 2021

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Using multidecadal time series of ground-based and satellite Fourier transform infrared measurements of inorganic fluorine (i.e., total fluorine resident in stratospheric fluorine reservoirs), we investigate stratospheric circulation changes over the past 20 years. The representation of these changes in five modern reanalyses is further analyzed through chemical-transport model (CTM) simulations. From the observations but also from all reanalyses, we show that the inorganic fluorine is accumulating less rapidly in the Southern Hemisphere than in the Northern Hemisphere during the 21st century. Comparisons with a study evaluating the age-of-air of these reanalyses using the same CTM allow us to link this hemispheric asymmetry to changes in the Brewer-Dobson circulation (BDC), with the ageof-air of the Southern Hemisphere getting younger relative to that of the Northern Hemisphere. Large differences in simulated total columns and absolute trend values are, nevertheless, depicted between our simulations driven by the five reanalyses. Superimposed on this multidecadal change, we, furthermore, confirm a 5-7-year variability of the BDC that was first described in a recent study analyzing long-term time series of hydrogen chloride (HCl) and nitric acid (HNO 3 ). It is important to stress that our results, based on observations and meteorological reanalyses, are in contrast with the projections of chemistryclimate models in response to the coupled increase of greenhouse gases and decrease of ozone-depleting substances, calling for further investigations and the continuation of long-term observations. Plain Language SummaryThe overturning circulation of the stratosphere is projected to change in response to increases in greenhouse gases and decreases in ozone-depleting substances, with the Southern Hemisphere branch expected to get weaker relative to the Northern Hemisphere. Here, we use 30-year time series of observations and simulations of a long-lived tracer to investigate stratospheric circulation changes. The observations analyzed are from ground-based and satellite instruments. We compare them with simulations that use a chemical-transport model driven by winds from meteorological reanalyses of 1990-2019. A reanalysis assimilates meteorological measurements into a forecast model to simulate the best possible representation of the atmospheric state. All five simulations, which use different reanalyses, agree with the observational analysis showing that the analyzed tracer is accumulating less rapidly in the Southern Hemisphere than in the Northern Hemisphere through 2019. This hemispheric asymmetry is attributed to changes in the stratospheric transport circulation, with the Southern Hemisphere branch getting stronger relative to the Northern Hemisphere. Our results support the conclusions of a recent observational study but do not support circulation changes projected by chemistry-climate models. This study highlights the crucial importance of long-term observation time series.

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“…First, due to possible correlations between velocities and mixing ratios, products of prime terms in the zonal mean of the Reynolds decomposition of the tendency formulation of the continuity equation do not cancel out. Following Tung (1982)…”

Section: Discussionmentioning

confidence: 99%

“…2 There are other approaches than that of Tung (1982) to interpret 2-D circulation, using different approximations. Depending on the approach chosen, the calculation of effective 2-D velocities from 3-D fields involves different terms.…”

Section: Discussionmentioning

confidence: 99%

The middle atmospheric meridional circulation for 2002–2012 derived from MIPAS observations

et al. 2021

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Abstract. Measurements of long-lived trace gases (SF6, CFC-11, CFC-12, HCFC-22, CCl4, N2O, CH4, H2O, and CO) performed with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have been used to infer the stratospheric and mesospheric meridional circulation. The MIPAS data set covers the time period from July 2002 to April 2012. The method used for this purpose was the direct inversion of the two-dimensional continuity equation for the concentrations of trace gases and air density. This inversion predicts an “effective velocity” that gives the best fit for the evolution of the concentrations on the assumption that an explicit treatment of Fickian diffusion can be neglected. These effective velocity fields are used to characterize the mean meridional circulation. Multiannual monthly mean effective velocity fields are presented, along with their variabilities. According to this measure, the stratospheric circulation is found to be highly variable over the year, with a quite robust annual cycle. The new method allows us to track the evolution of various circulation patterns over the year in more detail than before. According to the effective velocity characterization of the circulation, the deep branch of the Brewer–Dobson circulation and the mesospheric overturning pole-to-pole circulation are not separate but intertwined phenomena. The latitude of stratospheric uplift in the middle and upper stratosphere is found to be quite variable and is not always found at equatorial latitudes. The usual schematic of stratospheric circulation with the deep and the shallow branch of the Brewer–Dobson circulation and the mesospheric overturning circulation is an idealization which best describes the observed atmosphere around equinox. Sudden stratospheric warmings and the quasi-biennial oscillation cause a pronounced year-to-year variability of the meridional circulation.

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Observed Hemispheric Asymmetry in Stratospheric Transport Trends From 1994 to 2018

Cited by 14 publications

References 55 publications

Measurement report: regional trends of stratospheric ozone evaluated using the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP)

Measurement report: regional trends of stratospheric ozone evaluated using the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP)

Stratospheric Fluorine as a Tracer of Circulation Changes: Comparison Between Infrared Remote‐Sensing Observations and Simulations With Five Modern Reanalyses

The middle atmospheric meridional circulation for 2002–2012 derived from MIPAS observations

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