Polar Vortex Ozone Research Articles

On the pattern of interannual polar vortex–ozone co-variability during northern hemispheric winter

Abstract. Stratospheric ozone is important for both stratospheric and surface climate. In the lower stratosphere during winter, its variability is governed primarily by transport dynamics induced by wave–mean flow interactions. In this work, we analyze interannual co-variations between the distribution of zonal-mean ozone and the strength of the polar vortex as a measure of dynamical activity during northern hemispheric winter. Specifically, we study co-variability between the seasonal means of the ozone field from modern reanalyses and polar-cap-averaged temperature at 100 hPa, which represents a robust and well-defined index for polar vortex strength. We focus on the vertically resolved structure of the associated extratropical ozone anomalies relative to the winter climatology and shed light on the transport mechanisms that are responsible for this response pattern. In particular, regression analysis in pressure coordinates shows that anomalously weak polar vortex years are associated with three pronounced local ozone maxima just above the polar tropopause, in the lower to mid-stratosphere and near the stratopause. In contrast, in isentropic coordinates, using ERA-Interim reanalysis data, only the mid- to lower stratosphere shows increased ozone, while a small negative ozone anomaly appears in the lowermost stratosphere. These differences are related to contributions due to anomalous adiabatic vertical motion, which are implicit in potential temperature coordinates. Our analyses of the ozone budget in the extratropical middle stratosphere show that the polar ozone response maximum around 600 K and the negative anomalies around 450 K beneath both reflect the combined effects of anomalous diabatic downwelling and quasi-isentropic eddy mixing, which are associated with consecutive counteracting anomalous ozone tendencies on daily timescales. We find that approx. 71 % of the total variability in polar column ozone in the stratosphere is associated with year-by-year variations in polar vortex strength based on ERA5 reanalyses for the winter seasons 1980–2022. MLS observations for 2005–2020 show that around 86 % can be explained by these co-variations with the polar vortex.

Middle stratospheric polar vortex ozone budget during the warming Arctic winter, 2002–2003

The ozone budget inside the middle stratospheric polar vortex (24–36 km) during the 2002–2003 Arctic winter is studied by analyzing Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite data. A comprehensive global chemical transport model (Model for Ozone and Related Chemical Tracers, MOZART-3) is used to analyze the observed variation in polar vortex ozone during the stratospheric sudden warming (SSW) events. Both MIPAS measurement and MOZART-3 calculation show that a pronounced increase (26–28 DU) in the polar vortex ozone due to the SSW events. Due to the weakening of the polar vortex, the exchange of ozone mass across the edge of the polar vortex increases substantially and amounts to about 3.0×107 kg according to MOZART-3 calculation. The enhanced downward transport offsets about 80% of polar vortex ozone mass increase by horizontal transport. A “passive ozone” experiment shows that only ∼55% of the vertical ozone mass flux in February and March can be attributed to the variation in vertical transport. It is also shown that the enhanced downward ozone above ∼32 km should be attributed to the springtime photochemical ozone production. Due to the increase of air temperature, the NO x reaction rate increases by 40%–80% during the SSW events. As a result, NO x catalytic cycle causes another 44% decrease in polar vortex ozone compared to the net ozone changes due to dynamical transport. It is also shown that the largest change in polar vortex ozone is due to horizontal advection by planetary waves in January 2003.

Extreme events in total ozone over the Northern mid-latitudes: an analysis based on long-term data sets from five European ground-based stations

We apply methods from extreme value theory to identify extreme events in high (termed EHOs) and low (termed ELOs) total ozone and to describe the distribution tails (i.e. very high and very low values) of five long-term European ground-based total ozone time series. The influence of these extreme events on observed mean values, long-term trends and changes is analysed. The results show a decrease in EHOs and an increase in ELOs during the last decades, and establish that the observed downward trend in column ozone during the 1970–1990s is strongly dominated by changes in the frequency of extreme events. Furthermore, it is shown that clear ‘fingerprints’ of atmospheric dynamics (NAO, ENSO) and chemistry [ozone depleting substances (ODSs), polar vortex ozone loss] can be found in the frequency distribution of ozone extremes, even if no attribution is possible from standard metrics (e.g. annual mean values). The analysis complements earlier analysis for the world’s longest total ozone record at Arosa, Switzerland, confirming and revealing the strong influence of atmospheric dynamics on observed ozone changes. The results provide clear evidence that in addition to ODS, volcanic eruptions and strong/moderate ENSO and NAO events had significant influence on column ozone in the European sector.

Extreme events in total ozone over Arosa – Part 1: Application of extreme value theory

Abstract. In this study ideas from extreme value theory are for the first time applied in the field of stratospheric ozone research, because statistical analysis showed that previously used concepts assuming a Gaussian distribution (e.g. fixed deviations from mean values) of total ozone data do not adequately address the structure of the extremes. We show that statistical extreme value methods are appropriate to identify ozone extremes and to describe the tails of the Arosa (Switzerland) total ozone time series. In order to accommodate the seasonal cycle in total ozone, a daily moving threshold was determined and used, with tools from extreme value theory, to analyse the frequency of days with extreme low (termed ELOs) and high (termed EHOs) total ozone at Arosa. The analysis shows that the Generalized Pareto Distribution (GPD) provides an appropriate model for the frequency distribution of total ozone above or below a mathematically well-defined threshold, thus providing a statistical description of ELOs and EHOs. The results show an increase in ELOs and a decrease in EHOs during the last decades. The fitted model represents the tails of the total ozone data set with high accuracy over the entire range (including absolute monthly minima and maxima), and enables a precise computation of the frequency distribution of ozone mini-holes (using constant thresholds). Analyzing the tails instead of a small fraction of days below constant thresholds provides deeper insight into the time series properties. Fingerprints of dynamical (e.g. ENSO, NAO) and chemical features (e.g. strong polar vortex ozone loss), and major volcanic eruptions, can be identified in the observed frequency of extreme events throughout the time series. Overall the new approach to analysis of extremes provides more information on time series properties and variability than previous approaches that use only monthly averages and/or mini-holes and mini-highs.

The influence of polar vortex ozone depletion on NH mid-latitude ozone trends in spring

Abstract. Reverse domain-filling trajectory calculations have been performed for the years 1993, 1995, 1996, 1997, and 2000 to calculate the spreading of ozone depleted air from the polar vortex to midlatitudes in spring. We find that for these years with massive Arctic ozone depletion the zonal mean total ozone column at midlatitudes is reduced with between 7 and 12 DU in the April-May period. The polar vortex and remnants have preferred locations which leads to longitudinal differences in the midlatitude ozone trends. Together with decadal variations in circulation the dilution of ozone depleted air may explain the major fraction of longitudinal differences in midlatitude ozone trends. For the period 1979–1997 the dilution may explain 50% of the longitudinal differences in ozone trends and for the period 1979–2002 it may explain 45%. The dilution also has a significant impact on the zonal mean ozone trends in the April-May period. Although uncertainties are large due to uncertainties in the ozone depletion values and neglect of ozone depletion in other years than 1993, 1995, 1996, 1997, and 2000 we have tried to calculate the size of this effect. We estimate that dilution may explain 29% of the trend in the period 1979–1997 and 33% of the trend in the period 1979–2002 as a lower limit.

Estimation of Arctic polar vortex ozone loss during the winter of 1999–2000 using vortex‐averaged airborne differential absorption lidar ozone measurements referenced to N2O isopleths

The NASA Langley UV differential absorption lidar (DIAL) system flew on the NASA DC‐8 aircraft during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) mission from 30 November 1999 to 15 March 2000. The UV DIAL system measured ozone (O3) profiles at altitudes from about 1 km above the aircraft up to about 26 km with a vertical resolution of 750 m and a horizontal resolution of 70 km below 19 km and 140 km above 19 km. In comparison with electrochemical concentration cell ozonesonde profiles, the UV DIAL O3 measurements agreed to within 5% up to 20 km and 10% from 20 to 25 km. Ozone loss during the season was determined using the UV DIAL O3 data along with air mass subsidence determined using N2O as a conservative tracer at five levels from 50 to 250 ppbv [Greenblatt et al., 2002]. O3 mixing ratios were determined inside the polar vortex, away from the collar region along these five levels during the mission. The maximum O3 loss determined from 30 November to 12 March was 1.55 ± 0.3 ppmv at the 440–450 K potential temperature (Θ) level, while the loss there between 20 January and 15 March was 1.3 ± 0.3 ppmv. These results are comparable to many of the other reported losses for these periods, but lower than several. Some of the determinations of higher losses used a different method to determine descent during the season. These results indicate that a series of vertical profiles of O3 that sample much of the vortex during the winter, along with determinations of the descent of air masses inside the vortex, can give a reasonable estimate of the O3 changes during the season.

Influence of Arctic polar ozone depletion on lower stratospheric ozone amounts at Haute‐Provence Observatory (43.92°N, 5.71°E)

Lidar and ozone sonde measurements performed at Haute‐Provence Observatory are used together with a high‐resolution potential vorticity (PV) transport model to study the influence of Arctic polar vortex ozone depletion on ozone amounts at this location prior to vortex dilution. The study focuses on four Arctic winters from 1996 to 2000. The transport model is used to investigate the presence of polar air masses above the station. These air masses, which are characterized by high PV values, can extend toward midlatitude regions during winter. Polar air masses are detected using a daily threshold value defined from the PV fields. The monthly average fraction of polar air generally increases with altitude from a few percent in the lower stratosphere to 10% or more above 500 K. The source of presence of polar air is largely dominated by filament events in the lower stratosphere and is equally divided between filaments and vortex excursions above the station in the middle stratosphere. The presence of polar air above the station shows high interannual variability. In the winter of 1999/2000 the least amount of polar air was detected above the station. However, vortex excursions above the station from January to March 2000 led to a significant average ozone reduction, estimated to 1.6% in the 400–650 K potential temperature range using a chemical transport model (CTM) evaluation of ozone loss at the vortex edge. Cold vortex, such as observed in 1999/2000, results in less transport toward midlatitude, but strong ozone depletion within the vortex combined with transient excursions of polar air can have a significant impact on ozone amounts in the midlatitude regions.

Chemical loss of polar vortex ozone inferred from UARS MLS measurements of ClO during the Arctic and Antarctic late winters of 1993

A computationally cheap, and easily initialized photochemical model utilizing UARS MLS measurements of ClO to calculate ozone destruction rates within the polar vortices due to the ClO + ClO, ClO + BrO, and ClO + O catalytic cycles is developed. The method involves calculating local reactive chlorine concentrations from individual ClO retrievals, and then inferring the diurnal cycle of ClO from a quadratic expression using the relevant kinetic parameters. In test integrations this simple treatment is shown to give good agreement with more detailed model calculations. Analysis of the late Arctic and Antarctic winters of 1993 yields similar vortex‐averaged ozone loss rates at 465 K of ∼1% per day in both hemispheres, while the reactive chlorine remains enhanced. Net ozone destruction in the north is less, largely because the elevated ClO and Cl2O2 concentrations are less persistent. The estimated chemical destruction on isentropic surfaces in the lower stratosphere is broadly similar to the observed change in ozone distribution, implying that the change is dominated by chemical destruction.

Chemical loss of polar vortex ozone inferred from UARS MLS measurements of ClO during the Arctic and Antarctic late winters of 1993

Chemical loss of polar vortex ozone inferred from UARS MLS measurements of ClO during the Arctic and Antarctic late winters of 1993