Ozone Minimum Research Articles

The ozone hole and a phase change in lower stratospheric temperature

Depletion of ozone over Antarctica was first observed in the late 1970s, and discovery of the Antarctic ozone hole was announced in the 1980s as having started in 1979. The ozone hole was defined as the area with total column ozone less than 220 Dobson units. Analysis of ozone, temperature, chlorofluorocarbon and nitrous oxide data from 1963 onwards suggests that the annual ozone minimum at the South Pole is related to lower stratospheric temperature independently of chlorofluorocarbons and nitrous oxide. There were ozone holes, ie. column ozone less than 220 Dobson Units, at the South Pole in several years before 1979 (the date that the ozone hole is reported to have first appeared) when chlorofluorocarbon concentrations were much lower than today and lower than in 1979. An early 1980s phase change in the lower stratospheric temperature at the South Pole at altitudes between 250 hPa and 100 hPa, and at some lower altitudes, coincides with a phase change in the annual South Pole ozone minimum. The phase change is not visible in chlorofluorocarbon or nitrous oxide data. This raises the possibility that, over a multi-annual or decadal timescale, lower stratospheric temperature has more effect than chlorofluorocarbons or nitrous oxide on atmospheric ozone concentration over the South Pole. Alternatively, temperature and ozone may both be reacting to some other influence.

Arctic stratosphere changes in the 21st century in the Earth system model SOCOLv4

Two ensemble simulations of a new Earth system model (ESM) SOCOLv4 (SOlar Climate Ozone Links, version 4) for the period from 2015 to 2099 under moderate (SSP2-4.5) and severe (SSP5-8.5) scenarios of greenhouse gas (GHG) emission growth were analyzed to investigate changes in key dynamical processes relevant for Arctic stratospheric ozone. The model shows a 5–10 K cooling and 5%–20% humidity increase in the Arctic lower–upper stratosphere in March (when the most considerable ozone depletion may occur) between 2080–2099 and 2015–2034. The minimal temperature in the lower polar stratosphere in March, which defines the strength of ozone depletion, appears when the zonal mean meridional heat flux in the lower stratosphere in the preceding January–February is the lowest. In the late 21st century, the strengthening of the zonal mean meridional heat flux with a maximum of up to 20 K m/s (∼25%) in the upper stratosphere close to 70°N in January–February is obtained in the moderate scenario of GHG emission, while only a slight increase in this parameter over 50 N–60 N with the maximum up to 5 K m/s in the upper stratosphere and a decrease with the comparable values over the high latitudes is revealed in the severe GHG emission scenario. Although the model simulations confirm the expected ozone layer recovery, particularly total ozone minimum values inside the Arctic polar cap in March throughout the 21st century are characterized by a positive trend in both scenarios, the large-scale negative ozone anomalies in March up to −80 DU–100 DU, comparable to the second lowest ones observed in March 2011 but weaker than record values in March 2020, are possible in the Arctic until the late 21st century. The volume of low stratospheric air with temperatures below the solid nitric acid trihydrate polar stratospheric cloud (PSC NAT) formation threshold is reconstructed from 3D potential vorticity and temperature fields inside the stratospheric polar vortex. A significant positive trend is shown in this parameter in March in the SSP5-8.5 scenario. Furthermore, according to the model data, an increase in the polar vortex isolation throughout the 21st century indicates its possible strengthening in the lower stratosphere. Positive trends of the surface area density (SAD) of PSC NAT particles in March in the lower Arctic stratosphere over the period of 2015–2099 are significant in the severe GHG emission scenario. The polar vortex longitudinal shift toward northern Eurasia is expected in the lower stratosphere in the late 21st century in both scenarios. The statistically significant long-term stratospheric sulfuric acid aerosol trend in March is expected only in the SSP5.8-5 scenario, most probably due to cooler stratosphere and stronger Brewer–Dobson circulation intensification. Both scenarios predict an increase in the residual meridional circulation (RMC) in March by the end of the 21st century. In some regions of the stratosphere, the RMC enhancement under the severe GHG scenario can exceed 20%.

South Pole Station ozonesondes: variability and trends in the springtime Antarctic ozone hole 1986–2021

Abstract. Balloon-borne ozonesondes launched weekly from South Pole Station (1986–2021) measure high-vertical-resolution profiles of ozone and temperature from the surface to 30–35 km altitude. The launch frequency is increased in late winter before the onset of rapid stratospheric ozone loss in September. Ozone hole metrics show that the yearly total column ozone and 14–21 km partial column ozone minimum values and September loss rate trends have been improving (less severe) since 2001. The 36-year record also shows interannual variability, especially in recent years (2019–2021). Here we show additional details of these 3 years by comparing annual minimum profiles observed on the date when the lowest integrated total column ozone occurs. We also compare the July–December time series of the 14–21 km partial column ozone values to the 36-year median with percentile intervals. The 2019 anomalous vortex breakdown showed stratospheric temperatures began warming in early September followed by reduced ozone loss. The minimum total column ozone of 180 Dobson units (DU) was observed on 24 September. This was followed by two stable and cold polar vortex years during 2020 and 2021 with total column ozone minimums at 104 DU (1 October) and 102 DU (7 October), respectively. These years also showed broad near-zero-ozone (loss saturation) regions within the 14–21 km layer by the end of September which persisted into October. Validation of the ozonesonde observations is conducted through the ongoing comparison of total column ozone measurements with the South Pole ground-based Dobson spectrophotometer. The ozonesondes show a more positive bias of 2 ± 3 % (higher) than the Dobson following a thorough evaluation and homogenization of the long-term ozonesonde record completed in 2018.

Chemical Evolution of the Exceptional Arctic Stratospheric Winter 2019/2020 Compared to Previous Arctic and Antarctic Winters

AbstractThe winter 2019/2020 showed the lowest ozone mixing ratios ever observed in the Arctic winter stratosphere. It was the coldest Arctic stratospheric winter on record and was characterized by an unusually strong and long‐lasting polar vortex. We study the chemical evolution and ozone depletion in the winter 2019/2020 using the global Chemistry and Transport Model ATLAS. We examine whether the chemical processes in 2019/2020 are more characteristic of typical conditions in Antarctic winters or in average Arctic winters. Model runs for the winter 2019/2020 are compared to simulations of the Arctic winters 2004/2005, 2009/2010, and 2010/2011 and of the Antarctic winters 2006 and 2011, to assess differences in chemical evolution in winters with different meteorological conditions. In some respects, the winter 2019/2020 (and also the winter 2010/2011) was a hybrid between Arctic and Antarctic conditions, for example, with respect to the fraction of chlorine deactivation into HCl versus ClONO2, the amount of denitrification, and the importance of the heterogeneous HOCl + HCl reaction for chlorine activation. The pronounced ozone minimum of less than 0.2 ppm at about 450 K potential temperature that was observed in about 20% of the polar vortex area in 2019/2020 was caused by exceptionally long periods in the history of these air masses with low temperatures in sunlight. Based on a simple extrapolation of observed loss rates, only an additional 21–46 h spent below the upper temperature limit for polar stratospheric cloud formation and in sunlight would have been necessary to reduce ozone to near zero values (0.05 ppm) in these parts of the vortex.

The 2020 Arctic ozone depletion and signs of its effect on the ozone column at lower latitudes.

The present study discusses the effect of the ozone depletion that occurred over the Arctic in 2020 on the ozone column in central and southern Europe by analysing a data set obtained from ground-based measurements at six stations placed from 79 to 42°N. Over the northernmost site (Ny-Ålesund), the ozone column decreased by about 45% compared to the climatological average at the beginning of April, and its values returned to the normal levels at the end of the month. Southwards, the anomaly gradually reduced to nearly 15% at 42°N (Rome) and the ozone minimum was detected with a delay from about 6 days at 65°N to 20 days at 42°N. At the same time, the evolution of the ozone column at the considered stations placed below the polar circle corresponded to that observed at Ny-Ålesund, but at 42°–46°N, the ozone column turned back to the typical values at the end of May. This similarity in the ozone evolutional patterns at different latitudes and the gradually increasing delay of the minimum occurrences towards the south allows the assumption that the ozone columns at lower latitudes were affected by the phenomenon in the Arctic. The ozone decrease observed at Aosta (46°N) combined with predominantly cloud-free conditions resulted in about an 18% increase in the erythemally weighted solar ultraviolet irradiance reaching the Earth’s surface in May.

Unprecedented Spring 2020 Ozone Depletion in the Context of 20 Years of Measurements at Eureka, Canada

AbstractIn the winter and spring of 2019/2020, the unusually cold, strong, and stable polar vortex created favorable conditions for ozone depletion in the Arctic. Chemical ozone loss started earlier than in any previous year in the satellite era and continued until late March, resulting in the unprecedented reduction of the ozone column. The vortex was located above the Polar Environment Atmospheric Research Laboratory in Eureka, Canada (80°N, 86°W) from late February to the end of April, presenting an excellent opportunity to examine ozone loss from a single ground station. Measurements from a suite of instruments show that total column ozone was at an all‐time low in the 20‐year data set, 22–102 DU below previous records set in 2011. Ozone minima (<200 DU), enhanced OClO and BrO slant columns, and unusually low‐HCl, ClONO2, and HNO3 columns were observed in March. Polar stratospheric clouds were present as late as 20 March, and ozonesondes show unprecedented depletion in the March and April profiles (to <0.2 ppmv). While both chemical and dynamical factors lead to reduced ozone when the vortex is cold, the contribution of chemical depletion (based on the variable correlation of ozone and temperature) was exceptional in spring 2020 when compared to typical Arctic winters. Mean chemical ozone loss over Eureka was estimated to be 111–126 DU (27%–31%) using April measurements and passive ozone from the SLIMCAT chemical transport model. While absolute ozone loss was generally smaller in 2020 than in 2011, percentage ozone loss was greater in 2020.

Long-term analysis of the Antarctic total ozone zonal asymmetry by MERRA-2 and CMIP6 data

Objectives. To analyze ozone monthly mean data from the MERRA-2 reanalysis and CMIP6 model. To determine Antarctic ozone asymmetry climatology for austral spring months (September, October, November) over the 1980–2014 period. Methods. Processing and visualization of the MERRA-2, CMIP6 data on total ozone and ozone partial pressure, following analysis, interpretation, and comparison. Getting 2D (total ozone column) and 3D (ozone partial pressure) monthly mean ozone values for the zonal band (0°–90° S) at pressure levels (1000–0.1 hPa) for each month of the chosen period. Calculating climatology of the total ozone and ozone partial pressure. Comparison of model and reanalysis of results. Results. The amplitude of ozone zonal asymmetry was calculated to provide the monthly, latitudinal, longitudinal and altitudinal analysis. It is shown that the largest ozone zonal asymmetry is observed in spring, especially in October, with dominant wave-1 structure with zonal minimum over 0°–90° W, and maximum over 120°–180° E longitudinal sectors. The area with high ozone content is located at the 40°–80° S zonal band and gradually shifts to the south from September to November. The model underestimates amplitude of ozone zonal asymmetry, especially in October. Conclusions. Latitudinal mean maximums in zonal mean ozone distribution are observed over 62° S, in October over 66° S, and in November over 68° S for MERRA-2 and over 64° S, 65° S and 66° S respectively for CMIP6. The poleward shift of ozone latitude maximum continues until March with decreasing of ozone level, but in April, the shift reverses its direction to equatorward and ozone level starts to increase, however in the model this process is slower. In September the shift again becomes poleward. In the longitudinal distribution wave-1 pattern dominates with a shift of longitude ozone minimum. From September to October the shift is eastward, and from October to November westward by MERRA-2 data and only eastward by CMIP6 data. The highest difference in altitude ozone distribution is observed during October in the stratosphere between ozone zonal minimum and maximum points and reaches approximately 68% (44%) of the zonal average value at 65° S (65.4° S) by MERRA-2 (CMIP6) data. MERRA-2 profiles unlike CMIP6 one show higher location of altitudinal maximum over the zonal minimum and lower over the zonal maximum with the zonal mean in the middle. All three CMIP6 profiles have the same height of altitude maximum.

Evaluation of El Niño-Southern oscillation influence on ozone exceedances along the United States Gulf Coast

An investigation into climate-scale influences on tropospheric ozone concentrations in cities along the United States Gulf Coast was performed using a thirty-year database of observed surface ozone data. Hourly surface ozone data were obtained from eight surface Environmental Protection Agency monitoring stations from Texas to Florida. Eight-hour peak concentrations were computed for each day in the record and a database created for further study. To account for regulatory changes, each time history was detrended over the thirty-year period. Days with precipitation, which tend to have low surface ozone concentrations due to low solar insolation and wet deposition of ozone precursors on surfaces, were also removed. The resulting database was stratified by Oceanic Niño Index, which is a measure of the state of the El Niño-Southern Oscillation (ENSO) based on water temperatures in the eastern Pacific Ocean. A common seasonal dependency was identified for all eight stations, with peaks in ozone concentrations in spring and autumn regardless of ENSO phase. The summer ozone minimum was more pronounced for the western Gulf of Mexico than the east. This extension of work done for the city of Houston, Texas confirmed that the influence of ENSO on surface air quality applies to the entire coast of the Gulf of Mexico. Statistically significant enhancements of 5–10 ppbv were found during the months of March and April for El Niño years relative to neutral years. Distributions fit to each city's dataset of 8-h peak ozone values for spring and fall confirmed the difference between the behavior of ozone concentrations in spring and fall for different ENSO phases. El Niño spring data possessed a broader distribution more centered at a higher mean value than the neutral or La Niña datasets for each city. Taken together, the higher mean and broader distribution of 8-h ozone concentrations lead to 30% more exceedances of the National Ambient Air Quality Standard of 70 ppbv for El Niño years relative to neutral years for the composite Gulf Coast dataset. These changes in the ozone climate of the Gulf Coast during El Niño years can be attributed in part to an area of anomalously low pressure in the eastern Gulf of Mexico which influences meridional and zonal flow along the coast. This feature leads to stagnation and a persistent continental airmass along the northern Gulf coast. Smaller but still statistically significant differences between El Niño and neutral autumn were also identified for some stations and were attributed to increased frontal activity during El Niño autumn which leads to an earlier, longer ozone season in previous research. This work extends and improves understanding of the influence of the El Niño-Southern Oscillation on air quality in a large and economically important region of the United States.

Middle atmospheric ozone, nitrogen dioxide and nitrogen trioxide in 2002–2011: SD-WACCM simulations compared to GOMOS observations

Abstract. Most of our understanding of the atmosphere is based on observations and their comparison with model simulations. In middle atmosphere studies it is common practice to use an approach, where the model dynamics are at least partly based on temperature and wind fields from an external meteorological model. In this work we test how closely satellite measurements of a few central trace gases agree with this kind of model simulation. We use collocated vertical profiles where each satellite measurement is compared to the closest model data. We compare profiles and distributions of O3, NO2 and NO3 from the Global Ozone Monitoring by Occultation of Stars instrument (GOMOS) on the Envisat satellite with simulations by the Whole Atmosphere Community Climate Model (WACCM). GOMOS measurements are from nighttime. Our comparisons show that in the stratosphere outside the polar regions differences in ozone between WACCM and GOMOS are small, between 0 and 6%. The correlation of 5-day time series show a very high 0.9–0.95. In the tropical region 10° S–10° N below 10 hPa WACCM values are up to 20 % larger than GOMOS. In the Arctic below 6 hPa WACCM ozone values are up to 20 % larger than GOMOS. In the mesosphere between 0.04 and 1 hPa the WACCM is at most 20 % smaller than GOMOS. Above the ozone minimum at 0.01 hPa (or 80 km) large differences are found between WACCM and GOMOS. The correlation can still be high, but at the second ozone peak the correlation falls strongly and the ozone abundance from WACCM is about 60 % smaller than that from GOMOS. The total ozone columns (above 50 hPa) of GOMOS and WACCM agree within ±2 % except in the Arctic where WACCM is 10 % larger than GOMOS. Outside the polar areas and in the validity region of GOMOS NO2 measurements (0.3–37 hPa) WACCM and GOMOS NO2 agree within −5 to +25 % and the correlation is high (0.7–0.95) except in the upper stratosphere at the southern latitudes. In the polar areas, where solar particle precipitation and downward transport from the thermosphere enhance NO2 abundance, large differences up to −90 % are found between WACCM and GOMOS NO2 and the correlation varies between 0.3 and 0.9. For NO3, we find that the WACCM and GOMOS difference is between −20 and 5 % with a very high correlation of 0.7–0.95. We show that NO3 values strongly depend on temperature and the dependency can be fitted by the exponential function of temperature. The ratio of NO3 to O3 from WACCM and GOMOS closely follow the prediction from the equilibrium chemical theory. Abrupt temperature increases from sudden stratospheric warmings (SSWs) are reflected as sudden enhancements of WACCM and GOMOS NO3 values.

Study of Ozone Layer Variability near St. Petersburg on the Basis of SBUV Satellite Measurements and Numerical Simulation (2000–2014)

A comparison between the numerical simulation results of ozone fields with different experimental data makes it possible to estimate the quality of models for their further use in reliable forecasts of ozone layer evolution. We analyze time series of satellite (SBUV) measurements of the total ozone column (TOC) and the ozone partial columns in two atmospheric layers (0–25 and 25–60 km) and compare them with the results of numerical simulation in the chemistry transport model (CTM) for the low and middle atmosphere and the chemistry climate model EMAC. The daily and monthly average ozone values, short-term periods of ozone depletion, and long-term trends of ozone columns are considered; all data sets relate to St. Petersburg and the period between 2000 and 2014. The statistical parameters (means, standard deviations, variations, medians, asymmetry parameter, etc.) of the ozone time series are quite similar for all datasets. However, the EMAC model systematically underestimates the ozone columns in all layers considered. The corresponding differences between satellite measurements and EMAC numerical simulations are (5 ± 5)% and (7 ± 7)% and (1 ± 4)% for the ozone column in the 0–25 and 25–60 km layers, respectively. The correspondent differences between SBUV measurements and CTM results amount to (0 ± 7)%, (1 ± 9)%, and (–2 ± 8)%. Both models describe the sudden episodes of the ozone minimum well, but the EMAC accuracy is much higher than that of the CTM, which often underestimates the ozone minima. Assessments of the long-term linear trends show that they are close to zero for all datasets for the period under study.

Evolution of the eastward shift in the quasi-stationary minimum of the Antarctic total ozone column

Abstract. The quasi-stationary pattern of the Antarctic total ozone has changed during the last 4 decades, showing an eastward shift in the zonal ozone minimum. In this work, the association between the longitudinal shift of the zonal ozone minimum and changes in meteorological fields in austral spring (September–November) for 1979–2014 is analyzed using ERA-Interim and NCEP–NCAR reanalyses. Regressive, correlative and anomaly composite analyses are applied to reanalysis data. Patterns of the Southern Annular Mode and quasi-stationary zonal waves 1 and 3 in the meteorological fields show relationships with interannual variability in the longitude of the zonal ozone minimum. On decadal timescales, consistent longitudinal shifts of the zonal ozone minimum and zonal wave 3 pattern in the middle-troposphere temperature at the southern midlatitudes are shown. Attribution runs of the chemistry–climate version of the Australian Community Climate and Earth System Simulator (ACCESS-CCM) model suggest that long-term shifts of the zonal ozone minimum are separately contributed by changes in ozone-depleting substances and greenhouse gases. As is known, Antarctic ozone depletion in spring is strongly projected on the Southern Annular Mode in summer and impacts summertime surface climate across the Southern Hemisphere. The results of this study suggest that changes in zonal ozone asymmetry accompanying ozone depletion could be associated with regional climate changes in the Southern Hemisphere in spring.

Changes in the total ozone distribution in the atmosphere over Antarctica

The data obtained by the authors during the last decade from satellite measurements in 1979–2016 and related to changes in zonal asymmetry of the Antarctic ozone and to their coupling with atmospheric parameters in the Southern Hemisphere are summarized in this work. The spring levels of the Antarctic ozone in 2000s–2010s do not show increase of the ozone hole size observed in 1980s–1990s. Stabilization and the first evidence of the ozone hole area decrease are considered as consequence of Montreal Protocol 1987 on restriction of emissions of ozone depleted substances into the atmosphere. Long3term changes of total ozone content in atmosphere over the Antarctic region in spring are accompanied by changes in its asymmetric distribution relatively the South Pole. Interannual variations of the longitudinal ozone minimum position demonstrate statistically significant relation to structure of the quasi3stationary planetary waves in distribution of atmospheric parameters. Long3term longitudinal shift of the ozone minimum is similar to shift in zonal structure of planetary waves in the tropospheric parameter distribution and is also accompanied by meridional displacement of the climatic anomalies toward the equator. The obtained relationships characterize interdependence between the large3scale tropospheric and stratospheric disturbances in the Southern Hemisphere during the ozone hole season.

Interannual variability of the boreal summer tropical UTLS in observations and CCMVal-2 simulations

Abstract. During boreal summer the upper troposphere/lower stratosphere (UTLS) in the Northern Hemisphere shows a distinct maximum in water vapour (H2O) mixing ratios and a coincident minimum in ozone (O3) mixing ratios, both confined within the Asian monsoon anticyclone (AMA). This well-known feature has been related to transport processes emerging above the convective systems during the Asian summer monsoon (ASM), further modified by the dynamics of the AMA. We compare the ability of chemistry–climate models (CCMs) to reproduce the climatological characteristics and variability of H2O, O3, and temperature in the UTLS during the boreal summer with MIPAS satellite observations and ERA-Interim reanalyses. By using a multiple linear regression model the main driving factors, the strength of the ASM, the quasi-biennial oscillation (QBO), and the El Niño–Southern Oscillation (ENSO), are separated. The regression patterns related to ENSO show a coherent, zonally asymmetric signal for temperatures and H2O mixing ratios for ERA-Interim and the CCMs and suggest a weakening of the ASM during ENSO warm events. The QBO modulation of the lower-stratospheric temperature near the Equator is well represented as a zonally symmetric pattern in the CCMs. Changes in H2O and O3 mixing ratios are consistent with the QBO-induced temperature and circulation anomalies but less zonally symmetric than the temperature pattern. Regarding the ASM, the results of the regression analysis show for ERA-Interim and the CCMs enhanced H2O and reduced O3 mixing ratios within the AMA for stronger ASM seasons. The CCM results can further confirm earlier studies which emphasize the importance of the Tibetan Plateau/southern slope of the Himalayas as the main source region for H2O in the AMA. The results suggest that H2O is transported towards higher latitudes at the north-eastern edge of the AMA rather than towards low equatorial latitudes to be fed into the tropical pipe.

On the processes influencing the vertical distribution of ozone over the central Himalayas: Analysis of yearlong ozonesonde observations

First yearlong (2011) balloon-borne measurements of ozone vertical distribution (EN-SCI 2ZV7 ECC Ozonesonde) and meteorological parameters (iMet-1-RSB 403 MHz GPS Radiosonde) over Nainital (79.5°E, 29.4°N, 1958 m amsl) in the central Himalayas are presented. Lower tropospheric ozone shows a prominent seasonality with highest levels during spring (∼70–110 ppbv in May) and lowest levels during summer-monsoon (∼20–50 ppbv), which is consistent with the ground-based observations. The lower tropospheric ozone minimum coincides with highest values of relative humidity (80–100%) during the summer-monsoon. However, ozone mixing ratios in the middle-upper troposphere show less pronounced and different seasonality. Influences of subtropical jets are observed (wind speed: ∼40–80 m s−1) in the middle-upper troposphere, particularly during winter. A stratospheric intrusion event during winter is observed, which enhances the ozone levels by ∼180% in the middle-upper troposphere. A noticeable feature of secondary ozone peaks (∼140–250 ppbv) is observed in the middle troposphere (∼8–12 km), more frequently during spring. Ozone levels in 2–4 km altitude range are higher by 19.9 ± 4.6 ppbv during the springtime high fire activity period over the northern India. Moreover, the lower tropospheric ozone levels over Nainital during spring are found to be considerably (∼30 ppbv) higher than those over Ahmedabad in the western India. This ozone enhancement is attributed mainly to the regional pollution of the Indo-Gangetic Plain (IGP) supplemented with the northern Indian biomass burning. It is suggested that regional photochemistry and biomass burning processes play controlling role in the lower troposphere, while, the middle-upper tropospheric variations are driven by dynamical processes including advection and stratospheric intrusion.

Quantifying the deep convective temperature signal within the tropical tropopause layer (TTL)

Abstract. Dynamics on a vast range of spatial and temporal scales, from individual convective plumes to planetary-scale circulations, play a role in driving the temperature variability in the tropical tropopause layer (TTL). Here, we aim to better quantify the deep convective temperature signal within the TTL using multiple datasets. First, we investigate the link between ozone and temperature in the TTL using the Southern Hemisphere Additional Ozonesondes (SHADOZ) dataset. Low ozone concentrations in the TTL are indicative of deep convective transport from the boundary layer. We confirm the usefulness of ozone as an indicator of deep convection by identifying a typical temperature signal associated with reduced ozone events: an anomalously warm mid to upper troposphere and an anomalously cold upper TTL. We quantify these temperature signals using two diagnostics: (1) the "ozone minimum" diagnostic, which has been used in previous studies and identifies the upper tropospheric minimum ozone concentration as a proxy for the level of main convective outflow; and (2) the "ozone mixing height", which we introduce in order to identify the maximum altitude in a vertical ozone profile up to which reduced ozone concentrations, typical of transport from the boundary layer are observed. Results indicate that the ozone mixing height diagnostic better separates profiles with convective influence than the ozone minimum diagnostic. Next, we collocate deep convective clouds identified by CloudSat 2B-CLDCLASS with temperature profiles based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Position System (GPS) radio occultations. We find a robust large-scale deep convective TTL temperature signal, that is persistent in time. However, it is only the convective events that penetrate into the upper half of the TTL that have a significant impact on TTL temperature. A distinct seasonal difference in the spatial scale and the persistence of the temperature signal is identified. Deep-convective cloud top heights are on average found to be well described by the level of neutral buoyancy.

Seasonal and diurnal variations of ozone at a high-altitude mountain baseline station in East Asia

Abstract Continuous measurements of tropospheric ozone were conducted at the Lulin Atmospheric Background Station (LABS) at an altitude of 2862 m from April 2006 to the end of 2009. Distinct seasonal variations in the ozone concentration were observed at the LABS, with a springtime maximum and a summertime minimum. Based on a backward trajectory analysis, CO data, and ozonesondes, the springtime maximum was most likely caused by the long-range transport of air masses from Southeast Asia, where biomass burning was intense in spring. In contrast, a greater Pacific influence contributed to the summertime minimum. In addition to seasonal variations, a distinct diurnal pattern was also observed at the LABS, with a daytime minimum and a nighttime maximum. The daytime ozone minimum was presumably caused by sinks of dry deposition and NO titration during the up-slope transport of surface air. The higher nighttime values, however, could be the result of air subsidence at night bringing ozone aloft to the LABS. After filtering out the daytime data to remove possible local surface contributions, the average background ozone value for the period of 2006–2009 was approximately 36.6 ppb, increased from 32.3 ppb prior to data filtering, without any changes in the seasonal pattern. By applying HYSPLIT4 model analysis, the origins of the air masses contributing to the background ozone observed at the LABS were investigated.

Effect that jet streams have on the vertical ozone distribution and characteristics of tropopause inversion layer in the far east region

The paper describes a lidar and presents the results of lidar sensing of the vertical ozone distribution (VOD); the lidar measurements are analyzed together with data from a network of meteorological stations situated along the 132° E meridian. VODs over Primorye and Japan in the winter period are compared. An analysis showed that an interrelation exists between the subtropical jet stream and the structures of VOD and tropopause inversion layer. Specifically, the region of the VOD local maximum above the tropopause is in the upper part of the tropopause inversion layer and the width of the maximum depends on the distance from the core of the subtropical jet stream. It is found that the local ozone minimum in the lower stratosphere corresponds to the local minimum of the squared Brunt-Vaisala frequency within this same altitude range in the winter season, when two tropopauses frequently overlap. It is conjectured that the local ozone maximum and tropopause inversion layer may be associated with mixing processes in the layer where stratospheric and tropospheric circulation cells come into contact near the core of the subtropical jet stream.

Very high ozone columns at northern mid-latitudes in 2010

[1] For the year 2010, both ground- and satellite-based measurements have recorded unusually high annual mean total ozone columns over much of the Northern hemisphere. At the mid-latitude station Hohenpeissenberg (48°N, 11°E), the 2010 annual mean reached 339 Dobson Units (DU), the highest value observed since 1982, and the 8th highest in the 43 year record at Hohenpeissenberg. The 45°N to 55°N annual zonal mean exceeded 360 DU, also one of the highest values observed in the last 20 to 25 years. The 2010 annual mean was about 12 DU higher than in 2009, and almost 35 DU higher than the long-term minimum observed in 1992 and 1993. An unusually pronounced and persistent negative phase of the Arctic Oscillation and North Atlantic Oscillation in 2010, last seen in this magnitude in 1968 and 1969, and the co-incidence of northern winter 2009/2010 with the easterly wind-shear phase of the quasi biennial oscillation of stratospheric winds at the equator (QBO) have been major contributors to the high total ozone of 2010. Multiple linear regression analysis of the Hohenpeissenberg time series (since 1968) attributes about +8 DU ±2 DU (1σ) of the 2010 annual mean to the Arctic Oscillation, and about +4 DU ±1.3 DU (1σ) to the QBO. A small ozone increase since the ozone minimum of the mid 1990s might also be due to the recent decline of stratospheric chlorine and bromine.

Ozone concentration changes in the Asian summer monsoon anticyclone and lower stratospheric water vapour: An idealised model study

[1] Satellite observations and model studies have previously established the impact of the Asian Summer Monsoon on the composition of the upper troposphere and lower stratosphere, where a region of enhanced water vapour and decreased ozone is found in the Monsoon anticyclone. We investigate a potential link between the magnitude of the Monsoon-induced ozone minimum and water vapour concentrations. In three idealised climate model experiments we prescribe ozone climatologies, decreasing or increasing ozone in the anticyclone region relative to the annual cycle during northern hemisphere summer. We discuss the modelled temperature and water vapour response. While water vapour decreases significantly when lower ozone is prescribed, it changes very little when higher ozone is prescribed, illustrating an important asymmetry between forcing and response.

Optimally coherent sets in geophysical flows: A transfer-operator approach to delimiting the stratospheric polar vortex

The "edge" of the Antarctic polar vortex is known to behave as a barrier to the meridional (poleward) transport of ozone during the austral winter. This chemical isolation of the polar vortex from the middle and low latitudes produces an ozone minimum in the vortex region, intensifying the ozone hole relative to that which would be produced by photochemical processes alone. Observational determination of the vortex edge remains an active field of research. In this paper, we obtain objective estimates of the structure of the polar vortex by introducing a technique based on transfer operators that aims to find regions with minimal external transport. Applying this technique to European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 three-dimensional velocity data, we produce an improved three-dimensional estimate of the vortex location in the upper stratosphere where the vortex is most pronounced. This computational approach has wide potential application in detecting and analyzing mixing structures in a variety of atmospheric, oceanographic, and general fluid dynamical settings.