Stratospheric Research Articles

Characteristics of Changes in the Ozone Content in the Upper Stratosphere over Moscow during the Cold Half-Years of 2014–2015 and 2015–2016

The results of ground-based microwave measurements of the stratospheric ozone profiles over Moscow during the cold half-years of 2014–2015 and 2015–2016 are presented. The causes of the observed changes in the ozone in the upper stratosphere are considered. Increased planetary wave activity, strong temperature decreases in the beginning of winter, and decreased temperatures from January to March were detected during the winter of 2014–2015. The polar vortex was long-lived but not deep; the cold air of the vortex was over Moscow in February–March. This led to a strong negative correlation of the measured ozone content with the temperature. The highest ozone content at the 2-mb level was observed in mid-March. Conversely, an intense polar vortex formed in November–December 2015 under lower planetary wave activity; it was completely destroyed by the major final warming in the beginning of March 2016. The ozone variations in the upper stratosphere over Moscow in December 2015 and January 2016 were related to the alternation of air masses of the vortex and regions outside the vortex. Higher temperatures (as compared to those in the beginning of 2015) led to a decreased ozone content in the beginning of 2016. The interannual difference in the ozone content in the first half of March exceeded 40% of the monthly mean value.

Stratospheric initial conditions provide seasonal predictability of the North Atlantic and Arctic Oscillations

The North Atlantic Oscillation (NAO), the regional manifestation of the Arctic Oscillation (AO), dominates winter climate variability in Europe and North America. Skilful seasonal forecasting of the winter NAO/AO has been demonstrated recently by dynamical prediction systems. However, the role of initial conditions in this predictability remains unknown. Using a latest generation seasonal forecasting system and reanalysis data, we show that the initial upper stratospheric zonal wind anomaly contributes to winter NAO/AO predictability through downward propagation of initial conditions. An initial polar westerly/easterly anomaly in the upper stratosphere propagates down to the troposphere in early winter, favoring a poleward/equatorward shift of the tropospheric mid-latitude jet. This tropospheric anomaly persists well into the late winter and induces the positive/negative phase of NAO/AO in the troposphere. Our results imply that good representation of stratospheric initial condition and stratosphere-troposphere coupling in models is important for winter climate prediction.

The SPARC water vapour assessment II: profile-to-profile and climatological comparisons of stratospheric <i>δ</i>D(H<sub>2</sub>O) observations from satellite

Abstract. Within the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II), we evaluated five data sets of δD(H2O) obtained from observations by Odin/SMR (Sub-Millimetre Radiometer), Envisat/MIPAS (Environmental Satellite/Michelson Interferometer for Passive Atmospheric Sounding), and SCISAT/ACE-FTS (Science Satellite/Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) using profile-to-profile and climatological comparisons. These comparisons aimed to provide a comprehensive overview of typical uncertainties in the observational database that could be considered in the future in observational and modelling studies. Our primary focus is on stratospheric altitudes, but results for the upper troposphere and lower mesosphere are also shown. There are clear quantitative differences in the measurements of the isotopic ratio, mainly with regard to comparisons between the SMR data set and both the MIPAS and ACE-FTS data sets. In the lower stratosphere, the SMR data set shows a higher depletion in δD than the MIPAS and ACE-FTS data sets. The differences maximise close to 50 hPa and exceed 200 ‰. With increasing altitude, the biases decrease. Above 4 hPa, the SMR data set shows a lower δD depletion than the MIPAS data sets, occasionally exceeding 100 ‰. Overall, the δD biases of the SMR data set are driven by HDO biases in the lower stratosphere and by H2O biases in the upper stratosphere and lower mesosphere. In between, in the middle stratosphere, the biases in δD are the result of deviations in both HDO and H2O. These biases are attributed to issues with the calibration, in particular in terms of the sideband filtering, and uncertainties in spectroscopic parameters. The MIPAS and ACE-FTS data sets agree rather well between about 100 and 10 hPa. The MIPAS data sets show less depletion below approximately 15 hPa (up to about 30 ‰), due to differences in both HDO and H2O. Higher up this behaviour is reversed, and towards the upper stratosphere the biases increase. This is driven by increasing biases in H2O, and on occasion the differences in δD exceed 80 ‰. Below 100 hPa, the differences between the MIPAS and ACE-FTS data sets are even larger. In the climatological comparisons, the MIPAS data sets continue to show less depletion in δD than the ACE-FTS data sets below 15 hPa during all seasons, with some variations in magnitude. The differences between the MIPAS and ACE-FTS data have multiple causes, such as differences in the temporal and spatial sampling (except for the profile-to-profile comparisons), cloud influence, vertical resolution, and the microwindows and spectroscopic database chosen. Differences between data sets from the same instrument are typically small in the stratosphere. Overall, if the data sets are considered together, the differences in δD among them in key areas of scientific interest (e.g. tropical and polar lower stratosphere, lower mesosphere, and upper troposphere) are too large to draw robust conclusions on atmospheric processes affecting the water vapour budget and distribution, e.g. the relative importance of different mechanisms transporting water vapour into the stratosphere.

Recent Trends in Stratospheric Chlorine From Very Short-Lived Substances.

Very short‐lived substances (VSLS), including dichloromethane (CH2Cl2), chloroform (CHCl3), perchloroethylene (C2Cl4), and 1,2‐dichloroethane (C2H4Cl2), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCltot) using a chemical transport model and atmospheric measurements, including novel high‐altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCltot increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases. The modeled evolution of chlorine source gas injection agrees well with historical aircraft data, which corroborate reported surface CH2Cl2 increases since the mid‐2000s. The relative contribution of VSLS to total stratospheric chlorine increased from ~2% in 2000 to ~3.4% in 2017, reflecting both VSLS growth and decreases in long‐lived halocarbons. We derive a mean VSLCltot growth rate of 3.8 (±0.3) ppt Cl/year between 2004 and 2017, though year‐to‐year growth rates are variable and were small or negative in the period 2015–2017. Whether this is a transient effect, or longer‐term stabilization, requires monitoring. In the upper stratosphere, the modeled rate of HCl decline (2004–2017) is −5.2% per decade with VSLS included, in good agreement to ACE satellite data (−4.8% per decade), and 15% slower than a model simulation without VSLS. Thus, VSLS have offset a portion of stratospheric chlorine reductions since the mid‐2000s.

Trend quality ozone from NPP OMPS: the version 2 processing

Abstract. A version 2 processing of data from two ozone monitoring instruments on Suomi NPP, the OMPS nadir ozone mapper and the OMPS nadir ozone profiler, has now been completed. The previously released data were useful for many purposes but were not suitable for use in ozone trend analysis. In this processing, instrument artifacts have been identified and corrected, an improved scattered light correction and wavelength registration have been applied, and soft calibration techniques were implemented to produce a calibration consistent with data from the series of SBUV/2 instruments. The result is a high-quality ozone time series suitable for trend analysis. Total column ozone data from the OMPS nadir mapper now agree with data from the SBUV/2 instrument on NOAA 19 with a zonal average bias of −0.2 % over the 60∘ S to 60∘ N latitude zone. Differences are somewhat larger between OMPS nadir profiler and N19 total column ozone, with an average difference of −1.1 % over the 60∘ S to 60∘ N latitude zone and a residual seasonal variation of about 2 % at latitudes higher than about 50∘. For the profile retrieval, zonal average ozone in the upper stratosphere (between 2.5 and 4 hPa) agrees with that from NOAA 19 within ±3 % and an average bias of −1.1 %. In the lower stratosphere (between 25 and 40 hPa) agreement is within ±3 % with an average bias of +1.1 %. Tropospheric ozone produced by subtracting stratospheric ozone measured by the OMPS limb profiler from total column ozone measured by the nadir mapper is consistent with tropospheric ozone produced by subtracting stratospheric ozone from MLS from total ozone from the OMI instrument on Aura. The agreement of tropospheric ozone is within 10 % in most locations.

The Upper Stratospheric Solar Cycle Ozone Response

AbstractThe solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data‐merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U‐shaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASICv2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used.

A new MesosphEO data set of temperature profiles from 35 to 85 km using Rayleigh scattering at limb from GOMOS/ENVISAT daytime observations

Abstract. Given that the scattering of sunlight by the Earth's atmosphere above 30–35 km is primarily due to molecular Rayleigh scattering, the intensity of scattered photons can be assumed to be directly proportional to the atmospheric density. From the measured relative density profile it is possible to retrieve an absolute temperature profile by assuming local hydrostatic equilibrium, the perfect gas law, and an a priori temperature from a climatological model at the top of the atmosphere. This technique has been applied to Rayleigh lidar observations for over 35 years. The GOMOS star occultation spectrometer includes spectral channels used to observe daytime limb scattered sunlight along the line of sight to a reference star. GOMOS Rayleigh scattering profiles in the spectral range of 420–480 nm have been used to retrieve temperature profiles between 35 and 85 km with a 2 km vertical resolution. Using this technique, a database of more than 309 000 temperature profiles has been created from GOMOS measurements. A global climatology was constructed using the new GOMOS database and is compared to an external model. In the upper stratosphere, the external model is based on the ECMWF reanalysis and the agreement with GOMOS is better than 2 K. In the mesosphere the external model follows the MSIS climatology and 5 to 10 K differences are observed with respect to the GOMOS temperature profiles. Comparisons to night-time collocated Rayleigh lidar profiles above the south of France show some vertical structured temperature differences, which may be partially explained by the contributions of the thermal diurnal tide. The equatorial temperature series shows clear examples of mesospheric inversion layers in the temperature profiles. The inversion layers have global longitudinal extension and temporal evolution, descending from 80 to 70 km over the course of a month. The climatology shows a semi-annual temperature variation in the upper stratosphere, a stratopause altitude varying between 47 and 54 km, and an annual variation in the temperatures of the mesosphere. The technique that derive temperature profiles from Rayleigh limb scattering can be applied to any other limb-scatter sounder, providing that the observations are in the spectral range 350–500 nm. Due to the simplicity of the principles involved, this technique is also a good candidate for a future missions where constellations of small satellites are deployed.

Causes of non-stationary relationships between geomagnetic activity and the North Atlantic Oscillation

The North Atlantic Oscillation (NAO) is known to be influenced by internal variability of the atmosphere and the ocean and respond to natural or anthropogenic external forcing. However, there is no consensus on the exact mechanisms. The NAO correlates with geomagnetic activity (considered as the parameter for the solar wind intensity) positively during one period (i.e. 1951–1996) but negatively in another period (i.e.1870–1950), making the Sun-climate connection a controversial subject. We try to explain this non-stationary relationship and to find the causes why the correlation had changed the sign during the past 148 years. At the times of low geomagnetic activity before 1950 and after 1997 the correlation between geomagnetic activity and the NAO was relatively weak. The variability of the NAO during those periods was mainly due to other processes. In order to answer the question why a more positive NAO phase has prevailed over the last 30 years of the past century, we study the geomagnetic signal near the surface conditioning upon the strength, shape and location of the stratospheric polar vortex and examine the immediate effect of geomagnetic storms in the troposphere. At times of prevailing high geomagnetic activity (1951–1996) the polar vortex strengthened. The effect of the solar wind was mainly over northern Europe in association with the positive phase of the NAO; a strengthened mid-latitude westerly jet kept the cold air in the Arctic and northern mid-latitudes became milder than average. When geomagnetic activity decreased, the stratospheric polar vortex also weakened. The solar wind signal prevailed over Canada in association with the negative NAO index and more of Arctic air was able to penetrate North America and Eurasia. We finally show that the geomagnetic storms may play a role in the acceleration of the downward penetration of pressure anomalies from the upper stratosphere into the troposphere.

Simulating the Antarctic stratospheric vortex transport barrier: comparing the Unified Model to reanalysis

An assessment has been made of the ability of the UK Met Office Unified Model (UM) to simulate the Antarctic stratospheric circumpolar vortex and, in particular, the extent to which the vortex acts as a barrier to meridional transport. It is important that models simulate this barrier well as it determines spatial gradients in radiatively active gases, such as ozone, which then determine the spatial morphology of the radiative forcing field. The assessment was made by comparing metrics of meridional impermeability calculated from dynamical fields extracted from UM simulations and from analogous fields obtained from NCEP-CFSR reanalysis. Two different UM configurations were assessed: global atmosphere 3.0 (GA3.0) using the New Dynamics dynamical core, and GA7.0 using the newer ENDGame dynamical core, with both versions run at N96 resolution (1.25 $$^{\circ }$$ latitude by 1.875 $$^{\circ }$$ longitude). The GA7.0 configuration appears to better simulate the dynamical isolation of the Antarctic stratospheric vortex in the lower stratosphere up to about 600 K, while GA3.0 provides a better simulation in the upper stratosphere. However, neither UM configuration simulates the same degree of dynamical isolation suggested by the reanalysis. In particular the UM configurations produce a wider and more poleward meridional band of high wind-speed and steep PV gradients when compared with the NCEP-CFSR reanalysis, leading to a stronger barrier in GA7.0 and a weaker barrier in GA3.0. Possible causes of discrepancies between model simulations and reanalysis and between the two model configurations are discussed. It is pointed out that further work is needed to identify ways of resolving these discrepancies in model simulations.

Double cores of the Ozone Low in the vertical direction over the Asian continent in satellite data sets

Using four satellite data sets (TOMS/SBUV, OMI, MLS, and HALOE), we analyze the seasonal variations of the total column ozone (TCO) and its zonal deviation (TCO*), and reveal the vertical structure of the Ozone Low (OV) over the Asian continent. Our principal findings are: (1) The TCO over the Asian continent reaches its maximum in the spring and its minimum in the autumn. The Ozone Low exists from May to September. (2) The Ozone Low has two negative cores, located in the lower and the upper stratosphere. The lower core is near 30 hPa in the winter and 70 hPa in the other seasons. The upper core varies from 10 hPa to 1 hPa among the four seasons. (3) The position of the Ozone Low in the lower and the upper stratosphere over the Asian continent shows seasonal variability.

Observations of Meteoric Aerosol in the Upper Stratosphere–Lower Mesosphere by the Method of Two-Wavelength Lidar Sensing

We present the results of two-wavelength lidar sensing of the middle atmosphere in the altitude range from 30 to 60 km over Obninsk (55.1° N, 36.6° E) in 2012–2017. Monthly average values of the ratio of aerosol and Rayleigh backscattering coefficients (RARC) at a wavelength of 532 nm, averaged over the layers of 40–50 km and 50–60 km, vary from 0 to 0.02, while the average peak RARC levels in these layers vary from 0.1 to 0.2. Short-term (shorter than 1 month) and long-term (half-year and longer) variations in backscattering are observed. Short-term variations are time concurrent with the occurrence of meteor showers. Long-term enhancements of backscattering in the layer of 50–60 km were observed in 2013 after the Chelyabinsk meteorite fall, as well as in the first half of 2016. In 2014–2015, the monthly average RARC was zero within measurement errors at altitudes from 40 to 60 km. We analyzed the possibility for meteoric aerosol to manifest in backscattering, taking into account the fluxes of meteoric material, gravitational sedimentation of aerosol, and the effect of vertical wind. The flux of visible meteors with masses larger than 10−6 kg and bolides is shown to be insufficient for a long-term enhancement of backscattering in the layer of 50–60 km. It is hypothesized that the enhancement in backscattering is most likely to be due to the occurrence of an enlarged fraction of meteoric smoke particles, formed by ablation of radio meteors and penetrating into the upper stratosphere in the region of the stratospheric polar vortex. In early 2016, this was favored by the formation of an extremely strong stratospheric polar vortex and its shift toward Eurasia.

Evaluating the Brewer–Dobson circulation and its responses to ENSO, QBO, and the solar cycle in different reanalyses

This study compares the climatology and long-term trend of northern winter stratospheric residual mean meridional circulation (RMMC), as well as its responses to El Nino-Southern Oscillation (ENSO), stratospheric Quasi Biennial Oscillation (QBO), and solar cycle in ten reanalyses and a stratosphere-resolving model, CESM1-WACCM. The RMMC is a large-scale meridional circulation cell in the stratosphere, usually referred to as the estimate of the Brewer Dobson circulation (BDC). The distribution of the BDC is generally consistent among multiple reanalyses except that the NOAA twentieth century reanalysis (20RC) largely underestimates it. Most reanalyses (except ERA40 and ERA-Interim) show a strengthening trend for the BDC during 1979–2010. All reanalyses and CESM1-WACCM consistently reveal that the deep branch of the BDC is significantly enhanced in El Nino winters as more waves from the troposphere dissipate in the stratospheric polar vortex region. A secondary circulation cell is coupled to the temperature anomalies below the QBO easterly center at 50 hPa with tropical upwelling/cooling and midlatitude downwelling/warming, and similar secondary circulation cells also appear between 50–10 hPa and above 10 hPa to balance the temperature anomalies. The direct BDC response to QBO in the upper stratosphere creates a barrier near 30°N to prevent waves from propagating to midlatitudes, contributing to the weakening of the polar vortex. The shallow branch of the BDC in the lower stratosphere is intensified during solar minima, and the downwelling warms the Arctic lower stratosphere. The stratospheric responses to QBO and solar cycle in most reanalyses are generally consistent except in the two 20CRs.

Dynamical Precursors for Statistical Prediction of Stratospheric Sudden Warming Events

AbstractThis work explores dynamical arguments for statistical prediction of stratospheric sudden warming events (SSWs). Based on climate model output, it focuses on two predictors, upward wave activity in the lower stratosphere and meridional potential vorticity gradient in the upper stratosphere, and detects large values of these predictors. Then it quantifies how many SSWs are preceded by predictor events and, inversely, how many events are followed by SSWs. This allows to compute conditional probabilities of future SSW occurrence. It is found that upward wave activity leads to important increases in SSW probability within the following 3 weeks but is less important thereafter. A weak potential vorticity gradient is associated with increased SSW probability at short lags and, perhaps more importantly, decreased SSW probability at long lags. Finally, when both predictors are considered in combination, the information gain is large on the weekly and small but significant on the intraseasonal time scale.

Approaches for Surveying Cosmic Radiation Damage in Large Populations of Arabidopsis thaliana Seeds – Antarctic Balloons and Particle Beams

Abstract The Cosmic Ray Exposure Sequencing Science (CRESS) payload system was a proof of concept experiment to assess the genomic impact of space radiation on seeds. CRESS was designed as a secondary payload for the December 2016 high-altitude, long-duration south polar balloon flight carrying the Boron and Carbon Cosmic Rays in the Upper Stratosphere (BACCUS) experiment. Investigation of the biological effects of Galactic Cosmic Radiation (GCR), particularly those of ions with High-Z and Energy (HZE), was of interest due to the genomic damage this type of radiation inflicts. The biological effects of radiation above Antarctica (ANT) were studied using Arabidopsis thaliana seeds and compared to a simulation of GCR at Brookhaven National Laboratory (BNL) and to laboratory control seeds. The CRESS payload was broadly designed to 1U CubeSat specifications (10 cm × 10 cm × 10 cm, ≤1.33 kg), maintained 1 atm internal pressure, and carried an internal cargo of 580,000 seeds and twelve CR-39 Solid-State Nuclear Track Detectors (SSNTDs). Exposed BNL and ANT M0 seeds showed significantly reduced germination rates and elevated somatic mutation rates when compared to non-irradiated controls, with the BNL mutation rate also being higher than that of ANT. Genomic DNA from plants presenting distinct aberrant phenotypes was evaluated with whole-genome sequencing using PacBio SMRT technology, which revealed an array of structural genome variants in the M0 and M1 plants. This study was the first whole-genome characterization of space-irradiated seeds and demonstrated both the efficiency and efficacy of Antarctic long-duration balloons for the study of space radiation effects on eukaryote genomes.

Response of Arctic ozone to sudden stratospheric warmings

Abstract. Sudden stratospheric warmings (SSWs) are the main source of intra-seasonal and interannual variability in the extratropical stratosphere. The profound alterations to the stratospheric circulation that accompany such events produce rapid changes in the atmospheric composition. The goal of this study is to deepen our understanding of the dynamics that control changes of Arctic ozone during the life cycle of SSWs, providing a quantitative analysis of advective transport and mixing. We use output from four ensemble members (60 years each) of the Whole Atmospheric Community Climate Model version 4 performed for the Chemistry Climate Model Initiative and also use reanalysis and satellite data for validation purposes. The composite evolution of ozone displays positive mixing ratio anomalies of up to 0.5–0.6 ppmv above 550 K (∼ 50 hPa) around the central warming date and negative anomalies below (−0.2 to −0.3 ppmv), consistently in observations, reanalysis, and the model. Our analysis shows a clear temporal offset between ozone eddy transport and diffusive ozone fluxes. The initial changes in ozone are mainly driven by isentropic eddy fluxes linked to enhanced wave drag responsible for the SSW. The recovery of climatological values in the aftermath of SSWs is slower in the lower than in the upper stratosphere and is driven by the competing effects of cross-isentropic motions (which work towards the recovery) and isentropic irreversible mixing (which delays the recovery). These features are enhanced in strength and duration during sufficiently deep SSWs, particularly those followed by polar-night jet oscillation (PJO) events. It is found that SSW-induced ozone concentration anomalies below 600 K (∼ 40 hPa), as well as total column estimates, persist around 1 month longer in PJO than in non-PJO warmings.

Seasonal Evolution of Stratosphere‐Troposphere Coupling in the Southern Hemisphere and Implications for the Predictability of Surface Climate

AbstractStratosphere‐troposphere coupling in the Southern Hemisphere (SH) polar vortex is an important dynamical process that provides predictability of the tropospheric Southern Annular Mode (SAM) and its associated surface impacts. SH stratosphere‐troposphere coupling is explored by height‐time domain empirical orthogonal function (EOF) analysis applied to the zonal mean‐zonal wind anomalies averaged over the Antarctic circumpolar region (55–65°S; U55–65°S). The leading EOF explains 42% of the height‐time variance of U55–65°S and depicts the variations of the vortex that is tightly tied to the seasonal breakdown of the vortex during late spring. The leading EOF pattern, defined here as the stratosphere‐troposphere coupled mode, is characterized by variations in U55–65°S that develop in early winter near the stratopause, change sign from late winter to early spring, gain maximum amplitude during October in the upper stratosphere, and then extend downward to the surface from October to January. This stratosphere‐troposphere coupling during the spring months appears to be preconditioned by anomalies in upward propagating planetary wave activity and a meridional shift of the vortex as high as the stratopause and as early as June. Interannual variations of the stratosphere‐troposphere coupled mode are highly correlated with those of the tropospheric SAM, Antarctic stratospheric ozone concentration, Antarctic sea ice concentrations in the South Pacific and the Weddell Sea, and SH regional climate during late spring–early summer. Anomalies in the upper stratospheric flow as early as June are thus a potentially important source of predictability for the tropospheric SAM and its associated impacts on surface climate in spring and summer.

Investigation of the Structure and Predictability of the First Mode of Stratospheric Variability Based on the INM RAS Climate Model

The first empirical orthogonal function (EOF) of intraannual evolution of temperature averaged along the circle of latitude in the 0-60-km layer is calcul ated using the data of the 500-year preindustrial experiment with the climate model of the Institute of Numerical Mathematics of Russian Academy of Sciences (INM RAS). It is shown that the first EOF represents temperature anomalies which propagate downward from the upper stratosphere during December-April. Such anomalies are preceded by the anomaly of the meridional heat flux in the polar upper stratosphere in December. Using the ensemble of numerical experiments with the climate model, it was demonstrated that it is possible to predict the projection of temperature anomaly corresponding to the first EOF in December-April, to the first mode according to initial data for December 1.

Analysis of Simulation of Stratosphere-troposphere Dynamical Coupling with the INM-CM5 Climate Model

The simulation of stratosphere-troposphere dynamic coupling is considered in five 50-year realizations of ensemble calculations with the 5th version of the INM-CM5 climate model developed in the Marchuk Institute of Numerical Mathematics of Russian Academy of Sciences. The model also includes the ocean model and the improved vertical resolution in the upper stratosphere and lower mesosphere.

Is global ozone recovering?

Thanks to the Montreal Protocol, the stratospheric concentrations of ozone-depleting chlorine and bromine have been declining since their peak in the late 1990s. Global ozone has responded: The substantial ozone decline observed since the 1960s ended in the late 1990s. Since then, ozone levels have remained low, but have not declined further. Now general ozone increases and a slow recovery of the ozone layer is expected. The clearest signs of increasing ozone, so far, are seen in the upper stratosphere and for total ozone columns above Antarctica in spring. These two regions had also seen the largest ozone depletions in the past. Total column ozone at most latitudes, however, does not show clear increases yet. This is not unexpected, because the removal of chlorine and bromine from the stratosphere is three to four times slower than their previous increase. Detecting significant increases in total column ozone, therefore, will require much more time than the detection of its previous decline. The search is complicated by variations in ozone that are not caused by declining chlorine or bromine, but are due, e.g., to transport changes in the global Brewer–Dobson circulation. Also, very accurate observations are necessary to detect the expected small increases. Nevertheless, observations and model simulations indicate that the stratosphere is on the path to ozone recovery. This recovery process will take many decades. As chlorine and bromine decline, other factors will become more important. These include climate change and its effects on stratospheric temperatures, changes in the Brewer–Dobson circulation (both due to increasing CO2), increasing emissions of trace gases like N2O, CH4, possibly large future increases of short-lived substances (like CCl2H2) from both natural and anthropogenic sources, and changes in tropospheric ozone.

Future ozone in a changing climate

The stratospheric ozone layer is expected to recover as a result of the regulations of the Montreal Protocol on chlorine and bromine containing ozone-depleting substances (ODSs). Model simulations project a return of global annually averaged total column ozone to 1980 levels before the middle of the 21st century, well before the ODSs will return to 1980 levels. This earlier ozone return date is due to the effects of rising greenhouse gas (GHG) concentrations. GHGs influence ozone directly by chemical reactions, but also indirectly by changing stratospheric temperature and the Brewer–Dobson circulation. Based on projections of chemistry–climate models, this article summarizes the effects of GHGs on stratospheric and total column ozone in the mid-latitude upper stratosphere, Arctic and Antarctic spring, and the tropics. The sensitivity of future ozone change to the GHG scenario is discussed, as well as the specific role of a future increase in nitrous oxide and methane.