Northern Hemisphere Ozone Research Articles

On the relationship between sea ice extent dynamics in the Northern Hemisphere and total atmospheric ozone.

On the relationship between sea ice extent dynamics in the Northern Hemisphere and total atmospheric ozone.

Связь изменения площади морских льдов в Северном полушарии и общего содержания озона в атмосфере

Связь изменения площади морских льдов в Северном полушарии и общего содержания озона в атмосфере

Stratospheric ozone trends for 1985–2018: sensitivity to recent large variability

Abstract. The Montreal Protocol, and its subsequent amendments, has successfully prevented catastrophic losses of stratospheric ozone, and signs of recovery are now evident. Nevertheless, recent work has suggested that ozone in the lower stratosphere (< 24 km) continued to decline over the 1998–2016 period, offsetting recovery at higher altitudes and preventing a statistically significant increase in quasi-global (60∘ S–60∘ N) total column ozone. In 2017, a large lower stratospheric ozone resurgence over less than 12 months was estimated (using a chemistry transport model; CTM) to have offset the long-term decline in the quasi-global integrated lower stratospheric ozone column. Here, we extend the analysis of space-based ozone observations to December 2018 using the BASICSG ozone composite. We find that the observed 2017 resurgence was only around half that modelled by the CTM, was of comparable magnitude to other strong interannual changes in the past, and was restricted to Southern Hemisphere (SH) midlatitudes (60–30∘ S). In the SH midlatitude lower stratosphere, the data suggest that by the end of 2018 ozone is still likely lower than in 1998 (probability ∼80 %). In contrast, tropical and Northern Hemisphere (NH) ozone continue to display ongoing decreases, exceeding 90 % probability. Robust tropical (>95 %, 30∘ S–30∘ N) decreases dominate the quasi-global integrated decrease (99 % probability); the integrated tropical stratospheric column (1–100 hPa, 30∘ S–30∘ N) displays a significant overall ozone decrease, with 95 % probability. These decreases do not reveal an inefficacy of the Montreal Protocol; rather, they suggest that other effects are at work, mainly dynamical variability on long or short timescales, counteracting the positive effects of the Montreal Protocol on stratospheric ozone recovery. We demonstrate that large interannual midlatitude (30–60∘) variations, such as the 2017 resurgence, are driven by non-linear quasi-biennial oscillation (QBO) phase-dependent seasonal variability. However, this variability is not represented in current regression analyses. To understand if observed lower stratospheric ozone decreases are a transient or long-term phenomenon, progress needs to be made in accounting for this dynamically driven variability.

Decadal Variations in the Winter Beaufort High and the Stratospheric Polar Vortex

AbstractWe show that a weakened Beaufort High in late winter is becoming more common since the late 1980s, and this weakening is related to decadal changes in Northern Hemisphere ozone depletion. During this time, the stratospheric polar vortex has experienced a decadal northeastward displacement. Such displacement is associated with the variability of the East Asia‐eastern North America dipole. A positive Asia‐eastern North America dipole leads to zonal asymmetry in the ozone depletion with maximum loss over eastern Eurasia. Positive feedback with the zonally asymmetric ozone loss contributes to increased occurrence of the northeastward displacement of the stratospheric polar vortex. The northeastward displaced polar vortex enhances baroclinicity over the Eurasian Arctic and causes an increase in the frequency and intensity of cyclones and a decrease in anticyclones over the Eurasian Arctic. Concomitantly, the Beaufort High tends to have weakened.

Ozone impacts of gas–aerosol uptake in global chemistry transport models

Abstract. The impact of six heterogeneous gas–aerosol uptake reactions on tropospheric ozone and nitrogen species was studied using two chemical transport models, the Meteorological Synthesizing Centre-West of the European Monitoring and Evaluation Programme (EMEP MSC-W) and the European Centre Hamburg general circulation model combined with versions of the Hamburg Aerosol Model and Model for Ozone and Related chemical Tracers (ECHAM-HAMMOZ). Species undergoing heterogeneous reactions in both models include N2O5, NO3, NO2, O3, HNO3, and HO2. Since heterogeneous reactions take place at the aerosol surface area, the modelled surface area density (Sa) of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in east Asia. The impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. The analysis of the sensitivity runs confirms that the globally most important heterogeneous reaction is the one of N2O5. Nevertheless, NO2, HNO3, and HO2 heterogeneous reactions gain relevance particularly in east Asia due to the presence of high NOx concentrations and high Sa in the same region. The heterogeneous reaction of O3 itself on dust is of minor relevance compared to the other heterogeneous reactions. The impacts of the N2O5 reactions show strong seasonal variations, with the biggest impacts on O3 in springtime when photochemical reactions are active and N2O5 levels still high. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations in terms of concentration levels, variability, and temporal correlations at most sites when the heterogeneous reactions are incorporated. Our results are loosely consistent with results from earlier studies, although the magnitude of changes induced by N2O5 reaction is at the low end of estimates, which seems to fit a trend, whereby the more recent the study the lower the impacts of these reactions.

Relationship of climate changes with geomagnetic field. P. 3. Northern and Southern hemispheres

Differences of relations between geomagnetic field and climate for Northern and Southern hemispheres considered earlier have been shown. They are connected, first of all, with the depth of penetration of the charged particles into the Earth’s atmosphere, modulated by geomagnetic field and their impact on the ozone balance near the tropopause. In the Northern hemisphere ozone formation in the lower stratosphere occurs during ionic-molecular autocatalitic cycle of ozone production, initiated by GCR, and in the Southern one — as a result of “self-reduction” of ozone initiated by solar energetic particles. Explanation of the observed simultaneous warming in the Western Antarctica and the fall of temperature in the Central and Eastern Antarctica has also been presented.

Anomalies of Northern Hemisphere ozone associated with a tropopause‐lower stratosphere teleconnection during summer

ABSTRACTUsing the ozone data set from the satellite observations and the atmospheric reanalysis data sets during 1979–2005, we examine the variability of a tropopause‐lower stratosphere (TS) teleconnection a and its relationship with the ozone change over the Northern Hemisphere (NH) during summer. The TS teleconnection has an approximate opposite phase to that in the upper‐troposphere Asian‐Pacific Oscillation (APO), and the TS teleconnection index (the TS index) is also related well to the APO index. Corresponding to a higher TS index, the ozone generally decreases in the NH mid‐high latitudes (near 40°N and the Far East of Russia). This link between the TS teleconnection and the ozone is physically supported by the changes of the background atmospheric circulation. When the TS index is higher, the decrease of the ozone is closely associated with an increase of the local tropopause height. The upward and downward motion variations in the upper troposphere and the lower stratosphere in the east and west parts of the anomalous anticyclones associated with the TS index strengthen the exchanges of the ozone between the troposphere and the lower stratosphere, which may cause a decrease of the ozone. The horizontal advection of the ozone could also contribute to the ozone decreases over these regions.

Variability of extratropical ozone stratosphere–troposphere exchange using microwave limb sounder observations

The extratropical stratosphere–troposphere exchange (STE) of ozone from 2005 to 2010 is estimated by combining Microwave Limb Sounder ozone observations and MERRA reanalysis meteorological fields in an established direct diagnostic framework. The multiyear mean ozone STE is 275 Tg yr−1 and 214 Tg yr−1 in the Northern and Southern Hemispheres, respectively. The year‐to‐year variability is greater in the Northern Hemisphere, where the difference between the highest and the lowest annual flux is 15% of the multiyear mean compared with 6% in the Southern Hemisphere. Variability of lower stratospheric ozone and variability of the net mass flux both contribute to interannual variability in the Northern Hemisphere ozone flux. The flux across the extratropical 380 K surface determines the amount of flux across the extratropical tropopause, and the greatest seasonal variability of the 380 K ozone flux occurs in the late winter/early spring, around the time of greatest flux. Both the mass flux and the ozone mixing ratios on the 380 K surface show recurring spatial patterns, but interannual variability of these quantities and their alignment contribute to the ozone flux variability. The spatial and temporal variability are not well represented when zonal and/or monthly mean fields are used to calculate the ozone STE, although this results in a small high bias of the seasonal amplitude and annual magnitude. If the climatological variability over these 6 years is representative, the estimated number of years required to detect a 2 − 3% decade−1 trend in ozone STE using this diagnostic is 35 − 39 years.

Climate/chemistry feedbacks and biogenic emissions

The oxidizing capacity of the atmosphere is affected by anthropogenic emissions and is projected to change in the future. Model calculations indicate that the change in surface ozone at some locations could be large and have significant implications for human health. The calculations depend on the precise scenarios used for the anthropogenic emissions and on the details of the feedback processes included in the model. One important factor is how natural biogenic emissions will change in the future. We carry out a sensitivity calculation to address the possible increase in isoprene emissions consequent on increased surface temperature in a future climate. The changes in ozone are significant but depend crucially on the background chemical regime. In these calculations, we find that increased isoprene will increase ozone in the Northern Hemisphere but decrease ozone in the tropics. We also consider the role of bromine compounds in tropospheric chemistry and consider cases where, in a future climate, the impact of bromine could change.

Residual mean transport in the stratosphere: Contributions from wave driving and seasonal transience

A three‐dimensional model of dynamics and photochemistry is used to evaluate the contributions to residual mean motion and ozone transport from planetary wave drag, gravity wave drag and from the seasonal transience of diabatic cooling. The integrations reveal that over much of the winter hemisphere, seasonal transience plays a major role in driving residual mean motion. During autumn, when the seasonal drift of radiative equilibrium temperature is fast, that contribution dominates. Following solstice, the dominant contribution to residual mean motion swings to wave driving. Similar dependence is reflected in the wintertime increase of total ozone and in the transfer of stratospheric ozone to the troposphere. Owing to the substantial contribution from seasonal transience, only about half of the net wintertime increase of Northern Hemisphere ozone (spring‐autumn) is actually available to change through changes of wave driving. Observed changes then represent nearly all of the wintertime increase that is available to change.

Systematic Changes of Northern Hemisphere Ozone and Their Relationship to Random Interannual Changes

Abstract Northern Hemisphere ozone underwent a monotonic decline during the 1980s and 1990s. Systematic changes associated with that trend are shown to have a close relationship to random changes of ozone. These two components of interannual variability share a common structure. In it, ozone changes at high latitude are compensated at low latitude by changes of opposite sign. The out-of-phase relationship between ozone changes at high and low latitudes is consistent with a change of the residual mean circulation of the stratosphere, and so is the seasonality of systematic changes. Compensating trends at high and low latitudes amplify simultaneously—during winter, when the polar-night vortex is disturbed by planetary waves that force residual motion. Analogous relationships are obeyed by Northern Hemisphere temperature. The strong resemblance between systematic and random changes of Northern Hemisphere ozone implies that a major portion of its decline during the 1980s and 1990s involved a systematic weakening of the residual circulation. Anomalous forcing of the residual circulation is strongly correlated to random changes of ozone, which in turn have the same structure as systematic changes. The magnitude and structure of the ozone trend are broadly consistent with the climate sensitivity of ozone with respect to a change of the residual circulation. Derived from random changes over a large population of winters, the climate sensitivity implies an ozone trend quite similar to the observed trend, but with about two-thirds of its magnitude. When account is taken of both the anomalous residual circulation and anomalous photochemistry, the climate sensitivity of ozone reproduces the major structure as well as the magnitude of the observed trend.

The Influence of Large-Scale Eddy Flux Variability on the Zonal Mean Ozone Distribution

The influence of the variability of large-scale eddy heat and momentum fluxes on interannual and decadal changes in the zonal mean ozone distribution is investigated based on a two-dimensional circulation model with interactively coupled transport and chemistry. The large-scale eddy fluxes are prescribed according to observations, that is, in terms of monthly mean eddy mixing coefficients that are derived from ECMWF reanalysis 1979–93 (ERA-15). The results show that the eddy-forced changes in the lower-stratospheric residual circulation and eddy mixing processes induce coherent changes in temperature, ozone, and other chemical tracers. Significant ozone declines are found mainly in the lower stratosphere during winter, with maximum values of about −1.2 Dobson units (DU) per kilometer per decade at midlatitudes and more than −2 DU km−1 decade−1 at polar latitudes. The seasonal and vertical structure of the observed Northern Hemispheric ozone trend is captured in a remarkable way. It is also shown that, at midlatitudes, maximum declines in the zonal mean lower-stratospheric ozone are mainly related to the eddy mixing processes, and, at polar latitudes, to the induced changes in the lower-stratospheric temperatures.

Relationship between North Atlantic Oscillation changes and stratospheric ozone recovery in the Northern Hemisphere in a chemistry‐climate model

The relationship between North Atlantic Oscillation (NAO) changes and northern stratospheric ozone recovery in the near future is investigated using four timeslice scenarios (1960, 1980, 1990, 2015) of the chemistry‐climate model ECHAM4.L39(DLR)/CHEM. A wintertime NAO index composite study of the scenario “1990” and of the ECMWF reanalyses shows the typical NAO patterns: in the positive phase the stratospheric polar vortex is stronger and colder than in the negative phase. In the troposphere, the positive phase is marked by increased variance across the North Atlantic stormtrack whereas the negative phase is suggestive of blocking. Consistently, vertical stationary (transient) wave propagation is reduced (enhanced) in the positive phase. The model NAO index decreases significantly from “1990” to “2015”. This coincides with enhanced vertical stationary wave propagation and a dynamical heating of the northern polar stratosphere. Thus, tropospheric circulation changes might influence stratospheric dynamics and hence northern hemisphere ozone evolution.

A comparison of Northern and Southern Hemisphere cross‐tropopause ozone flux

The downward flux of ozone across the midlatitude (30°–60°) tropopause is calculated using changes in potential vorticity (PV) and a statistical relationship between the PV changes and ozone flux. This approach separates dynamical aspects of transport from the seasonal cycle of ozone in the lowermost stratosphere. The Northern Hemisphere (NH) ozone flux is larger (∼24%) than that calculated in the Southern Hemisphere (SH) during the year 2000. The midlatitude SH total horizontal area of exchange is equal to or slightly greater than the area of exchange in the NH throughout an annual cycle. The mean changes in potential vorticity of parcels near the tropopause are also similar or slightly greater in the SH, suggesting that NH and SH downward air mass transport to the troposphere are comparable. These results show that the greater NH midlatitude ozone flux is mostly due to the amount of ozone available for exchange rather than dynamical differences near the tropopause level at these latitudes.

Seasonally averaged ozone and nitrous oxide in the Northern Hemisphere lower stratosphere

Northern Hemisphere ozone (O3) measurements in the lower stratosphere made from 1989 to 1997 are presented along with simultaneous measurements of the conserved tracer nitrous oxide (N2O) to help separate O3 changes due to photochemistry from those due to transport. This model‐independent analysis represents 139 flights aboard the ER‐2 aircraft and 12 profiles from balloons and uses zonal, isobaric, and isentropic seasonal averages of O3 and N2O to examine seasonal changes in O3 distributions. The resulting seasonal families of curves at constant latitude are somewhat intertwined, while the families of isobaric and isentropic curves are not. Although some of the isobaric curves cross, the isentropic curves are sufficiently separated to confidently estimate O3 by specifying season, N2O, and potential temperature, then interpolating between the curves. Such estimates may be useful for testing of photochemical models with transport, and perhaps more importantly, the families of curves could serve as baseline references for estimating high latitude photochemical O3 loss and as an indicator of O3 recovery in the lower stratosphere.

A study of impacts of tropospheric synoptic processes on the genesis and evolution of extreme total ozone anomalies over southern South America

During the austral autumn of 1997, a sequence of record low ozone events with anomalous behavior occurred at subtropical latitudes to midlatitudes over southern South America, also known as the South Cone (Chile, Argentina, Uruguay, and Southern Brazil). The extreme low ozone events took place in May and early June 1997, i.e., at a time of the year when according to the climatological studies for Northern Hemisphere ozone miniholes, the most significant events would not be expected (if such studies could be simply extrapolated to the Southern Hemisphere). The first and most prominent ozone minihole, with a quasi‐stationary evolution, reached values near 200 DU, i.e., a negative anomaly near 90 DU, close to 40°S. Simultaneously, extreme weather conditions were observed over the South Cone: three significant blocking events took place separated by short intervals. Both the behavior of the ozone layer over the region and the evolution of the blocking events were analyzed. As expected, the evolution of the total ozone column is shown to be linked to these perturbed weather conditions. Despite the apparently similar nature of the blocking events and of the ozone decrease during each of these events, the present study shows that the response of the UT/LS region is different in each case. The respective roles of the vertical displacement of the tropopause and the horizontal advection/divergence of ozone is discussed for the two most important events, showing how these two mechanisms combine in different ways to yield very low total ozone values. The vertical displacement of the tropopause, coupled to the size of the tropopause pressure gradient, appears to be the most efficient mechanism to modify the total ozone column amounts.

Very strong negative trends in laminae in ozone profiles

A very strong negative trend in the overall ozone content in the positive laminae in ozone profiles, a decrease by 50% during about 20–25 years, was found in the 1970s, 1980s and early 1990s in data of eight Northern Hemisphere ozone sounding stations. They were located at high and middle latitudes in Europe, Canada and Japan. Only the station Wallops Island in US ( 38 ° N ) revealed much smaller reduction of ozone in laminae. This means among others that the negative trend is basically the same for Resolute Bay at 75 ° N and Tateno at 36 ° N in spite of twice as high ozone content in laminae at Resolute Bay. The trends have been broadly studied for large laminae with the peak ozone concentration higher by 40 nbar and more than the background ozone concentration. However, analyses of laminae with the peak ozone concentration higher than 30 or 20 nbar against background for a few stations revealed similar strong negative trends. The trends are almost height independent, but the contribution of laminae to overall ozone content clearly peaks in the lowermost stratosphere. The overall ozone content in laminae has a strong seasonal variation (factor 5 or even more) with a maximum in late winter/early spring, when the negative trend in laminae may be responsible for as much as one third of the observed ozone depletion in European middle latitudes. Laminae seem to contribute substantially to seasonal variation of trends in total ozone.

Role of climate feedback on methane and ozone studied with a Coupled Ocean‐Atmosphere‐Chemistry Model

We present results from two experiments carried out with a coupled ocean‐atmosphere‐tropospheric chemistry model run continously over the period 1990 to 2100. In the control experiment, climate is unforced, but emissions of trace gases to the chemical model increase in line with an illustrative scenario for future trace gas emissions with medium high growth. In the climate change experiment trace gas emissions are identical to the control, but climate is also forced using greenhouse gas concentrations and SO2 emissions from the same scenario. Global average methane in the climate change experiment increased from 1670 ppbv in 1990 to 3230 ppbv by 2100, compared to 3650 ppbv by 2100 in the control. The methane increase in the control experiment is therefore 27% more than in the control. This difference is due to both temperature and OH changes which increase the rate of methane oxidation and act in the opposite direction to the negative feedback of methane on itself through OH. Mid‐latitude northern hemisphere ozone concentrations in July for the mid‐troposphere rose from 39 ppbv in 1990s to 64 ppbv in the 2090s in the control experiment and to 49 ppbv in the climate change experiment. The direct role of climate change is therefore predicted to be a negative feedback on the radiative forcing from the change to tropospheric ozone and methane concentrations.

Influence of solar ultraviolet-B on pelagic fish embryos: osmolality, mortality and viable hatch

Eggs of dab (Limanda limanda) and plaice (Pleuronectes platessa) were experimentally exposed to ultraviolet-B (UV-B) radiation in a solar radiation simulator. The experimental design tried to simulate present and future conditions with reference to increased UV-B exposure due to northern hemisphere ozone loss, employing mainly two scenarios, a reduction to 270 (S1) and to 180 (S2) Dobson units (DU) in single or repetitive exposures of 2, 4 or 6 h. Depending on the total dose of UV-B irradiation and the developmental stage, exposed eggs displayed loss of buoyancy as a sublethal effect, as well as increased embryo mortality and reduced viable hatch. In the single exposure experiments only under conditions of 180 DU for 6 h were effects apparent. Double exposure under conditions of 270 DU did not lead to lasting effects. At the sublethal effect level, i.e. loss of buoyancy, considerable photorepair was observed. It was concluded, that under the present general weather conditions in spring and at the present levels of environmental ozone, allowing for a reduction to 180 DU, the embryonic development of North Sea spring spawning fish is not endangered by UV-B radiation.

Wintertime climatology of MOZAIC ozone based on the potential vorticity and ozone analogy

A climatology is compiled of wintertime ozone measured by MOZAIC aircraft. It spans the winters of 1994/1995 to 1997/1998. It is generated employing and in the process confirming the analogy between potential vorticity and ozone. The methodology consists of interpolating equivalent latitude derived from analyzed potential vorticity onto flight tracks of the aircraft. In a second step the measurements are cast into a gridded form; this generates seasonal synopses of ozone in the coordinate space spanned by time, potential temperature, and equivalent latitude. At low equivalent latitudes the irregular appearance of high‐ozone transients in combination with the relatively small measurement density renders a determination of seasonal‐mean ozone problematic. However, in middle and high equivalent latitudes of the Northern Hemisphere ozone mixing ratios are well summarized by stating seasonal means and seasonal increases only. The results derived for the four winters exhibit some marked interannual variability. The method allows the determination of “expected” ozone along the flight tracks from the gridded ozone. A comparison with measured ozone for two selected periods of time suggests that discrepancies between expected and measured ozone hint at the presence of filamentary structure in the ozone field and associated stratosphere‐troposphere exchange. In the four‐winter mean such “outliers” of measured ozone occur most frequently in the vicinity of the North Atlantic storm track, corroborating earlier studies on filamentation activity.