The impacts of volcanic aerosol on stratospheric ozone and the Northern Hemisphere polar vortex: separating radiative-dynamical changes from direct effects due to enhanced aerosol heterogeneous chemistry (original) (raw)
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Impact of stratospheric dynamics and chemistry on northern hemisphere midlatitude ozone loss
Journal of Geophysical Research, 1998
The importance of dynamics for stratospheric ozone distribution in the northern hemisphere is investigated by using multiannual simulations of the coupled dynamic-chemical general circulation model ECHAM3/CHEM. This model includes a parameterization for heterogeneous reactions on the surfaces of polar stratospheric clouds (PSCs) and on sulfate aerosols. A warm and a cold stratospheric winter are examined to estimate the range of chemical ozone loss in the model due to heterogeneous reactions on PSCs. Ozone depletion in the model mainly occurs inside the polar vortex. An additional ozone reduction due to heterogeneous reactions on PSCs is found outside the polar vortex. Secondary vortex formation and vortex contraction after an elongation lead to a transport of air masses with chemically reduced ozone values out of the vortex. Except for such events the edge of the modeled polar vortex acts as a barrier to transport. During the formation of secondary vortices no additional heterogeneous reactions occur therein. Other dynamic events, such as the elongation of the polar vortex and its displacement to lower latitudes, lead t,o an intense ozone depletion. A minor stratospheric warming in the model causes a total aleactivation of chlorine compounds and prevents further ozone depletion. In midlatitudes, the amplitude of short-term variations of total ozone is amplified by PSC heterogeneous chemical ozone reduction. 1. Introduction After the discovery of the Antarctic ozone hole [Farman et al., 1985], several studies addressed the question of the importance of distinct chemical and dynamic reasons for the observed ozone depletion [e.g., Crutzen and Arnold, 1986; Solomon, 1986] (see World Meteorological Organization (WMO) [1992] for more detailed discussion). From satellite measurements it was obvious that the ozone decrease over the last decades was not restricted to the southern hemisphere high latitudes but also occurs in the northern hemisphere and at midlatitudes of both hemispheres [Stolarski et al., 1991, 1992; Randel and Wu, 1995]. This finding led to an intense debate on the characteristics of the stratospheric polar vortex and related effects on stratospheric transport processes at its edge, i.e., whether the polar vortex acts as a "containment vessel" [Mcintyre, 1989; Schoeberl et al., 1989] or as a "flowing processor" [Tuck, 1989; Proffittet al., 1989]. A comprehensive discussion was given by Schoeberl et al. [1992], Randel [1993], and Wanben Paper number 98JD01830. 0148-0227 / 98 / 98 JD-01830509.00 et al. [1997]. Measurements revealed that near the edge of the vortex the meridional poleward transport in winter has been reduced, resulting in different compositions of the air inside and outside the polar vortex (e.g., for southern hemisphere conditions [Tuck, 1989; Margitan et al., 1989] and for northern hemisphere conditions [Proffitt et al., 1990]). However, model studies [Juckes and Mcintyre, 1987] and observational studies [e.g., Tuck, 1989] clearly showed that the polar vortex
Journal of Geophysical Research, 2002
The morphology and evolution of the stratospheric ozone (03) distribution at high latitudes in the Northern Hemisphere (NH) are examined for the late summer and fall seasons of 1999. This time period sets the 0 3 initial condition for the SOLVE/THESEO field mission performed during winter 1999-2000. In situ and satellite data are used along with a three-dimensional model of chemistry and transport (CTM) to determine the key processes that control the distribution of 03 in the lower-to-middle stratosphere.
J. Geophys. …, 2002
1] Observations show that strong equatorial volcanic eruptions have been followed by a pronounced positive phase of the Arctic Oscillation (AO) for one or two Northern Hemisphere winters. It has been previously assumed that this effect is forced by strengthening of the equator-to-pole temperature gradient in the lower stratosphere, caused by aerosol radiative heating in the tropics. To understand atmospheric processes that cause the AO response, we studied the impact of the 1991 Mount Pinatubo eruption, which produced the largest global volcanic aerosol cloud in the twentieth century. A series of control and perturbation experiments were conducted with the GFDL SKYHI general circulation model to examine the evolution of the circulation in the 2 years following the Pinatubo eruption. In one set of perturbation experiments, the full radiative effects of the observed Pinatubo aerosol cloud were included, while in another only the effects of the aerosols in reducing the solar flux in the troposphere were included, and the aerosol heating effects in the stratosphere were suppressed. A third set of perturbation experiments imposed the stratospheric ozone losses observed in the post-Pinatubo period. We conducted ensembles of four to eight realizations for each case. Forced by aerosols, SKYHI produces a statistically significant positive phase of the AO in winter, as observed. Ozone depletion causes a positive phase of the AO in late winter and early spring by cooling the lower stratosphere in high latitudes, strengthening the polar night jet, and delaying the final warming. A positive phase of the AO was also produced in the experiment with only the tropospheric effect of aerosols, showing that aerosol heating in the lower tropical stratosphere is not necessary to force positive AO response, as was previously assumed. Aerosol-induced tropospheric cooling in the subtropics decreases the meridional temperature gradient in the winter troposphere between 30°N and 60°N. The corresponding reduction of mean zonal energy and amplitudes of planetary waves in the troposphere decreases wave activity flux into the lower stratosphere. The resulting strengthening of the polar vortex forces a positive phase of the AO. We suggest that this mechanism can also contribute to the observed long-term AO trend being caused by greenhouse gas increases because they also weaken the tropospheric meridional temperature gradient due to polar amplification of warming. Oscillation response to the 1991 Mount Pinatubo eruption: Effects of volcanic aerosols and ozone depletion,
Temporal development of ozone within the Arctic vortex during the winter of 1991/92
Geophysical Research Letters, 1994
In this study we address the question of temporal ozone trends on isentropic surfaces within the Arctic polar vortex during EASOE. We have combined ozone sonde data from twelve campaign stations distributed throughout the European sector of the Arctic. The development of ozone at the 425,475, 550 and 700 K levels is presented, using analysed fields of isentropic potential vorticity and isentropic back-trajectories to separate inner vortex air from air staying outside the vortex.
Chemical Loss of Ozone in the Arctic Polar Vortex in the Winter of 1991-1992
Science, 1993
The H, O trend is estimated by calculating the difference between the average H20 with the H, O residual estimated in K. Kelly et a/. [Geophys. Res. Lett. 17, 465 (1989)], and scaling with the CH, trend. The H20 difference is a result of CH, oxidation in the stratosphere. 17. The HNO, trend is estimated by assuming that the NO, trend is the same as the N, O trend (0 2%) and using the scaling of NO, (10). 18. Projected injections of NO, and H, O are taken from scenario F in M. Prather et a/. [NASA Ref. Publ. 1272 (1992)l. In this report, NO is estimated to increase 4 ppbv and H, O will rncrease by about 1 ppmv, for an emission index of 15 and a Mach number 3.2. 19. T. Peter et a/. [Geophys. Res. Lett. 18, 1465 (1991)l calculated a doubling of the PSC probability for future fleets of stratospheric aircraft (a 1.7 K increase in the 50-hPa NAT saturation temperature using a two-dimensional chemistry model). 20. We thank all the partic~pants in the AASE II mission.
Dynamics, stratospheric ozone, and climate change
Atmosphere-Ocean, 2008
Dynamics affects the distribution and abundance of stratospheric ozone directly through transport of ozone itself and indirectly through its effect on ozone chemistry via temperature and transport of other chemical species. Dynamical processes must be considered in order to understand past ozone changes, especially in the northern hemisphere where there appears to be significant low-frequency variability which can look "trend-like" on decadal time scales. A major challenge is to quantify the predictable, or deterministic, component of past ozone changes. Over the coming century, changes in climate will affect the expected recovery of ozone. For policy reasons it is important to be able to distinguish and separately attribute the effects of ozone-depleting substances and greenhouse gases on both ozone and climate. While the radiative-chemical effects can be relatively easily identified, this is not so evident for dynamics-yet dynamical changes (e.g., changes in the Brewer-Dobson circulation) could have a first-order effect on ozone over particular regions. Understanding the predictability and robustness of such dynamical changes represents another major challenge. Chemistry-climate models have recently emerged as useful tools for addressing these questions, as they provide a self-consistent representation of dynamical aspects of climate and their coupling to ozone chemistry. We can expect such models to play an increasingly central role in the study of ozone and climate in the future, analogous to the central role of global climate models in the study of tropospheric climate change. RÉSUMÉ [Traduit par la rédaction] La dynamique influence la distribution et l'abondance de l'ozone stratosphérique, directement par le transport de l'ozone même et indirectement par ses effets sur la chimie de l'ozone, effets qui sont liés à la température et au transport d'autres espèces chimiques. Il faut prendre en compte les processus dynamiques pour comprendre les changements passés dans l'ozone, en particulier dans l'hémisphère Nord, où il semble y avoir une importante variabilité de basse fréquence qui peut avoir l'air d'une tendance à une échelle de temps décennale. Quantifier la composante prévisible, ou déterministe, des changements passés dans l'ozone est un défi majeur. Au cours du siècle à venir, les changements climatiques modifieront le remplacement attendu de l'ozone. Pour des raisons d'ordre politique, il importe de pouvoir distinguer et de pouvoir attribuer séparément les effets des substances destructrices de l'ozone et des gaz à effet de serre tant sur l'ozone que sur le climat. Bien qu'il soit assez facile d'identifier les effets radiatifs-chimiques, il est plus difficile de le faire pour la dynamique-encore que les changements dynamiques (p. ex. les changements dans la circulation de Brewer-Dobson) pourraient avoir un effet de premier ordre sur l'ozone dans certaines régions. Comprendre la prévisibilité et la robustesse de tels changements dynamiques est un autre grand défi. Les modèles de chimie climatique ont récemment fait leur apparition en tant qu'outils utiles pour l'étude de ces questions, car ils fournissent une représentation cohérente en elle-même des aspects dynamiques du climat et de leur couplage avec la chimie de l'ozone. On peut s'attendre à ce que, dans le futur, de tels modèles jouent un rôle de plus en plus central dans l'étude de l'ozone et du climat, un rôle analogue à celui des modèles climatiques globaux dans l'étude du changement climatique troposphérique.
The effect of zonally asymmetric ozone heating on the Northern Hemisphere winter polar stratosphere
Geophysical Research Letters, 2011
1] Previous modeling studies have found significant differences in winter extratropical stratospheric temperatures depending on the presence or absence of zonally asymmetric ozone heating (ZAOH), yet the physical mechanism causing these differences has not been fully explained. The present study describes the effect of ZAOH on the dynamics of the Northern Hemisphere extratropical stratosphere using an ensemble of free-running atmospheric general circulation model simulations over the 1 December -31 March period. We find that the simulations including ZAOH produce a significantly warmer and weaker stratospheric polar vortex in mid-February due to more frequent major stratospheric sudden warmings compared to the simulations using only zonal mean ozone heating. This is due to regions of enhanced Eliassen-Palm flux convergence found in the region between 40°N-70°N latitude and 10-0.05 hPa. These results are consistent with changes in the propagation of planetary waves in the presence of ZAOH predicted by an ozone-modified refractive index. Citation: McCormack, J. P., T. R. Nathan, and E. C. Cordero (2011), The effect of zonally asymmetric ozone heating on the Northern Hemisphere winter polar stratosphere, Geophys. Res. Lett., 38, L03802,
Latitudinal -Longitudinal Dependence of Stratospheric Response to Particles’ Forcing in January 2005
1-st workshop proceedings of EU FP7 project BlackSeaHazNet, May 2011, 2011
This study is aimed to analyze irregularities in the spatial distribution of temperature and ozone that could be related to the solar proton event in January 2005 (SPE'05). Unlike the common opinion that precipitating particles deplete the O 3 (through forcing of HO x and NO x destructive cycle) we have shown that regional response of the mid-latitude stratospheric ozone could be positive. This O 3 abundance is explained with the reduction of the O 3 optical depth aloft, due to its chemical losses at mesospheric levels -an effect known as ozone self-healing. Using a simple analytical model we have estimated quantitatively its effect on the lower level ozone, depending on the amount of it destruction at higher levels, temperature and concentration of OH radicals. For the first time we show that UV radiation with length close to the maximum of O 3 absorption cross-section (i.e. 240 nm) is the most effective in the process of the ozone selfhealing, due to a delicate balance between dissociation of molecular oxygen (producing ozone) and O 3 . We have shown also that the mid-latitude O 3 enhancement during SPE'05 could be attributed to precipitating particles from Earth's radiation belts, which reduce the O 3 optical depth aloft and force the effect of ozone self-healing at lower levels. This mechanism is capable of explaining the observed -by MLS on Aura and TOMS on Earth Probe -and modeled by ERA Interim reanalysis latitude-longitude variations of the middle atmospheric ozone and temperature. Keywords: relativistic electrons; lower energetic protons; stratospheric ozone and temperature; solar proton events Proceedings of the 1 -st workshop of the EU FP7 project BlackSeaHazNet, May 2011, Ohrid, FYRO Maredonia
Aspects of stratospheric long-term changes induced by ozone depletion
Climate Dynamics, 2006
The effect of the stratospheric ozone depletion on the thermal and dynamical structure of the middle atmosphere is assessed using two 5-member ensembles of transient GCM simulations; one including linear trends in ozone, the other not, for the 1980-1999 period. Simulated temperatures and observations are in good agreement in terms of mean values, autocorrelations and cross correlations. Annual-mean and seasonal temperature trends have been calculated using the same statistical analysis. Simulations show that ozone trends are responsible for reduced wave activity in the Arctic lower stratosphere in February and March, confirming both the role of dynamics in controlling March temperatures and a recently proposed mechanism whereby Arctic ozone depletion causes the reduction in wave activity entering the lower stratosphere. Changes in wave activity are consistent with an intensification of the polar vortex at the time of ozone depletion and with a weakened Brewer-Dobson circulation: A decrease of the dynamical warming/cooling associated with the descending/ascending branch of the wintertime mean residual circulation at high/low latitudes has been obtained through the analysis of temperature observations (1980-1999). Ozone is responsible of about one third of the decrease of this dynamical cooling at high latitudes. An increase in the residual mean circulation is seen in the observations for the 1965-1980 period.