Atmospheric Chemistry and Physics Discussions, 2015
ABSTRACT After strong volcanic eruptions stratospheric ozone changes are modulated by heterogeneo... more ABSTRACT After strong volcanic eruptions stratospheric ozone changes are modulated by heterogeneous chemical reactions (HET) and dynamical perturbations related to the radiative heating in the lower stratosphere (RAD). Here, we assess the relative importance of both processes as well as the effect of the resulting ozone changes on the dynamics using ensemble simulations with the atmosphere–ocean–chemistry–climate model (AOCCM) SOCOL-MPIOM forced by eruptions with different strength. The simulations are performed under present day and preindustrial conditions to investigate changes in the response behaviour. The results show that the HET effect is only relevant under present day conditions and causes a pronounced global reduction of column ozone. These ozone changes further lead to a slight weakening of the Northern Hemisphere (NH) polar vortex during mid-winter. Independent from the climate state the RAD mechanism changes the column ozone pattern with negative anomalies in the tropics and positive anomalies in the mid-latitudes. The influence of the climate state on the RAD mechanism significantly differs in the polar latitudes, where an amplified ozone depletion during the winter months is simulated under present day conditions. This is in contrast to the preindustrial state showing a positive column ozone response also in the polar area. The dynamical response of the stratosphere is clearly dominated by the RAD mechanism showing an intensification of the NH polar vortex in winter. Still under present day conditions ozone changes due to the RAD mechanism slightly reduce the response of the polar vortex after the eruption.
The Atlantic Multidecadal Oscillation (AMO) is an important mode of variability in the Atlantic r... more The Atlantic Multidecadal Oscillation (AMO) is an important mode of variability in the Atlantic region with impacts on the regional to hemispheric scale and links to various phenomena from Sahel drought to tropical hurricane frequencies. Whether the AMO is a persistent oscillatory phenomenon or to some some extent driven by external forcings is still under debate. In the last years this question was assessed in a number of reconstruction and modeling studies. In general, two different approaches are applied: (1) methods which focus on the internal variability by decomposing the data into externally forced variations and a residuum (i.e. the AMO) and (2) methods which use the original data including the external signal. The former has the disadvantage that an attribution of AMO variations to external forcing is per definition no longer possible and the characteristics of the residuum may depend on the decomposition method. For this study, we compare both methods and analyze the role ...
Journal of Geophysical Research: Atmospheres, 2014
ABSTRACT An important key for the understanding of the dynamic response to large tropical volcani... more ABSTRACT An important key for the understanding of the dynamic response to large tropical volcanic eruptions is the warming of the tropical lower stratosphere and the concomitant intensification of the polar vortices. Although this mechanism is reproduced by most general circulation models today, most models still fail in producing an appropriate winter warming pattern in the Northern Hemisphere. In this study ensemble sensitivity experiments were carried out with a coupled atmosphere-ocean model to assess the influence of different ozone climatologies on the atmospheric dynamics and in particular on the northern hemispheric winter warming. The ensemble experiments were perturbed by a single Tambora-like eruption. Larger meridional gradients in the lower stratospheric ozone favor the coupling of zonal wind anomalies between the stratosphere and the troposphere after the eruption. The associated sea level pressure, temperature, and precipitation patterns are more pronounced and the northern hemispheric winter warming is highly significant. Conversely, weaker meridional ozone gradients lead to a weaker response of the winter warming and the associated patterns. The differences in the number of stratosphere-troposphere coupling events between the ensembles experiments indicate a nonlinear response behavior of the dynamics with respect to the ozone and the volcanic forcing.
The role of different background ozone climatologies for the dynamic response to tropical volcani... more The role of different background ozone climatologies for the dynamic response to tropical volcanic eruptions is analyzed using an ensemble of simulation with the atmospheric-chemistry-ocean model SOCOL/MPIOM. In this sensitivity study a single tropical eruption of Tambora-size is applied to an ensemble with either pre-industrial ozone concentrations or present day concentrations respectively. The analysis focuses on the characteristic of the Northern Europe winter warming pattern following the eruption, that has been identified after several eruptions in observations and in proxy data. The sensitivity study reveals a higher probability for a large and significant winter warming pattern with pre-industrial ozone levels, when the dynamic response of the chemistry to the eruption is disabled in the model. The positive temperature anomaly is driven by a positive NAO-like pressure pattern that lead to the advection of warm Atlantic air towards Northern Europe. With present day concentrat...
After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogen... more After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogeneous chemistry on the particle surfaces (HET-AER) and from dy-namical effects related to the radiative heating of the lower stratosphere (RAD-DYN). We carry out a series of experiments with an atmosphere–ocean–chemistry–climate model to assess how these two processes change stratospheric ozone and Northern Hemispheric (NH) polar vortex dynamics. Ensemble simulations are performed under present day and preindustrial conditions, and with aerosol forcings representative of different eruption strength, to investigate changes in the response behaviour. We show that the halogen component of the HET-AER effect dominates under present-day conditions with a global reduction of ozone (−21 DU for the strongest eruption) particularly at high latitudes, whereas the HET-AER effect increases stratospheric ozone due to N 2 O 5 hydrolysis in a preindustrial atmosphere (maximum anomalies +4 DU). The halogen-induced ozone changes in the present-day atmosphere offset part of the strengthening of the NH polar vortex during midwinter (reduction of up to −16 m s −1 in January) and slightly amplify the dynamical changes in the polar stratosphere in late winter (+11 m s −1 in March). The RAD-DYN mechanism leads to positive column ozone anomalies which are reduced in a present-day atmosphere by amplified polar ozone depletion (maximum anomalies +12 and +18 DU for present day and preindus-trial, respectively). For preindustrial conditions, the ozone response is consequently dominated by RAD-DYN processes, while under present-day conditions, HET-AER effects dominate. The dynamical response of the stratosphere is dominated by the RAD-DYN mechanism showing an intensifica-tion of the NH polar vortex in winter (up to +10 m s −1 in January). Ozone changes due to the RAD-DYN mechanism slightly reduce the response of the polar vortex after the eruption under present-day conditions.
For the period 1970-2007, the relationship between heat stress and mortality in Vienna was analyz... more For the period 1970-2007, the relationship between heat stress and mortality in Vienna was analyzed using a human biometeorological thermal index. Using the PET (Physiologically Equivalent Temperature) at 14 CET mortality is significant below the baseline for days with PET < 29°C and significant above for hotter days. On days with extreme heat stress (PET ≥ 41°C) an additional mortality of +13.0 % was found. The sensitivity to heat stress is significantly higher for women and for patients with cardiovascular diseases. To assess the impact of climate change on the heat-related mortality, we used the two regional climate models REMO and CLM and the emissions scenarios A1B and B1. The heat related mortality was assessed by one scenario without any long-term adaptation and one scenario including continuous long-term adaptation. In both scenarios, heat-related mortality could increase until 2071-2100. Till 2011-2040 no significant changes to the period of examination were found. Adaptation measures should focus on the extreme heat days (PET ≥ 41°C), were the mortality will increase even with long-term adaptation.
HINTERGRUND: Starke Hitzebelastung beeinträchtigt den menschlichen Organismus, die Mortalität ste... more HINTERGRUND: Starke Hitzebelastung beeinträchtigt den menschlichen Organismus, die Mortalität steigt während Hitzeperioden. Der "Jahrhundertsommer 2003" mit mehreren langanhaltenden Hitzewellen führte besonders in West-Europa zu zahlreichen zusätzlichen Todesfällen; auch Wien war davon betroffen. In dieser Untersuchung betrachten wir den Sommer 2003 in einem größeren zeitlichen Kontext um zu beurteilen, ob wie sehr sich die hitzebedingte Mortalität 2003 von anderen Jahren unterscheidet. METHODE: Die Untersuchung basiert auf meteorologischen Daten und Mortalitätsdaten des Bundeslands Wien für den Zeitraum 1970–2007. Die thermische Belastung wurde über den human-meteorologischen Parameter Physiologisch Äquivalente Temperatur (PET) berechnet, kurzfristige Anpassungseffekte wurden über den HeRATE-Ansatz berücksichtigt. Basierend auf thermo-physiologischen Belastungsklassen wurde der Einfluss der Hitzebelastung auf die Mortalität bestimmt. Zwei verschiedene Ansätze berücksichtigen langfristige Veränderungen in der Sensitivität. ERGEBNISSE: Die hitzebedingte Mortalität steigt mit zunehmender thermischer Belastung, im Laufe der Untersuchungsperiode verflachte sich jedoch dieser Anstieg. Eine über den Untersuchungszeitraum gemittelte Sensitivität, ergibt auch für Wien die höchsten Werte im Sommer 2003. Mit Berücksichtigung der abnehmenden Sensitivität wiesen jedoch die Sommer 1992, 1994 und 2000 eine höhere Zahl hitzebedingter Todesopfer auf. DISKUSSION: Trotz oder vielleicht wegen der signifikanten Zunahme der Tage mit Hitzebelastung ist die Sensitivität gegenüber Hitzebelastung zurückgegangen. Dies könnte ein Hinweis auf langfristige Anpassungsprozesse an die veränderten klimatischen Bedingungen sein. Deswegen war das Jahr 2003 in Wien ein Jahr mit deutlich erhöhter Sterblichkeit durch Hitzestress, ohne jedoch außergewöhnlich gewesen zu sein. BACKGROUND: Strong heat load has negative impacts on the human health and results in higher mortality during heat waves. In Europe, the summer 2003 was responsible for a high number of heat-related deaths, especially in Western Europe. Vienna was only partially affected. The aim of this study is to compare the heat-related mortality of 2003 with other years and to analyze whether 2003 was exceptional in Vienna. METHODS: The analysis is based on both meteorological and mortality data for the federal state of Vienna (Austria) for 1970–2007. We used the human-biometeorological index Physiologically Equivalent Temperature (PET) in order to assess the heat load affecting the human body, and considered short-term adaptation by the HeRATE approach. Each day between April and October was classified according to its thermal stress level and the mean mortality for each class was analyzed. Two approaches, with and without long-term sensitivity trends were considered. RESULTS: Mortality increases significantly with thermal stress, but this increase attenuated in the last decades. Based on the sensitivity for the period of investigation, 2003 was the year with the highest heat-related mortality. Including the long-term sensitivity trend, other years (1992, 1994 and 2000) were characterised by higher values. DISCUSSION: In the last decades the number of days with heat stress increased, but the sensitivity to heat stress decreased. This could indicate long-term adaptation processes. Hence, heat-related mortality in 2003 was high, but not exceptionally high.
Atmospheric Chemistry and Physics Discussions, 2015
ABSTRACT After strong volcanic eruptions stratospheric ozone changes are modulated by heterogeneo... more ABSTRACT After strong volcanic eruptions stratospheric ozone changes are modulated by heterogeneous chemical reactions (HET) and dynamical perturbations related to the radiative heating in the lower stratosphere (RAD). Here, we assess the relative importance of both processes as well as the effect of the resulting ozone changes on the dynamics using ensemble simulations with the atmosphere–ocean–chemistry–climate model (AOCCM) SOCOL-MPIOM forced by eruptions with different strength. The simulations are performed under present day and preindustrial conditions to investigate changes in the response behaviour. The results show that the HET effect is only relevant under present day conditions and causes a pronounced global reduction of column ozone. These ozone changes further lead to a slight weakening of the Northern Hemisphere (NH) polar vortex during mid-winter. Independent from the climate state the RAD mechanism changes the column ozone pattern with negative anomalies in the tropics and positive anomalies in the mid-latitudes. The influence of the climate state on the RAD mechanism significantly differs in the polar latitudes, where an amplified ozone depletion during the winter months is simulated under present day conditions. This is in contrast to the preindustrial state showing a positive column ozone response also in the polar area. The dynamical response of the stratosphere is clearly dominated by the RAD mechanism showing an intensification of the NH polar vortex in winter. Still under present day conditions ozone changes due to the RAD mechanism slightly reduce the response of the polar vortex after the eruption.
The Atlantic Multidecadal Oscillation (AMO) is an important mode of variability in the Atlantic r... more The Atlantic Multidecadal Oscillation (AMO) is an important mode of variability in the Atlantic region with impacts on the regional to hemispheric scale and links to various phenomena from Sahel drought to tropical hurricane frequencies. Whether the AMO is a persistent oscillatory phenomenon or to some some extent driven by external forcings is still under debate. In the last years this question was assessed in a number of reconstruction and modeling studies. In general, two different approaches are applied: (1) methods which focus on the internal variability by decomposing the data into externally forced variations and a residuum (i.e. the AMO) and (2) methods which use the original data including the external signal. The former has the disadvantage that an attribution of AMO variations to external forcing is per definition no longer possible and the characteristics of the residuum may depend on the decomposition method. For this study, we compare both methods and analyze the role ...
Journal of Geophysical Research: Atmospheres, 2014
ABSTRACT An important key for the understanding of the dynamic response to large tropical volcani... more ABSTRACT An important key for the understanding of the dynamic response to large tropical volcanic eruptions is the warming of the tropical lower stratosphere and the concomitant intensification of the polar vortices. Although this mechanism is reproduced by most general circulation models today, most models still fail in producing an appropriate winter warming pattern in the Northern Hemisphere. In this study ensemble sensitivity experiments were carried out with a coupled atmosphere-ocean model to assess the influence of different ozone climatologies on the atmospheric dynamics and in particular on the northern hemispheric winter warming. The ensemble experiments were perturbed by a single Tambora-like eruption. Larger meridional gradients in the lower stratospheric ozone favor the coupling of zonal wind anomalies between the stratosphere and the troposphere after the eruption. The associated sea level pressure, temperature, and precipitation patterns are more pronounced and the northern hemispheric winter warming is highly significant. Conversely, weaker meridional ozone gradients lead to a weaker response of the winter warming and the associated patterns. The differences in the number of stratosphere-troposphere coupling events between the ensembles experiments indicate a nonlinear response behavior of the dynamics with respect to the ozone and the volcanic forcing.
The role of different background ozone climatologies for the dynamic response to tropical volcani... more The role of different background ozone climatologies for the dynamic response to tropical volcanic eruptions is analyzed using an ensemble of simulation with the atmospheric-chemistry-ocean model SOCOL/MPIOM. In this sensitivity study a single tropical eruption of Tambora-size is applied to an ensemble with either pre-industrial ozone concentrations or present day concentrations respectively. The analysis focuses on the characteristic of the Northern Europe winter warming pattern following the eruption, that has been identified after several eruptions in observations and in proxy data. The sensitivity study reveals a higher probability for a large and significant winter warming pattern with pre-industrial ozone levels, when the dynamic response of the chemistry to the eruption is disabled in the model. The positive temperature anomaly is driven by a positive NAO-like pressure pattern that lead to the advection of warm Atlantic air towards Northern Europe. With present day concentrat...
After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogen... more After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogeneous chemistry on the particle surfaces (HET-AER) and from dy-namical effects related to the radiative heating of the lower stratosphere (RAD-DYN). We carry out a series of experiments with an atmosphere–ocean–chemistry–climate model to assess how these two processes change stratospheric ozone and Northern Hemispheric (NH) polar vortex dynamics. Ensemble simulations are performed under present day and preindustrial conditions, and with aerosol forcings representative of different eruption strength, to investigate changes in the response behaviour. We show that the halogen component of the HET-AER effect dominates under present-day conditions with a global reduction of ozone (−21 DU for the strongest eruption) particularly at high latitudes, whereas the HET-AER effect increases stratospheric ozone due to N 2 O 5 hydrolysis in a preindustrial atmosphere (maximum anomalies +4 DU). The halogen-induced ozone changes in the present-day atmosphere offset part of the strengthening of the NH polar vortex during midwinter (reduction of up to −16 m s −1 in January) and slightly amplify the dynamical changes in the polar stratosphere in late winter (+11 m s −1 in March). The RAD-DYN mechanism leads to positive column ozone anomalies which are reduced in a present-day atmosphere by amplified polar ozone depletion (maximum anomalies +12 and +18 DU for present day and preindus-trial, respectively). For preindustrial conditions, the ozone response is consequently dominated by RAD-DYN processes, while under present-day conditions, HET-AER effects dominate. The dynamical response of the stratosphere is dominated by the RAD-DYN mechanism showing an intensifica-tion of the NH polar vortex in winter (up to +10 m s −1 in January). Ozone changes due to the RAD-DYN mechanism slightly reduce the response of the polar vortex after the eruption under present-day conditions.
For the period 1970-2007, the relationship between heat stress and mortality in Vienna was analyz... more For the period 1970-2007, the relationship between heat stress and mortality in Vienna was analyzed using a human biometeorological thermal index. Using the PET (Physiologically Equivalent Temperature) at 14 CET mortality is significant below the baseline for days with PET < 29°C and significant above for hotter days. On days with extreme heat stress (PET ≥ 41°C) an additional mortality of +13.0 % was found. The sensitivity to heat stress is significantly higher for women and for patients with cardiovascular diseases. To assess the impact of climate change on the heat-related mortality, we used the two regional climate models REMO and CLM and the emissions scenarios A1B and B1. The heat related mortality was assessed by one scenario without any long-term adaptation and one scenario including continuous long-term adaptation. In both scenarios, heat-related mortality could increase until 2071-2100. Till 2011-2040 no significant changes to the period of examination were found. Adaptation measures should focus on the extreme heat days (PET ≥ 41°C), were the mortality will increase even with long-term adaptation.
HINTERGRUND: Starke Hitzebelastung beeinträchtigt den menschlichen Organismus, die Mortalität ste... more HINTERGRUND: Starke Hitzebelastung beeinträchtigt den menschlichen Organismus, die Mortalität steigt während Hitzeperioden. Der "Jahrhundertsommer 2003" mit mehreren langanhaltenden Hitzewellen führte besonders in West-Europa zu zahlreichen zusätzlichen Todesfällen; auch Wien war davon betroffen. In dieser Untersuchung betrachten wir den Sommer 2003 in einem größeren zeitlichen Kontext um zu beurteilen, ob wie sehr sich die hitzebedingte Mortalität 2003 von anderen Jahren unterscheidet. METHODE: Die Untersuchung basiert auf meteorologischen Daten und Mortalitätsdaten des Bundeslands Wien für den Zeitraum 1970–2007. Die thermische Belastung wurde über den human-meteorologischen Parameter Physiologisch Äquivalente Temperatur (PET) berechnet, kurzfristige Anpassungseffekte wurden über den HeRATE-Ansatz berücksichtigt. Basierend auf thermo-physiologischen Belastungsklassen wurde der Einfluss der Hitzebelastung auf die Mortalität bestimmt. Zwei verschiedene Ansätze berücksichtigen langfristige Veränderungen in der Sensitivität. ERGEBNISSE: Die hitzebedingte Mortalität steigt mit zunehmender thermischer Belastung, im Laufe der Untersuchungsperiode verflachte sich jedoch dieser Anstieg. Eine über den Untersuchungszeitraum gemittelte Sensitivität, ergibt auch für Wien die höchsten Werte im Sommer 2003. Mit Berücksichtigung der abnehmenden Sensitivität wiesen jedoch die Sommer 1992, 1994 und 2000 eine höhere Zahl hitzebedingter Todesopfer auf. DISKUSSION: Trotz oder vielleicht wegen der signifikanten Zunahme der Tage mit Hitzebelastung ist die Sensitivität gegenüber Hitzebelastung zurückgegangen. Dies könnte ein Hinweis auf langfristige Anpassungsprozesse an die veränderten klimatischen Bedingungen sein. Deswegen war das Jahr 2003 in Wien ein Jahr mit deutlich erhöhter Sterblichkeit durch Hitzestress, ohne jedoch außergewöhnlich gewesen zu sein. BACKGROUND: Strong heat load has negative impacts on the human health and results in higher mortality during heat waves. In Europe, the summer 2003 was responsible for a high number of heat-related deaths, especially in Western Europe. Vienna was only partially affected. The aim of this study is to compare the heat-related mortality of 2003 with other years and to analyze whether 2003 was exceptional in Vienna. METHODS: The analysis is based on both meteorological and mortality data for the federal state of Vienna (Austria) for 1970–2007. We used the human-biometeorological index Physiologically Equivalent Temperature (PET) in order to assess the heat load affecting the human body, and considered short-term adaptation by the HeRATE approach. Each day between April and October was classified according to its thermal stress level and the mean mortality for each class was analyzed. Two approaches, with and without long-term sensitivity trends were considered. RESULTS: Mortality increases significantly with thermal stress, but this increase attenuated in the last decades. Based on the sensitivity for the period of investigation, 2003 was the year with the highest heat-related mortality. Including the long-term sensitivity trend, other years (1992, 1994 and 2000) were characterised by higher values. DISCUSSION: In the last decades the number of days with heat stress increased, but the sensitivity to heat stress decreased. This could indicate long-term adaptation processes. Hence, heat-related mortality in 2003 was high, but not exceptionally high.
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Papers by Stefan Muthers