Stefan Muthers | Bern University (original) (raw)

Papers by Stefan Muthers

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 ...

Geoscientific Model Development Discussions, 2014

The newly developed atmosphere-ocean-chemistry-climate model SOCOL-MPIOM is presented by demonstr... more The newly developed atmosphere-ocean-chemistry-climate model SOCOL-MPIOM is presented by demonstrating the influence of the interactive chemistry module on the climate state and the variability. Therefore, we compare pre-industrial control simulations with (CHEM) and without (NOCHEM) interactive chemistry. In general, the influence of 5 the chemistry on the mean state and the variability is small and mainly restricted to the stratosphere and mesosphere. The largest differences are found for the atmospheric dynamics in the polar regions, with slightly stronger northern and southern winter polar vortices in CHEM. The strengthening of the vortex is related to larger stratospheric temperature gradients, which are attributed to a parametrization of the absorption of ozone 10 and oxygen in the Lyman-alpha, Schumann-Runge, Hartley, and Higgins bands. This effect is parametrized in the version with interactive chemistry only. A second reason for the temperature differences between CHEM and NOCHEM is related to diurnal variations in the ozone concentrations in the higher atmosphere, which are missing in NOCHEM. Furthermore, stratospheric water vapour concentrations differ substantially 15 between the two experiments, but their effect on the temperatures is small. In both setups, the simulated intensity and variability of the northern polar vortex is inside the range of present day observations. Sudden stratospheric warming events are well reproduced in terms of their frequency, but the distribution amongst the winter months is too uniform.

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.

Climate of the Past Discussions, 2013

The aim of this work is to elucidate the impact of changes in solar irradiance and energetic part... more The aim of this work is to elucidate the impact of changes in solar irradiance and energetic particles versus volcanic eruptions on tropospheric global climate during the Dalton Minimum (DM, AD 1780-1840. Separate variations in the (i) solar irradiance in the UV-C with wavelengths λ < 250 nm, (ii) irradiance at wavelengths λ > 250 nm, (iii) in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed separately, and (v) in combination, by means of small ensemble calculations using a coupled atmosphere-ocean chemistry-climate model. Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decreased global mean temperature by up to 0.5 K for 2-3 years after the eruption. However, while the volcanic effect is clearly discernible in the Southern Hemispheric mean temperature, it is less significant in the Northern Hemisphere, partly because the two largest volcanic eruptions occurred in the SH tropics and during seasons when the aerosols were mainly transported southward, partly because of the higher northern internal variability. In the simulation including all forcings, temperatures are in reasonable agreement with the tree ring-based temperature anomalies of the Northern Hemisphere. Interestingly, the model suggests that solar irradiance changes at λ < 250 nm and in energetic particle spectra have only an insignificant impact on the climate during the Dalton Minimum. This downscales the importance of top-down processes (stemming from changes at λ < 250 nm) relative to bottom-up processes (from λ > 250 nm). Reduction of irradiance at λ > 250 nm leads to a significant (up to 2 %) decrease in the ocean heat content (OHC) between 0 and 300 m in depth, whereas the changes in irradiance at λ < 250 nm or in energetic particles have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5 %. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8-15 years after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift in the intertropical convergence zone. www.clim-past.net/10/921/2014/ Clim. Past, 10, 921-938, 2014 www.clim-past.net/10/921/2014/ Clim. Past, 10, 921-938, 2014 Clim. Past, 10, 921-938, 2014 www.clim-past.net/10/921/2014/ J. G. Anet et al.: Sun and volcanoes: effect on the troposphere in the DM 935 efficient and appealing visualization of the model data. E. Rozanov, A.

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...

Meteorologische Zeitschrift, 2012

Tourism and recreation are important economic factors which are directly connected to weather and... more Tourism and recreation are important economic factors which are directly connected to weather and climate of a specific destination. Based on the observation network of the Central Institute of Meteorology and Geodynamics of Austria (ZAMG), data of 37 stations has been collected and analysed for tourism and recreation purposes. The analysis was based on long term data sets which were processed in relevant ways for tourism and recreation, resulting in frequency diagrams of Physiologically Equivalent Temperature (PET) and precipitation. Additionally, we prepared the results according to the demands of tourism and recreation authorities and industry using the Climate-Tourism/Transfer-Information-Scheme (CTIS). Applying data from the regional climate models REMO and CLM we can provide information on future climate conditions in Austria's recreation areas. We chose two different time slices and IPCC emission scenarios (A1B, B1). The data was processed based on the threshold factors which are included in the CTIS (e.g. thermal comfort, heat stress, cold stress, sunshine, etc.). For the time slice 2021-2050 only moderate changes can be expected. But for 2071-2100 one can observe a distinct decrease of cold stress and the skiing potential. On the other hand, moderate increases of thermal comfort, heat stress, sultriness and sunshine are expected. No tendencies can be seen in precipitation and wind conditions.

International Journal of Cardiology, 2014

International Journal of Biometeorology, 2014

Here we present, for the first time, a glossary of biometeorological terms. The glossary aims to ... more Here we present, for the first time, a glossary of biometeorological terms. The glossary aims to address the need for a reliable source of biometeorological definitions, thereby facilitating communication and mutual understanding in this rapidly expanding field. A total of 171 terms are defined, with reference to 234 citations. It is anticipated that the glossary will be revisited in coming years, updating terms and adding new terms, as appropriate. The glossary is intended to provide a useful resource to the biometeorology community, and to this end, readers are encouraged to contact the lead author to suggest additional terms for inclusion in later versions of the glossary as a result of new and emerging developments in the field.

Geophysical Research Letters, 2013

Atmospheric Chemistry and Physics, 2013

Wiener klinische Wochenschrift, 2010

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.

Wiener Klinische Wochenschrift, 2010

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.

International Journal of …, Jan 1, 2010

The potential development of heat-related mortality in the 21th century for Vienna (Austria) was ... more The potential development of heat-related mortality in the 21th century for Vienna (Austria) was assessed by the use of two regional climate models based on the IPCC emissions scenarios A1B and B1. Heat stress was described with the humanbiometeorological index PET (Physiologically Equivalent Temperature). Based on the relation between heat stress and mortality in 1970-2007, we developed two approaches to estimate the increases with and without long-term adaptation. Until 2011-2040 no significant changes will take place compared to 1970-2000, but in the following decades heat-related mortality could increase up to 129% until the end of the century, if no adaptation takes place. The strongest increase occurred due to extreme heat stress (PET ≥ 41 °C). With long-term adaptation the increase is less pronounced, but still notable. This encourages the requirement for additional adaptation measurements.

Wiener Klinische Wochenschrift, Jan 1, 2010

Theoretical and Applied Climatology, Jan 1, 2010

urbanclimate.net

The development of mortality due to heat stress in Vienna was assesses by using two regional clim... more The development of mortality due to heat stress in Vienna was assesses by using two regional climate models in the emissions scenarios A1B and B1. Heat stress was described using the human-biometeorological index PET. Two approaches were applied, to estimate the increases with and without long-term adaptation. Until 2011-2040 no significant changes compared to 1971-2000 were found. In the following decades heat-related mortality could increase up to 129 % until the end of the century, if no adaptation takes place. The strongest increase occurred due to extreme heat stress (PET ≥ 41° C). With long-term adaptation the increase is less pronounced, but still notably. This encourages the need for additional adaptation measurements.

Meteorologische Zeitschrift, Jan 1, 2010