Papers by Claudia Timmreck
The interannual and interseasonal variability of natural aerosol components (seasalt and soil dus... more The interannual and interseasonal variability of natural aerosol components (seasalt and soil dust) has been investigated with the climate model ECHAM4. ECHAM4 can be operated in different modes, such as in a nudged mode and in a climatological mode. A big advantage of a nudged simulation is that realistic transport of the aerosol facilitates any comparison to observations, while for climate change experiments the model develops its own meteorology, We have investigated how the geographical distribution and the interannual and seasonal variability of seasalt and mineral dust aerosol change between the different modes of operation of the climate model. Such changes can be a source of error in estimating the climate effect of natural aerosol components. Four experiments have been performed: a climatological with prescribed climatological sea surface temperature (SST), two experiments with prescribed SSTs from the particular years 1986 and 1989 and a nudged experiment where the model is forced by ECMWF Reanalysis data of the years 1986-1991 and corresponding SSTs from each year. Our results indicate that the mode of operation of the climate model seems to be as important as the interannual variability of the natural aerosol component by climate variations alone. The model results have been carefully compared with satellite observations from METEOSAT and with ground based measurements. Special emphasis is placed on the ability of the model to reflect the observed correlation of aerosol distribution with the North Atlantic oscillation, which is a prominent atmospheric variability mode and major reason for interannual variability in aerosol load and transport over the North Atlantic.
Journal of Aerosol Science, Sep 1, 2000
Journal of Geophysical Research Atmospheres, 2001
All of the referees' comments have been considered in the paper. One reviewer (D. Stevenson) made... more All of the referees' comments have been considered in the paper. One reviewer (D. Stevenson) made suggestions concerning the English. We went carefully over the text and included all suggestions for improving the English. In the following, we will briefly answer to specific points.
Journal of Geophysical Research Atmospheres
Meteorologische Zeitschrift
Wiley Interdisciplinary Reviews: Climate Change, 2012
Geophysical Monograph Series, 2000
ABSTRACT
All of the referees' comments have been considered in the paper. One reviewer (D. Stevenson)... more All of the referees' comments have been considered in the paper. One reviewer (D. Stevenson) made suggestions concerning the English. We went carefully over the text and included all suggestions for improving the English. In the following, we will briefly answer to specific points.
Theoretical and Applied Climatology, 1999
We study the three-dimensional transport of Mt. Pinatubo volcanic cloud with the climate model EC... more We study the three-dimensional transport of Mt. Pinatubo volcanic cloud with the climate model ECHAM4. In order to obtain model results comparable with observations a Newtonian relaxation technique was applied, which forces prognostic model variables towards the observations. A comparison of the simulated aerosol distribution with satellite data reveals good agreement for the ®rst months after the eruption. The model, however, is unable to simulate the tropical aerosol maximum in 1992 and also overestimates the vertical downward and northward transport of aerosols. Substantial improvement was achieved with the introduction of reduced advective vertical transport through the 380 K isentropic layer. Heating rates and top of the atmosphere¯uxes, which were calculated online for the ®rst half year after the eruption, are in the observed range. A comparison of Pinatubo simulations between three different vertical ECHAM4 versions (ECHAM4 L19, ECHAM4 L39, MA/ECHAM4) indicates that a vertical resolution of % 700 m in the tropopause region is suf®cient to realistically reduce the vertical transport through the tropopause. Consideration of the upper branch of the Brewer Dobson circulation in the MA/ECHAM4 model improves the geographical distribution of the volcanic cloud. The application of a relaxation technique can further reduce major shortcomings of stratospheric simulations with the standard climate model. There remain, however some critical points in the global transport characteristics in all three models which are not fully understood.
Journal of Geophysical Research: Atmospheres, 2001
A sulfuric acid aerosol model has been implemented in the global general circulation model ECHAM4... more A sulfuric acid aerosol model has been implemented in the global general circulation model ECHAM4. This model treats the formation, the development, and the transport of stratospheric sulfuric acid aerosol. The aerosol size distribution and the sulfuric acid mass fraction are calculated as a function of the H•SO4/H•O concentration, temperature, and air pressure in a size range between 0.001 and 2.58 •m. Binary homogeneous nucleation of H•SO4/H20, condensation and evaporation of H2SO4 and H20, Brownian coagulation and gravitational sedimentation are included. The microphysical model for stratospheric sulfate aerosol and a stratospheric sulfur chemistry are combined with a representation of the tropospheric sulfur chemistry. This tropospheric scheme accounts for the natural and anthropogenic emissions, chemistry, and dry and wet deposition of DMS, SO2, and SO•-. Globally and seasonally different SO2-and SO•-sources for stratospheric aerosol can therefore be taken into account. Results of a multiannual simulation show that the simulated SO2 and H2SO4 concentrations are generally in good agreement with available observations. The formation of new particles through homogeneous nucleation takes place in the tropical lower stratosphere and upper troposphere and in polar spring. The aerosol surface area density and the aerosol mass concentration reproduce lower stratospheric background conditions quite well. Effective radius and aerosol mixing ratio agree also with satellite and in situ measurements at Northern Hemisphere midlatitudes. 1. Introduction Stratospheric aerosol has various effects on the global climate system. It changes the chemical composition of the stratosphere because of heterogeneous reactions [Holmann and Solomon, 1989], provides condensation nuclei for the formation of polar stratospheric clouds and cirrus, and disturbs the radiative balance of the atmosphere in changing the albedo [Lacis et al., 1992]. These different atmospheric mechanisms are especially strong when the aerosol background layer is perturbed in response to strong volcanic eruptions or possibly in the future to high-speed civil transport aircraft. After the eruption of Mount Pinatubo (15.1øN, 120.4øE) in June 1991 a temperature increase in the lower stratosphere of •-2-3 K [Labitzke and McCormick, 1992] and a cooling of the global lower troposphere and the Earth's surface of • 0.5 K were detected [Dutton and Christy, 1992]. Furthermore, in 1992 and 1993 unusually strong ozone depletion due to chemical and dynamical processes was observed [Grant et al., 1994; Her-; Randel et al., 1995]. Stratospheric aerosol consists mainly of supercooled hydrated H2SO4 particles with a sulfuric acid mass fraction in the range of 50-80%. The particles form a persistent aerosol layer (Junge layer), which extends from the tropopause up to 30 km altitude. Height and maximum of the layer are seasonally and latitudinally dependent [Yue and Deepak, 1984]. The stratospheric aerosol particles are either directly formed in the stratosphere because of homogeneous nucleation or transported through the tropopause. In order to better understand the role of stratospheric aerosol in the atmospheric system several aerosol models were developed. At the end of the seventies, [ Turco et al., [1979] and [Turco et al., [1979] developed a one-dimensional (l-D) model, which was later refined by Toon et al. [1988] and Zhao et al. [1995]. Recently, Kgircher [1998] developed a coupled microphysical-chemical-dynamical box trajectory model for aircraft-generated liquid aerosols, which could also be applied to liquid H2SO4/HNOs/H•O aerosols. In the last years several studies with two-dimensional (2-D) chemistry transport models including sulfate aerosol microphysics were published in the literature. Theses studies focus on the impact of either aircraft emis-
Journal of Geophysical Research, 2001
A simulation of radiative forcing and zonal mean temperature effects is presented for the Laacher... more A simulation of radiative forcing and zonal mean temperature effects is presented for the Laacher See eruption (10,900 B.C.). A climate model which also covers the middle atmosphere is forced with background conditions representative of the Younger Dryas period. The Laacher See eruption is simulated by the injection of 15 Mt of SO2 to the lower stratosphere. The resulting sulfate loading in the stratosphere is comparable with post-Pinatubo (1991) observations, but clearly restricted to the Northern Hemisphere. The sulfate aerosol decays with an e-folding time of approximately 11 months, that is, also similar to recent observations. The high concentration of aerosol in the high latitudes leads to strongly intensified cooling in the polar night and to an intensified polar vortex. This produces midlatitude "continental winter warming" in the troposphere as observed after tropical eruptions. After tropical eruptions, strong absorption of terrestrial and near-infrared solar radiation in the lower latitudes is responsible for the strengthening of the polar vortex. However,
Atmospheric Chemistry and Physics, 2006
The chemistry climate model MAECHAM4/ CHEM with interactive and prognostic volcanic aerosol and o... more The chemistry climate model MAECHAM4/ CHEM with interactive and prognostic volcanic aerosol and ozone was used to study the initial dispersal and radiative forcing of a possible Northern Hemisphere mid-latitude super eruption. Tropospheric climate anomalies are not analysed since sea surface temperatures are kept fixed. Our experiments show that the global dispersal of a super eruption located at Yellowstone, Wy. is strongly dependent on the season of the eruption. In Northern Hemisphere summer the volcanic cloud is transported westward and preferentially southward, while in Northern Hemisphere winter the cloud is transported eastward and more northward compared to the summer case. Aerosol induced heating leads to a more global spreading with a pronounced cross equatorial transport. For a summer eruption aerosol is transported much further to the Southern Hemisphere than for a winter eruption. In contrast to Pinatubo case studies, strong cooling tendencies appear with maximum peak values of less than −1.6 K/day three months after the eruption in the upper tropical stratosphere. This strong cooling effect weakens with decreasing aerosol density over time and initially prevents the aerosol laden air from further active rising. All-sky net radiative flux changes of less than −32 W/m 2 at the surface are about a factor of 6 larger than for the Pinatubo eruption. Large positive flux anomalies of more than 16 W/m 2 are found in the first months in the tropics and sub tropics. These strong forcings call for a fully coupled ocean/atmosphere/chemistry model to study climate sensitivity to such a super-eruption.
pa.op.dlr.de
... 197 Particles and Cirrus Clouds (PAZI): Overview of results 2000 - 2003 ... 207 Ice-nucleatin... more ... 197 Particles and Cirrus Clouds (PAZI): Overview of results 2000 - 2003 ... 207 Ice-nucleating ability of soot particles in UT/LS J. Suzanne * ,D. Ferry F. CRMC2-CNRS, Campus de Luminy, Case 913, F-13288 Marseille cedex 9, France ...
Volcanic eruptions are unsteady multiphase phenomena, which encompass many inter-related processe... more Volcanic eruptions are unsteady multiphase phenomena, which encompass many inter-related processes across the whole range of scales from molecular and microscopic to macroscopic, synoptic and global. We provide an overview of recent advances in numerical modelling of volcanic effects, from conduit and eruption column processes to those on the Earth's climate. Conduit flow models examine ascent dynamics and multiphase processes like fragmentation, chemical reactions and mass transfer below the Earth surface. Other models simulate atmospheric dispersal of the erupted gas-particle mixture, focusing on rapid processes occurring in the jet, the lower convective regions, and pyroclastic density currents. The ascending eruption column and intrusive gravity current generated by it, as well as sedimentation and ash dispersal from those flows in the immediate environment of the volcano are examined with modular and generic models. These apply simplifications to the equations describing the system depending on the specific focus of scrutiny. The atmospheric dispersion of volcanic clouds is simulated by ash tracking models. These are inadequate for the first hours of spreading in many cases but focus on long-range prediction of ash location to prevent hazardous aircraft -ash encounters. The climate impact is investigated with global models. All processes and effects of explosive eruptions cannot be simulated by a single model, due to the complexity and hugely contrasting spatial and temporal scales involved. There is now the opportunity to establish a closer integration between different models and to develop the first comprehensive description of explosive eruptions and of their effects on the ground, in the atmosphere, and on the global climate.
The impact of volcanic eruptions on the marine carbon cycle is investigated for the example of th... more The impact of volcanic eruptions on the marine carbon cycle is investigated for the example of the Pinatubo eruption with model simulations of the distribution of the ash cloud and deposition on the ocean surface and the impact of the nutrient addition from ash leachates on the oceanic biological production and hence biological carbon pump. Natural variations of aerosols, especially due to large-magnitude volcanic eruptions, are recognized as a significant climate forcing, altering the Earth's radiation balance and thus tending to cause global temperature changes. While the impact of such events on climate and the terrestrial biosphere is relatively well documented, scientific knowledge of their effects on marine ecosystems and consequent feedbacks to the atmosphere is still very limited. In the deep sea, subaerial eruptive events of global significance are commonly recorded as widespread ash layers, which were often found to be associated with increased abundances of planktic organisms. This has led to the hypothesis that the influx of volcanic ash may provide an external nutrient source for primary production (in particular through iron fertilization) in ocean surface waters. Recent laboratory experiments have demonstrated that pristine volcanic ash indeed releases significant amounts of macronutrients and bioactive trace metals (including phosphate, iron and silica) adsorbed to the surface of the ash particles. The release of these components most likely has its largest impact in ocean regions where their availability is crucial for the growth of oceanic biomass, which are the high-nutrient but low-productivity (low-iron) areas in the Pacific and the Southern Ocean. These in turn are neighbored by most of those subaerially active volcanoes that are capable of ejecting huge amounts of aerosols into the high-velocity stratospheric wind fields. The dispersal and fallout of ash thus has a high potential to induce globally significant, transient net CO2 removal from the upper ocean and hence the atmosphere. Large-magnitude eruptions such as of Mount Pinatubo in 1991 were in fact followed by a slowing-down in the increase of atmospheric CO2 for several years, entailing a weakening of the global warming trend. For Mount Pinatubo it has been argued that the estimated CO2 uptake (1.6 x 1015 g C) could have been caused by rapid iron fertilization of the Southern Ocean with about 6.3 x 1015 g of ash. However, this would approximate the overall amount of the ash generated by the eruption, of which about 80% fell out over the South China Sea (~4.9 x 1015 g). This suggests additional avenues for the removal of CO2, among which the 1991 explosive eruption of Cerro Hudson could have played an important role as more than 2 km3 of the aerosols released by the volcano fell out directly over the Southern Ocean.
Egu General Assembly Conference Abstracts, May 1, 2010
Volcanic aerosols are an active component of the climate system and play multiple roles in physic... more Volcanic aerosols are an active component of the climate system and play multiple roles in physical and biogeochemical exchanges between the atmosphere, land, surface and ocean. To study the influence of volcanic aerosol on atmospheric dynamics and composition, dependent on the geographical latitude, interactive simulations of major volcanic eruptions are required. For our studies we use the middle atmosphere general circulation model MAECHAM5 including the global aerosol module HAM. HAM calculates the aerosol microphysics of sulfate and other species and their source and sink processes. The model setup has been validated for the Pinatubo eruption, showing good agreement with satellite data. Model studies have been performed for different major volcanic eruptions in the tropics and mid and high Northern latitudes (Pinatubo, Vesuvius, Katmai) with the strength and the eruption height of the Pinatubo eruption. All volcanic eruptions have been initialized in Northern Hemisphere summer and calculated for two years. The global distribution of the aerosol optical depth shows that the Pinatubo cloud is distributed over both hemispheres and has a global effect on climate. Volcanic aerosol of the Vesuvius eruption is mostly located in the Northern Hemisphere and has a more hemispheric effect but a certain fraction is also found in the Southern Hemisphere. Similar to the Pinatubo eruption the Vesuvius cloud is distributed fast to the north with the transition from summer to winter circulation. The volcanic aerosol of a Katmai eruption is only found in the Northern Hemisphere between 30°N und 90°N. The atmospheric life time of the volcanic aerosol varies with the geographic latitude of the volcano, Katmai has the shortest life time with 1.5 years and Pinatubo the longest one with 2.5 years. The strongest stratospheric temperature anomalies occur for the Pinatubo eruption in the tropics although chemical feedback mechanism not included in our simulation which might dampen the effect.
1] Volcanic emissions may have the potential to alter cirrus cloud properties. Here we conduct di... more 1] Volcanic emissions may have the potential to alter cirrus cloud properties. Here we conduct different sensitivity studies with the ECHAM4 general circulation model for 2.5 years after the Mount Pinatubo eruption (July 1991 to December 1993) and compare homogeneous cirrus formation caused by sedimenting sulfate particles produced in the eruption plume with homogeneous cirrus formation in the undisturbed atmosphere. In the first scenario, the sulfate aerosol mass from Pinatubo is added to the background aerosol concentration assuming a monomodal aerosol. Here the aerosol concentration increases by up to 3000 cm À3 in 1992, which can be regarded as an upper limit more representative for the first months after the eruption. The ice crystal number concentration increases by up to 1 cm À3 near the tropical tropopause more than doubling the pre-existing concentration in this region one year after the eruption. In the second, more realistic, scenario the Pinatubo aerosol is added to a bimodal background size distribution as a separate large particle mode. Here the aerosol number concentration increases by 10-25 cm À3 , which can be regarded as a lower bound more representative for what has been observed in 1992. Then the ice crystal number increases at most 50% in the tropics in 1992. Satellite observations show an increase in ice water path starting in 1992 that could be related to either the Mount Pinatubo eruption or the El Niño event or both but a decrease in total cloud cover. While there is no trend on cloud microphysical or optical properties in our second scenario, the first scenario shows a pronounced increase in ice water path and a noticeable impact on cloud radiative forcing.
In recent years, several methods have been suggested for "geoengineering" the c... more In recent years, several methods have been suggested for "geoengineering" the climate to limit global temperature increase. One of these geoengineering techniques follows the natural example of volcanic eruptions, emitting large amounts of sulfur dioxide (SO2) into the stratosphere. Chemical and microphysical reactions cause the formation of sulfate aerosols, which reduces the incoming solar radiation. Recently, several studies on this
Super eruptions exert an extreme forcing on the Earth System. The emitted volcanic aerosol stays ... more Super eruptions exert an extreme forcing on the Earth System. The emitted volcanic aerosol stays several years in the stratosphere, causing strong radiative effects with consequences for atmospheric processes. The interactive simulation of formation, dispersal and temporal development of a very large volcanic cloud is a challenging task for every aerosol climate model. For our studies we use the middle
Uploads
Papers by Claudia Timmreck