The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa ... more The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa layer were studied shortly after violent volcanic eruptions. After all tropical eruptions, the polar stratospheric vortex was intensified. The tropospheric anomaly patterns after tropical eruptions are very similar to those of Winter months with a very strong stratospheric vortex, irrespective of whether volcanically forced or not. Hence, if they have any effect on the wintertime tropospheric circulation, tropical eruptions seem to force a natural mode of the stratospheric Winter circulation which is associated with a specific response of the tropospheric circulation with maximum amplitude over the North Atlantic and adjacent continental regions. Therefore, it remains difficult to give statistical evidence of volcanic impact on climate on the basis of the few observations after these rare events. A combination of observational studies and model experiments may help to overcome these difficulties in the future.
The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an ... more The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an analysis of the errors themselves. Direct estimates of systematic initial tendency errors (SITEs) determined by assimilation of reanalysis data will on the other hand point more directly to the model components causing the errors. For use with atmospheric climate models (GCMs) three different methods of SITE detection by assimilation of high resolution ECMWF reanalysis data have been tested. The horizontally truncated and vertically interpolated reanalysis data are available only every sixth hour, i.e. at the synoptic times. Between these times interpolated values are used. The initial tendency errors should be computed from initial model stages as close as possible to the reality, defined by the reanalysis. However, by the truncation and the interpolations in the vertical and in time, imbalances are created, which leads to spurious systematic tendency errors, when inserted directly. In ...
The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an ... more The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an analysis of the errors themselves. Direct estimates of systematic initial tendency errors (SITEs) determined by assimilation of reanalysis data will on the other hand point more directly to the model components causing the errors. The ECMWF Reanalysis (ERA-15) data for the
The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa ... more The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa layer were studied shortly after violent volcanic eruptions. After all tropical eruptions, the polar stratospheric vortex was intensified. The tropospheric anomaly patterns after tropical eruptions are very similar to those of Winter months with a very strong stratospheric vortex, irrespective of whether volcanically forced or not. Hence, if they have any effect on the wintertime tropospheric circulation, tropical eruptions seem to force a natural mode of the stratospheric Winter circulation which is associated with a specific response of the tropospheric circulation with maximum amplitude over the North Atlantic and adjacent continental regions. Therefore, it remains difficult to give statistical evidence of volcanic impact on climate on the basis of the few observations after these rare events. A combination of observational studies and model experiments may help to overcome these diff...
The Mount Pinatubo volcanic eruption in June 1991 had significant impact on stratospheric and tro... more The Mount Pinatubo volcanic eruption in June 1991 had significant impact on stratospheric and tropospheric climate and circulation. Enhanced radiative heating caused by the aerosol absorption of solar and terrestrial radiation changed stratospheric temperature and circulation. Using the stratospheric mesospheric version of the Hamburg climate model MA/ECHAM4, we performed an interactive Pinatubo simulation with prognostic stratospheric aerosol. Interactive and noninteractive model results for the years 1991 and 1992 are compared with satellite data and in situ measurements. The on-line calculated heating rates are in good agreement with radiation transfer models indicating maximum heating rates of about 0.3 K/d in October 1991. The dynamic feedback in the MA/ECHAM4
Stratospheric climate has changed significantly during the last decades. The causes of these chan... more Stratospheric climate has changed significantly during the last decades. The causes of these changes are discussed on the basis of two different general circulation model experiments forced by observed greenhouse gas and ozone concentration. There is a clear and significant response of the lower stratosphere temperature and geopotential in the model simulations forced by observed ozone changes that is in accord with observed trends in summer in middle and high latitudes of the northern hemisphere. Little effect is seen in the tropics. In spring there occur the strongest anomalies/trends in both hemispheres at polar latitudes; however, the model response is late by 1 to 2 months and is much weaker than the observed effects. The ozone-forced model in winter of both hemispheres produces slight warming or no change instead of the slight cooling observed. The effects of enhanced greenhouse gases as taken from a transient IPCC scenario AGCM run do enhance the cooling in high latitudes in spring, but the effect is much smaller than observed. Hence neither of the two forcings (reduced ozone and increased greenhouse gases) in the cold seasons is able to produce the recent stratospheric and tropospheric trend patterns alone. These trends clearly resemble a natural mode of variability both in the model and in the real worldø This mode associates a strengthened polar night vortex with an enhanced North Atlantic oscillation. The excitation of this mode cannot yet be attributed to anthropogenic forcing.
The aim of our project related to the CAWSES programme is to investigate the long-term changes of... more The aim of our project related to the CAWSES programme is to investigate the long-term changes of planetary wave patterns in stratospheric ozone and water vapour and their influence on the vertical coupling of atmospheric layers due to the induced radiation perturbations. For this purpose, we derived zonally asymmetric components of ozone and water vapour from assimilated data (ERA-40, ERA-Interim) and satellite data (SAGE, GOME, ODIN). For northern winter, we found a pronounced quasi-stationary wave one structure in both stratospheric ozone and strato- and mesospheric water vapour with maximum amplitudes of about 20% of zonal mean values during the last decades. We found also a nearly linear increase of the amplitude during the last decades and some pronounced variations which may partly be due to the 11-year cycle in solar radiation activity. In the southern hemisphere, pronounced amplitudes occur particularly during polar vortex breakup period. Based on model simulations with the GCM MAECHAM5 and the CCM HAMMONIA, we discuss the dynamical and chemical processes which lead to the observed planetary wave patterns in ozone and water vapour, as well as their vertical structure, their interannual and decadal variability and their feedback on temperature, dynamics and chemistry. For example, MAECHAM5 model calculations with and without prescribed zonally asymmetric ozone (O3*) show significant changes in temperature and geopotential from lower stratosphere to mesosphere due to an O3*-induced increase in amplitude and a shift in phase of stratospheric wave one structure, accompanied by a shift of up- and eastward directed quasi-stationary wave trains from the eastern to the western hemisphere, indicating a feedback to the forcing of planetary waves from troposphere. We analysed also long-term equilibrium simulations with the CCM HAMMONIA to understand the involved dynamical-chemical interactions configuring the observed planetary wave patterns and to verify the effect of the 11-year cycle in solar radiation activity on planetary wave patterns. Overall, the results suggest that zonally asymmetric anomalies in ozone, water vapour and other important absorbers contribute largely to observed long-term changes in temperature, planetary waves and atmospheric circulation, and provide a new perspective for validating and improving GCMs and CCMs.
Http Dx Doi Org 10 1080 07055900 2013 878833, Feb 6, 2015
ABSTRACT In a sensitivity study, the influence of an observed stratospheric zonal ozone anomaly o... more ABSTRACT In a sensitivity study, the influence of an observed stratospheric zonal ozone anomaly on the atmospheric circulation was investigated using the Fifth Generation European Centre Hamburg Model (ECHAM5) which is a general circulation model. The model was run from 1960 to 1999 (40 years) with a mean seasonal cycle of zonally symmetric ozone. In order to isolate the induced dynamical influence of the observed zonally asymmetric part of the three-dimensional stratospheric ozone, a second run was performed for the boreal extratropics using prescribed monthly means from the 40-year reanalysis dataset from the European Centre for Medium-range Weather Forecasts (ERA-40). The main findings are the interdecadal westward shift of the polar vortex at about 65°N and a significant increase in the number of stratospheric sudden warmings during the 1980–99 period. Under the action of zonally asymmetric ozone a decrease in the Arctic Oscillation was identified between the mid-1980s and the mid-1990s. The lag correlation between the mean Arctic Oscillation at the surface and the daily stratospheric northern annular mode increased in mid-winter. Furthermore, we examined the influence of the stratospheric zonal ozone anomaly on Rossby wave breaking in the upper troposphere and found a significant westward shift of poleward Rossby wave breaking events over western Europe in the winter. By this we show that the stratospheric zonal ozone anomaly has a strong influence on the tropospheric circulation as a result of enhanced dynamical coupling processes.
One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quant... more One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quantification of outflow from the Asian continent. Global an regional models of atmospheric chemistry were used to provide tracer forecasts in the field and they are now employed together with the observations to analyse the budgets of trace gases and aerosols over the Pacific and to evaluate emission inventories. We have participated in this effort with a new version of the global general circulation model ECHAM, to which we added a tagged CO module with prescribed chemistry. In or- der to simulate realistic meteorological conditions, we use forecast fields or analysed winds, temperature, and surface pressure from ECMWF. Generally, the model is able to capture the CO concentrations in the lower and middle troposphere very well, even if we use the relatively coarse resolution of T42L19 (~2.8x2.8 deg, 19 vertical levels). However, there are several cases when the model does not detect significant amounts of pollution, in particular in the 10-12 km altitude range. We present a detailed evalua- tion of the model including a comparison of forecast and analysis fields and the impact of the model resolution on the quality of the simulation.
We present a climate modeling approach to reproduce the rainfall patterns over Iran due to the cl... more We present a climate modeling approach to reproduce the rainfall patterns over Iran due to the climatic forcings during the past 6000 years. The selected periods are simulated using a spatially high-resolved atmosphere General Circulation Model (GCM). Our results show that the winter rainfall patterns over Iran have changed due to the changes in solar insolation with a wetter condition starting around 3 ka BP and reaching its maximum during the Medieval Climate Anomaly ca. 1 ka BP. The rainfall variability can be explained by the changes in atmospheric conditions as a result of changing incoming solar irradiance based on the Milankovitch theory. A shift in the Earth's energy budget leads to the modulation of the West Asian Subtropical Westerly Jet (WASWJ). The investigations support the hypothesis that during the Holocene a northward shift in the WASWJ contributes to the less cyclonic activities over Iran. This brings less moisture into the region during the winter.
Often studies concerning troposphere-stratosphere interaction are based on zonally symmetric feat... more Often studies concerning troposphere-stratosphere interaction are based on zonally symmetric features (e.g. zonal mean wind, Northern Annular Mode etc.). Also model simulations, used to study the effects of stratospheric ozone depletion or volcanic eruptions generally are forced by zonal symmetric anomalies. In many cases these simulations partly fail to reproduce the observed anomaly patterns. Reasons can be manifold, reaching from missing processes, model biases and inadequate surface conditions (to name but a few), to inadequate forcing. Here we will use two examples showing that the zonally asymmetric part of forcing in the UTLS, even if it only represents a fraction of the zonal mean forcing, may contribute significantly to the resulting anomaly pattern and amplitude. The examples are trends in stratospheric ozone representing decadal variability and volcanic aerosol representing interannual variability. Basically it could be any radiatively active substances, including water v...
Data management in geosciences, especially at university and other research institutes commonly i... more Data management in geosciences, especially at university and other research institutes commonly isn't very well coordinated. Due to changing staff and limited funding this topic has no priority in general. The process to implement policies regulating data management in an university institute is complex. First of all existing structures and workflows had to be reviewed. That means an inventory of different data sets, reviewing quality tests, but also data requirements of scientists as well as their willingness to follow rules simplifying their work. Awareness of complying with regulations is essential for the acceptance of policies. A leading team, formed by several scientists, will bring together different points of view to control the development of institutional policies. Determining the actual state of personal data management using a questionary was one of the activities in the project EWIG (Developing workflow components for long-term archiving of research data in geoscien...
ABSTRACT The radiation perturbation due to zonal asymmetries in stratospheric ozone ( O3 ) is an ... more ABSTRACT The radiation perturbation due to zonal asymmetries in stratospheric ozone ( O3 ) is an important factor in the atmosphere-ocean circulation system, affecting the coupling processes between the middle atmosphere, the troposphere and the ocean. We investigate the effects of observed O3 in general circulation model simulations without and with an interactively coupled ocean (GCM, AOGCM). Observations show a pronounced wave one pattern in O∗3 during northern winter, with amplitudes of 10–20 % of zonal mean values. Based on sensitivity studies with the GCM MAECHAM5, and accompanying linear solutions of forced Rossby waves, we demonstrate that the radiative forcing due to O3 affects the stratospheric circulation by imposing a wave perturbation in geopotential height (in the order of 10–20 % of the zonal mean values) and the associated large-scale flow. Subsequent changes due to non-linear stratosphere-troposphere coupling indicate an intensification of the tropospheric Aleutian low but a weakening of the Iceland low, i.e. a shift of tropospheric circulation towards negative phase of North Atlantic Oscillation (NAO). Multi-decadal simulations with the AOGCM COSMOS show that this signal is more pronounced and spatially southward shifted due to additional interactions between the troposphere and the ocean. In particular, we identify significant changes in surface temperatures, precipitation, wind-driven ocean currents and sea ice thickness induced by the wave one pattern in O3 . The results suggest that including the effects of zonal asymmetries in stratospheric ozone and other important absorbers may help to improve current general circulation models and climate change studies.
One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quant... more One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quantification of outflow from the Asian continent. Global an regional models of atmospheric chemistry were used to provide tracer forecasts in the field and they are now employed together with the observations to analyse the budgets of trace gases and aerosols over the Pacific
This study focuses on the atmospheric temperature response to dust deduced from a new source of d... more This study focuses on the atmospheric temperature response to dust deduced from a new source of data-the European Reanalysis (ERA) increments. These increments are the systematic errors of global climate models, generated in the reanalysis procedure. The model errors result not only from the lack of desert dust but also from a complex combination of many kinds of model errors. Over the Sahara desert the lack of dust radiative effect is believed to be a predominant model defect which should significantly affect the increments. This dust effect was examined by considering correlation between the increments and remotely sensed dust. Comparisons were made between April temporal variations of the ERA analysis increments and the variations of the Total Ozone Mapping Spectrometer aerosol index (AI) between 1979 and 1993. The distinctive structure was identified in the distribution of correlation composed of three nested areas with high positive correlation (>0.5), low correlation and high negative correlation (< −0.5). The innermost positive correlation area (PCA) is a large area near the center of the Sahara desert. For some local maxima inside this area the correlation even exceeds 0.8. The outermost negative correlation area (NCA) is not uniform. It consists of some areas over the eastern and western parts of North Africa with a relatively small amount of dust. Inside those areas both positive and negative high correlations exist at pressure levels ranging from 850 to 700 hPa, with the peak values near 775 hPa. Dust-forced heating (cooling) inside the PCA (NCA) is accompanied by changes in the static instability of the atmosphere above the dust layer. The reanalysis data of the European Center for Medium Range Weather Forecast (ECMWF) suggest that the PCA (NCA) corresponds mainly to anticyclonic (cyclonic) flow, negative (positive) vorticity and downward (upward) airflow. These findings are associated with the interaction between dust-forced heating/cooling and atmospheric circulation. This paper contributes to a better understanding of dust radiative processes missed in the model.
The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa ... more The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa layer were studied shortly after violent volcanic eruptions. After all tropical eruptions, the polar stratospheric vortex was intensified. The tropospheric anomaly patterns after tropical eruptions are very similar to those of Winter months with a very strong stratospheric vortex, irrespective of whether volcanically forced or not. Hence, if they have any effect on the wintertime tropospheric circulation, tropical eruptions seem to force a natural mode of the stratospheric Winter circulation which is associated with a specific response of the tropospheric circulation with maximum amplitude over the North Atlantic and adjacent continental regions. Therefore, it remains difficult to give statistical evidence of volcanic impact on climate on the basis of the few observations after these rare events. A combination of observational studies and model experiments may help to overcome these difficulties in the future.
The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an ... more The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an analysis of the errors themselves. Direct estimates of systematic initial tendency errors (SITEs) determined by assimilation of reanalysis data will on the other hand point more directly to the model components causing the errors. For use with atmospheric climate models (GCMs) three different methods of SITE detection by assimilation of high resolution ECMWF reanalysis data have been tested. The horizontally truncated and vertically interpolated reanalysis data are available only every sixth hour, i.e. at the synoptic times. Between these times interpolated values are used. The initial tendency errors should be computed from initial model stages as close as possible to the reality, defined by the reanalysis. However, by the truncation and the interpolations in the vertical and in time, imbalances are created, which leads to spurious systematic tendency errors, when inserted directly. In ...
The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an ... more The causes of systematic errors in the time mean fields of a GCM are difficult to detect from an analysis of the errors themselves. Direct estimates of systematic initial tendency errors (SITEs) determined by assimilation of reanalysis data will on the other hand point more directly to the model components causing the errors. The ECMWF Reanalysis (ERA-15) data for the
The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa ... more The strengths of the polar stratospheric vortex and geopotential height anomalies of the 500 hPa layer were studied shortly after violent volcanic eruptions. After all tropical eruptions, the polar stratospheric vortex was intensified. The tropospheric anomaly patterns after tropical eruptions are very similar to those of Winter months with a very strong stratospheric vortex, irrespective of whether volcanically forced or not. Hence, if they have any effect on the wintertime tropospheric circulation, tropical eruptions seem to force a natural mode of the stratospheric Winter circulation which is associated with a specific response of the tropospheric circulation with maximum amplitude over the North Atlantic and adjacent continental regions. Therefore, it remains difficult to give statistical evidence of volcanic impact on climate on the basis of the few observations after these rare events. A combination of observational studies and model experiments may help to overcome these diff...
The Mount Pinatubo volcanic eruption in June 1991 had significant impact on stratospheric and tro... more The Mount Pinatubo volcanic eruption in June 1991 had significant impact on stratospheric and tropospheric climate and circulation. Enhanced radiative heating caused by the aerosol absorption of solar and terrestrial radiation changed stratospheric temperature and circulation. Using the stratospheric mesospheric version of the Hamburg climate model MA/ECHAM4, we performed an interactive Pinatubo simulation with prognostic stratospheric aerosol. Interactive and noninteractive model results for the years 1991 and 1992 are compared with satellite data and in situ measurements. The on-line calculated heating rates are in good agreement with radiation transfer models indicating maximum heating rates of about 0.3 K/d in October 1991. The dynamic feedback in the MA/ECHAM4
Stratospheric climate has changed significantly during the last decades. The causes of these chan... more Stratospheric climate has changed significantly during the last decades. The causes of these changes are discussed on the basis of two different general circulation model experiments forced by observed greenhouse gas and ozone concentration. There is a clear and significant response of the lower stratosphere temperature and geopotential in the model simulations forced by observed ozone changes that is in accord with observed trends in summer in middle and high latitudes of the northern hemisphere. Little effect is seen in the tropics. In spring there occur the strongest anomalies/trends in both hemispheres at polar latitudes; however, the model response is late by 1 to 2 months and is much weaker than the observed effects. The ozone-forced model in winter of both hemispheres produces slight warming or no change instead of the slight cooling observed. The effects of enhanced greenhouse gases as taken from a transient IPCC scenario AGCM run do enhance the cooling in high latitudes in spring, but the effect is much smaller than observed. Hence neither of the two forcings (reduced ozone and increased greenhouse gases) in the cold seasons is able to produce the recent stratospheric and tropospheric trend patterns alone. These trends clearly resemble a natural mode of variability both in the model and in the real worldø This mode associates a strengthened polar night vortex with an enhanced North Atlantic oscillation. The excitation of this mode cannot yet be attributed to anthropogenic forcing.
The aim of our project related to the CAWSES programme is to investigate the long-term changes of... more The aim of our project related to the CAWSES programme is to investigate the long-term changes of planetary wave patterns in stratospheric ozone and water vapour and their influence on the vertical coupling of atmospheric layers due to the induced radiation perturbations. For this purpose, we derived zonally asymmetric components of ozone and water vapour from assimilated data (ERA-40, ERA-Interim) and satellite data (SAGE, GOME, ODIN). For northern winter, we found a pronounced quasi-stationary wave one structure in both stratospheric ozone and strato- and mesospheric water vapour with maximum amplitudes of about 20% of zonal mean values during the last decades. We found also a nearly linear increase of the amplitude during the last decades and some pronounced variations which may partly be due to the 11-year cycle in solar radiation activity. In the southern hemisphere, pronounced amplitudes occur particularly during polar vortex breakup period. Based on model simulations with the GCM MAECHAM5 and the CCM HAMMONIA, we discuss the dynamical and chemical processes which lead to the observed planetary wave patterns in ozone and water vapour, as well as their vertical structure, their interannual and decadal variability and their feedback on temperature, dynamics and chemistry. For example, MAECHAM5 model calculations with and without prescribed zonally asymmetric ozone (O3*) show significant changes in temperature and geopotential from lower stratosphere to mesosphere due to an O3*-induced increase in amplitude and a shift in phase of stratospheric wave one structure, accompanied by a shift of up- and eastward directed quasi-stationary wave trains from the eastern to the western hemisphere, indicating a feedback to the forcing of planetary waves from troposphere. We analysed also long-term equilibrium simulations with the CCM HAMMONIA to understand the involved dynamical-chemical interactions configuring the observed planetary wave patterns and to verify the effect of the 11-year cycle in solar radiation activity on planetary wave patterns. Overall, the results suggest that zonally asymmetric anomalies in ozone, water vapour and other important absorbers contribute largely to observed long-term changes in temperature, planetary waves and atmospheric circulation, and provide a new perspective for validating and improving GCMs and CCMs.
Http Dx Doi Org 10 1080 07055900 2013 878833, Feb 6, 2015
ABSTRACT In a sensitivity study, the influence of an observed stratospheric zonal ozone anomaly o... more ABSTRACT In a sensitivity study, the influence of an observed stratospheric zonal ozone anomaly on the atmospheric circulation was investigated using the Fifth Generation European Centre Hamburg Model (ECHAM5) which is a general circulation model. The model was run from 1960 to 1999 (40 years) with a mean seasonal cycle of zonally symmetric ozone. In order to isolate the induced dynamical influence of the observed zonally asymmetric part of the three-dimensional stratospheric ozone, a second run was performed for the boreal extratropics using prescribed monthly means from the 40-year reanalysis dataset from the European Centre for Medium-range Weather Forecasts (ERA-40). The main findings are the interdecadal westward shift of the polar vortex at about 65°N and a significant increase in the number of stratospheric sudden warmings during the 1980–99 period. Under the action of zonally asymmetric ozone a decrease in the Arctic Oscillation was identified between the mid-1980s and the mid-1990s. The lag correlation between the mean Arctic Oscillation at the surface and the daily stratospheric northern annular mode increased in mid-winter. Furthermore, we examined the influence of the stratospheric zonal ozone anomaly on Rossby wave breaking in the upper troposphere and found a significant westward shift of poleward Rossby wave breaking events over western Europe in the winter. By this we show that the stratospheric zonal ozone anomaly has a strong influence on the tropospheric circulation as a result of enhanced dynamical coupling processes.
One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quant... more One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quantification of outflow from the Asian continent. Global an regional models of atmospheric chemistry were used to provide tracer forecasts in the field and they are now employed together with the observations to analyse the budgets of trace gases and aerosols over the Pacific and to evaluate emission inventories. We have participated in this effort with a new version of the global general circulation model ECHAM, to which we added a tagged CO module with prescribed chemistry. In or- der to simulate realistic meteorological conditions, we use forecast fields or analysed winds, temperature, and surface pressure from ECMWF. Generally, the model is able to capture the CO concentrations in the lower and middle troposphere very well, even if we use the relatively coarse resolution of T42L19 (~2.8x2.8 deg, 19 vertical levels). However, there are several cases when the model does not detect significant amounts of pollution, in particular in the 10-12 km altitude range. We present a detailed evalua- tion of the model including a comparison of forecast and analysis fields and the impact of the model resolution on the quality of the simulation.
We present a climate modeling approach to reproduce the rainfall patterns over Iran due to the cl... more We present a climate modeling approach to reproduce the rainfall patterns over Iran due to the climatic forcings during the past 6000 years. The selected periods are simulated using a spatially high-resolved atmosphere General Circulation Model (GCM). Our results show that the winter rainfall patterns over Iran have changed due to the changes in solar insolation with a wetter condition starting around 3 ka BP and reaching its maximum during the Medieval Climate Anomaly ca. 1 ka BP. The rainfall variability can be explained by the changes in atmospheric conditions as a result of changing incoming solar irradiance based on the Milankovitch theory. A shift in the Earth's energy budget leads to the modulation of the West Asian Subtropical Westerly Jet (WASWJ). The investigations support the hypothesis that during the Holocene a northward shift in the WASWJ contributes to the less cyclonic activities over Iran. This brings less moisture into the region during the winter.
Often studies concerning troposphere-stratosphere interaction are based on zonally symmetric feat... more Often studies concerning troposphere-stratosphere interaction are based on zonally symmetric features (e.g. zonal mean wind, Northern Annular Mode etc.). Also model simulations, used to study the effects of stratospheric ozone depletion or volcanic eruptions generally are forced by zonal symmetric anomalies. In many cases these simulations partly fail to reproduce the observed anomaly patterns. Reasons can be manifold, reaching from missing processes, model biases and inadequate surface conditions (to name but a few), to inadequate forcing. Here we will use two examples showing that the zonally asymmetric part of forcing in the UTLS, even if it only represents a fraction of the zonal mean forcing, may contribute significantly to the resulting anomaly pattern and amplitude. The examples are trends in stratospheric ozone representing decadal variability and volcanic aerosol representing interannual variability. Basically it could be any radiatively active substances, including water v...
Data management in geosciences, especially at university and other research institutes commonly i... more Data management in geosciences, especially at university and other research institutes commonly isn't very well coordinated. Due to changing staff and limited funding this topic has no priority in general. The process to implement policies regulating data management in an university institute is complex. First of all existing structures and workflows had to be reviewed. That means an inventory of different data sets, reviewing quality tests, but also data requirements of scientists as well as their willingness to follow rules simplifying their work. Awareness of complying with regulations is essential for the acceptance of policies. A leading team, formed by several scientists, will bring together different points of view to control the development of institutional policies. Determining the actual state of personal data management using a questionary was one of the activities in the project EWIG (Developing workflow components for long-term archiving of research data in geoscien...
ABSTRACT The radiation perturbation due to zonal asymmetries in stratospheric ozone ( O3 ) is an ... more ABSTRACT The radiation perturbation due to zonal asymmetries in stratospheric ozone ( O3 ) is an important factor in the atmosphere-ocean circulation system, affecting the coupling processes between the middle atmosphere, the troposphere and the ocean. We investigate the effects of observed O3 in general circulation model simulations without and with an interactively coupled ocean (GCM, AOGCM). Observations show a pronounced wave one pattern in O∗3 during northern winter, with amplitudes of 10–20 % of zonal mean values. Based on sensitivity studies with the GCM MAECHAM5, and accompanying linear solutions of forced Rossby waves, we demonstrate that the radiative forcing due to O3 affects the stratospheric circulation by imposing a wave perturbation in geopotential height (in the order of 10–20 % of the zonal mean values) and the associated large-scale flow. Subsequent changes due to non-linear stratosphere-troposphere coupling indicate an intensification of the tropospheric Aleutian low but a weakening of the Iceland low, i.e. a shift of tropospheric circulation towards negative phase of North Atlantic Oscillation (NAO). Multi-decadal simulations with the AOGCM COSMOS show that this signal is more pronounced and spatially southward shifted due to additional interactions between the troposphere and the ocean. In particular, we identify significant changes in surface temperatures, precipitation, wind-driven ocean currents and sea ice thickness induced by the wave one pattern in O3 . The results suggest that including the effects of zonal asymmetries in stratospheric ozone and other important absorbers may help to improve current general circulation models and climate change studies.
One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quant... more One of the major goals of the spring 2001 TRACE-P experiment was the character- isation and quantification of outflow from the Asian continent. Global an regional models of atmospheric chemistry were used to provide tracer forecasts in the field and they are now employed together with the observations to analyse the budgets of trace gases and aerosols over the Pacific
This study focuses on the atmospheric temperature response to dust deduced from a new source of d... more This study focuses on the atmospheric temperature response to dust deduced from a new source of data-the European Reanalysis (ERA) increments. These increments are the systematic errors of global climate models, generated in the reanalysis procedure. The model errors result not only from the lack of desert dust but also from a complex combination of many kinds of model errors. Over the Sahara desert the lack of dust radiative effect is believed to be a predominant model defect which should significantly affect the increments. This dust effect was examined by considering correlation between the increments and remotely sensed dust. Comparisons were made between April temporal variations of the ERA analysis increments and the variations of the Total Ozone Mapping Spectrometer aerosol index (AI) between 1979 and 1993. The distinctive structure was identified in the distribution of correlation composed of three nested areas with high positive correlation (>0.5), low correlation and high negative correlation (< −0.5). The innermost positive correlation area (PCA) is a large area near the center of the Sahara desert. For some local maxima inside this area the correlation even exceeds 0.8. The outermost negative correlation area (NCA) is not uniform. It consists of some areas over the eastern and western parts of North Africa with a relatively small amount of dust. Inside those areas both positive and negative high correlations exist at pressure levels ranging from 850 to 700 hPa, with the peak values near 775 hPa. Dust-forced heating (cooling) inside the PCA (NCA) is accompanied by changes in the static instability of the atmosphere above the dust layer. The reanalysis data of the European Center for Medium Range Weather Forecast (ECMWF) suggest that the PCA (NCA) corresponds mainly to anticyclonic (cyclonic) flow, negative (positive) vorticity and downward (upward) airflow. These findings are associated with the interaction between dust-forced heating/cooling and atmospheric circulation. This paper contributes to a better understanding of dust radiative processes missed in the model.
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Papers by Ingo Kirchner