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The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high-energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X-ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high-energy photons extends the applicability of the TDS-based approach to organic compounds which would suffer from radiation damage at lower photon energies.
The seasonality of transport and mixing of air into the lowermost stratosphere (LMS) is studied using distributions of mean age of air and a~mass balance approach, based on in-situ observations of SF6 and CO2 during the SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) aircraft campaigns. Combining the information of the mean age of air and the water vapour distributions we demonstrate that the tropospheric air transported into the LMS above the extratropical tropopause layer (ExTL) originates predominantly from the tropical tropopause layer (TTL). The concept of our mass balance is based on simultaneous measurements of the two passive tracers and the assumption that transport into the LMS can be described by age spectra which are superposition of two different modes. Based on this concept we conclude that the stratospheric influence on LMS composition is strongest in April with tropospheric fractions (α1) below 20% and that the strongest tropospheric signatures are found in October with (α1 greater than 80%. Beyond the fractions, our mass balance concept allows to calculate the associated transit times for transport of tropospheric air from the tropics into the LMS. The shortest transit times (<0.3 years) are derived for the summer, continuously increasing up to 0.8 years by the end of spring. These findings suggest that strong quasi-horizontal mixing across the weak subtropical jet from summer to mid of autumn and the considerably shorter residual transport time-scales within the lower branch of the Brewer-Dobson circulation in summer than in winter dominates the tropospheric influence in the LMS until the beginning of next year's summer.
The seasonality of transport and mixing of air into the lowermost stratosphere (LMS) is studied using distributions of mean age of air and a mass balance approach, based on in-situ observations of SF6 and CO2 during the SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) aircraft campaigns. Combining the information of the mean age of air and the water vapour distributions we demonstrate that the tropospheric air transported into the LMS above the extratropical tropopause layer (ExTL) originates predominantly from the tropical tropopause layer (TTL). The concept of our mass balance is based on simultaneous measurements of the two passive tracers and the assumption that transport into the LMS can be described by age spectra which are superposition of two different modes. Based on this concept we conclude that the stratospheric influence on LMS composition is strongest in April with extreme values of the tropospheric fractions (alpha1) below 20% and that the strongest tropospheric signatures are found in October with alpha1 greater than 80%. Beyond the fractions, our mass balance concept allows us to calculate the associated transit times for transport of tropospheric air from the tropics into the LMS. The shortest transit times (<0.3 years) are derived for the summer, continuously increasing up to 0.8 years by the end of spring. These findings suggest that strong quasi-horizontal mixing across the weak subtropical jet from summer to mid of autumn and the considerably shorter residual transport time-scales within the lower branch of the Brewer-Dobson circulation in summer than in winter dominates the tropospheric influence in the LMS until the beginning of next year's summer.
In this paper we present evidence that the observed increase in tropical upwelling after the year 2000 may be attributed to a change in the Brewer-Dobson circulation pattern. For this purpose, we use the concept of transit times derived from residual circulation trajectories and different in-situ measurements of ozone and nitrous dioxide. Observations from the Canadian midlatitude ozone profile record, probability density functions of in-situ N2O observations and a shift of the N2O-O3 correlation slopes, taken together, indicate that the increased upwelling in the tropics after the year 2000 appears to have triggered an intensification of tracer transport from the tropics into the extratropics in the lower stratosphere below about 500 K. This finding is corroborated by the fact that transit times along the shallow branch of the residual circulation into the LMS have decreased for the same time period (1993–2003). On a longer time scale (1979–2009), the transit time of the shallow residual circulation branch show a steady decrease of about −1 month/decade over the last 30 years, while the transit times of the deep branch remain unchanged. This highlights the fact that a change in the upwelling across the tropical tropopause is not a direct indicator for changes of the whole Brewer-Dobson circulation.
In this paper we present evidence that the observed increase in tropical upwelling after the year 2000 may be attributed to a change in the Brewer-Dobson circulation pattern. For this purpose, we use the concept of transit times derived from residual circulation trajectories and different in-situ measurements of ozone and nitrous dioxide. Observations from the Canadian midlatitude ozone profile record, probability density functions of in-situ N2O observations and a shift of the N2O-O3 correlation slopes, taken together, indicate that the increased upwelling in the tropics after the year 2000 appears to have triggered an intensification of tracer transport from the tropics into the extratropics in the lower stratosphere below about 500 K. This finding is corroborated by the fact that transit times along the shallow branch of the residual circulation into the LMS have decreased for the same time period (1993–2003). On a longer time scale (1979–2009), the transit time of the shallow residual circulation branch show a steady decrease of about −1 month/decade over the last 30 yr, while the transit times of the deep branch remain unchanged. This highlights that changes in the upwelling across the tropical tropopause are not sufficient as an indicator for changes in the entire Brewer-Dobson circulation.
Development of a Bioaerosol single particle detector (BIO IN) for the Fast Ice Nucleus CHamber FINCH
(2010)
In this work we present the setup and first tests of our new BIO IN detector. This detector was constructed to classify atmospheric ice nuclei (IN) for their biological content. It is designed to be coupled to the Fast Ice Nucleus CHamber FINCH. If one particle acts as an ice nucleus, it will be at least partly covered with ice at the end of the development section of the FINCH chamber. The device combines an auto-fluorescence detector and a circular depolarization detector for simultaneous detection of biological material and discrimination between water droplets, ice crystals and non activated large aerosol particles. The excitation of biological material with UV light and analysis of auto-fluorescence is a common principle used for flow cytometry, fluorescence microscopy, spectroscopy and imaging. The detection of auto-fluorescence of airborne single particles demands some more experimental effort. However, expensive commercial sensors are available for special purposes, e.g. size distribution measurements. But these sensors will not fit the specifications needed for the FINCH IN counter (e.g. high sample flow of up 10 LPM). The newly developed -low cost- BIO IN sensor uses a single high-power UV LED for the electronic excitation instead of much more expensive UV lasers. Other key advantages of the new sensor are the low weight, compact size, and the little effect on the aerosol sample, which allows it to be coupled with other instruments for further analysis. The instrument will be flown on one of the first missions of the new German research aircraft "HALO" (High Altitude and LOng range).
In this work we present the setup and first tests of our new BIO IN detector. This detector is designed to classify atmospheric ice nuclei (IN) for their biological content. Biological material is identified via its auto-fluorescence (intrinsic fluorescence) after irradiation with UV radiation. Ice nuclei are key substances for precipitation development via the Bergeron–Findeisen process. The level of scientific knowledge regarding origin and climatology (temporal and spatial distribution) of IN is very low. Some biological material is known to be active as IN even at relatively high temperatures of up to –2°C (e.g. pseudomonas syringae bacteria). These biological IN could have a strong influence on the formation of clouds and precipitation. We have designed the new BIO IN sensor to analyze the abundance of IN of biological origin. The instrument will be flown on one of the first missions of the new German research aircraft ''HALO'' (High Altitude and LOng Range).
Soil water potential is crucial to plant transpiration and thus to carbon cycling and biosphere–atmosphere interactions, yet it is difficult to measure in the field. Volumetric and gravimetric water contents are easy and cheap to measure in the field, but can be a poor proxy of plant-available water. Soil water content can be transformed to water potential using soil moisture retention curves. We provide empirically derived soil moisture retention curves for seven soil types in the Kruger National Park, South Africa. Site-specific curves produced excellent estimates of soil water potential from soil water content values. Curves from soils derived from the same geological substrate were similar, potentially allowing for the use of one curve for basalt soils and another for granite soils. It is anticipated that this dataset will help hydrologists and ecophysiologists understand water dynamics, carbon cycling and biosphere–atmosphere interactions under current and changing climatic conditions in the region.
In old and heavily weathered soils, the availability of P might be so small that the primary production of plants is limited. However, plants have evolved several mechanisms to actively take up P from the soil or mine it to overcome this limitation. These mechanisms involve the active uptake of P mediated by mycorrhiza, biotic de-occlusion through root clusters, and the biotic enhancement of weathering through root exudation. The objective of this paper is to investigate how and where these processes contribute to alleviate P limitation on primary productivity. To do so, we propose a process-based model accounting for the major processes of the carbon, water, and P cycle including chemical weathering at the global scale. We use simulation experiments to assess the relative importance of the different uptake mechanisms to alleviate P limitation on biomass production. Implementing P limitation on biomass synthesis allows the assessment of the efficiencies of biomass production across different ecosystems.
We find that active P-uptake is an essential mechanism for sustaining P availability on long time scales, whereas biotic de-occlusion might serve as a buffer on time scales shorter than 10 000 yr. Although active P uptake is essential for reducing P losses by leaching, humid lowland soils reach P limitation after around 100 000 yr of soil evolution. Given the generalized modeling framework, our model results compare reasonably with observed or independently estimated patterns and ranges of P concentrations in soils and vegetation. Furthermore, our simulations suggest that P limitation might be an important driver of biomass production efficiency (the fraction of the gross primary productivity used for biomass growth), and that vegetation on older soils becomes P-limited leading to a smaller biomass production efficiency.
With this study, we provide a theoretical basis for investigating the responses of terrestrial ecosystems to P availability linking geological and ecological time scales under different environmental settings.
In old and heavily weathered soils, the availability of P might be so small that the primary production of plants is limited. However, plants have evolved several mechanisms to actively take up P from the soil or mine it to overcome this limitation. These mechanisms involve the active uptake of P mediated by mycorrhiza, biotic de-occlusion through root clusters, and the biotic enhancement of weathering through root exudation. The objective of this paper is to investigate how and where these processes contribute to alleviate P limitation on primary productivity. To do so, we propose a process-based model accounting for the major processes of the carbon, water, and P cycles including chemical weathering at the global scale. Implementing P limitation on biomass synthesis allows the assessment of the efficiencies of biomass production across different ecosystems. We use simulation experiments to assess the relative importance of the different uptake mechanisms to alleviate P limitation on biomass production. We find that active P uptake is an essential mechanism for sustaining P availability on long timescales, whereas biotic de-occlusion might serve as a buffer on timescales shorter than 10 000 yr. Although active P uptake is essential for reducing P losses by leaching, humid lowland soils reach P limitation after around 100 000 yr of soil evolution. Given the generalized modelling framework, our model results compare reasonably with observed or independently estimated patterns and ranges of P concentrations in soils and vegetation. Furthermore, our simulations suggest that P limitation might be an important driver of biomass production efficiency (the fraction of the gross primary productivity used for biomass growth), and that vegetation on old soils has a smaller biomass production rate when P becomes limiting. With this study, we provide a theoretical basis for investigating the responses of terrestrial ecosystems to P availability linking geological and ecological timescales under different environmental settings.
Convection-permitting climate model are promising tools for improved representation of extremes, but the number of regions for which these models have been evaluated are still rather limited to make robust conclusions. In addition, an integrated interpretation of near-surface characteristics (typically temperature and precipitation) together with cloud properties is limited. The objective of this paper is to comprehensively evaluate the performance of a ‘state-of-the-art’ regional convection-permitting climate model for a mid-latitude coastal region with little orographic forcing. For this purpose, an 11-year integration with the COSMO-CLM model at Convection-Permitting Scale (CPS) using a grid spacing of 2.8 km was compared with in-situ and satellite-based observations of precipitation, temperature, cloud properties and radiation (both at the surface and the top of the atmosphere). CPS clearly improves the representation of precipitation, in especially the diurnal cycle, intensity and spatial distribution of hourly precipitation. Improvements in the representation of temperature are less obvious. In fact the CPS integration overestimates both low and high temperature extremes. The underlying cause for the overestimation of high temperature extremes was attributed to deficiencies in the cloud properties: The modelled cloud fraction is only 46 % whereas a cloud fraction of 65 % was observed. Surprisingly, the effect of this deficiency was less pronounced at the radiation balance at the top of the atmosphere due to a compensating error, in particular an overestimation of the reflectivity of clouds when they are present. Overall, a better representation of convective precipitation and a very good representation of the daily cycle in different cloud types were demonstrated. However, to overcome remaining deficiencies, additional efforts are necessary to improve cloud characteristics in CPS. This will be a challenging task due to compensating deficiencies that currently exist in ‘state-of-the-art’ models, yielding a good representation of average climate conditions. In the light of using the CPS models to study climate change it is necessary that these deficiencies are addressed in future research.
It is common practice to use a 30-year period to derive climatological values, as recommended by the World Meteorological Organization. However this convention relies on important assumptions, of which the validity can be examined by deriving the uncertainty inherent to using a limited time-period for deriving climatological values. In this study a new method, aiming at deriving this uncertainty, has been developed with an application to precipitation for a station in Europe (Westdorpe) and one in Africa (Gulu). The weather generator framework is used to produce synthetic daily precipitation time-series that can also be regarded as alternative climate realizations. The framework consists of an improved Markov model, which shows good performance in reproducing the 5-day precipitation variability. The sub-seasonal, seasonal and the inter-annual signals are introduced in the weather generator framework by including covariates. These covariates are derived from an empirical mode decomposition analysis with an improved stability and significance assessment. Introducing covariates was found to substantially improve the monthly precipitation variability for Gulu. From the weather generator, 1,000 synthetic time-series were produced. The divergence between these time-series demonstrates an uncertainty, inherent to using a 30-year period for mean precipitation, of 11 % for Westdorpe and 15 % for Gulu. The uncertainty for precipitation 10-year return levels was found to be 37 % for both sites.
Convection-permitting models (CPMs) have proven their usefulness in representing precipitation on a sub-daily scale. However, investigations on sub-hourly scales are still lacking, even though these are the scales for which showers exhibit the most variability. A Lagrangian approach is implemented here to evaluate the representation of showers in a CPM, using the limited-area climate model COSMO-CLM. This approach consists of tracking 5‑min precipitation fields to retrieve different features of showers (e.g., temporal pattern, horizontal speed, lifetime). In total, 312 cases are simulated at a resolution of 0.01 ° over Central Germany, and among these cases, 78 are evaluated against a radar dataset. The model is able to represent most observed features for different types of convective cells. In addition, the CPM reproduced well the observed relationship between the precipitation characteristics and temperature indicating that the COSMO-CLM model is sophisticated enough to represent the climatological features of showers.
A satellite-based climate record of monthly mean surface solar irradiance (SIS) is investigated with regard to possible inhomogeneities in time. The data record is provided by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on Climate Monitoring (CM SAF) for the period of 1983 to 2005, covering a disk area between ±70° in latitude and longitude. The Standard Normal Homogeneity Test (SNHT) and two other homogeneity tests are applied with and without the use of reference SIS data (from the Baseline Surface Radiation Network (BSRN) and from the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA -Interim reanalysis. The focus is on the detection of break-like inhomogeneities, which may occur due to satellite or SIS retrieval algorithm changes. In comparison with the few suitable BSRN SIS observation series with limited extension in time (no data before 1992), the CM SAF SIS time series do not show significant inhomogeneities, even though slight discrepancies in the surface measurements appear. The investigation of the full CM SAF SIS domain reveal inhomogeneities related to most of the documented satellite and retrieval changes, but only for relatively small domain fractions (especially in mountainous desert-like areas in Africa). In these regions the retrieval algorithm is not capable of adjusting for the changes of the satellite instruments. For other areas, e.g., Europe, no such breaks in the time series are found. We conclude that the CM SAF SIS data record has to be further assessed and regionally homogenized before climate trend investigations can be conducted.
We conducted measurements of up to the five important short-lived brominated species in the marine boundary layer (MBL) of the mid-latitudes (List/Sylt, North Sea) in June 2009 and of the tropical Western Pacific during the TransBrom ship campaign in October 2009. For the one-week time series in List mean mixing ratios of 2.0, 1.1, 0.2, 0.1 ppt were analysed for CHBr3, CH2Br2, CHBr2Cl and CH2BrCl, with maxima of 5.8 and 1.6 ppt for the two main components CHBr3 and CH2Br2. Along the cruise track in the Western Pacific (between 41° N and 13° S) mean mixing ratios of 1.0, 0.9, 0.2, 0.1 and 0.1 ppt for CHBr3, CH2Br2, CHBrCl2, CHBr2Cl and CH2BrCl were determined. Air samples with coastal influence showed considerably higher mixing ratios than the samples with open ocean origin. Correlation analyses of the two datasets yielded strong linear relationships between the mixing ratios of four of the five species (except for CH2BrCl). Using a combined dataset from the two campaigns, rough estimates of the molar emission ratios between the correlated substances were derived as follows: 9/1/0.3/0.3 for CHBr3/CH2Br2/CHBrCl2/CHBr2Cl. Additional measurements were made in the tropical tropopause layer (TTL) above Teresina (Brazil, 5.07° S, 42.87° W) in June 2008, using balloon-borne cryogenic whole air sampling technique. Near the level of zero clear-sky net radiative heating (LZRH) at 14.8 km about 2.25 ppt organic bromine was bound to the five short-lived species, making up 13 % of total organic bromine (17.82 ppt). CH2Br2 (1.45 ppt) and CHBr3 (0.56 ppt) accounted for 90 % of the budget of short-lived compounds in that region. Near the tropopause (at 17.5 km) organic bromine from short-lived substances was reduced to 1.35 ppt, with 1.07 ppt and 0.12 ppt attributed to CH2Br2 and CHBr3 respectively.
We conducted measurements of the five important short-lived organic bromine species in the marine boundary layer (MBL). Measurements were made in the Northern Hemisphere mid-latitudes (Sylt Island, North Sea) in June 2009 and in the tropical Western Pacific during the TransBrom ship campaign in October 2009. For the one-week time series on Sylt Island, mean mixing ratios of CHBr3, CH2Br2, CHBr2Cl and CH2BrCl were 2.0, 1.1, 0.2, 0.1 ppt, respectively. We found maxima of 5.8 and 1.6 ppt for the two main components CHBr3 and CH2Br2. Along the cruise track in the Western Pacific (between 41° N and 13° S) we measured mean mixing ratios of 0.9, 0.9, 0.2, 0.1 and 0.1 ppt for CHBr3, CH2Br2, CHBrCl2, CHBr2Cl and CH2BrCl. Air samples with coastal influence showed considerably higher mixing ratios than the samples with open ocean origin. Correlation analyses of the two data sets yielded strong linear relationships between the mixing ratios of four of the five species (except for CH2BrCl). Using a combined data set from the two campaigns and a comparison with the results from two former studies, rough estimates of the molar emission ratios between the correlated substances were: 9/1/0.35/0.35 for CHBr3/CH2Br2/CHBrCl2/CHBr2Cl. Additional measurements were made in the tropical tropopause layer (TTL) above Teresina (Brazil, 5° S) in June 2008, using balloon-borne cryogenic whole air sampling technique. Near the level of zero clear-sky net radiative heating (LZRH) at 14.8 km about 2.25 ppt organic bromine was bound to the five short-lived species, making up 13% of total organic bromine (17.82 ppt). CH2Br2 (1.45 ppt) and CHBr3 (0.56 ppt) accounted for 90% of the budget of short-lived compounds in that region. Near the tropopause (at 17.5 km) organic bromine from these substances was reduced to 1.35 ppt, with 1.07 and 0.12 ppt attributed to CH2Br2 and CHBr3, respectively.
Staubwolken sind im Universum die Geburtsstätten neuer Sterne. Dort wiederholen sich Prozesse, die vor 4,56 Milliarden Jahren auch zur Entstehung unseres Sonnensystems geführt haben. Noch heute gibt es Zeugen aus dieser Zeit: Kometenstaub, Sternenstaub und interstellarer Staub. Die »Stardust-Mission« hat sie eingefangen, und Frankfurter Geowissenschaftler haben darin – dank modernster Labor-Analytik – erstaunliche Funde gemacht.
We have developed and characterized the novel PTR3, a proton transfer reaction-time-of-flight mass spectrometer (PTR-TOF) using a new gas inlet and an innovative reaction chamber design. The reaction chamber consists of a tripole operated with rf voltages generating an electric field only in the radial direction. An elevated electrical field is necessary to reduce clustering of primary hydronium (H3O+) and product ions with water molecules present in the sample gas. The axial movement of the ions is achieved by the sample gas flow only. Therefore, the new design allows a 30-fold longer reaction time and a 40-fold increase in pressure compared to standard PTR-TOF-MS. First calibration tests show sensitivities of up to 18000 counts per second/parts per billion and volume (cps/ppbv) at a mass resolution of >8000 m/Δm (fwhm). The new inlet using center-sampling through a critical orifice reduces wall losses of low volatility compounds. Therefore, the new PTR3 instrument is sensitive to VOC typically present in the ppbv range as well as to semivolatile organic compounds (SVOC) and even highly oxidized organic molecules (HOMs) present in the parts per quadrillion per volume (ppqv) range in the atmosphere.
In the original manuscript, Figs. 7–16 included fonts which were not correctly embedded in the file. As such, unless certain propriety software (ArcGIS) is installed on the viewing platform, the figures will appear corrupted. In this Corrigendum, Figs. 7–16 and their captions are reproduced with the fonts correctly embedded. Please find the correct figures below.
The late Miocene palaeorecord provides evidence for a warmer and wetter climate than that of today, and there is uncertainty in the palaeo-CO2 record of at least 200 ppm. We present results from fully coupled atmosphere-ocean-vegetation simulations for the late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that these data accurately reflect the late Miocene climate, and that the late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that:
1. Both palaeogeography and atmospheric CO2 contribute to the proxy-derived precipitation differences between the late Miocene and modern reference climates. However these contributions exibit synergy and so do not add linearly.
2. The vast majority of the proxy-derived temperature differences between the late Miocene and modern reference climates can only be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates.