1,721,414 research outputs found
Studien über die Zusammensetzung der Stratosphäre unter Verwendung der
No full textThe Airborne Submillimeter Radiometer (ASUR) was deployed aboard the Falcon research aircraft during the SCIAVALUE (SCIAMACHY - Scanning Imaging Absorption Spectrometer for Atmospheric ChartographY - Validation Utilization Experiment), the EUPLEX (European Polar and Lee wave Experiment), and the PAVE (Polar Aura Validation Experiment) campaigns. An impressive array of microwave measurements of O3, N2O, HCl, HNO3 and ClO is amassed during the missions from the tropics to the Arctic in various seasons.Using the data various satellite sensor measurements for different molecules are validated. In addition, a new model, the Bremen Chemical Transport Model (CTMB), is introduced. Evaluation of the Linearized ozone chemistry shows that the ozone profiles simulated with the Linoz model are accurate enough to be used for stratospheric chemistry and transport studies though the simulations show a low bias of about 9% in the middle stratosphere and a high bias of 10-30% in the lower and upper stratosphere, depending on altitude. The simulations for various years suggest that the N2O and NOy calculations depend greatly on the accuracy of the meteorological analyses used in the model. The simulations reveal that the N2O VMRs calculated with the parameterized chemistry are slightly smaller in the lower stratosphere. The inaccuracies in the wind analyses and in the model transport and uncertainties in the chemical reaction rates can be the reasons for the lower values. The N2O-NOy coupled chemistry is in good shape and the transport barriers are reasonably represented in the model. The comparison among the ASUR, the SLIMCAT and the CTMB profiles reveal the upper stratospheric ozone deficit in the SLIMCAT calculations. The comparisons also indicate that the transport process in the models is still to be improved
Morphologische Entwicklung des deutschen Wattenmeeres von 1996 bis 2009, bestimmt aus SAR- und Landsat-Bildern mit der Wasserlinienmethode
No full textThe Dutch, German, and Danish Wadden Sea contains some of the largest undisturbed tidal flats in the world of about 10,000 km2. The research areas covered in this thesis are the North Frisian, Neuwerk, and Cuxhaven regions of the German Wadden Sea. The goal of the thesis is to use the waterline method with SAR and optical images to derive topographic maps in order to analyze the morphological development of this valuable ecological system on large spatial and engineering time scales (90 km and 14 years). Compared to earlier applications, the method is improved with respect to the geocoding step and the data coverage of the complete tidal range. The results also allow analyzing smaller scale s developmental details, such as sandbars and estuaries. Topographical maps from 1996 to 1999, and 2004 to 2009 were generated. The largest morphological differences occurred between 2009 and 1996, also observed in the -2 m isobaths map. The Bed Elevation Range of the tidal flats includes all the elevation information from 1996 to 2009 in order to identify the maximum changes during the investigation period. It shows high morphodynamic regions are outer parts of the tidal flat, sandbars, and estuaries. Vertical nodal linear regression gives the direction of the morphological development (erosion or sedimentation). Our result shows that the rate of change is mostly between -0.1 to 0.1 m/yr. Extreme erosion rate reaches over -0.3 m/yr, while extreme sedimentation rate is up to 0.36 m/yr. The absolute amount of elevation change called turnover height has a growth rate of 8.2 mm/yr, indicating the growing morphodynamic activity over the investigation period. The net balance height of the whole investigation region shows an increasing trend of 6.8 mm/yr, demonstrating an overall sedimentation. According to large-scale analyses, the most dynamic areas are the sandbars. Tertiussand, D-Steert, Gelbsand, and Medemgrund/Medemsand are given detailed discussion in this thesis. The west side of the sandbars except for Medemgrund/Medemsand face the high wave and tidal energy arriving from the open North sea, and cause large erosion towards east, while Medemgrund/Medemsand located in the Elbe estuary show migration in the opposite direction. The three cross sections of Tertiussand, Gelbsand and Medemgrund all show clearly increasing elevation if comparing the average elevation over the years 1996-1999 and 2004-2009. Since the areas of Tertiussand and Gelbsand decreased, their increased elevation might relate to internal sediment redistribution. Medemgrund increasead in area, so its increased elevation could be compensated by the adjacent tidal flat Medemsand which has significant erosion towards the north and the sediment brought from Elbe River
Bestimmung der Oberflächenemissivität von Meereis und Temperaturprofilenüber Meereis aus Daten passiver Mikrowellenradiometer.
No full textPolar regions play a key role in the global climate. The information on atmospheric parameters in these regions is sparse. Among the polar surfaces, sea ice varies in extent and physical properties with region and season and so does the surface emissivity. In the present study a method to retrieve the emissivity is applied over two selected regions in the Arctic, one covered by first-year ice and the other by multiyear ice and it investigates the application of them in the improvement of temperature profile retrieval ver sea ice. The retrieval of surface emissivity is done by combining simulated brightness temperatures with the satellite measured brightness temperature. In order to determine the surface emissivity of sea ice, the observations of the microwave instruments amsu (Advanced Microwave Sounding Unit) and amsr-e (Advanced Microwave Scanning Radiometer- Earth Observing System) are used. Determination of emissivity requires the knowledge of the temperature of the emitting layer. The penetration depth of microwaves in sea ice varies between millimeters and decimeters depending on the frequency and micro-physical structure. A year-round observation of temperature profiles of sea ice from the Surface Heat Budget of the Arctic Ocean (sheba) campaign at a first-year and a multiyear ice site is used to derive a set of coefficients a and b to linearly relate the lowest level air temperature and the different emitting layer temperatures. The method accounts for the variation of the penetration depthwith frequency, air temperature and sea ice temperature. An algorithm to retrieve temperature profiles from amsu data is modified using the retrieved emissivities and the derived temperature correction factors so that the retrieval accuracy of temperature profiles over sea can be improved
Marine Ölaustritte vom Weltraum aus gesehen : ein automatische System zur Detektierung, Kartierung und Quantifizierung, basierend auf Radar mit Synthetischer Apertur (SAR)
No full textOffshore oil seepage is believed to be the largest source of marine oil, yet very few of their locations and seepage fluxes have been discovered and reported. Natural oil seep sites are important as they serve as potential energy sources and because they are hosts to a very varied marine ecosystem. These seeps can also be associated with gas hydrates and methane emissions and hence, locating natural oil seeps can provide locations where the sources of greenhouse gases could be studied and quantified. A quantification of the amount of crude oil released from natural oil seeps is important as it can be used to set a background against which the excess anthropogenic sources of marine oil can be checked. This will provide an estimate of the 'contamination' of marine waters from anthropogenic sources. Until the onset of remote sensing techniques, field measurements and techniques like hydroacoustic measurements or piston core analysis were used to obtain knowledge about the geological settings of the seeps. The remote sensing techniques either involved manual or semi-automatic image analysis. An automatic algorithm that could quantitatively and qualitatively estimate the locations of oil seeps around the world would reduce the time and costs involved by a considerable margin. Synthetic Aperture Radar (SAR) sensors provide an illumination and weather independent source of ocean images that can be used to detect offshore oil seeps. Oil slicks on the ocean surface dampen the small wind driven waves present on the ocean surface and appear darker against the brighter ocean surface. They can, hence, be detected in SAR image. With the launch of the latest Sentinel-1 satellite aimed at providing free SAR data, an algorithm that detects oil slicks and estimates seep location is very beneficial. The global data coverage and the reduction of processing times for the large amounts of SAR data would be unmatchable. The aim of this thesis was to create such an algorithm that could automatically detect oil slicks in SAR images, map the location of the estimated oil seeps and quantify their seepage fluxes. The thesis consists of three studies that are compiled into one of more manuscripts that are published, accepted for publication or ready for submission. The first study of this thesis involves the creation of the Automatic Seep Location Estimator (ASLE) which detects oil slicks in marine SAR images and estimates offshore oil seepage sites. This, the first fully automatic oil seep location estimation algorithm, has been implemented in the programming language Python and has been tested and validated on ENVISAT images of the Black Sea. The second study reported in this thesis focuses on the optimisation of the created ASLE and comparison of the ASLE with other existing algorithms. It also describes the efficiency of the ASLE with respect to other existing algorithms and the results show that the ASLE can successfully detect seeps of active seepages. The third study aimed to provide the status of the offshore seepage in the southern Gulf of Mexico estimated from the ASLE using SAR images from ENVISAT and RADARSAT-1. The ASLE was used to detect natural oil slicks from SAR images and estimate the locations of feeding seeps. The estimated seep locations and the slicks contributing to these estimations were then analysed to quantify their seepage fluxes and rates. The three case studies illustrate that an automatic offshore seepage detection and estimation system such as the Automatic Seep Location Estimator (ASLE) is very beneficial in order to locate global oil seeps and estimate global seepage fluxes. It provides a technique to detect offshore seeps and their seepage fluxes in a fast and highly efficient manner by using Synthetic Aperture Radar images. This allows global accessibility of offshore oil seepage sites. The availability of large amounts of historic SAR datasets, the presence of 5 active SAR satellites and the latest launch of the European Space Agency satellite Sentinel-1, which provides free data, shows that there is no shortage in the availability of SAR data. The result of the work done in this thesis provides a means to utilise this large SAR dataset for the purpose of offshore oil seepage detection and offshore seepage related geophysical applications. The created system will be an important tool in the future not just to estimate offshore seepage in local seas but in global oceans that are otherwise challenging for field analysis
Bestimmung von optische Dicken von Aerosolen über Schnee und Eis in der Arktis aus AATSR (Advanced Along Track Scanning Radiometer) Beobachtungen
No full textAerosols in the Arctic cause radiative forcing and a variety of climatic feedbacks, which affect climate of both local and global scales. In order to assess the state of the Arctic climate, information on the aerosol type and amount is needed. Harsh conditions and remoteness of the Arctic region result in very few ground based measurements of aerosol optical thickness. Remote sensing has the potential to provide the necessary temporal and spatial coverage. A non-trivial task of aerosol retrieval over a very bright surface is being solved within the thesis; the developed retrieval consists of cloud screening over snow and two types of aerosol retrieval over snow - in the visible and infrared spectral regions. A number of validation and case studies has been performed to assess the quality of the retrieval. The developed algorithm applies to the data of Advanced Along Track Scanning Radiometer and produces maps of aerosol optical thickness over snow and ice
Flugzeuggetragene Submillimeterwellenmessungen von Spurengasen der arktischen mittleren Atmosphäre: Nachweis von Denitrifizierung in der arktischen polaren Stratosphäre
No full textDenitrification inside the Arctic vortex in winter 1999/2000 was studied based on measurements of HNO:sub:3:/sub: and N:sub:2:/sub:O by the airborne submillimeter radiometer ASUR for the first time. Vortexwide denitrification was found in mid-March 2000 compared to early-December 1999 shown by a vortex averaged NO:sub:y:/sub: deficit between 1.2±0.9 ppb at ~16 km and 5.3±2.7 ppb at ~20.5 km altitude. A trend of stronger denitrification with increasing equivalent latitude was evident. The observations were compared with runs of the SLIMCAT model applying different denitrification schemes based on ice, large NAT particles in equilibrium, and non-equilibrium NAT particles (DLAPSE). The DLAPSE scheme showed the best agreement with the observed denitrification in winter 1999/2000. Denitrification was also studied in winter 2002/2003. Calculations applying the DLAPSE scheme were able to reproduce the observed HNO:sub:3:/sub: levels north of 75° on 19/1/2003 reasonably well. During the major stratospheric warming in mid-January 2003 unusually high mixing ratios of ozone and N:sub:2:/sub:O were observed by ASUR in the middle stratosphere on 23/1/2003 around 69°N. The observed similarities above a potential temperature of ~800 K with profiles measured around 20°N on 1/3/2003 lead to the conclusion that the airmasses must have been transported from the tropics to the Arctic by rapid isentropic transport in ~3-7 days. To extend the altitude range of ASUR´s measurement capabilities into the mesosphere a high resolution chirp-transform spectrometer has been integrated in the ASUR. A scheme for the retrieval of mesospheric ozone has been developed using measurements from September 2002. Retrievals with total integration times of ~180-720 seconds show reasonable results up to 64-68 km altitude with a total error of ~25%. Measurements of the diurnal variation of mesospheric ozone were in reasonable agreement with the results calculated by a mesospheric chemistry model
Atmospherische Spurengas-Messungen in den Tropen
No full textFourier Transform Infrared (FTIR) spectrometry has been used for ground-based solar absorption, laboratory and flux measurements, to study the atmospheric composition, as well as physical and chemical processes in the atmosphere.The solar absorption FTIR measurements have been performed in Paramaribo, Suriname (5.8 N, 55.2 W) between September 2004 and November 2007 and represent the first remote sensing measurements in the inner tropics over severalyears. These measurements are of great importance for a better understanding of global climate and physical and chemical processes of the tropical atmosphere as well as for satellite validations. Vertical profiles of carbon monoxide (CO) and ethane (C2H6) and total columns of methane (CH4), hydrogen cyanide (HCN) and acetylene (C2H2) have been retrieved from the FTIR spectra. The quality of the methane retrieval was limited by the available spectroscopic data. Laboratory cell-based FTIR measurements have been performed to correct the methane spectroscopy in the infrared spectral region, which significantly improved the retrieval of methane from SCIAMACHY and FTIR spectra. The retrieval of methane profiles from near-infrared FTIR spectra by optimal estimation significantly improved the results. The FTIR observations of methane are compared with TM5 model simulations and satellite observations from SCIAMACHY, and are the first validation of the SCIAMACHY retrieval in the tropics using remote sensing techniques. The ratio CH4/CO2, which can be measured directly from SCIAMACHY and FTIR, compares very good, while the column averaged volume mixing ratio (XVMR(CH4)) of SCIAMACHY do not agree with the FTIR observations. Model assumptions areused in the SCIAMACHY retrieval to derive the XVMR(CH4) from the directly measured CH4/CO2 ratio. The worse agreement of SCIAMACHY XVMR(CH4) with FTIR compared to the SCIAMACHY CH4/CO2 ratio with FTIR could be attributed to unrealistic model assumptions used in the SCIAMACHY retrieval that led to wrong time series of the column averaged CH4 VMR. There is a good agreement of the FTIR XVMR(CH4) with the TM5 model. FTIR observations of carbon monoxide agree well with satellite data from the MOPITT instrument for all of the measurement campaigns. Simulations of CO and C2H6 from the MATCH-MPIC model reproduce the mean vertical structure of the FTIR observations. The model is generally not able to reproduce the extreme enhancements seen during the specific biomass burning events by both observation instruments. Nevertheless, the model indicates that beyond the backgroundsource of CO from methane oxidation, the main contributions to the CO mixing ratios are the episodic convective injection of NMHCs and CO from South American biomass burning into the upper troposphere, along with long range transport of African biomass burning CO, particularly during spring. Revised simulation of the MATCH-MPIC model with improved biomass burning emissions still fails toreproduce most of the individual observed pollution events. It generally underestimates the observed concentrations of carbon monoxide and ethane. The revised model is in better agreement with the observations in the upper troposphere, while in the boundary layer and lower troposphere the revised model underestimates the FTIR measurements and results in underestimated total columns. Current generationatmospheric chemistry models underestimate OH is the tropical region and compensate for this part by too low isoprene emissions. It is speculated that, if a mechanism like e.g. isoprene recycling and realistic isoprene emissions would be included in current models, it would result in a powerful CO source in the boundary layer over Suriname from the isoprene oxidation. The CO oxidationrate would also increase due to higher OH concentrations. Because of the complex chemistry and transport processes, it is difficult to predict the exact changes without having done the simulations. The last part of this work presents the development of an advanced flux measurement technique, consisting of a cell-based FTIR analyser and a Relaxed Eddy Accumulation (REA) system, to enable automated and continuous flux measurements of atmospheric trace gases. The combination of the REA technique with the FTIR analyzer was tested successfully in the lab and during a three weeks field campaign. The FTIR-REA technique offers the capacity to measure a range of gases simultaneously under field conditions and enables long-term measurements and monitoring of atmospheric greenhouse gas fluxes
Modellierung stabiler Isotope im Wasserkreislauf des Eem und des Holozän
No full textThe climate of interglacials within the Quaternary is of particular interest for palaeoclimatology due to its similarity to present-day conditions. This thesis evolves around a set of simulations with the isotope-enabled version of the atmospheric general circulation model ECHAM4. Stable isotopes of oxygen and hydrogen, respectively, are transported in the modelled hydrological cycle, altered by fractionation during phase changes. The simulations represent time slices of the Eemian (124 ka BP) and a series of six mid- to late Holocene time slices (6 to 1 ka BP), respectively. Boundary conditions include sea surface temperatures from a coupled atmosphere-ocean general circulation model (ECHO-G) and insolation anomalies according to changes in orbital parameters. The study focuses on the analysis of the isotopic composition of precipitation. Anomalies of delta-18-O are interpreted in terms of anomalies of precipitation amount and air temperature, respectively. The simulation results are compared to measured isotope values from various climate archives. The physical processes that lead to the simulated isotopic composition of precipitation are shown for case studies and from a global perspective. A prominent feature of both Eemian and Holocene conditions is the insolation anomaly during boreal summer months. Tropical and subtropical African climate is affected significantly by increased zonal flow that increases rainfall amount and decreases air temperature. The spatial distribution of delta-18-O in the simulations indicates that changes in zonal moisture transport rather than a meridional shift in the ITCZ alter the hydrological cycle and trigger the observed northward extension of the rainfall area. Knowledge about the annual distribution of rainfall is crucial for accurate analysis of isotopic signatures from climate archives. This thesis shows orbitally induced changes of the seasonality and associated delta-18-O values. The extent and type of the anomalies varies greatly with location. Some tropical areas may experience a shift from a double to a single cycle, while delta-18-O from extra-tropical regions are more affected by temperature changes without significant changes in the timing of the main precipitation season
Ground-based remote sensing of aerosol properties using the emission FTS in Ny-Ålesund, Spitsbergen (78°N)
No full textArctic amplification, the rapid warming of the Arctic compared to the global average, re
mains partially understood. Key processes include temperature feedback, surface albedo feedback, and cloud and water vapor feedback, with aerosols playing a critical role. Since 2019, a Fourier-Transform Infrared Spectrometer (FTS) at the AWIPEV research base in Ny-Ålesund, Spitsbergen, has been used to measure aerosol components. An algorithm based on the Line-by-Line Radiative Transfer Model and DIScrete Ordinate Radiative Transfer model (LBLDIS) was developed for retrieving aerosol composition.
In order to show this measurement technique in details, a case study for an aerosol-only
case is presented with data from the 10th of June 2020. In the aerosol-only case, the retrieval results show that sulfate (τ900cm−1=0.007 ± 0.0027) is the dominant aerosol during the whole day, followedbydust(τ900cm−1=0.0039 ± 0.0029) and black carbon (τ900cm−1=0.0017 ± 0.0007). Sea salt (τ900cm−1=0.0012 ± 0.0002), which has the weakest emission ability in the infrared waveband, shows the lowest AOD value. Such proportions of sulfate, dust and BC also show good agreement with MERRA-2 reanalysis data. Additionally, the comparison with a sun-photometer (AERONET) shows the daily variation of aerosol AOD retrieved from FTS to be similar with that of the sun-photometer. Based on this retrieval method, long time period observations dataset using FTS is retrieved and presented in this study.
Based on the observed data, the infrared radiation effects of different aerosol compo
sition are analyzed. The results show that the hygroscopic aerosols, such as sea salt and sulfate, have a warming effect in the Arctic during winter. These aerosols absorb atmospheric water vapor, leading to wet growth, increased size, and enhanced longwave downward radiation emission, defined as the Aerosol Infrared Radiation Effect (ARE). Observations of aerosols, especially their composition, are challenging during the Arctic winter. We use an emission Fourier Transform Spectrometer to measure aerosol composition. Observations show that the ARE of dry aerosols is limited to about 1.45 ±2.00 Wm−2. Wet growth significantly increases the ARE of aerosols. During winter, at relative humidity levels between 60% and 80%, wet aerosols exhibit the ARE approximately 10 times greater than dry aerosols. When relative humidity exceeds 80%, the effect can be up to 50 times higher (30- 100 Wm−2). Sea salt aerosols in Ny-Ålesund demonstrate high effect values, while non-hygroscopic aerosols like black carbon and dust show consistently low values. Reanalysis data indicates increased water vapor and sea salt aerosol optical depth in Ny-Ålesund after 2000, correlating with significant positive temperature anomalies in this area. Besides, wet aerosols can remain activated even in dry environments, continuously contributing high effects, thereby expanding the area affected by aerosol-induced warming. This warming effect may exacerbate Arctic warming, acting as a positive feedback mechanism.
Additionally, the rapid Arctic warming, which is occurring faster than in other regions,
leads to a meandering atmospheric circulation pattern. Recently, a new pathway for African dust transport to the Arctic has been identified. This study provides a detailed description of the Rapid Pathway (RP) and investigates the temporal variation of African dust influx into the Arctic via this route. Using GEOS-Chem model simulations, we demonstrate the RP’s enhanced efficiency in accelerating African dust transport to the Arctic within approximately one week, compared to other pathways. Our analysis reveals a significant shift in African dust transport routes after 2000, with a marked increase in dust transport through the central North Atlantic (RP region), particularly in March and April. ERA5 wind field data reveal significant positive anomalies in poleward winds over the North Atlantic in March and April after 2000, facilitating northward dust transport via the RP region. In contrast, negative wind anomalies over Europe suggest a diminished role for the European pathway in Arctic dust transport
Einfluss kurzlebiger Substanzen auf den stratosphärischen Bromgehalt
No full textRecent studies have shown the importance of very short-lived substances (VSLS) for the abundance of stratospheric bromine. In this work, the transport of bromine VSLS into the stratosphere is investigated with a three-dimensional chemistry transport model. The novelty of this approach is the explicit treatment of convective transport in a purely isentropic model, a key prerequisite for the realistic reproduction of the complex interplay of horizontal advection, local deep convection and large-scale diabatic heating in the tropical tropopause layer. Comparisons with observations show that the model is generally able to produce realistic distributions of the two major bromine VSLS, bromoform (CHBr3) and dibromomethane (CH2Br2). In addition, an analysis of the regional transport efficiency suggests that the Western Pacific is the most important source area for VSLS into the stratosphere; approximately 50% of the total amount of bromine VSLS in the TTL is contributed by this region. Another important question is how dehydration in the tropical tropopause impacts on stratospheric bromine loading. An idealized modeling approach assuming total solubility for inorganic bromine predicts that about 60% of bromine originated from VSLS is able to reach the stratosphere, which is consistent with earlier modeling approaches that use a comparable simple dehydration mechanism. However, when applying a more complete chemistry scheme the model results show that virtually the entire amount of bromine contributed by VSLS enters the stratosphere, rendering the impact of dehydration and scavenging on inorganic bromine insignificant in the TTL. This discrepancy is mainly caused by the low fraction of actually soluble inorganic bromine, the small available particle surface area density that restricts adsorption and finally heterogeneous reactions which are able to release adsorbed species into gas phase. Long-term calculations of VSLS injection into the stratosphere reveal a robust correlation between sea surface temperature, convective activity and the amount of short-lived source gases in the TTL, which becomes especially clear during the perturbations induced by El Nino seasons. Finally, the impact of additional bromine originated from VSLS on stratospheric ozone depletion is analyzed. The model predicts that for 5 parts per trillion by volume (pptv) of bromine contributed by VSLS on average about 1.3% of global total column ozone is destroyed
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