| 1. |
- Khosravi, Maryam, 1975
(författare)
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Diurnal variation of stratospheric short-lived species
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diurnal variation of stratospheric short-lived speciesMaryam KhosraviChalmers University of TechnologyDepartment of Earth and Space SciencesAbstractThe depletion of ozone in the stratosphere has a direct impact on the amount of ultravioletradiation reaching the Earth’s surface. The ozone abundance and distributionis controlled by the photo-chemical reactions and catalytic cycles involving halogens(chlorine and bromine), odd hydrogen and odd nitrogen species as well as by atmospherictransport.An introduction to ozone related chemistry of the stratosphere and modelling ofshort-lived species using photo-chemical models is presented. A one dimensional (1D)atmospheric model is used in two distinct studies: modeling of short-lived species inthe Arctic lower stratosphere (paper I) and in the tropical mid to upper stratosphere(paper II).The first part of this thesis describes the diurnal variation of chlorine monoxide,ClO, which is the most important short-lived species controlling ozone in the polarlower stratosphere during winter and early-spring. The ClO-dimer cycle, involvingClO and its nighttime reservoir Cl2O2, contributes to about 75%of the polar ozone loss.ClO measurements from an airborne submillimeter radiometer in the Arctic twilighthave been compared with the results from a 1D photo-chemical model (MISU-1D), inorder to validate the model and to test the kinetics of the reactions controlling the partitioningof chlorine species during the course of a day. The results show that crosssections leading to faster photolysis rates of Cl2O2 match best with the ClO observations.This is consistent with the recent version of the chemical kinetics evaluation bythe Jet Propulsion Laboratory. Slower photolysis rates can not be reconciled with theobservations since active chlorine higher than the total available chlorine would be required.The model reproduces higher nighttime ClO than the observations, howeverthe nighttime ClOmodelled using recent JPL recommendations of the thermal equilibriumconstant agree within the uncertainty range of the observations. The sensitivityof the model to the assumed albedo and temperature are also tested. Neither the temperaturenor the albedo uncertainties allow us to reconcile the model with the lowerobserved nighttime ClO. Moreover, it is found that the ClO-BrO cycle decreases ClOmostly around sunrise and sunset.The second part of the thesis presents the partitioning and diurnal variation of chlorine,bromine, hydrogen, nitrogen and oxygen species in the tropics from the stratosphereto the lower mesosphere. Model results of the diurnal variation of HOCl (asone of the chlorine reservoirs), the related short-lived species ClO and HO2 and HCl(as the main chlorine reservoir) for the tropics and three altitudes (35, 45 and 55 km)are compared with measurements from five satellite instruments. The model resultsgenerally agree with the observations both in terms of the absolute values and the differencesbetween day and night.
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| 2. |
- Karlsson, Emma, 1980-
(författare)
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Organic geochemical investigation of sources, transport and fate of terrestrial organic matter in the southeast Laptev Sea
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Permafrost carbon stores have been suggested to react to warming trends with increased terrestrial loading to its coastal waters. Presently, the warming has been seen to be especially high in the East Siberian Arctic and the fate of the major release of terrestrial matter to these coasts is yet to be detailed.Our work is focused on the East Siberian Shelf (ESS) – which is the largest continental shelf in the world. It receives substantial inputs of terrestrial organic matter both from the large Russian rivers and from eroding coastlines. The largest of its rivers, the Lena, discharges in Buor-Khaya Bay, which is also a hot spot for coastal erosion.Previous studies of molecular and δ¹3C and Δ¹⁴C composition of terrestrial organic matter received by Arctic coastal waters have suggested a different propensity of different terrestrial source materials towards bacterial degradation. This detailed isotopic and molecular marker survey which is the basis for this thesis reveals clearly distinguished source patterns both between surface water (POC) and sea floor (SOC) as well as with distance away from the sources. The heavy terrestrial dominance over marine/planktonic sources are clearly detected in gradients of high POC and SOC levels, as well as depleted δ13C -OC and high HMW/LMW n-alkane ratios. Furthermore, data suggests that terr-OC was substantially older yet less degraded in the surface sediment than in the surface waters. This unusual vertical degradation trend was only recently found also for the coastal and central East Siberian Sea. It seems that the riverine terr-OC component comprising mainly annual thaw layer surface soil dominates the buoyant surface water POC and is readily degraded. This is in contrast to the coastline-erosion terr-OC which is associated with minerals and therefore ballasted to the sediments where it makes up the key OC component and seems relatively protected from degradation.The study area of this work is a region with strong terrestrial influence hosting many of the important carbon cycling processes, and data reveal two important OC contributors of different origin, mineral associated coastal erosion matter and riverine borne surface soil matter. These two components may well represent different propensities to contribute to a positive feedback to climate warming by converting OC from coastal and inland permafrost into CO₂.
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| 3. |
- Acosta Navarro, Juan Camilo
(författare)
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Historical anthropogenic radiative forcing of changes in biogenic secondary organic aerosol
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human activities have lead to changes in the energy balance of the Earth and the global climate. Changes in atmospheric aerosols are the second largest contributor to climate change after greenhouse gases since 1750 A.D. Land-use practices and other environmental drivers have caused changes in the emission of biogenic volatile organic compounds (BVOCs) and secondary organic aerosol (SOA) well before 1750 A.D, possibly causing climate effects through aerosol-radiation and aerosol-cloud interactions. Two numerical emission models LPJ-GUESS and MEGAN were used to quantify the changes in aerosol forming BVOC emissions in the past millennium. A chemical transport model of the atmosphere (GEOS-Chem-TOMAS) was driven with those BVOC emissions to quantify the effects on radiation caused by millennial changes in SOA.The specific objectives of this licentiate thesis are: 1) to understand what drove the changes in aerosol-forming BVOC emissions (i.e. isoprene, monoterpenes and sesquiterpenes) and to quantify these changes; 2) to calculate for the first time the combined historical aerosol direct and aerosol-cloud albedo effects on radiation from changing BVOC emissions through SOA formation; 3) to investigate how important the biological climate feedback associated to BVOC emissions and SOA formation is from a global climate perspective.We find that global isoprene emissions decreased after 1800 A.D. by about 12% - 15%. This decrease was dominated by losses of natural vegetation, whereas monoterpene and sesquiterpene emissions increased by about 2% - 10%, driven mostly by rising surface air temperatures. From 1000 A.D. to 1800 A.D, isoprene, monoterpene and sesquiterpene emissions decline by 3% - 8% driven by both, natural vegetation losses, and the moderate global cooling between the medieval climate anomaly and the little ice age. The millennial reduction in BVOC emissions lead to a 0.5% to 2% reduction in climatically relevant aerosol particles (> 80 nm) and cause a direct radiative forcing between +0.02 W/m² and +0.07 W/m², and an indirect radiative forcing between -0.02 W/m² and +0.02 W/m². The suggested biological climate feedback seems to be too small to have observable consequences on the global climate in the recent past.
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| 4. |
- Grieco, Francesco, 1992
(författare)
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Recovery and validation of Odin/SMR measurements of mesospheric CO and H2O
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although life on Earth is concentrated in the troposphere, not only the processes happening here are of interest, since tropospheric processes are not the only ones that have an impact on the climate. Coupling mechanisms between different layers are such that changes in middle atmospheric dynamics and composition have an effect on what happens at lower altitudes. Therefore there is the need to extend climate models to include higher altitudes and to perform measurements of the middle atmosphere. Among the species that can be observed in the middle atmosphere, carbon monoxide (CO) and water vapour (H2O) are of high scientific interest thanks to their aptness to being used as circulation tracers. This is due to their long photochemical lifetime which is longer or equal to zonal, meridional and vertical transport time scales. Moreover, H2O plays a decisive role for O3 chemistry. In the mesosphere, meridional circulation is driven by momentum deposition from breaking gravity waves. This originates an annual cycle which affects mostly high latitudes: with measurements it can be observed how CO-rich dry air descends towards the lower mesosphere at the winter pole while moist and CO-poor air is uplifted towards upper mesosphere and lower thermosphere at the summer pole. Gravity waves also give rise to the Semi- Annual Oscillation (SAO) in zonal winds resulting in concentration oscillations that can be observed in CO and H2O measurements, mostly at the tropics. Among the satellite instruments currently performing remote sensing of the middle atmosphere, the Sub-Millimetre Radiometer (SMR) on board the Odin satellite is one of the most long-lived. In fact, SMR has been performing limb sounding of the middle atmosphere for 19 years, providing valuable long term datasets. However, the CO and H2O datasets are both affected by instrumental artifacts that resulted in a misestimation of the two species’ concentration. The two papers included in this thesis focus on identifying the causes and correcting such artifacts. CO observation modes were affected by a malfunctioning of the Phase-Lock Loop (PLL) of the local oscillator (LO) which was causing frequency shifts in the spectra and line broadening. An algorithm that shifts the line back to its theoretical position has been developed and the line broadening has been quantified and taken into account when performing new retrievals. Regarding the H2O observation modes, underestimation of sideband leakage resulted in artifacts in the spectra that caused the misestimation of the retrieved concentration and temperature. For this reason SMR agreed poorly with other instruments measurements. An improvement was brought by assuming a larger sideband leakage than previously thought. For both species new inversions have been performed using the Optimal Estimation Method (OEM) with the Atmospheric Radiative Transfer Simulator (ARTS) as forward model. The recovery and correction of these products resulted in two new long-term and global data sets that are now available to the scientific community to study middle atmospheric dynamics.
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| 5. |
- Jones, Ashley, 1977
(författare)
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Techniques for the validation of Odin and ENVISAT satellite data
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The depletion of ozone from the stratosphere and the impact of global warming have been identified as phenomena caused as a result of anthropogenic activity. Scientists are thus trying to find quicker and more reliable ways to analyse these environmental problems. Remote sensing of the atmosphere using satellites is perhaps the most cost effective method. One beneficial application is the acquisition of vertical profiles of atmospheric species on a global scale with good spatial and temporal resolutions. An example of an instrument that can achieve this is the Sub-Millimetre Radiometer (SMR) aboard the Odin satellite that launched in 2001, which retrieves vertical limb profiles of numerous trace gases, including stratospheric ozone.This thesis presents a validation for Odin/SMR ozone data products, V1.2, V2.0 and V2.1 (for the 501.8 GHz band in the microwave region). Comparisons were made to V4.61 data from the Interferometer for Passive Atmospheric Soundings (MIPAS) instrument, on board the ENVISAT satellite. Further analysis was carried out by comparing Odin/SMR mixing ratios to balloon sonde data. By validating these three versions of Odin/SMR data, we can establish if any further adjustments need be made to the settings and calibrations of the instruments for the production of subsequent data sets. Such an investigation can be achieved either by matching coincident data using time and distance constraints directly or by using a data assimilation modelThe latest and current version, V2.1, of Odin/SMR showed comparisons with MIPAS V4.61 and balloon sonde data to have the smallest systematic differences with respect to the previous two versions, especially below 25 km. In this lower stratospheric region, V2.1 was only slightly smaller than MIPAS by less than 0.25 ppmv, while comparisons to sonde measurements showed an agreement within +/-0.3 ppmv. The largest systematic differences for this version were seen in the tropics, where a bias of ~0.7 ppmv between 25-37 km was found. An analysis was done in order to prove that data assimilation is a valid method for validation of satellite measurements when very few coincident data are available between satellite measurements and balloon sondes. Results showed that mean differences between the Isentropic Assimilation model For Stratospheric Ozone (IASCO) produced ozone profiles and co-located ozone sondes contained systematic differences similar to those obtained from co-located MIPAS and ozone sonde coincidences. Spatial and temporal constraints were used to obtain the MIPAS/sonde matches, where 12 hours and 800 km produced the best results for statistical analysis. The largest residual between the IASCO/sonde mean difference and MIPAS/sonde mean difference using these constraints was less than 0.25 ppmv between potential temperature altitudes of 425-975 K
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| 6. |
- Larsson, Anna
(författare)
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Holocene carbon and nitrogen accumulation rates and contemporary carbon export in discharge : a study from a boreal fen catchment
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The contemporary role of mires in land-atmosphere exchange of carbon dioxide (CO₂) is the subject of intense scientific debate. Investigating patterns and mechanisms of variations in past carbon (C) accumulation rates as well as contemporary C fluxes of peatlands facilitates predictions of future mire C sink strength under a changing climate. Nitrogen (N) is an important macro-nutrient and thereby strongly coupled to the C accumulation rate. Thus, I have investigated Holocene C and N accumulation rates and their potential controls, and the annual and seasonal stream C export during the Holocene at the oligotrophic fen Degerö Stormyr in northern Sweden. The mean (±SD) long-term apparent rates of C and N accumulation (LORCA and LORNA) were estimated to 13.7±5.5 g C m⁻² yr⁻¹ and 0.28±0.14 g N m⁻² yr⁻¹, respectively. These rates were relatively low compared to those of other northern peatlands. Variations in C and N accumulation rates exhibited similar temporal patterns largely coinciding with major changes in botanical remains, and mainly primary production controlled the accumulation rates. The botanical composition had a major impact on the degree of decomposition, with indications of enrichment of recalcitrant compounds in highly degraded peat, as well as differences in ¹³C-¹²C composition of litter at the onset of decomposition. There were also indications of preferential plant uptake of ¹⁴N at higher N availability. Stream total C export was primarily driven by discharge, with average annual C export estimated to 12.2 g m⁻² yr⁻¹ over twelve years. This flux typically corresponded to 25-37% of the mean annual net uptake of CO₂ (NEE). However, during a year with a dry summer and wet autumn the discharge C export corresponded to as much as 90%, highlighting the importance of seasonality. The highest TOC export was exhibited during summer when accounting for differences in discharge, underlining the importance of timing of precipitation for the seasonal C export. Seasonal variations in C quality (SUVA₂₅₄) indicate different within mire sources of TOC during the year. In this thesis I conclude the importance of primary production for C and N accumulation rates, and highlight the importance of seasonality for stream C export from mires.
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| 7. |
- Ning, Tong, 1975
(författare)
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Global Navigation Satellite Systems: Applications With Time Scales From Seconds to Decades
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global Navigation Satellite Systems (GNSS) can be used formany applications with time scales varying from seconds to decades.For~example, due to the ability of high-rate sampling, GNSStechniques are suitable for the detection of the large co-seismicdisplacements, which are dominated by low-frequency signals andtherefore can be recorded at a few Hertz and estimated with rathersmall uncertainty (millimetres). Results~from this thesis show thatRoot-Mean-Square (RMS) differences are approximately 4 and 6 mm inthe east and north components, respectively. The~vertical componenthas a slightly higher RMS of 8 mm.Atmospheric water vapour is of fundamental interest for GNSS. A~goodmodeling of the atmospheric water vapour is desired not only forhigh accuracy positioning, but also for applications of usingestimates in climate research. Along~with densification andextension of permanent GNSS station networks globally or regionally,using GNSS measurements to provide estimates of the atmosphericwater vapour content above receivers on the ground is a promisingapplication. This~thesis shows that GNSS can estimate small lineartrends in the atmospheric water vapour which correlate withsimultaneously estimated trends in the ground temperature. The~longtime series (decades) of the GNSS-estimated atmospheric IntegratedWater Vapour (IWV) can also be used for comparison to and validationof climate models, and in turn improvethe performance of the models. To get the highest accuracy from GNSS measurements for positioningand IWV determinations, the elevation dependent systematic effects,i.e. antenna Phase Centre Variations (PCV) and multipath reflectionsshall be carefully investigated and mitigated. In~this thesis, acase study of implementing PCV calibrations, and using microwaveabsorbing material in different geometries around the GNSS antennawas carried out to study, quantify, and reduce the elevationdependent errors. The~results show that both the microwave absorbingmaterial and the PCV calibrations make significant positiveimpacts.
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| 8. |
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| 9. |
- Monteith, Albert, 1990
(författare)
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Radar Measurements of Temporal Variation in a Boreal Forest
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthetic aperture radar (SAR) on a satellite platform is a suitable technique for all-weather global monitoring of forest parameters such as biomass. This is important for increasing the accuracy of the global terrestrial carbon flux, the largest uncertainty in our current understanding of the Earth’s carbon cycle. In recent decades there has been increasing interest in relating SAR observables from current and future spaceborne SAR missions to forest parameters. Ideally, these SAR observables are only dependent on the forest parameters of interest, but they are also affected by temporal variations in the forest due to weather, diurnal and seasonal changes. These effects are not properly accounted for in current forest parameter estimation models using SAR data due to shortcomings in our understanding of these effects.To fill this knowledge gap, a tower-based radar has been developed for measuring temporal variation of radar signatures in a boreal forest site in southern Sweden. The instrument allows monitoring of radar signatures from the forest site over timescales ranging from less than a second to years. The experiment consists of a 50-m high tower equipped with 30 antennas, allowing fully-polarimetric tomographic imaging at microwave frequencies of P-band (420 - 450 MHz), L-band (1240 - 1375 MHz) and C-band (5250 - 5570 MHz). Results from an on-site weather station assists in interpretation of the radar results. The work in this thesis involves the design and implementation of the experimental setup and analysis of the first results. The results have provided new information about variations in forest radar backscatter during freeze-thaw cycles at P- and L-band, causing drops in backscatter of 4 to 10 dB. An effect where strong winds cause a drop in co-polarised backscatter at P-band has been directly observed for the first time. Finally, the tomographic capabilities of the instrument were demonstrated. Tomographic imaging quality was shown to be better than for measurement protocols used by previous tower-based radars when acquired while the trees were moving due to wind.The results of this experiment are important for understanding and modelling temporal variations in radar measurements over boreal forests such that these unwanted variations can be compensated for in forest parameter estimation algorithms using SAR data.
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| 10. |
- Singh, Jagdeep, 1985-
(författare)
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Towards a Sustainable Resource Management : A Broader Systems Approach to Product Design and Waste Management
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rapid economic growth, urbanisation and increasing population have caused (materially intensive) resource consumption to increase, and consequently the release of large amounts of waste to the environment. Numerous technological and operational approaches to resource management have been introduced throughout the system of production, consumption and waste management. This thesis concludes that the current, rather isolated, efforts to influence different systems for waste management, waste reduction and resource management are indeed not sufficient from a long-term sustainability perspective. To manage resources and waste sustainably, resource management requires a more systems-oriented approach, which addresses the root causes of the problems.This thesis identifies and discusses different sustainability challenges facing the global waste management system. To address these challenges a broader systems approach to waste management is proposed. The thesis argues that there is a need to recognise the multitudes of perspectives, cross-scale dynamics and actors’ interactions at various levels. The barriers and limitations to a systems-oriented management of waste generation including design, production, consumption and waste management are discussed. The study utilises soft systems methodology (by Checkland (2000)) within which different concepts and methods are utilised to present a worldwide view on resource dynamics and develop a research heuristic for sustainable resource management. The study emphasises the need for a shared vision among various actors across the chain of production and consumption. To assist better planning, the need for improved databases on resource use and wastes is emphasised.
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