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The Retrieval of Aerosols above Clouds and their Radiative Impact in Tropical OceansEswaran, Kruthika January 2016 (has links) (PDF)
Aerosols affect the global radiation budget which plays an important role in determining the state of the Earth's climate. The heterogeneous distribution of aerosols and the variety in their properties results in high uncertainty in the understanding of aerosols. Aerosols affect the radiation by scattering and absorption (direct effect) or by modifying the cloud properties which in turn affects the radiation (indirect effect). The current work focuses only on the direct radiative effect of aerosols.
The change in the top-of-atmosphere (TOA) reflected flux due to the perturbation of aerosols and their properties is called direct aerosol radiative forcing (ARFTOA). Estimation of ARFTOA using aerosol properties is done by solving the radiative transfer equation using a radiative transfer model. However, before using the radiative transfer model, it has to be validated with observations for consistency. This is done to check if the model is able to replicate values close to actual observations. The current work uses the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model. The output radiative fluxes from SBDART are validated by comparing with the Clouds and the Earth's Radiant Energy System (CERES) satellite data. Under clear-skies SBDART agreed with observed fluxes at TOA well within the error limits of satellite observations.
In the shortwave solar spectrum (0.25-4 µm) radiation is affected by change in various aerosol properties and also by water vapour and other gas molecules. To study the effect of each of these molecules separately on the aerosol forcing at TOA, SBDART is used. ARFTOA is found to depend on the aerosol loading (aerosol optical depth – AOD), aerosol type (SSA) and the angular distribution of scattered radiation (asymmetry parameter). The role of water vapour relative to the aerosol layer height was also investigated and for different aerosol types and aerosol layer heights, it was found that water vapour can induce a change of ~4 Wm-2 in TOA flux.
The relative importance of aerosol scattering versus absorption is evaluated through a parameter called single scattering albedo (SSA) which can be estimated from satellites. SSA defined as the ratio of scattering efficiency to total extinction efficiency, depends on the aerosol composition and wavelength. Aerosols with SSA close to 1 (sea-salt, sulphates) scatter the radiation and cool the atmosphere. Aerosols with SSA < 0.9 (black carbon, dust) absorb radiation and warm the atmosphere. Over high reflective surfaces a small change in SSA can change forcing from negative (cooling) to positive (warming). This makes SSA one of the most important and uncertain aerosol parameters. Currently, the SSA retrievals from the Ozone Monitoring Instrument (OMI) are highly sensitive to sub-pixel cloud contamination and change in aerosol height. Using the sensitivity of OMI to aerosol absorption and the superior cloud masking technique and accurate AOD retrieval of Moderate Resolution Imaging Spectroradiometer (MODIS), an algorithm to retrieve SSA (OMI-MODIS) was developed.
The algorithm was performed over global oceans (60S-60N) from 2008-2012. The difference in SSA estimated by OMI-MODIS and that of OMI depended on the aerosol type and aerosol layer height. Aerosol layer height plays an important role in the UV spectrum due to the dominance of Rayleigh scattering. This was verified using SBDART which otherwise would not have been possible using just satellite observations. Both the algorithms were validated with cruise measurements over Arabian Sea and Bay of Bengal. It was seen that when absorbing aerosols (low SSA values) were present closer to the surface, OMI overestimated the value of SSA. On the other hand OMI-MODIS algorithm, which made no assumption on the aerosol type or height, was better constrained than OMI and hence was closer to the cruise measurement The presence of clouds results in a more complex interaction between aerosols and radiation. Aerosols present above clouds are responsible to most of the direct radiative effect in cloudy regions.
The ARFTOA depends not only on the aerosol properties but also on the relative position of aerosols with clouds. When absorbing aerosols are present above clouds, the ARFTOA is highly influenced by the albedo of the underlying surface. Recent studies, over regions influenced by biomass burning aerosol, have shown that it is possible to define a ‘critical cloud fraction’ (CCF) at which the aerosol direct radiative forcing switch from a cooling to a warming effect. Similar analysis was done over BoB (6.5-21.5N; 82.5-97.5E) for the years 2008-2011. Aerosol properties were taken from satellite observations. Satellites cannot provide for aerosols present at different heights and hence SBDART was used to calculate the forcing due to aerosols present only above clouds.
Unlike previous studies which reported a single value of CCF, over BoB it was found that CCF varied from 0.28 to 0.13 from post-monsoon to winter as a result of shift from less absorbing to moderately absorbing aerosol. This implies that in winter, the absorbing aerosols present above clouds cause warming of the atmosphere even at low cloud fractions leading to lower CCF.
The use of multiple satellites in improving the retrieval of SSA has been presented in this thesis. The effect of aerosols present above clouds on the radiative forcing at TOA is shown to be different between Bay of Bengal and Atlantic Ocean. This was due to the change in SSA of aerosols during different seasons. The effect of aerosol height, aerosol type and water vapour on the TOA flux estimation is also studied using a radiative transfer model.
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Influence of River Discharge on Climate in A Coupled ModelSharif, Jahfer January 2013 (has links) (PDF)
River discharge can affect ocean surface temperature by altering stratification within the oceanic mixed layer. A hitherto unexplored aspect of present climate is the feedback of river runoff onto climate. This thesis presents an investigation of the impact of global river runoff on oceans and climate using a fully coupled global climate model, Community Climate System Model (CCSM). Two model simulations for a period of 100 years have been carried out: 1) a reference run (CTRL) that incorporates all the features of a global coupled model with river runoff into the ocean embedded in it, and 2) a sensitivity run (NoRiv) in which the global river runoff into the ocean is blocked. Comparison of model climate devoid of fluvial discharge with the reference run reveals the significance of fluvial discharge in the present climate.
By the end of 50 years of NoRiv experiment, salinity growth slows down and reaches a quasi-stable state. Regions close to river mouths exhibited maximum salinity rise that can potentially alter local density and stratification. On an average, denser and saltier waters in the NoRiv run annihilate barrier layer and form a deeper mixed layer, compared to CTRL run. Density gradient created by the modulation in salinity set forth anomalous currents and circulation across coastlines that carries coastal anomalies to open ocean, preventing local salinity buildup. Arctic Ocean, Bay of Bengal, northern high latitude Pacific and the Atlantic are the most affected regions in terms of changes in salinity and temperature. Model simulations demonstrate that major transformation in Arctic freshwater budget can have potential impact on northern Pacific and Atlantic climate. In the absence of runoff, global average sea surface temperature (SST) rise by about ~ 0.5oC, with major contribution from northern higher latitude oceans. In the Pacific, high latitude warming is related to deepening of mixed layer as well as the northward transport of low latitude warmer waters. Substantial cooling in the central equatorial Pacific (~1oC during winter) can alter large-scale ocean-atmosphere circulation, including El Niño-Southern Oscillation (ENSO). The reinforcement of Pacific and Atlantic western boundary currents aids the transport of warm saline water from low latitudes to higher latitudes. The results suggest that the river runoff can have potential impact on oceanic climate.
Response of Indian summer monsoon rainfall to global continental runoff is also examined. In the NoRiv run, average summer monsoon rainfall over India increased by ~ 0.55 mm day−1. Consistent with the increase in annual average Indian monsoon rainfall, all other northern hemispheric monsoon systems showed an increase, while southern hemispheric monsoons weakened. Associated with enhanced monsoon, the periodicity of ENSO in the NoRiv run changes as a result of cooling tendency in the equatorial Pacific, a sign of consistent La Niña. Equatorial Pacific cooling, in spite of a global ocean warming trend, is found to be primarily because of the enhanced local easterly winds and resultant strong equatorial upwelling. Cold anomaly due to upwelling spread entire equatorial Pacific basin within a span of 50 years. The La Niña situation in the Pacific favored increased monsoon rainfall over Indian subcontinent.
Another surprising result of this study is the strengthening of ENSO-monsoon relationship in the NoRiv run. This suggests that the river discharge can be considered as a dampening force in the ENSO-monsoon relationship. Northern hemisphere showed a clear warming in the NoRiv simulation compared to CTRL, the result of which is an enhanced trans-hemispheric gradient. Cross-equatorial winds triggered by this gradient blow from southern hemisphere and shift the Inter Tropical Convergence Zone (ITCZ) northward, increasing the precipitation in the northern hemisphere. The cooling in the eastern equatorial Indian Ocean and the warming in the west, reflected in the increase in number of positive Indian Ocean Dipole (IOD) events (9 positive and 5 negative IOD events in the last 50 years), also favored summer-time rainfall over India.
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Are you ready for a wet live-in? : explorations into listeningHolmstedt, Janna January 2017 (has links)
Listen. If I ask you to listen, what is it that I ask of you—that you will understand, or perhaps obey? Or is it some sort of readiness that is requested? What occurs with a body in the act of listening? How do sound and voice structure audio-visual-spatial relations in concrete situations? This doctoral thesis in fine arts consists of six artworks and an essay that documents the research process, or rather, acts as a travelogue as it stages and narrates a series of journeys into a predominantly sonic ecology. One entry into this field is offered by the animal “voice” and attempts to teach animals to speak human language. The first journey concerns a specific case where humanoid sounds were found to emanate from an unlikely source—the blowhole of a dolphin. Another point of entry is offered by the acousmatic voice, a voice split from its body, and more specifically, my encounter with the disembodied voice of Steve Buscemi in a prison in Philadelphia. This listening experience triggered a fascination with, and an inquiry into, the voices that exist alongside us, the parasitic relation that audio technology makes possible, and the way an accompanying voice changes one’s perceptions and even one’s behavior. In the case of both the animal and the acousmatic, the seemingly trivial act of attending to a voice quickly opens up a complex space of embodied entanglements with the potential to challenge much of what we take for granted. At the heart of my inquiry is a series of artworks made between 2012 and 2016, which constitute a third journey: the performance Limit-Cruisers (#1 Sphere), the praxis session Limit-Cruisers (#2 Crowd), the installations Therapy in Junkspace, Fluorescent You, and “Then, ere the bark above their shoulders grew,” and the lecture performance Articulations from the Orifice (The Dry and the Wet). The relationship between what is seen and heard is being explored and renegotiated in the arts and beyond. We are increasingly addressed by prerecorded and synthetic voices in both public and private spaces. Simultaneously, our notions of human communication are challenged and complicated by recent research in animal communication. My work attempts to address the shifts and complexities embodied in these developments. The three journeys are deeply entwined with theoretical inquiries into human-animal relationships, technology, and the philosophy of sound. In the essay, I consider as well how other artistic practices are exploring this same complex space. What I put forward is a materialist and concrete approach to listening understood as a situated practice. Listening is both a form of co-habitation and an ecology. In and through listening, I claim, one could be said to perform in concert with the things heard while at the same time being changed by them. / <p>Avhandlingen är även utgiven i serien: Malmö Faculty of Fine and Performing Arts, Lund University: DoctoralStudies and Research in Fine and Performing Arts, 16. ISSN: 1653-8617</p>
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Le statut juridique de l'eau à l'épreuve des exigences environnementales / Water's legal status proof against environmental issuesGudefin, Julia 09 December 2013 (has links)
Que l’on soit un simple promeneur ou un fin observateur, l’eau est présente partout. Pourtant, l’atout qu’elle représente pour les activités anthropiques cache souvent sa réalité environnementale, celle de son cycle. Ce constat se reflète dans l’appréhension juridique de l’eau laquelle est conçue comme un bien ou une chose. Cette qualification l’assigne donc à un statut juridique dont les manifestations révèlent la fonction utilitariste de la ressource. Or, l’émergence des problématiques environnementales confronte le statut juridique de l’eau à sa réalité physique. Ainsi, le droit et les exigences environnementales s’influencent réciproquement pour générer des règles protectrices de l’eau et des représentations juridiques du cycle hydrologique qui engendrent des évolutions du statut. Dès lors, ce dernier s’émancipe des catégories juridiques traditionnelles issues du droit des biens et s’habille d’une finalité protectrice dont les règles et les concepts, qui s’attachent à la fonction écologique de l’eau et à la réalité environnementale du cycle hydrologique, lui façonnent une autre condition juridique. / Along a simple stroll or through fine observations, you will always find water, wherever you go. However, the asset this resource represents for anthropogenic activities often hides its environmental reality, the one of its cycle. This is reflected in the legal definition of water which conceives it as property. This latter qualification assigns it to a judicial status which reveals the utilitarian function of the resource. Yet, the emergence of the environmental issues confronts water’s legal status to its tangible reality. Thus, the conflict between the law and water’s environmental demands makes way for protective regulations. Along with the hydrologic cycle’s legal representation, they both influence the evolution of water’s status. Consequently, the latter goes beyond property law traditional legal categories and arms itself with a protective purpose. Its rules and concepts are tied to the ecological function of water and to the environmental reality of the hydrologic cycle which shape yet another judicial condition for the water.
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"Nedskräpning förbjuden" : Elever på mellanstadiet resonerar kring nedskräpning, källsortering och föroreningar / “Littering prohibited” : Middle-school pupils reason about littering, waste sorting and pollutions.Melin, Daniéla January 2019 (has links)
Syftet med denna kvalitativa studie är att genom fokusgruppintervjuer undersöka vad elever i årskurserna 5-6 kan och resonerar om begreppen källsortering, nedskräpning och miljöförstöring Studien tar upp hur hållbar utveckling är upplagt i läroplanens inledande delar och kursplaner, hur de tre dimensionerna av hållbarhet definieras samt tidigare forskning inom ämnet. I det resultat som visualiseras framkom det hur 20 elever på en Grön Flaggskola och en icke Grön Flaggskola ser på nedskräpning och källsortering. Undersökningens resultat indikerar att eleverna är väl insatta i dagens miljöproblem och de vet hur de ska motverka dessa. Anmärkningsvärt visade eleverna på Grön Flaggskolan inte mer kunskap om till exempel hållbarhet. Dock påvisas det att majoriteten av eleverna på båda skolorna innehar en nonchalant inställning till problemen, lägger dessa på andra individer och skjuter problemen framför sig. I studien framförs slutligen en diskussion om införandet av ett nytt ämne i läroplanen, vem som bär ansvaret och hur lärarna kan engagera sina elever att arbeta för en bättre planet. / The purpose of this qualitative study is, through focus group interviews investigate what pupils in grades 5-6 can and reason about waste sorting, littering and pollutions. The study examines how sustainable development is presented in the curriculum's introductory parts and curricula, how the three dimensions of sustainability are defined and previous research within the subject. The result that emerged visualizes how 20 pupils at an Eco-School and a non-Eco-school look at littering and sorting waste. The results of the survey indicate that the pupils are well acquainted with today's environmental problems, and they know how to counteract with these. The pupils on the Eco School did remarkably not show more knowledge about for example sustainability. However, it is demonstrated that the majority of the pupils at both schools hold a nonchalant approach to the problems, place these on other individuals and postpone the problems before them. Finally, the study discusses the introduction of a new topic in the curriculum, who carries the responsibility and how the teachers can engage their students to work for a better planet.
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