Dissertations / Theses: 'Forcing of climate'

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Liebrand, Diederik. "Astronomical climate forcing during the Oligo-Miocene." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/374831/.

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In this thesis newly generated high-resolution Oligo-Miocene climate proxy records from Walvis Ridge ODP Site 1264 (south-eastern Atlantic Ocean) are presented (Chapters 2 and 3). The records are tuned to an eccentricity solution (Chapter 3) and they are compared to published Atlantic and Pacific palaeoclimate chronologies (Chapters 2 and 4). The main research objectives are 1) to identify astronomical pacemakers of global significance and test earlier pacing theories, 2) to describe global climate and oceanographic change on astronomical and tectonic time scales and 3) to test the strong hysteresis in ice sheet models that suggest a very stable Antarctic ice sheet once formed. Chapter 1 gives a general introduction on the “mid”-to-late Oligocene climatic, oceanographic, geographic and cryospheric settings. Climate evolution and dynamics, together with the major underlying processes are introduced. In Chapter 2, high-resolution early Miocene stable oxygen and carbon isotope chronologies from Walvis Ridge Site 1264 are presented. The data are analysed on an untuned age model to identify the principal astronomical pacemakers, without introducing power on orbital frequencies. A dominance of variance in all datasets on 100-kyr timescales is found. The δ18O data are used to parameterize a suite of 1D ice sheet models and show that between 20 – 80% (avg. ~50%) of the δ18O signal can be explained by changes in Antarctic ice volume. (This chapter has been published as: D. Liebrand, L. J. Lourens, D. A. Hodell, B. de Boer, R. S. W. van de Wal and H. Pälike. Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene. Climate of the Past, 7, 869–880, 2011) In Chapter 3, extended stable-isotope records together with X-ray fluorescence core scanning data from Walvis Ridge Site 1264 are presented. The records span an 11-Myr mid Oligocene through early Miocene time interval. Ages are calibrated to eccentricity, are in good agreement with the GTS2012 and independently confirm the Oligo-Miocene time scale to the ~100-kyr level. The ~2.4-Myr long-period eccentricity cycle is identified as the main pacemaker of Oligo-Miocene climate events, as identified in the benthic isotope records, at shorter astronomical (eccentricity) periodicities. In Chapter 4, the high-resolution Oligo-Miocene benthic stable-isotope chronology from Site 1264 is compared to published records from the Atlantic and Pacific to further identify and explore possible global climate pacemakers. In addition, an investigation of long-term trends and inter-/intra-basin isotopic gradients and their implications for ice volume reconstruction and palaeoceanographic studies are discussed. Methods are explored to quantify the apparent change in geometry of ~100-kyr cycles in our benthic δ18O data and the analyses indicate an increased cycle asymmetry (i.e. sawtooth patterns) throughout the Oligo-Miocene. This change in cycle geometry is interpreted as a measure of changing boundary conditions and used to track the evolution of a threshold response mechanism in Earth’s climate system. In Chapter 5 the main results of this thesis are summarised, the implications for our understanding of the Oligo-Miocene are discussed and perspectives are given on future work.

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Miller, William David. "Climate forcing of phytoplankton dynamics in Chesapeake Bay." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3705.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Marine-Estuarine-Environmental Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Andrews, Timothy. "A surface perspective on radiative forcing of climate." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531644.

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Mousavi, Zahra. "Radiative forcing, climate change and global hydrological cycle." Thesis, University of Reading, 2017. http://centaur.reading.ac.uk/75277/.

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Anthropogenic emissions of greenhouse gases and aerosols have led to climate change including changes in surface temperature and precipitation. The surface temperature response is better understood than the precipitation response as a result of observed data availability and the complexity of the physics governing hydrological cycle changes. The complex general climate models (GeMs) are computationally demanding and include many physical processes that contribute to the changing water cycle. It remains necessary to understand the main drivers of this change. In this thesis, the main aim is to understand the water cycle changes by examining the degree to which simple models can simulate global-average results emerging from GeMs. For this purpose, a simple atmospheric energy budget model is used to calculate the global mean precipitation changes for the historical period and future scenarios. The results are then compared with GeMs to understand the physical processes affecting the global precipitation changes. The original form of the simple atmospheric energy budget model does not take into account many different factors included in GeMs, such as regional temperature and precipitation changes, fast surface sensible heat flux changes, fast precipitation response of volcanic aerosols and inter-annual variability. This work examines whether it is possible to extend the simple model to include some of these factors or compare the idealised experiments with the results of complex models (Wu et al. 2010). The simple model does well in producing the total global precipitation anomalies compared with GeMs multi-model mean consistent with earlier studies. The results of the simple model for individual GeMs are in less good agreement and different reasons for this disagreement have been investigated. Substituting the temperature changes from each GeM and also normalising the radiative forcings of simple model to the adjusted GeM RFs lead to an increase in compatibility between the simple model and GeMs, indicating that the main differences are related to the temperature equation and RFs. Adding the fast response of volcanic aerosols also increased the correlation between the simple model and GeMs particularly in volcanic years. Using new results from (Precipitation Driver Response Model Intercomparison Project) PDRMIP, the effect of fast surface sensible heat changes has been investigated which shows a considerable contribution to atmospheric energy budget changes particularly for aerosols. The simple model has been modified by adding the fast sensible heat changes which leads to a small improvement in the simple model; however it is not possible to be certain how robust this improvement is. More data and more work is still required but generally it is concluded that the simple model performs well compared with complex models.

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Ma, Xiaoyan, Fangqun Yu, and Johannes Quaas. "Reassessment of satellite-based estimate of aerosol climate forcing." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177222.

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Large uncertainties exist in estimations of aerosol direct radiative forcing and indirect radiative forcing, and the values derived from globalmodeling differ substantially with satellite-based calculations. Following the approach of Quaas et al. (2008; hereafter named Quaas2008),we reassess satellite-based clear- and cloudy-sky radiative forcings and their seasonal variations by employing updated satellite products from 2004 to 2011 in combination with the anthropogenic aerosol optical depth (AOD) fraction obtained frommodel simulations using the Goddard Earth Observing System-Chemistry-Advanced ParticleMicrophysics (GEOS-Chem-APM). Our derived annual mean aerosol clear-sky forcing (-0.59 W m-2) is lower, while the cloudy-sky forcing (-0.34 W m-2) is higher than the corresponding results (-0.9Wm-2 and -0.2W m-2, respectively) reported in Quaas2008. Our study indicates that the derived forcings are sensitive to the anthropogenic AOD fraction and its spatial distribution but insensitive to the temporal resolution used to obtain the regression coefficients, i.e.,monthly or seasonal based. The forcing efficiency (i.e., the magnitude per anthropogenic AOD) for the clear-sky forcing based on this study is 19.9Wm-2, which is about 5% smaller than Quaas2008’s value of 21.1Wm-2. In contrast, the efficiency for the cloudy-sky forcing of this study (11 W m-2) is more than a factor of 2 larger than Quaas2008’s value of 4.7 W m-2. Uncertainties tests indicate that anthropogenic fraction of AOD strongly affects the computed forcings while using aerosol index instead of AOD from satellite data as aerosol proxy does not appear to cause any significant differences in regression slopes and derived forcings.

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Ma, Xiaoyan, Fangqun Yu, and Johannes Quaas. "Reassessment of satellite-based estimate of aerosol climate forcing." Wiley, 2014. https://ul.qucosa.de/id/qucosa%3A13449.

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Large uncertainties exist in estimations of aerosol direct radiative forcing and indirect radiative forcing, and the values derived from globalmodeling differ substantially with satellite-based calculations. Following the approach of Quaas et al. (2008; hereafter named Quaas2008),we reassess satellite-based clear- and cloudy-sky radiative forcings and their seasonal variations by employing updated satellite products from 2004 to 2011 in combination with the anthropogenic aerosol optical depth (AOD) fraction obtained frommodel simulations using the Goddard Earth Observing System-Chemistry-Advanced ParticleMicrophysics (GEOS-Chem-APM). Our derived annual mean aerosol clear-sky forcing (-0.59 W m-2) is lower, while the cloudy-sky forcing (-0.34 W m-2) is higher than the corresponding results (-0.9Wm-2 and -0.2W m-2, respectively) reported in Quaas2008. Our study indicates that the derived forcings are sensitive to the anthropogenic AOD fraction and its spatial distribution but insensitive to the temporal resolution used to obtain the regression coefficients, i.e.,monthly or seasonal based. The forcing efficiency (i.e., the magnitude per anthropogenic AOD) for the clear-sky forcing based on this study is 19.9Wm-2, which is about 5% smaller than Quaas2008’s value of 21.1Wm-2. In contrast, the efficiency for the cloudy-sky forcing of this study (11 W m-2) is more than a factor of 2 larger than Quaas2008’s value of 4.7 W m-2. Uncertainties tests indicate that anthropogenic fraction of AOD strongly affects the computed forcings while using aerosol index instead of AOD from satellite data as aerosol proxy does not appear to cause any significant differences in regression slopes and derived forcings.

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Richardson, Glen. "Climate response to fresh water forcing in the Southern Ocean." Thesis, University of East Anglia, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432442.

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Shannon, Debbie Anne. "Land surface response to climate change forcing over Southern Africa." Doctoral thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/5286.

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The land surface is important to the climate system for the exchanges of moisture, momentum and heat. Momentum, radiation, and sensible and latent heat fluxes between the atmosphere and the surface will likely affect atmospheric dynamics, temperature, precipitation and humidity fields (Sato et ai., 1989). These may subsequently feed back into the land surface processes as part of a cyclical system. Therefore it is evident that our livelihood is largely dependent on interactions and exchanges between the land surface and climate system (Henderson-Sellers et ai., 1993) and it is thus essential that we gain a better understanding of the interactive sensitivity. This is of particular relevance in the context of the portended future global climate change. In the present study the interactions between the land surface and the atmosphere are considered over the southern African region. This region has a climate showing a high degree of spatial and temporal variability, most notably with rainfall. Regional climates are characterised by summer, winter and all-year-round rainfall. There are steep vegetation gradients and a wide range of vegetation types adapted to suit the variable climate. These factors, combined with the societal implications of changes in the climate and land surface systems, make southern Africa a challenging and important study domain for examining the sensitivity between the different elements of the atmosphere and biosphere. This research makes use of a biosphere model driven by climate change data derived from a general circulation model (GCM). Regions susceptible and sensitive to changes on an annual and seasonal basis are identified and examined. The thesis comprises 8 chapters. The first chapter, Chapter 1, provides some background information on climate change, biosphereatmosphere interactions, GCMs and transient simulations, vegetation models and vegetation representation over southern Africa. This chapter also sets out the research objectives. The following chapter, Chapter 2, introduces the atmospheric GCM model data from the Hadley Centre Model (HadCM2) used in the analysis. The chapter additionally provides a detailed description of the biosphere model, the Integrated Biosphere Simulator (IBIS). Chapter 3 examines the Hadley Centre HadCM2 GCM input data used in driving the biosphere model, while Chapter 4 presents the input forcing data and configuration of the IBIS model. In Chapter 5 the results of the IBIS model simulation are examined on the annual scale and in Chapter 6 the results are examined on the seasonal scale. Some of the implications of climate change are considered in Chapter 7. This chapter also places the HadCM2 GCM model data used in driving IBIS into the context of the latest emissions scenarios. In the final chapter, Chapter 8, an overview summary is provided and conclusions are drawn.

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McFadden, Ellyn M. "Controls on West Greenland Outlet Glacier Sensitivity to Climate Forcing." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1267209212.

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Chung, Serena Hsin-Yi Seinfeld John H. Seinfeld John H. "Global distribution, radiative forcing, and climate impact of carbonaceous aerosols /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-02012005-131605.

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11

Christidis, Nikolaos. "Halocarbon radiative forcing in radiation and general circulation models." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312563.

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Harley, Mitchell Dean Civil &amp Environmental Engineering Faculty of Engineering UNSW. "Daily to decadal embayed beach response to wave and climate forcing." Publisher:University of New South Wales. Civil & Environmental Engineering, 2009. http://handle.unsw.edu.au/1959.4/44391.

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A multi-decadal survey program undertaken at the Collaroy-Narrabeen embayment in SE Australia identifies medium-term (~2-7 year) cycles of both erosion and accretion across the entire embayment ('beach oscillation') and at its two extremities ('beach rotation'). These cycles have been observed to respond to phase shifts in the El Ni??o/Southern Oscillation (ENSO). To investigate wave and climate controls of embayment variability in finer detail, this study combines historical surveys with 45 years of wave data from the ERA-40 reanalysis and four years of high-resolution beach measurements using RTK-GPS and image-derived survey techniques. ENSO and Southern Annular Mode (SAM) controls of wave variability in the Sydney region are first explored. In general, wave heights increase/decrease and wave directions become more easterly/southerly during La Ni??a/El Ni??o phases. A positive correlation is observed between the SAM and summer wave heights, and a negative correlation between the SAM and winter wave directions. Storm variability is observed to be modified by the ENSO, but not the SAM. In particular, La Ni??a phases are generally associated with longer duration, higher energy events from a more easterly direction when compared to those during El Ni??o phases. Wave controls of embayment variability are subsequently investigated. In the short-term (days - months), beach oscillation/rotation is observed to be the most dominant process, accounting for approx. 60%/20% of overall embayment variability. Beach oscillation is related to changes in wave height and storms, whereas beach rotation is related to changes in wave direction and/or wave period. An empirical model that estimates the beach response to individual storm events is developed. In the longer-term (months - years), beach rotation is observed to respond to both wave heights and directions. Larger waves are sheltered somewhat at the southern end, creating an apparent clockwise rotation under energetic wave conditions. Clockwise/anticlockwise rotations are also observed to follow southerly/easterly wave shifts at lags of up to 12 months. Comparisons between the ENSO and beach oscillation/rotation agree with previous observations that El Ni??o/La Ni??a phases are associated with an overall accretion/erosion and clockwise/anticlockwise rotation of the embayment. In general, the SAM shows little influence on embayment variability. While it is clear that beach oscillation is driven by cross-shore processes, to what extent beach rotation is a longshore and/or cross-shore phenomena requires further investigation.

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Wang, Qiaoqiao. "Global budget of black carbon aerosol and implications for climate forcing." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11237.

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This thesis explores the factors controlling the distribution of black carbon (BC) in the atmosphere/troposphere and its implications for climate forcing. BC is of great climate interest because of its warming potential. Estimates of BC climate forcing have large uncertainty, in part due to poor knowledge of the distribution of BC in the atmosphere. This dissertation first examines the factors controlling the sources of BC in the Arctic in winter and spring using a global chemical transport model (GEOS-Chem). Emission inventories of BC and wet scavenging of aerosols in the model are updated to reproduce observed atmospheric concentrations of BC as well as observed snow BC content in the Arctic in winter-spring. The simulation shows a dominant contribution of fuel (fossil fuel and biofuel) combustion to BC in Arctic spring. Arctic snow BC content is dominated by fuel combustion sources in winter, but has equal contributions from open fires and fuel combustion in spring. The estimated decrease in Arctic snow albedo due to BC deposition in spring is 0.6%, resulting in a regional surface radiative forcing of 1.2 W m-2. The dissertation then extends the evaluation of the BC simulation to the global scale using aircraft observations over source regions, continental outflow and remote regions and ground-based measurements. The observed low BC concentrations over the remote oceans imply more efficient BC removal than is currently implemented in models. The simulation that has total BC emissions of 6.5 Tg C a-1 and a mean tropospheric lifetime of 4.2 days for 2009 (vs. 6.8 ± 1.8 days for the AeroCom models) captures the principal features of observed BC. The simulation estimates a global mean BC absorbing aerosol optical depth of 0.0017 and a top-of-atmosphere direct radiative forcing (DRF) of 0.19 W m-2, with a range of 0.17-0.31 W m-2 based on uncertainties in the BC atmospheric distribution. The DRF is lower than previous estimates, which could be biased high because of excessive BC concentrations over the oceans and in the free troposphere.
Engineering and Applied Sciences

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Quaas, Johannes, Olivier Boucher, Nicolas Bellouin, and Stefan Kinne. "Satellite-based estimate of the direct and indirect aerosol climate forcing." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-177289.

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The main uncertainty in anthropogenic forcing of the Earth’s climate stems from pollution aerosols, particularly their ‘‘indirect effect’’ whereby aerosols modify cloud properties. We develop a new methodology to derive a measurement-based estimate using almost exclusively information from an Earth radiation budget instrument (CERES) and a radiometer (MODIS). We derive a statistical relationship between planetary albedo and cloud properties, and, further, between the cloud properties and column aerosol concentration. Combining these relationships with a data set of satellite-derived anthropogenic aerosol fraction, we estimate an anthropogenic radiative forcing of -0.9 ± 0.4 Wm-2 for the aerosol direct effect and of -0.2 ± 0.1 Wm-2 for the cloud albedo effect. Because of uncertainties in both satellite data and the method, the uncertainty of this result is likely larger than the values given here which correspond only to the quantifiable error estimates. The results nevertheless indicate that current global climate models may overestimate the cloud albedo effect.

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Ackerley, Duncan. "Uncertainties in the climate response to sulphate aerosol and CO2 forcing." Thesis, University of Reading, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440091.

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Quaas, Johannes, Olivier Boucher, Nicolas Bellouin, and Stefan Kinne. "Satellite-based estimate of the direct and indirect aerosol climate forcing." Wiley, 2008. https://ul.qucosa.de/id/qucosa%3A13453.

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The main uncertainty in anthropogenic forcing of the Earth’s climate stems from pollution aerosols, particularly their ‘‘indirect effect’’ whereby aerosols modify cloud properties. We develop a new methodology to derive a measurement-based estimate using almost exclusively information from an Earth radiation budget instrument (CERES) and a radiometer (MODIS). We derive a statistical relationship between planetary albedo and cloud properties, and, further, between the cloud properties and column aerosol concentration. Combining these relationships with a data set of satellite-derived anthropogenic aerosol fraction, we estimate an anthropogenic radiative forcing of -0.9 ± 0.4 Wm-2 for the aerosol direct effect and of -0.2 ± 0.1 Wm-2 for the cloud albedo effect. Because of uncertainties in both satellite data and the method, the uncertainty of this result is likely larger than the values given here which correspond only to the quantifiable error estimates. The results nevertheless indicate that current global climate models may overestimate the cloud albedo effect.

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Wong, Lawrence Man Kit. "Climate impact of aviation NOx̳ emissions : radiative forcing, temperature, and temporal heterogeneity." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93802.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.
In title on title page, double underscored "x" appears as subscript. Cataloged from PDF version of thesis.
Includes bibliographical references (pages 47-49).
Aviation NOx emissions are byproducts of combustion in the presence of molecular nitrogen. In the upper troposphere, NOx emissions result in the formation of O₃ but also reduce the lifetime of CH4 , causing an indirect reduction in the formation of O₃. Meta studies by Lee et al. and Prather et al. concluded that the short-lived O₃ radiative forcing (RF) was greater than the combined long-lived CH₄ and O₃ RFs, leading to a net positive RF (4.5 to 14.3 mW/m² per Tg of NOx emissions). However, few simulations assess the surface air temperature (SAT) response, or conduct a large ensemble simulation with climate feedback in the cases where SAT is predicted. We aim to quantify the climate forcing and temperature response of aviation NOx emissions. Eight 400-member ensemble simulations are conducted with an earth system model of intermediate complexity. Inter-scenario comparisons between emissions starting in 1991, 2016 and 2036 with mid-range and high anthropogenic emissions are performed. We then determine the existence of long-term temporal heterogeneity of climate forcing and impact. The global net RF of an aviation NO, emissions inventory is positive from 1991 to 2100 while leading to a global average SAT responses of -0.068 K in 2100. Despite the positive zonal RF in the Northern Hemisphere of up to 413.9 mW/m² at 45°N, all latitudes experience cooling after 2075. In another scenario, constant aviation NOx emissions at 4.1 Tg/year cause a global net RF of near zero while leading to a SAT response of -0.020 K in 2100. The unexpected temperature behavior in both scenarios is attributed to the forcing from CH₄ destruction being 64% more effective in generating a SAT response than the O₃ forcing. Despite the positive net RF, the probability of aviation NOx emissions being cooling is 67% because of the relative difference in O₃ and CH₄ efficacies.
by Lawrence Man Kit Wong.
S.M.

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Geach, Martin Roy. "Landscape forcing mechanisms on Quaternary timescales : the Tabernas Basin, SE Spain." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3357.

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Quaternary landform features and their associated sedimentary assemblages (river terraces and alluvial fans) often provide important records of long-term landscape evolution. The reconstruction of global terrace sequences has enabled the identification of numerous external and internal forcing mechanisms which operate within the Quaternary landscape system. The relative effects of these forcing mechanisms are highly variable over a range of spatial and temporal scales. In this research, a combined study approach is adopted in order to ascertain the significance of external (e.g. tectonics, climate) and/or internal (e.g. lithological thresholds) forcing mechanisms upon patterns of Quaternary landscape development within the Tabernas Basin, SE Spain. The results of extensive field investigation have developed a four-tiered landform stratigraphy (i.e. basin wide terrace levels) for the Tabernas Basin. Chronological constraints for the Quaternary stratigraphy were obtained from Optically Stimulated Luminescence dating. Age estimations develop a pattern of climatically driven terrace aggradations during glacial phases throughout the Middle to Late Pleistocene. This pattern fits well with regional models of enhanced terrace formation during glacial phases after the Middle Pleistocene. The Quaternary stratigraphy of the Tabernas Basin was investigated by methods of geospatial interpolation and numerical modelling. The results of conceptual and quantitative modelling approaches highlight the dominance of non-uniform rates of base-level change driven by variable rates of tectonic uplift throughout the Mid-Late Pleistocene. Enhanced uplift in the west of the basin associates well with regional patterns, with tectonically driven base-level changes focused in the eastern Alpujarran Corridor. Internal landscape thresholds were important in the Holocene development of the Tabernas basin. Increased rates of incision in the final stages of basin development were likely attributed to the effects of lithological controls coupled with anthropogenic activity in the basin catchment.

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Brandefelt, Jenny. "Atmospheric circulation regimes and climate change." Doctoral thesis, Stockholm : Dept. of Meteorology, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-530.

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Cherian, Ribu, Johannes Quaas, Marc Salzmann, and Martin Wild. "Pollution trends over Europe constrain global aerosol forcing as simulated by climate models." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-176389.

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An increasing trend in surface solar radiation (solar brightening) has been observed over Europe since the 1990s, linked to economic developments and air pollution regulations and their direct as well as cloud-mediated effects on radiation. Here, we find that the all-sky solar brightening trend (1990–2005) over Europe from seven out of eight models (historical simulations in the Fifth Coupled Model Intercomparison Project) scales well with the regional and global mean effective forcing by anthropogenic aerosols (idealized “present-day” minus “preindustrial” runs). The reason for this relationship is that models that simulate stronger forcing efficiencies and stronger radiative effects by aerosol-cloud interactions show both a stronger aerosol forcing and a stronger solar brightening. The all-sky solar brightening is the observable from measurements (4.06 ± 0.60Wm−2 decade−1), which then allows to infer a global mean total aerosol effective forcing at about −1.30Wm−2 with standard deviation ±0.40Wm−2.

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Cherian, Ribu, Johannes Quaas, Marc Salzmann, and Martin Wild. "Pollution trends over Europe constrain global aerosol forcing as simulated by climate models." Wiley, 2014. https://ul.qucosa.de/id/qucosa%3A13436.

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An increasing trend in surface solar radiation (solar brightening) has been observed over Europe since the 1990s, linked to economic developments and air pollution regulations and their direct as well as cloud-mediated effects on radiation. Here, we find that the all-sky solar brightening trend (1990–2005) over Europe from seven out of eight models (historical simulations in the Fifth Coupled Model Intercomparison Project) scales well with the regional and global mean effective forcing by anthropogenic aerosols (idealized “present-day” minus “preindustrial” runs). The reason for this relationship is that models that simulate stronger forcing efficiencies and stronger radiative effects by aerosol-cloud interactions show both a stronger aerosol forcing and a stronger solar brightening. The all-sky solar brightening is the observable from measurements (4.06 ± 0.60Wm−2 decade−1), which then allows to infer a global mean total aerosol effective forcing at about −1.30Wm−2 with standard deviation ±0.40Wm−2.

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Paulis, Victor. "THE RESPONSE OF A GENERAL CIRCULATION CLIMATE MODEL TOHIGH LATITUDE FRESHWATER FORCING IN THE ATLANTIC BASINWITH RESPECT TOTROPI." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3848.

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The current cycle of climate change along with increases in hurricane activity, changing precipitation patterns, glacial melt, and other extremes of weather has led to interest and research into the global correlation or teleconnection between these events. Examination of historical climate records, proxies and observations is leading to formulation of hypotheses of climate dynamics with modeling and simulation being used to test these hypotheses as well as making projections. Ocean currents are believed to be an important factor in climate change with thermohaline circulation (THC) fluctuations being implicated in past cycles of abrupt change. Freshwater water discharge into high-latitude oceans attributed to changing precipitation patterns and glacial melt, particularly the North Atlantic, has also been associated with historical abrupt climate changes and is believed to have inhibited or shut down the THC overturning mechanism by diluting saline surface waters transported from the tropics. Here we analyze outputs of general circulation model (GCM) simulations parameterized by different levels of freshwater flux (no flux (control), 0.1 Sverdrup (Sv) and 1.0 Sv) with respect to tropical cyclone-like vortices (TCLVs) to determine any trend in simulated tropical storm frequency, duration, and location relative to flux level, as well as considering the applicability of using GCMs for tropical weather research. Increasing flux levels produced fewer storms and storm days, increased storm duration, a southerly and westerly shift (more pronounced for the 0.1 Sv level) in geographic distribution and increased activity near the African coast (more pronounced for the 1.0 Sv level). Storm intensities and tracks were not realistic compared to observational (real-life) values and is attributed to the GCM resolution not being fine enough to realistically simulate storm (microscale) dynamics.
Ph.D.
Other
Sciences
Modeling and Simulation PhD

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YU, SHAOCAI. "A STUDY OF DIRECT AND CLOUD-MEDIATED RADIATIVE FORCING OF CLIMATE DUE TO AEROSOLS." NCSU, 1999. http://www.lib.ncsu.edu/theses/available/etd-19990924-062253.

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The Intergovernmental Panel on Climate Change (IPCC) has reported that in the southeastern US and eastern China, the general greenhouse warming due to anthropogenic gaseous emissions is dominated by the cooling effect of anthropogenic aerosols. To verify this model prediction in eastern China and southeastern US, we analyzed regional patterns of climate changes at 72 stations in eastern China during 1951-94 (44 years), and at 52 stations in the southeastern US during 1949-94 (46 years) to detect the fingerprint of aerosol radiative forcing. It was found that the mean rates of change of annual mean daily, maximum, minimum temperatures and diurnal temperature range (DTR) in eastern China were 0.8, -0.2, 1.8, and -2.0 C/100 years respectively, while the mean rates of change of annual mean daily, maximum, minimum temperatures and DTR in the southeastern US were -0.2, -0.6, 0.2, and -0.8 C/100 years, respectively. This indicates that the high rate of increase in annual mean minimum temperature in eastern China results in a slightly warming trend of daily temperature, while the high rate of decrease in annual mean maximum temperature and low rate of increase in annual mean minimum temperature lead to the cooling trend of daily temperature in the southeastern US. We found that the warming from the longwave forcing due to both greenhouse gases and aerosols was completely counteracted by the shortwave aerosol forcing in the southeastern US in the past 46 years. A slightly overall warming trend in eastern China is evident; winters have become milder. This finding is explained by hypothesizing that increasing energy usage during the past 44 years has resulted in more coal and biomass burning, thus increasing the emission of absorbing soot and organic aerosols in eastern China. Such emissions, in addition to well-known Asia dust and greenhouse gases, may be responsible for the winter warming trend in eastern China that we have reported here.The sensitivity of aerosol radiative properties to aerosol composition, size distribution, relative humidity (RH) is examined for the following aerosol systems: inorganic and organic ions (Cl-, Br-, NO3-, SO42-, Na+, NH4+, K+, Ca2+, Mg2+, HCOO-, CH3COO-, CH3CH2COO-, CH3COCOO-, OOCCOO2-, MSA-1); water-insoluble inorganic and organic compounds (elemental carbon, n-alkanes, SiO2, Al2O3, Fe2O3 and other organic compounds). The partial molar refraction method was used to calculate the real part of the refractive index. It was found that the asymmetry factor increased by ~48% with the real part varying from 1.40 to 1.65, and the single scattering albedo decreased by 24% with the imaginary part varying from -0.005 to -0.1. The asymmetry factor increased by 5.4 times with the geometric standard deviation varying from 1.2 to 3.0. The radiation transmission is very sensitive to the change in size distribution; other factors are not as significant.To determine the aerosol direct radiative forcing (ADRF), the aerosol optical depth (AOD) values at the three operational wavelengths (415, 500 and 673 nm) were determined at a regionally representative site, namely, Mt. Gibbs (35.780 N, 82.290 W, elevation 2006 m) in Mt. Mitchell State Park, NC, and a site located in an adjacent valley (Black Mountain, 35.660 N, 82.380 W, elevation 951 m) in the southeastern US. The two sites are separated horizontally by 10 km and vertically by 1 km. It was found that the representative total AOD values at 500 nm at the valley site for highly polluted (HP), marine (M) and continental (C) air masses were 0.68+/-0.33, 0.29+/-0.19 and 0.10+/-0.04, respectively. A search-graph method was used to retrieve the columnar size distribution (number concentration N, effective radius reff and geometric standard deviation sg) from the optical depth observations at three operational wavelengths. The ground albedo, single scattering albedo and imaginary part of the refractive index were calculated using a mathematically unique procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, AOD, and diffuse-direct irradiance ratio. It was found that N, reff and sg were in the ranges of 10 to 1.7x104 cm-3, 0.09 to 0.68 mm and 1.12 to 2.95, respectively. The asymmetry factor and single scattering albedo were in the ranges of 0.63 to 0.75 and 0.74 to 0.97 respectively. The ground albedo for the forested terrain and imaginary part of refractive index were found to be in the ranges of 0.06 to 0.29 and 0.005 to 0.051 respectively. On the basis of these aerosol radiative properties obtained at the research sites and computations using the Column Radiation Model (CRM) of National Center of Atmospheric Research (NCAR) Community Climate Model (CCM3), it was found that the average cloud-free 24-hour ADRF values were -13+/-8, -8+/3, -33+/-16 W m-2 for marine, continental, and polluted air masses, respectively. On the assumption that the fractional coverage of clouds is 0.61, it was estimated that the annual mean ADRF was 7+/-2 W m-2 in the southeastern US.The review with respect to the current knowledge of organic acids shows that aerosol formate and acetate concentrations range from 0.02 to 5.3 nmol/m3 and from 0.03 to 12.4 nmol/m3 respectively, and that between 34% to 77% of formate and between 21% to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98-99%) of these volatile organic acids were present in the gas phase, their concentrations in the aerosol particles were sufficient to make them a good candidate for cloud condensation nuclei (CCN). It is hypothesized that organic acids are at least one of the primary sources of CCN in the atmosphere due to their ubiquitous presence in the troposphere, especially over the continental forested areas. The results of our measurements at Palmer Station, Antarctica show that the daily average CCN concentrations at 0.3% and 1% supersaturations ranged from 0.3 to 160 cm-3 and from 4 to 168 cm-3, respectively, during the period from 17 January to 26 February, 1994. New evidence for substantial and definitive CCN enhancement near and within cloud has been observed at Mt. Mitchell, North Carolina. The results show that the average monthly CCN concentrations were 460+/-217, 386+/-286, 429+/-228 and 238+/-134 cm-3 for in-cloud, overcast, clear and rainy conditions, respectively. The typical CCN spectra show that there were a lot of small CCN produced and the ion concentrations (especially H+ and SO42-) were very high during the CCN enhancement period. The significantly positive correlation between black carbon (BC) and CCN at 1% supersaturation indicates that a percentage of the BC measured at the site may be in the form of an internal mixture and participated in the formation of CCN.

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Marín, Saul. "The response of precipitation and surface hydrology to tropical macro-climate forcing in Colombia." Access citation, abstract and download form; downloadable file 15.62 Mb, 2004. http://wwwlib.umi.com/dissertations/fullcit/3131688.

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Mantsis, Damianos F. "Atmospheric Response to Orbital Forcing and 20th Century Sea Surface Temperatures." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/597.

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This study investigates modes of atmospheric variability in response to changes in Earth's orbit and changes in 20th century sea surface temperatures (SST). The orbital forcing is manifested by a change in obliquity and precession, and changes the distribution of the top-of-atmosphere insolation. A smaller obliquity reduces the the annual insolation that the poles receive and increases the annual insolation in the tropics. As the meridional insolation gradient increases, the zonal mean atmospheric-ocean circulation increases. The resulting climate also has a reduced global mean temperature due to the effect of climate feedbacks. This cooling can be attributed to a reduced lapse rate, increased cloud fraction. reduced water vapor in the atmosphere, and an increase in the surface albedo. A change in the precession, as the perihelion shifts from the winter to the summer solstice, causes a strengthening as well as an expansion of the N. Pacific summer subtropical anticyclone. This anticyclonic anomaly can be attributed to the weakening of the baroclinic activity, but also represents the circulation response to remote and local diabatic heating. The remote diabatic heating is associated with monsoonal activity in the SE Asia and North Africa. Regarding the 20th century SST forcing, it is represented by a multidecadal variability in the inter-hemispheric SST difference. This change in the SST causes a latitudinal shift in the ascending branch of the Hadley cell and precipitation in the tropics, as well as an increase in the atmospheric meridional heat transport from the warmer to the colder hemisphere.

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Lohmann, Ulrike, Leon Rotstayn, Trude Storelvmo, Andrew Jones, Surabi Menon, Johannes Quaas, Annica M. L. Ekman, Dorothy Koch, and Reto A. Ruedy. "Total aerosol effect: radiative forcing or radiative flux perturbation?" Copernicus Publications, 2010. https://ul.qucosa.de/id/qucosa%3A13832.

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Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of precipitation formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to define properly. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

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Kapur, Atul. "Role of Stochastic Forcing in ENSO Variability in a Coupled GCM." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/168.

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A systematic procedure is designed to evaluate the role of stochastic forcing (SF) in El Nino ? Southern Oscillation (ENSO) exhibited by coupled ocean-atmosphere general circulation models (CGCMs). The procedure is applied on a 163-year run of a CGCM which has realistic representation of ENSO and SF. The realism of ENSO in the CGCM is determined by statistical comparison with a 29-year global reanalysis product. SF is extracted from both the CGCM and reanalysis as residual atmospheric variability uncoupled to the ocean. Further, the Madden-Julian Oscillation (MJO) and non-MJO components are isolated from SF. The CGCM stochastic components are compared to those from the reanalysis to validate their representation. A coupled ocean-atmosphere model of intermediate complexity is first forced with stochastic components from the reanalysis. The resulting ENSO is examined for realism to evaluate the strengths and weaknesses of the intermediate coupled model, which is then forced with the stochastic components from the CGCM. Results are diagnosed to investigate the role of SF. It is found that the SF can play an important role in ENSO in the CGCM, especially in its warm events. The role is similar to reanalysis SF in generating ENSO period and spring predictability barrier. However, unlike in case of the reanalysis, the seasonal dependence of ENSO variance in the CGCM does not seem to be originating from its SF. The contribution to statistics appears to be higher from the MJO component of SF compared to the non-MJO component. The intermediate model simulations also suggest that both in CGCM and nature, the SF operates on a weakly stable coupled system to produce ENSO variability.

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Becerra, Patricio, Michael M. Sori, and Shane Byrne. "Signals of astronomical climate forcing in the exposure topography of the North Polar Layered Deposits of Mars." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/622944.

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Using high-resolution topography, we link the stratigraphy of layered ice deposits at the north pole of Mars to astronomically driven climate variability. Observations of trough exposures within these deposits are used to construct virtual ice cores at 16 sites, to which we apply wavelet analysis to identify periodicities in layer properties. To confidently relate these periodicities to climatic forcing, we identify overlapping dominant stratigraphic wavelengths and compare their ratios to that of the two dominant modes of insolation variability. The average ratio of stratigraphic wavelengths in the profiles is 1.90.1, lower than the ratio of 2.3 between dominant insolation periodicities. A similar analysis of synthetic stratigraphic profiles created with a climate-driven model of ice and dust accumulation shows that this lower stratigraphic ratio is a natural consequence of time-variable ice accumulation rates.

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Huybers, Peter 1974. "On the origins of the ice ages : insolation forcing, age models, and nonlinear climate change." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/88360.

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Thesis (Sc. D. in Climate Physics and Chemistry)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004.
Includes bibliographical references (p. 229-245).
This thesis revolves about the relationship between orbital forcing and climate variability. To place paleo and modern climate variability in context, the spectrum of temperature variability is estimated from time-scales of months to hundreds of thou- sands of years using a patchwork of proxy and instrumental records. There is an energetic background continuum and rich spatial structure associated with temperature variability which both scale according to simple spectral power-laws. To complement the spatial and temporal analysis of temperature variability, a description of the full insolation forcing is also developed using Legendre polynomials to represent the spatial modes of variability and singular vectors to represent seasonal and long-term changes. The leading four spatial and temporal modes describe over 99% of the insolation variability making this a relatively simple and compact description of the full insolation forcing. Particular attention is paid to the insolation variations resulting from the precession of the equinoxes. There is no mean annual insolation variability associated with precession - precession only modulates the seasonal cycle. Nonlinear rectification of the seasonal cycle generates precession-period variability, and such rectification naturally occurs in the climate system but also results from the seasonality inherent to many climate proxies. One must distinguish this latter instrumental effect from true climate responses. Another potential source of spurious low-frequency variability results from the stretching and squeezing of an age-model so that noise in a record is made to align with an orbital signal.
(cont.) Furthermore, and contrary to assertions made elsewhere, such orbital-tuning can also generate an eccentricity-like amplitude modulation in records that have been narrow-band-pass filtered over the precession bands. An accurate age-model is the linchpin required to connect insolation forcing with any resulting climatic responses, and to avoid circular reasoning, this age-model should make no orbital assumptions. A new chronology of glaciation, spanning the last 780 kilo-years, is estimated from 21 marine sediment cores using a compaction corrected depth scale as a proxy for time. Age-model uncertainty estimates are made using a stochastic model of marine sediment accumulation. The depth-derived ages are estimated to be accurate to within L9, 000 years, and within this uncertainty are consistent with the orbitally-tuned age estimates. Nonetheless, the remaining differences between the depth and orbitally derived chronologies produce important differences in the spectral domain. From the 6180 record, using the depth-derived ages, evidence is found for a nonlinear coupling involving the 100KY and obliquity frequency bands which generates interaction bands at sum and difference frequencies. If an orbitally-tuned age-model is instead applied, these interactions are suppressed, with the system appearing more nearly linear. A generalized phase synchronization analysis is used to further assess the nonlinear coupling between obliquity and the glacial cycles. Using a formal hypothesis testing procedure, it is shown that glacial terminations are associated with high obliquity states at the 95% significance level. The association of terminations with eccentricity or precession is indistinguishable from chance.
(cont.) A simple excitable system is introduced to explore potential mechanisms by which obliquity paces the glacial cycles. After tuning a small number of adjustable parameters, the excitable model repro- duces the correct timing for each termination as well as the linear and nonlinear features earlier identified in the 6180 record. Under a wide range of conditions the model exhibits a chaotic amplitude response to insolation forcing. One chaotic mode gives a train of small and nearly equal amplitude 40KY cycles. Another mode permits ice to accumulate over two (80KY) or three obliquity cycles (120KY) prior to rapidly ablating and thus, on average, generates 100KY variability. The model spontaneously switches between these 40 and 100KY chaotic modes, suggesting that the Mid-Pleistocene Transition may be independent of any major shifts in the background state of the climate system.
by Peter Huybers.
Sc.D.in Climate Physics and Chemistry

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Drew, Gillian. "Modelling vegetation dynamics and their feedbacks over Southern Africa in response to climate change forcing." Doctoral thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/4846.

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Includes bibliographical references.
The importance of vegetation feedbacks to the atmosphere has been highlighted in many recent research studies. The influence of climate on vegetation has long been established, and climate has regularly been used to predict vegetation distribution. However, the influence of vegetation on climate is a relatively new research area. The need to understand vegetation-atmosphere interactions is growing in light of the increasing atmospheric carbon dioxide concentrations and the change in climate associated with these increases. These linkages are analysed over southern Africa with the use of sophisticated computer models of the climate and vegetation. The models are used to explore some of the vegetation-atmosphere interactions for this region, but without attempting a definitive study of either system.

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Shepard, Christopher. "Soil Modulation of Ecosystem Response to Climate Forcing and Change Across the US Desert Southwest." Thesis, The University of Arizona, 2014. http://hdl.handle.net/10150/323416.

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The dryland ecosystems of the US Desert Southwest (SW) are dependent on soil moisture for aboveground productivity; the generation of soil moisture in the SW is dependent on both soil physical properties and climate forcing. This study is one of the first regional point-scale analyses that explores the role of soil physical properties in modulating aboveground vegetation dynamics in response to climate forcing in the SW. Soil texture accounted for significant differences in average aboveground primary productivity across the SW. However, soil texture could not account for differences in inter-annual aboveground productivity variation across the SW. Subsurface soil texture was tightly coupled with precipitation seasonality in accounting for differences in long-term average seasonal aboveground productivity in the Mojave and Sonoran Deserts. The results of this study indicate that the subsurface is a significant factor in modulating aboveground primary productivity, and needs to be included in future modeling exercises of dryland ecosystem response to climate forcing and change.

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Schuch, Ursula K. "Forcing Containerized Roses in a Retractable Roof Greenhouse and Outdoors in a Semi-Arid Climate." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004. http://hdl.handle.net/10150/216552.

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Sales of containerized roses have increased dramatically in recent years and producing flowering plants in containers in a timely manner is important to the nursery industry. An experiment was conducted to determine whether forcing containerized roses will be faster in a retractable roof greenhouse compared to outdoors. Results suggest that forcing roses in a retractable roof greenhouse can shorten the production time and increase quality of finished plants, however, cultivar, time of harvesting, and time in cold storage also affect these parameters.

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Bistinas, Ioannis. "Global interactions between fire and vegetation, human activities and climate." Doctoral thesis, ISA-UL, 2016. http://hdl.handle.net/10400.5/12022.

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Doutoramento em Engenharia Florestal - Instituto Superior de Agronomia - UL
Vegetation fires are an important component of the earth’s system land processes and have a significant impact on the vegetation and CO2 dynamics. The global fire patterns are not thoroughly explored and the drivers of fire regimes in global scale are interconnected. However, several modelling assumptions are contradicted by exploring those relationships partially. At global scale, fire extent is fuel limited, with climatic variables showing both positive and negative influence on fuel moisture conditions, and humans showing a negative net effect. When isolating the influence of population density and assuming spatial nonstationarity, the human impact is very detailed and reflects the main land use activities with emphasis on cropland and rangeland management at continental scale. The footprint of fire into the Earth system can be measured in terms of radiative forcing from pre and post-fire albedo changes, with the forest biomes driving the extremes on annual basis. Additionally this thesis explores the patterns and the trends of contemporary fire activity. Contrary to previous studies, the results show non-monotonic patterns at grid cell level. The findings of this thesis give a better insight into the spatial variability and the controls of fire at global scale using satellite derived datasets with a focus to the anthropogenic land use activities

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Pillar, Helen. "Sensitivity of the Atlantic meridional overturning circulation to surface forcing." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:42366dc7-e699-4349-95d2-89a97033d957.

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The determination of the mechanisms setting the strength and structure of the large scale circulation is a fundamental and long-standing problem in physical oceanography. In this thesis, we seek to explore the mechanisms contributing to the steady state and variability of the large scale flow, with a focus on better understanding the dynamics of the Atlantic meridional overturning circulation (AMOC). In the first part of this thesis, we explore the linear sensitivity of the monthly mean subtropical AMOC to surface fluxes of buoyancy and momentum. Our approach is to use a numerical adjoint. Key insights are provided into the memory of the AMOC to historic atmospheric forcing. We find that significant memory to wind forcing is confined to timescales of less than a year. In contrast, we identify significant memory to surface buoyancy forcing spanning multi-decadal timescales and characterised by a large scale oscillation in the sign of sensitivity between the eastern and western North Atlantic basin. An important result is that to understand the origins of seasonal variability in the modelled AMOC, we must examine the response to a multidecadal history of atmospheric forcing. In the second part of this thesis, a new tool is presented that enables a clean diagnosis of the force balance controlling the circulation regime for a Boussinesq fluid. Specifically, the tool is based on the development of the "rotational momentum" equations and sets of scalar "velocity potentials" and analogous "force functions". The latter allow the projection of all forces onto the acceleration of the vertical shears and external modes of overturning to be visualised in isolation. The rotational momentum decomposition is applied to the modelled circulation in idealised Atlantic and global configurations of the MITgcm, with a focus on elucidating the dynamics of the simulated AMOC. We discuss the key role played by the rotational buoyancy forcing right on the western boundary.

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Johansson, Eva. "Samband mellan vulkanutbrott och klimatförändringar : Analys och värdering av teorier om vulkanisk aska och gasers påverkan på det globala klimatet." Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-114312.

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This literature review analyses and discusses different theories and results regarding impact of volcanic eruptions on climate change in Earth's history. Present global warming has been attributed to anthropogenic emissions of greenhouse gases, mainly carbon dioxide, however changes in global temperatures have occurred before the onset of anthropogenic emissions. Certain prehistoric climate changes are thought to be caused by emissions of volcanic gases to the atmosphere. Many studies have investigated the connection between volcanic events and subsequent changes in global temperatures. A majority have concluded that volcanic sulfur dioxide is the main direct and indirect climate forcing gas influencing temperatures over time. Increased volcanic activity over the last 15 years is thought to be an inhibiting factor on present global warming. This is supported by evidence of past volcanic events preceding global cooling and warming periods during Holocene and prehistoric times. Further, there are indications that factors such as geographical position, season, gas composition, magnitude and duration of an eruption influences the extent of the climate forcing.Records of climate such as ice cores and tree growth rings and isotopic characterization have made it possible to identify volcano eruptions over time and determine the identity of the erupting volcano. Past and present data from these can be used to gain a better understanding of past climate changes as well as making predictions about future changes as a result volcanic eruptions. However, accuracy regarding temporal and spatial resolution of these records is of great importance for the validity of the results.

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Monni, Suvi. "Estimation of country contributions to the climate change : viewpoints of radiative forcing and uncertainty of emissions /." [Espoo, Finland] : VTT Technical Research Centre of Finland, 2005. http://www.vtt.fi/inf/pdf/publications/2005/P577.pdf.

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Haywood, James Matthew. "Model investigations into the radiative forcing of climate by anthropogenic emissions of sulphate and soot aerosol." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283234.

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Quaas, Johannes, Olivier Boucher, Nicolas Bellouin, and Stefan Kinne. "Which of satellite- or model-based estimates is closer to reality for aerosol indirect forcing?" Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189545.

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In their contribution to PNAS, Penner et al. (1) used a climate model to estimate the radiative forcing by the aerosol first indirect effect (cloud albedo effect) in two different ways: first, by deriving a statistical relationship between the logarithm of cloud droplet number concentration, ln Nc, and the logarithm of aerosol optical depth, ln AOD (or the logarithm of the aerosol index, ln AI) for present-day and preindustrial aerosol fields, a method that was applied earlier to satellite data (2), and, second, by computing the radiative flux perturbation between two simulations with and without anthropogenic aerosol sources. They find a radiative forcing that is a factor of 3 lower in the former approach than in the latter [as Penner et al. (1) correctly noted, only their “inline” results are useful for the comparison].

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Laucks, Mary Lisa. "Quantifying the uncertainties in measurements of aerosol optical properties relevant to the direct shortwave forcing of climate /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10314.

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Goddard, Paul Brent, and Paul Brent Goddard. "Oceanic Controls of North American East Coast Sea Level Rise and Ocean Warming of the Antarctic Shelf." Diss., The University of Arizona, 2018. http://hdl.handle.net/10150/626684.

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Sea level rise (SLR) threatens coastal communities, infrastructure, and ecosystems. Worldwide, stakeholders critically depend on SLR projections with the associated uncertainty for risk assessments, decision-making and coastal planning. Recent research suggests that the Antarctic ice sheet mass loss during the 21st century may contribute up to an additional one meter of global SLR by year 2100. While uncertainty still exists, this value would double the ‘likely’ (> 66% probability) range of global SLR (0.52-0.98 m) by the year 2100, as found by Chapter 13 on Sea Level Change in the Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Here, we present three studies that assess mechanisms relevant to 21st century local, regional, and global SLR. Appendix A examines the effect of large-scale oceanic and atmospheric circulation variability on extreme sea levels along the East Coast of North America. Appendices B and C analyze ocean warming on the Antarctic shelf and its implications for future ice shelf basal melt and Antarctic Ice Sheet mass loss. These studies will contribute to more accurate projections of local, regional, and global SLR. In Appendix A, we analyze long-term tide gauge records from the North American eastern seaboard and find an extreme SLR event during 2009-2010. Within this two-year period, coastal sea levels spiked between Montauk, New York and Southern Canada by up to 128 mm. This two-year spike is unprecedented in the tide gauge record and found to be a 1-in-850 year event. We show that a 30% reduction in strength of the Atlantic meridional overturning circulation (AMOC) and a strong negative North Atlantic Oscillation (NAO) index caused the extreme SLR event. Climate models project that the AMOC will weaken and NAO variability will remain high over the 21st century. Consequently, extreme SLR events on the Northeast Coast could become more frequent during the 21st century in response to climate change and SLR. In Appendix B, we use a fine-resolution global climate model (GFDL CM2.6) that resolves an eddying ocean. With this state-of-the-art coupled model, we quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized experiment of doubling of the atmospheric CO2 concentration. The results show that the CO2 forcing leads to the shelf region warming both in the upper 100 m ocean and at depths near the sea floor. These warming patterns are controlled by different mechanisms. In the upper 100 m, the heat anomalies are primarily controlled by increased heat transport into the shelf region associated with the warmer near-surface waters from lower latitudes. Below 100 m, the heat anomalies develop due to increased onshore intrusions of relatively warm Circumpolar Deep Water and reduced vertical mixing of heat in the water column. A complete heat budget analysis is performed for the Antarctic shelf region as well as for six subdomains and three depth ranges (0-100 m, 100-700 m, and 700-1000 m). The results show that certain regions of the Antarctic shelf are more susceptible to large CO2-forced warming. These findings have implications for future Antarctic Ice Sheet mass loss and SLR, and can provide more detailed and accurate ocean boundary conditions for dynamical ice sheet models. In Appendix C, we use CM2.6 to examine the connections among ocean freshening and the magnitude and location of ocean warming on the Antarctic shelf. We find that CO2 forcing freshens the Antarctic shelf seas via increases in local precipitation, sea ice loss, liquid runoff, and iceberg calving. The freshening induces three heat budget-relevant responses: (1) reduced vertical mixing; (2) strengthening of the Antarctic Slope Front (ASF); and (3) increased eddy kinetic energy (EKE) near the ASF. First, heat can accumulate at depth (100-1000 m) as freshening increases the vertical stratification on the shelf and reduces upward mixing of heat associated with diffusion and convective processes. Second, freshening near the shelf break strengthens the ASF by increasing the lateral density gradient and by steepening and deepening the associated isopycnals. This response limits cross-ASF onshore heat transport at many locations around Antarctica. Third, EKE increases near the ASF may contribute to shelf warming by increasing cross-ASF onshore eddy heat transport. These results demonstrate the importance of shelf freshening to the development of positive heat anomalies on the Antarctic shelf. The findings provide new insight to the location of future shelf warming and ice shelf basal melting as well as provide significant information for projecting regional and global SLR.

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Hood, Lon L., and Boris E. Soukharev. "The Lower-Stratospheric Response to 11-Yr Solar Forcing: Coupling to the Troposphere–Ocean Response." American Meteorological Society (Boston, MA), 2012. http://hdl.handle.net/10150/623318.

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The origin of the tropical lower-stratospheric response to 11-yr solar forcing and its possible coupling to a troposphere–ocean response is investigated using multiple linear regression (MLR) analyses of stratospheric ozone and temperature data over the 1979–2009 period and tropospheric sea level pressure (SLP) data over the 1880–2009 period. Stratospheric MLR results, comparisons with simulations from a chemistry–climate model, and analyses of decadal variations of meridional eddy heat flux indicate that the tropical lower-stratospheric response is produced mainly by a solar-induced modulation of the Brewer–Dobson circulation (BDC), with a secondary contribution from the Hadley circulation in the lowermost stratosphere. MLR analyses of long-term SLP data confirm previous results indicating a distinct positive response, on average, during the northern winter season in the North Pacific. The mean response in the Northern Hemisphere resembles a positive Arctic Oscillation mode and can also be characterized as “La Niña–like,” implying a reduction of Rossby wave forcing, a weakening of the BDC, and an increase in tropical lower-stratospheric ozone and temperature near solar maxima. However, MLR analyses of different time periods show that the Pacific SLP response is not always present during every cycle; it was most clearly detected mainly during the ~1938–93 period when 11-yr solar variability was especially strong. During the 1979–93 period, the SLP response was strongly present when the lower-stratospheric responses were large. But during the 1994–2009 period, the SLP response was much less significant and the lower-stratospheric responses were weak, supporting the hypothesis that the lower-stratospheric and surface climate responses are dynamically coupled.

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Kazil, Jan, Philip Stier, Kai Zhang, Johannes Quaas, Stefan Kinne, D. O'Donnell, Sebastian Rast, et al. "Aerosol nucleation and its role for clouds and Earth’s radiative forcing in the aerosol-climate model ECHAM5-HAM." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-185342.

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Nucleation from the gas phase is an important source of aerosol particles in the Earth’s atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosolclimate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth’s radiative forcing. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are −1.15 W/m2 for charged H2SO4/H2O nucleation, −0.235 W/m2 for cluster activation, and −0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is −2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with −2.18 W/m2 to total absorbed solar short-wave radiation, compared to −0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth’s radiative forcing over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.

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Kazil, Jan, Philip Stier, Kai Zhang, Johannes Quaas, Stefan Kinne, D. O''Donnell, Sebastian Rast, et al. "Aerosol nucleation and its role for clouds and Earth’s radiative forcing in the aerosol-climate model ECHAM5-HAM." Copernicus Publication, 2010. https://ul.qucosa.de/id/qucosa%3A13791.

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Nucleation from the gas phase is an important source of aerosol particles in the Earth’s atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosolclimate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth’s radiative forcing. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are −1.15 W/m2 for charged H2SO4/H2O nucleation, −0.235 W/m2 for cluster activation, and −0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is −2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with −2.18 W/m2 to total absorbed solar short-wave radiation, compared to −0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth’s radiative forcing over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.

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Quaas, Johannes, and Olivier Boucher. "Constraining the first aerosol indirect radiative forcing in the LMDZ GCM using POLDER and MODIS satellite data." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189536.

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The indirect effects of anthropogenic aerosols are expected to cause a significant radiative forcing of the Earth’s climate whose magnitude, however, is still uncertain. Most climate models use parameterizations for the aerosol indirect effects based on so-called ‘‘empirical relationships’’ which link the cloud droplet number concentration to the aerosol concentration. New satellite datasets such as those from the POLDER and MODIS instruments are well suited to evaluate and improve such parameterizations at a global scale. We derive statistical relationships of cloud-top droplet radius and aerosol index (or aerosol optical depth) from satellite retrievals and fit an empirical parameterization in a general circulation model to match the relationships. When applying the fitted parameterizations in the model, the simulated radiative forcing by the first aerosol indirect effect is reduced by 50% as compared to our baseline simulation (down to -0.3 and -0.4 Wm-2 when using MODIS and POLDER satellite data, respectively).

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Marrapu, Pallavi. "Local and regional interactions between air quality and climate in New Delhi: a sector based analysis." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3497.

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Deteriorating air quality is one of the major problems faced worldwide and in particular in Asia. The world's most polluted megacities are located in Asia highlighting the urgent need for efforts to improve the air quality. New Delhi (India), one of the world's most polluted cities, was the host of the Common Wealth Games during the period of 4-14 October 2010. This high profile event provided a good opportunity to accelerate efforts to improve air quality. Computational advances now allow air quality forecast models to fully couple the meteorology with chemical constituents within a unified modeling system that allows two-way interactions. The WRF-Chem model is used to simulate air quality in New Delhi. The thesis focuses on evaluating air quality and meteorology feedbacks. Four nested domains ranging from South Asia, Northern India, NCR Delhi and Delhi city at 45km, 15km, 5km and 1.67km resolution for a period of 20day (26thsep-15thoct, 2010) are used in the study. The predicted mean surface concentrations of various pollutants show similar spatial distributions with peak values in the middle of the domain reflecting the traffic and population patterns in the city. Along with these activities, construction dust and industrial emissions contribute to high levels of criteria pollutants. The study evaluates the WRF-Chem capabilities using a new emission inventory developed over Delhi at a fine resolution of 1.67km and evaluating the results with observational data from 11 monitoring sties placed at various Game venues. The contribution of emission sectors including transportation, power, industry, and domestic to pollutant concentrations at targeted regions are studied and the results show that transportation and domestic sector are the major contributors to the pollution levels in Delhi, followed by industry. Apart from these sectors, emissions outside of Delhi contribute 20-50% to surface concentrations depending on the species. This indicates that pollution control efforts should take a regional perspective. Air quality projections in Delhi for 2030 are investigated. The Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model is used to generate a 2030 future emission scenario for Delhi using projections of air quality control measures and energy demands. Net reductions in CO concentrations by 50%, and increases of 140% and 40% in BC and NOx concentrations, respectively, are predicted. The net changes in concentration are associated with increases in transport and industry sectors. The domestic sector still has a significant contribution to air pollutant levels. The air quality levels show a profound effect under this scenario on the environment and human health. The increase in pollution from 2010 to 2030 is predicted to cause an increase in surface temperature by ~0.65K. These increasing pollution levels also show effects on the radiative forcing. The high aerosols loading i.e. BC, PM2.5 and PM10 levels show strong influence on the short and longwave fluxes causing strong surface dimming and strong atmosphere heating due to BC. These results indicate transport and domestic sectors should be targeted for air quality and climate mitigations.

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Quaas, Johannes, Olivier Boucher, Nicolas Bellouin, and Stefan Kinne. "Which of satellite- or model-based estimates is closer to reality for aerosol indirect forcing?" National Acadamy of Sciences, 2011. https://ul.qucosa.de/id/qucosa%3A13972.

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In their contribution to PNAS, Penner et al. (1) used a climate model to estimate the radiative forcing by the aerosol first indirect effect (cloud albedo effect) in two different ways: first, by deriving a statistical relationship between the logarithm of cloud droplet number concentration, ln Nc, and the logarithm of aerosol optical depth, ln AOD (or the logarithm of the aerosol index, ln AI) for present-day and preindustrial aerosol fields, a method that was applied earlier to satellite data (2), and, second, by computing the radiative flux perturbation between two simulations with and without anthropogenic aerosol sources. They find a radiative forcing that is a factor of 3 lower in the former approach than in the latter [as Penner et al. (1) correctly noted, only their “inline” results are useful for the comparison].

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Davies, Nicholas William. "The climate impacts of atmospheric aerosols using in-situ measurements, satellite retrievals and global climate model simulations." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34544.

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Aerosols contribute the largest uncertainty to estimates of radiative forcing of the Earth’s atmosphere, which are thought to exert a net negative radiative forcing, offsetting a potentially significant but poorly constrained fraction of the positive radiative forcing associated with greenhouse gases. Aerosols perturb the Earth’s radiative balance directly by absorbing and scattering radiation and indirectly by acting as cloud condensation nuclei, altering cloud albedo and potentially cloud lifetime. One of the major factors governing the uncertainty in estimates of aerosol direct radiative forcing is the poorly constrained aerosol single scattering albedo, which is the ratio of the aerosol scattering to extinction. In this thesis, I describe a new instrument for the measurement of aerosol optical properties using photoacoustic and cavity ring-down spectroscopy. Characterisation is performed by assessing the instrument minimum sensitivity and accuracy as well as verifying the accuracy of its calibration procedure. The instrument and calibration accuracies are assessed by comparing modelled to measured optical properties of well-characterised laboratory-generated aerosol. I then examine biases in traditional, filter-based absorption measurements by comparing to photoacoustic spectrometer absorption measurements for a range of aerosol sources at multiple wavelengths. Filter-based measurements consistently overestimate absorption although the bias magnitude is strongly source-dependent. Biases are consistently lowest when an advanced correction scheme is applied, irrespective of wavelength or aerosol source. Lastly, I assess the sensitivity of the direct radiative effect of biomass burning aerosols to aerosol and cloud optical properties over the Southeast Atlantic Ocean using a combination of offline radiative transfer modelling, satellite observations and global climate model simulations. Although the direct radiative effect depends on aerosol and cloud optical properties in a non-linear way, it appears to be only weakly dependent on sub-grid variability.

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Hood, Lon, Semjon Schimanke, Thomas Spangehl, Sourabh Bal, and Ulrich Cubasch. "The Surface Climate Response to 11-Yr Solar Forcing during Northern Winter: Observational Analyses and Comparisons with GCM Simulations." AMER METEOROLOGICAL SOC, 2013. http://hdl.handle.net/10150/623315.

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The surface climate response to 11-yr solar forcing during northern winter is first reestimated by applying a multiple linear regression (MLR) statistical model to Hadley Centre sea level pressure (SLP) and sea surface temperature (SST) data over the 1880–2009 period. In addition to a significant positive SLP response in the North Pacific found in previous studies, a positive SST response is obtained across the midlatitude North Pacific. Negative but insignificant SLP responses are obtained in the Arctic. The derived SLP response at zero lag therefore resembles a positive phase of the Arctic Oscillation (AO). Evaluation of the SLP and SST responses as a function of phase lag indicates that the response evolves from a negative AO-like mode a few years before solar maximum to a positive AO-like mode at and following solar maximum. For comparison, a similar MLR analysis is applied to model SLP and SST data from a series of simulations using an atmosphere–ocean general circulation model with a well-resolved stratosphere. The simulations differed only in the assumed solar cycle variation of stratospheric ozone. It is found that the simulation that assumed an ozone variation estimated from satellite data produces solar SLP and SST responses that are most consistent with the observational results, especially during a selected centennial period. In particular, a positive SLP response anomaly is obtained in the northeastern Pacific and a corresponding positive SST response anomaly extends across the midlatitude North Pacific. The model response versus phase lag also evolves from a mainly negative AO-like response before solar maximum to a mainly positive AO response at and following solar maximum.

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Stokes, Kimberley Laura. "Ecology of marine turtles under climate change." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/21847.

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Climate change threatens to disrupt biological systems around the globe, sparking debate over natural capacity for adaptation in a fragmented landscape. Marine turtles are evolutionarily ancient and have survived millions of years of prehistoric climate change, but are threatened by the rapidity of modern warming and a history of severe overexploitation that has left most populations depleted. This thesis explores a nesting aggregation of the green turtle (Chelonia mydas) in northern Cyprus, where a longitudinal programme of both intensive and extensive monitoring enables insight into individual and population level parameters and processes. Nesting on the two coastlines covered by this project is in the early stages of recovery, possibly in response to exhaustive nest protection efforts over the last twenty years. Saturation tagging at one key site allows us to confirm that recruitment of new breeders is an important driver of this trend, and that average clutch frequency has remained stable around three nests per female per year, validating nest-count derived abundance estimates at a regional scale. Concern has been raised, however, regarding recent changes in fishing practices which are impacting the local juvenile neritic phase, which may have a lagged effect on the recovery of this nesting population. A collaborative tracking effort including all other countries with major nesting in the Mediterranean allows us to identify major foraging grounds for this species, with two hotspots accounting for >50% of tracked individuals, as well as coastal and pelagic seasonal corridors of high use. Bycatch levels and mortality rates for turtles in these key areas are largely unknown and should be prioritised for investigation. Hatchling sex ratios from the main study beach are extremely female-biased (estimated 97% female for the twenty year period 1993-2012). A 1oC rise in average incubation temperatures threatens near complete hatchling feminisation on this beach, whilst a 2oC rise could reduce hatch success to less than 50%. Thermal effects on hatchling morphometrics are evident, with a 1oC rise in temperature reducing average length, width and weight by 1%, 2% and 3% respectively. More favourable incubation conditions were found early in the season, in deeper nests laid by larger females, and on beaches of lighter sand. In contrast, adult sex ratios at the main site are male-biased, posing questions regarding sex-specific survival rates and optimal hatchling sex ratios. A phenological shift towards earlier nesting is demonstrated for the first time in this species, and could potentially ameliorate warming effects. Carry-over climate forcing effects from the foraging ground influence the breeding frequency of individuals, driving population level responses in annual magnitude of nesting. This work emphasises the utility and necessity of long-term individual-based monitoring programmes in elucidating population trends and climate responses in iteroparous species with non-annual breeding.

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Marzocchi, Alice. "Modelling the impact of orbital forcing on late Miocene climate : implications for the Mediterranean Sea and the Messinian Salinity Crisis." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.701976.

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Orbital forcing is a dominant climate driver on multi-millennial time scales, as it modulates the seasonal distribution of incoming solar radiation on the Earth's surface. Geological evidence of orbitally-forced cyclicity is found globally in numerous sedimentary sequences, especially in marginal basins such as the Mediterranean Sea. In the late Miocene (11.61-5.33 Ma), a large portion of the North African catchment is thought to have drained in the Mediterranean Sea, as the main fresh water input into the basin, regulated by precessional changes the North Arican summer monsoon. The distinctive sedimentary cyclicity observed in the Mediterranean Sea is thought to result from the basins biogeochemical response to oscillations in its hydrologic budget, which represents the balance between inflowing (precipitation and river input) and outflowing (evaporation) water, and exchange with other basins. Yet until now, most of the hypotheses about the phasing between orbital forcing and Mediterranean cyclic sedimentary sequences, through changes in the hydrology, are largely untested. The global late Miocene proxy record is sparse and patchy, but the majority of the data are concentrated in the Mediterranean region, which contains palaeoarchives with an exceptionally high temporal resolution. This thesis combines a unique ensemble of numerical simulations through a full precession cycle with the interpretation of geological data; with this experimental design, model results can be compared directly to the Mediterranean sedimentary record. This enables the testing and quantification of a variety of processes relative to past extreme environmental changes in this region, such as the Messinian Salinity Crisis. Seasonal changes in the North Arican monsoon and in the Mediterraneans hydrologic fluxes are explored on precessional timescales, but additional orbitally-driven moisture sources affecting the basin are also investigated. Implications for the sedimentary record are drawn globally and regionally for both the Mediterranean Sea and the Paratethys (the precursor of the Black and Caspian seas). In addition, this work emphasises the reduction in the global model-data mismatch for the late Miocene when orbital variability is included in the climate simulations.

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Dissertations / Theses on the topic 'Forcing of climate'

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