1,720,958 research outputs found
Isolating the observed influence of vegetation variability of La Plata River basin on the climate of South America
Get PDFLand surface variability and change can affect the overlying atmosphere through biogeophysical and biogeochemical feedbacks. The goal of our work is to isolate and quantify the local and remote influences of vegetation on the climate of South America using observational records. We find that the dominant mode of vegetation variability over the La Plata River basin in austral Spring is linked with warmer temperature and enhanced precipitation over central and south La Plata basin. A key aspect of this study is the use of remotely sensed land-surface characteristics alongside reanalysis data, and the use of the generalized equilibrium feedback assessment (GEFA) to isolate the effects of each forcing. The analysis uses a 34-year (1981-2014) record of the modified enhanced vegetation index (EVI2) from the NASA MEaSUREs Vegetation Index and Phenology dataset and the third generation normalized difference vegetation index (NDVI3g) from the Global Inventory Modeling and Mapping Studies. The dominant patterns of variability in space and time are analyzed using empirical orthogonal function/principal component (EOF/PC) analysis on a basin-wide scale. The dominant mode looks like a vegetation dipole, and can be explained using observed records of precipitation provided by the University of Delaware and the University of East Anglia Climate Research Unit. The second part of the study analyzes how these dominant modes of variability affect the overlying atmosphere at the continental scale. We use GEFA and its refinement, the stepwise GEFA, to statistically quantify the observed seasonal impacts of dominant terrestrial and oceanic forcings on the South American climate. This observed impact of vegetation on the seasonal accumulation of precipitation in the agricultural growing season holds crucial importance for the most heavily populated and economically active region of South America.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-08-01The student, Divyansh Chug, accepted the attached license on 2018-07-10 at 16:37.The student, Divyansh Chug, submitted this Thesis for approval on 2018-07-10 at 16:44.This Thesis was approved for publication on 2018-07-13 at 11:18.DSpace SAF Submission Ingestion Package generated from Vireo submission #12807 on 2018-09-27 at 11:18:57Made available in DSpace on 2018-09-27T16:30:30Z (GMT). No. of bitstreams: 2
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Previous issue date: 2018-07-13Embargo set by: Seth Robbins for item 107797
Lift date: 2020-09-27T16:30:34Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107797
Lift date: 2020-09-27T16:31:43Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107797
Lift date: 2020-09-27T16:34:29Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107797 on 2020-09-28T09:15:07Z
Multi-scale land-atmosphere interactions over South America
Get PDFSubmission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2023-04-12 without embargo termsThe student, Divyansh Chug, accepted the attached license on 2022-11-28 at 16:08.The student, Divyansh Chug, submitted this Dissertation for approval on 2022-11-28 at 16:25.This Dissertation was approved for publication on 2022-12-01 at 09:34.DSpace SAF Submission Ingestion Package generated from Vireo submission #18654 on 2023-04-12 at 07:34:16The land surface exerts biogeophysical feedbacks on the atmosphere at time scales ranging from seconds to years. The atmospheric component of this dynamically coupled system evolves differently than what would be expected in the absence of this feedback, due to exchanges of heat, moisture and momentum. These interactions result in numerous pathways through which land modulates the structure of the atmosphere and precipitation from local to global spatial scales. The La Plata river basin (LPB) in South America, one of the most important socio-economic regions in the world, is a "hotspot" of such land-atmosphere (L-A) interactions where land surface feedbacks are important drivers of the regional climate. Past work on L-A feedback processes has established that this region exhibits the necessary "ingredients" for a strong role of the land surface in weather and climate predictability, i.e. large variability in precipitation and surface soil moisture, strong control of soil moisture variability on the variability of surface energy fluxes (latent and sensible), and a heavy dependence on terrestrial sources of moisture for wet season rainfall. Together, these ingredients lead to three important feedback processes (among others) across a range of scales, namely precipitation recycling of terrestrial moisture at the continental scale, thermal feedback of persistent soil moisture anomalies at the regional scale, and mesoscale circulations, a thermal feedback due to soil moisture heterogeneity at the mesoscale. Accurately capturing these feedbacks can improve our ability to predict the weather at a variety of of time-scales ranging from sub-daily to seasonal, and reduce land surface-related biases in climate projections. However, a complete understanding of the role of these feedbacks is lacking due to the following limitations: • The state of our knowledge of the transport and precipitation of terrestrial moisture over South America has primarily been derived from studies that aggregate estimates at seasonal or longer time-scales for individual river basins. The relative importance of the major terrestrial moisture sources at intra-seasonal time-scale is unknown. • The current understanding of the role of land surface variability in atmospheric prediction over South America has largely been derived from numerical modeling experiments. There is little observational validation to support the results and hypothesis derived from modeling studies. • The physical understanding of mesoscale circulations and their role in convection over land has been derived from idealized numerical experiments with idealized representation of soil moisture heterogeneity. The empirical representation of spontaneous patchiness of soil moisture, such as in the real world, is lacking. • There is no past work on quantifying the role of mesoscale circulations forced by soil moisture heterogeneity on convective initiation over subtropical South America. The goal of this dissertation is to advance our current state-of-knowledge about the aforementioned L-A feedback processes over the LPB in South America. Together, these feedback processes represent major biases in climate models and can lead to significant improvements in weather and climate prediction. Through a combined observational and modeling framework, this dissertation addresses the following questions about L-A interactions over South America: 1. What is the role of the land surface as a source of moisture for precipitation over South America at intra-seasonal to seasonal time scales? Using tracers embedded in the Weather Research and Forecasting model, this work quantities the role of the Amazon and the LPB basins as a moisture source to understand the intraseasonal variability in the long-range transport and precipitation of moisture from these sources over the South American continent. Results show an intraseasonal "sloshing" of terrestrial moisture over South America and a relatively larger direct contribution of the LPB source (23%) compared to the Amazon source (5%) for precipitation over southeastern South America during periods of intraseasonal enhancement. 2. Does the antecedent land surface state exert appreciable feedback to the atmosphere at subseasonal time scales over LPB? Using remotely-sensed and reanalysed atmospheric and surface measurements, this work identities the consistently recurring land surface patterns that can potentially induce strong intraseasonal feedbacks at the regional scale and inform future numerical experiments to isolate the physical mechanisms. 3. How does surface heterogeneity, specifically mesoscale gradients in soil moisture, affect convective initiation over subtropical South America? Using satellite data and convection-permitting climate simulations, this work investigates the role of mesoscale circulations induced by soil moisture heterogeneity on atmospheric convection over South America. Results show the first observational evidence for preferential convective initiation on the dry side of mesoscale soil moisture gradients, specifically over "dry patches" on the order of tens of kilometers. The subsequent work quantified and validated the same preference for the first time using long-term (20 years) convection-permitting climate simulations. The research questions addressed in this work are novel for the South American continent. The original contributions of this work include regional moisture budget assessment over South America through improved representation of terrestrial moisture transport, quantification of intra-seasonal variability in terrestrial moisture transport and recycling, identification of organized and persistent soil moisture anomalies associated with the intra-seasonal hydroclimate oscillation, observational evidence for the preference of convective initiation on the dry side of soil moisture gradients on the order of tens of kilometers, and an improved understanding of the length scales of soil moisture heterogeneity associated with convective development. These contributions provide an improved understanding of L-A feedbacks over the most heavily populated and economically active region of South America where accurate weather forecasts and climate prediction are crucial for the prosperity of its 67 million inhabitants
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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