1,720,954 research outputs found
Numerical modelling of the Angola Low and the Botswana High during a neutral and two El Ni˜no summers
No full textThe Angola Low and Botswana High pressure systems are thought to play a crucial role in the variability of summer rainfall over southern Africa. However, very little is known about their variability during the summer half of the year and how their influence on rainfall patterns during ENSO and non-ENSO summers may vary. In simple terms, a weaker Angola Low is expected to lead to decreased rainfall as is a stronger Botswana High. This study looks at the monthly evolution of the Angola Low and the Botswana High during the neutral summer of 2012/13 and the two strong El Ni˜no summers of 1997/98 and 2015/16 using the WRF model. CFSR and CFSv2 reanalyses, satellite derived winds, GPCC rainfall and TRMM satellite-derived rainfall estimates are used to validate the model. The model was integrated from September through to April for each run with observed sea surface temperature and reanalyses as boundary conditions. During the neutral summer of 2012/13, the Angola Low became clearly evident in the model during the pentad of 6-10 October whereas during the 1997/98 and 2015/16 El Ni˜no summers, it became evident during the pentads of 6-10 November and 16-20 November respectively. In addition to these differences in onset, there were also differences in the date after which the Low was no longer present in the model fields. These dates were 26-28 February 2013 and 26-31 March 1998 while in the 2015/16 case, the Low remained present throughout the whole of March. In each year, the Botswana High was present throughout the entire summer half of the year. The WRF simulation indicated that during the strong El Ni˜no event of 1997/98, the Angola Low did not weaken whereas the Botswana High was weaker than normal. However, during the strong El Ni˜no event of 2015/16, the Angola Low was weaker and the Botswana High was relatively strong. The strengthening of the Angola Low and the weakening of the Botswana High during the strong 1997/98 El Ni˜no led to substantial rainfall over southern Africa. The near to above average rainfall over subtropical southern Africa during 1997/98 was unexpected given the strength of the El Ni˜no and the SST anomalies in the Indian and Pacific Oceans. The weaker Angola Low and stronger Botswana High during the strong 2015/16 El Ni˜no led to severe drought over the region. The study highlights the importance of modulations in the Angola Low and the Botswana High for rainfall anomalies during ENSO and non-ENSO summers as very different rainfall patterns may occur over southern Africa during similar strength ENSO events. The significance of these regional circulation systems is reinforced by the fact that during the 2012/13 neutral summer, the Angola Low was stronger than average and the Botswana High was relatively weak leading to good rainfall. The relationship between the Angola Low, the Botswana High and southern Africa rainfall is found to be relatively strong through the 1979-2017 period. Thus, monitoring and better understanding these regional circulation systems is important and complements ongoing efforts to monitor and predict ENSO
Long-lived mesoscale convective systems over Eastern South Africa
Get PDFPrevious studies on severe weather in South Africa have often focused on synoptic-scale systems such as cut off lows, tropical extratropical cloud bands, and tropical cyclones, with little attention placed on the smaller mesoscale convective systems (MCSs). On a global scale, MCSs are not only important as key rainfall producers, but are often responsible for flooding, severe winds, hail and sometimes tornadoes. MCSs in South Africa remain poorly understood with there being little evidence of any long-term climatology studies of these systems over the region. A climatology of large, long-lived MCSs over eastern South Africa for the extended austral summer (September-April) from 1985-2008 is presented. On average, 63 MCSs occur here in summer, but with considerable interannual variability in frequency. The systems mainly occur between November and March, with a December peak. This seasonal cycle in MCS activity is shown to coincide with favorable convective available potential energy (CAPE) and vertical shear profiles across the domain. Most systems tend to occur along the eastern escarpment with its sharp topographic gradients close to the warm waters of the northern Agulhas Current. The eastern escarpment can act as a convective trigger by mechanically uplifting sufficiently moist and unstable air masses. In addition, strong latent heat fluxes from the northern Agulhas Current help to create high-CAPE conditions. Typically, initiation begins in the early afternoon, MCS status is reached mid-afternoon, maximum extent early in the night and termination around midnight or shortly thereafter. The analysis also considered MCSs that developed over land versus those over the adjacent ocean. It is found that most MCSs initiate over land, but systems that initiate over the ocean tend to last longer than those that develop over land. The results also show that there are differences in the seasonal cycle between continental and oceanic MCSs, with oceanic systems containing two intraseasonal peaks (December and April). There is a relatively strong positive relationship between the southern annular mode (SAM) and early summer MCS frequency. For the late summer, the frequency of MCSs appears related to the strength of the Mascarene high and Mozambique Channel trough, which modulate the inflow of moisture into eastern South Africa and the stability of the lower atmosphere over the region. The 6 results indicated that there is considerable variability in the long-lived MCS frequency on interannual time scales and such variability can have considerable impacts on regional rainfall totals during the summer months over eastern South Africa. MCSs are known to produce heavy rainfall that is often associated with floods, which can be devastating to livestock, crops, infrastructure, and humankind. However, these systems also provide important rainfall within a short time span that is significant for rain-fed agriculture for a semi-arid country as South Africa. Using Climate Hazards Infrared Precipitation with Stations (CHIRPS) satellite rainfall data for 1985-2008, this study identified 38 daily extreme rainfall events which account for 40% of the top 50 extreme rainfall events over the two sub-domains of the eastern parts of South Africa that are linked to long-lived MCSs. Of the 38 events, systems duration ranged between 6-51 hours with 23 systems lasting for longer than 12 hours. Individual MCS-associated extreme daily rainfall events contribute between 21% - 54% to the total seasonal amount of rainfall over eastern South Africa. There is also noticeable interannual variability of seasonal rainfall over the northern and the southern domain, and considerable spatial variability in seasonal rainfall of MCS-related extreme rainfall events over the two sub-domains. In general, the thesis has contributed to a better understanding of the wider group of large, longlived MCS characteristics over eastern South Africa in terms of their distribution, frequency, life cycle, seasonal cycle and large-scale environmental conditions and the relationship between MCS frequency and interannual climate mode of variability such as El Niño-Southern Oscillation (ENSO), the subtropical south Indian Ocean dipole (SIOD), and SAM. The study also contributed to a better understand the role MCSs play in eastern South Africa summer rainfall and particularly extreme rainfall in the region
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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