14 research outputs found
General circulation model simulations of Southern African regional climate.
Dissertation submitted to the Faculty of Science,
University of the Witwatersraild, Johannesburg
for the Degree of Master of Science.Six general circulation model simulations of present-day southern African
climate are assessed, Each of these models are early-generation equilibrium
climate models linked to simple mixed-slab oceans. Simulations of surface
air temperature over the subcontinent are sensitive to the grid-scale
parameterisation of convection in summer. At high latitudes, large simulation
errors are caused by errors in the specification of sea-ice albedo feedbacks.
Increased spatial resolution and the inclusion of a gravity wave drag term in
the momentum equations results in a markedly-improved simulated mean sea
level pressure distribution. Tho models successfully simulate the pattern of
rainfall seasonality over the Subcontinent, although grid-point simulation of
precipitation is unreliable. Treatment of convection, cloud radiative feedbacks
and the oceans by this generation of models is simplistic, and consequently
there is a large degree of uncertainty associated with predictions of future
climate under doubled-carbon dioxide conditions. For this reason, more
reliable estimates of future conditions will be achieved using only those
models which reproduce present climate most accurately. Early-generation
general circulation models suggest a warming of 4°C to 5°C for the southern
African region as a whole throughout the year. Over the subcontinent,
warming is expected to be least in the tropics, and greatest in the dry
subtropical regions in winter. Estimated changes in mean sea level pressure
indicate a southward shlft of all pressure systems, with a weakening of the
subtropical high pressure belt and mid-latitude westerlies. Little agreement
exists between the models concerning predictions of regional precipitation
change. However, broad scale changes in precipitation patterns are in
accordance with predicted circulation changes over the subcontinent.
Generally wetter conditions may be expected in the tropics throughout the
year and over the summer rainfall region during summer. Decreased winter
rainfall may be expected over the winter rainfall region of the south-western
Cape. However, estimated precipitation changes are grid-point specific and
therefore must riot be over-interpreted. The present climate validation has
resulted in more reliable estimates of future conditions for the southern
African region. This approach should be extended to recent slrnulations which
include more comprehensive treatment of important physical processes.Andrew Chakane 201
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Simulated changes in extreme rainfall over southern Africa
A general circulation model simulation is used to investigate possible changes in rainfall over southern Africa resulting from a doubling of atmospheric carbon dioxide. Simulated increases in rainfall intensity are found to be a spatially coherent and an apparently less regionally dependent signal of climatic change than changes in annual means or number of rainâdays. Accordingly, increases in both the frequency and intensity of extreme daily rainfall events are simulated throughout most of the subcontinent. Simulated increases in the intensity of the lowest frequency floods are shown to be particularly severe, suggesting that greenhouseârelated climatic change may be most detectable through an increase in extreme flood events rather than changes in longâterm means. Similar results are evident when changes in the frequency and intensity of prolonged rainfall events, measured over a period of five consecutive days, are analysed. All results are qualitatively similar to those for the Australian region, except that the model's sensitivity to sharp changes in topography over southern Africa is highlighted
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Droughts over southern Africa in a doubled-CO2 climate
The southern African region is susceptible to climatic extremes and particularly to extended dry periods. Possible changes in the probability of dry years under doubledâCO2 conditions are examined using output from the CSIRO nineâlevel general circulation model. Changes in annual mean rainfall are not expected to be significant. However, the model simulates an increase in the probability of dry years in the tropics, to the southâwest of the subcontinent, as well as over the western and eastern parts of South Africa and southern Mozambique, where large percentage increases in the most intense dry spells are indicated. A decrease in the frequency of dry years is simulated over much of the interior of the subcontinent south of 10°S. In regions where the frequency of dry years decreases, the most severe events occur less often. The CSIRO nineâlevel model indicates a shift in the frequency distribution of daily rainfall events under doubledâCO2 conditions. A small change in the frequency distribution of daily rainfall events may have further implications for the frequency of midâsummer droughts during the peak summer rainfall period of DecemberâFebruary. Increases in the frequency of midâsummer droughts are simulated over the eastern part of the subcontinent south of 20°S
Modelling present and future climates over Southern Africa.
Thesis submitted to the Faculty of Science, Department of Geography and Environmental Studies, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the Degree of Doctor of PhilosophyThe representation of contemporary southern African climate by a wide range of general
circulation models used in climate studies is evaluated. In addition, projections of regional
climate change by the models are interpreted in terms of their present climate performance.
Projections of regional climate change by two different types of climate models are
considered. First, projections of the equilibrium response to an instantaneous doubling of
atmospheric carbon dioxide using atmospheric models linked to simple mixed-layer oceans
are assessed. Second, projections of the transient response to gradually-increasing
anthropogenic forcing by fully-coupled ocean-atmosphere general circulation models are
considered.
All of the mixed-layer models considered have been developed since 1990 and are more
recent and generally higher-resolution versions of the models considered previously for
southern Africa. The improved resolution and model physics result in a general
improvement in the representation of several features of circulation around southern
Africa. Specifically, these include the meridional pressure gradient, the zonal wind profile,
the intensity and seasonal location of the circumpolar trough and the subtropical
anticyclones, as well as planetary wave structure at 500 hPa. Atmospheric models forced
by observed sea-surface temperatures simulate the large-scale circulation adjustments
around southern Africa known to accompany periods of above- and below-average rainfall
over the subcontinent. Fully-coupled models simulate the observed features of intra- and
intra- annual variability in mean sea-level pressure, although the simulated variability is
weaker than observed. Summer rainfall totals throughout southern Africa are overestimated
by all of the models, although the pattern of rainfall seasonality over the
subcontinent as a whole is well-reproduced. The inclusion of sulphate aerosols in addition
to greenhouse gases does not result in a statistically significant improvement in the
simulation of contemporary temperature variability over southern Africa.
Warming projected by fully-coupled models is smaller than projections by mixed-layer
models due to the fact that the transient response of the fully-coupled system and not an
equilibrium response of an atmospheric model linked to a mixed-layer ocean is simulated.
The inclusion of sulphate aerosols results in a reduction in the magnitude and rate of
warming over southern Africa. Projected changes in the diurnal temperature range are
seasonally-dependent, with increases in summer and autumn and decreases in winter.
Simulated changes in mean sea-level pressure are small but similar in magnitude to
observed anomalies associated with extended wet and dry spells over the subcontinent. No change in rainfall seasonality over southern Africa is expected. Nonetheless, little
confidence exists in projected changes in total rainfall. While both types of model simulate
a 10-15% decrease in summer rainfall on average, projected changes are smaller than the simulation errors and little inter-model consensus in terms of the sign of projected changes
exists. No change in the location or intensity of anticyclonic circulation and divergence at
700 hPa in winter is expected. While fully-coupled models provide a more comprehensive
treatment of the global climate system and the process of climate change, there is no
evidence to conclude that current fully-coupled models should be used to the exclusion of
mixed-layer models when developing regional climate change scenarios for southern
Africa.Andrew Chakane 201
UniLingua: intercambio lingĂŒĂstico interuniversitario Complutense
UniLingua es un proyecto de intercambio lingĂŒĂstico virtual cuya misiĂłn es poner en contacto a los alumnos de la Universidad Complutense de Madrid con alumnos de otras universidades extranjeras para que desarrollen sesiones de intercambio lingĂŒĂstico en lĂnea. En esta memoria, se resumen el desarrollo y los resultados de la cuarta ediciĂłn del proyecto, llevada a cabo en el curso acadĂ©mico 2023-2024.Depto. de Lengua Española y TeorĂa de la LiteraturaFac. de FilologĂaFALSEsubmittedAPC financiada por la UC
Guidelines for the use and interpretation of assays for monitoring autophagy
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field
Guidelines for the use and interpretation of assays for monitoring autophagy
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field