This dissertation investigates three topics concerning high clouds: 1) convectively coupled equatorial wave (CCEW) signals derived from cloud top temperature (CTT) and cirrus optical thickness retrieved from satellite observations; 2) investigation of the physical mechanism governing the fixed anvil temperature (FAT) hypothesis and test of FAT hypothesis with CTT measurements; and 3) the intercomparison of cloud fraction and radiative effects between satellite-based observations and reanalysis product and simulations from general circulation models (GCMs). A wealth of information on CCEWs is derived from Aqua/MODIS cloud-top properties. We apply space-time spectral analysis on more than 6 years of CTT and isolate various modes of CCEWs including Kelvin, n = 1 equatorial Rossby, mixed Rossby-gravity, n = 0 eastward inertio-gravity waves, and the Madden-Julian oscillation. The successful application of the same method to cirrus cloud optical thickness confirms robust convective signals at upper troposphere. Consistent with the physical governing mechanism of the FAT hypothesis, the peak clear-sky diabatic subsidence, convergence and cloud fraction are located at roughly the same level (200 hPa), which is fundamentally determined by the rapid decrease of water vapor concentration above this level. The geographical maxima of cloud fraction agree well with that of water vapor, clear-sky cooling rates, diabatic subsidence and convergence at 200 hPa. An analysis of the response of the tropical mean CTT anomaly time series to sea surface temperature indicates that a possible negative relationship is present. In addition, we suggest interpreting the FAT hypothesis, and the more recent proportionately higher anvil temperature (PHAT) hypothesis, by using the temperature at the maximum cloud detrainment level instead of the CTT. Simulations of cloud fraction and radiative properties using two versions of the NCAR CAM models indicate that an overall improvement is observed in CAM5 compared to CAM3. However, an apparent bias in CAM5 shortwave (SW) cloud radiative forcing (CRF) simulation is shown in boreal winter southern mid latitude. This bias is primarily due to the underestimation of fraction-weighted SW CRF related to both high and middle top clouds. Additionally, apparent compensation errors are observed in models.

<p>The Southeastern United States (SE US) is one of the fastest developing regions of the nation, where summer precipitation becomes increasingly important to sustain population and economic growth. In recent decades, the variability of SE US summer precipitation has significantly intensified, leading to more frequent and severe climate extremes. However, the processes that have caused such enhanced climate variability have been poorly understood. By analyzing atmospheric hydrological cycle, diagnosing atmospheric circulation dynamics, and performing regional climate simulations, this dissertation investigates the mechanisms responsible for SE US summer precipitation variability. </p><p>Analysis of regional moisture budget indicates that the variability of SE US summer precipitation is primarily controlled by moisture transport processes associated with the variation of the North Atlantic Subtropical High (NASH) western ridge, while local water recycling is secondary. As the ridge moves northwestward (NW) into the US continent, moisture transport pathway is away from the SE US and the upward motion is depressed. Thus, rainfall decreases over the SE US, leading to dry summers. In contrast, when the ridge moves southwestward (SW), moisture convergence tends to be enhanced over the SE US, facilitating heavier rainfall and causing wetter summers. However, as the ridge is located relatively eastward, its influence on the summer precipitation is weakened. The intensified precipitation variability in recent decades is attributed to the more frequent occurrence of NW- and SW-type ridges, according to the "NASH western ridge - SE US summer precipitation" relationship. </p><p>In addition, the "NASH western ridge - SE US summer precipitation" relationship acts as a primary mechanism to determine general circulation model (GCM) and regional climate model (RCM) skill in simulating SE US summer precipitation. Generally, the state-of-the-art GCMs that are capable of representing the abovementioned relationship perform better in simulating the variability of SE US summer precipitation. Similarly, the RCM simulated summer precipitation bias over the SE US is largely caused by the errors in the NASH western ridge circulation, with the physical parameterization playing a secondary role. </p><p>Furthermore, the relationship between the NASH western ridge and SE US summer precipitation well explains the projected future precipitation changes. According to the projection by the ensemble of phase-5 of Coupled Model Intercomparison Project (CMIP5) models, summer precipitation over the SE US will become more variable in a warming climate. The enhancement of precipitation variability is due mainly to the atmospheric circulation dynamics, resulting from the pattern shift of the NASH western ridge circulation. In a warming climate, the NASH circulation tends to intensify, which forces its western ridge to extend further westward, exerting stronger impact on the SE US summertime climate. As the ridge extends westward, the NW- and SW-type ridges occur more frequently, resulting in an increased occurrence of extreme summers over the SE US. </p><p>In summary, the studies presented in this dissertation identify the NASH western ridge as a primary regulator of SE US summer precipitation at seasonal scale. The "NASH western ridge - SE US summer precipitation" relationship established in this study serves as a first order mechanism for understanding and simulating processes that influence the statistics of extreme events over the SE in the current and future climate.</p> / Dissertation

This thesis documents a series of studies performed on the lower atmosphere over the region of the Ross Ice Shelf, Antarctica, and its surroundings. In particular, much of the thesis focuses on the area in the vicinity of Ross Island, a mountainous protrusion in the far north-west of the permanent floating ice shelf. Weather in both the smaller and larger regions is naturally complex and generated by a range of localised and larger scale interactions. In order to better understand the meteorology of the Ross Ice Shelf, including Ross Island, we produce a synoptic climatology of the region based on surface wind output provided by the ERA Interim reanalysis. Output is taken from 1979 to 2011 and thus represents a much longer time scale than covered by previous studies of Ross Ice Shelf winds. The climatology is generated through a clustering routine based on the widely-used $k$-means technique. The results of the routine are discussed and we find that the reanalysis is capable of representing the previously reported features of the region. Cluster composites are also shown to be coherent between reanalysis output and data collected by in situ monitoring devices. We confirm that the Ross Ice Shelf Air Stream (RAS), a jet of fast-moving air that propagates from the Siple Coast across the ice shelf, is a robust feature of the climatology of the region and we find that it has a large impact on the surface temperature. The analysis is continued with reference to two widely studied modes of internal variability, the Southern Annular Mode (SAM) and El Nino-Southern Oscillation (ENSO), which are known to affect local conditions in the Ross Sea region via modulation of the Amundsen-Bellingshausen Sea low. Reanalysis output and results from the clustering routine allow us to examine the impacts of these modes upon the Ross Ice Shelf and Ross Sea in unprecedented detail. Further, we are able to tie changes in the mean pattern to variability within and between particular clusters, allowing us to ascertain the dominant synoptic patterns in forcing the mean variability. The impact on surface temperatures for both modes is found to be high and significant, which we explain with reference to changes in circulation patterns. We further use the results of the clustering algorithm to explore the climatology of the region surrounding Ross Island. By producing composites of local in situ records based on the clustering technique described previously, we are able to generate a climatology of the region that is not hampered by gaps in the observational record. We find that the climate of Ross Island is sensitive to RAS events, due to the ability of strong flows to dramatically increase the temperature. At Scott Base, on the southern tip of the Hut Point Peninsula, the temperature is found to be particularly sensitive to these events. McMurdo Station, which is located less than 3 km away, is observed to be much less sensitive, due to the modulation of synoptic flows by localised topographic influences. Particularly salient is the difference in temperature trends between these two locations, which we show to be statistically significant in the annual and seasonal means from 1979 onwards. By applying a novel temperature reconstruction technique based on the output of the clustering routine, we are able to assess the contribution of changes in circulation to temperature trends at these two locations. We conclude that a large amount of the change in temperature at Scott Base can be explained through circulatory variability over the Ross Ice Shelf. However, the trend at McMurdo Station can not be explained using this technique and may be the result of extremely localised forcing. Data availability in Antarctica is widely known to be low, due to the relative sparsity of observations and ongoing problems with data collection due to extremely inhospitable conditions and challenging logistical considerations. The lack of data at the mesoscale has hampered the understanding of localised processes in the Antarctic atmosphere that may be important for forecasting. Through the development and deployment of a distributed system of atmospheric sensors called

The aim of this thesis is to explore the under-studied area of deliberative democratic politics at the local level, while adding to the literature on deliberative theory itself. Empirical research was conducted through the qualitative tools of participant observation in Project Lyttelton’s Energy Matters Workshop and in-depth interviews with Project Lyttelton members, workshop participants and local government representatives. A comparative analysis was also undertaken between two locally focussed initiatives looking at citizen engagement and democracy in relation to climate change. The findings of this research suggest that Project Lyttelton’s Energy Matters Workshop answers the call for a deliberative approach through its use of the key institutional features of deliberative democratic processes. The research findings also show that local deliberative initiatives may not be about reaching consensus or agreement in relation to a particular issue such as climate change. Rather, they may be focused on building up a network of citizens that discuss new ideas, build awareness, invigorate public engagement, highlight shared interests and motivate new initiatives. However, the research data also draws attention to compelling, and as yet unanswered questions, about just what conditions are needed for local deliberation to affect public policy and climate change decision-making, how deliberative practices could be integrated within government structures themselves, how the current political framework (and context) could act as a spur to those at the local level, and how local participation and deliberation could have a voice in the largely international climate change arena. This research adds to the scholarship on deliberative theory by examining what deliberation looks like at the local level, while providing further empirical research for deliberative theory itself.

This thesis is about rainmaking amongst the Ihanzu (or Isanzu), a 30,000-strong matrilineal, Bantu-speaking agricultural group of north-central Tanzania. By examining rain rituals and their cosmological underpinnings as locally envisaged, I suggest that central to the Ihanzu cultural imagination lies the notion of gender complementarity. In a number of contexts, but particularly in the context of rainmaking, I show how masculine and feminine principles of a gendered universe, when combined, are seen as a site of cosmic and divine powers. To join the genders is to transform, to create, to rejuvenate. Using oral and archival sources, the first section examines the nature of the Ihanzu dual monarchy between 1885 and 1976. In spite of the radical political, economic and social changes that took place throughout this period, the dual leadership-with one male and one female-and people's understandings of royal power and legitimacy remained constant: control over rains is control over reigns. Section two examines annual rainmaking rites as they occur today. The point is to show the extent to which gender complementarity pervades these rites, and the local logic as to why this must be so. An indigenously grounded, gendered model of transformation is developed that applies equally to making children as to making rain. Power, in Ihanzu eyes, comes in gendered pairs. Section three discusses measures taken when annual rain rites fail to bring rain, and how the gendered model of transformation applies to these remedial rites. The penultimate chapter, on rain-witchcraft, suggests that gendered witches are a cosmological inversion of gendered rulers, yet for both duos their powers are based on gender complementarity. In the conclusion it is argued that the notion of gendered complementarity as developed in the thesis might be equally useful in explaining rain rites elsewhere in Africa.

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No description available.

The California Current is the Eastern Boundary Current associated with the North Pacific Subtropical Gyre, transporting cold, nutrient-rich water equatorward. It is also an area of strong mesoscale eddy variance, as well as subsurface zonal currents known as striations. This work examines the causes and variability of these transports using a set of eddy-resolving ocean model simulations. Large-scale meridional transports are found to be driven interannually by the dominant local pattern of wind stress curl variability. This contrasts with earlier work that suggested that these transports were forced principally by tropically-originating coastal- trapped waves. While mesoscale eddies possess a large fraction of intrinsic variance, there is a deterministic component as well. North of the Southern California Bight this component is driven by the same pattern of wind forcing. To the south, eddies respond nonlinearly to both atmospheric and oceanic forcing. Striations are found to develop in response to irregularities in the California coastline. They spin up along with the large-scale circulation, and their magnitude is constrained by the shelf.

Salinity associated with irrigation is and will remain a major obstacle for farmers in most semi-arid regions throughout the world, like the Orange-Riet and Vaalharts Irrigation Schemes in South Africa. On-farm water and salt management should, therefore, be continually evaluated and/or improved. Especially in water table soils where the saturated zone within or just below the potential root zone is not stagnant and lateral flow occurs to lower lying areas and/or artificial drainage systems, which present unique management complexities. Hence, the aim of this study was to evaluate and/or improve on-farm water and salt management of irrigated field crops grown under these conditions. To accomplish this aim the following best water and salt management practices were formulated from literature, i.e. i) use of efficient irrigation systems, ii) introduce scheduling practices that optimize water and salt applications and reduce drainage losses, iii) utilize shallow water tables as a source of water for crop water requirements and iv) monitor root zone salinity to decide when to apply controlled, irrigation-induced leaching for salt removal. Some of these practices were evaluated on a case study basis on two farms within the Orange-Riet and Vaalharts Irrigation Schemes by comparing them to current water and salt management practices. Some aspects of this comparison are difficult to accomplish under field conditions. Supplementing field measurements with mathematical modeling was, therefore, critical to the successful completion of the study. This, however, presented some difficulties because most models require extensive effort to determine input variables and unambiguous numerical model parameters. From the multitude of available models, the Soil WAter Management Program, SWAMP, was selected. According to the aggregated accuracy, correlation and pattern analysis (ISWAMP) of SWAMP, it was found that water uptake of wheat, peas and maize from non-saline water table soils was simulated well (>70%). Consequently it was shown that the soil water balance under fluctuating water table conditions at field level can be solved successfully by SWAMP with limited easily obtainable input variables. This was accomplished by optimizing simply measured in situ field observations, which is vital towards the successful evaluation of water and salt management by irrigation farmers in the region. However, in order to truly revise on-farm water and salt management practices, mathematical models that can simulate the dynamic response of crops to both water (matric) and salt (osmotic) stress are required. A salinity subroutine for SWAMP was, therefore, developed and validated, i.e. mathematical algorithms that can simulate upward and downward salt movement in water table soils according to the cascading principle, and the effect of osmotic stress on water uptake and yield according to the layer water supply rate approach. It was found that SWAMP was able to simulate the accumulation of salt within the root zone above the water table due to irrigation and capillary rise well, and consequently simulate the effect on crop yield. This was possible because SWAMP was able to successfully (ISWAMP > 70%) simulate a reduction in water uptake during the growing season of field crops due to osmotic stress. Consequently SWAMP was used in the case study to solve the water and salt balances of two irrigated fields over four growing seasons and investigate whether the farmers employed best water and salt management practices, using different scheduling approaches. It was concluded that with both centre pivots, crop water stress was prevented, therefore, apparently detracting from the merits of irrigation scheduling. However, it was possible to conserve 20% of irrigation water using scientific based objective, compared to intuitive subjective scheduling, while at the same time also reducing salt additions considerably. Despite less irrigation due to objective scheduling, almost all of the applied salt was still leached into the water table. This was because the presence of a water table within or just below the potential root zone limits storage for rainfall and/or irrigation above the capillary fringe, hence presenting favorable leaching conditions. Since the water below the water table, at both fields, was not stagnant, lateral flow of water through the saturated zone was responsible for removal of the salts. This continual removal of salt is generally not considered good practice because ideally salt must be allowed to accumulate and only periodically leached during high rainfall events and/or fallow periods. Although both scheduling approaches resulted in similar yields, better on-farm water and salt management was achieved with scientific objective scheduling. In doing so farmers can address the environmental problems associated with irrigation, i.e. degradation of water resources due to uncontrolled leaching while achieving similar yields using less water.

Several environmental factors constantly play a role in crop failures. Of these high temperature and limited water supply are major factors that limit plant productivity and threatens food security. Hence, a search for alternative crops with good tolerance characteristics towards abiotic stress is an ongoing process. Amaranth has been established as an annual vegetable and grain crop and is seen as a prospective alternative crop. Seed germination and seedling development are presumed to be the most critical stages in the life cycle of many seed propagated crops. This served as a rationale for the underlying study on two amaranth species in terms of seed germination, as well as the morphological and physiological response of seedlings to different temperature (25, 30, 35, 40ËC) and water potential (0, -250, -500, -750, -1000, -1250 kPa) regimes. For A. cruentus the optimum temperature was between 25 and 30oC and between 30 and 35oC for A. hybridus in terms of seed germination and early seedling growth. A. hybridus showed a greater level of adaptation to the higher temperature regimes as well as when simultaneously exposed to a rather stringent water potential of -1250 kPa by maintaining root growth better than A. cruentus. Moreover, the imposed temperature/drought stress condition had no significant effect on either of the physiological parameters tested in the former species. These included sugar and total water soluble protein levels as well as photosynthesis and respiratory capacity. Together with the ability of stressed seedlings to maintain growth, the latter strongly suggests that the metabolic events were scarcely affected in A. hybridus, supporting the postulate that it showed a higher degree of tolerance towards abiotic stress conditions. Alternatively, more than half of these events were found to be upgraded in A. cruentus seedlings and interpreted as an attempt by this species to counteract the stress effects, but not successfully, as measured by its inability to maintain seedling growth under these stress conditions.