TRACT (maximum 200 words) The Northern Oscillation Index (NOI), an atmospheric climate index relating climate variations in the tropical Pacific and Northeast Pacific was used to selectively average output from the Parallel Ocean Climate Model (POCM 4C) for 1979-1998. Composites, or smart climatologies, were made representing El Nino (EN) and La Nina (LN) conditions, as well as a long term mean (LTM) average or traditional climatology, for November to March. Conditions in the California Current System (CCS) in the smart climatologies were consistent with large scale features noted in previously published studies of EN and LN. Overall, the patterns of anomalies (POCM 4C Smart Climatology minus POCM 4C Traditional Climatology) in salinity, temperature, and currents were opposite in sign and magnitude between the EN and LN composites. This was expected for opposite phases of the same climate variation, and many of the model's EN/LN differences were found to be statistically significant. Therefore, POCM 4C smart climatologies provide better estimates of ocean state and circulation patterns than traditional climatology. Such smart climatologies offer improved environmental information to Naval operational and strategic planners. They are also useful for studying climate variations, and in improving boundary and initial conditions for ocean and atmosphere models.

Naval Aviation has been known for over half a century as being one of the most fascinating professions. Although aircrew may always play a role in the mishap rate, the Navy has shifted its focus to aviation maintenance safety climate as a possible indicator of a future mishap. The School of Aviation Safety developed and implemented a survey, the Maintenance Climate Assessment Survey (MCAS), to assess the safety climate of Naval Aviation squadrons. Researchers have begun reviewing the possible direct relationship between the maintainer, how they view their squadron's climate and aviation mishaps. This thesis examines the construct of squadron maintenance safety climate survey and its relationship to aviation mishaps. The raw data employed includes MCAS responses from 126,058 maintainers between August 2000 and August 2005. This study finds that the MCAS survey construction needs to be revised. The findings are substantial to verify that most questions are formulated to focus on the same factor. Since the survey requires reconstruction, the question of whether it can determine the likelihood of mishaps was never visited. Revising the survey, based on psychometrics, may produce more significant results and gauge maintenance safety climate based on separate and distinct factors.

The dynamic response of the oceanic mixed-layer to the thermodynamic forcing at the sea surface is analyzed in order to describe the pattern of the oceanic meridional overturning. The technique proposed in this study is based on residual-mean theory, which takes into account the transport of buoyancy and tracers by transient eddies. From the observed air-sea density flux and mixed-layer density distributions, we estimate the two components of the Meridional Overturning Circulation (MOC) corresponding to the adiabatic (along-isopycnal) advection and the diabatic (cross-isopycnal) flux. Calculations are performed for the global ocean and, additionally, for each oceanic basin. The proposed method extends the Walin (1982) mass transformation theory, and permits, for the first time, assessment of the strength of the MOC adiabatic component from the sea surface data. This study offers a statistical description of the atmospheric and oceanic databases and gives some suggestions for the choice of specific datasets. In particular, the two most reliable atmospheric climatology databases (ECMWF and NCEP/NCAR re-analyses) are compared, and the impact of their inaccuracies on the MOC calculations is evaluated.

The Madden-Julian Oscillation (MJO) has been associated with extreme precipitation events in western North America. However, the mechanisms for, and predictability of, these associations are not clear. We have examined the influence of the MJO on North Pacific - North America (NPNA) circulation and precipitation anomalies during the boreal winter. We constructed composites of MJO events during 1979-2005 determined from the Wheeler RMM1/RMM2 index of MJO activity. Our analyses of NPNA anomalies were based primarily on the National Centers for Environmental Prediction reanalysis data set. We focused our investigations on the impacts on NPNA circulation and precipitation of: (1) the location and amplitude of the convective and subsidence components of the MJO; (2) the season of MJO occurrence; and (3) concurrent El Nino (EN) or La Nina (LN) events. We found that the NPNA response to the MJO is sensitive to the location of both the convective and subsidence components of the MJO, the season of MJO occurrence, and to the existence of concurrent EN or LN events. EN or LN events affect the extratropical response to the MJO by altering the equatorial Rossby-Kelvin wave response to the components of the MJO. This in turn affects the anomalous extratropical wave trains initiated by the MJO, and alters the strength and location of the resulting NPNA precipitation anomalies. Our results have allowed us to identify characteristic patterns associated with the MJO that can be related to the location and intensity of extreme NPNA precipitation. MJO events are relatively persistent phenomena. Thus, increased understanding of the mechanisms by which they impact the extratropics has the potential to improve extratropical extended range forecasting. Our results provide a substantial foundation for improving forecasts of NPNA circulation and precipitation.

A detailed examination of low visibility (LV) occurrences and the weather types that cause low visibility, with a focus on fog, was performed for five weather stations in the western Canadian Arctic, in the vicinity of the Amundsen Gulf area of the eastern Beaufort Sea. A series of climatologies were developed that established patterns of LV occurrence as a proportion of all observations and as a function of LV events caused by fog. Frequency climatologies for other weather types were also performed; in particular, for snow, blowing snow, rain, and drizzle. Annual climatologies were used to identify trends in several weather parameters over the 1980-2015 period of study. Monthlies were used to identify typical patterns of occurrence over the course of a year, and hourlies over the course of a day. A dataset of multi-hour fog events was also created; some of these were related to synoptic patterns. Analysis was also broken down by season. Results indicate several things. Monthly climatologies showed considerable diversity across the study area. Three distinct groupings were noted: Tuktoyaktuk and Ulukhaktok with a maximum frequency of LV conditions in February, Aklavik and Inuvik with a maxiumum frequency in October, and Sachs Harbour in August. The February maximum in Tuktoyaktuk and Ulukhaktok was related to cold air temperatures combined with small amounts of moisture from sea ice leads. The Alkavik and Inuvik October maximum was related to moisture advected over land from remaining open water, as well as diurnal snow melt adding moisture to the boundary layer that condenses as the evening cools off. The August maximum in Sachs Harbour is a reflection of proximity to open water and cold air temperatures. Hourly climatologies in the spring/fall season showed most stations have maximum occurrence of LV events caused by fog in the early morning. This is a radiative effect; cooling overnight causes radiation fog that peaks in occurrence just as morning begins. This peak is pushed into the midday in the winter, and is much weaker in the summer, both reflections of the changing pattern of daylight hours. / Graduate

In the year 2002 the Swedish Energy Agency assigned the department of Earth science at Uppsala University a research assignment to make a detailed wind climatology mapping covering Sweden. A survey of the Swedish wind climate has been made earlier in some areas, using the Danish model WASP. In this study the MIUU-model is usedwhich is a mesoscale three dimensional numerical model with a turbulence closure scheme of level 2.5. The MIUU-model is computer time demanding. Therefore a method to minimize the total number of simulations is wanted, without negative effects on the result. In this thesis the main issue is to compare the sensitivities and differences between climatological wind calculations using runs with different forcing parameters, i.e. with different meteorological conditions. Primarily the climatological results received with different geostrophic wind forcing are studied and compared. The idea is to find combinations with as small deviations as possible. The parameters investigated, called flow forcing parameters, are; geostrophic wind (magnitude and direction), thermal wind and thermal stratification. To compare the calculations a reference run is used. In theruns studying the influence of the geostrophic wind, calculations where made with 1, 2, 3 and 6 geostrophic wind speeds and with 4, 8, 16 and 32 wind directions. All compared to the reference that is based on 3 wind speeds and 8 wind directions. The model has earlier been used without any thermal wind influence. Therefore radio sonde data have been used to calculate the geostrophic mean wind profile introduced in the model to make new runs. The thermal stratification has also been modified in April and October to find out the sensitivities in the model. The result shows that there are only a few possible shortcuts in the number of runs needed and in the verification of the parameters. The question is if it is worth searching for them, since they might not be valid in other areas with more complex terrain. To be on the safe side, runs like the reference runs should at least be used in order to get accurate results as regards the wind climate. / År 2002 gav Statens Energimyndighet ett uppdrag till Institutionen för geovetenskaper vid Uppsala Universitet att kartlägga det svenska vindklimatet. En kartläggning av vindklimatet i vissa delar av Sverige har gjorts tidigare med hjälp av den danska modellen WASP. I denna avhandling används MIUU-modellen som är en mesoskalig tredimensionell numerisk modell med ett ’closure scheme of level 2.5’. MIUU-modellen kräver mycket datorkraft och därför söks ett sätt att minimera antalet modellkörningar utan försämrat värde på resultaten. I denna avhandling är huvuduppgiften att jämföra känsligheten och skillnaderna mellan klimatologiska beräkningar från modellkörningar med olika drivande parametrar i modellerna, d v s med olika meteorologiska förhållanden. De erhållna klimatologiska resultaten från olika geostrofiska vindhastigheter är plottade. För att jämföra resultaten ritas en ny plott som visar avvikelserna mellan de två originalresultaten. Syftet är att hitta plottar med så små skillnader som möjligt. De undersökta parametrarna, som är av stor betydelse för modellen är: geostrofisk vind (styrka och riktning), termisk vind och temperaturskiktning. För att jämföra beräkningarna används en referenskörning. I modellkörningarna med den geostrofiska vinden görs beräkningar med 1, 2, 3 och 6 olika geostrofiska vindstyrkor och med 4, 8, 16 och 32 vindriktningar. Alla jämförs med referensen som är beräknad på 3 vindstyrkor och 8 vindriktningar. Modellen har tidigare använts utan termisk vind. Från Universitetet i Wyoming har därför data hämtats för att beräkna den geostrofiska medelvindprofilen som införts i modellen för nya modellberäkningar. Temperaturskiktningen har också modifierats i april och oktober för att kontrollera känsligheten i modellen. Resultaten visar att det bara finns några få genvägar bland parametrarna. Frågan är om det är värt att leta efter dem, eftersom de mest troligt inte är de samma om man tittar på andra områden med mer kuperad terräng. För att vara på den säkra sidan är beräkningarna med samma parametrar som referenskörningarna det bästa sättet att få bra resultat avseende vindklimatet.

Orientador: João Afonso Zavattini / Banca: Marcos Norberto Boin / Banca: José Bueno Conti / Resumo: Por fazer parte de uma região cuja dinâmica climática ainda é pouco conhecida, objetivou-se, ao estudar o Distrito Federal, oferecer uma contribuição para a caracterização do quadro climático local. Para isto, foi feita uma breve caracterização do quadro climático regional no qual esta área encontra-se inserida para, então, chegar-se à caracterização de seu regime pluviométrico. Tendo em vista que nas regiões tropicais as variações pluviais traduzem o ritmo atmosférico, a partir da caracterização do regime das chuvas no Distrito Federal, foram analisados, sob o ponto de vista da climatologia dinâmica, episódios pluviais de caráter habitual e excepcional. Os resultados climatológicos obtidos permitiram que se chegasse à compreensão do regime pluvial, bem como do ritmo de sucessão de alguns estados atmosféricos que ocorrem na área em questão. Espera-se, assim, que este trabalho represente um estudo de base que possa servir de subsídio a futuras pesquisas de climatologia sobre a área em questão. / Abstract: Being part of an area in wich the climatic dynamics still isn't well know the study of Distrito Federal aims a contribution to the characterization of the local climatic configuration. For that, a small characterization of the regional configuration was done, in wich this area is inserted, reaching then a characterization of the pluviometrical regime. Knowing that in the tropical areas the pluvial variations state the atmospherical rithm, based in the characterization of the rain's regime in the Distrito Federal, under the dynamical climatology's point of view, pluvial episodes of habitual and exceptional nature were analysed. The climatologic results allowed to comprehend the pluviometrical regime, as well as the succession's rithm of several atmospherical states, which occur in the studied area. Hope is that work represents a study which serves as a sudsidy for future climatological researches of this area. / Mestre

The Southwest United States (SWUS) is facing an ongoing drought which has led to water short- ages, in addition to forest mortality due to wildfire and bark beetle outbreaks associated with increased temperatures. This region has a population of 9.6 million people and is one of the fastest growing parts of the United States, and pressure on its resources can be expected to increase in the future. The SWUS is also projected to become more arid in the coming century under greenhouse gas induced climate change, which will impact its environmental, economic and social vitality. This thesis explores the climate dynamics which control water availability, streamflow, and vegetation green-up in the SWUS, in order to constrain our understanding of the mechanisms controlling the ecohydrology of the region, and to inform projections for the 21st century. Chapters 1 and 2 investigate the climate drivers responsible for producing the observed vari- ability in streamflow for the Gila River, a tributary of the Colorado, and the upper Rio Grande. The Gila is the southernmost snowfed river in the SWUS, and has a spring streamflow peak that responds to melting of the snowpack at its headwaters in New Mexico. The Gila is also sufficiently south so that it has a secondary streamflow peak in the summer which is fed by rains from the North American Monsoon (NAM). On interannual timescales, the Gila’s spring peak is primarily influenced by natural variability associated with Pacific sea surface temperature (SST), while the summer peak apparently does not respond to interannual variability. The upper Rio Grande is fur- ther north and east in the SWUS, and only has one streamflow peak occurring in spring-summer which is influenced by both tropical Pacific SST and Atlantic SST. Spring streamflow has also declined in each river post-1998, and this is due to a shift in the tropical Pacific leading to negative precipitation anomalies and drying in the SWUS. Chapter 2 assess a region of the SWUS that receives both winter storm track precipitation and NAM, and therefore has two periods of vegetation green-up annually with an intervening spring dry season. The first peak in vegetation occurs during the spring, and is influenced by the magnitude of winter precipitation and snowmelt, which gradually adds water to the soils. The second peak in vegetation follows the spring dry season when soil moisture recovers with the arrival of the NAM. A climatic shift in the tropical Pacific occurred in 1997/98 and produced a shift to an earlier and more severe spring dry season, and reduced vegetation green-up. An earlier extended dry period in the mid-century (1948 to 1966) also was influenced by a cool phase of the tropical Pacific, which led to a reduction in precipitation of a similar magnitude as the recent drought. However, the recent drought is more severe - and temperatures also have been greater during the recent period. Using a decomposition of the impact of precipitation and potential evapotranspiration (PET) on soil moisture, we found that PET contributed 39% to the negative soil drying anomalies in the recent post-1998 drought, compared to 8% during the earlier extended dry period. This indicates an increased role of temperature during the recent drying. In Chapter 4 we evaluated 18 CMIP5 models based on comparisons with observations of pre- cipitation, net ecosystem exchange, leaf area index and soil moisture from land surface model output. Following our evaluation, we selected three models which best simulated the bimodal region: CanEMS2, GFDL-ESM2G and GFDL-ESM2M. These models indicate that overall this region will be drier in the 21st century; runoff is projected to decrease, particularly in the spring, soil moisture is reduced, and snow fall declines. The variability in projected precipitation, how- ever, is large, and we find that for the most part does not exceed what can be expected from model natural climate variability. The multi-model ensemble from the rest of the CMIP5 models indicate an overall decline in annual precipitation by the end of the 21st century, particularly during the spring. The three models also project an increase in net primary productivity in both the spring and summer growing seasons due to the effects of CO2 fertilization. Enhanced vegetation growth is likely to further exacerbate drying of the soils as vegetation draws down moisture, and enhances water losses via evapotranspiration. The fertilization process is, however, still uncertain and fur- ther studies are needed on the representation of CO2 enhanced vegetation growth in the SWUS to constrain this result. The findings of this thesis have contributed enhanced our knowledge of how climate dynamics, natural variability, and recent warming have influenced the ecohydrology of the SWUS, and also inform future climate projections. Constraining our understanding of this region is of importance given the growing populations, mounting pressures on natural resources, and anthropogenically induced climate change which is expected to affect this region in the 21st century.

Tornadoes cause numerous deaths and significant property damage each year, yet how tornado activity varies across climate states, particularly under global warming, remains poorly understood. Importantly, severe weather events arise during transient periods of extreme thermodynamic environments whose variability may differ from that of the environmental mean state. This study analyzes the climatological relationships between commonly-used severe weather environmental proxies (the product of convective available potential energy and bulk vertical wind shear, energy-helicity index, and the significant tornado parameter) and tornado density on three dominant timescales of climate forcing: diurnal, seasonal, and interannual. We utilize reanalysis data to calculate the spatial distributions of the mean, median, and a range of extreme percentiles of these proxies across each timescale as well as for the full climatology. We then test the extent to which each measure captures the spatiotemporal variability of tornado density over the continental United States. Results indicate that the mean is a suitable statistic when used with the full climatology of the energy-helicity index and the significant tornado parameter without using convective inhibition in calculations, the diurnal cycle for convective available potential energy and the product of convective available potential energy and bulk vertical wind shear, and the interannual variations for all proxies except convective available potential energy. The mean is outperformed by extreme percentiles otherwise. This understanding of climatological relationships between tornadoes and the large scale environments can improve prediction of tornado frequency and provides a foundation for understanding how changes in the statistics of large-scale environments may affect tornado activity in a future warmer climate state.

This thesis develops an innovative process-based analysis of contemporary model performance of precipitation over southern Africa. This region is typically understudied and not fully understood due to the complexity of various influences and drivers of precipitation. Historical simulations of precipitation are assessed including principal drivers, sources of biases and dominant modes of interannual variability. The South Indian Ocean Convergence Zone (SIOCZ), a large-scale, austral summer rainfall feature extending across southern Africa into the south-west Indian Ocean, is evaluated as the feature of interest in historical simulations. Most CMIP5 models simulate an SIOCZ feature, but are typically too zonally oriented and discontinued between land and the adjacent Indian Ocean. Excessive precipitation over the continent is likely associated with excessively high low-level moisture flux around the Angola Low, which is almost entirely due to model circulation biases. Drivers of precipitation over southern Africa include three dominant moisture flux transport pathways which originate from flow around the SIOHP and SAOHP and monsoon winds. Interannual variability in the SIOCZ is shown by a clear dipole pattern, indicative of a northeast-southwest movement of the SIOCZ. Drivers of this shift are significantly related to the El Niño Southern Oscillation and the subtropical Indian Ocean dipole in observations. However models do not capture these teleconnections well, limiting confidence in model representation of variability. A large majority of the population rely heavily on precipitation over southern Africa for agricultural purposes. Therefore spatial and temporal changes in precipitation are crucial to identify and understand with intentions to ultimately provide useful climate information regarding water security over the region. Key climate change signals over southern Africa are established in this thesis (OND and DJF), in which the dominant regional mechanisms of precipitation change over southern Africa are quantified. Robustness and credibility of these changes are additionally quantified. The most notable projected change in precipitation over southern Africa is the distinct drying signal evident in the pre-summer season (OND). This has the implication of delaying the onset of the rainy season affecting planting and harvesting times. Future projections of the SIOCZ are determined, which indicate a northward shift of approximately 200km. A dipole pattern of precipitation wetting/drying is evident, where wetting occurs to the north of the climatological axis of maximum rainfall, hence implying a northward shift of the ITCZ, consistent with the SIOCZ shift. Using a decomposition method it is established that ΔP's dipole pattern emerges largely from the dynamic component, which holds most uncertainty, particularly over the south-west Indian Ocean. Changes in precipitation over land are not solely driven by dynamical changes but additionally driven by thermodynamic contributions, implying projected changes over land and ocean regions require different approaches. SST patterns of warming over the Indian Ocean corroborate the warmest-get-wetter mechanism driving wetting over the south-west Indian Ocean, which is robust in both key seasons. Coherent model behaviour is understood via across model correlation plots of principal components, whereby patterns of coherent warming patterns are identified. Composite analyses of diagnostic variables across models illustrate patterns driving projected precipitation changes. Drying is more robust over land than over the south-west Indian Ocean. Clear robust drying signal in OND, however magnitude is uncertain. Drivers of uncertainty include SST pattern changes, which modulate atmospheric circulation patterns. Therefore reductions in uncertainty rely on the accurate representation of these processes within climate models to become more robust. There is a desire from both climate scientists and policy-makers to reduce uncertainty in future projections. No one particular methodology is unanimously agreed upon, however one approach is analysed in this thesis. Uncertainties of future precipitation projections are addressed using a process-based model ranking framework. Several metrics most applicable to southern African climate are selected and ranked, which include aspects of both mean state and variability. A sensitivity test via a Monte Carlo approach is performed for various sub-samples of “top” performing models within the CMIP5 model dataset. Uncertainty is significantly reduced when particular sub-sets of “top” performing models are selected, however only for austral summer over the continent. The result has the implication that potential value is established in performing a process-based model ranking over southern Africa. However additional investigation is required before such an approach may become viable and sufficiently credible and robust. Reductions in model spread are additionally established in SIOCZ projections, whereby model processes of change exhibit agreement, despite differing initial SIOCZ conditions. Therefore model process convergence and coherence is established with respect to projected changes in the SIOCZ, irrespective of initial climatology biases.