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.

The impact of the Madden Julian Oscillation (MJO), a major source of intraseasonal variability in the tropical atmosphere, on the Indonesia Seas is investigated using satellite-derived, reanalysis and mooring data. The MJO footprint on the Indonesian Seas is evident from the surface layer into the pycnocline. In the surface, MJO air-sea heat fluxes govern the intraseasonal sea surface temperature (SST) variations. Within the pycnocline, the MJO reduces the transfer of the Pacific water to the Indian Ocean, the Indonesian Throughflow (ITF). In addition to the ocean’s response, the oceanic feedback to the MJO is also examined. Warmer SST in the Indonesian Seas during the suppressed phase of the MJO promotes the MJO convective phase to propagate eastward over the maritime continent (MC). Intraseasonal SST variation accounts for 55 - 60% of the total non-seasonal SST variance across the Indonesian Seas. It is most energetic in Banda and Timor Seas, with its standard deviation varying between 0.4 – 0.5°C. Coupled to the MJO surface fluxes, the intraseasonal SST exhibits stronger variation in boreal winter than in summer. A slab ocean model indicates that MJO surface heat fluxes account for 69-78% of the intraseasonal SST variability. The SST increases by 1.1° - 2°C, on average, in response to intense surface heating and weak winds over the suppressed (dry) MJO phase, and then decreases by 1.8° - 2.1°C over the course of the ensuing MJO active phase that is characterized by enhanced convective cooling and westerly wind bursts. Intraseasonal variability is also significant in the Sulawesi Sea SST, but it is mostly derived from eddies and local winds. Over the period 1980 - 2012, we observe 86 significant MJO (Real-time Multi variate MJO index > 1) events occurring in the Indian Ocean, of which 51 events achieve eastward propagation (EP) over the MC, while 35 events attentuate in the eastern Indian Ocean, or show no propagation (NP) over the MC. Eastward propagation (EP) MJO events occur more frequently during La Niña years than during El Niño years. Analyses of SST across the Indonesian Seas during the suppressed phase of the MJO events indicate that the SST in Java, Banda, and Timor Seas attributed to the EP MJO events is warmer by 0.5oC that associated with the NP MJO events. The warmer SST corresponds with enhanced surface latent heat flux, sensible heat flux, and low-level moisture in the atmospheric boundary layer, driven by diurnal activity. The EP MJO events are more frequent during La Niña, as the SST response to MJO events is influenced by the thermocline depth: shallower thermocline during El Niño enables cooler subsurface water under the MJO forcing to reduce SST that then attenuates MJO activity, with deeper thermocline of La Niña having the opposite outcome. Moored velocity data in Makassar Strait between 2004 – August 2011 and August 2013 – August 2015 document substantial direct impacts of the MJO on the ITF, particularly with the surface layer (< 80 m ). A composite of the along-strait velocity within the surface layer for 10 MJO events observed during the observational period exhibits strong northward velocity within days, following the peak of MJO wind stress. The MJO forces both northward along-strait pressure gradient and the resultant of northward wind stress and turbulent stress at the base of the surface layer that, together with the seasonal forcing, maintain the reduction or even reversal of the ITF southward transport on timescales of 1-3 months during boreal winter.

Weather and climate forecasts are almost exclusively produced by computer models, which use atmospheric measurements as starting points. It is a well-known and joked-about fact that model predictions can be incorrect at times. One of the reasons this happens is due to gaps in our knowledge of atmospheric conditions in areas where measurements don’t often taken place, such as the mesosphere, which stretches from roughly 45-90 km altitude. A lidar is a device that can shoot out short bursts of laser light to measure things such as atmospheric thickness at a distance. From this information one can then derive the temperature in the upper atmosphere. Using temperature measurements taken by lidar at Utah State University (41.74° N, 111.81° W) and temperatures from three popular atmospheric models, a comparison is made covering the period 1993-2004 at 45 km altitude. This comparison demonstrates poor predictive capabilities of the models at the target altitude and suggests the need for integrating datasets such as lidar data into future models. The modeling community depends on real measurement comparisons to bolster the reliability and credibility of their own work, and the comparison done here is intended to highlight an area in need of improvement.

No description available.

Typescript (photocopy) / ix, 171 leaves, 2 leaves of plates : ill. ; 30cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1980

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 105-110).

L'eau tensile est de l'eau liquide métastable qui persiste dans le champ de stabilité de lavapeur à pression négative, sa durée de vie est finie. Des états de traction de l'eau jusqu'à -1400 baront été mesurés de façon spécifique dans des micro-inclusions intracristallines. La nucléation devapeur (Tn) marque le retour à l'équilibre. Les effets destructeurs liés à la rupture d'états transitoiresd'eau tensile sont observés dans le milieu naturel : explosions phréato-magmatiques, geysers.Modéliser la cinétique de l'eau métastable est fondamental pour gérer les risques qui lui sontassociés. Des inclusions fluides synthétiques (IF) de composition et de densité connues, piégées dansdu quartz, ont été placées dans le champ métastable par refroidissement isochore et leurs gammesde métastabilité ont été mesurées. On montre que la traction maximale de l'eau dans chaque IFdépend de son volume et de sa forme, de la méthode de synthèse de l'IF, de la chimie des solutionsoccluses. Des expériences de durée de vie ont été ensuite réalisées sur des IF placées de 0,5° à10°C au-dessus de leurs Tn. Les 8 IF choisies rende nt compte de la diversité des formes, desvolumes, des densités et gammes de traction observées. Les résultats montrent que la durée de viede l'eau tensile en IF est d'autant plus courte que la traction de l'eau est plus forte. Une loiempirique est proposée qui permet de calculer la durée de vie de la métastabilité pour chaque IF deTn et volume fixés. Par ailleurs, nos données peuvent être rendues compatibles avec la ThéorieClassique de la Nucléation. Nos résultats montrent que l'eau dans les réservoirs poreux naturels peutrester métastable pendant des durées géologiques et ainsi, contrôler les interactions fluides-rochesdans la croûte.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983. / Includes bibliographical references (p. 226-229).

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Removing the effects of the atmosphere from remote sensing data requires accurate knowledge of the physical properties of the atmosphere during the time of measurement. There is a nonlinear relationship that maps atmospheric composition to emitted spectra, but it cannot be easily inverted. The time evolution of atmospheric composition is approximately Markovian, and can be estimated using hyperspectral measurements of the atmosphere with particle filters. The difficulties associated with particle filtering high-dimension data can be mitigated by incorporating future measurement data with the proposal density.