Dissertations / Theses on the topic 'Atmospheric circulation Australia, Northern'

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2006.
Dickinson, Robert, Committee Member ; Black, Robert, Committee Chair ; Cunnold, Derek, Committee Member ; Fu, Rong, Committee Member ; Knox, John, Committee Member.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.
Includes bibliographical references (leaves 150-157).
by Edward Paul Dever.
Ph.D.

Recent observational and modeling studies indicate a robust dynamical coupling between the stratosphere and troposphere during boreal winter. This coupling occurs in association with the Northern Annular Mode (NAM), which itself accounts for a significant fraction of the variability of the extratropical circulation. While monthly NAM dynamics have been studied previously, the mechanisms that give rise to NAM variability on short intraseasonal timescale are still unclear. We perform regression analyses, case studies, and composites based on periods of dynamical growth/decay to investigate the roles of the different proposed mechanisms in driving the atmospheric variability observed in association with the NAM on short intraseasonal timescales. More specifically, lag-regression analyses are used to identify the mean canonical structures present during the evolution of a typical NAM event. Illustrative case studies of robust stratospheric NAM events but with different tropospheric signals are contrasted in order to identify the underlying dynamical reasons for the observed differences. Finally, composite analyses of NAM tendencies are performed to isolate the structural and dynamical evolution of NAM events. Zonal-mean and three-dimensional eddy-flux diagnoses are used to examine the role of eddy-mean flow interaction in driving the wind tendencies characteristic of the NAM. In particular, Plumb flux analyses are employed to quantify the contribution of regional stationary wave anomalies toward the zonal mean wind tendency field. Potential vorticity inversions are also used to determine the role of stratospheric anomalies in inducing tropospheric circulations. The case study analyses indicate that preexisting tropospheric PV anomalies can mask the downward penetration of an initial stratospheric NAM signal into the troposphere. PV inversions further suggest that a minimum requirement for a direct downward stratospheric influence is that the stratospheric NAM signal be robust in the lower stratosphere. The dynamical composites show a remarkable degree of reverse symmetry between the zonal-mean dynamical evolution of positive and negative NAM events. Anomalous Eliassen-Palm fluxes are observed in the troposphere and stratosphere, consistent with index of refraction considerations and an indirect downward influence of the stratosphere on the troposphere. The patterns of anomalous wave driving, primarily due to low-frequency planetary scale waves, provide the main forcing of the zonal mean wind tendency field. Regional wave activity fluxes indicate that the wave driving pattern represents the manifestation of planetary scale anomalies over the North Atlantic.

Diss. (sammanfattning) Stockholm : Stockholms universitet, 2009.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 5: In progress.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.
Accompanied by one map on folded leaf in pocket.
Includes bibliographical references (p. 56-61).
by S. Julio Friedmann.
M.S.

Abstract This thesis studies the long-term relation between the solar wind driven energetic particle forcing into the atmosphere and the tropospheric circulation in the Northern Hemisphere winter. The work covers the period of more than one hundred years since the turn of the 20th century to present. The thesis makes a statistical analysis of satellite measurements of precipitating energetic electrons, sunspot number data and geomagnetic activity, and compares them with temperature and pressure measurements made at the Earth's surface. Recent results, both observational and from chemistry climate models, have indicated significant effects in the Earth's middle atmosphere due to the energetic electrons precipitating from the magnetosphere. These effects include the formation of reactive hydrogen and nitrogen oxides in the high latitude mesosphere and the depletion of ozone caused by them. Ozone is a radiatively active and important gas, which affects the thermal structure and dynamics of the middle atmosphere. Accordingly, the depletion of ozone can intensify the large scale stratospheric circulation pattern called the polar vortex. Winter weather conditions on the surface have been shown to be dependent on the polar vortex strength. This thesis shows that there is a significant relation between the average fluxes of medium energy (ten to hundred keVs) precipitating electrons and surface temperatures in parts of the Northern Hemisphere in winter time. Temperatures are positively correlated with electron fluxes in North Eurasia and negatively correlated in Greenland during the period 1980-2010 which is covered by direct satellite observations of precipitating particles. This difference is especially notable when major sudden stratospheric warmings and the quasi-biennial oscillation (QBO), which both are known to affect the polar vortex strength, are taken into account. When extended to the late 19th century, the analysis shows that a similar temperature pattern is predominated during the declining phase of the sunspot cycle. The high speed solar wind streams and energetic particle precipitation typically maximize also at the declining phase of the solar cycle. This specific temperature pattern is related to the variability of the northern annular mode (NAM), which is the most significant circulation pattern in the Northern Hemisphere winter. Before the space era, geomagnetic activity measured by ground observations can be used as a proxy for energetic particle precipitation. Earlier studies have found a significant positive correlation between geomagnetic activity and NAM since the 1960s. We find that, when the QBO measured at 30 hPa height is in the easterly phase, a positive correlation is extended to the beginning of 1900s. We also show that high geomagnetic activity causes a stronger effect in the Northern Hemisphere winter than high sunspot activity, especially in the Atlantic and Eurasia. A comprehensive knowledge of the Earth's climate system and all its drivers is crucial for the future projection of climate. Solar variability effects have been estimated to produce only a small factor to the global climate change. However, there is increasing evidence, including the results presented in this thesis, that the different forms of solar variability can have a substantial effect to regional and seasonal climate variability. With this new evidence, the solar wind related particle effects in the atmosphere are now gaining increasing attention. These effects will soon be included in the next coupled model inter comparison project (CMIP6) as an additional solar related climate effect. This emphasizes the relevance of this thesis.

Weather and climate are truly arresting in Australia's far north. They set the 'Top End' - the northernmost parts of the Northern Territory - apart; not only from 'temperate' Australia, but also from other tropical locales. Weather and climate are integral to the experience of the place. Authoritative histories of the Northern Territory, with justification, routinely discuss its weather and climate. They indicate the ineluctable physical parameters that bound human activity in this region and which also set the stage for the dramas of human history played out there. In this study weather and climate are the drama. They are the characters, and they are the plot. Elements of the great aerial ocean in which the 'Top End' is immersed - rain, wind and heat - are studied on a variety of time scales. Events are examined: their intensity, duration, chronology and patterns in time. Just as nature and culture are inextricably entwined, so these elements cannot intelligibly be amputated from human experience. To paraphrase US environmental historian William Cronen, this is a study of stories about stories about weather and climate. The third dimension of this history is its interrogation of the cultural biases and philosophical assumptions both underlying and revealed by these stories about weather and climate. However, this work focuses on one constellation of encounters and responses: those of the colonial invaders. The ideas and (mis)understandings of this group have determined how weather and climate have been seen since colonial times. Now, in the Anthropocene, as the effects of anthropogenic climate change unfold, this understanding is pivotal in dealing with this looming problem. This study is a history of a plausible, coherent misunderstanding. It is also a history of the northernmost region of the Northern Territory, a history refracted through a different prism to those of its worthy predecessors. Here the subject is the colonial encounter with tropical skies, science in colonial and northern Australia and experience-based efforts to grasp something so foreign to people from temperate environs. It reveals how western ideas of time have distorted understandings of weather and climate. It demonstrates the poor fit of received ideas of seasonality and climate to historical experience. Reflecting on important contingencies of this place between 1800 and 1942, this history situates human experience in the Northern Territory firmly in the global currents of both environmental history and intellectual history.

The atmospheric response to the oceanic forcing in the eastern Pacific along the northern equatorial sea surface temperature (SST) front is investigated in terms of sensible and latent heat flux during the 6-month period 28 July 1999 through 27 January 2000. Of particular interest is the atmospheric boundary layer (ABL) response to oceanic Tropical Instability Waves (TIWs) that distort the SST front during May through January in normal years. In previous studies, time series of boundary layer properties clearly show the influence of TIWs but the relationship to spatial patterns of SST and wind stress has been inferred only from sparse in situ data. In this study, satellite observations are used to composite in situ data from moorings to compensate for the lack of a spatially dense mooring array. The variability in the position of the SST front caused by propagating TIWs enables fixed mooring locations to measure the atmospheric boundary layer (ABL) response from a large range of locations relative to the front. The satellite data enable determination of the precise location of the mooring relative to the front. The advantage of this strategy is the recurring measurement of the ABL response to the SST front over the six month period considered here. The results indicate that the TIW-induced perturbations of sensible and latent heat flux are spatially shifted in phase towards the east relative to the perturbations of SST. The maximum fluxes are not centered directly over the warmest water, but are shifted towards the portion of the frontal region where a disequilibrium boundary layer is expected due to the advection of colder air from the equatorial region. The changes of sensible and latent heat fluxes across the SST front have magnitudes of about 11 Wm⁻² and 126 Wm⁻², respectively. The sensible and latent heat flux patterns are interpreted in two complementary ways: (1) as an atmospheric response to the change of oceanic forcing as air flows across the SST front; and (2) as the atmospheric response to westward propagating TIWs along the SST front.
Graduation date: 2001