No description available.

Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, August 1999. / Includes bibliographical references. Also available on the Internet.

Stratosphere-troposphere exchange processes are responsible for controlling the distribution of chemically and radiatively important trace gases in the upper troposphere and lower stratosphere. Extensive characterization of exchange processes is critical to the development of our understanding and prediction of the climate system. This study examines the occurrence and dynamical and chemical characteristics related to two primary stratosphere-troposphere exchange processes: Rossby wavebreaking and moist convection. Intrusions of air from the tropical upper troposphere into the extratropical stratosphere above the subtropical jet via Rossby wavebreaking potentially have a significant impact on the composition of the lowermost stratosphere (the stratospheric part of the "middleworld"). We first present an analysis of tropospheric intrusion events observed in aircraft observations using kinematic and chemical diagnostics. The transport processes operating during each event are discussed using high-resolution model analyses and backward trajectory calculations. In situ chemical observations of the tropospheric intrusions are used to estimate the mixing timescales of the observed intrusions through use of a simple box model and trace species with different photo-chemical lifetimes. We estimate that the timescale for an intrusion to mix with the background stratospheric air is 5 to 6 days. Detailed analysis of small-scale features with tropospheric characteristics observed in the stratosphere suggests frequent irreversible transport associated with tropospheric intrusions. We also present a 30-year climatology (1981-2010) of anticyclonically and cyclonically sheared Rossby wave-breaking events along the boundary of the tropics in the 350-500 K potential temperature range from ECMWF ERA-Interim reanalyses. Lagrangian transport analyses show poleward transport at altitudes below and above the 370-390 K layer. Poleward transport at lower levels is in disagreement with previous studies and is shown to be largely dependent on the choice of tropical boundary. In addition, transport analyses reveal three modes of transport for anticyclonic wavebreaking events near the tropical tropopause (380 K): poleward, equatorward, and bidirectional. These transport modes are associated with distinct characteristics in the geometry of the mean flow. Stratospheric intrusions (tropopause folds) are known to be major contributors to stratosphere-troposphere exchange. The specific mixing processes that lead to irreversible exchange between stratospheric intrusions and the surrounding troposphere, however, are not entirely understood. This study presents direct observations of moist convection penetrating into stratospheric intrusions. The characteristics of convective injection are shown by using in situ aircraft measurements, radar reflectivities, and model analyses. Convective injection is observed at altitudes up to 5 km above the bottom of a stratospheric intrusion. Aircraft measurements show that convective injection in stratospheric intrusions can be uniquely identified by coincident observations of water vapor greater than about 100 ppmv and ozone greater than about 125 ppbv. Trajectory analyses show that convective injection can impact transport in both directions: from troposphere to stratosphere and from stratosphere to troposphere. We present a conceptual model of the synoptic meteorological conditions conducive to convective injection in stratospheric intrusions. In particular, convective injection is found to be associated with a "split front" where the upper-level frontal boundary outruns the surface cold front.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 79-98).

The increased application of digital terrestrial microwave radio links in communication networks has renewed attention in techniques of estimating the probability of multipath fading distributions. Nevertheless, the unpredictable variation of the wireless transmission medium remains a challenge. It has been ascertained that the refraction of electromagnetic waves is due to the inhomogeneous spatial distribution of the refractive index, and causes adverse effects such as multipath and diffraction fading. The knowledge of the characteristics of such causes of these fading phenomena is essential for the accurate design of terrestrial line of sight (LOS) links of high performance and availability. Refractivity variation is random in space and time and cannot be described in a deterministic manner and has to be considered as a random variable with probabilistic characteristics. In this dissertation, radiosonde soundings data is used in characterizing the atmospheric conditions and determining the geoclimatic factor K used in predicting the distribution of multipath fading for five locations in South Africa. The limitations of radiosonde measurements are lack of time resolution and poor spatial resolution. The latter has been reduced by spatial interpolation techniques in our study, specifcally, the Inverse Distance Weighting (IDW) method. This is used in determining the point refractivity gradient not exceeded for 1 % of the time from which the geoclimatic factor is estimated. Fade depth and outage probability due to multipath propagation is then predicted from the International Telecommunications Union Recommendations (ITU-R) techniques. The results are compared with values from Central Africa. The results obtained using the ITU-R method are also compared with region-based models of Bannett-Vigants of USA and Morita of Japan. Three spatial interpolation techniques (Kriging, Thin-Plate Spline and Inverse Distance Weighting) are then used in interpolating the geoclimatic factor K in places where radiosonde data is not available. The estimated values have been used to develop contour maps for geoclimatic factor K for South Africa. Statistical assessment of these methods is done by calculating the root mean square error (RMSE) and the mean absolute error (MAE) between a set of control points and the interpolated results. The best performing method is used to map the seasonal geoclimatic factor K for the entire study region. The estimated values of geoclimatic factor will improve accuracy in predicting outage probability due to multipath propagation in LOS links in the region which is a key contribution of this work. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

Since 1950's there has been a growing interest of understanding the effects of cosmic ray radiation on the increase in average global temperature. Recent studies showed that galactic cosmic rays play a significant role in the formation of low cloud coverage and its consequent impact on the global temperature variation of the earth. A long-term measurement of the cosmic ray flux distribution at the surface of the earth has been established at Georgia State University. The current effort is focused on understanding the correlations between the cosmic ray particle flux distribution and the atmospheric and space weather measurements. In order to understand the observed atmospheric effects on cosmic ray flux, numerical simulations of cosmic muon and neutron flux variations at the surface of the earth have been carried out with varying air densities in the troposphere and stratosphere based on the Geant4 package. The simulation results show a remarkably good agreement with observations. The simulation results also show that the stratosphere air density variation dominates the effects on the muon flux changes while the density variation in the troposphere mainly influences the neutron count variation. This suggests that the long-term variation of muon flux could possibly direct us to a new path to understand the global climate warming trend.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references. Online version available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (p. 205-225).

Severe ozone depletion in the polar lower stratosphere has been linked to significant changes in tropospheric circulation patterns in the both hemispheres. Observed Southern Hemisphere circulation changes are easily reproduced in climate models and may be achieved by either increasing ozone depleting substances in a chemistry-climate model(CCM) or by imposing observed ozone losses as a zonally-symmetric perturbation in a prescribed-ozone global circulation model (GCM). In the Northern Hemisphere however, only the CCM method produces a circulation response in agreement with analysis of observations, while the GCM method is unable to produce any significant tropospheric circulation changes from imposing observed zonal-mean Arctic ozone losses. Confidence in a mechanistic link between Arctic stratospheric ozone change and changes in tropospheric circulation is greatly increased if the change can be reproduced using a GCM in addition to being reproducible in a CCM. This thesis demonstrates that by allowing ozone to vary along longitude, and by imposing ozone depletion during a realistic timeframe, the GCM method can produce circulation changes compatible with both the CCM method and observations. An equivalent-latitude coordinate allows the prescribed ozone field, and imposed ozone losses, to follow the polar vortex as it is systematically disturbed or displaced off the pole throughout the winter, producing a realistic circulation response in the troposphere in contrast to when ozone and its imposed losses are zonally-symmetric. Timing the imposed ozone depletion with the breakup of the polar vortex reveals that the appearance of the circulation response is very sensitive to the relative timing of these events and to the pre-existing dynamical state of the polar vortex. These results demonstrate that prescribing ozone as a zonally symmetric climatology within a GCM, as has been recent practice in the literature, is only representative of the Southern Hemisphere and is inappropriate for accurately representing processes within the Arctic stratosphere. Moreover this work demonstrates that these dynamically-evolving zonal asymmetries in ozone, which are not present in zonally-symmetric ozone schemes, play a crucial role in allowing perturbations in the Arctic stratosphere to influence the troposphere and surface conditions.

No description available.