Large-eddy simulations of the atmospheric boundary layer have been performed over a range of stabilities between neutral and free convective conditions. The variation of various non-dimensionalized turbulence statistics over this stability range is presented and the results are compared with observations where possible. The robustness of the model results is also assessed by comparing those from high and low resolution simulations, and by reference to a number of additional sensitivity tests. The simulation results for the variation with stability of the mean wind and temperature profiles and various similarity coefficients are presented. The large-eddy model datasets are then used to evaluate critically the performance of a number of simple closure schemes suitable for use in boundary layer parametrizations in large-scale weather forecasting and climate prediction models. The potential significance of the shortcomings of the simplest mixing length schemes is discussed, and an assessment is made of the types of closure most likely to give a significant improvement in performance without an excessive computational overhead. Results are also presented from large-eddy simulations of the baroclinic boundary layer. The effects of the shear in the geostrophic wind on scaled turbulence statistics and the mean wind profiles are discussed. It is shown that this shear does not lead to significant degradation of the performance of two simple closure models, in either neutral or convective conditions. Finally simulation results for the entrainment flux at the top of the boundary layer are presented. A parametrization of this flux is developed, based on the boundary layer root mean square vertical velocity.

<p> The connection between ionospheric conductivity and the dynamics of the magnetosphere was investigated, using several methods to change the ionospheric conductivity and then study the resultant changes to the magnetosphere. Computer simulations of the Earth's geospace environment were utilized using OpenGGCM coupled with an ionosphere model CTIM and a ring current model RCM. </p><p> Three methods were used to modify ionospheric conductivity. The incoming particle precipitation was modified by several orders of magnitude &alpha; = .01, .1, 1, 10, the ionospheric conductivity was increased or decreased by factors &beta; = .25, .5, 1, 2, and 4, and for the last method differing values of <i>F</i>_10.7, 70, 110, 150, 200, and 250 were used. Each of the methods is different because <i>F</i>_10.7 mostly affects the dayside, while precipitation mostly affects the nightside, then using the &beta; changes the conductivity over the whole ionosphere. This gives a good range for studying the effects of ionospheric conductivity on the magnetosphere. </p><p> The magnetospheric dynamics studied are: the dayside magnetopause location, the reconnection rate of the Earth's magnetosphere, X-line formation in the magnetotail, and substorm dynamics, both the frequency and magnitude of substorm occurrence. </p><p> To understand the effect of particle precipitation on conductivity two events were simulated, a calm period on 4 May 2005 and a strong storm period on 17 March 2013. Scaling the precipitation energy flux by several orders of magnitude, conductivities in the auroral oval were influenced which, in turn, influence the cross polar cap potentials. With the change in conductance, magnetospheric convection is enhanced or reduced, and the location of the subsolar distance of the magnetopause can change by up to one <i>R_E</i>. The investigation of the reconnection rate for the varying precipitation simulations using the Hesse-Forbes-Bern method shows that particle precipitation affects the magnetic reconnection rate in these two events. The most notable differences, up to 40\%, occur on short time scales, that is, hours. A relation for longer time scales (tens of hours) between precipitation and reconnection for these two events is more difficult to ascertain. Differences in cross polar cap potential (CPCP) and reconnection rate (R) can be explained by viscous interactions and polar cap saturation. When precipitation was decreased, polar conductance was decreased, viscous interactions are stronger, and CPCP is higher than R. For high precipitation, high conductance cases the polar cap is in the saturation regime and CPCP is lower than R. Hemispheric asymmetries were found in the cross polar cap potential and in the calculated reconnection rate derived from the Northern and Southern Hemispheres. The majority of this research has already been published in the Journal of Geophysical Research: Space physics, "Particle Precipitation Effects on Convection and the Magnetic Reconnection Rate in Earth's Magnetosphere" https://doi.org/10.1002/2017JA024030. </p><p> For the whole ionospheric conductivity study, different values of &beta; = .25, .5, 1, 2, 4 were used to modify the ionospheric conductivity after it had been calculated by the ionosphere model. A moderate storm period, 16 May 2011 was simulated. Many of the same conclusions found in the precipitation study were found in this study as well, such as, CPCP decreasing as conductivity increases, the point at which the polar cap saturates decreases with increasing conductivity, and reconnection rates change on short time scales, but the overall average rate remains very similar. The incoming precipitation was used to identify auroral brightening that is linked with substorms. The criteria for auroral brightenings used in this study is where the maximum precipitation increased by at least 1 <i>mW/m</i>² within 20 minutes. The criteria for substorms is that the maximum precipitation increases by 80\% within 20 minutes. Identifying all the auroral brightenings and substorms showed that as conductivity increased the maximum amount of precipitation decreased, and also the number and frequency of both the substorms and auroral brightenings decreased. The occurrence of extended X-lines in the magnetotail was analyzed, where if an earthward flow of greater than 50 km/s extended for greater than 10 <i>R_e</i> in <i>Y_GSE</i> was classified as an extended X-line. This is not to be confused with a bursty bulk flow or dipolarization front, which happen from reconnection but usually do not have a large extent in <i>Y_GSE</i>. Identifying extended X-lines in this manner showed a similar trend that as conductivity increased the number of extended X-lines decreased, and while there was not much of an indication if the size or location is affected much, the amount of time the simulation had extended X-lines present decreased. </p><p> For the <i>F</i>_10.7 study, using values of 70, 110, 150, 200, and 250, the ionospheric conductivity was influenced mostly on the dayside. (Abstract shortened by ProQuest.) </p><p>

abstract: This thesis examines the synoptic characteristics associated with ozone exceedance events in Arizona during the time period of 2011 to 2013. Finding explanations and sources to the ground level ozone in this state is crucial to maintaining the state’s adherence to federal air quality regulations. This analysis utilizes ambient ozone concentration data, surface meteorological conditions, upper air analyses, and HYSPLIT modeling to analyze the synoptic characteristics of ozone events. Based on these data and analyses, five categories were determined to be associated with these events. The five categories all exhibit distinct upper air patterns and surface conditions conducive to the formation of ozone, as well as distinct potential transport pathways of ozone from different nearby regions. These findings indicate that ozone events in Arizona can be linked to synoptic-scale patterns and potential regional transport of ozone. These results can be useful in the forecasting of high ozone pollution and influential on the legislative reduction of ozone pollution. / Dissertation/Thesis / Masters Thesis Geography 2016

The high-latitude ionosphere is a dynamic region, in which a variety of phenomena including particle precipitation, currents and waves contribute to the energy budget. In this thesis, statistical and case studies of ion frictional heating are presented, including investigations into the dependence of enhanced ion temperature on time and altitude. The relationship between parallel ion temperature and ion velocity is compared to simplified forms of the ion energy balance equation. In addition, the generation mechanisms of atmospheric gravity waves are studied by means of measurements made during the WAGS campaign of October 1985. The results indicate that auroral precipitation can influence frictional heating events to a greater extent than has previously been realised and that during frictional heating the molecular content of the lower ionosphere is enhanced, affecting the electron density. Any analysis which takes no account of the modified composition underestimates the parallel ion temperature, particularly between 200 and 300 km altitude. The relationship between ion velocity and parallel ion temperature is most easily explained by an anisotropic ion velocity distribution, consistent with resonant charge exchange collisions. The relationship varies with altitude, however, possibly due to ion-ion collisions. An experimental method is described by which the temperature anisotropy can be obtained directly and early results are discussed. For the investigation of atmospheric gravity waves and their sources, HF Doppler observations in the UK enabled wave speeds and azimuths to be deduced, whilst EISCAT simultaneously observed the possible source region. Although the study was characterised by moderate activity, more active days showed higher phase speeds and southerly azimuths. Some of these waves may have originated at high latitudes during positive bay activity, when both Joule heating and the Lorentz force contributed to wave generation.

<p> Satellite cloud remote sensing provides us the opportunity to study the spatial and temporal distributions of marine boundary layer clouds, as well as their connections with environments on a global scale. However, cloud remote sensing is not without difficulties; retrievals require numerous simplifying assumptions, placing limits on our understanding of cloud processes. Passive remote sensing retrievals often assume that clouds are homogeneous slabs, when in reality, these clouds often have complex inhomogeneous vertical and horizontal structures. Enhancing our understanding of how cloud inhomogeneity influences passive cloud remote sensing requires comparison between cloud retrievals and the underlying cloud properties. In observational data-sets this can become problematic, as it is difficult to compare satellite and airborne measurements because they have both different observed spatial scales and sensitivities to cloud properties. To avoid these complications, this work is based on a satellite retrieval simulator &ndash; a Large-Eddy Simulation (LES) cloud model coupled to radiative transfer and retrieval algorithms. The LES-satellite simulator can be used to study the source of retrieval biases. It provides the underlying realistic cloud structure as a reference, informing conclusions about its impact on various cloud retrieval methods. In the first step we focus on cloud vertical profile, finding that the selection of appropriate vertical profile assumptions for the retrieval of cloud liquid water path. Confirming previous studies, drizzle and cloud top entrainment of dry air are identified as physical features that bias liquid water path retrievals away from adiabatic and toward homogeneous profile assumptions. The mean bias induced by drizzle-influenced profiles was shown to be on the order of 5&ndash;10 grams per meter squared. In contrast, the influence of cloud top entrainment was found to be smaller by about a factor of 2. A theoretical framework is also developed to explain variability in LWP retrievals by introducing modifications to the adiabatic effective radius profile. The second step focuses on horizontal inhomogeneity and exploring a comparison of both the bispectral and polarimetric cloud retrieval techniques. Using the satellite retrieval simulator we are able to verify that at high spatial resolution (50 meters) the bispectral and polarimetric retrievals are indeed highly correlated with one another. The small differences at high spatial resolution can be attributed to different sensitivity limitations of the two retrievals. In contrast, a systematic difference between the two effective radius retrievals emerges at coarser resolution. This bias largely stems from differences related to sensitivity of the two retrievals to unresolved inhomogeneities in effective variance and optical thickness. The influence of coarse angular resolution is found to increase uncertainty in the polarimetric effective radius retrieval, but generally maintains a constant mean value. The third study focuses on 3-D radiative effects influencing both total and polarized reflectances and retrievals. Comparisons between the 1-D and 3-D reflectances are made in order to study horizontal photon transfer and radiative smoothing. We find noticeable differences between the total and polarized reflectance 3-D effects, with radiative smoothing and roughening occurring at different scales as well as viewing geometry dependence. Despite these apparently strong 3-D effects on polarized reflectances, the polarimetric retrieval is robust to the influence of 3-D effects &ndash; with only sub-micron biases in the retrieval of effective radius.</p><p>

<p> Snowfall presents a hazard to drivers by reducing visibility and increasing safe stopping distances. As a result, some drivers cancel trips if snowfall is occurring or forecasted, and traffic volumes often decrease on snowy days. Lake-effect snow is very localized and is thus hypothesized to have a lesser influence on traffic volume than synoptic-scale snow, which usually covers a broader areal extent. Traffic volume in northeast Ohio and northern Indiana is studied using a matched-pair analysis to determine if volumes differ between lake-effect and synoptic-scale snowfall in these regions. While little statistical evidence is found to support this hypothesis, other relationships are discovered: lake-effect traffic volume is shown to be dependent in part on distance from the lake and population density of the surrounding area. Other trends relating traffic volume to time-of-day and accident patterns are also explored. Findings presented herein can assist in transportation planning, risk analysis, and roadway safety.</p><p>

<p> The study described in this thesis aims to assess the effects of wind-generated noise on potential infrasound measurements on future Mars missions. Infrasonic sensing on Mars is being considered as a means to probe the long-scale atmospheric dynamics, thermal balance, and also to infer bolide impact statistics. In this study, a preliminary framework for predicting the principal wind noise mechanisms to the signal detected by a sensor placed inside a hemispherical porous dome on the Martian surface is developed. The method involves calculating the pressure power density spectra in the infrasonic range generated by turbulent interactions and filtered by dome shaped filters of varying porosities. Knowing the overall noise power spectrum will allow it to be subtracted from raw signals of interest and aid in the development of infrasound sensors for the Martian environment. In order to make these power spectral predictions, the study utilizes the Martian Climate Database (MCD) global circulation model, developed by Laboratoire de Meteorologie Dynamique in Paris, France. Velocity profiles are generated and used in semi empirical functions generated by von K&aacute;rm&aacute;n along with equations for describing the physical turbulent interactions. With these, turbulent interactions in the free atmosphere above the Martian surface are described. For interactions of turbulence with the porous filter, semi-empirical formulations are adapted to the Martian parameters generated by the MCD and plotted alongside contributions in the free atmosphere outside and inside the dome to obtain the total wind noise contribution from turbulence. In conclusion, the plots of power spectral densities versus frequency are analyzed to determine what porosity filter would provide the best wind-noise suppression when measured at the center the dome. The study shows that 55% (0.02 to 5 Hz) and 80% (6 to 20 Hz) porosities prove to be the better of the five porosities tested. </p><p>

Severe impacts result from extreme events such as heat waves, droughts, cold spells, and floods. Characterizing and predicting variations in climate that give rise to these phenomena is important for mitigating their effects on human and natural systems. This thesis investigates whether climate variability is measurably changing and describes the observational basis for recent shifts in the temperature distribution. New methodology is presented that robustly estimates local distributional changes and permits for mapping them to regional or global scales, overcoming limitations of previous analyses. Contrary to the widespread view that climate variability has increased in recent decades, these analyses show that temperature variability has generally declined — albeit with important regional differences. Historical observations of temperature are crucial for long-term monitoring of Earth's climate. However, hundreds of millions of daily observations contain precision-related biases that prevent their use in distributional analyses. A new machine-learning algorithm automatically corrects for these biases, enabling their use in long-term climate studies. The algorithm increases the number of usable observations by an order of magnitude and has many applications in quality control and signal classification. As the observations sample Earth's climate sparsely in space and time, sophisticated statistical methods are used to map local signals to estimates of the full spatial field and its uncertainties. Much of the observed contraction of variability is shown to stem from decreased meridional temperature gradients due to amplified arctic warming in the northern hemisphere. Short-term extremes are also contextualized with the low frequency variability inferred from paleoclimate observations and simulations. Spectral estimates used to measure variability on different time scales are shown to be surprisingly robust to unavoidable time-uncertainty present in all proxy records. Oxygen isotope records from Greenland that are widely used as temperature proxies therefore contain reliable signals of past climate variability on 1–60,000 year time scales, though the extent to which these reliably preserve temperature signals remains uncertain. In a further study we examine the validity of this temperature proxy using a set of global paleoclimate simulations with moisture source tracking, quantifying a seasonality bias that may explain the paleothermometer's damped response during glacial periods. / Engineering and Applied Sciences - Applied Math

Methane (CH_4) and nitrous oxide (N_2O) are the second- and third-most important long-lived greenhouse gas species after carbon dioxide (CO_2) in terms of radiative forcing. This thesis describes the magnitude, spatial distribution, and seasonality of N_2O and CH_4 sources over North America using atmospheric data. We also investigate the environmental drivers and/or anthropogenic source sectors that can explain these emissions patterns. Overall, this thesis provides information on the magnitude, distribution, and likely drivers of greenhouse gas emissions to aid existing or future climate change mitigation policies in the US and Canada. We estimate anthropogenic N_2O and CH_4 emissions that greatly exceed most existing inventory estimates. Our US budgets for N_2O and CH_4 are approximately 2.8 and 1.5 times higher, respectively, than inventory estimates from the US EPA. Much of the discrepancy in methane appears to stem from oil and natural gas industry and agricultural emissions. In contrast, we estimate natural CH_4 sources that are smaller than most existing process-based biogeochemical models. These estimated fluxes have a spatial distribution centered around the Hudson Bay Lowlands. Most existing models estimate fluxes that are far more spatially distributed across the Canadian shield. These estimates provide negative information on the spatial distribution of fluxes relative to a spatially-constant model. We find that a simple model using only three environmental variables can describe flux patterns (as seen by the atmospheric observations) as well as any process-based estimate. / Earth and Planetary Sciences

This study aims to advance our understanding of the inner-core dynamics of tropical cyclones (TCs) from the perspective of vortex Rossby waves (VRWs) through investigating wave kinematics, propagation feature, and wave-mean-flow interaction in three dimensional TC-like baroclinic vortices. Using the Wenzel-Kramers-Brillouin analysis in the asymmetric balanced model framework, the generalized wave dispersion relation, group velocities, and stagnation radius/height of VRW wave-packets in both pseudo-height and isentropic coordinates are derived. It is found that the VRW dispersion relation associated with baroclinic vortices in an isentropic coordinate has the same format as that of barotropic vortices in a pseudo-height coordinate. However, baroclinicity causes the vertical wavenumber to increase, resulting in wave propagation features different from those in barotropic vortices. The stagnation radius and height are strictly constrained by the geometry of the 'critical’ surface determined by the initial properties of wave-packets and basic-state vortices. Baroclinicity substantially promotes the vertical propagation of VRWs but suppresses the corresponding wave radial propagation under the constraint of the ‘critical’ surface. Asymmetries excited at the surface are trapped in the low layer with substantial radial propagation, whereas the waves excited in the low to mid-troposphere in the vortex inner-core region can effectively propagate upward but their radial propagation is suppressed. Only low azimuthal wavenumber asymmetries can have meaningful radial and vertical propagation. The theoretical prediction of wave kinematics is confirmed by the non-hydrostatic simulations performed by the Weather Research and Forecasting (WRF) model. The WRF simulations show that the VRWs in baroclinic vortices can be classified into a surface quasi-barotropic regime and an upper baroclinic regime. The distinct wave kinematics in these two regimes results in different wave-mean-flow interaction. The former causes a strong vortex spin-up just outside the center of the initial asymmetry similar to those in barotropic vortices, whereas the latter confines the mean angular momentum inside the center of initial asymmetry but substantially supports the upward transport of angular momentum. The vortex intensification in baroclinic vortices is shown to be governed by the tilting of wave phase, the radial and vertical eddy momentum fluxes, and the vortex symmetric response to asymmetric momentum forcing.