Tropical cyclones (TC) in the western North Pacific (WNP) pose a serious threat to the coastal regions of Eastern Asia when they make landfall. The limited amount of observational data and the high computational cost of running TC-permitting dynamical models indicate a need for statistical models that can simulate large ensembles of TCs in order to cover the full range of possible activity that results from a given climate change. I construct and apply a statistical track model from the 1945-2007 observed "best tracks" in the IBTrACS database for the WNP. The lifecycle components--genesis, track propagation, and death--of each simulated track is determined stochastically based on the statistics of historical occurrences. The length scale that dictates what historical data to consider as "local" for each lifecycle component is calculated objectively through optimization. Overall, I demonstrate how a statistical model can be used as a tool to translate climate-induced changes in TC activity into implications for risk.In contrast to other studies, I show that the El Niño/Southern Oscillation (ENSO) has an effect on track propagation separate from the genesis effect. The ENSO effect on genesis results in higher landfall rates during La Niña years due to the shift in genesis location to the northeast. The effect on tracks is more geographically and seasonally varied due to local changes in the mid-level winds. I use local regression techniques to capture the relationship between ENSO, cyclogenesis, and track propagation. Stationary climate simulations are run for extreme ENSO states in order to better understand changes in TC activity and their implication for regional landfall. Additionally, Several diagnostics are performed on model realizations of the historical period, confirming the model's ability to capture the geographical distribution and interannual variability of observed TCs. Lastly, as a step to connect synthetic TC track simulations to economic damage risk assessment, I use a Damage Index and total damage data for U.S. landfalling hurricanes and fit generalized Pareto distributions (GPD) to them. The Damage Index uniquely separates out the effects of the physical damage capacity of a TC and the local economic vulnerability of a coastal region. GPD fits are also performed using covariates in the scale parameter, where bathymetric slope and landfall intensity are found to be useful covariates for the Damage Index. Using the Damage Index with covariates model, two examples are shown of assessing damage risk for different climates. The first takes landfall data input from a statistical-deterministic TC model downscaled from GFDL and ECHAM model current and future climates. The second takes landfall data from a fully statistical track model with different values of relative sea surface temperature given as a statistical predictor.

This thesis seeks an improved understanding of what has been driving changes in the large scale tropospheric circulation. First, we consider the effects of stratospheric water vapor levels, which exhibit significant changes on both interannual and decadal timescales. It is shown that idealized thermal forcings mimicking increases in stratospheric water vapor produce poleward expansion of the Hadley cells (HCs) and poleward shifts of the midlatitude jets. Quantitatively, the circulation responses are comparable to those produced by increased well-mixed greenhouse gases. This suggests that stratospheric water vapor may be a significant contribution to past and projected changes in the tropospheric circulation. The second part of this thesis focuses on the response to idealized thermal forcings in the troposphere. It is found that zonally uniform warming confined to a narrow region around the equator produces contraction of the HCs and equatorward shifts of the midlatitude jets. Forcings with wider meridional extent produce the opposite effect: HC expansion and poleward shifts of the jets. If the forcing is confined to the midlatitudes, the amount of HC expansion is more than three times that of a forcing of comparable amplitude that is spread over the tropics. This finding may be relevant to recently observed trends of amplified warming in the midlatitudes. Furthermore, a simple diffusive model is constructed to explain the sensitivity of the circulation response to the meridional structure of the thermal forcing. The final part of this thesis considers the possible influence of solar forcing on the tropospheric circulation. Of particular interest is the steady state response to a 0.1% increase in total solar irradiance (TSI), the approximate amplitude of the 11-year solar cycle. Using a comprehensive atmospheric general circulation model coupled to a mixed layer ocean, it is found that a 0.1% TSI increase produces a circulation response that has a high dependence on the background state. Specifically, a TSI perturbation applied to a present day climate produces an equatorward shift of the Southern Hemisphere (SH) midlatitude jet, while the same forcing applied to a warmer climate produces a poleward shift of the SH jet. Opposite-signed responses are also evident in regions of the sea surface temperature, sea level pressure, and precipitation fields. These divergent responses may help to explain why earlier studies reach highly disparate conclusions about the influence of solar variations on climate.

This study explores seasonal patterns and structures of moisture transport pathways from the North Atlantic Ocean and the Gulf of Mexico that lead to extreme large-scale precipitation and floods over land. Storm tracks, such as the tropical cyclone tracks in the Northern Atlantic Ocean, are an example of moisture transport pathways. In the first part, North Atlantic cyclone tracks are clustered by the moments to identify common traits in genesis locations, track shapes, intensities, life spans, landfalls, seasonal patterns, and trends. The clustering results of part one show the dynamical behavior differences of tropical cyclones born in different parts of the basin. Drawing on these conclusions, in the second part, statistical track segment model is developed for simulation of tracks to improve reliability of tropical cyclone risk probabilities. Moisture transport pathways from the North Atlantic Ocean are also explored though the specific regional flood dynamics of the U.S. Midwest and the United Kingdom in part three of the dissertation. Part I. Classifying North Atlantic Tropical Cyclones Tracks by Mass Moments. A new method for classifying tropical cyclones or similar features is introduced. The cyclone track is considered as an open spatial curve, with the wind speed or power information along the curve considered as a mass attribute. The first and second moments of the resulting object are computed and then used to classify the historical tracks using standard clustering algorithms. Mass moments allow the whole track shape, length and location to be incorporated into the clustering methodology. Tropical cyclones in the North Atlantic basin are clustered with K-means by mass moments producing an optimum of six clusters with differing genesis locations, track shapes, intensities, life spans, landfalls, seasonality, and trends. Even variables that are not directly clustered show distinct separation between clusters. A trend analysis confirms recent conclusions of increasing tropical cyclones in the basin over the past two decades. However, the trends vary across clusters. Part II: Tropical cyclone Intensity and Track Simulator (HITS) with Atlantic Ocean Applications for Risk Assessment. A nonparametric stochastic model is developed and tested for the simulation of tropical cyclone tracks. Tropical cyclone tracks demonstrate continuity and memory over many time and space steps. Clusters of tracks can be coherent, and the separation between clusters may be marked by geographical locations where groups of tracks diverge due to the physics of the underlying process. Consequently, their evolution may be non-Markovian. Markovian simulation models, as often used, may produce tracks that potentially diverge or lose memory quicker than nature. This is addressed here through a model that simulates tracks by randomly sampling track segments of varying length, selected from historical tracks. For performance evaluation, a spatial grid is imposed on the domain of interest. For each grid box, long-term tropical cyclone risk is assessed through the annual probability distributions of the number of storm hours, landfalls, winds, and other statistics. Total storm length is determined at birth by local distribution, and movement to other tropical cyclone segments by distance to neighbor tracks, comparative vector, and age of track. An assessment of the performance for tropical cyclone track simulation and potential directions for the improvement and use of such model are discussed. Part III: Dynamical Structure of Extreme Floods in the U.S. Midwest and the United Kingdom. Twenty extreme spring floods that occurred in the Ohio Basin between 1901 and 2008, identified from daily river discharge data, are investigated and compared to the April 2011 Ohio River flood event. Composites of synoptic fields for the flood events show that all these floods are associated with a similar pattern of sustained advection of low-level moisture and warm air from the tropical Atlantic Ocean and the Gulf of Mexico. The typical flow conditions are governed by an anomalous semi-stationary ridge situated east of the US East Coast, which steers the moisture and converges it into the Ohio Valley. Significantly, the moisture path common to all the 20 cases studied here as well as the case of April 2011 is distinctly different from the normal path of Atlantic moisture during spring, which occurs further west. It is shown further that the Ohio basin moisture convergence responsible for the floods is caused primarily by the atmospheric circulation anomaly advecting the climatological mean moisture field. Transport and related convergence due to the covariance between moisture anomalies and circulation anomalies are of secondary but non-negligible importance. The importance of atmospheric circulation anomalies to floods is confirmed by conducting a similar analysis for a series of winter floods on the River Eden in northwest England.

When forced with increasing greenhouse gases, global climate models project changes to the seasonality of several key climate variables. These include delays in the phase of surface temperature, precipitation, and vertical motion indicating maxima and minima occurring later in the year. The changes also include an increase in the amplitude (or annual range) of low-latitude surface temperature and tropical precipitation and a decrease in the amplitude of high-latitude surface temperature and vertical motion. The aim of this thesis is to detail these changes, understand the links between them and ultimately relate them to simple physical mechanisms. At high latitudes, all of the global climate models of the CMIP3 intercomparison suite project a phase delay and amplitude decrease in surface temperature. Evidence is provided that the changes are mainly driven by sea ice loss: as sea ice melts during the 21st century, the previously unexposed open ocean increases the effective heat capacity of the surface layer, slowing and damping the temperature response at the surface. In the tropics and subtropics, changes in phase and amplitude are smaller and less spatially uniform than near the poles, but they are still prevalent in the models. These regions experience a small phase delay, but an amplitude increase of the surface temperature cycle, a combination that is inconsistent with changes to the effective heat capacity of the system. Evidence suggests that changes in the tropics and subtropics are linked to changes in surface heat fluxes. The next chapter investigates the nature of the projected phase delay and amplitude increase of precipitation using AGCM experiments forced by SST perturbations representing idealizations of the changes in annual mean, amplitude, and phase as simulated by CMIP5 models. A uniform SST warming is sufficient to force both an amplification and a delay of the annual cycle of precipitation. The amplification is due to an increase in the annual mean vertical water vapor gradient, while the delay is linked to a phase delay in the annual cycle of the circulation. A budget analysis of this simulation reveals a large degree of similarity with the CMIP5 results. In the second experiment, only the seasonal characteristics of SST are changed. For an amplified annual cycle of SST there is an amplified annual cycle of precipitation, while for a delayed SST there is a delayed annual cycle of precipitation. Assuming that SST changes can entirely explain the seasonal precipitation changes, the AGCM simulations suggest that the annual mean warming explains most of the amplitude increase and much of the phase delay in the CMIP5 models. However, imperfect agreement between the changes in the SST-forced AGCM simulations and the CMIP5 coupled simulations suggests that coupled effects may play a significant role. Finally, the connections between changes in the seasonality of precipitation, temperature and circulation are studied in the tropics using models of varying complexity. These models include coupled model simulations with idealized forcing, a simple, semi-empirical model to describe the effect of land-ocean interactions, an aquaplanet model, and a dry, dynamical model. Each gives insights into the projected CMIP changes. Taken together they suggest that changes in the amplitude of vertical motions are consistent with a weakening of the annual mean circulation and can explain part of the changes in the amplitude of precipitation over both ocean and land, when combined with the thermodynamic effect described previously. By increasing the amplitude of the annual cycle of surface winds, the changes in circulation may also increase the amplitude of the surface temperature via the surface energy balance. The delay in the phase of circulation directly leads to a delay in the phase of precipitation, especially over ocean.

The hydroclimate of East Africa shows distinctive variabilities on seasonal to decadal time scales and poses a great challenge to climatologists attempting to project its response to anthropogenic emissions of greenhouse gases (GHGs). Increased frequency and intensity of droughts over East Africa in recent decades raise the question of whether the drying trend will continue into the future. To address this question, we first examine the decadal variability of the East African rainfall during March to May (MAM, the major rainy season in East Africa) and assess how well a series of models simulate the observed features. Observational results show that the drying trend during MAM is associated with decadal natural variability of sea surface temperature (SST) variations over the Pacific Ocean. The multimodel mean of the SST forced, Coupled Model Intercomparison Project Phase 5 (CMIP5) AMIP experiment models reproduces both the climatological annual cycle and the drying trend in recent decades. The fully coupled models from the CMIP5 historical experiment, however, have systematic errors in simulating the East African rainfall annual cycle by underestimating the MAM rainfall while overestimating the October to December (OND, the second rainy season in East Africa) rainfall. The multimodel mean of the historical coupled runs of the MAM rainfall anomalies, which is the best estimate of the radiatively forced change, shows a weak wetting trend associated with anthropogenic forcing. However, the SST anomaly pattern associated with the MAM rainfall has large discrepancies with the observations. The errors in simulating the East African hydroclimate with coupled models raise questions about how reliable model projections of future East African climate are. This motivates a fundamental study of why East African climate is the way it is and why coupled models get it wrong. East African hydroclimate is characterized by a dry annual mean climatology compared to other deep tropical land areas and a bimodal annual cycle with the major rainy season during MAM (often called the ``long rains'' by local people) and the second during OND (the ``short rains''). To explore these distinctive features, we use the ERA Interim Re Analysis data to analyze the associated annual cycles of atmospheric convective stability, circulation and moisture budget. The atmosphere over East Africa is found to be convectively stable, in general, year round but with an annual cycle dominated by the surface moist static energy (MSE), which is in phase with the precipitation annual cycle. Throughout the year, the atmospheric circulation is dominated by a pattern of convergence near the surface, divergence in the lower troposphere and convergence again at upper levels. Consistently, the convergence of the vertically integrated moisture flux is mostly negative across the year, but becomes weakly positive in the two rainy seasons. It is suggested the semi-arid/arid climate in East Africa and its bimodal rainfall annual cycle can be explained by the ventilation mechanism, in which the atmospheric convective stability over East Africa is controlled by the import of low MSE air from the relatively cool Indian Ocean off the coast and the cold winter hemisphere. During the rainy seasons, however, the off coast SST increases (and is warmest during the long rains season) and the northerly or southerly weakens, and consequently the air imported into East Africa becomes less stable. The MSE framework is then applied to study the coupling induced bias of the East African rainfall annual cycle often found in CMIP3/5 coupled models that overestimates the OND rainfall and underestimates the MAM rainfall, by comparing the historical (coupled) and the AMIP runs (SST forced) for each model. It is found that a warm north and cold south SST bias over the Indian Ocean induced in coupled models is responsible for the dry MAM rainfall bias over East Africa while the ocean dynamics induced warm west and cold east SST bias over the Indian Ocean contributes to the wet OND rainfall bias in East Africa. Finally, to understand the East African regional climate in the context of the broader tropical climate and circulation, zonal momentum balance of the tropical atmospheric circulation during the global monsoon mature months (January and July) are analyzed in three dimensions based on the ERA-Interim Re-Analysis. It is found that the dominant terms in the balance of the atmospheric boundary layer (ABL) in both months are the pressure gradient force, the Coriolis force and friction. The nonlinear advection term plays a significant role only in the Asian summer monsoon regions including off East Africa. In the upper troposphere, the pressure gradient force, the Coriolis force and nonlinear advection are the dominant terms. The transient eddy force and the residual force (which can be explained as convective momentum transfer over open oceans) are secondary yet can not be neglected near the equator. Zonal mean equatorial upper troposphere easterlies are maintained by the absolute angular momentum advection associated with the cross equatorial Hadley circulation. Equatorial upper troposphere easterlies over the Asian monsoon regions are also controlled by the absolute angular momentum advection but are mainly maintained by the pressure gradient force in January. The equivalent linear Rayleigh friction, which is widely applied in simple tropical models, is calculated and the corresponding spatial distribution of local coefficient and damping time scale are estimated from the linear regression. It is found that the linear momentum model is in general capable of crudely describing the tropical atmospheric circulation dynamics yet the caveat should be kept in mind that the friction coefficient is not uniformly distributed and is even negative in some regions.

Thesis (M.S. in geology with a major in hydrogeology)--Washington State University, December 2007. / Includes bibliographical references (p. 57-67).

No description available.

The results of measurements of the fluxes of momentum, moisture and sensible heat in the marine boundary layer are described. Two techniques for obtaining the fluxes are discussed. The fluxes of these quantities are most directly obtained by the eddy correlation method, that is, by measuring the fluctuating vertical and downstream velocity (w and u), temperature (T) and humidity (q) and computing the covariances wu, wT and wq. The fluxes are also computed by obtaining a measure of the energy dissipation rate from second-order structure functions and relating the dissipation to the production of energy. To use the dissipation methods, values of universal inertial-convective subrange constants (Kolmogoroff constants) are required. Kolmogoroff constants are computed from second and third-order structure functions. Most of the data were collected on R.V. FLIP during BOMEX (Barbados Oceanographic and Meteorological Experiment) and during a pre-BOMEX trial cruise near San Diego. A small amount of additional data was collected from a site at South Beach, Oregon. The value of the Kolmogoroff constant for velocity is consistent with other recent observations. The temperature and humidity constants are found to be equal within the measurement error and have values of about 0.8. The two methods for computing the fluxes agree on average for momentum and moisture flux. The two methods do not agree for sensible heat flux during BOMEX although there is fair agreement for the San Diego data. / Graduation date: 1972

The Penn-State/NCAR MM5 mesoscale model was adapted for mesoscale simulations of the Martian atmosphere (the OSU MMM5). The NASA Ames Mars GCM provides initial and boundary conditions. High-resolution maps for albedo, thermal inertia and topography were developed from Mars Global Surveyor (MGS) data; these baseline maps are processed to appropriate resolutions for use in the GCM and the mesoscale model. The OSU MMM5 is validated in Chapter 2 by comparing with surface meteorology observed at the Viking Lander 1 (VL1) and Mars Pathfinder (MPF) landing sites. How the diurnal cycle of surface pressure (the surface pressure tide) is affected by boundaries, domain/nest choices and the resolution of surface properties (topography, albedo and thermal inertia) is examined. Chapter 2 additionally shows the influence of regional slope flows in the diurnal surface pressure cycle for certain locations on Mars. Building on the methods of Chapter 2, Chapter 3 describes the northern midsummer polar circulation and the circulations (both large and small scale) that influence it. Improvements to the model for these studies include: the topographical gradient is now considered when computing surface insolation, and the thermal inertia maps and model initialization are improved for high latitudes; this yields a realistic simulation of surface temperatures for the North Pole Residual Cap (NPRC) and the surrounding region. The midsummer polar circulation is vigorous, with abundant and dynamically important transient eddies. The preferred locations of transients varies significantly during this study, between L[subscript s]=l20 and L[subscript s]=l50. At L[subscript s]=l20 transient circulations are seen primarily along the NPRC margin, consistently producing strong flow over the residual cap (~l5 m/s). By L[subscript s]=135, transient eddies form a "storm track" between the northern slopes of Tharsis and the NPRC. By L[subscript s]=150, the circulation is becoming strong and winter-like. These transient eddies may be important in the Martian annual water cycle; many of the observed circulations are poorly (or not) simulated in present day Mars GCMs. Increased resolution and polar stereographic domains provide improvement over GCMs for high latitude studies of atmospheric circulations. These results are in agreement with recent observations. Future work includes model refinements and water vapor transport studies. / Graduation date: 2005

Spectral analysis was used to investigate semidaily mean sea levels and atmospheric pressures at San Francisco, California, Coos Bay, Oregon, and Tofino, British Columbia, in the frequency band 0 to 0.5 cpd. Cross spectral analysis of semidaily mean sea levels and atmospheric pressures at the three stations show that the response of sea level to low-frequency atmospheric pressure fluctuations is nonbarometric in the frequency band studied, and varies with season. Cross spectral analysis of semidaily mean sea levels between adjacent stations shows that there exists significant coherence between the Coos Bay and Tofino sea levels within the frequency band studied and phase difference between the stations is consistent with the hypothesis of continental shelf waves traveling from south to north along the coast. / Graduation date: 1970