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Item Open Access Breakup of temperature inversions in Colorado mountain valleys(Colorado State University. Libraries, 1980) Whiteman, C. D. (Charles David), 1948-, author; McKee, Thomas B., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Economic impacts and analysis methods of extreme precipitation estimates for eastern Colorado(Colorado State University. Libraries, 1986) Changnon, David, authorDams are designed to store water and to insure human safety and as such they must withstand, in their lifetimes, any extreme precipitation event in their drainage basin. Correct estimation of this event is critical because on one hand it must provide an adequate level of safety to not occur, but it must not be any greater than needed since the high costs of dam construction and modifications are directly related to the magnitude of the estimated extreme event. Most frequently the extreme precipitation event is labeled as the Probable Maximum Precipitation, or PMP. National and state concerns over the adequacy of existing dams in the United States as well as increased development of the Front Range led to a federal reassessment and redefinition of new PMP values issued for Colorado in 1984. The study area included the region from the Continental Divide to the 103rd Meridian. Study of these new PMP values and their potential economic impacts in Colorado reveals that an enormous cost will result in Colorado. Techniques for estimating cost of modifications for spillways were developed. Among 162 high risk dams, the estimated total cost for modification was approximately $184 million. The economic value of this precipitation estimate is $9.45 million per inch change of rainfall in this limited study area. In one elevation region, 7000 to 9000 feet, the cost is approximately $15.76 million per inch change of rainfall. Regional cost analyses revealed the South Platte River Division had the greatest costs. Inherent limitations in the PMP procedure and the cost of spillway modifications have made evaluating other alternatives necessary. Special aspects of estimates for extreme precipitation, such as snowmelt runoff versus extreme precipitation events and climate variations were examined. Four methods for estimating extreme precipitation events were evaluated; the traditional PMP, the paleogeological, the cloud/mesoscale dynamic model, and the statistical approaches. A collection of approaches were recommended for Colorado dam design in three elevation regions: the plains, the foothills, and the mountains.Item Open Access Understanding and forecasting tropical cyclone intensity change(Colorado State University. Libraries, 1995) Fitzpatrick, Patrick J., author; Gray, William M., advisor; Schubert, Wayne, committee member; Montgomery, Michael, committee member; Mielke, Paul, committee memberThis research investigates several issues pertaining to tropical cyclone intensity change. Previous research on tropical cyclone intensity change is reviewed in great detail. The applicability of upper-level forcing theories is questioned. Inner-core processes related to intensity change are studied, with particular attention on the relationship between the vertical profile of the tangential wind (Vt) field in the eyewall region and future pressure changes. It is hypothesized that a vertically conserved wind profile is conducive to fast intensification. Observations support this theory. By stratifying inner-core data into fast and slow developers, it is shown that fast developing tropical cyclones contain a more vertically stacked inner-core vortex than slow developers. It is also shown that a direct correlation exists between inner-core upper-level winds and tropical cyclone intensification, with the rate of intensification proportional to the magnitude and symmetry of upper-level Vt. An alternative air-sea interaction theory is presented which incorporates boundary layer cooling. The buoyancy calculations include partial water-loading and ice microphysics, and their relevance to CAPE calculations in the tropics is discussed. It is shown that the lateral extension of the eye, above a sloping eyewall, is the crucial component in maintaining the air-sea interaction despite boundary layer cooling. Implications on the maximum intensity a storm may achieve are discussed. A multiple regression scheme with intensity change as the dependent variable has been developed. The new scheme is titled the Typhoon Intensity Prediction Scheme (TIPS), and is similar to one used operationally at the National Hurricane Center. However, TIPS contains two major differences: it is developed for the western North Pacific Ocean, and utilizes digitized satellite data. It is shown that the satellite data can distinguish between fast and slow developing tropical cyclones. The importance of other statistical predictors (such as SSTs, wind shear, persistence, and climatology) to intensity change are also clarified. The statistics reveal threshold values useful to forecasters. It is shown that TIPS is competitive with the Joint Typhoon Warning Center.Item Open Access Simulation of alpine snow distributions in the northern Colorado Rocky Mountains using a numerical snow-transport model(Colorado State University. Libraries, 1999) Greene, Ethan M., authorTwo methodologies for simulating winter snow distributions I alpine terrain are presented. First, a numerical snow-transport model (SnowTran-3D) is driven from direct meteorological observations, and second, SnowTran-3D is driven from a regional atmospheric model (ClimRAMS). In each case the simulated snow distributions are compared to observed snow depth transects within two alpine sites in the Northern Colorado Rocky Mountains, Rocky Mountain National Park, and Medicine Bow Mountains. The atmospheric conditions at these sites are characterized by persistent westerly winds with average speeds of 13 m/s, which is significantly greater than the threshold for snow transport (approximately 5 m/s). Consequently, snow redistribution by wind is the dominate component in this environment Drift features in these areas form around rocks, alpine vegetation, and small and large topographic variations. The model successfully simulated the large-scale snow drifts, but due to the relatively coarse resolution of the vegetation and topographic data inputs (30 m), the model was unable to reproduce some of the smaller scale snow drift features. The model built large drifts in the upper regions of the east facing cirques in Rocky Mountain National Park, in regions where large perennial snow fields are observed. The model result support the theory that snow transport by wind is an important factor in sustaining these snow fields.Item Open Access Vertical distribution of water vapor using satellite sounding methods with new aircraft data validation(Colorado State University. Libraries, 2001) McNoldy, Brian D., author; Vonder Haar, Thomas, advisor; Stephens, Graeme, committee member; She, Chiao-Yao, committee memberThe importance of water vapor in Earth's climate system is undisputedly immense. Its meteorological impacts range from radiative transfer to the hydrologic cycle, on scales ranging from local to planetary. It affects military operations, commercial flights, and private industry. However, global measurements of water vapor can currently only be obtained from satellites, since ground stations are sparse and ocean stations are nearly non-existent. Unfortunately, the satellites cannot directly measure water vapor; instead, they detect radiation at discrete frequencies. The signals originate from different altitudes in the atmosphere, providing vertical resolution. A complex mathematical inversion is necessary to retrieve the desired quantity (water vapor) from the measured quantity (brightness temperatures). Both the satellite calibration and the retrieval algorithm contribute to errors in the retrieved parameters. The focus here is on the validation of a satellite-based retrieval using in-situ measurements of water vapor made by commercial aircraft. The Aircraft Communications Addressing and Reporting System (ACARS) routinely records a plethora of meteorological parameters, including temperature, pressure, wind velocities, and turbulence. The new Water Vapor Sensing System (WVSS) added water vapor mixing ratio and dewpoint to the array of parameters. These measurements will be compared to the humidity measurements retrieved from the satellite-based TIROS Operational Vertical Sounder (TOVS) High-resolution Infrared Radiation Sounder (HIRS) radiances over the continental United States. This study shows that the water vapor retrieval algorithm is approximately 20% too dry through most of the atmosphere when compared to aircraft measurements of the same parameter.Item Open Access Forecasting of Atlantic tropical cyclones using a kilo-member ensemble(Colorado State University. Libraries, 2004) Vigh, Jonathan L., author; Schubert, Wayne H., advisor; DeMaria, Mark, committee member; Gray, William M., committee member; Taylor, Gerald D., committee memberThe past 30 years have witnessed steady improvements in the skill of tropical cyclone track forecasts. These increases have been largely driven by improved numerical weather prediction models and increased surveillance of the storm environment through aircraft reconnaissance and satellite remote sensing. The skill of deterministic track forecasts from full-physics models is gradually approaching the theoretical limit of predictability that arises due to the atmosphere's chaotic nature and limitations in determining the initial state. To make further progress, it is necessary to treat the uncertainty of the initial condition. One practical approach is to sample this uncertainty by perturbing the initial state. The resulting suite of forecasts that result from integrating such perturbations is known as an ensemble. This thesis describes the design, implementation, and evaluation of a semi-operational ensemble forecasting system using an efficient multigrid barotropic vorticity equation model (MBAR). Five perturbation classes are used to simulate uncertainties in the storm environment and vortex structure. Uncertainties in the storm environment are simulated by using the background environmental flow evolutions provided by the NCEP Global Forecasting System (GFS) ensemble forecasts. Several deep layer-mean wind averages account for uncertainty in the depth of the storm steering layer. Uncertainties in the decomposition of the tropical atmosphere's vertical modes are simulated by varying the model equivalent phase speed. Finally, uncertainties in the vortex structure are simulated by varying the vortex size and storm motion vector. Each perturbation in a given class is cross-multiplied with all other perturbations of other classes to obtain an ensemble with 1980 members. One of the fundamental questions addressed by this research is whether such cross-multiplication increases the degrees of freedom in the ensemble. The ensemble is run for 294 cases from the 2001-2003 Atlantic hurricane seasons. Theory dictates that a properly-perturbed ensemble should, on average, be more accurate than any single ensemble member, but it was found that the kilo-ensemble mean forecast did not demonstrate substantial improvement over the control forecast. However, the ensemble mean did show substantial skill relative to the five-day climatology and persistence model (CLP5) throughout the 120-h forecast period. The ensemble mean spread (the mean distance of the individual members from the ensemble mean), x-bias, and y-bias statistics are also evaluated. Probabilistic interpretations are valid with an ensemble of this size, so cumulative strike probabilities are calculated explicitly from the kilo-ensemble output. In a related possibilistic interpretation, the ensemble can be looked upon as mapping out the subspace of all possible storm tracks, so the reliability of this ensemble envelope is examined. Finally, if the ensemble can accurately simulate the uncertainties in the dynamical system, then there should be a positive relationship between ensemble mean spread and the error of the ensemble mean forecast. A strong relationship allows useful forecasts of forecast skill to be made at the time of the forecast. The kilo-member ensemble was found to have a weak spread-error relationship that peaks at 60 h.Item Open Access Investigation of the summer climate of North America: a regional atmospheric modeling study(Colorado State University. Libraries, 2005) Castro, Christopher Lawrence, authorThe Regional Atmospheric Modeling System (RAMS) is used to investigate model sensitivity and the summer climate of North America. The value restored and added by dynamical downscaling is first evaluated. At large scales, RAMS underestimates atmospheric variability and this worsens as the grid spacing increases or domain size increases. The model simulated evolution of kinetic energy relative to the driving reanalysis kinetic energy exhibits a decrease with time which is more pronounced with larger grid spacing. The surface boundary forcing is the dominant factor in generating atmospheric variability and exerts greater control on the model as the influence of lateral boundary conditions diminish. The sensitivity to surface forcing is also influenced by the model parameterizations. Dynamical downscaling with RAMS does not retain value of the large scale of that which exists in the driving global reanalysis. The value added is to resolve smaller-scale features which have a greater dependence on the surface boundary. The NCEP Reanalysis is then dynamically downscaled with RAMS to generate a regional model climatology of the contiguous U.S. and Mexico (1950-2002). The simulations capture climatic features and seasonal transitions associated with the North American monsoon system. The diurnal cycle is the dominant time-varying mode of convective activity and is modulated by the large-scale circulation. Lower frequency modes account for the variability of convection at a remote distance from elevated terrain. The climatology is evaluated with respected to the dominant modes of global sea surface temperature. An additional series of simulations dynamically downscales data from a general circulation model executed with idealized sea surface temperature corresponding to the modes with greatest variability in the Pacific, to establish a casual link to remote sea surface temperature forcing. Time-evolving teleconnections related to tropical Pacific sea surface temperature modulate the evolution of North American summer climate, in particular the low-level moisture transport into the continental interior and convective activity. The most significant response occurs in early summer and affects the distribution of rainfall at that time. A global increase in tropical sea surface temperature over the period has also significantly affected North American summer climate.Item Open Access The birth and death of the MJO: an observation study(Colorado State University. Libraries, 2005) Benedict, James J., author; Randall, David A. (David Allan), 1948-, advisor; Kirkpatrick, Allan Thompson, committee member; Madden, Roland A., committee member; Thompson, David W. J., committee memberThe Madden-Julian Oscillation (MJO), an eastward-propagating equatorial wave most active during the boreal winter, dominates atmospheric intraseasonal (10-100 day) variability in the tropical Indian and West Pacific Ocean areas. This phenomenon is characterized by cyclic periods of suppressed convection (dry phase) and intense rainfall (wet phase). In this study, we examine important physical mechanisms observed during the "birth" (wet phase approach) and "death" (wet phase departure) of the MJO. Analyses of single events and event composites based on TRMM precipitation highlight cogent features of the MJO. Unlike previous studies, we base MJO events on hydrological activity due to its strong ties to latent heating, the primary driver of tropical circulations. Dynamical fields of mesoscale resolution are diagnosed from ECMWF reanalysis datasets (ERA40). Prior to the onset of intense rainfall, a slow increase in low-level temperature and moisture leads to greater instability. An enhancement of shallow cumulus activity, as inferred from the reanalysis data, is associated with increased moisture detrainment and an erosion of a mid-tropospheric dry layer. In this stage, vertical moisture advection is dominant over the horizontal component. The "death" of the MJO involves immediate and delayed drying processes. Within five days after maximum rainfall, we observe anomalous low-level drying by horizontal advection during a time of weak moistening by vertical motions. This immediate drying has not been analyzed explicitly in previous composite studies. Subsidence drying is delayed, beginning and then peaking one and two weeks after intense precipitation, respectively. Physical attributes of the composite results are compared to current wave instability theories. Our findings lend support to the discharge-recharge mechanism which involves a gradual, local build-up of instability. Currently, no widely-accepted theory exists that can fully explain the MJO. Accurately diagnosing and modeling this phenomenon is of critical importance for weather and climate studies. It is our hope that this study contributes toward an improved understanding of the MJO and its depiction in atmospheric models.Item Open Access A parametric optimal estimation retrieval of the non-precipitating parameters over the global oceans(Colorado State University. Libraries, 2006) Elsaesser, Gregory S., author; Kummerow, Chris, advisor; Reising, Steven C., committee member; Randall, David, committee memberThere are a multitude of spacebome microwave sensors in orbit, including the TRMM Microwave Imager (TMI), the Special Sensor Microwave/lmager (SSM/I) onboard the DMSP satellites, the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E), SSMIS, WINDSAT, and others. Future missions, such as the planned Global Precipitation Measurement (GPM) Mission, will incorporate additional spacebome microwave sensors. The need for consistent geophysical parameter retrievals among an ever-increasing number of microwave sensors requires the development of a physical retrieval scheme independent of any particular sensor and flexible enough so that future microwave sensors can be added with relative ease. To this end, we attempt to develop a parametric retrieval algorithm currently applicable to the non-precipitating atmosphere with the goal of having consistent non-precipitating geophysical parameter products. An algorithm of this nature makes is easier to merge separate products, which, when combined, would allow for additional global sampling or longer time series of the retrieved global geophysical parameters for climate purposes. This algorithm is currently applied to TMI, SSM/I and AMSR-E with results that are comparable to other independent microwave retrievals of the non-precipitating parameters designed for specific sensors. The physical retrieval is developed within the optimal estimation framework. The development of the retrieval within this framework ensures that the simulated radiances corresponding to the retrieved geophysical parameters will always agree with observed radiances regardless of the sensor being used. Furthermore, a framework of this nature allows one to easily add additional physics to describe radiation propagation through raining scenes, thus allowing for the merger of cloud and precipitation retrievals, if so desired. Additionally, optimal estimation provides error estimates on the retrieval, a product often not available in other algorithms, information on potential forward model/sensor biases, and a number of useful diagnostics providing information on the validity and significance of the retrieval (such as Chi-Square, indicative of the general "fit" between the model and observations and the A-Matrix, indicating the sensitivity of the model to a change in the geophysical parameters). There is an expected global response of these diagnostics based on the scene being observed, such as in the case of a raining scene. Fortunately, since TRMM has a precipitation radar (TRMM PR) in addition to a radiometer (TMI) flying on-board, the expected response of the retrieval diagnostics to rainfall can be evaluated. It is shown that a potentially powerful rainfall screen can then be developed for use in passive microwave rainfall and cloud property retrieval algorithms with the possibility of discriminating between precipitating and nonprecipitating scenes, and further indicating the possible contamination of rainfall in cloud liquid water path microwave retrievals.Item Open Access Characteristics and organization of precipitating features during NAME 2004 and their relationship to environmental conditions(Colorado State University. Libraries, 2008) Pereira, Luis Gustavo P., author; Rutledge, Steven A., advisor; Johnson, Richard H., committee member; Kummerow, Christian D., committee member; Cifelli, Robert C., committee member; Chandrasekar, V., committee memberThe focus of this study is to examine the characteristics of convective precipitating features (PFs) during the 2004 North American Monsoon Experiment (NAME) and their precursor environmental conditions. The goal is to gain a better insight into the predictability and variability of warm season convective processes in the southern portion of the North American Monsoon core region. The organization and characteristics of PFs are evaluated using composite radar reflectivity images over the southern portion of the Gulf of California. The environmental conditions are assessed using satellite images and a plethora of atmospheric observational analysis maps, such as winds at multiple levels, upper-level divergence, vorticity, vertical air motion, moisture and vertical cross-sections. Our study reveals that most PFs occurred during the afternoon and evening over land, especially near the foothills of the Sierra Madre Occidental. The vast majority of the precipitating features (~95%) were small, isolated, unorganized, short-lived convective cells. Mesoscale convective systems (MCSs) made up only 5% of the PF population. Nonetheless, these large, long-lived, precipitating features were responsible for 72% of the total precipitation within the radar composite region. An analysis of the number and rainfall produced by these MCSs revealed that they were not constant from day to day, but rather, varied significantly throughout NAME. We found that MCSs were more frequent when the atmosphere is thermodynamically unstable and the wind shear or large-scale dynamics favors the development of organized convection. Lastly, we examined the synoptic conditions associated with episodes of above average MCS rainfall in the southern portion of the NAME core region. Tropical waves were found to be an essential source of moisture and instability in the region. We also found that transient upper-level inverted troughs interact with the upper-level anticyclone to produce a "North American Monsoon Jet Streak" that created favorable dynamical uplift and wind shear conditions for MCS development.Item Open Access Paleo-feedbacks in the hydrological and energy cycles in the Community Climate System Model 3(Colorado State University. Libraries, 2008) Burt, Melissa A., author; Randall, David A., advisor; Denning, Scott, committee member; Wohl, Ellen E., 1962-, committee member; Otto-Bliesner, Bette, committee memberThis research focuses on the joint variability of the hydrological and energy cycles for the atmosphere and lower boundary and climate feedbacks associated with these changes at the Last Glacial Maximum. The LGM simulated climate experiences a global cooling of 4.9 K compared to the PI climate, with greatest cooling in the high latitudes of both hemispheres. Additional cooling also exists over the continental ice sheets in North America, Northern Europe, and Antarctica. Precipitation and evaporation are reduced by 10%, and precipitable water by 20%, compared to conditions at PI. Overall, from LGM to PI the changes in clouds are weak. The water vapor, ice-albedo, and cloud feedbacks act to amplify the climate change from LGM to PI. The positive water vapor and ice-albedo feedbacks account for 5.04 W m-2 K-1 and 2.38 W m-2 K-1, respectively of the climate change. The cloud feedbacks produces -2.83 of the change. An interesting and unexpected result was that the sign of the ice-albedo feedback changed regionally and is driven by changes in ocean basin size. Combined, the radiative feedbacks from LGM to PI act to amplify the climate change by 5.67 W m-2 K-1 and are balanced by an increase in surface evaporation.Item Open Access A study of the relationship between thunderstorm processes and cloud-top ice crystal size(Colorado State University. Libraries, 2008) Lindsey, Daniel T., author; Johnson, Richard H., advisorSatellite observations and numerical models are used to understand the physical mechanisms responsible for thunderstorms with varying cloud-top ice crystal sizes. Geostationary Operational Environmental Satellite (GOES) data are used to create a three-year climatology of cloud-top 3.9 µm reflectivity, a quantity which is closely correlated with particle size. Maximum mean values are found over the High Plains and Rocky Mountain regions of the U.S., suggesting that convection over that region tends to generate smaller anvil ice crystals than areas throughout much of the eastern U.S. To correct for preferred forward scattering by the cloud-top ice crystals, an effective radius retrieval using GOES is developed. Forward radiative transfer simulations are run for a wide range of cloud-top ice crystal sizes and sun-cloud-satellite scattering angles. The output is used to generate a lookup table, so that GOES-measured radiances may be used along with sun-satellite geometry to obtain an estimate for particle size. Validation of the retrieval shows that the assumed scattering properties perform quite well. To help explain the geographical variation in cloud-top ice crystal size, a composite analysis is performed in the High Plains region by averaging environmental conditions for days which produced both small and large ice crystal storms. Small ice is found to occur with relatively high based storms and steep mid-level lapse rates. Additionally, observational evidence from a pyrocumulonimbus event is presented to show the effect of low-level cloud condensation nuclei (CCN) on cloud-top ice crystal size. Model simulations using the Colorado State University Regional Atmospheric Modeling System (RAMS) are performed to help understand the physical mechanisms responsible for cloud-top ice crystal size. Through a series of sensitivity tests, it is found that larger low-level CCN concentrations lead to smaller anvil ice. In addition, as cloud-base temperature decreases (and cloud-base height increases), storm-top ice crystals get smaller. A weaker updraft strength is found to have very little effect on ice crystal size.Item Open Access Model evaluation using space-borne lidar observations(Colorado State University. Libraries, 2008) Ahlgrimm, Maike, author; Randall, David A., advisorIn this study, the use of space-borne lidar observations for the comparison with, and evaluation of modeled clouds is explored. Four version of the ECMWF Integrated Forecast System and two versions of the Goddard Earth Observing System (GEOS-5) model are assessed for their ability to produce marine boundary layer clouds. The cause of some of the model deficiencies is investigated, and specific suggestions for improvements are made and tested. In order to do so, two cloud types are defined: a stratocumulus type (Sc), and a trade cumulus or transitional cumulus type (TCu). Samples in four oceanic regions are classified into those categories, and the frequency of occurrence, location, and properties of the samples compared between models and observations.Item Open Access Atmospheric nitrogen and sulfur deposition in Rocky Mountain National Park(Colorado State University. Libraries, 2008) Beem, Katherine B., author; Collett, Jeffrey L., advisor; Davis, Jessica G., committee member; Kreidenweis, Sonia M., committee memberRocky Mountain National Park (RMNP) is experiencing a number of adverse effects due to atmospheric nitrogen (N) and sulfur (S) compounds. Airborne nitrate and sulfate particles contribute to visibility degradation in the park while nitrogen deposition is producing changes in ecosystem function and surface water chemistry. Both sulfur and nitrogen compounds are essential nutrients for life; however, some environments have naturally limited supplies of sulfur and nitrogen which restrict biological activity. Increasing the amounts of these compounds can be toxic, even life threatening, to the ecosystem. Concerns about increasing deposition are especially important in national parks where excess nitrogen and sulfur can upset the delicate balance between species of flora and fauna in prized natural ecosystems. Measurements were made during the Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study to quantify both N and S wet and dry deposition and to determine the most important species and pathways contributing to N deposition. Gas and particle concentrations were measured and precipitation samples were collected to gain a better understanding of nitrogen and sulfur transport to and deposition in RMNP. Samples were collected at 12 sites across the state of Colorado in March and April 2006 and at 13 sites in north central Colorado in July and August 2006. Historical data suggest that these are the seasons when N deposition in RMNP is greatest. The majority of wet deposition in the spring was from a single, large upslope snowstorm, while in the summer wet deposition inputs were spread across many more events. Total wet deposition of N in the summer was larger than during spring. Ammonium was the largest contributor to both spring and summer wet deposition in the park, followed by nitrate. Organic nitrogen, which is not routinely measured, contributed an average of 616.39 μg N/m2/event in the spring and 847.2 μg N/m2/event in the summer at the core sampling site. These deposition amounts were 22% and 16%, respectively, of total wet nitrogen deposition at this site. Dry deposition in RMNP was dominated by gaseous species which feature higher deposition velocities than accumulation mode aerosol particles. Ammonia, which is not routinely measured, was the largest contributor to dry N deposition followed by nitric acid. Dry deposition of fine particle nitrate and ammonium made only small contributions to total N deposition. Total N inputs were dominated by wet processes during both spring and summer. Wet deposition of organic nitrogen and dry deposition of gaseous ammonia comprised the 3rd and 4th largest contributions to the total N deposition budget. Together these pathways contributed nearly one-third of total measured N deposition, suggesting they should be examined more closely in assessing nitrogen impacts on national park ecosystems.Item Open Access Estimating contributions of primary biomass combustion to fine particulate matter at sites in the western United States(Colorado State University. Libraries, 2008) Holden, Amanda S., author; Collett, Jeffrey L., advisor; Henry, Charles S., committee member; Kreidenweis, Sonia M., committee memberBiomass combustion occurs throughout the world and has many implications for human health, air quality and visibility, and climate change. To better understand the impacts of biomass combustion in the western United States, six-day integrated fine particle samples were collected during the winter and summer seasons of 2004-2006 at seven IMPROVE sampling sites using Hi-Vol samplers. These sites included both urban and rural locations. Filter samples were analyzed for organic and elemental carbon, levoglucosan, and a suite of particulate ions. Levoglucosan, a thermal degradation product of cellulose, is a widely used tracer for primary biomass combustion. Measurements of levoglucosan and other carbohydrates were made using a new approach involving aqueous filter extraction followed by direct analysis using High Performance Anion Exchange Chromatography. In this method carbohydrates are separated on a Dionex Carbopac PA-10 column and detected using pulsed amperometry. Source profiles for primary biomass combustion were applied to each of these samples to estimate the contributions of carbon from both residential wood burning (during the winter seasons) and wildland fires (during the summer seasons). Wildland fire source profiles were determined from FLAME (Fire Lab at Missoula Experiment) campaigns at the USFS/USDA Fire Science Lab in Missoula, MT, during which fine particle samples were collected from source burns of approximately 30 fuel types. Residential wood combustion source profiles were collected from the literature. Primary biomass combustion contributions to contemporary PM2.5 carbon, determined separately from carbon isotope measurements at Lawrence Livermore National Laboratory, ranged from 0.4% to more than 100%. Contributions of primary biomass combustion were higher at rural sites, while urban sites showed greater contributions of fossil carbon. Primary biomass combustion contributed a larger fraction of total carbon in the summer at southern sites, while northern sites had larger contributions during the colder winter months.Item Open Access The optical, chemical, and physical properties of aerosols and gases emitted by the laboratory combustion of wildland fuels(Colorado State University. Libraries, 2008) McMeeking, Gavin R., author; Kreidenweis, Sonia M., advisorBiomass burning is a major source of trace gases and particles that have a profound impact on the atmosphere. Trace gases emitted by fires include the greenhouse gases CO2 and CH4, as well as CO and volatile organic compounds that affect air quality. Particle emissions affect climate, visibility, the hydrologic cycle, and human health. This work presents measurements of trace gas and aerosol emissions from a series of controlled laboratory burns for various plant species common to North America. Over 30 fuels were tested through ~250 individual burns during the Fire Laboratory at Missoula Experiment. Emission factors are presented as a function of modified combustion efficiency (MCE), a measure of the fire combustion conditions. The emissions of many trace gas and aerosol species depended strongly on MCE: smoldering-phase combustion dominated fires (low MCE) emitted roughly four times as much gas-phase hydrocarbon species and organic aerosols than flaming-phase dominated fires (high MCE). Inorganic aerosol emissions depended more strongly on plant species and components than on MCE. Flaming-phase dominated fires tended to produce aerosol with high mass fractions of strongly light-absorbing elemental carbon. Smoldering-phase fires produced aerosol with large mass fractions of more weakly light absorbing organic carbon, but this material was found to have a strong wavelength dependence of absorption, greater than the inverse wavelength relationship typically assumed for light absorbing aerosol. A two component model-featuring elemental carbon with a weak wavelength dependence but high mass-normalized absorption efficiency and organic carbon with a strong wavelength dependence but low mass-normalized absorption efficiency-is shown to represent the bulk absorption spectra of biomass burning aerosol. The results show that at wavelengths below ~450 nm, organic carbon light absorption could rival that of elemental carbon for aerosol dominated by organic carbon. If ignored, the light absorption by organic carbon can cause errors in predicted surface ultraviolet and visible radiation fluxes and photochemical photolysis rates in regions affected by biomass burning emissions. The dependence of spectral aerosol optical properties on combustion conditions means that fire behavior must be accurately assessed and predicted to ensure accurate emissions inventories and estimates of biomass burning atmospheric impacts.Item Open Access Tropical cyclone evolution via internal asymmetric dynamics(Colorado State University. Libraries, 2008) Hendricks, Eric A., author; Schubert, Wayne, advisorThis dissertation advances our understanding by which tropical cyclones (TCs) evolve solely due to internal dynamics, in the absence of large-scale environmental factors and surface fluxes, using a hierarchy of numerical model simulations, diagnostics and observations. In the first part, the role of inner-core (eye and eyewall) transport and mixing processes in TC structure and evolution is examined, and in the second part, some asymmetric dynamics of tropical cyclone evolution are studied: spontaneous inertia-gravity wave radiation from active TC cores and an observational case study of the role of vortical hot towers in tropical transition. The role of two-dimensional transport and mixing in TC structure and intensity change is quantified. First, the mixing properties of idealized hurricane-like vortices are assessed using the effective diffusivity diagnostic. Both monotonic and dynamically unstable vortices are considered. For generic deformations to monotonic vortices, axisymmetrization induces potential vorticity (PV) wave breaking outside the radius of maximum wind, forming a finite radial length surf zone characterized by chaotic mixing. Although on a much smaller scale, this surf zone is analogous to the surf zone outside the wintertime stratospheric polar vortex. For unstable rings, during barotropic instability both the inner and outer breaking PV waves create horizontal mixing regions. For thin ring breakdowns, the entire inner-core becomes a strong mixing region and passive tracers can be transported quickly over large horizontal distances. For thick ring breakdowns, an asymmetric partial barrier region may remain intact at the hurricane tangential jet, with mixing regions on each side where the waves break. The inner, breaking PV wave is quite effective at mixing passive tracers between the eye and eyewall; with a monotonic low-level equivalent potential temperature radial profile, these results support the hurricane super-intensity mechanism. Next, a systematic study of inner-core PV mixing resulting from unstable vortex breakdowns is conducted. After verifying linear theory, the instabilities are followed into their nonlinear regime and the resultant end states are assessed for 170 different PV rings, covering a wide spectrum of real hurricanes.Item Open Access Characteristics of precipitation: CloudSat observations and model predictions of the current and future climate(Colorado State University. Libraries, 2008) Ellis, Todd Douglas, author; Stephens, Graeme L., advisorThe overall purpose of this study is to examine the characteristics of precipitation as they are predicted to change in a typical climate change scenario and as they exist now and how well model reproduces those observations. The first part of this study examines the controls on global precipitation evident in a transient carbon dioxide doubling experiment conducted using coupled climate models collected for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). As noted in other studies, the ensemble mean changes in water vapor occur at a rate more than three times that of precipitation. A simple ratio of these changes is introduced as a type of measure of the efficiency of the atmospheric hydrologic cycle in responding to changes in moisture, and varies between about 0.09 and 0.25 for the models studied. It is shown that the change in precipitation sensitivity is primarily governed by how emission of radiation from the clear-sky atmosphere increases as water vapor increases. This relationship closely matches one derived from simple energy balance arguments involving changes to water vapor emission alone. The study also presents the precipitation incidence over the global oceans as calculated from the CloudSat satellite, showing precipitation into the high latitudes and calculating that precipitation occurs 11% of the time over the oceans. These data are verified using ship-based (ICOADS) and island-based (GSOD) data. This study then extends the use of these data to an analysis of the observed cloud structures that are associated with rainfall over the oceans and then comparing them to special runs of the ECMWF weather forecast and HadGAM1 climate prediction models. These comparisons show that the models don't predict shallow precipitation nor layered precipitation structures as often as they are observed, and predict incorrect global precipitation incidences.Item Open Access Properties of the tropical hydrologic cycle as analyzed through 3-dimensional k-means cluster analysis(Colorado State University. Libraries, 2008) Rogers, Matthew Alan, author; Stephens, Graeme, advisorAs the primary locations of deep convective activity and unrestrained tropical wave dynamics, the tropical West Pacific and East Indian oceans are among the most important regions in the tropics. Given that most of the region consists of unpopulated expanses of ocean, observations of tropical atmospheric properties in this important region is exceptionally difficult. Only with the help of satellite observations are we capable of gleaning valuable data from this region, and our utilization of advanced analysis techniques allows us to gain more from these observations then would otherwise be possible. In that vein, this dissertation reports on the use of a unique statistical technique, long known to other fields of research, as applied to a combined-instrument satellite observation dataset over the warm pool region of the tropical West Pacific ocean. The statistical technique, known as k-means cluster analysis, is used to delineate self-similar populations of cloud type, hereafter referred to as cloud regimes, from frequency-distribution histograms of cloud-top height, cloud optical thickness, and rainfall amount. We will show that four primary cloud regimes exist in the tropical region discussed, that the four regimes vary primarily through differences in convective activity, and that these four cloud regimes exist in a coherent temporal structure that explains the long-observed variability in convective activity seen in the tropics. Combining this regime information with satellite observations, along with reanalysis data, we then examine the individual properties of each cloud regime. These observations give us the means to understand the forcings behind cloud regime change in the region. We confirm the structural properties of these regimes using analysis from a cloud-resolving model, and apply our new understanding of the mechanism behind this large-scale forcing to the governance of the tropical hydrologic cycle as a whole. The insights gained from this analysis have benefits to both the fields of atmospheric remote sensing, and of cloud- and climate modeling of the tropical atmosphere. Applications of this technique are of particular interest to researchers developing retrieval algorithms for latent heat profiles using active sensors such as the cloud-profiling radar aboard CloudSat.Item Open Access Mechanisms of observed sea surface temperature variability in the extratropical southern hemisphere(Colorado State University. Libraries, 2008) Ciasto, Laura M., author; Thompson, David, advisorThe physical mechanisms that drive sea surface temperature (SST) variability in the extratropical Southern Hemisphere (SH) are examined using multiple ocean temperature datasets. The first part of the study provides a detailed analysis of the relationships between variability in SH SST anomalies, the Southern Annular Mode (SAM) and the El-Niño/Southern Oscillation (ENSO) during the warm (November-April) and cold (May-October) seasons. It is shown that the signatures of the SAM and ENSO in the SST field vary as a function of season, both in terms of their amplitudes and structures. SAM-related SST anomalies are primarily driven by surface turbulent heat fluxes with a smaller contribution from heat advection by Ekman currents. The role of turbulent heat fluxes in generating ENSO-related SST anomalies is less clear. Analyses of the temporal evolution of the relationships between the SAM and the SST field demonstrate that SST anomalies are largest when SSTs lag by ~1 week and persist for up to 8 weeks. In the absence of ENSO, cold season SAM-related SST anomalies persist longer than their warm season counterparts, consistent with seasonal variations in the depth of the mixed layer. The second part of the study uses observations of subsurface temperatures to examine the winter-to-winter "reemergence" of SST anomalies in the extratropical South Pacific. Reemergence is the mechanism whereby SST anomalies formed in the late winter are sequestered beneath the shallow summer mixed layer and then re-entrained into the deepening mixed layer during the following fall/winter. The results exhibit a pronounced reemergence signal in which surface temperature anomalies during the late winter season are strongly correlated with surface temperature anomalies during the subsequent early winter months, but are only significantly correlated with temperature anomalies beneath the mixed layer during the intervening summer months. The results are robust to small changes in the period of analysis and are qualitatively similar to existing evidence of reemergence in the Northern Hemisphere. The signal of reemergence evident in the subsurface data is readily apparent in SST data in the western South Pacific. Reemergence is less evident in SST data in the eastern South Pacific.