Browsing by Author "Reising, Steven, committee member"
Now showing 1 - 18 of 18
Results Per Page
Sort Options
Item Open Access Analysis of precipitation and convection in the west Pacific during the PISTON field campaign(Colorado State University. Libraries, 2022) Chudler, Kyle, author; Rutledge, Steven, advisor; Bell, Michael, committee member; Maloney, Eric, committee member; Reising, Steven, committee memberTropical convection is a meteorological phenomenon with important impacts on the atmosphere, both locally and globally. Consequently, it has been an intensely studied topic for many years. Importantly, several ship-based field campaigns have taken place over tropical oceans. Such field campaigns are vital to the advancement of knowledge in this field, as meteorological observations over these open oceans are otherwise scant or non-existent. The latest project to examine tropical convection is the Propagation of Intraseasonal Oscillations (PISTON) field campaign, which took place in the western North Pacific in the late-summer and early-fall of 2018 and 2019. On board the PISTON ships was the SEA-POL weather radar, the first polarimetric weather radar designed specifically for deployment at sea. In addition to taking traditional radar measurements of precipitation intensity and velocity, SEA-POL's polarimetric measurements also provide insights into the size, shape, and composition of hydrometeors within precipitating systems. By combining SEA-POL's unique measurements with other meteorological datasets, this work presented in this dissertation provides new insights in tropical convection in the Pacific warm pool. Chapter 2 of this dissertation provides an overview of the variability in convection observed during the PISTON cruises, and relates this variability to large-scale atmospheric conditions. Using an objective classification algorithm, precipitation features are identified and labeled by their size (isolated, sub-MCS, MCS) and degree of convective organization (nonlinear, linear). It is shown that although large mesoscale convective systems (MCSs) occurred infrequently (present in 13% of radar scans), they contributed a disproportionately large portion (56%) of the total rain volume. Conversely, small isolated features were present in 91% of scans, yet these features contributed just 11% of the total rain volume, with the bulk of the rainfall owing to warm rain production. Convective rain rates and 30-dBZ echo-top heights increased with feature size and degree of organization. MCSs occurred more frequently in periods of low-level southwesterly winds, and when low-level wind shear was enhanced. By compositing radar and sounding data by phases of easterly waves (of which there were several in 2018), troughs are shown to be associated with increased precipitation and a higher relative frequency of MCS feature occurrence, while ridges are shown to be associated with decreased precipitation and a higher relative frequency of isolated convective features. During PISTON, SEA-POL routinely measured extreme values of differential reflectivity in the cores of small, isolated convection, owing to the presence of large drops. Chapter 3 examines the structure and frequency of cells containing large drops. Cells with high differential reflectivity (> 3.5 dB) were present in 24% of all radar scans. The cells were typically small (8 km2 mean area), short lived (usually < 10 minutes), and shallow (3.7 km mean height). High differential reflectivity was more often found on the upwind side of these cells, suggesting a size sorting mechanism which establishes a low concentration of large drops on the upwind side. Differential reflectivity also tended to increase at lower altitudes, which is hypothesized to be due to continued drop growth, increasing temperature (dielectric effect), and evaporation of smaller drops. Rapid vertical cross section radar scans, as well as transects made by a Learjet aircraft with on-board particle probes, are also used to analyze these cells, and support the conclusions drawn from statistical analysis. In Chapter 4, the observations of precipitation from spaceborne Ku-Band precipitation radar (KuPR) from the Global Precipitation Mission Dual-Frequency Precipitation Radar is compared surface observations from SEA-POL. Over the 18 instances where KuPR and SEA-POL made concurrent measurements of precipitation, the average rain rate in KuPR was 50% lower than in SEA-POL, but the raining area was 113% higher. The net effect of these two differences of opposite sign was for KUPR to have 23% more rain volume than SEA-POL. The limited resolution of KuPR (5x5 km) causes it to underestimate rain rate in small convective cores, but also over-broaden raining features beyond their true extent. It is also shown that KuPR tends to slightly overestimate rain rate below the melting layer in stratiform rain, likely due to overcorrection of attenuation below radar bright bands. Using a statistical model to simulate KuPR rain volume, it was found that KuPR would theoretically overestimate rain volume during trough phases of the easterly waves observed during PISTON (when there was more precipitating area), and underestimate rainfall during ridge phases (when there was less precipitating area).Item Open Access Buck converter for on-chip reference generation(Colorado State University. Libraries, 2010) Rai, Abhay K., author; Collins, George, advisor; Yalin, Azer, committee member; Reising, Steven, committee memberMost modern day chips use an on chip voltage reference, also known as a bandgap voltage reference generator, to provide a stable reference, independent of power supply voltage (VDD) ripples and compensated for temperature variations. When power supply voltage decreases as the process feature size (gate length) decreases, it imposes challenges in terms of headroom and other factors to achieve a stable bandgap voltage reference. It also needs to be scaled down to VDD/2 for practical uses and provide a common mode voltage of VDD/2 of on-chip circuits. This thesis discusses a buck converter which uses an alternative to pulse width modulation (PWM) for stable reference generation and directly generates a VDD/2 reference using a novel inductor ripple current cancellation technique, which cancels inductor ripple current and therefore does not require a large capacitance for filtering of inductor ripple. An alternative to the pulse width modulation (PWM) technique is proposed, which uses common mode bias and transconductance (gm) tuning to keep the reference output constant for variable loads, and a temperature compensation techniques is used to minimize temperature sensitivity.Item Open Access Cloud process information from a fleet of small satellites: synthetic retrievals using an optimal estimation algorithm(Colorado State University. Libraries, 2018) Schulte, Richard M., author; Kummerow, Christian, advisor; Bell, Michael, committee member; Reising, Steven, committee memberThe great importance of clouds in understanding atmospheric phenomena is widely recognized, yet faithful representations of cloud and precipitation processes in models at nearly all scales remain elusive. In order to properly constrain model parameters, it is important to obtain reliable observations of cloud properties in varying atmospheric environments. The Temporal Experiment for Storms and Tropical Systems (TEMPEST) mission was proposed to help address this need by deploying a cluster of CubeSats, each containing an identical, five-frequency passive microwave radiometer, into the same orbit. Doing so would allow for the observation of cloud processes at a high temporal resolution and on a global scale. In order for such a mission to be useful in understanding cloud processes, it is crucial to develop a retrieval algorithm that can distinguish true changes in the atmospheric state from the noise induced by making repeated observations only a few minutes apart at different view angles. To this end, a physical optimal estimation algorithm is developed for the retrieval of water vapor, cloud water, and frozen hydrometeors from cross-track microwave sounders such as the TEMPEST radiometer. The performance of the algorithm is assessed by using high resolution Weather Research and Forecasting (WRF) model output to generate synthetic radiometer observations, while incorporating realistic error estimates, and then comparing the parameters retrieved using the synthetic observations to the actual model parameters. For rapidly changing clouds, differences in parameters retrieved at various view angles, while not trivial, are small enough that changes in cloud properties can be discerned. This is especially true for view angles near nadir, where the field of view is smaller and changes less rapidly with time. Experiments simulating a cluster of TEMPEST instruments successively observing the same cloud system suggest that using the higher-quality retrievals near nadir to constrain preceding and subsequent observations allows for cloud changes to be observed more clearly. An analysis of the contribution of various forward model errors indicates that incorporating more accurate a-priori information about wind speed, cloud coverage, and cloud heights, perhaps obtained from coincident measurements by other spaceborne instruments, would further constrain the retrieval and mitigate some of the view angle induced biases.Item Open Access Comparative analysis of model-based systems engineering and traditional systems engineering approaches for architecting robotic space systems through knowledge categorization, automatic information transfer, and automatic knowledge processing measures(Colorado State University. Libraries, 2021) Younse, Paulo, author; Bradley, Thomas, advisor; Borky, John, committee member; Sega, Ron, committee member; Reising, Steven, committee memberRobotic space systems have enabled us to explore the far reaches of our solar system. However, these missions are high-cost, high-risk, and prone to accidents due to their complex nature. As these systems continue to grow even more capable and complex, spacecraft costs and mission success risk are also expected to grow. Current systems engineering approaches are finding it challenging to manage this growth in system complexity. Model-Based Systems Engineering (MBSE) offers techniques to aid in the development of complex systems, aiming to reduce design errors, reduce cost through prevention of costly rework, and improve system quality and project performance over traditional systems engineering techniques. Robotic space systems have much to benefit from an MBSE approach due to their intrinsic complexity, particularly if MBSE is implemented during the early architecting phase of the project. Case studies from the literature assert that there are benefits to using MBSE when applied to developing complex systems. However, none of these studies perform in-depth quantitative comparative analysis of applying MBSE vs. non-MBSE approaches, and there currently is a lack of substantial and compelling evidence to establish broad adoption of MBSE within the systems engineering community. This research measures the benefits of MBSE approaches over traditional, non-MBSE approaches for architecting robotic space systems though comparative analysis, focusing on quantitative evidence supporting how MBSE better describes, develops, and evaluates the system architecture, all which can aid in the adoption of MBSE within the robotics space systems domain. These advantages will be investigated through studying 1) how an MBSE approach better captures the information content for describing a robotic space system architecture relative to a non-MBSE approach, 2) how an MBSE approach reduces the implementation effort required to developing a robotic space system architecture relative to a non-MBSE approach, and 3) how an MBSE approach more efficiently evaluates a robotic space system architecture relative to a non-MBSE approach. A Mars orbiting sample Capture and Orient Module (COM) system for a Capture, Contain, and Return System (CCRS) payload concept for the notional Mars Sample Return (MSR) campaign develop at the NASA Jet Propulsion Laboratory was used as a case study to investigate the advantages of MBSE. The MBSE approach provided measurable advantages to architecting the COM robotic space system in terms of a higher fraction of formally captured architecture content in the appropriate knowledge category, a higher quantity of automatic information transfer between architecting tasks, and a higher quantity of automatic knowledge processing during modeling and simulation activities.Item Open Access Electromagnetic model subdivision and iterative solvers for surface and volume double higher order numerical methods and applications(Colorado State University. Libraries, 2019) Manić, Sanja B., author; Notaroš, Branislav, advisor; Reising, Steven, committee member; Chandrasekar, V., committee member; Oprea, Iuliana, committee member; Ilić, Milan, committee memberHigher order methods have been established in the numerical analysis of electromagnetic structures decreasing the number of unknowns compared to the low order discretization. In order to decrease memory requirements even further, model subdivision in the computational analysis of electrically large structures has been used. The technique is based on clustering elements and solving/approximating subsystems separately, and it is often implemented in conjunction with iterative solvers. This thesis addresses unique theoretical and implementation details specific to model subdivision of the structures discretized by the Double Higher Order (DHO) elements analyzed by i) Finite Element Method - Mode Matching (FEM-MM) technique for closed-region (waveguide) structures and ii) Surface Integral Equation Method of Moments (SIE-MoM) in combination with (Multi-Level) Fast Multipole Method for open-region bodies. Besides standard application in decreasing the model size, DHO FEM-MM is applied to modeling communication system in tunnels by means of Standard Impedance Boundary Condition (SIBC), and excellent agreement is achieved with measurements performed in Massif Central tunnel. To increase accuracy of the SIE-MoM computation, novel method for numerical evaluation of the 2-D surface integrals in MoM matrix entries has been improved to achieve better accuracy than traditional method. To demonstrate its efficiency and practicality, SIE-MoM technique is applied to analysis of the rain event containing significant percentage of the oscillating drops recorded by 2D video disdrometer. An excellent agreement with previously-obtained radar measurements has been established providing the benefits of accurately modeling precipitation particles.Item Open Access Evaluation of inter-annual variability and trends of cloud liquid water path in climate models using a multi-decadal record of passive microwave observations(Colorado State University. Libraries, 2016) Manaster, Andrew, author; Kummerow, Christian, advisor; O'Dell, Christopher W., advisor; Randall, David, committee member; Reising, Steven, committee memberLong term satellite records of cloud changes have only been available for the past several decades and have just recently been used to diagnose cloud-climate feedbacks. However, due to issues with satellite drift, calibration, and other artifacts, the validity of these cloud changes has been called into question. It is therefore pertinent that we look for other observational datasets that can help to diagnose changes in variables relevant to cloud-radiation feedbacks. One such dataset is the Multisensor Advanced Climatology of Liquid Water Path (MAC-LWP), which blends cloud liquid water path (LWP) observations from 12 different passive microwave sensors over the past 27 years. In this study, observed LWP trends from the MAC-LWP dataset are compared to LWP trends from 16 models in the Coupled Model Intercomparison Project 5 (CMIP5) in order to assess how well the models capture these trends and thus related radiative forcing variables (e.g., cloud radiative forcing). Mean state values of observed LWP are compared to those of previous observed climatologies and are found to have relatively good quantitative and qualitative agreements. Mean state observed LWP variables are compared both qualitatively and quantitatively to our suite of CMIP5 models. These models tend to capture mean state and mean seasonal cycle LWP features, but the magnitudes exhibit large variations from model to model. Several metrics were used to compare observed mean state LWP and mean seasonal cycle amplitude and the mean state LWP and mean seasonal cycle amplitude in each model. However, the models' performance in regards to these metrics is found to not be indicative of their abilities to accurately reproduce trends on a regional or global scale. Global trends in the observations and the model means are compared. It is found that observational trends are roughly 2-3 times larger in magnitude in most regions globally when compared to the model mean although this is thought to be at least partly caused by cancellation effects due to differing inter-annual variability and physics between models. Several regions (e.g., the Southern Ocean) have consistent signs in trends between the observations and the model mean while others do not due to spatial inconsistencies in certain trend features in the model mean relative to the observations. Trends are examined in individual regions. In four of the six regions analyzed, the observational trends are statistically different from zero, while, in most regions, very few models have trends that are statistically significant. In certain regions, the majority of modeled trends are statistically consistent with the observed trends although this is typically due to large estimated errors in the observations and/or models, most likely caused by large inter-annual variability. The Southern Ocean and globally averaged trends show the strongest similarities to the observed trends. Almost all Southern Ocean trends are robustly positive and statistically significant with the majority of models being statistically consistent with the observations. Similarly, the observed and global trends are all positive with the majority being statistically significant and statistically consistent. We discuss why a large positive Southern Ocean trend is unlikely to be due to a trend in cloud phase. CMIP5 model mean and observational LWP trends are compared regionally to Atmospheric Model Intercomparison Project (AMIP) and ERA-interim reanalysis trends. It is found that AMIP model mean and ERA LWPs are better than the CMIP5 model mean at capturing the inter-annual variability in the observed time series in most of the regions examined. The AMIP model mean better replicates the observed trends when the inter-annual variability is better captured. The ERA reanalysis tends to better reproduce the observed inter-annual variability when compared to the AMIP model mean in almost every region, but, surprisingly, it is either worse or roughly the same in regards to matching observed trends. Our results suggest that observed trends are due to a combination of inter-annual and decadal-scale internal variability, in addition to external forced trends due to anthropogenic influences on the climate system. With a record spanning three decades, many modeled trends are statistically consistent with the observed trends, but a true climatically forced signal is not yet apparent in the models that agrees with the observations. The primary exception to this is in the Southern Ocean, where virtually all models and observations indicate an increasing amount of cloud liquid water path.Item Open Access Fast and accurate double-higher-order method of moments accelerated by Diakoptic Domain Decomposition and memory efficient parallelization for high performance computing systems(Colorado State University. Libraries, 2015) Manić, Ana, author; Notaros, Branislav, advisor; Reising, Steven, committee member; Oprea, Iuliana, committee member; Roy, Sourajeet, committee member; Ilić, Milan, committee memberTo view the abstract, please see the full text of the document.Item Open Access Higher order volume/surface integral equation modeling of antennas and scatterers using diakoptics and method of moments(Colorado State University. Libraries, 2015) Chobanyan, Elene, author; Notaros, Branislav M., advisor; Reising, Steven, committee member; Oprea, Iuliana, committee member; Chandrasekar, V., committee member; Pezeshki, Ali, committee memberThe principal objective of this dissertation is to develop, test, and optimize accurate, efficient, and robust computational methodology and tools for modeling of general antennas and scatterers based on solutions of electromagnetic integral equation formulations using the method of moments (MoM) and diakoptics. The approaches and implementations include the volume integral equation (VIE) method and its hybridization with the surface integral equation (SIE) method, in two ways. The first way combines the VIE method for dielectric parts and the SIE method for metallic parts of the structure. The second way performs subdivision of the entire structure into SIE domains of different constant permittivities, while modeling the inhomogeneity within each domain by the VIE method and employing different Green's functions, with describing the inhomogeneity within each domain in terms of a perturbation with respect to the background permittivity. The first approach is very suitable for analysis of composite wire-plate-dielectric radiation/scattering structures. The second approach provides a particularly efficient solution to problems involving inhomogineities embedded within high-contrast homogeneous dielectric scatterers. The efficiency of computation is enhanced by applying the diakoptic domain decomposition. In the VIE-SIE diakoptic method, the interior diakoptic subsystems containing inhomogeneous dielectric materials are analyzed completely independently applying the VIE-SIE MoM solver, and the solution to the original problem is obtained from linear relations between electric and magnetic surface-current diakoptic coefficients on diakoptic surfaces, written in the form of matrices. The techniques implement Lagrange-type generalized curved parametric hexahedral MoM-VIE volume elements and quadrilateral MoM-SIE and diakoptic patches of arbitrary geometrical-mapping orders, and divergence-conforming hierarchical polynomial vector basis functions of arbitrary current expansion orders. The hexahedra can be filled with inhomogeneous dielectric materials with continuous spatial variations of the permittivity described by Lagrange interpolation polynomials of arbitrary material-representation orders. Numerical computation is further accelerated by MPI parallelization to enable analysis of large electromagnetic problems.Item Open Access Impact of the Boreal Summer Intraseasonal Oscillation on the diurnal cycle of precipitation in the island of Luzon(Colorado State University. Libraries, 2019) Chudler, Kyle, author; Rutledge, Steven, advisor; Xu, Weixin, committee member; Bell, Michael, committee member; Reising, Steven, committee memberThe Asian Summer Monsoon (ASM) is a major component of the global weather system with impacts on multiple scales. Driven by the thermal contrast between the Asian continent and the Indian and Pacific Oceans, the monsoon winds bring warm, moist air into the south Asian and maritime continents. Along with this influx of tropical air often comes copious amounts of rain, which can be both beneficial to agriculture and devastating to flood-prone regions. On a larger scale, the immense amount of latent heat released into the upper troposphere from condensation and deposition of water vapor can impact weather patterns across the globe. One striking feature in rainfall climatology of the ASM is the precipitation maxima located off the western shores of the Western Ghats, Myanmar, and the Philippines. These locations all feature elevated terrain features along their western shores. Many studies have examined why, when monsoon winds impinge upon these mountains, the precipitation preferentially falls off-shore, rather than directly over the mountains where orographic enhancement is strongest. Several theories have been proposed, including convergence of the monsoon winds with a land breeze, afternoon land-based convection which either propagates off-shore or creates a cold pool, and generation of off-shore instability through propagation of gravity waves generated from daytime heating of the boundary layer. Notably, all of these mechanisms are closely tied to the diurnal cycle. The main source of intraseasonal variability during the summer months in the ASM region is the Boreal Summer Intraseasonal Oscillation (BSISO). Characterized by a broad region of convection which propagates SW to NE from the Indian Ocean to the West Pacific, the BSISO brings alternating 2-3-week periods of inactive and active weather conditions to the monsoon region. Inactive periods are characterized by relatively clear skies, weaker winds, and localized but more intense convection over land. Active periods bring an increase in strong low-level monsoon winds and frequent, widespread precipitation and cloud cover. In this study, the impact of the BSISO on the occurrence of off-shore precipitation around the island of Luzon is examined. Satellite precipitation estimates show that off-shore precipitation occurs much more frequently during active BSISO phases. Importantly, results also show that a clear diurnal cycle still exists over land during these phases, despite increased cloud cover and reduced solar heating/instability generation. It is hypothesized that the interaction between strong low-level monsoon winds and the diurnal cycle over land is what promotes off-shore precipitation, either through the generation of wind shear (which supports off-shore propagation), or convergence between these winds and a cold pool or land breeze. The stronger low-level winds also cause greater ocean surface energy fluxes, which further promote precipitation. During inactive phases, despite the stronger diurnal cycle over land, the lack of a strong low-level wind results in an environment less conducive to off-shore rainfall.Item Open Access Investigations of the uncertainties associated with HID algorithms and guiding input to a novel, synthetic polarimetric radar simulator(Colorado State University. Libraries, 2018) Barnum, Julie I., author; Rutledge, Steven, advisor; Reising, Steven, committee member; Bell, Michael, committee member; Dolan, Brenda, committee memberA methodology for model evaluation against observations is presented. With the advent of polarimetric radars, the need to produce simulated radar observables from model has also become apparent, in order to directly compare the same quantities between observations and models (e.g. rain rate calculations, hydrometeor identification - HID). To the end of evaluating model performance, for both a spectral bin microphysics (SBM) scheme and bulk microphysics scheme (BMS), a novel, synthetic polarimetric radar simulator created by Matsui et al. (2017) was implemented in this study: POLArimetric Radar Retrieval and Instrument Simulator (POLARRIS). POLARRIS takes in model data and simulates polarimetric radar variables in the forward component (POLARRIS-f), and then the inverse component of POLARRIS (iPOLARRIS) utilizes retrieval algorithms that are also employed in observations to make direct 1-to-1 comparisons between model simulations and observations. This inverse component is novel in its ability to help bridge the gap between model output and observations due to the fact that model output and observations without this framework are not directly comparable. The simulation of ice hydrometeors is not straightforward, and several assumptions are required to create polarimetric data for these species, such as the assumption of the size distribution, particle densities, particle melting, the input axis ratio, and canting angle assumptions. The last two variables are notoriously difficult to pin down for ice hydrometeors. This work aims to narrow down the appropriate inputs for axis ratio and canting angle assumptions that create the most comparable results with observations for three ice hydrometeors: aggregates, ice crystals, and graupel for two different meteorological regimes (mid-latitude supercell and tropical, monsoon MCS). Rain was also carried through as a check on model output. Through various sensitivity tests, it was concluded that, when run through the range of potential values, changes in axis ratio had a larger impact on the resulting polarimetric data than did changes in the canting angle assumptions. With this in mind, the 18 Z integrated hour from the 23 January 2006 monsoon MCS TWP – ICE case and the 22 Z integrated hour mid-latitude supercell from the 23 May 2011 MC3E case were simulated to help determine, for each hydrometeor type, the most appropriate axis ratio value(s) and canting angle assumptions that produced comparable results with observations. It was found using co-variance plots that, for 4ICE, the use of a singular axis ratio, mean canting angle, and degree of particle tumbling often produced differential reflectivity and specific differential phase values that converged to one value. While these values were within the observed values, they did not manage to simulate the breadth of observed values. Reflectivity values were also much too low compared to observations. SBM results, regardless of the type of input assumptions, tended to produce broader ranges for these variables, and also managed to better capture the reflectivity range seen in observations than was the case for the BMS. However, the reflectivity ranges seen in SBM were at times too expansive. The differences between SBM output and BMS output is likely due to the differing inherent assumptions in each microphysical scheme. The sensitivity of the simulated hydrometeors' polarimetric data was also probed against changing axis ratio and canting angle input assumptions. It was found that, in particular, BMS differential reflectivity values were quite sensitive to changes in input assumptions, regardless of the regime (tropical MCS vs. mid-latitude supercell). HID was found to be the most effective method to evaluate the performance of the two different model microphysical schemes (SBM vs. BMS) with respect to observations. Input assumptions that produced the most comparable results with respect to observations for each hydrometeor were compared using HID stacked frequency by altitude (SFAD) diagrams for convective and stratiform precipitation. This analysis found that although the co-variance plots revealed many model shortcomings, the HID proved to be fairly robust, especially for MC3E. The sensitivity of the HID retrieval itself was also investigated with respect to changing inputs (i.e. the membership beta functions) to the HID algorithm. The resulting HID was fairly sensitive to changes in the inputs to HID, particularly for model simulations. Observations seemed less responsive to changes in these input assumptions to HID. Longer simulation time frames, the potential inclusion of simulated melting hydrometeors, and investigation of other radar wavelengths are all suggested to help further utilize this methodology for evaluating model microphysical schemes' abilities to accurately simulate polarimetric data and HID retrievals with respect to observations.Item Open Access Lightning channel locations, LNOx production, and advection in anomalous and normal polarity thunderstorms(Colorado State University. Libraries, 2018) Davis, Trenton, author; Rutledge, Steven A., advisor; Barth, Mary, committee member; Fischer, Emily, committee member; Reising, Steven, committee memberTropospheric ozone is a powerful greenhouse gas and OH precursor, thus understanding its sources is important. Its production is also widely studied in atmospheric science today as global climate modelers attempt to estimate future warming within the troposphere. Nitrogen oxides (NO + NO2 = NOx), serve as a precursor to ozone production. In areas where higher concentrations of OH are present, NOx will undergo reactions to produce nitric acid, thereby shortening its lifetime and limiting the production of ozone. Due to lower concentrations of OH in the upper troposphere, NOx tends to experience a longer lifetime (on the order of days) and greater ozone production at these heights. Lightning produces an appreciable amount of NOx (a.k.a. LNOx) but the final distribution of resulting LNOx, and thus its ozone production, remains poorly understood. Therefore, it is important that this source of NOx be further investigated to improve current LNOx parameterizations. Numerical modeling methods attempt to study this issue by parameterizing the nature of lightning within thunderstorms. Often, the vertical distribution of flash channels (and LNOx) is produced according to a parameterized flash rate within a defined vertical profile and reflectivity volume threshold. The structure and intensity of thunderstorms are highly variable though, causing the location of lightning within a thunderstorm to differ from one thunderstorm to the next. Furthermore, one remaining goal of the Deep Convective Clouds and Chemistry (DC3) field campaign (May – June 2012) was to compare the lightning flash locations and contributions to upper tropospheric LNOx between storms of normal and anomalous charge polarity. To address this remaining goal, five cases with over 5600 total flashes are analyzed in detail using data from DC3, three in northern Colorado and two in northern Alabama. Lightning sources are combined into 3-dimensional (3-D) flash channels and flash channel parcels, with each parcel containing the LNOx produced by its parent flash channel. Parcels are then advected forward in time during the lifetime of each storm using 3-D wind fields produced from dual-Doppler analyses. Results reveal a greater number of flashes and flash channels within anomalous polarity thunderstorms compared to normal polarity thunderstorms at a mean initiation height around 5 km. Flashes in these storms also appear to transect areas of higher vertical velocities resulting in roughly half of flash channel parcels being advected to the upper troposphere (z > 8 km). Contrary to some assumptions, an appreciable fraction of these parcels and NOx contributions remain in the boundary layer of these storms. In the two normal polarity thunderstorm cases, flash channels tend to initiate around 8 km with roughly half of the flash channel parcels remaining near or above 8 km. While both storm types appear to transport roughly 50% of their flash channel parcels to the upper troposphere, significantly larger flash counts and total flash length in the anomalous polarity storms lead to much higher mixing ratios of LNOx in the upper troposphere. These results may help chemistry modelers in parameterizing LNOx formation in both normal and anomalous thunderstorm polarity structures, which will also improve global climate model parameterizations of tropospheric ozone production.Item Open Access Microphysical and macrophysical responses of marine stratocumulus polluted by underlying ships(Colorado State University. Libraries, 2012) Christensen, Matthew Wells, author; Stephens, Graeme, advisor; Kummerow, Christian, committee member; van den Heever, Susan C., committee member; Reising, Steven, committee memberMultiple sensors flying in the A-train constellation of satellites were used to determine the extent to which aerosol plumes from ships passing below marine stratocumulus alter the microphysical and macrophysical properties of the clouds. Aerosol plumes generated by ships sometimes influence cloud microphysical properties (effective radius) and, to a largely undetermined extent, cloud macrophysical properties (liquid water path, coverage, depth, precipitation, and longevity). Aerosol indirect effects were brought into focus, using observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the 94-GHZ radar onboard CloudSat. To assess local cloud scale responses to aerosol, the locations of over one thousand ship tracks coinciding with the radar were meticulously logged by hand from the Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. MODIS imagery was used to distinguish ship tracks that were embedded in closed, open, and unclassifiable mesoscale cellular cloud structures. The impact of aerosol on the microphysical cloud properties in both the closed and open cell regimes were consistent with the changes predicted by the Twomey hypothesis. For the macrophysical changes, differences in the sign and magnitude of these properties were observed between cloud regimes. The results demonstrate that the spatial extent of rainfall (rain cover fraction) and intensity decrease in the clouds contaminated by the ship plume compared to the ambient pristine clouds. Although reductions of precipitation were common amongst the clouds with detectable rainfall (72% of cases), a substantial fraction of ship tracks (28% of cases) exhibited the opposite response. The sign and strength of the response was tied to the type of stratocumulus (e.g., closed vs open cells), depth of the boundary layer, and humidity in the free-troposphere. When closed cellular clouds were identified, liquid water path, drizzle rate, and rain cover fraction (an average relative decrease of 61%) was significantly smaller in the ship-contaminated clouds. Differences in drizzle rate resulted primarily from the reductions in rain cover fraction (i.e., fewer pixels were identified with rain in the clouds polluted by the ship). The opposite occurred in the open cell regime. Ship plumes ingested into this regime resulted in significantly deeper and brighter clouds with higher liquid water amounts and rain rates. Enhanced rain rates (average relative increase of 89%) were primarily due to the changes in intensity (i.e., rain rates on the 1.1 km pixel scale were higher in the ship contaminated clouds) and, to a lesser extent, rain cover fraction. One implication for these differences is that the local aerosol indirect radiative forcing was more than five times larger for ship tracks observed in the open cell regime (-59 W m-2) compared to those identified in the closed cell regime (-12 W m-2). The results presented here underline the need to consider the mesoscale structure of stratocumulus when examining the cloud dynamic response to changes in aerosol concentration. In the final part of the dissertation, the focus shifted to the climate scale to examine the impact of shipping on the Earth's radiation budget. Two studies were employed, in the first; changes to the radiative properties of boundary layer clouds (i.e., cloud top heights less than 3 km) were examined in response to the substantial decreases in ship traffic that resulted from the recent world economic recession in 2008. Differences in the annually averaged droplet effective radius and top of atmosphere outgoing shortwave radiative flux between 2007 and 2009 did not manifest as a clear response in the climate system and, was probably masked either due to competing aerosol cloud feedbacks or by interannual climate variability. In the second study, a method was developed to estimate the radiative forcing from shipping by convolving lanes of densely populated ships onto the global distributions of closed and open cell stratocumulus clouds. Closed cells were observed more than twice as often as open cells. Despite the smaller abundance of open cells, a significant portion of the radiative forcing from shipping was claimed by this regime. On the whole, the global radiative forcing from ship tracks was small (approximately -0.45 mW m-2) compared to the radiative forcing associated with the atmospheric buildup of anthropogenic CO2.Item Open Access Prediction of total lightning in Colorado and Alabama thunderstorms based on storm dynamical and microphysical variables(Colorado State University. Libraries, 2015) Basarab, Brett Michael, author; Rutledge, Steven, advisor; Deierling, Wiebke, committee member; Kreidenweis, Sonia, committee member; Reising, Steven, committee memberThunderstorms impact their environment in a variety of ways, including the production of nitrogen oxides (NOₓ) by lightning (LNOₓ). Accurate prediction of total lightning flash rate in thunderstorms is important to improve estimates of LNOₓ from the storm scale to the global scale. New flash rate parameterization schemes have been developed based on observed relationships between lightning flash rate and storm parameters for Colorado thunderstorms during the Deep Convective Clouds and Chemistry (DC3) experiment. Storm total flash rates are determined using an automated flash counting algorithm that clusters very high frequency (VHF) radiation sources emitted by electrical breakdown in clouds and detected by the northern Colorado lightning mapping array (LMA). Storm parameters such as hydrometeor echo volumes and ice masses are calculated from polarimetric radar retrievals. Measurements of updraft strength are obtained by synthesizing radial velocity retrievals from the CSU-CHILL and CSU-Pawnee radars to determine three-dimensional wind fields. Bulk storm parameters including the graupel echo volume, 30-dBZ echo volume, and precipitating ice mass are found to be robustly correlated to flash rate (R² ~ 0.8). It is shown that simple flash rate parameterization schemes based on these quantities predict gross flash rate behavior reasonably well. Updraft intensity-based flash rate schemes are also developed, but updraft parameters were not as strongly correlated to flash rate as storm volume quantities. The use of multiple storm parameters to predict flash rate is also investigated, since flash rate may be sensitive to multiple processes or characteristics within thunderstorms. A simple approach is found to be most effective: storm-total graupel and reflectivity echo volumes were split up into representative area and height dimensions and regressed against flash rate. The combined quantities predict flash rate variability somewhat better than simpler single-parameter flash rate schemes. All new flash rate schemes are tested against observations of Alabama thunderstorms documented during DC3 to examine their potential regional limitations. The flash rate schemes developed work best for strong Colorado storms with sustained high flash rates. Finally, relationships between total flash rate and flash size are discussed, with implications for the improved prediction of LNOₓ.Item Open Access Regional aerosol effects on precipitation: an observational study(Colorado State University. Libraries, 2011) Boyd, Kathryn J., author; Kummerow, Christian, advisor; van den Heever, Susan, committee member; Reising, Steven, committee memberThere have been a multitude of studies on the effects increased amounts of aerosols may have on clouds. The connection between increased cloud condensation nuclei (CCN) and cloud microphysics has been established by in situ observations as well as modeling studies. However, the impact on precipitation is less well established. Of the studies that have assessed aerosol effects on precipitation most have been limited to modeling studies or global studies using satellite data. The few observational studies that have examined these relationships have been mainly limited to data from short-lived field campaign, such as oceanic stratocumulus decks or biomass burning areas. This study attempts to examine regional aerosol effects on precipitation in areas not previously examined in field campaigns, using data from two different sites, one from an Atmospheric Radiation Measurement (ARM) Program permanent facility in Oklahoma and the other from a mobile facility located in the Azores. These two sites were chosen in order to illustrate the differences between a marine and a continental location. Meteorological conditions were taken into account in both locations through surface and sounding data and trends in precipitation were found with increasing aerosol concentrations. The marine site witnessed a suppression of precipitation, consistent with past studies and proposed theories of aerosol effects. This was not true for clouds with liquid water paths exceeding 200g/m2. These clouds appear to contain sufficient amounts of water to overcome the aerosol effect. The continental site, however, experienced an opposite trend, with enhancement of precipitation witnessed in all clouds examined in this study. This is thought to be due to a buffering mechanism in these types of clouds, as introduced by Stevens and Feingold (2009). Results were separated by season and cloud type using the horizontal variability of radar reflectivity at cloud top height. The seasonal results generally either were in line with the year round results or were too noisy to interpret. The results separated by cloud type give a concrete result, illustrating the fact that differing cloud dynamics may lead to opposing trends in precipitation with increasing aerosols. Competing effects of aerosols within clouds appear to dampen any effect on precipitation to the point that it is not detectable from the in-situ observations considered here.Item Open Access Regional analysis of convective systems during the West African monsoon(Colorado State University. Libraries, 2012) Guy, Bradley Nicholas, author; Rutledge, Steven, advisor; Tao, Wei-Kuo, advisor; Kummerow, Christian, committee member; van den Heever, Sue, committee member; Cifelli, Rob, committee member; Reising, Steven, committee memberThe West African monsoon (WAM) occurs during the boreal summer and is responsible for a majority of precipitation in the northern portion of West Africa. A distinct shift of precipitation, often driven by large propagating mesoscale convective systems, is indicated from satellite observations. Excepting the coarser satellite observations, sparse data across the continent has prevented understanding of mesoscale variability of these important systems. The interaction between synoptic and mesoscale features appears to be an important part of the WAM system. Without an understanding of the mesoscale properties of precipitating systems, improved understanding of the feedback mechanism between spatial scales cannot be attained. Convective and microphysical characteristics of West African convective systems are explored using various observational data sets. Focus is directed toward meso -α and -β scale convective systems to improve our understanding of characteristics at this spatial scale and contextualize their interaction with the larger-scale. Ground-based radar observations at three distinct geographical locations in West Africa along a common latitudinal band (Niamey, Niger [continental], Kawsara, Senegal [coastal], and Praia, Republic of Cape Verde [maritime]) are analyzed to determine convective system characteristics in each domain during a 29 day period in 2006. Ancillary datasets provided by the African Monsoon Multidisciplinary Analyses (AMMA) and NASA-AMMA (NAMMA) field campaigns are also used to place the radar observations in context. Results show that the total precipitation is dominated by propagating mesoscale convective systems. Convective characteristics vary according to environmental properties, such as vertical shear, CAPE, and the degree of synoptic forcing. Data are bifurcated based on the presence or absence of African easterly waves. In general, African easterly waves appear to enhance mesoscale convective system strength characteristics (e.g. total precipitation and vertical reflectivity profiles) at the inland and maritime sites. The wave regime also resulted in an increased population of the largest observed mesoscale convective systems observed near the coast, which led to an increase in stratiform precipitation. Despite this increase, differentiation of convective strength characteristics was less obvious between wave and no-wave regimes at the coast. Due to the propagating nature of these advecting mesoscale convective systems, interaction with the regional thermodynamic and dynamic environment appears to result in more variability than enhancements due to the wave regime, independent of location. A 13-year (1998-2010) climatology of mesoscale convective characteristics associated with the West African monsoon are also investigated using precipitation radar and passive microwave data from the NASA Tropical Rainfall Measuring Mission satellite. Seven regions defined as continental northeast and northwest, southeast and southwest, coastal, and maritime north and south are compared to analyze zonal and meridional differences. Data are categorized according to identified African easterly wave (AEW) phase and when no wave is present. While some enhancements are observed in association with AEW regimes, regional differences were generally more apparent than wave vs. no-wave differences. Convective intensity metrics confirm that land-based systems exhibit stronger characteristics, such as higher storm top and maximum 30-dBZ heights and significant 85-GHz brightness temperature depressions. Continental systems also contain a lower fraction of points identified as stratiform. Results suggest that precipitation processes also varied depending upon region and AEW regime, with warm-rain processes more apparent over the ocean and the southwest continental region and ice-based microphysics more dominant over land, including mixed-phase processes. AEW regimes did show variability in stratiform fraction and ice and liquid water content, suggesting modulation of mesoscale characteristics possibly through feedback with the synoptic environment. Two mesoscale convective systems (MCSs) observed during the African Monsoon Multidisciplinary Analyses (AMMA) experiment are simulated using the three-dimensional (3D) Goddard Cumulus Ensemble model. One of the MCSs, the 8 September 2006 system, is associated with the passage of an African easterly wave trough while the other, the 14 July 2006 case, is not. Simulations are performed using 1 km horizontal grid spacing, a lower limit on current embedded cloud resolving models within a multi-scale modeling framework. Simulated system structure is compared to radar observations using contoured frequency-by-altitude diagrams (CFADs), calculated ice and water mass, and identified hydrometeor variables. Results indicate general agreement in the temporal distribution of hydrometeors. Vertical distributions show that ice hydrometeors are often underestimated at mid- and upper-levels, partially due to the inability of the model to produce adequate system heights. Abundance of high reflectivity values below and near the melting level in the simulation led to a broadening of the CFAD distributions. Observed vertical reflectivity profiles indicate larger reflectivities aloft compared to simulated values. Despite these differences and biases, the radar-observed differences between the two cases are noticeable in the simulations as well, suggesting that the model is able to capture gross observed differences between the two MCSs.Item Open Access Turning night into day: the creation, validation, and application of synthetic lunar reflectance values from the day-night band and infrared sensors for use with JPSS VIIRS and GOES ABI(Colorado State University. Libraries, 2023) Pasillas, Chandra M., author; Kummerow, Christian, advisor; Bell, Michael, advisor; Miller, Steven D, committee member; Rasmussen, Kristen, committee member; Reising, Steven, committee memberInvestigation of the dynamics of tropical cyclone precipitation structure using radar observations and numerical modeling Satellite remote sensing revolutionized weather forecasting and observing in the 1960s providing a true bird's eye view of the weather beyond what could be achieved from balloon and aircraft reconnaissance. With advances in observing systems came the desire for more capabilities and a better understanding of the Earth system, leading to rapid increases in satellite imaging capabilities. The most popular imager products come from solar reflective radiation in the form of visible imagery as they are the most intuitive to users. Similar benefits were later made possible by equivalent nighttime imagery; first available through the operational lines can system (OLS) and then the Day/Night Band (DNB), but these sensors have limited revisit time due to their low Earth orbits. A day-night band sensor in geostationary orbit would greatly enhance the utility of this measurement for now casters, but it does not exist. Work towards a pseudo-nighttime visible imagery to fill this gap has been done with varying results (Chirokova et al., 2018; Kim et al., 2019; Kim and Hong, 2019; Mohandoss et al., 2020; Harder et al., 2020). This dissertation demonstrates the creation and implementation of a machine learning model to turn night into day by transforming satellite radiance observations into representative full moon lunar reflectance values that provide quantifiable metrics and visible-like imagery to its users. In Chapter 2, a method is described that utilizes a feed-forward neural network model to replicate DNB lunar reflectance using brightness temperatures and brightness temperature differences in the short and long-wave infrared (IR) spectrum as the primary input. The goal was to improve upon the performance of the DNB during new moon periods, and lay the foundation for transitioning the algorithm to the Geostationary Operational Environmental Satellite (GOES) Advanced Baseline Imager (ABI). Results from this method are the first to quantitatively validate low-light visible nighttime imagery with lunar reflectance calculated from DNB radiances. This work further demonstrated that there is a relationship between full moon lunar reflectance and IR that can be captured to create imagery that is visually consistent across the full lunar cycle regardless of moon phase and angle. In Chapter 3, the machine learning (ML) nighttime visible imagery (NVI) model is applied to the GOES ABI utilizing wavelength relationships and satellite inter-calibrations information. This demonstrates that a model trained and validated on VIIRS polar orbiting imagery can work on sensors aboard geostationary satellites. It also confirms why the 10.3μm channel is the preferred substitution for the 10.7μm centered band over the 11.2μm channel. Furthermore, it demonstrates that lunar reflectance derived from IR can be replicated across sensors with similar spectral response functions providing enhanced geographic and temporal resolution that is not possible on the JPSS platforms. The final section of the dissertation transitions into forecaster applications by examining case studies concerning tropical cyclones and fog in greater detail. Focused on low cloud detection, NVI provides additional information not possible from IR and current analysis products available. It can detect tropical cyclone low-level circulations through cirrus cloud and identify fog extent more readily. The findings in this doctoral study will advance remote sensing of clouds at night, further reducing weather now-casting errors and increasing weather-related safety. In Chapter 2, a method is described that utilizes a feed-forward neural network model to replicate DNB lunar reflectance using brightness temperatures and brightness temperature differences in the short and long-wave infrared (IR) spectrum as the primary input. The goal was to improve upon the performance of the DNB during new moon periods, and lay the foundation for transitioning the algorithm to the Geostationary Operational Environmental Satellite (GOES) Advanced Baseline Imager (ABI). Results from this method are the first to quantitatively validate low-light visible nighttime imagery with lunar reflectance calculated from DNB radiances. This work further demonstrated that there is a relationship between full moon lunar reflectance and IR that can be captured to create imagery that is visually consistent across the full lunar cycle regardless of moon phase and angle. In Chapter 3, the machine learning (ML) nighttime visible imagery (NVI) model is applied to the GOES ABI utilizing wavelength relationships and satellite inter-calibrations information. This demonstrates that a model trained and validated on VIIRS polar orbiting imagery can work on sensors aboard geostationary satellites. It also confirms why the 10.3 µm channel is the preferred substitution for the 10.7 µm centered band over the 11.2 µm channel. Furthermore, it demonstrates that lunar reflectance derived from IR can be replicated across sensors with similar spectral response functions providing enhanced geographic and temporal resolution that is not possible on the JPSS platforms. The final section of the dissertation transitions into forecaster applications by examining case studies concerning tropical cyclones and fog in greater detail. Focused on low cloud detection, NVI provides additional information not possible from IR and current analysis products available. It can detect tropical cyclone low-level circulations through cirrus cloud and identify fog extent more readily. The findings in this doctoral study will advance remote sensing of clouds at night, further reducing weather now-casting errors and increasing weather-related safety.Item Open Access Understanding and quantifying the uncertainties in satellite warm rain retrievals(Colorado State University. Libraries, 2022) Schulte, Richard, author; Kummerow, Christian D., advisor; Bell, Michael, committee member; Boukabara, Sid, committee member; Reising, Steven, committee member; van Leeuwen, Peter Jan, committee memberSatellite-based oceanic precipitation estimates, particularly those derived from the Global Precipitation Measurement (GPM) satellite and CloudSat, suffer from significant disagreement over regions of the globe where warm rain processes are dominant. Part of the uncertainty stems from differing assumptions about drop size distributions (DSDs). Satellite radar-based retrieval algorithms rely on DSD assumptions that may be overly simplistic, while radiometers further struggle to distinguish cloud water from rain. The aim of this study is to quantify uncertainties related to DSD assumptions in satellite precipitation retrievals, contextualize these uncertainties by comparing them to the uncertainty caused by other important factors like nonuniform beam filling, surface clutter, and vertical variability, and to see if GPM and CloudSat warm rainfall estimates can be partially reconciled if a consistent DSD model is assumed. Surface disdrometer data are used to examine the impact of DSD variability on the ability of three satellite architectures to accurately estimate warm rainfall rates. Two architectures are similar to existing instrument combinations on the GPM Core Observatory and CloudSat, while the third is a theoretical triple frequency radar/radiometer architecture. An optimal estimation algorithm is developed to retrieve rain rates from synthetic satellite measurements, and it is found that the assumed DSD shape can have a large impact on retrieved rain rate, with biases on the order of 100% in some cases. To compare these uncertainties against the effects of horizontal and vertical inhomogeneity, satellite measurements are also simulated using output from a high-resolution cloud resolving model. Finally, the optimal estimation algorithm is used to retrieve rain rates from near-coincident observations made by GPM and CloudSat. The algorithm retrieves more rain from the CloudSat observations than from the GPM observations, due in large part to GPM's insensitivity to light rain. However, the results also suggest an important role for DSD assumptions in explaining the discrepancy. When DSD assumptions are made consistent between the two retrievals, the gap in total accumulation between GPM and CloudSat is reduced by about 25%.Item Open Access Yttrium iron garnet nano films: epitaxial growth, damping, spin pumping, and magnetic proximity effect(Colorado State University. Libraries, 2014) Sun, Yiyan, author; Wu, Mingzhong, advisor; Patton, Carl, committee member; Field, Stuart, committee member; Reising, Steven, committee member; Celinski, Zbigniew, committee memberRecently, a new research field called magnetic insulator-based spintronics opened the door to a large amount of potential applications in the electronics industry. In this field, low-damping materials in the nanometer scale are critically needed for both fundamental studies, such as spin pumping, and device applications, such as spin-torque nano-oscillators. Yttrium iron garnet (YIG) materials are the best candidate among other materials. There is a critical demand for high-quality nanometer-thick YIG films. This dissertation reports experimental studies on YIG films with the thickness ranged from several nanometers to several hundreds of nanometers. Firstly, the feasibility of low-damping YIG nano films growth via pulsed laser deposition (PLD) techniques is demonstrated. A 5-nm-thick YIG film, for example, shows a peak-to-peak ferromagnetic resonance (FMR) linewidth of <10 Oe at 10 GHz. Optimization of PLD control parameters and post-deposition annealing processes and surface modification by ion beam etching for the realization of high-quality films are discussed in detail. The second main topic is on spin pumping and magnetic proximity effects in YIG nano films. Specifically, the dissertation touches on (1) the spin pumping efficiency of YIG nano films and (2) damping enhancement in YIG nano films due to Pt capping layers. Knowing the efficiency of spin angular momentum transfers across YIG/normal metal (NM) interfaces is critical to the use of YIG films for spintronics. Under subtopic (1), the spin transfer efficiency at YIG/NM interfaces is determined through the measurement of spin pumping-caused additional damping in YIG nano films. A fairly large portion of recent studies on YIG-based spintronics made use of a Pt capping layer either as a detector to measure spin currents or as a spin-current source. Work under subtopic (2), however, indicates that the growth of a Pt capping layer onto a YIG film can result in a significant damping enhancement in the YIG film. Fortunately, this damping can be completely suppressed simply by the addition of a thin Cu spacer in-between the YIG and Pt films. The interpretation of the observed damping enhancement in terms of the magnetic proximity effect in the Pt film is presented. The last topic addresses the growth of high-quality YIG thin films on metallic substrates. It is demonstrated that one can grow YIG thin films on Cu via the use of a protection layer of high entropy alloy nitrides. The YIG films showed a peak-to-peak FMR linewidth of about 1.1 Oe at 9.45 GHz. This work provides implications for the future development of YIG thin film-based monolithic devices for high frequency processing.