Browsing by Author "Li, Liming"
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Item An Iterative Direct Phasing Algorithm for Protein Structure Determination(2019-12) Jiang, Mengchao 1991-; Su, Wu-Pei; Gunaratne, Gemunu H.; Jackson, David R.; Li, Liming; Miller, John H., Jr.An iterative phasing method based on the hybrid input-output (HIO) algorithm, proposed by He & Su (2015), is improved to retrieve phases of protein crystals. By testing the method on a protein crystal with 65% solvent content, it is proved that this method is capable of phasing protein crystals with an intermediate solvent content. Results from a blind test have yielded an interpretable density map, which shows that the phasing method is capable of solving completely unknown protein structures. The phasing method was tested on medium- and low-resolution diffraction data of a membrane protein, which shows that the atomic structure can be solved directly from the diffraction data with resolution higher than 3.5Å. For data of lower resolutions, secondary structures and the protein boundary can still be obtained. The results also indicate that there is an optimal histogram to use for data at various resolutions. By averaging over tens of successful runs, the resulting density map can be greatly improved and the final phase error can be reduced by about 10 degrees, thus leading to a better reconstructed model. Finally, a density constraint called non-crystallographic symmetry (NCS) is employed to overcome the undersampling condition of protein crystals with low solvent content. The phasing method has been applied to a protein crystal with 3-fold rotational NCS and 45% solvent content. The results show that, when the NCS axis is well positioned, the protein envelope and the NCS mask can be automatically rebuilt. By employing NCS averaging, this method is thus capable of solving protein crystals with low solvent content.Item Anomalous Elastic Behavior in Berea Sandstone(2018-12) Davis, Eric Sean 1991-; Pinsky, Lawrence S.; Pantea, Cristian; Wood, Lowell T.; Weglein, Arthur B.; Li, LimingBerea sandstone is a well-studied oilfield reservoir material that is commonly used as a reference material when the exact constituents of a reservoir are unknown. Although it has been extensively studied, there are still several unanswered questions that remain due to the complexity of the mechanical system, being a network of hard grains cemented together with a soft bonding system. In particular, the origin of the nonlinear and nonequilibrium dynamics in Berea is still poorly understood. In this dissertation, the anomalous elastic behavior of Berea sandstone in which the sandstone softens with cooling for a set temperature range is explored using multiple experiment sets to shed light on the possible mechanisms involved. By using a combination of Resonant Ultrasound Spectroscopy (RUS), Through-Transmission technique (TT), and resonance tracking, several qualitative and quantitative aspects of this anomalous elastic behavior are detailed. Specifically, it was found that the bulk modulus of Berea sandstone decreases with cooling from 205 °C to 110 °C and then increases an almost identical amount with additional cooling from 110 °C to room temperature. Resonance tracking determined that equilibration time did not seem to affect the anomalous elastic behavior with cooling. Higher starting temperatures did not affect the critical temperature in which the anomalous behavior returned to normal behavior with cooling. The anomalous behavior was only found in Berea sandstone and Buff Berea, whereas several other reservoir materials exhibited normal behavior. Normal elastic behavior was also found in fused silica, making it less likely that the anomalous elastic behavior originates from the constituents of Berea sandstone. The anomalous behavior did not extend to heating in Berea sandstone, causing a hysteresis loop in the elastic constants when heated and then cooled. Finally, the anomalous behavior was seen in both heating and cooling for Buff Berea, however, and the qualitative behavior for both heating and cooling was near identical.Item Applications Of The Hybrid Input-Output Method In Protein Crystallography(2022-05) Cheng, Yunpeng; Su, Wu-Pei; Gunaratne, Gemunu H.; Jackson, David R.; Li, Liming; Miller, John H., Jr.An iterative phasing method based on the hybrid input-output (HIO) algorithm is a promising method for solving the phase problem in protein crystallography. Two approaches for improving the iterative phasing method are proposed in this dissertation. During the phase retrieval, the iterative phasing method does not always succeed in the initial trial calculations. Even though there is no obvious sudden drop in the error metrics, there is still useful information in the results, such as the boundary information of the structure. Therefore, a two-step iterative phasing method with HIO is proposed. The first step is to determine a protein mask from the diffraction data with several thousand iterations. A good protein mask can be selected from the results with lower R values. The second step is to retrieve phases while keeping the pre-selected protein mask fixed. Two structures are solved successfully with the two-step iterative phasing method with HIO. The evolutions of the error metrics are presented, the final mean phase error is around $40^{\circ}$. The calculated density map matches well with the deposited protein structure. Therefore, the failed results still contain useful information for further exploration. The iterative phasing method can incorporate partial structures to solve structures with low solvent content. Trial calculations are presented, assuming one of the chains is known. In each iteration, the calculated densities in the known region are set to the densities of the known partial structure. Most calculations retrieve the phases successfully.Item Atmospheric Composition Changes During Droughts in the Continental U.S.(2023-04-22) Li, Wei; Wang, Yuxuan; Jiang, Xun; Flynn, James H., III; Li, LimingThe abnormal meteorological conditions under droughts can impose large changes in atmospheric compositions. In this dissertation, we quantified these changes using long-term atmospheric composition observations over the continental U.S. during summertime. Specifically, we revealed the spatial east-west variation in ozone (O3) response to drought: higher O3 enhancement in the southeast U.S. (SEUS) and no significant change or even a decrease in the west. We attributed this spatial discrepancy to O3 chemistry caused by the opposite response of isoprene: a 37% decrease in isoprene under exceptional drought in California in contrast to a 41% increase in Georgia. The enhanced isoprene in the SEUS also contributes to the 24% higher value of organic aerosol (OA), which can be largely attributed to the increase of isoprene epoxydiols derived secondary organic aerosol (IEPOX SOA) with a high dependence on sulfate. The elevated OA in the Pacific Northwest under droughts is caused by increasingly higher wildfire emissions. We evaluated the chemical transport model GEOS-Chem regarding its capability in capturing the observed drought-air pollution relationships. The model under- and overestimates the drought-induced O3 and OA changes in the SEUS, respectively, which can be partly caused by the overprediction of biogenic isoprene emissions. A satellite-derived drought stress factor by minimizing the model-to-observed bias of formaldehyde column to temperature sensitivity was implemented in GEOS-Chem. The resulted reduction in isoprene emissions can lower the OA positive bias by 7%-12% and improve the O3 enhancement by 1-3 ppb over low-NOx regions. We also found a decrease of 11% in surface fine dust over the SEUS under droughts in contrast to the expected increase in other regions. Through the teleconnection to the negative North Atlantic Oscillation, a lower-than-normal and more northeastward displacement of the Bermuda High is present during SEUS droughts, resulting in less dust being transported into the SEUS. The enhanced precipitation in the Sahel associated with the northward shift of the Intertropical Convergence Zone also leads to lower dust emissions therein. The GEOS-Chem model can capture the weakened African dust transport and reproduce the reduced dust in the SEUS while misses the enhanced dust in the western areas.Item Computing the Radiant Energy Budget of Enceladus(2022-04-14) Luu, CindyOne of the most important findings from the 20-year (1997-2017) Cassini mission is the discovery of jet plumes on Enceladus (e.g., a small satellite of Saturn with a size ~ 500 km). These jet plumes (~ a few hundred kilometers in height) are driven by liquid water/water ice and have led Enceladus to become one of the best candidates in finding a place suitable for past or present life in our solar system. Here we seek to better understand the geological system of Enceladus by analyzing its radiant energy budget with Cassini's observations. The radiant energy budget, determined by the emitted thermal energy and absorbed solar energy, can be used to estimate the internal heat which plays a critical role in driving the jet plumes. The thermal spectra recorded by one infrared instrument (i.e., CIRS) aboard the Cassini spacecraft are used to measure the emitted thermal energy. Data from the visible and near-infrared instruments (i.e., ISS and VIMS) on Cassini are used to measure the absorbed solar energy. Based on the measurements of the emitted thermal energy and the absorbed solar energy, we can determine Enceladus' radiant energy budget and the related internal heat. We have achieved some promising results (e.g., the solar flux and the full-disk albedo of Enceladus at some wavelengths). We will finish the measurements of Enceladus' radiant energy budget, which will be used to improve models of Enceladus’ thermal structure and explain the incredible jet plumes.Item Convergence Acceleration in Scattering Series and Seismic Waveform Inversion Using Nonlinear Shanks Transformation(2018-05) Eftekhar, Roya 1974-; Zheng, Yingcai; Li, Liming; Gunaratne, Gemunu H.; Xu, Shoujun; Wood, Lowell T.An iterative solution process is fundamental in seismic inversion, such as in full-waveform inversions and inverse scattering methods. However, the convergence process could be slow or even divergent depending on the initial model used in the iteration. We propose to apply Shanks transformation (ST for short) to accelerate the convergence of the iterative solution. ST is a local nonlinear transformation, which transforms a series locally into another series with improved convergence property. ST separates the smooth background trend called the secular term versus the oscillatory transient term and then accelerates the convergence of the secular term. Because the transformation is local, we do not need to know all the terms in the original series and this is very important in the numerical application of ST. I propose to apply the ST in the context of both the forward Born series and the inverse scattering series (ISS). I test the performance of the ST in accelerating the convergence using several numerical examples, including three examples of forward modeling using the Born series and two examples of velocity inversion based on ISS. We observe that ST is very helpful in accelerating the convergence and it can achieve convergence even for a weakly divergent scattering series. As such, it provides us a useful technique to invert for a large-contrast medium perturbation in seismic inversion.The method developed in this dissertation can also be used in other fields such as in electromagnetics, quantum mechanics, and possibility medical imaging.Item Incorporation of Partial Structure Information in Macromolecular Crystallographic Phasing(2017-05) Fang, Hengrui 1988-; Su, Wu-Pei; Hor, Pei-Herng; Jackson, David R.; Li, Liming; Wood, Lowell T.Solving the phase problem can be a limiting step in the structure determination of macromolecular X-ray crystallography. Recent development of the iterative projection algorithm shows that it is a promising tool for phase retrieval. Two approaches for enhancing the iterative projection algorithm are proposed in this thesis for solving the macromolecular crystallographic phase problem. When using a homologous molecule in the molecular replacement method to determine a new macromolecular structure, even if a proper template structure is positioned, the insufficient similarity between the template and target structures may cause its resistance to the conventional molecular replacement method. A modified phasing method is presented with better convergence properties and can effectively overcome the difference between the template and target structures. This is illustrated by the reconstruction of one trial structure, which has also been solved and analyzed in several subsequent molecular replacement methods studies. Uniqueness of the phase problem in macromolecular crystallography limits the ab initio phasing. To enlarge the the radius of convergence of the iterative projection algorithm in macromolecular crystallography, an enhanced density modification method is proposed by incorporating partial structure information. Four trial calculations show a variety of potential applications of this method in novel structure determination and model validation.Item Investigating the Temporal and Spatial Variability of Precipitation(2015-05) Trammell, James H. 1975-; Jiang, Xun; Li, Liming; Talbot, Robert W.; Choi, YunsooTo explore the temporal and spatial variability of precipitation, a statistical tool called Principal Component Analysis (PCA) is applied to precipitation data from Tropical Rainfall Measuring Mission (TRMM), Global Precipitation Climatology Project (GPCP), and Community Atmosphere Model (CAM5). Results for the tropical domain reveal the first leading mode is related to the El Niño Southern Oscillation (ENSO). Further, it is found that the second principal component mode demonstrates correlation with a separate phenomenon, named El Niño Modoki. Results show a positive phase of El Niño Modoki produces positive precipitation anomalies over central Pacific and negative over western and eastern Pacific, analogous to those of typical ENSO episodes. Both observations and the CAM5 model are able to capture the ENSO and El Niño Modoki signals in the tropical precipitation, although the signals in the model are weaker than the observation. In the polar regions, spatial analysis and time series correlations with Northern Annular Mode/Southern Annular Mode Indices suggest the strength of the polar vortex can influence the temporal and spatial variability of precipitation in the high and mid-latitudes. The CAM5 precipitation simulations demonstrate patterns similar to that of the observed GPCP, although they slightly under predict magnitudes. Next, high and low precipitation areas are defined with climatological monthly mean precipitation larger than 200 millimeters per month (mm/mon) and less than 50 mm/mon. Observed temporal variation reveals that precipitation has an increasing tendency in the wet areas and a decreasing tendency in the dry areas. The NASA Goddard Institute for Space Studies (GISS) model is utilized, and simulations imply that the increasing greenhouse gases can affect the temporal variation of precipitation over the wet and dry areas, consistent with the observed “rich-get-richer” mechanism. Results further reveal that the atmospheric dynamics related to the convective stability, and hence the vertical motions, contribute to the increased precipitation over the tropical area as a result of global warming. However, the vertical motion in the dry areas does not demonstrate significant change, making the physics of the negative trend of precipitation in these regions more complicated.Item Investigation of Cloud Variability, Hydrological and Carbon Cycle in the Atmosphere in Response to Global Warming(2017-05) Kao, Angela 1989-; Jiang, Xun; Li, Liming; Choi, Yunsoo; Talbot, Robert W.The goal of this research is to increase the understanding of changes in the hydrological and carbon cycles in response to global warming. Global oceanic recycling rate, along with meteorological variables are analyzed using the thirteen Coupled Models Inter-comparison Project (CMIP5) data from 1988 to 2008. On a worldwide scale, there has been a long-term decreasing trend of the global average oceanic recycling rate. On a regional scale, there are positive trends of the recycling rate over the Intertropical Convergence Zone (ITCZ) and negative trends over the sub-tropical dry areas. To better understand the hydrological cycle over the wet and dry areas, we examined the precipitation, vertical velocity, cloud, and water vapor contents from CMIP5 models. All meteorological variables associated with precipitation demonstrate favorable conditions for increasing precipitation over the wet areas and decreasing precipitation over the dry areas. The consistent trends in these variables, such as vertical velocity, cloud, and liquid and ice water contents, as provided by the CMIP5 models, yield a clearer picture of the dynamics and physics behind the temporal variation of precipitation over different areas. Atmospheric Infrared Sounder (AIRS) CO2 data is used to study the impact of drought on mid-tropospheric CO2 concentrations. For the first time, it is found that the mid-tropospheric CO2 concentration is approximately one part per million by volume higher during the dry years than the wet years over the southwest USA. During drought conditions, there is increased rising air over most of the regions, which can bring high surface CO2 concentrations into the mid-troposphere. In addition to the circulation, there is added CO2 emitted from the biosphere during times of drought, which can contribute to higher concentrations of CO2 in the atmosphere. A multiple-regression method is applied to explore the relationship between Pacific North American pattern (PNA) and CO2 concentrations. During the positive phase of PNA, there are positive CO2 anomalies over the northwestern part of North America, which are related to increased CO2 emissions from bacteria in the soil and greater CO2 being released from melting permafrost.Item Spatiotemporal Variability of CO2, Solar-Induced Fluorescence, And Precipitation Over the Tropical Rainforests(2023-08) Albright, Ronald Joe; Jiang, Xun; Li, Liming; Wang, Yuxuan; Choi, YunsooTropical rainforest ecosystems change forest dynamics during the dry/fire season, transitioning from an atmospheric CO2 sink to a CO2 source. The Amazon basin, Congo basin, and the tropical Indo-Pacific play vital roles in biospheric processes, which contribute to Earth’s atmospheric CO2 concentration. This investigation will use various space-based and ground-based datasets and empirical models to explore photosynthetic activity, spatiotemporal variability, and correlation among critical variables (e.g., Solar-induced chlorophyll fluorescence (SIF), CO2, precipitation, high vapor pressure deficit (VPD), and burned areas). Specifically, we use Orbiting Carbon Observatory 2 (OCO-2) SIF, OCO-2 CO2, Global Precipitation Climatology Project (GPCP) precipitation, Moderate Resolution Imaging Spectrometer (MODIS) burned area, and CarbonTracker Model. Over the entire Amazon basin from September 2014 to December 2019, we found a positive temporal correlation (0.94) between OCO-2 SIF and GPCP precipitation and a negative temporal correlation (–0.64) between OCO-2 SIF and OCO-2 CO2. These findings suggest that precipitation enhances photosynthesis, thus resulting in higher values for SIF and the rate of removal of atmospheric CO2 in the Amazon region. We also identify seasonal variations in the spatial distributions of these variables across the Amazon region. Over the Congo basin, during the same timeframe (Sep 2014-Dec 2019), we find that the atmospheric CO2 is ~2 ppm higher than the regional background during the boreal summer (June–August), primarily due to biomass burning and significantly reduced photosynthetic activities during the dry season. Over the tropical Indo-Pacific, we explore the spatial distributions of SIF, CO2, and precipitation during El Niño events verse other months. The CarbonTracker Model is employed to assess the impact of El Niño on atmospheric CO2. Various datasets of deseasonalized precipitation, deseasonalized SIF, and deseasonalized CO2 are analyzed in time series averaged over 10S-10N, 100E-160E. We have discovered that there is less precipitation, more sinking air, lower SIF, and higher CO2 over the Indo-Pacific region during the El Niño events. The CarbonTracker model can simulate the increase of atmospheric column CO2 during the El Niño event, although there are some difficulties in capturing the correct spatial distribution of CO2 anomalies. These findings suggest that improved seasonal fire management practices in these tropical regions are critical components needed to achieve successful and timely reductions in global carbon emissions, as set forth by international agreements.Item Spatiotemporal Variations Of Saturn's Zonal Winds Based On Cassini Long-term (2004-2017) Multi-Instrument Observations(2020-05) Studwell, Aaron Mark; Li, Liming; Jiang, Xun; Choi, Yunsoo; Wang, Yuxuan; Wood, Lowell T.The observations of Saturn by the Cassini mission spanned thirteen years (2004-2017) and provided scientists data and images that will expand our knowledge for decades to come. This dissertation is divided into four tasks: 1) Develop and validate a more general form of thermal wind equation (TWE), which does not apply the assumptions used in the classical TWE; 2) Apply the new TWE to study the spatiotemporal patterns of the atmospheric winds above the visible cloud layer, ~1 to 500 mbar; 3) Develop a global profile of the atmospheric winds below the visible cloud layer, ~1,000 to 3,000 mbar; and 4) Utilize atmospheric winds to investigate Saturn’s 2010 Great White Storm with particular attention to its asymmetric development. The results from Tasks 1, 2 and 3 provides a relatively complete picture of the seasonal variations of Saturn’s winds. Some important characteristics of Saturn’s winds are revealed: (1) The global profile of zonal winds in the deep troposphere is generated for the first time; (2) In the polar region, the 2,000-mbar winds undergo temporal variation; (3) Within the visible cloud layer, the zonal winds did not significantly change between 2009 and 2015; and (4) The stratospheric equatorial zonal jets weakened from ~500 m s-1 in 2009 to 0 m s-1 in 2015. This is the first systematic analysis of the seasonal changes of Saturn’s zonal winds across both the troposphere and stratosphere, expanding our understanding of spatiotemporal variations of Saturn’s atmosphere. In particular, the vertical structure and its changes over time yield new insight on the atmospheric dynamics (e.g., stability), which in turn aid in the development of new theories and models of the atmospheric systems of the giant planets. In Task 4, the wind field and the associated vorticity field are used to investigate 2010 Great White Storm. Specifically, during the mature phase of this event, the associated bright clouds expanded significantly equatorward, but its poleward growth was limited. The analysis of the wind and vorticity fields suggest that large meridional gradients of quasi-geostrophic potential vorticity, acting as a barrier to cloud mixing, was a factor in the asymmetric expansion.Item Spectral Phase Contrast Imaging and Phase Retrieval(2020-12) Vazquez, Ivan; Das, Mini; Gifford, Howard C.; Li, Liming; Meier, Mark A.Phase-contrast X-ray imaging (PCI) can significantly improve the contrast of small and weakly-absorbing materials. This is because of the sensitivity of PCI measurements to changes in both the attenuation and phase of an X-ray wavefield due to interactions with matter. Yet, quantitative estimates of material properties from PCI measurements require the use of phase retrieval (PR) algorithms. Our team developed a capable PR strategy for propagation-based PCI that estimates a pair of material properties from two or more energy-resolved measurements. Part of this work is dedicated to broadening our understanding of the key advantages and practical limitations of our method. To this end, a comprehensive analysis of the underlying theory and the sensitivity to factors such as noise are provided. Based on our findings, we proposed a set of strategies that can help enhance the quality and accuracy of estimated values. We also examined the performance of the PR method with laboratory measurements of a heterogeneous sample. To simultaneously obtain multiple energy-resolved measurements, we used a polychromatic (laboratory) source in combination with high-resolution photon-counting detectors. Our findings demonstrate that the properties of multiple (more than two) unique materials can be estimated with accuracies above 90\%. Additionally, our strategy produced results with satisfactory accuracy and image quality even when the detected photon counts were as low as 250 photons per pixel. The underpinning theory in our approach relies on the weak object approximation to simplify the transport-of-intensity equation (TIE). Thus, a section of this work is dedicated to examining the errors related to enforcing the weak object approximation when deriving a TIE-based PR algorithm. We also tested other prevalent methods to simplify the TIE. Experimental results revealed that errors introduced by the weak object approximation were below 5\% even for the case of aluminum, which has a relatively high atomic number.Item STATISTICAL MACHINE LEARNING AND PHYSICS INFORMED NEURAL NETWORKS IN ASTRONOMICAL SIMULATIONS(2023-08) Dai, Zhenyu; Vilalta, Ricardo; Gunaratne, Gemunu H.; Li, Liming; Shastri, Dvijesh J.The emergence of machine learning has revolutionized many fields of science and engineering, and in the last decade, it has become increasingly popular due to the availability of large datasets and powerful computational resources. One recent development in the field is the application of physics-informed neural networks (PINNs), which have shown significant potential in solving complex systems, partial differential equations, and hydrodynamic simulations in cosmology. Firstly, we implemented kernel density estimation, a traditional machine learning method, to provide a novel constraint on the high-temperature nuclear equation of state (EOS) and determine which EOS candidates are favorable based on an information-theoretic metric. This approach provided a valuable tool for testing and refining nuclear models and predicting the properties of dense matter. Next, we have explored the applications of PINNs in various contexts. We investigated the bias and variance trade-off of PINNs for solving Burgers' equation under noisy data. We discovered that the variance of the predictions increases monotonically with the noise level, highlighting the need for careful consideration of the noise level in PINN applications. Finally, we developed a new PINN model embedding physics knowledge to predict baryonic properties from dark matter halos. We introduced a new loss function that includes a mean squared error, Kullback-Leibler divergence (KLD), and a stellar-to-halo mass relation to recovering the scatter properties of baryonic matter, which has been an unsolved problem in other machine learning approaches to hydrodynamic simulations.Item The Gas Giant Evolutions of Jupiter and Saturn During the Cassini Era(2014-12) Trammell, Harold Justin 1987-; Li, Liming; Jiang, Xun; Lefer, Barry L.; Nixon, Conor A.There have been many significant shifts in the dynamics on Jupiter and Saturn during the Cassini era. This study explores observations from the Imaging Science Subsystem (ISS) on Cassini. This work conducted a global survey of Saturn’s vortices, which shows that there are significant variations in vortex activities across the globe. ISS images at different wavelengths also suggest complicated vertical structures for Saturn’s vortices. The study also addresses the comparative analysis between vortex activities on Jupiter and Saturn. The long-term Cassini imaging also captured the eruption of a giant storm in Saturn’s NH in December 2010. With the unprecedented observational resources from the ground-based telescopes coupled with the Cassini spacecraft, some important characteristics of the dynamical and thermal structures of the giant storm have been previously studied. This study attempts to quantify any precursors to this storm and analyzes the ripple across Saturn’s dynamic atmosphere. Primary results show a change in northern hemispheric vortex count on Saturn from the years 2008, 2010, 2011, 2012, to 2013 from 11±2, to 7±1, to 5±1, to 14±1 and 18±1, respectively. The giant storm mainly developed in the first half of 2011, and dissipated in August 2011 (Sayanagi et al., 2012; Sanchez-Lavega et al., 2012) even though its remnants had a lingering influence that lasted long after the storm subsided. Our analyses indicate there are correlations between the development of the 2010 giant storm and Saturn’s vortices. However, we cannot rule out the roles of Saturn’s seasonal cycle in the temporal variation of Saturn’s vortices during this time frame. Jupiter’s two hemispheres have roughly the same number of vortices, which is different from Saturn where the SH has many more vortices than in the NH from 2004 – 2010. Variations are due to the different obliquities and hence different seasonal cycles between the two planets. The comparison also reveals that a correlation exists between the highest number of vortices and the easterly zonal velocity minima between Jupiter and Saturn. This suggests that atmospheric instabilities play a critical role in generating vortices on both planets.Item The Influence of Large-Scale Circulation on Carbon Dioxide(2018-05) La, Jason 1989-; Jiang, Xun; Li, Liming; Talbot, Robert W.Carbon dioxide (CO2) has been shown to have adverse effects on a global scale as a major contributor to climate change, yielding changes to temperature, environments and habitats of all life on Earth. With improvements in satellite technology, newer and more precise measurements of CO2 concentrations have been collected. The Orbiting Carbon Observatory 2 (OCO-2), the first dedicated CO2 satellite launched by NASA, and the Greenhouse Gas Observing Satellite (GOSAT),first CO2 satellite developed by Japan, offer new insight to CO2 column measurements within the lower troposphere. First, the validity of the new OCO-2 and GOSAT CO2 data in comparison to in situ CO2 measurements from known TCCON sites was examined. Both OCO-2and GOSAT CO2 data agreed reasonably well with TCCON in situ measurements. Afterwards, the effects of the South Atlantic Walker Circulation on the distribution of OCO-2 and GOSAT CO2 in the lower troposphere in these regions was investigated. The research showed OCO-2 and GOSAT CO2 concentrations are lower over the South Atlantic Ocean than the South America by 1 parts per million (ppm) during December to March, which is consistent with the large-scale South Atlantic Walker Circulation. During December to March, surface temperatures are high over the South America, which causes air to rise. The rising air can bring high surface CO2 concentrations to the lower troposphere, which leads to a positive CO2 anomaly over the South America. Sinking air over South Atlantic Ocean can bring low upper-level CO2concentrations to the lower troposphere, causing a negative CO2 anomaly over the South Atlantic Ocean. Results in this study will lead to a better understanding of how large-scale atmospheric processes affect lower troposphere CO2 measurements regionally, therefore, lead to a better understanding of the CO2 global cycle.Item The Lorenz Energy Cycle of the Global Atmosphere during the past 35 Years (1979-2013)(2015-12) Pan, Yefeng 1989-; Li, Liming; Gunaratne, Gemunu H.; Stokes, Donna W.; Su, Wu-Pei; Jiang, XunThe Lorenz energy cycle (Lorenz 1955) describes how the solar heating generates potential energy that can be converted into kinetic energy to drive Earth’s atmospheric system. Therefore, the studies of the Lorenz energy cycle can help us understand the atmospheric system from a unique energy perspective. Based on two best global meteorological datasets, we systematically study the Lorenz energy cycle of the global atmosphere during the modern satellite era (1979-2013). Our analyses provide the most reliable characteristics of the Lorenz energy cycle of the global atmosphere. The mean state of the 35-year Lorenz energy cycle generates the best global picture of the Lorenz energy cycle. Our analyses also reveal important temporal characteristics of the Lorenz energy cycle of the global atmosphere. Significant positive trends are shown in both the eddy available potential energy (P_E) and the eddy kinetic energy (K_E) especially in the Southern Hemisphere, which are mainly due to the increasing storm activities over the Southern Ocean storm track areas. At the same time, a negative trend is seen in the mean available potential energy (P_M) especially around the North Pole near the surface, which is probably related to the inhomogeneous global warming. As a result, the total mechanical energy does not show any significant trend during the past 35 years, which suggests that the climate system remains close to a dynamical balance. Our analyses also suggest positive trends in all conversion rates and in the dissipation of kinetic energy, which implies that the efficiency of the global atmosphere as a heat engine increased during the modern satellite era. The statistical characteristics of the Lorenz energy cycle revealed in our analyses will provide a powerful tool to validate and develop the atmospheric and climate models. The temporal characteristic of the Lorenz energy cycle will also benefit the monitoring and predicting of climate change, for the atmospheric energetics are an important component of climate system of Earth.Item The Radiant Energy Budgets of Titan and Mars(2022-11-21) Creecy, Ellen Catherine; Li, Liming; Jiang, Xun; Wang, Yuxuan; Choi, Yunsoo; Nixon, Conor A.The radiant energy budget of planets and moons is of wide interest in the fields of geoscience and planetary science, as it is essential to understanding surface and atmospheric processes. In this work, we report the seasonal variations of the energy budget for both Titan and Mars and examine the surface emissivity of high latitude regions on Mars. Based on the Cassini multi-instrument observations, we find the global‐average emitted power decreased by 6.8 ± 0.4%, while the absorbed solar power decreased 18.7% ± 0.5% during the Cassini period (2004–2017). We find Titan's radiant energy budget is not balanced from 2004 to 2017, with the absorbed solar energy being (1.208 ± 0.008) x 10^23 J and the emitted thermal energy being (1.174 ± 0.005) x 10^23 J. There is an energy imbalance of 2.9 ± 0.8% of the emitted thermal energy. Titan's global radiant energy budget is not balanced at the timescales of Earth's years and Titan's seasons, and the imbalance can be beyond 10% of the emitted thermal energy at the timescale of an Earth year. Based on the observations from Mars Global Surveyor, Curiosity, and InSight, we find Mars’ global-average emitted power is 111.7 ± 2.4 Wm-2. There are strong seasonal variations in the emitted energy, and energy imbalances at the time scale of Mars’ seasons (e.g., ∼15.3% of the emitted power in the Northern autumn for the Southern Hemisphere), which could play a role in generating dust storms on Mars. We find the 2001 global dust storm decreased the global-average emitted power during daytime but increased the global-average emitted power at nighttime. This suggests that global dust storms play a significant role in modifying Mars’ radiant energy budget. Using data from the Mars Climate Sounder, we compute a solid-angle integrated emissivity and relative emissivity for the Southern and Northern high latitude regions, respectively, with 5 degree resolution in latitude and 10 degree resolution in longitude. We find the solid-angle integrated emissivity is typically a few percent less than the emissivity at nadir, with no strong correlation to known surface features (e.g., cryptic vs. anti-cryptic terrain).Item Validation, Analysis of Annual Cycle, and Biogenic Sequestration of CO2, and Modulation of CH4(2018-05) Corbett, Abigail 1990-; Jiang, Xun; Li, Liming; Talbot, Robert W.; Choi, YunsooGreenhouse gases, such as carbon dioxide (CO2) and methane (CH4), play a critical role in the processes of global warming and climate change. Retrieved CO2 from satellites (e.g., OCO 2, GOSAT, AIRS, TES) offer a fresh opportunity to understand the variability of CO2 over the global domain that was unattainable before due to sparse in situ measurements. First, two innovative satellite data sets, Orbiting Carbon Observatory (OCO-2) and Greenhouse Gases Observing Satellite (GOSAT), which have vertical sensitivities in the lower atmosphere were compared, with ground-based measurements to validate the new retrievals. This established that the GOSAT and OCO-2 CO2 data sets are close to the in situ measurements. The overall GOSAT CO2 uncertainty was -0.63 ppm; whereas, OCO-2 uncertainty was 0.23 ppm. Second, the long-term trend and annual variability of CO2 using satellite retrievals were explored. A multiple regression method was used to estimate CO2 seasonal cycle from the satellite CO2 retrievals and in situ CO2 measurements to better understand surface, mid-tropospheric, and column CO2 seasonal cycles. Third, novel satellite-retrieved Solar-induced Fluorescence (SIF) datasets were studied to investigate the contributions of the biosphere to CO2. This analysis allows for a better understanding of how the biosphere acts as a source and also a sink for global CO2, yielding a better understanding of the CO2 global cycle. An inverse relationship was found between atmospheric CO2 and SIF. During each hemisphere’s summer season, SIF values are high because there is more photosynthesis, which leads to a low levels of atmospheric CO2. Finally, the influence of El Niño-Southern Oscillation on mid-tropospheric methane was studied. Enhanced rising air in the central Pacific during El Niño months advects lower surface concentrations of CH4 over the ocean to the middle troposphere, with less CH4 over the central Pacific than the western Pacific. Furthermore, rising air can transport low surface concentrations of CH4 to the middle troposphere over the western Pacific in La Niña months, contributing to lower CH4 concentrations over the western Pacific than the central Pacific during La Niña months.