South Pacific Atmospheric Internal Variability and Its Role in El Niño-Southern Oscillation

Accurate long-range seasonal prediction of the El Niño-Southern Oscillation (ENSO) phenomenon is of critical importance to predict regional and global climate anomalies. The overarching goal of this work is to seek the extratropical precursors for ENSO events with a focus on the South Pacific. More specifically, this work investigates the impacts of the South Pacific atmospheric internal variability on the occurrence, intensity, evolution, and flavors of ENSO events in the context of the coupled atmosphere-ocean system. In general, both the tropically forced and intrinsic atmospheric variability in the South Pacific features a large-scale meridional sea level pressure (SLP) dipole with anomalies out-of-phase between the middle and high latitudes. The dipole is termed the South Pacific Oscillation (SPO) in the present thesis. The internal component of the SPO initiates the South Pacific Meridional Mode (SPMM), which acts as an effective conduit transmitting the extratropical wind and sea surface temperature (SST) anomalies (SSTA) into the central-eastern equatorial Pacific via the wind-evaporation-SST (WES) feedback. Modulated by the seasonal cycle of the oceanic mixed layer depth and the lower amplitude of the mean seasonal cycle in the Southern Hemisphere, the WES feedback involved with the SPMM is most effective during the austral summer, providing a favorable timing for the SPMM to prime an ENSO event. The SPMM-induced anomalies in the central-eastern tropical Pacific interfere constructively or destructively with the contemporaneous western tropical anomalies driven by the North Pacific Meridional Mode (NPMM) to shape the occurrence, evolution, amplitude, and potentially the longitudinal position of the maximum SSTA associated with ENSO events. Both the Pacific meridional modes are most efficient at triggering ENSO events when the subsurface equatorial Pacific Ocean is preconditioned with the anomalous heat content buildup. The NPMM and SPMM during the austral winter (February-May) operate as skillful predictors for the boreal winter SSTA in the Pacific basin. Despite considerable improvements to long-lead forecasts of ENSO activity over the past decades, the model prediction of the ENSO flavor is constrained to about one-to-two season lead time. Our results indicate that the austral winter SPO appears to be a primary source contributing to uncertainty in ENSO forecasts and provides important implications for the seasonal prediction of the ensuing ENSO flavors. Specifically, the spatial structure and amplitude of the austral winter SPO are considerably regulated by atmospheric intrinsic process, which affects the strength of the South Pacific subtropical high, forces stochastic zonal wind stresses and regulates discharge of the ocean heat content in the eastern equatorial Pacific. Although the wind stress relevant to the internal variability decays rapidly, it initiates coupled instability that grows into ENSO-like structure by the Bjerknes feedback. Given that internal variability is, by definition, unpredictable even with a perfect model, the austral winter SPO might serve as a natural limit for ENSO prediction. Collectively, the current study highlights the importance of the South Pacific atmospheric internal variability and provides potential enhancements to understand and predict ENSO events. The findings contribute to the existing literature on the connection between North Pacific and ENSO to include the South Pacific. Although this thesis primarily focuses on the interannual variability, the role of the SPMM in Pacific decadal variability and its connection to ENSO under anthropogenic climate change warrant future investigations

Observed trends in South Asian monsoon low-pressure systems and rainfall extremes since the late 1970s

The core Indian monsoon region receives more than half of the rainfall extremes from low-pressure systems (LPSs), which typically form over the Bay of Bengal and propagate upstream against the time-mean low-level westerlies. Yet, the relationship between the trends of LPSs and rainfall extremes remains uncertain. Using two tracking algorithms and reanalyses-derived LPSs, we find that LPS activity and extreme rainfall exhibit coherent trends during the post-1979 satellite era. Over time, the LPSs propagate preferentially into south-central India rather than north-central India, imparting a corresponding dipole footprint in rainfall extremes. Consistent with existing theories that the diabatic heating is instrumental in shifting the LPSs west-southwestward, the LPSs traveling through south-central India have stronger updrafts on their west-southwestern flank than those passing through north-central India. The increased frequency of LPSs propagating into south-central India is likely due to a strengthened cross-equatorial moisture transport, which favors stronger storm ascents

Low-Pressure Systems and Extreme Precipitation in Southeast and East Asian Monsoon Regions

Understanding the physical mechanisms behind the secular trends of summer rainfall extremes over the heavily populated Southeast and East Asian monsoon regions is not only of scientific importance but also of considerable socioeconomic implications. In this study, the relevance of the excessive-rain-producing low pressure systems (LPSs) to extreme rainfall is quantified. Using an objective feature-tracking algorithm, the synoptic-scale LPSs are identified and tracked in the 40-yr ECMWF interim reanalysis. The region experiences approximately 16 terrestrial and 18 marine LPSs each summer. The terrestrial LPSs form near the downwind side of the Tibetan Plateau and travel northeastward toward jet latitudes. The marine LPSs form over the western North Pacific Ocean and migrate along the western periphery of the subtropical high. While both types of LPSs account for a large portion of upper-tail rainfall, the terrestrial LPSs predominantly impact the extreme rainfall over inland areas, and the marine LPSs primarily affect the coastal regions where they frequently make landfall. The historical extreme rainfall trend during 1979–2018 aligns with the changes in LPS tracks. The decreasing number of northeastward-moving terrestrial LPSs leads to an extreme rainfall dipole with negative trends in north-central China and positive trends in southern China, while the increasing number of northward-recurving marine LPSs enhances the extreme rainfall in the eastern China coast but suppresses it over the South China Sea. These trends are driven dynamically by the weakening of the monsoonal southwesterlies and the eastward retreat of the subtropical high, which might be attributable to anthropogenic forcings

Heavy Rain-producing Terrestrial Low-Pressure Systems Over East Asian Summer Monsoon Region: Evolution, Energetics, and Trend

The synoptic low pressure systems (LPSs) formed over the downwind side of the Tibetan Plateau explain a substantial portion of summer rainfall extremes along their paths. Recent studies have found that the total extreme rainfall trend over the East Asian landmass, which features the “south flood–north drought” pattern, can be understood to a great extent by the changes in terrestrial LPSs. Yet, the energy sources fueling these storms and the environmental drivers of their long-term trends remain unclear. Utilizing a probabilistic clustering method, three clusters of terrestrial LPS tracks for the period 1979–2018 are identified. Besides the differences in trajectories that distinguish the clusters into northeastward-migrating and quasi-stationary types, prominent intercluster differences are found in the LPS evolution, energetics, and trends. The Lorenz energetics suggest that while condensational heating is indispensable for all three clusters, the migratory type, which has greater intensity and faster development, is more closely tied to baroclinicity. Nonetheless, the summer baroclinicity alone is not enough to sustain these LPSs as these storms dissipate quickly after propagating out of the humid monsoon region and into the drier extratropics. Over time, occurrences of migratory LPSs decrease, and those of quasi-stationary LPSs increase. Using a Poisson model that links the LPS genesis to local environmental conditions, the decreasing occurrence of migratory LPSs is shown to result from the weakened baroclinicity, whereas the increasing occurrence of quasi-stationary LPSs is primarily driven by enhanced relative humidity and reduced steering flow in the mid-to-lower troposphere over East Asia

Causal Discovery in Radiographic Markers of Knee Osteoarthritis and Prediction for Knee Osteoarthritis Severity With Attention-Long Short-Term Memory.

The goal of this study is to build a prognostic model to predict the severity of radiographic knee osteoarthritis (KOA) and to identify long-term disease progression risk factors for early intervention and treatment. We designed a long short-term memory (LSTM) model with an attention mechanism to predict Kellgren/Lawrence (KL) grade for knee osteoarthritis patients. The attention scores reveal a time-associated impact of different variables on KL grades. We also employed a fast causal inference (FCI) algorithm to estimate the causal relation of key variables, which will aid in clinical interpretability. Based on the clinical information of current visits, we accurately predicted the KL grade of the patient\u27s next visits with 90% accuracy. We found that joint space narrowing was a major contributor to KOA progression. Furthermore, our causal structure model indicated that knee alignments may lead to joint space narrowing, while symptoms (swelling, grinding, catching, and limited mobility) have little impact on KOA progression. This study evaluated a broad spectrum of potential risk factors from clinical data, questionnaires, and radiographic markers that are rarely considered in previous studies. Using our statistical model, providers are able to predict the risk of the future progression of KOA, which will provide a basis for selecting proper interventions, such as proceeding to joint arthroplasty for patients. Our causal model suggests that knee alignment should be considered in the primary treatment and KOA progression was independent of clinical symptoms

Indocyanine Green Loaded Reduced Graphene Oxide for In Vivo Photoacoustic/Fluorescence Dual-Modality Tumor Imaging

Multimodality imaging based on multifunctional nanocomposites holds great promise to fundamentally augment the capability of biomedical imaging. Specifically, photoacoustic and fluorescence dual-modality imaging is gaining much interest because of their non-invasiveness and the complementary nature of the two modalities in terms of imaging resolution, depth, sensitivity, and speed. Herein, using a green and facile method, we synthesize indocyanine green (ICG) loaded, polyethylene glycol (PEG) ylated, reduced nano-graphene oxide nanocomposite (rNGO-PEG/ICG) as a new type of fluorescence and photoacoustic dual-modality imaging contrast. The nanocomposite is shown to have minimal toxicity and excellent photoacoustic/fluorescence signals both in vitro and in vivo. Compared with free ICG, the nanocomposite is demonstrated to possess greater stability, longer blood circulation time, and superior passive tumor targeting capability. In vivo study shows that the circulation time of rNGO-PEG/ICG in the mouse body can sustain up to 6 h upon intravenous injection; while after 1 day, no obvious accumulation of rNGO-PEG/ICG is found in any major organs except the tumor regions. The demonstrated high fluorescence/photoacoustic dual contrasts, together with its low toxicity and excellent circulation life time, suggest that the synthesized rNGO-PEG/ICG can be a promising candidate for further translational studies on both the early diagnosis and image-guided therapy/surgery of cancer.11248Ysciescopu

Relative Importance of Greenhouse Gases, Sulfate, Organic Carbon, and Black Carbon Aerosol for South Asian Monsoon Rainfall Changes

The contribution of individual aerosol species and greenhouse gases to precipitation changes during the South Asian summer monsoon is uncertain. Mechanisms driving responses to anthropogenic forcings need further characterization. We use an atmosphere-only climate model to simulate the fast response of the summer monsoon to different anthropogenic aerosol types and to anthropogenic greenhouse gases. Without normalization, sulfate is the largest driver of precipitation change between 1850 and 2000, followed by black carbon and greenhouse gases. Normalized by radiative forcing, the most effective driver is black carbon. The precipitation and moisture budget responses to combinations of aerosol species perturbed together scale as a linear superposition of their individual responses. We use both a circulation-based and moisture budget-based argument to identify mechanisms of aerosol and greenhouse gas induced changes to precipitation and find that in all cases the dynamic contribution is the dominant driver to precipitation change in the monsoon region

South Asian summer monsoon response to aerosol-forced sea surface temperatures

Climate models suggest that anthropogenic aerosol‐induced drying dominates the historicalrainfall changes over the heavily populated South Asian monsoon region. The regional response dependson both the aerosol fast radiative effect and the slow process through sea surface temperature (SST)cooling. Two atmospheric general circulation models, NCAR‐CAM5 and GFDL‐AM3, are used to investigatethe monsoon response to prescribed aerosol‐forced SSTs. The total SST is separated into uniform cooling anda spatially varying component characterized by interhemispheric asymmetry. The monsoon rainfall ispredominantly controlled by the nonuniform SSTs, in the local Indian Ocean, South, and East China Seas(IO‐CSs). The reduced meridional SST gradient in the IO‐ CSs leads to weakened monsoon circulation,which drives a north‐south dipole rainfall change. The latitudinal location of the dipole shows modeldependence due to differences in local SSTs and their meridional gradient, which determines the latitudinallocation of the meridional overturning circulation responses

Characterization of suspended sand concentrations in the Yangtze River Estuary and adjacent waters

IntroductionThe study on the distribution characteristics of suspended sediment concentration (SSC) in estuaries is an important subject in the study of estuaries and coasts, which has important theoretical significance and practical value.MethodsIn order to fully understand the characteristics of SSC in the Yangtze River Estuary and its adjacent waters, this paper uses fixed vertical observation data and navigation type large area observation data as data sources to analyze the distribution characteristics of SSC in the Yangtze River Estuary and its adjacent waters under different tidal current states and its vertical profile characteristics. It discusses the impact of tidal current velocity on SSC and the changes of SSC in the Yangtze River Estuary and its adjacent waters from 2018 to 2020. And the applicability of the Rouse and Soulsby formulas in the Yangtze River Estuary and its adjacent waters was verified.ResultsIt was found that the Rouse and Soulsby models have high applicability in the study area, and the prediction accuracy based on the Li’s Soulsby model is higher. This study provides effective support for carrying out marine forecasting, analysis and evaluation, and provides theoretical basis for carrying out analysis of the current situation of estuarine mudflat resources and prediction of the evolution trend. It plays an important role in scientific and comprehensive research and management of mudflat resources in Shanghai.DiscussionHowever, this study only explored the characteristic patterns of SSC in the Yangtze River Estuary and its adjacent waters based on field observations, but SSC is a more complex water environment parameter that is influenced by a variety of factors. The effects of salinity, temperature and wind speed should be considered in subsequent studies