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Under the influence of Asian summer monsoon, extremely heavy summer rainfall could occur in Southeast China, causing catastrophic social-economic impacts to the region. However, due to limited historical records, it is difficult to anticipate the risks of unprecedented extreme rainfall episodes. In this study the UNSEEN method (UNprecedented Simulated Extremes using ENsembles) is applied for studying these events, by sampling large ensemble climate model simulations of Version 6 of the Met Office Global Seasonal Forecasting System (GloSea6). We first perform fidelity tests on gridboxes in Southeast China and show that the climate model can represent observations realistically. Probabilities of unprecedented Southeast China rainfall are then computed for each of the five gridboxes within Southeast China, revealing probabilities of about 6% (up to 9%) in summer. The circulation dynamics associated with such events is also examined. For gridboxes close to the western north Pacific, a strengthened western Pacific subtropical high (WPSH) leads to anomalous low-level southerlies onshore to Southeast China, thereby contributing to heavy rainfall there. For gridboxes along 35° N, unprecedented events are often associated with an upper-level stationary wave pattern along the climatological jet, inducing vertical motion conducive to convection. For gridboxes along 25° N, extreme rainfall events are often associated with a southward shifted subtropical jet. Finally, the importance of the shifted jet and the WPSH strength in generating the unprecedented rainfall in the southern gridboxes along 25° N is also investigated. A southward-shifted jet could lead to extreme rainfall in the southern gridboxes even when the WPSH displacement is not strong. Overall, anomalous upper-level flow and WPSH activity can be equally important in triggering unprecedented summer rainfall in Southeast China. In short, we demonstrate that the UNSEEN method can be applied for estimating the risk of extreme monsoon rainfall in Southeast China and understanding the associated mechanisms.

Our society increasingly depends on computer-based systems; the number of applications deployed has increased dramatically in recent years and this trend is accelerating. Many of these applications are expected to provide their services continuously. The Service Availability Forum has recognized this need and developed a set of specifications to help software designers and developers to focus on the value added function of applications, leaving the availability management functions for the middleware. A practical and informative reference for the Service Availability Forum specifications, this book gives a cohesive explanation of the founding principles, motivation behind the design of the specifications, and the solutions, usage scenarios and limitations that a final system may have. Avoiding complex mathematical explanations, the book takes a pragmatic approach by discussing issues that are as close as possible to the daily software design/development by practitioners, and yet at a level that still takes in the overall picture. As a result, practitioners will be able to use the specifications as intended. Takes a practical approach, giving guidance on the use of the specifications to explain the architecture, redundancy models and dependencies of the Service Availability (SA) Forum services Explains how service availability provides fault tolerance at the service level Clarifies how the SA Forum solution is supported by open source implementations of the middleware Includes fragments of code, simple example and use cases to give readers a practical understanding of the topic Provides a stepping stone for applications and system designers, developers and advanced students to help them understand and use the specifications

This study investigates the influence of synoptic-scale activities on extreme precipitation during March–April–May (MAM) over Southern East Asia (SEA) using observational data and compares the results with the outputs from 20 Coupled Model Intercomparison Project phase 6 (CMIP6) historical runs. Observations show that SEA intense daily precipitation in MAM is linked to enhanced upper-level synoptic-scale waves; these disturbances are associated with significant anomalous temperature advection as well as moisture flux convergence, creating favorable conditions for extreme rainfall. Furthermore, it is found that a temperature advection index (TAI) can be utilized to characterize such synoptic-scale activities. Inspection of CMIP6 historical runs reveals that, among 20 models, 13 models perform well in accurately capturing the observed SEA rainfall pattern; such extreme events are also closely linked to TAI in the model environment. Overall, observed (simulated) results show that 78% (75%) of extreme events in the Yangtze River Basin–South Korea–south of Japan region can be attributed to positive TAI. Additionally, the related circulation anomalies such as the upper-level synoptic-scale wave feature, temperature advection, and moisture anomalies from these models closely resemble those observed during extreme precipitation days in SEA. Our findings suggest that TAI can effectively indicate both the frequency and intensity of extreme rainfall events in SEA, along with the associated synoptic-scale activities. Further study reveals a close lead-lag correlation between TAI and rainfall patterns over SEA. This correlation is characterized by eastward-propagating wave trains across the entire troposphere. Consequently, TAI not only acts as a benchmark for quantifying synoptic-scale extreme rainfall in SEA but also shows potential in predicting SEA rainfall linked to synoptic-scale disturbances.

This study compares the impacts of global warming and intense anthropogenic heat (AH) on extreme hourly precipitation over the Pearl River Delta (PRD) megacity, located in coastal South China. Using the cloud-resolving Weather Research and Forecasting (WRF) model coupled with the single-layer urban canopy model (SLUCM), three downscaling experiments were carried out: the first (second) having zero (300W/m2 as diurnal maximum) AH values prescribed over PRD urban grids, under the same current climate conditions. The third experiment with AH=300W/m2 under future projected climate representative concentration pathway (RCP) 8.5. Boundary conditions were derived from PRD extreme rainfall episodes, identified from the Geophysical Fluid Dynamics Laboratory Earth System Model (GFDL-ESM2M) historical and RCP8.5 runs. Global warming forcing leads to ~20 to more than 100% increase in the probability of hourly precipitation with the magnitude of 20-100mm/hr over urban locations. The enhancements from intense AH forcing were similar. However, two types of forcings have distinct signatures in modulating the thermodynamic environment. Warming due to AH is limited to the lowest 1km above ground, while global warming warms up the whole troposphere. Intense AH results in enhanced convective available potential energy (CAPE) and reduced convective inhibition (CIN) within the megacity, allowing convection to be triggered more easily and with more vigor. On the other hand, global warming enhances both CAPE and CIN, over both urban and rural areas. Our results highlight the different physical mechanisms of AH and global warming in exacerbating extreme urban rainfall, despite their having similar impacts on the rainfall intensity.

The impact of El Niño and Southern Oscillation (ENSO) on different types of atmospheric transient activity is studied, based on data from an ensemble general circulation model (GCM) experiment and the National Centers for Environmental Prediction (NCEP)-National Center for Atmospheric Research (NCAR) Reanalysis Project. In particular, the Madden-Julian Oscillation (MJO), North Pacific low-frequency (subseasonal/intraseasonal) circulation anomalies and summertime tropical synoptic-scale disturbances are considered. Extensive comparisons between reanalyses results and those based on ensemble GCM integrations are carried out. The MJO activity from the GCM and reanalyses agree in several aspects, such as their spectral characteristics, regions with large amplitudes and their phase speed. MJO convection within the central Pacific is enhanced during warm ENSO events, suppressed during cold events. Positive values of the instability index, based on the vertical gradient of the moist static energy, are found to precede MJO convection at the equator. During warm events, there are stronger signals of this index over the central Pacific, which could be important for the further eastward penetration of convective anomalies in the region. The life cycle of low-frequency circulation anomalies over the North Pacific is studied. During cold ENSO events, eddies in general are stronger, with more prominent dispersion downstream over the west coast of U.S. GCM results show that stronger incoming wave activity from the subtropics is accompanied by stronger intraseasonal convection in the tropical western Pacific, suggesting that the MJO plays a role on how ENSO affects extratropical low-frequency activity. The GCM is able to reproduce qualitatively the propagation and growth/decay behavior of tropical summertime synoptic-scale disturbances. During warm ENSO events, storm tracks over the western Pacific are displaced eastward. Stronger barotropic conversion from the mean to eddy kinetic energy is related to increased low-level cyclonic wind shear in the region. Finally, equatorward energy dispersion from eddies is also located more to the east in the warm phase of ENSO. The relationship between the structure of the eddies and their related dispersion pattern is examined.