Sub-Seasonal Prediction of the Maritime Continent Rainfall of Wet-Dry Transitional Seasons in the NCEP Climate Forecast Version 2

This study investigates the characteristics and prediction of the Maritime Continent (MC) rainfall for the transitional periods between wet and dry seasons. Several observational data sets and the output from the 45-day hindcast by the U.S. National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) are used. Results show that the MC experiences a sudden transition from wet season to dry season (WTD) around the 27th pentad, and a gradual transition from dry season to wet season (DTW) around the 59th pentad. Correspondingly, the westerlies over the equatorial Indian Ocean, the easterlies over the equatorial Pacific Ocean, and the Australia High become weaker, contributing to weakening of the convergence over the MC. The subtropical western Pacific high intensifies and extends northeastward during the WTD. The Mascarene High becomes weaker, an anomalous anticyclonic circulation forms over the northeast of the Philippines, and an anomalous low-level convergence occurs over the western MC during the DTW. The NCEP CFSv2 captures the major features of rainfall and related atmospheric circulation when forecast lead time is less than three weeks for WTD and two weeks for DTW. The model predicts a weaker amplitude of the changes in rainfall and related atmospheric circulation for both WTD and DTW as lead time increases

Concurrent drought and heatwave events over the Asian monsoon region: insights from a statistically downscaling CMIP6 dataset

Concurrent drought and heatwave (CONDH) can cause tremendous ramifications on socioeconomic activities and human health, and the drought-heatwave (D-H) dependence was revealed to be one of the major factors of the CONDH across most global land regions. However, insufficient attention has been paid on the CONDH over the Asian monsoon region, and the impact of the D-H dependence is even more rarely considered. Based on a statistically downscaling the Coupled Model Intercomparison Project Phase 6 (CMIP6) dataset, we explore the spatial distributions of the intensity, frequency, and duration of the CONDH. In addition, the qualitative impacts of D-H dependence on the intensity, frequency, and duration of the CONDH have been further investigated via comparing these three metrics of the CONDH with those of heatwave. In the period of 1961–2014, the spatial pattern of intensity and duration of the CONDH bear a large resemblance to that of heatwave, with more severe CONDH (heatwave) occurring over South Asia, and relatively long-lasting CONDH (heatwave) occupying over the low latitudes of the Asian monsoon region. The frequency of the CONDH presents large discrepancies with that of heatwave. East Asia (South Asia) is hit by more frequent CONDH (heatwave) than other sub-regions. The D-H dependence is conducive to the intensity, frequency, and duration of the CONDH, especially over the East Asia, Eastern Siberia, and Western Siberia. In the period of 2015–2100, the intensity and duration of the CONDH and heatwave maintain the historical spatial structures. The frequency of the CONDH and heatwave change remarkably relative to 1961–2014, with largest value over eastern central Asia. The D-H dependence is conducive to the three features of the CONDH, and such positive contributions would weaken in response to global warming, especially under higher emission scenario

Sub-Seasonal Prediction of the Maritime Continent Rainfall of Wet-Dry Transitional Seasons in the NCEP Climate Forecast Version 2

This study investigates the characteristics and prediction of the Maritime Continent (MC) rainfall for the transitional periods between wet and dry seasons. Several observational data sets and the output from the 45-day hindcast by the U.S. National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) are used. Results show that the MC experiences a sudden transition from wet season to dry season (WTD) around the 27th pentad, and a gradual transition from dry season to wet season (DTW) around the 59th pentad. Correspondingly, the westerlies over the equatorial Indian Ocean, the easterlies over the equatorial Pacific Ocean, and the Australia High become weaker, contributing to weakening of the convergence over the MC. The subtropical western Pacific high intensifies and extends northeastward during the WTD. The Mascarene High becomes weaker, an anomalous anticyclonic circulation forms over the northeast of the Philippines, and an anomalous low-level convergence occurs over the western MC during the DTW. The NCEP CFSv2 captures the major features of rainfall and related atmospheric circulation when forecast lead time is less than three weeks for WTD and two weeks for DTW. The model predicts a weaker amplitude of the changes in rainfall and related atmospheric circulation for both WTD and DTW as lead time increases

Changes in concurrent precipitation and temperature extremes over the Asian monsoon region: observation and projection

Concurrent precipitation and temperature extremes exert amplified impacts on the ecosystems and human society; however, they have not been well documented over the Asian monsoon region with dense population and agricultures. In this study, the spatiotemporal variations of four concurrent extreme modes (cold/dry, cold/wet, warm/dry, and warm/wet) are detected based on observations and model projections. From 1961 to 2014, the ‘dry’ modes manifest large values at high latitudes, while the ‘wet’ modes occur frequently in tropical regions. Based on the linear congruency, the trends of the four modes are largely determined by extreme temperature. Furthermore, the interaction between extreme precipitation and extreme temperature (IEPET) facilitates the trends of the dry modes, and inhibits the trends of the wet modes. Three modeling datasets (CMIP6, NEX-GDDP-CMIP6, and BCSD_CMIP6) are employed to project future changes in the occurrences of four concurrent modes. The BCSD_CMIP6, generated by statistical downscaling of the CMIP6 simulations, stands out in simulating the observed features of extreme precipitation and extreme temperature over the Asian monsoon region. Extreme temperature is also identified as the main driver in the future trends of the four modes, while the IEPET is not conducive to the decreasing trend of the cold/dry mode, implying that the IEPET would change under global warming. The warm/wet mode manifests the largest change among the four compound extremes from 1995 to 2014 and two projected periods (2046–2065 and 2080–2099) relative to 1961–1980. On the annual timescale, the change magnitudes over Southeast Asia, South Asia, the Tibetan Plateau, and Eastern Central Asia are relatively larger than in the other sub-regions during historical and future periods, which are quantified as the hotspots of the warm/wet mode. On the seasonal timescale, the future hotspots will change relative to the historical period. Our findings are critical for formulating adaptation strategies to cope with the adverse effects of compound extremes

Diverse impacts of the Indian summer monsoon on ENSO among CMIP6 models and its possible causes

This study examines the performance of 52 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6) in capturing the effects of the Indian summer monsoon (ISM) on the evolution of El Niño–Southern Oscillation (ENSO). The ISM's impacts on ENSO show a substantial diversity among the models. While some models simulate the strength of the impacts comparable to observations, others represent much weaker influences. Results indicate that the diversity is highly related to inter-model spread in interannual variability of ISM rainfall among the models. Models with a larger ISM rainfall variability simulate stronger ISM-induced anomalies in precipitation and atmospheric circulation over the western North Pacific during the monsoon season. As a result, these models exhibit larger wind anomalies induced by monsoon on the south flank of the anomalous circulation in the western Pacific, thereby influencing subsequent ENSO evolution more significantly by causing stronger air-sea coupling processes over the tropical Pacific

The Impact of Tides and Monsoons on Tritium Migration and Diffusion in Coastal Harbours: A Simulation Study in Lianyungang Haizhou Bay, China

Many nuclear power plants have been built along China’s coasts, and the migration and diffusion of radioactive nuclides in coastal harbours is very concerning. In this study, considering the decay and free diffusion of radioactive nuclides, a local hydrodynamic model based on the FVCOM was built to investigate the migration and diffusion of the radioactive nuclide tritium in Haizhou Bay, China. This model was calibrated according to the observed tidal level and flow velocity and direction, which provide an accurate background. This study aimed to evaluate the impact of tides and monsoons on the migration path and concentration variations in tritium over time. The results demonstrated that the simulated flow field can reflect real-life receiving waters. The distribution of the tritium concentration is affected by the flow field, which is related to the tides. Moreover, more severe radioactive contamination was exhibited in winter than in summer because monsoons may have hindered the migration and diffusion of tritium within the harbour. Given the poor hydrodynamic conditions and slow water exchange in the open ocean in Haizhou Bay, the diffusion rate of radioactive nuclides outside the bay area was higher than that within it

Disentangling physical and dynamical drivers of the 2016/17 record-breaking warm winter in China

Understanding the physical and dynamical origin of regional climate extremes remains a major challenge in our effort to anticipate the occurrences and mitigate the adverse impacts of these extremes. China was hit by a record-breaking hot winter in 2016/17 with remarkable surface warming over the northern and southeastern regions. Here we made a quantitative attribution of this 2016/17 winter’s surface temperature anomalies utilizing an updated version of the coupled atmosphere-surface climate feedback response analysis method (CFRAM), that recently incorporates the effect of aerosols and more species of trace gases (CFRAM-A). The CFRAM-A analysis reveals that the overall warming pattern may be largely attributed to the effects of anomalous water vapor, atmospheric dynamics, and aerosols, followed by anomalies of surface albedo, clouds, solar irradiance, ozone, and carbon dioxide. The effect of methane turns out to be negligible. Anomalies in surface dynamics provides an overall cooling effect, compensating the warming associated with other processes to some extent. Among the three major positive contributors, effects of water vapor and atmospheric dynamics prevail over both northern and southeastern China while the impact of anthropogenic aerosols appears much more pronounced over southeastern China, likely due to the implementation of highly effective emission reduction policies in China since 2013. The CFRAM-A thus provides an efficient, model-free approach for quantitatively understanding sources of regional temperature extremes and for assessing the impacts of environmental policies regulating anthropogenic emissions of aerosols and atmospheric trace gases

Multi-Stage Flotation for the Removal of Ash from Fine Graphite Using Mechanical and Centrifugal Forces

Graphite ore collected from Hunan province, south China was characterized by chemical analysis, X-ray diffraction, and optical microscopy. Rougher and multi-stage flotation tests using a mechanical flotation cell and a flotation column containing an additional centrifugal force field were carried out to promote its grade and economic value. In rougher flotation, both the mechanical flotation cell and flotation column reduced the ash content of the graphite ore from 15.43% to 10.8%, while the yield of the flotation column (91.41%) was much higher than that of the mechanical flotation cell (50%). In the presence of hydrophobic graphite, the seriously entrained gangue restricted further improvement in the quality and economic value of the graphite ore. Therefore, multi-stage flotation circuits were employed to diminish this entrainment. Multi-stage flotation circuits using the two flotation devices further decreased the ash content of the graphite ore to ~8%, while the yield when using the flotation column was much higher than that obtained from the mechanical flotation cell employed. On the other hand, the ash removal efficiency of the flotation column was 3.82-fold higher than that observed for the mechanical flotation cell. The Cleaner 3 flotation circuit using the flotation column decreased the ash content in graphite from 15.43% to 7.97% with a yield of 77.53%