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China experienced worsening ground-level ozone (O3) pollution from 2013 to 2019. In this study, meteorological parameters, including surface temperature (T2), solar radiation (SW), and wind speed (WS), were classified into two aspects, (1) Photochemical Reaction Condition (PRC = T2 × SW) and (2) Physical Dispersion Capacity (PDC = WS). In this way, a Meteorology Synthetic Index (MSI = PRC/PDC) was developed for the quantification of meteorology-induced ground-level O3 pollution. The positive linear relationship between the 90th percentile of MDA8 (maximum daily 8-h average) O3 concentration and MSI determined that the contribution of meteorological changes to ground-level O−3 varied on a latitudinal gradient, decreasing from ∼40% in southern China to 10%–20% in northern China. Favorable photochemical reaction conditions were more important for ground-level O3 pollution. This study proposes a universally applicable index for fast diagnosis of meteorological roles in ground-level O3 variability, which enables the assessment of the observed effects of precursor emissions reductions that can be used for designing future control policies. Electronic Supplementary Material Supplementary material is available in the online version of this article at 10.1007/s00376-021-1257-x.

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content (OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year’s record value by 14 ± 11 ZJ (1 zetta J = 1021 J) using the IAP/CAS dataset and by 16 ± 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Niño-Southern Oscillation (ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans, and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation.

Highly unusual amounts of rainfall were seen in the 2020 summer in many parts of China, Japan, and South Korea. At the intercontinental scale, case studies have attributed this exceptional event to a displacement of the climatological western North Pacific subtropical anticyclone, potentially associated Indian Ocean sea surface temperature patterns and a mid-latitude wave train emanating from the North Atlantic. Using clusters of spatial patterns of sea level pressure, we show that an unprecedented 80% of the 2020 summer days in East Asia were dominated by clusters of surface pressure greater than normal over the South China Sea. By examining the rainfall and water vapor fluxes in other years when these clusters were also prevalent, we find that the frequency of these types of clusters was likely to have been largely responsible for the unusual rainfall of 2020. From two ensembles of future climate projections, we show that summers like 2020 in East Asia may become more frequent and considerably wetter in a warmer world with an enhanced moisture supply.2020 年夏季, 中国、 日本和韩国的诸多地区均出现了创纪录的极端强降水. 该事件的个例研究将这一特殊事件归因于西北太平洋副热带反气旋的位置移动, 可能与印度洋海表面温度异常和自北大西洋发出的中纬度波列有关. 本工作通过对东亚逐日海平面气压 (SLP) 空间场的聚类分析, 发现 2020 年夏季南海地区为正 SLP 异常的天气型出现天数达到整个夏季的 80%, 为 1979 年以来之最. 通过与其他环流型所对应的降水和水汽通量异常对比, 发现这类天气型的频繁出现很可能是造成 2020 年梅雨期降水偏多的主要原因. 该研究进一步分析了两个大样本集合气候模拟预估结果, 发现未来在全球进一步增暖、 水分供应相应增加的情景下, 像 2020 年这样的东亚夏季环流可能会出现得更加频繁, 中国降水也会更强.

A better knowledge of aerosol properties is of great significance for elucidating the complex mechanisms behind frequently occurring haze pollution events. In this study, we examine the temporal and spatial variations in both PM1 and its major chemical constituents using three-year field measurements that were collected in six representative regions in China between 2012 and 2014. Our results show that both PM1 and its chemical compositions varied significantly in space and time, with high PM1 loadings mainly observed in the winter. By comparing chemical constituents between clean and polluted episodes, we find that the elevated PM1 mass concentration during pollution events should be largely attributable to significant increases in organic matter (OM) and inorganic aerosols like sulfate, nitrate, and ammonium (SNA), indicative of the critical role of primary emissions and secondary aerosols in elevating PM1 pollution levels. The ratios of PM1/PM2.5 are found to be generally high in Shanghai and Guangzhou, while relatively low ratios are seen in Xi’an and Chengdu, indicating anthropogenic emissions were more likely to accumulate in forms of finer particles. With respect to the relative importance of chemical components and meteorological factors quantified via statistical modeling practices, we find that primary emissions and secondary aerosols were the two leading factors contributing to PM1 variations, though meteorological factors also played important roles in regulating the dispersion of atmospheric PM.

The record-breaking mei-yu in the Yangtze-Huaihe River valley (YHRV) in 2020 was characterized by an early onset, a delayed retreat, a long duration, a wide meridional rainbelt, abundant precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation (QBWO) during the mei-yu season of 2020 that was associated with the onset and retreat of mei-yu, a northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly, during the mei-yu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the upper-level East Asian westerly jet, and the low-level southwesterly jet, experienced periodic oscillations linked with the QBWO. Most notably, the repeated establishment of a large southerly center, with relatively stable latitude, led to moisture convergence and ascent which was observed to develop repeatedly. This was accompanied by a long-term duration of the mei-yu rainfall in the YHRV and frequent occurrences of rainstorm processes. Moreover, two blocking highs were present in the middle to high latitudes over Eurasia, and a trough along the East Asian coast was also active, which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths. The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV. The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH, which was observed to be favorable for excessive rainfall over YHRV.2020年江淮流域梅雨开始早, 结束晚, 持续时间长, 雨带南北跨度大, 降水量大, 暴雨过程多, 是一次破纪录的梅雨事件. 分析发现, 东亚季风环流系统表现出明显的准双周振荡 (QBWO), 它与梅雨的开始和结束、 雨带的北移和停滞、 强降水过程的发生和维持有很好的对应关系. 梅雨期包括西太平洋副热带高压、 高层东亚西风急流和低空西南风急流在内的多个季风环流子系统均经历了与 QBWO 相关的周期性振荡, 尤其是低空西南急流的不断加强, 南风大值中心反复建立和位置的相对稳定, 使得源自热带的水汽输送一次次加强, 水汽辐合与上升运动反复发展, 从而导致梅雨在江淮流域长时间持续, 暴雨过程频频发生. 另一方面, 梅雨期欧亚中高纬度地区环流呈现出 “两脊一槽” 型, 阻塞高压活动频繁, 东亚沿岸低槽活跃, 经西北和/或东北路径的冷空气不断南侵我国, 与低层一次次加强的西南暖湿水汽在江淮区域频繁交汇, 这是造成今年梅雨异常偏强的另一重要因素. 作为一个重要的外强迫因子, 热带印度洋的持续增暖使得东亚地区环流呈现出 EAP/PJ 型遥相关型, 对应西太副高偏强偏南, 从而有利于长江中下游地区降水明显偏多.