Observed decadal shifts and trends in global tropical cyclone activities from 1980 to 2021

This study investigates the variability of annual tropical cyclone (TC) frequency and intensity over six major ocean basins from 1980 to 2021. Statistical change-point and trend analyses were performed on the TC time series to detect significant decadal variation in TC activities. In the middle of the last decade of the 20th century, the frequency of TC genesis in the North Atlantic basin (NA) and North Indian Ocean (NIO) increased dramatically. In contrast, the frequency in the western North Pacific (WNP) decreased significantly at the end of the century. The other three basins—the East Pacific, southern Indian, and South Pacific—all experienced a declining trend in annual TC frequency. Over recent decades, the average TC intensity has decreased in the East Pacific and the NA, whereas it has risen in the other ocean basins. Specifically, from 2013 to 2021, the average peak TC intensity in the NIO has enhanced significantly. The magnitude of the Genesis Potential Index exhibits fluctuation that is consistent with large-scale parameters in the NIO, NA, and WNP, emphasizing the enhancing and declining trends in TCs. In addition, a trend and correlation analysis of the averaged large-scale characteristics with TCs revealed significant associations between the vertical wind shear and TC frequency over the NIO, NA, and WNP. Therefore, global TC trends and decadal variations associated with environmental parameters deserve further investigation in the future, mainly linked to the significant climate modes.摘要研究发现在1980–2021期间全球6个海域每年热带气旋的发生频次和强度具有显著年代际变化规律, 最近几十年, 北大西洋和北印度洋的热带气旋发生频次明显增加, 但西北太平洋的热带气旋却显著下降. 另外三个海域, 东太平洋, 南印度洋和南太平洋发现所生成的热带气旋有减少趋势. 但在过去十几年, 平均热带气旋的强度除了在东太平洋和北大西洋有所减弱但在其他几个海域有所加强, 特别是在 2013–2021期间, 北印度洋的平均热带气旋的强度增强明显. 热带气旋的潜在生成指数 (GPI) 增加或减少趋势变化与北印度洋, 北大西洋和西太平洋热带气旋变化相关的大尺度环流一致. 另外, 北印度洋, 北大西洋和西太平洋上空的垂直风切变是影响其区域热带气旋发生频次变化的主要因子, 不同的气候模态也可能对全球热带气旋的趋势变化和年代际变化有影响, 值得进一步研究.     

Distribution of lightning spatial modes and climatic causes in China

This paper investigates the distribution of spatial modes of cloud-to-ground (CG) lightning activity across China's land areas during the period 2010–20 and their possible causes based on the CG lightning dataset of the China National Lightning Detection Network. It is found that the first empirical orthogonal function mode (EOF1) occupies 32.86% of the total variance of the summer CG lightning anomaly variation. Also, it exhibits a negative–positive–negative meridional seesaw pattern from north to south. When the SST of the East Pacific and Indian Ocean warms abnormally and the SST of the Northwest Pacific becomes abnormally cold, a cyclonic circulation is stimulated in the Yellow Sea, East China Sea, and tropical West Pacific region of China. As the water vapor continues to move southwards, it converges with the water vapor deriving from the Bay of Bengal in South China, and ascending motion strengthens here, thus enhancing the CG lightning activity of this area. Affected by the abnormal high pressure, the corresponding CG lightning activities in North China and Northeast China are relatively weak. The ENSO phenomenon is the climate driver for the CG lightning activity occurring in land areas of China.摘要本文利用中国气象局国家雷电监测网 (CNLDN) 的地闪观测数据集, 分析了2010–2020年中国陆地区域地闪空间模态分布特征及其可能的气候成因. 研究发现, 夏季地闪第一模态的方差贡献率为32.86%, 其分布从北到南呈现出“−+−”的经向跷跷板模式. 当东太平洋和印度洋的海温异常增暖, 西北太平洋的海温异常变冷时, 在中国黄海, 东海及热带西太平洋地区激发出气旋性环流. 随着水汽南下至华南地区, 与来自孟加拉湾的水汽汇合, 上升运动在此加强, 从而使得该地区的雷电活动增强. 表明厄尔尼诺-南方涛动 (ENSO) 现象, 是发生在中国陆地区域的地闪活动的气候驱动因子.     

Influence of the pace of El Niño decay on tropical cyclone frequency over the western north pacific during decaying El Niño summers

This study investigated the distinct responses of western North Pacific (WNP) tropical cyclone (TC) activity during different decaying El Niño summers. The El Niño events were classified into two types according to the periodicity of the ENSO cycle, with positive SST anomalies in the equatorial central-eastern Pacific maintaining positive values into the following summer as the slow decaying (SD) cases, but transforming to negative values in the following summer as the rapid decaying (RD) cases. Compared with that in SD El Niño summers, the TC occurrence frequency over the WNP is significantly lower in RD El Niño summers, led by a much weaker WNP monsoon trough with more unfavorable environmental factors for TC genesis and development. Further examination showed that the apparent warming over the tropical Indian Ocean basin and cooling over the equatorial central-eastern Pacific contribute together to an enhanced lower-tropospheric anticyclone through modulation of the descending branch of the large-scale Walker circulation over the WNP, which may play a crucial role in suppressing the TC activity during the decaying summer of RD El Niño cases. In contrast, the warming equatorial central-eastern Pacific and remote western Indian Ocean induce a weakening WNP anticyclone and less suppressed deep convection during the decaying summer of SD El Niño cases. Thus, the different evolution of SST anomalies associated with different paces of El Niño decay results in the linkage between the preceding winter El Niño and the decreased WNP TC frequency in summer being more (less) robust for RD (SD) El Niño cases.摘要本文分析了El Niño事件衰减速度的差异对衰退年夏季西北太平洋热带气旋 (tropical cyclone, TC) 频数的不同影响. 按照El Niño事件衰减速度不同, 将其划分为迅速衰减 (rapid decaying, RD) 和缓慢衰减 (slow decaying, SD) 的El Niño事件. SD (RD) El Niño事件的衰退年夏季, 赤道中东太平洋海温仍维持正异常 (衰减为负异常) . 与SD El Niño事件相比, RD El Niño事件衰退年夏季西北太平洋TC频数显著减少. 进一步的分析揭示了导致TC频数差异的大尺度环境要素, 指出热带印度洋-太平洋海温异常密切相关的西北太平洋低层反气旋异常在其中起到了关键作用.     

A deep learning–based U-Net model for ENSO-related precipitation responses to sea surface temperature anomalies over the tropical Pacific

SST–precipitation feedback plays an important role in ENSO evolution over the tropical Pacific and thus it is critically important to realistically represent precipitation-induced feedback for accurate simulations and predictions of ENSO. Typically, in hybrid coupled modeling for ENSO predictions, statistical atmospheric models are adopted to determine linear precipitation responses to interannual SST anomalies. However, in current coupled climate models, the observed precipitation–SST relationship is not well represented. In this study, a data-driven deep learning-based U-Net model was used to construct a nonlinear response model of interannual precipitation variability to SST anomalies. It was found that the U-Net model outperformed the traditional EOF-based method in calculating the precipitation variability. Particularly over the western-central tropical Pacific, the mean-square error (MSE) of the precipitation estimates in the U-Net model was smaller than that in the EOF model. The performance of the U-Net model was further improved when additional tendency information on SST and precipitation variability was also introduced as input variables, leading to a pronounced MSE reduction over the ITCZ.摘要SST–降水反馈过程在热带太平洋ENSO演变过程中起着重要作用, 能否真实地在数值模式中表征SST–降水年际异常之间的关系及相关反馈过程, 对于准确模拟和预测ENSO至关重要. 例如, 在一些模拟ENSO的混合型耦合模式中, 通常采用大气统计模型 (如经验正交函数; EOF) 来表征降水 (海气界面淡水通量的一个重要分量) 对SST年际异常的线性响应. 然而在当前的耦合模式中, 真实观测到的降水–SST统计关系还不能被很好地再现出来, 从而引起 ENSO模拟误差和不确定性. 在本研究中, 使用基于深度学习的U-Net模型来构建热带太平洋降水异常场对SST年际异常的非线性响应模型. 研究发现: U-Net模型的性能优于传统的基于EOF方法的模型. 特别是在热带西太平洋海区, U-Net模型估算的降水误差远小于EOF模型的模拟. 此外, 当SST和降水异常的趋势信息作为输入变量也被同时引入以进一步约束模式训练时, U-Net模型的性能可以进一步提高, 如能使热带辐合带区域的误差显著降低.     

Association between tropospheric temperature and tropical cyclone peak intensity over the North Pacific and North Atlantic

台风作为一种灾害性天气,其破坏性大小与自身强度有很大的关系.因此,本项研究利用NCEP-NCAR和MERRA再分析数据,考查了北大西洋,西北太平洋,东北太平洋台风强度峰值与对流层温度的关系.台风强度峰值与大气温度的相关系数,以及极大和极小台风强度峰值下大气温度的差值,共同显示:北大西洋台风强度峰值受到对流层顶低温和对流...     

Different response of North Pacific storm tracks in the upper and lower troposphere to jet strength

The midwinter suppression of North Pacific storm tracks (NPSTs) reflects that the linear relationship between the NPST and baroclinicity breaks in winter. Based on the reanalysis data during the cold seasons of 1979–2019 and a tracking algorithm, this study analyzes the eddy growth process and shows that an enhanced upper-tropospheric jet favors the generation of upper-level eddies on the northeast side of the Pacific jet, but increasingly suppresses the generation of those in the Northwest Pacific. The upper-level eddies generated upstream of the jet core are unable to grow sufficiently throughout the whole cold season, and only those generated downstream of the jet core can grow normally and constitute the main body of the upper-level NPST. By contrast, the main lower-level eddy genesis area and growth area coincide with the baroclinic zone, with the genesis number and local growth rate increasing with the baroclinicity.摘要北太平洋风暴轴的深冬抑制表明风暴轴强度与斜压性之间的线性关系在冬季破裂. 本研究基于1979–2019年冷季的再分析数据和拉格朗日跟踪算法, 对比分析了高低层扰动的具体生长过程. 结果表明太平洋急流的增强有利于高层扰动在急流核东北侧产生, 但却抑制其在西北太平洋的生成. 在急流核上游产生的高层扰动在整个冷季都无法充分发展, 只有在急流核下游产生的高层扰动才能正常生长且它们是构成高层太平洋风暴轴的主体. 相比之下, 低层扰动的生成区和生长区都与斜压区重合, 并且它们的生成数量和局部增长率随着斜压性的增强而增强.     

Detection of the synoptic southeastward-extending Siberian cold high during 1978–2017

To better understand the relationship between anticyclones in Siberia and cold-air activities and temperature changes in East Asia, this study proposes a 2D anticyclone identification method based on a deep-learning model, Mask R-CNN, which can reliably detect the changes in the morphological characteristics of anticyclones. Using the new method, the authors identified the southeastward-extending Siberian cold high (SEESCH), which greatly affects wintertime temperatures in China. This type of cold high is one of the main synoptic systems (45.7%) emerging from Siberia in winter. Cold air carried by SEESCH has a significant negative correlation with the temperature changes in the downstream area, and 52% of SEESCHs are accompanied by cold-air accumulation in North and East China, which has a significant impact on regional cooling. These results provide clues for studying the interconnection between SEESCHs and extreme cold events.摘要为了更好地研究西伯利亚地区反气旋与冷空气活动,东亚地区气温变化之间的关联, 本文提出一种基于Mask R-CNN的反气旋识别方法, 能够较为准确地刻画反气旋形态特征变化. 使用该方法能够识别对中国冬季气温具有较大影响的东南延伸型西伯利亚冷高压(SEESCH), 这种冷高压是冬季出现在西伯利亚地区的主要天气系统之一(45.7%). SEESCH携带的冷空气与下游地区温度变化呈显著负相关, 52%的SEESCH伴随着华北华东地区冷空气聚集, 对区域降温有显著影响. 这些结果为研究 SEESCH 与极端寒冷事件之间的联系提供线索.     

Factors responsible for the increasing trend of mei-yu season rainfall during 1979–2020 over the western and eastern mei-yu domain

The mei-yu season (June–July) rainfall over the mei-yu monitoring domain (MMD) in the Yangtze–Huaihe Basin has shown an increasing trend in recent decades. This study examines the dominant factors responsible for this increasing trend for the period 1979–2020 based on station-observed rainfall and ERA5 reanalysis datasets from the perspective of changes in atmospheric circulation. Although significantly increasing trends exist in the mei-yu season rainfall over the entire MMD, the magnitude of the trends is slightly larger over the eastern MMD (EMMD) than over the western MMD (WMMD). Quantitative diagnoses demonstrate that the relative contributions of anomalous evaporation and moisture advection to the increasing rainfall trend are different between the EMMD and WMMD. The increasing rainfall trend over the WMMD (EMMD) is attributable to increased evaporation (enhanced vertical moisture advection), which is dependent on an anomalous cyclonic circulation in the middle-lower troposphere over the MMD. Such an anomalous cyclone on the northwestern side of the climatological western North Pacific subtropical high facilitates an increase in moisture divergence above 600 hPa over the EMMD, leading to enhanced vertical moisture advection in conjunction with strengthened moisture convergence at 850 hPa. By contrast, the anomalous cyclone favors increasing local evaporation over the WMMD.摘要近几十年来, 江淮流域梅雨监测区 (MMD) 的梅雨期 (6–7月) 降水呈增加趋势. 本文基于1979–2020年台站观测降水资料和ERA5再分析数据, 从大气环流变异的角度揭示了这种长期增加趋势的主要影响因素. 发现在MMD范围内, 梅雨期降水趋势的增幅东部大于西部. 水汽收支定量诊断表明, 异常的蒸发和水汽平流对MMD西部和东部降水增加趋势的相对贡献是不同的. MMD西部 (东部) 的降水趋势主要归咎于增强的局地蒸发 (增强的垂直水汽平流) , 后者又取决于MMD对流层中, 低层的异常气旋环流. 这种位于气候平均的西太平洋副热带高压西北侧的异常气旋有助于MMD东部600 hPa以上的水汽辐散增加, 伴随加强的850 hPa水汽辐合, 从而导致垂直水汽平流的增强. 相反, 该异常气旋则有利于增强MMD西部的局地蒸发.     

Possible contribution of the PDO to the eastward retreat of the western pacific subtropical high: PDO对西太平洋副热带高压年代际东退的可能贡献

Previous studies have demonstrated that the western Pacific subtropical high (WPSH) has experienced an eastward retreat since the late 1970s. In this study, the authors propose that this eastward retreat of the WPSH can be partly attributed to atmospheric responses to the positive phase of the Pacific decadal oscillation (PDO), based on idealized SST forcing experiments using the Community Atmosphere Model, version 4. Associated with the positive phase of the PDO, convective heating from the Indian Peninsula to the western Pacific and over the eastern tropical Pacific has increased, which has subsequently forced a Gill-type response to modulate the WPSH. The resulting cyclonic gyre over the Asian continent and the western Pacific in the lower troposphere is favorable for the eastward retreat of the WPSH. Additionally, the resulting anticyclonic gyre in the upper troposphere is favorable for the strengthening and southward expansion of the East Asian westerly jet, which can modulate the jet-related secondary meridional–vertical circulation over the western Pacific and promote the eastward retreat of the WPSH.摘要以往的研究已证实, 西太平洋副热带高压 (副高) 在1970s后期减弱东退.基于大气模式 (CAM4) 的理想型海温强迫试验, 结果表明:副高的东退可能是大气对于正位相太平洋年代际振荡 (PDO) 的相应.伴随着PDO转变为正位相, 西太平洋至印度半岛以及热带东太平洋的对流加热增强, 大气表现为Gill型响应, 在亚洲大陆至西太平洋上空低层产生气旋性异常, 有利于副高东退.同时, 高层产生反气旋异常, 使得东亚西风急流加强和向南扩展, 进而调节西太平洋上空的次级环流, 进一步有利于副高东退.     

A spatiotemporal 3D convolutional neural network model for ENSO predictions: A test case for the 2020/21 La Niña conditions

Many coupled models are unable to accurately depict the multi-year La Niña conditions in the tropical Pacific during 2020–22, which poses a new challenge for real-time El Niño–Southern Oscillation (ENSO) predictions. Yet, the corresponding processes responsible for the multi-year coolings are still not understood well. In this paper, reanalysis products are analyzed to examine the ocean–atmosphere interactions in the tropical Pacific that have led to the evolution of sea surface temperature (SST) in the central-eastern equatorial Pacific, including the strong anomalous southeasterly winds over the southeastern tropical Pacific and the related subsurface thermal anomalies. Meanwhile, a divided temporal and spatial (TS) 3D convolution neural network (CNN) model, named TS-3DCNN, was developed to make predictions of the 2020/21 La Niña conditions; results from this novel data-driven model are compared with those from a physics-based intermediate coupled model (ICM). The prediction results made using the TS-3DCNN model for the 2020–22 La Niña indicate that this deep learning–based model can capture the two-year La Niña event to some extent, and is comparable to the IOCAS ICM; the latter dynamical model yields a successful real-time prediction of the Niño3.4 SST anomaly in late 2021 when it is initiated from early 2021. For physical interpretability, sensitivity experiments were designed and carried out to confirm the dominant roles played by the anomalous southeasterly wind and subsurface temperature fields in sustaining the second-year cooling in late 2021. As a potential approach to improving predictions for diversities of ENSO events, additional studies on effectively combining neural networks with dynamical processes and mechanisms are expected to significantly enhance the ENSO prediction capability.摘要2020–22年间热带太平洋经历了持续性多年的拉尼娜事件, 多数耦合模式都难以准确预测其演变过程, 这为厄尔尼诺-南方涛动(ENSO)的实时预测带来了很大的挑战. 同时, 目前学术界对此次持续性双拉尼娜事件的发展仍缺乏合理的物理解释, 其所涉及的物理过程和机制有待于进一步分析. 本研究利用再分析数据产品分析了热带东南太平洋东南风异常及其引起的次表层海温异常在此次热带太平洋海表温度(SST)异常演变中的作用, 并构建了一个时空分离(Time-Space)的三维(3D)卷积神经网络模型(TS-3DCNN)对此次双拉尼娜事件进行实时预测和过程分析. 通过将TS-3DCNN与中国科学院海洋研究所(IOCAS)中等复杂程度海气耦合模式(IOCAS ICM)的预测结果对比, 表明TS-3DCNN模型对2020–22年双重拉尼娜现象的预测能力与IOCAS ICM相当, 二者均能够从2021年初的初始场开始较好地预测2021年末 El Niño3.4区SST的演变. 此外, 基于TS-3DCNN和IOCAS ICM的敏感性试验也验证了赤道外风场异常和次表层海温异常在2021年末赤道中东太平洋海表二次变冷过程中的关键作用. 未来将神经网络与动力 模式模式间的有效结合, 进一步发展神经网络与物理过程相结合的混合建模是进一步提高ENSO事件预测能力的有效途径.     

Distinct influential mechanisms of the warm pool Madden–Julian Oscillation on persistent extreme cold events in Northeast China

This study investigates whether and how the Madden–Julian Oscillation (MJO) influences persistent extreme cold events (PECEs), a major type of natural disaster in boreal winter, over Northeast China. Significantly increased occurrence probabilities of PECEs over Northeast China are observed in phases 3 and 5 of the MJO, when MJO-related convection is located over the eastern Indian Ocean and the western Pacific, respectively. Using the temperature tendency equation, it is found that the physical processes resulting in the cooling effects required for the occurrence of PECEs are distinct in the two phases of the MJO when MJO-related convection is consistently located over the warm pool area. The PECEs in phase 3 of the MJO mainly occur as a result of adiabatic cooling associated with ascending motion of the low-pressure anomaly over Northeast Asia. The cooling effect associated with phase 5 is stronger and longer than that in phase 3. The PECEs associated with phase 5 of the MJO are linked with the northwesterly cold advection of a cyclonic anomaly, which is part of the subtropical Rossby wave train induced by MJO-related convection in the tropical western Pacific.摘要 本文利用高分辨率气温数据和热带季节内振荡 (MJO) 实时指数, 研究了1979–2015年冬季MJO活动对中国东北持续性极端低温事件 (PECE) 的影响特征和机理.结果表明:当MJO对流分别位于暖池地区的东印度洋 (位相3) 和西太平洋 (位相5) 时, 中国东北PECE的发生频率显著增加.利用温度方程诊断分析发现MJO两个位相所导致的冷却过程不同: 当 MJO处于位相3时, 中国东北地区为低压异常, 上升运动引起绝热冷却作用; 而位相5所形成的气旋性环流为中国东北地区带来西北风冷平流, 降温过程更强且持续更长时间.     

Intelligent identification of oceanic eddies in remote sensing data via Dual-Pyramid UNet

Oceanic eddies are an omnipresent phenomenon of seawater flow and critical in transporting oceanic energy and material. Consequently, mastering and comprehending the characteristics of ocean eddies through detecting and recognizing eddies contributes to the understanding of oceanography. In traditional oceanography, a series of methods to identify eddies with physical or geometric characteristics have been developed. Deep learning frameworks have recently been applied in the eddy detection field. In this paper, a Dual-Pyramid UNet architecture that combines a pyramid split attention (PSA) module and atrous spatial pyramid pooling (ASPP) is proposed to identify oceanic eddies from remote sensing data. The encoder and decoder parts can effectively integrate low-level and high-level features, thus ensuring that feature information is not lost in large quantities after the nonlinear connection mode. In addition, the PSA and ASPP modules are introduced into the encoding, decoding, and skip connections to enhance feature extraction. Experiments were implemented in two typical study areas—the North Atlantic and South Atlantic. The recognition results demonstrate that Dual-Pyramid UNet can outperform four other competitive AI-based methods, especially for eddy edges and small-scale eddies.摘要海洋涡旋是大洋中重要的组成部分, 对海洋能量和物质的输送至关重要. 海洋涡旋的检测和表征无论是对于海洋气象学, 海洋声学还是海洋生物学等领域都具有重要的研究价值. 本文基于UNet架构, 并结合金字塔分割注意力(PSA)模块和空洞空间卷积池化金字塔(ASPP)构造了Dual-Pyramid UNet模型, 以平面异常和海表面温度数据中进行海洋涡旋的识别. 实验在北大西洋和南大西洋两个涡旋活跃区域进行并选用多个评价指标对识别结果进行评价以证明模型的优异性能.     

Analysis of aerosol distribution variations over China for the period 2045–2050 under different Representative Concentration Pathway scenarios: 不同代表性浓度路径情景下 2045-2050 年中国气溶胶分布变化的分析

The regional air quality modeling system RAMS-CMAQ was applied to simulate the aerosol concentration for the period 2045–2050 over China based on the downscaled meteorological field of three RCP scenarios from CESM (NCAR's Community Earth System Model) in CMIP5. The downscaling simulation of the meteorological field of the three RCP scenarios showed that, compared with that under RCP2.6, the difference in near-surface temperature between North and South China is weakened and the wind speed increases over North and South China and decreases over central China under RCP4.5 and RCP8.5. Under RCP2.6, from 2045 to 2050, the modeled average PM_2.5 concentration is highest, with a value of 40–50 µg m⁻³, over the North China Plain, part of the Yangtze River Delta, and the Sichuan Basin. Meanwhile, it is 30–40 µg m⁻³ over central China and part of the Pearl River Delta. Compared with RCP2.6, PM_2.5 increases by 4–12 µg m⁻³ under both RCP4.5 and RCP8.5, of which the SO₄²⁻ and NH₄⁺ concentration increases under both RCP4.5 and RCP8.5; the NO₃⁻ concentration decreases under RCP4.5 and increases under RCP8.5; and the black carbon concentration changes very slightly, and organic carbon concentration decreases, under RCP4.5 and RCP8.5, with some increase over part of Southwest and Southeast China under RCP8.5. The difference between RCP4.5 and RCP2.6 and the difference between RCP8.5 and RCP2.6 have similar annual variation for different aerosol species, indicating that the impact of climate change on different species tends to be consistent.摘要基于来自于 CMIP5 中 CESM 模式的三种 RCP 情景下的气象场的降尺度模拟, 应用区域空气质量模式系统 RAMS-CMAQ 模拟 2045-2050 年中国地区气溶胶浓度.三种 RCP 情景下气象场的降尺度模拟表明, 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, 华北和华南的近地表温度差减小, 风速在华北和华南地区增加, 在中部地区下降. RCP2.6 情景下, 模拟的 2045 年到 2050 年平均的 PM _2.5浓度在华北平原, 长三角的部分地区和四川盆地最高, 约为 40-50 µg m^–3, 在中国中部和珠三角的部分地区约为 30-40 µg m^–3. 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, PM_2.5增加了 4-12 µg m^–3, 其中在 RCP4.5 和 RCP8.5 下, SO₄^2–和 NH₄⁺的浓度增加, 在 RCP4.5 下, NO^3–浓度降低, 在 RCP8.5 下, NO^3–浓度升高, 在 RCP4.5 和 RCP8.5 下, BC 浓度变化很小, 而 OC 浓度下降, 其中在 RCP8.5 下, 西南和东南部分地区的 OC 有所增加.不同的气溶胶物种浓度在 RCP4.5 和 RCP2.6 之间的差异以及 RCP8.5 和 RCP2.6 之间的差异具有相似的年度变化, 这表明气候变化对不同物种的影响趋于一致.     

山东2009年10月降水气候背景及前期海温与大气环流特征

利用1951—2009年北半球500hPa高度、北太平洋海温、环流特征量、降水等资料,采用相关分析、合成分析、经验函数正交分解(EOF)、子波分析等多种统计技术,对影响山东2009年10月降水趋势的各种因素进行分析和研究。结果表明:山东10月降水大致存在3种降水分布型;在不同时间尺度的气候背景上,2009年10月山东基本处于一个少雨或由少雨向多雨转换的气候阶段;2009年春季加利福尼亚冷流的减弱,2009年6月开始的厄尔尼诺事件及6月起西太平洋副高持续的偏强、偏西、正常或偏南状态,各种指标均指示山东10月降水偏少的可能性大,预测与实况基本吻合。     

Influence of the North American Dipole on ENSO onset as simulated by a coupled ocean-Atmosphere model

北美偶极子(NAD)是热带北大西洋西部和北美东北部的南北向海平面气压异常偶极型模态.以往的观测研究表明,NAD可以有效地影响ENSO事件的爆发.本文利用全球耦合模式FGOALS-g2,评估了NAD与ENSO的关系.结果表明,该模式能较好地重现NAD模态.进一步的分析验证了冬季NAD可以通过强迫冬末春初副热带东北太平洋上空的反气旋和暖海温的出现,在随后的冬季触发El Ni?o事件.此外,在同化NAD实验中,发生El Ni?o事件的概率增加了将近一倍.相比之下,NAO未能在副热带东北太平洋上空引起表面风和海温的异常,因而不能有效地激发次年冬季ENSO事件.     

The impacts of the East Asian subtropical westerly jet on weather extremes over China in early and late summer

Summer weather extremes (e.g., heavy rainfall, heat waves) in China have been linked to anomalies of summer monsoon circulations. The East Asian subtropical westerly jet (EASWJ), an important component of the summer monsoon circulations, was investigated to elucidate the dynamical linkages between its intraseasonal variations and local weather extremes. Based on EOF analysis, the dominant mode of the EASWJ in early summer is characterized by anomalous westerlies centered over North China and anomalous easterlies centered over the south of Japan. This mode is conducive to the occurrence of precipitation extremes over Central and North China and humid heat extremes over most areas of China except Northwest and Northeast China. The centers of the dominant mode of the EASWJ in late summer extend more to the west and north than in early summer, and induce anomalous weather extremes in the corresponding areas. The dominant mode of the EASWJ in late summer is characterized by anomalous westerlies centered over the south of Lake Baikal and anomalous easterlies centered over Central China, which is favorable for the occurrence of precipitation extremes over northern and southern China and humid heat extremes over most areas of China except parts of southern China and northern Xinjiang Province. The variability of the EASWJ can influence precipitation and humid heat extremes by driving anomalous vertical motion and water vapor transport over the corresponding areas in early and late summer.摘要东亚副热带西风急流是影响中国极端天气的重要原因之一, 然而之前的研究主要关注整个夏季急流的变率, 对其早夏和晚夏变率的区别及其对极端天气的影响关注较少. 本文研究了早夏和晚夏东亚副热带西风急流季节内变化特征的区别, 以及这种区别带来的极端天气的差异及其可能的动力学机制. 研究结果表明, 相比于早夏, 晚夏急流季节内变化中心位置偏西偏北, 通过改变垂直运动和水汽输送可以影响极端降水和湿热浪在相应区域的发生概率.     

Distinct patterns of monthly Southern Annular Mode events

The Southern Annular Mode (SAM) is the leading mode of atmospheric variability in the mid–high latitudes of the Southern Hemisphere, representing large-scale variations in pressure and the polar front jet (PFJ). In SAM events, the combination of the SAM and other modes may result in different atmospheric patterns. In this study, a neural-network-based cluster technique, the self-organizing map, was applied to extract the distinct patterns of SAM events on the monthly time scale based on geopotential height anomalies at 500 hPa. Four pairs of distinguishable patterns of positive and negative SAM events were identified, representing the diversity in spatial distribution, especially the zonal symmetry of the center of action at high latitudes—that is, symmetric patterns, split-center patterns, West Antarctica patterns, and a tripole pattern. Although the SAM is well known to be belt-shaped, within the selected SAM events, the occurrence frequency of symmetric patterns is only 23.8%—less than that of West Antarctica patterns. Diverse PFJ variations were found in the symmetric and asymmetric patterns of SAM events. The more asymmetric the spatial distribution of the pressure anomaly, the more localized the adjusted zonal wind anomaly. The adjusted PFJ varied in meridional displacement and strength in different patterns of SAM events. In addition, the entrance and exit of the jet changed in most of the patterns, especially in the asymmetric patterns, which might result in different climate impacts of the SAM.摘要南半球环状模 (SAM) 是南半球中–高纬度地区大气变化的主导模态, 表现为气压和极锋急流 (PFJ) 的大尺度变动, 形成强烈的气候影响. 当SAM事件发生时, 气压场异常可呈现出不同的空间结构. 本文利用自组织映射网络方法对月尺度的SAM事件进行分类, 可识别出四对具有显著差异的正, 负SAM事件类型, 包括对称型, 中心分裂型, 西南极洲型和一种三极型分布. 气压异常的空间分布越不对称, 调整后的纬向风异常越局地化. PFJ的经向位移和强度变化入口和出口的变化, 可能导致了SAM的不同气候影响.     

An interdecadal decrease in extreme heat days in August over Northeast China around the early 1990s 1990年代初东北8月极端高温频次的年代际减少

Northeast China (NEC) witnessed an interdecadal increase in summer extreme heat days (EHDs) around the mid-1990s. The current study reveals that this interdecadal increase only occurs in June and July, while August features a unique interdecadal decrease in EHDs around the early 1990s. Plausible reasons for the interdecadal decrease in EHDs in August are further investigated. Results show that the interdecadal decrease in EHDs in August is due to the deceased variability of daily maximum temperature (T_max). Overall, the variation of the T_max over NEC in August is modulated by the Eurasian teleconnection pattern, Silk Road pattern, and East Asia–Pacific pattern. However, the influence of the Silk Road pattern dramatically weakens after the early 1990s because the meridional wind variability along the westerly jet significantly decreases. The weakened influence of the Silk Road pattern contributes to the decreased T_max variability over NEC. Meanwhile, the convection over the western North Pacific, which accompanies the East Asia–Pacific pattern, presents a significant decrease in variance after the early 1990s, further decreasing the T_max variability over NEC.摘要东北夏季极端高温频次在1990年代中期出现年代际增多.本文指出该年代际增多只出现在6–7月, 而8月则呈现特殊性, 即在1990年代初出现年代际减少.进一步分析表明, 东北8月极端高温频次的年代际减少由日最高温度变率的年代际减小造成.东北日最高温度受到欧亚遥相关,丝绸之路遥相关和东亚-太平洋遥相关的共同调制.1990年代初之后, 西风急流上的经向风变率显著减小, 丝绸之路遥相关对下游的影响减弱, 导致东北日最高温度变率减小.同时, 西北太平洋热带对流的变率也在1990年代初出现年代际减小, 通过东亚-太平洋遥相关使东北日最高温度变率进一步减小.     

Dominant patterns of winter surface air temperature over Central Asia and their connection with atmospheric circulation

The dominant patterns of the winter (December–February) surface air temperature anomalies (SATAs) over Central Asia (CA) are investigated in this study. The first two leading modes revealed by empirical orthogonal function (EOF) analysis represent the patterns by explaining 74% of the total variance. The positive phase of EOF1 is characterized by a monopole pattern, corresponding to cold SATAs over CA, while the positive phase of EOF2 shows a meridional dipole pattern with warm and cold SATAs over northern and southern CA. EOF1 is mainly modulated by the negative phase of the Arctic Oscillation (AO) in the troposphere, and the negative AO phase may be caused by the downward propagation of the precursory anomalies of the stratospheric polar vortex. EOF2 is mainly influenced by the Ural blocking pattern and the winter North Atlantic Oscillation (NAO). The SATAs associated with EOF2 can be attributed to a dipole-like pattern of geopotential height anomalies over CA. The dipole-like pattern is mainly caused by the Ural blocking pattern, and the NAO can also contribute to the northern part of the dipole.摘要本文利用经验正交函数分解方法 (Empirical orthogonal function, EOF) , 针对1979–2019年冬季 (12月–2月) 中亚地区地面气温异常进行了研究. 结果表明, 中亚地区冬季地面气温异常的前两个EOF模态解释方差总占比可达74%. 其中, 第一模态 (EOF1) 正位相为一致型变化, 对应中亚地区气温冷异常; 第二模态 (EOF2) 正位相则为南北偶极型变化, 对应于中亚地区南冷北暖型气温异常. EOF1可能受到冬季北极涛动 (Arctic Oscillation, AO) 负位相的调制, 而AO的负位相则可能来自于前期平流层极涡正位势高度异常下传. EOF2则可能受到乌拉尔山阻塞及冬季北大西洋涛动 (North Atlantic Oscillation, NAO) 的共同调制. 乌拉尔山阻塞可引起中亚区域南北偶极型气温异常, 而冬季NAO可对该偶极型气温异常的北侧产生贡献.     

Strengthened influence of the East Asian trough on spring extreme precipitation variability over eastern Southwest China after the late 1980s

The relationship between variations in the East Asian trough (EAT) intensity and spring extreme precipitation over Southwest China (SWC) during 1961–2020 is investigated. The results indicate that there is an interdecadal increase in the relationship between the EAT and spring extreme precipitation over eastern SWC around the late 1980s. During the latter period, the weak (strong) EAT corresponds to a strong and large-scale anomalous anticyclone (cyclone) over the East Asia–Northwest Pacific region. The EAT-related anomalous southerlies (northerlies) dominate eastern SWC, leading to significant upward (downward) motion and moisture convergence (divergence) over the region, providing favorable (unfavorable) dynamic and moisture conditions for extreme precipitation over eastern SWC. In contrast, during the former period, the EAT-related circulation anomalies are weak and cover a relatively smaller region, which cannot significantly affect the moisture and dynamic conditions over eastern SWC; therefore, the response in extreme precipitation over eastern SWC to EAT is weak over the period. The interdecadal change in the relationship between eastern SWC spring extreme precipitation and the EAT could be related to the interdecadal change in the EAT variability. The large (small) variability of the EAT is associated with significant (insignificant) changes in spring extreme precipitation over eastern SWC during the latter (former) period.摘要本文研究表明东亚大槽强度与中国西南地区东部春季极端降水的关系在20世纪80年代末后显著增强, 这可能与东亚大槽自身变率的年代际变化有关. 在80年代末之后, 东亚大槽的变率显著增强, 其对应的大气环流异常也偏强, 范围偏大, 可以显著影响西南地区东部的水汽和动力条件, 从而引起该地区春季极端降水的显著变化. 而在80年代末之前, 东亚大槽的变率偏弱, 其对应的大气环流异常也偏弱, 范围偏小, 因此不能对西南地区东部春季极端降水的变化产生显著影响.