Atmospheric and Oceanic Science Letters最新文献

Summer precipitation in the Three Rivers Source Region (TRSR) of China is vital for the headwaters of the Yellow, Yangtze, and Lancang rivers and exhibits significant interdecadal variability. This study investigates the influence of the East Asian westerly jet (EAWJ) on TRSR rainfall. A strong correlation is found between TRSR summer precipitation and the Jet Zonal Position Index (JZPI) of the EAWJ from 1961 to 2019 (R = 0.619, p < 0.01). During periods when a positive JZPI indicates a westward shift in the EAWJ, enhanced water vapor anomalies, warmer air, and low-level convergence anomalies contribute to increased TRSR summer precipitation. Using empirical orthogonal function and regression analyses, this research identifies the influence of large-scale circulation anomalies associated with the Atlantic–Eurasian teleconnection (AEA) from the North Atlantic (NA). The interdecadal variability between the NA and central tropical Pacific (CTP) significantly affects TRSR precipitation. This influence is mediated through the AEA via a Rossby wave train extending eastward along the EAWJ, and another south of 45°N. Moreover, the NA–CTP Opposite Phase Index (OPI), which quantifies the difference between the summer mean sea surface temperatures of the NA and the CTP, is identified as a critical factor in modulating the strength of this teleconnection and influencing the zonal position of the EAWJ.

摘要

本研究探讨了年代际东亚西风急流的纬向移动对黄河, 长江和澜沧江源头—三江源区夏季降水的影响. 研究发现, 在1961–2019年间, 三江源区夏季降水量与急流纬向位置指数 (JZPI) 在年代际尺度上存在强正相关 (R=0.619, p<0.01) . 当JZPI呈正值, 也就是东亚西风急流向西移动时, 增强的水汽, 温暖的气流和低层辐合异常有助于三江源区夏季降水增加. 北大西洋与中太平洋之间的年代际变化对三江源区的降水有着显著的影响, 主要以北大西洋–欧亚遥相关 (AEA) 方式, 通过沿东亚西风急流向东延伸的罗斯贝波列, 以及45°N以南的另一波列来影响三江源区的降水. 进一步分析发现, 北大西洋与中太平洋反向相位指数 (OPI) 作为一个关键因素, 可量化北大西洋与中太平洋之间夏季平均海表温度的差异, 调控该遥相关的强度并影响急流的纬向位置.

Air quality in China has continued to improve since 2013, although severe pollution events still occur over the North China Plain (NCP). It is noticeable that contributions from secondary pollutants have increased, but understanding of their formation and variations with changing emissions and meteorological conditions remains limited. In this study, the warm season of May to September from 2018 to 2022 was selected to explore the response of secondary pollutants to meteorology and emissions using the Community Multi-scale Air Quality model (CMAQ). Fine particulate matter (PM_2.5) concentrations over the NCP decreased significantly by 31%–37% from 2018 to 2022, while ozone (O₃) and nitrogen dioxide (NO₂) generally showed decreasing trends by 1% and 0.5% per year, respectively. Secondary inorganic aerosol (including sulfate, nitrate, and ammonium) and secondary organic aerosol (SOA) also decreased significantly, by 9% and 6% per year, respectively. The results showed that emissions contributed 96% to the decreases in PM_2.5 concentrations, while O₃ fluctuated due to meteorological changes. Although the decreases in sulfate and ammonium were mainly associated with emission reductions, that of nitrate was more sensitive to meteorological changes. Meteorological and emission changes were similarly important for the overall decrease in SOA, with anthropogenic SOA being more sensitive to emissions control, while biogenic SOA was more easily attributed to meteorological changes. This research emphasizes the importance of controlling anthropogenic emissions in relieving summer secondary pollution in the NCP region.

摘要

自2013年起, 中国空气质量虽改善, 但华北平原(NCP)重污染仍存在且二次污染加剧, 而人们对其成因和变化了解有限. 本研究利用2018–2022年数据, 借助CMAQ模型探讨此污染响应. 结果显示, 在2018–2022年间, PM_2.5浓度显著下降31%–37%, O₃和NO₂的年下降速率分别为1%和0.5%. SIA和SOA也显著减少, 每年分别减少9%和6%. PM_2.5主要因排放减少而下降, 而O₃则受气象影响而波动. 硫酸盐和铵下降的主因是减排, 而硝酸盐对气象变化敏感. 排放和气象变化对SOA的总体减少同样重要, 但人为SOA对排放控制敏感, 生物SOA易受气象变化影响. 研究强调了控制人为排放对缓解NCP地区夏季二次污染的重要性.

Convolutional long short-term memory (ConvLSTM) and convolutional gated recurrent unit (ConvGRU) are two widely adopted deep learning models that combine recurrent mechanisms with convolutional operations for spatiotemporal sequences forecasting. To clarify the convergence speed and classification ability of the above two models, using the same model architecture to predict the same classification problem is necessary. This research treats the district-level warning of short-duration heavy rainfall in Beijing as a binary classification problem in deep learning, and composite radar reflectivity data of the Beijing–Tianjin–Hebei radar network and rainfall data from automatic weather stations in Beijing are used for training and performance evaluation. The results show that the convergence speed of ConvGRU is approximately 25% faster than that of ConvLSTM. The early-warning performances of ConvLSTM and ConvGRU have similar trends with region, time, and rain intensity, but most of the scores of ConvLSTM are higher, and in a few cases, ConvGRU has higher scores.

摘要

卷积长短期记忆单元ConvLSTM和卷积门控循环单元ConvGRU是两种广泛应用的深度学习单元, 通过将循环机制与卷积运算相结合, 常常用于时空序列的预测. 为了明确上述两种模型的收敛速度和分类能力, 需要使用相同的模型架构对相同的分类问题进行预测. 本研究将北京短时强降水区级预警问题看作深度学习中的二分类问题, 使用京津冀雷达网的组合反射率数据和北京区域内的自动气象站降雨数据进行深度学习模型的训练和评估. 结果表明, ConvGRU的收敛速度比 ConvLSTM快约25%. ConvLSTM和ConvGRU的预警性能随地区, 时间, 降雨强度的变化趋势相似, 但大部分ConvLSTM的得分较高, 少数情况下ConvGRU的得分较高.

Cold wave (CW) events in East Asia have a significant impact on the social economy, ecosystems, and human health. Based on daily CW records from October to March during 1980–2019 and K-means clustering, this study identified two types of regional CW (T1 and T2) in China. T1 regional CWs mainly struck Northeast China, whereas T2 regional CWs primarily affected the northern and eastern regions of China. Compared to T1, T2 regional CWs were more intense, lasted longer, and had a broader region of influence. During 1980–2019, there was a significant increase in the frequency of T1 regional CWs, while the frequency of T2 regional CWs showed no trend. Although amplification of the Siberian high was observed in both T1 and T2 regional CW events, there were differences in the wave train patterns in the middle troposphere between the two regional CWs. During T1 regional CW events, a wave train with negative–positive 500-hPa geopotential height anomalies over Siberia–Mongolia weakened the East Asian trough, causing an eastward movement of cold air from Siberia. The increasing trend of T1 regional CW frequency may be attributable to the linear trends of 500-hPa geopotential height caused by global warming. The wave train associated with T2 regional CW events formed ridge–trough–ridge circulation anomalies over the Ural Mountains, Mongolia, and North China. This led to a southeastward intrusion of the cold air. The conclusions of this paper indicate that the Siberian high amplification and mid-tropospheric wave train pattern should be jointly considered in forecasting regional CW events in China.

摘要

寒潮事件对东亚地区的社会经济, 生态系统和人体健康影响巨大. 根据1980−2019 年间10月至次年3月的每日寒潮记录和K-means聚类, 本文识别出了中国两种不同类型的区域性寒潮(T1 和 T2). T1区域性寒潮主要影响东北地区, T2区域性寒潮则主要影响华北和东部地区. 与T1区域性寒潮相比, T2区域性寒潮强度更强, 持续时间更长, 影响范围更广. 1980–2019年期间, T1区域性寒潮的频率显著增加, 而T2区域性寒潮的频率则没有趋势变化. T1和T2区域性寒潮事件均与西伯利亚高压增强有关, 然而与它们相关的对流层中层波列明显不同. 在T1区域性寒潮事件发生期间, 西伯利亚-蒙古上空出现负-正模态的500-hPa位势高度异常波列, 削弱了东亚大槽, 导致西伯利亚冷空气东移. T1区域寒潮频次增加趋势可能与全球变暖引起的500-hPa位势高度的线性趋势变化有关. 与T2区域寒潮事件相关的波列则在乌拉尔山脉, 蒙古和华北地区形成了脊-槽-脊环流异常, 导致冷空气向东南方向入侵. 本文得出结论, 由于两类区域寒潮影响不同, 西伯利亚高压增强和对流层中层波列模态在我国区域性寒潮事件的预报中应综合考虑.

To better understand the mechanisms underlying the formation of blocking highs over the North Atlantic as a type of large-amplitude disturbance, this paper reports results from numerical experiments within the framework of local finite-amplitude wave activity (LWA). The numerical model employed in this study explicitly depicts two important atmospheric internal dynamic processes—nonlinear zonal eddy flux and Rossby wave packet propagation—which have been individually emphasized by different previous studies. The simulation results reveal that these two dynamic processes are the dominant contributors to the formation of Atlantic blocking cases. However, they exert different influences over different regions. The southern and northern parts of the primary LWA associated with the blocking cases are mainly induced by the nonlinear zonal eddy flux and Rossby wave packet propagation, respectively. Thus, this study reconciles and integrates insights from previous studies on Atlantic blocking events, providing a cohesive understanding of their formation.

摘要

为研究北大西洋阻高的形成机制, 本文在局部有限振幅波活动 (LWA) 框架下进行了一系列数值实验. 采用的数值模型能显式地描绘出两种重要的大气内部动力过程, 即非线性纬向位涡通量和Rossby波包传播. 模拟结果显示, 这两种动力学过程均是形成大西洋阻高的重要机理. 具体地, 非线性纬向位涡通量和Rossby波包传播, 分别是大西洋阻高南部和北部LWA形成的主导因子. 因此, 本研究综合了前人关于大西洋阻高的研究成果, 为其形成机理提供了新的认识.

Riverine dissolved inorganic nitrogen (DIN) transport plays an important role in the link between terrestrial and marine ecosystems, while the seasonal changes of water temperature exert a strong control on DIN dynamics. However, the response of the flow of DIN to dynamic water temperature in large rivers is not well known at the global scale. In this study, based on a recently developed land surface model coupled with riverine water temperature and DIN transport schemes, two numerical simulations, with and without dynamic water temperature, were implemented to investigate the seasonal constraint of dynamic water temperature on the change in riverine DIN flow. Results show that the water temperature could be a key controlling factor for the spatial distribution of global DIN flows. After integrating dynamic water temperature estimation into land surface modeling, the annual amplitudes of DIN flow were 5%–25% smaller than before between 30°N and 30°S, while approximately 10% larger in other latitudinal zones. Less denitrification was out of the scope of 40°N–20°S in summer. In eastern China, the dynamic water temperature made the DIN flow reduce by 1%–3% in summer, while it made it increase by 1%–5% in winter. A seasonal constraint of dynamic water temperature, making the amplitude of monthly fluctuation reduce by about 60%, was found in global large rivers. This study shows the importance of dynamic water temperature in the seasonal modeling of riverine DIN flow, and provides a scientific reference for land surface model development and water environment management.

摘要

水体温度变化对河流可溶性无机氮(DIN)输送有着强烈控制作用. 然而, 在全球尺度上河流DIN输送量对水温度变化的响应尚不清楚. 因此, 本文基于陆面过程模式, 耦合河流水温估算和DIN传输方案, 设定有, 无动态水温情景, 对比研究陆面模拟中水温变化对河流DIN通量变化的影响. 结果表明: 在考虑水温动态变化后, 在30°N和30°S之间, DIN通量年振幅减小5%–25%. 在中国东部地区, 水温动态变化使河流DIN通量在夏季减少1%–3%, 在冬季增加1%–5%, 对DIN通量具有明显的季节性约束作用, 表明动态水温的表达在河流DIN输送模拟中的重要性.

The warm core of a tropical cyclone (TC) reflects its intensity and evolution. In the past, microwave sounding data have been widely used for detecting the TC warm core. However, the observed magnitude of the TC warm core can vary with instruments. This study utilizes the oversampling data from the Advanced Technology Microwave Sounder (ATMS) to reconstruct the brightness temperature data consistent with the data from Advanced Microwave Sounding Unit-A (AMSU-A), which is referred to as AMSU-like data. Through comparisons, it is found that brightness temperature from the original ATMS has more detailed structures, depicting well the TC eye region and cloud bands. Both ATMS and AMSU-like data are used as inputs to the Global Scene-Dependent Atmospheric Retrieval Testbed (GSDART) to retrieve the warm cores of multiple TCs. At 250 hPa, the warm-core intensity retrieved using ATMS data is about 1–2 K higher than that from AMSU-like data and the warm-core structure from ATMS is more detailed. It is recommended that the warm-core intensity retrieved from AMSU-A be corrected to the ATMS values for multi-sensor monitoring of TCs using our newly defined relationship.

摘要

热带气旋(TC)的暖心反映了其强度和变化. 微波探测数据被广泛用于探测TC暖心, 但观测到的 TC 暖心强度可能因仪器而异. 本研究利用先进技术微波探测仪 (ATMS) 的过采样数据重采样至与先进微波探测仪 (AMSU-A) 一致的亮温, 称为类-AMSU数据. 通过对比发现, ATMS的观测更加细致, 较好地刻画了TC眼区和云带. 使用ATMS和类-AMSU数据反演多个TC的暖心发现, 在250 hPa, 使用ATMS数据反演的暖心强度比类-AMSU高约1–2K, 并且其暖心结构更详细.

Extreme wildfires broke out in Canada from May 2023 and persisted four months. Tremendous fire emissions posed significant impacts on the air quality in both local and downwind regions. Here, the authors explored the meteorological factors driving this wildfire episode and the associated large-scale circulation. Relative to the mean value of 2001–2022, the 2023 Canadian fires released 0.37 Gt more CO₂ (527.1%) during May–August. Such enhancement was strongly associated with the anomalous surface warming, especially in May–June, when the daily maximum temperature on average increased by 8.11°C, with regional hotspots up to 10°C in central and eastern Canada. Consistent with the surface warming, positive anomalies of geopotential height were observed at high levels in central and western Canada. The dispersion of Rossby waves led to the long-lasting dominance of high-pressure systems and the consequent warming through anomalous subsidence. The phase-locked wave pattern induced by favorable topography and the strong warming tendency in the pan-Arctic regions are expected to jointly escalate the probability of extreme wildfires over central and western Canada in the future.

摘要

2023年5月加拿大发生极端野火事件并持续4个月时间. 野火污染物排放对当地和下风向的空气质量造成了严重影响. 本文对驱动此次野火事件的气象因子和相关大尺度环流进行了探究. 研究表明, 此次极端野火排放的二氧化碳相较往年同期增长了0.37Gt (527.1%) . 受罗斯贝波频散影响, 同期加拿大中西部区域出现持续的位势高度正异常, 促进气流下沉并引发局地高温, 中西部区域5–6月最高温平均上升8.11°C, 部分区域甚至超过10°C, 导致野火排放的显著增长. 受有利地形和泛北极地区快速增暖的影响, 预期未来加拿大中西部发生极端野火的概率可能会显著上升.

The rainfall over North China (NC) in July 2021 was the most since 1980, and coincided with a meridional gradient of sea surface temperature anomaly (MGSSTA) in the Pacific. The present study shows that the gradient between the positive sea surface temperature anomaly (SSTA) over the northwestern Pacific and the negative SSTA over the tropical central Pacific was the main reason for the enhanced rainfall in NC in July 2021 because of its influence on the anomalous northward movements of the western North Pacific anticyclone (WNPAC) and its southern cyclone. The associated easterly wind anomalies along the southern flank of the WNPAC converged with the anomalous easterly along the north flank of the anomalous cyclone, transporting more moisture from south to NC. Meanwhile, the MGSSTA likely induced an anomalous reversed Hadley circulation accompanied by distinct southerly wind anomalies in the low troposphere. These anomalies favored a strong monsoon circulation, which is often accompanied by a rain band in a more northern location.

摘要

2021年7月, 华北地区的降水量突破1980年以来的极值, 这与太平洋海温异常的经向梯度相吻合. 研究表明, 西北太平洋正海温异常与热带中太平洋负海温异常之间的梯度是2021年7月华北地区降水异常偏多的主要原因, 该梯度使得西北太平洋反气旋及其南部的气旋北移, 汇合的偏东风将大量水汽从海洋输送到华北地区, 使得华北地区降水偏多. 同时, 太平洋海温异常的经向梯度可能在对流层低层触发异常的反向哈德利环流, 伴随着南风异常, 使得季风环流增强, 雨带偏北.

Extreme-heat research has largely focused on dry heat, while humid heat, which presents a major societal impact, especially on human health, remains relatively understudied. Previous studies have revealed that a wet-bulb temperature (TW) of 35 °C marks our upper physiological limit, and much lower values also have serious health impacts. Our evaluations from observations showed that the daily maximum TW values over China have been scarcely reported above 35 °C, but humid-heat extreme days of TW above 30 °C have been reported each year during the past four decades, being mainly centered over the highly populated regions, including East China, South China, and the Sichuan basin. Further analyses indicated that the recent rapid urbanization process in China has amplified the societal impacts of humid-heat extremes, and land exposure to humid heat over urban regions is expected to increase at a faster rate than other regions of China. This suggests increasing risks of humid-heat extremes on human health in big cities of densely populated regions due to rapid urbanization. As indicated here, the population of China has become increasingly exposed to such extremes, with a strong increasing tendency of about 3100 persons per day per year since 2000.

摘要

目前对于高温的研究主要侧重于干热, 针对湿热的研究相对较少, 但它通常会造成更大的社会影响, 尤其对人体健康的威胁. 已有研究证实, 当环境湿球温度超过35 °C时, 它会破坏人体正常生理代谢, 进而威胁人体健康. 本研究指出在过去四十年, 中国区域日最高湿球温度几乎没有超过35 °C, 但部分地区日最高湿球温度超过了30 °C, 主要集中在中国的人口密集区, 包括华东, 华南和四川盆地等. 进一步分析发现, 中国区域近期的快速城市化加剧了极端湿热事件的社会影响, 城市地区暴露于极端湿热事件的范围的增加速率明显大于其他地区, 这也意味着快速城市化使得人口密集区暴露于极端湿热事件的风险明显增加. 初步估算指出, 自2000年以来, 中国区域暴露于极端湿热事件的人口数以每年每天约3100人次的速率显著增加.