本期覆盖 2026-06-12 至 2026-06-19，共收录高置信度文章 25 篇，边缘相关 2 篇，待人工核实 1 篇。

本周亮点

亮点 1：Oceanic Spatio‐Temporal Patterns of Vertical Velocities in the Cape Basin and Agulhas Current Retroflection From Two Years of SWOT Altimetry

期刊：GRL ｜ DOI：https://doi.org/10.1029/2025gl120831

English summary

This study uses two years of SWOT altimetry data to reconstruct vertical velocities in the Cape Basin and Agulhas Current Retroflection region, achieving a spatial correlation of 0.6 with a high-resolution model. The work demonstrates the potential of SWOT to observe submesoscale dynamics, which are crucial for understanding ocean circulation and climate. This represents a major methodological advance in satellite oceanography.

中文解读

本研究利用两年的SWOT测高数据，重建了开普盆地和阿古拉斯回流区的垂直速度，与高分辨率模型的空间相关性达到0.6。该工作展示了SWOT观测亚中尺度动力学的潜力，对理解海洋环流和气候具有重要意义，是卫星海洋学方法的重大突破。

亮点 2：Long‐Lived Anticyclonic Eddies Facilitate Convection in the Greenland Sea Over Multiple Consecutive Winters

期刊：GRL ｜ DOI：https://doi.org/10.1029/2026gl123381

English summary

This study reveals that long-lived anticyclonic eddies in the Greenland Sea facilitate deep convection over multiple consecutive winters, a previously undocumented process. Using a model simulation and observations, the authors show that these eddies maintain weak stratification year-round, promoting convection. This challenges the traditional view of convection as a purely seasonal phenomenon and highlights the role of eddies in deep water formation.

中文解读

本研究揭示格陵兰海的长寿命反气旋涡旋可在多个连续冬季促进深层对流，这是此前未记录的过程。通过模型模拟和观测，作者发现这些涡旋全年维持弱层结，促进对流。这挑战了将对流视为纯粹季节性现象的传统观点，并强调了涡旋在深层水形成中的作用。

文章详览

1. JPO — Instabilities of Tidal Currents Flowing Through Bounded Channels: II. Observations in the Hampton-Seabrook Estuary

Abstract

Abstract Strong cross-channel shear of tidal currents through a bounded channel can lead to instabilities in the flow, causing a meandering of the mean along-channel current and potentially the spinoff of large eddies. To estimate the wavenumbers of shear instabilities within the Hampton-Seabrook Estuary, NH, a spatially-lagged array consisting of seven sensors measuring bi-directional horizontal currents and pressure were deployed for one week during the spring tide in May 2021. Using iterative maximum likelihood estimators, wavenumber-frequency spectra are estimated during 3–4 hour periods with approximately steady currents on both the flood and ebb tides. Dominant wavenumbers (± 0.002 – 0.02 m −1 ) of the low frequency motions (0.0006 – 0.01 s −1 ) are resolved and consistent with motions determined from barotropic linear stability analysis described in the companion paper (Kirk and Lippmann, in review ). The instabilities propagate into the inlet on flood tides and out of the inlet on the ebbs, consistent with the expected propagation of unstable modes. The normalized velocity-to-pressure variance ratio at each station shows that the infragravity band is dominated by rigid-lid-like motions characteristic of instabilities. The lack of breaking wave group modulations within the inlet and the presence of the seaward propagating instabilities on the ebb flow indicate that the presence of the instabilities can be attributed to the shear of the tidal current.

中文摘要

摘要 有界通道内潮汐流的强横向切变可导致流动失稳，引起平均沿通道流弯曲并可能产生大尺度涡旋脱落。为估算新罕布什尔州汉普顿-西布鲁克河口内切变不稳定波的波数，于2021年5月大潮期间部署了由七个传感器组成的空间滞后阵列，持续一周测量双向水平流和压力。采用迭代最大似然估计法，在涨潮和落潮期间约3-4小时准稳态流时段内估算了波数-频率谱。低频运动（0.0006–0.01 s⁻¹）的主控波数（±0.002–0.02 m⁻¹）得以解析，其与伴生论文（Kirk and Lippmann, 审稿中）描述的基于正压线性稳定性分析确定的运动特征一致。不稳定波在涨潮时向河口内传播，落潮时向河口外传播，这与不稳定模态的预期传播方向相符。各站点归一化流速-压力方差比表明，次重力频带以刚性盖型运动为主导，此类运动正是不稳定波的特征。河口内缺乏破碎波群调制现象，且落潮流中存在向海传播的不稳定波，表明这些不稳定波可归因于潮汐流的切变作用。

2. JPO — On the stationarity and predictability of internal tides in the northern South China Sea

Abstract

Abstract Internal tides (ITs) in the northern South China Sea exhibit pronounced spatiotemporal variability modulated by complex oceanic background conditions, complicating assessments of their predictability and intrinsic regularity. Using a high-resolution numerical simulation (MITgcm LLC4320), I evaluate IT predictability by quantifying how IT-induced baroclinic sea surface height (SSH) accounts for observed variability in along-track satellite altimetry, and assess IT regularity using both conventional stationarity and a newly developed Dynamical Regularity (DR) index based on Hilbert-Huang Transform. Stationary IT is reasonably captured by the model, whereas non-stationary variability substantially reduces the predictability of the total IT, highlighting the need for data assimilation strategies and improved internal-wave parameterization. Stationarity diagnosed from horizontal kinetic energy and baroclinic energy flux is generally high near the Luzon Strait and along main propagation beams, but results are sensitive to the diagnostic metric and sampling window length. Further analysis of baroclinic SSH suggests that non-stationary ITs retain notable dynamical regularity, rather than behaving random or unpredicatable. By explicitly incorporating variability in instantaneous frequency and energy, DR provides a time-resolved and physically consistent characterization of IT regularity. DR confirms high IT regularity near generation sites and reveals that low-mode ITs maintain pronounced regularity far downstream within the deep basin, in contrast to the downstream decay indicated by stationarity. DR also reveals reduced diurnal IT regularity in the northern Luzon Strait, underscoring the significant role of local dynamics such as the Kuroshio intrusion. Overall, the DR index captures a broader spectrum of IT dynamical behaviors than stationarity, offering a new framework capable of characterizing IT regularity in complex oceanic environments.

中文摘要

摘要：南海北部的内潮（ITs）呈现出显著的时空变异性，这种变异性受复杂海洋背景场调制，增加了对其可预测性和内在规律性评估的难度。利用高分辨率数值模拟（MITgcm LLC4320），通过量化内潮引起的斜压海面高度（SSH）对沿轨卫星测高观测变异的解释程度，评估了内潮的可预测性；同时采用传统平稳性指标和基于希尔伯特-黄变换新发展的动力学规律性（DR）指数，评估内潮的规律性。模型能够合理捕捉平稳内潮，而非平稳变异性显著降低了总内潮的可预测性，凸显了数据同化策略和改进内波参数化的必要性。基于水平动能和斜压能通量诊断的平稳性在吕宋海峡附近及主要传播波束区域普遍较高，但结果对诊断指标和采样窗口长度敏感。对斜压SSH的进一步分析表明，非平稳内潮仍保持显著的动力学规律性，而非表现为随机或不可预测行为。通过显式纳入瞬时频率和能量的变异性，DR提供了时间解析且物理一致的内潮规律性表征。DR证实了生成源附近内潮的高规律性，并揭示低模态内潮在深海盆下游区域仍保持显著规律性，这与平稳性指标所指示的下游衰减形成对比。DR还揭示了吕宋海峡北部日潮内潮规律性的降低，凸显了黑潮入侵等局地动力学的重要作用。总体而言，DR指数比平稳性指标捕捉到更广泛的内潮动力学行为谱，为表征复杂海洋环境中内潮规律性提供了新框架。

3. JC — Projected Arctic Ocean warming accompanied by a restructuring of the overturning at the Fram Strait and the Barents Sea Opening

Abstract

Abstract The Arctic Ocean is warming at over twice the rate of the global average, a phenomenon closely linked to enhanced ocean heat transport into the Arctic. Fram Strait and the Barents Sea Opening play a particularly important role serving as conduits to increased ocean heat transport (OHT) into the Arctic, partially linked to the overturning circulation at the two straits. Here we analyze the overturning at these Arctic gateways in the Community Earth System Model version 2 Large Ensemble over years 1920-2100. In particular, we examine the climatological overturning, determine how it changes under climate forcing, and quantify its contribution to the ocean heat transport. We find that during the 20 th century, the overturning is characterized by a net inflow (outflow) at high (low) densities into (out of) the Arctic Ocean. However, beginning in the early 21 st century, the inflow through both Fram Strait and the Barents Sea Opening shifts to much lower densities associated with the warming of the inflow, while the outflow maintains its original density until 2070. The lightening of the inflow leads to a sign change in the density-space overturning through the straits in high density classes. Both the Fram Strait inflow and outflow strengthen over the 21 st century, enhancing the overturning. This overturning pattern change strengthens OHT by 0.05 PW from 1920-1930 to 2090-2100, accounting for over half of the total OHT increase over that period.

中文摘要

摘要 北冰洋的变暖速度是全球平均水平的两倍以上，这一现象与进入北冰洋的海洋热输送增强密切相关。弗拉姆海峡和巴伦支海开口作为海洋热输送进入北冰洋的重要通道，发挥着尤为关键的作用，其部分原因与这两个海峡的翻转环流有关。本研究利用社区地球系统模型第二版大集合模拟，分析了1920-2100年间这些北极门户的翻转环流。我们重点考察了气候态翻转环流特征，确定了其在气候强迫下的变化方式，并量化了其对海洋热输送的贡献。研究发现，在20世纪，翻转环流表现为高密度层净流入北冰洋、低密度层净流出北冰洋的特征。然而，从21世纪初开始，通过弗拉姆海峡和巴伦支海开口的流入流密度显著降低，这与流入流的变暖有关，而流出流在2070年前保持原有密度。流入流密度的降低导致海峡高密度层在密度空间上的翻转环流符号发生改变。在整个21世纪，弗拉姆海峡的流入流和流出流均增强，从而加强了翻转环流。这种翻转环流模式的变化使得1920-1930年至2090-2100年期间的海洋热输送增强了0.05 PW，占该时期总海洋热输送增加量的一半以上。

4. JC — Spatial and Temporal Characteristics of Vertical Advective Heat Flux in the Arctic Ocean

Abstract

Abstract Vertical advective heat transport helps regulate upper-ocean heat exchange and ocean–ice interaction in the Arctic, yet the respective roles of mean circulation and mesoscale eddies remain poorly quantified. Using a 42-year, high-resolution, eddy-permitting ocean–sea ice reanalysis (RARE), we decompose resolved vertical advective heat flux into mean and eddy components and characterize their variability across Arctic basins. Both components exhibit pronounced cold-season intensification in the surface layer, with a weaker signal extending into the subsurface. Enhanced wind stress curl strengthens Ekman-driven upward mean heat flux along the Atlantic Water (AW) inflow pathway, while reduced stratification promotes more efficient eddy-driven upward redistribution of subsurface heat. Within the Arctic interior, upward advective heat fluxes differ strongly across basins because of contrasts in halocline structure and AW properties. The Canada Basin’s persistent, freshwater-maintained halocline insulates the upper ocean from AW heat, whereas the weaker halocline and shallower, warmer AW in the Eurasian Basin permit much more effective upward heat flux. Interannual variability in surface-layer mean heat flux is dominated by velocity-driven changes linked to large-scale atmospheric forcing, including the Arctic Oscillation, with additional low-frequency Atlantic-related modulation. Overall, these results suggest that Arctic upper-ocean vertical advective heat transport differs fundamentally from the globally integrated heat transport balance, where downward transport by the time-mean circulation is broadly offset by mesoscale eddy-induced upward transport. In the Arctic, salinity-controlled stratification and persistent temperature inversions place warm AW beneath a cold, fresh upper layer, allowing Ekman-driven upwelling to generate upward mean heat flux and play a major role in the spatial and temporal variation of vertical advective heat flux in the upper Arctic Ocean.

中文摘要

摘要 垂直平流热输送有助于调节北冰洋上层海洋热交换和海冰相互作用，然而平均环流与中尺度涡旋各自的作用仍缺乏定量评估。本研究利用一套42年高分辨率涡许可海洋-海冰再分析资料（RARE），将解析的垂直平流热通量分解为平均分量和涡旋分量，并刻画其在不同北冰洋海盆的变率特征。两个分量在表层均呈现显著的冷季增强现象，且较弱信号可延伸至次表层。增强的风应力旋度沿大西洋水（AW）流入路径强化了埃克曼驱动的向上平均热通量，而减弱的层结则促进了涡旋驱动的次表层热量更高效向上再分配。在北冰洋内部，由于盐跃层结构和大西洋水性质的差异，各海盆的向上平流热通量存在显著差异。加拿大海盆由淡水维持的持久盐跃层将上层海洋与大西洋水热量隔离，而欧亚海盆较弱的盐跃层及更浅更暖的大西洋水则允许更有效的向上热通量。表层平均热通量的年际变率主要受与大规模大气强迫（包括北极涛动）相关的流速驱动变化主导，并叠加了与北大西洋相关的低频调制。总体而言，这些结果表明北冰洋上层海洋垂直平流热输送与全球积分的热输送平衡存在根本差异——在后者中，时间平均环流的向下输送被中尺度涡旋诱导的向上输送广泛抵消。而在北冰洋，盐度控制的层结与持续的温度逆温将温暖的大西洋水置于冷而淡的上层之下，使得埃克曼驱动的上升流能够产生向上的平均热通量，并在北冰洋上层垂直平流热通量的时空变化中发挥重要作用。

5. GRL — Long‐Lived Anticyclonic Eddies Facilitate Convection in the Greenland Sea Over Multiple Consecutive Winters

Abstract

Abstract Wintertime open‐ocean convection is a key process in renewing deep water; however, the processes that promote convection on local scale remain poorly understood. We investigate the role of long‐lived anticyclonic eddies in facilitating deep convection in the Greenland Sea using a new model simulation and observations. We find a previously undocumented anticyclonic eddy in the Boreas Basin, in addition to a well‐observed anticyclonic eddy in the Greenland Basin. Both eddies feature year‐round lenses of weak stratification with upper‐domed isopycnals, facilitating convection over multiple winters.

中文摘要

摘要 冬季开阔大洋对流是更新深层水的关键过程；然而，促进局地尺度对流的机制仍知之甚少。我们利用新的模式模拟和观测资料，研究了长寿命反气旋涡在格陵兰海促进深对流中的作用。在博雷亚斯海盆发现了一个此前未被记录的反气旋涡，此外在格陵兰海盆还观测到一个已被充分研究的反气旋涡。这两个涡旋均具有全年存在的弱层结透镜状结构，且等密面呈上凸形态，从而促进了多个冬季的对流过程。

6. GRL — Correcting Underestimated Internal Variability Fails to Reconcile Models With Observed Pacific SST Gradient Strengthening

  • 作者：Yann Planton, Jérôme Vialard, Alexey V. Fedorov, Matthieu Lengaigne, Shayne McGregor, Malte F. Stuecker
  • 发表日期：2026-06-13
  • DOI：https://doi.org/10.1029/2025gl120001

Abstract

Abstract The equatorial Pacific zonal sea surface temperature (SST) gradient has strengthened since 1980, yet fewer than 1% of CMIP6 simulations reproduce this trend. We test whether underestimated internal variability explains this mismatch. Extreme El Niño events enhance interdecadal variability of the gradient, but CMIP6 models simulate them too infrequently, producing low Niño3 SST skewness that correlates (∼0.65) with interdecadal gradient variability. Applying this observational constraint to statistically correct modeled interdecadal gradient variability increases the fraction of simulations exceeding the observed trend to only ∼6%, indicating that enhancing variability alone cannot resolve the discrepancy. One‐third of models with large ensembles display a weak but forced recent strengthening that later reverses. Beyond +1.7°C of global warming, over 95% of simulations project a ∼15% weakening. Together, these results suggest that the recent strengthening includes a substantial externally forced transient component poorly simulated by models, while the projected long‐term weakening is robust.

中文摘要

摘要 自1980年以来，赤道太平洋纬向海表温度（SST）梯度持续增强，但仅有不到1%的CMIP6模拟能够再现这一趋势。我们检验了低估内部变率是否可解释此偏差。极端厄尔尼诺事件增强了该梯度的年代际变率，但CMIP6模式对其模拟频率过低，导致Niño3区SST偏度偏低，且该偏度与年代际梯度变率存在约0.65的相关性。将这一观测约束应用于统计校正后的模式年代际梯度变率后，超过观测趋势的模拟比例仅增至约6%，表明仅增强变率无法解决此差异。三分之一的大集合模式显示出微弱但受强迫驱动的近期增强趋势，该趋势随后发生逆转。当全球增温超过+1.7°C时，超过95%的模拟预测梯度将减弱约15%。综合来看，这些结果表明近期增强包含一个模式模拟不佳的显著外强迫瞬态分量，而预测的长期减弱趋势则具有稳健性。

7. JC — How Does the Ocean Influence the Asian Summer Monsoon Onset Sequence over the Arabian Sea, Bay of Bengal, and South China Sea?

Abstract

Abstract The Asian summer monsoon (ASM) onset exerts significant socioeconomic impacts on densely populated coastal regions of Asia, affecting vulnerable populations who rely on monsoon rains for their livelihoods. However, accurately predicting the ASM onset remains a challenge. This study investigates how the ocean impacts the spatiotemporal sequence of the ASM onset, through diagnostic analysis and numerical experiments. The results reveal that the asynchronous sea surface temperature (SST) warming in the Bay of Bengal (BOB), the eastern South China Sea (SCS), and the Arabian Sea (ArS), driven by premonsoon ocean thermodynamics, plays a key role in modulating this sequence. Sequential spring SST maximum preconditions local atmospheric instability through meridional gradients in moist static energy, driving equatorial intraseasonal oscillations (ISOs) into the ASM subregions and triggering the “BOB–SCS–ArS” sequence of ASM onset. This process manifests in three stages. First, in mid-April, rapid SST warming in the BOB creates a meridional SST gradient, promoting northward ISO propagation from the equatorial Indian Ocean into the BOB, triggering the earliest summer monsoon onset (SMO) at pentad 24. Then, in early May, an SST maximum forms in the eastern SCS, favoring ISO spread into the SCS, and triggers the SCSSMO at pentad 28. Finally, strong ascending over the BOB and SCS induces subsidence over the ArS, suppressing convection and allowing sustained warming until an SST maximum occurs in late May. This promotes northward propagation of tropical ISO, resulting in the Indian SMO around pentad 30. This finding highlights a cross-basin oceanic influence on the interconnected onset of ASM subsystems, complementing previous atmospheric dynamic perspectives. Significance Statement This study proposes a unified cross-basin oceanic mechanism underlying the onset of the Asian summer monsoon (ASM). The results demonstrate that springtime oceanic warming induces an asynchronous northward shift of the meridional SST maximum from the tropical Indian Ocean into the Bay of Bengal, the eastern South China Sea, and the Arabian Sea and preconditions the ASM onset. Our findings highlight the importance of this asynchronous development of regional SST maximum as a key oceanic precursor in modulating the propagation of intraseasonal oscillations, thereby governing the distinct spatiotemporal sequence of the ASM onset. This finding offers implications for improving predictions of ASM onset.

中文摘要

摘要 亚洲夏季风（ASM）的爆发对亚洲人口稠密的沿海地区产生显著的社会经济影响，影响着依赖季风降雨维持生计的脆弱人群。然而，准确预测ASM的爆发仍是一项挑战。本研究通过诊断分析和数值实验，探讨海洋如何影响ASM爆发的时空序列。结果表明，由季风前海洋热力学驱动的孟加拉湾（BOB）、南海东部（SCS）和阿拉伯海（ArS）海表温度（SST）的非同步增暖，在调节这一序列中起着关键作用。春季SST最大值通过湿静力能的经向梯度预先调节局地大气不稳定性，驱动赤道季节内振荡（ISOs）进入ASM子区域，并触发“BOB–SCS–ArS”的ASM爆发序列。这一过程表现为三个阶段。首先，在4月中旬，BOB的快速SST增暖形成经向SST梯度，促进赤道印度洋的ISO向北传播进入BOB，在候24触发最早的夏季风爆发（SMO）。随后，在5月初，SCS东部形成SST最大值，有利于ISO向SCS扩展，并在候28触发SCSSMO。最后，BOB和SCS上空的强上升气流在ArS诱导下沉，抑制对流，使得持续增暖直至5月下旬出现SST最大值。这促进了热带ISO的向北传播，导致印度SMO在候30左右爆发。这一发现揭示了跨海盆海洋影响对ASM子系统相互关联爆发的调控作用，补充了以往的大气动力学视角。意义声明 本研究提出了一个统一的跨海盆海洋机制，用于解释亚洲夏季风（ASM）的爆发。结果表明，春季海洋增暖导致经向SST最大值从热带印度洋非同步地向北移动至孟加拉湾、南海东部和阿拉伯海，并为ASM爆发预先创造条件。我们的发现强调了区域SST最大值这种非同步发展作为关键海洋前兆的重要性，它通过调节季节内振荡的传播，从而控制ASM爆发的独特时空序列。这一发现为改进ASM爆发的预测提供了启示。

8. JC — Characterizing Temperature and Precipitation Tails via Expected Shortfall Regression

Abstract

Abstract Global warming contributes to changes in local temperature and precipitation distributions. These shifts alter key statistical properties such as the mean, variance, and frequency of severe climate events, making accurate predictions more complex. In this study, we analyze temperature and precipitation data from the National Oceanic and Atmospheric Administration’s (NOAA) Twentieth Century Reanalysis Project, covering the period from 1950 to 2015 across the continental United States. We employ the expected shortfall (ES) regression method to examine trends in temperature and precipitation relative to time and El Niño–Southern Oscillation (ENSO). Unlike quantile regression, which focuses on specific conditional quantiles such as the median, ES provides insights into averages beyond a certain quantile, offering a more comprehensive description of the tails. Our findings reveal notable differences between ES and mean and quantile regression results, highlighting distinct spatial and temporal trends on interannual-to-decadal time scales. Specifically, ES regression captures significant temperature increases over the decadal time scale, especially in the upper tails, across the southern and central United States, which supports the disappearance of “global warming hole” over the recent decades. Additionally, ENSO events, particularly El Niño, are found to intensify cooling effects in the Gulf Coast region during the winter, particularly for upper tails. The findings demonstrate the usefulness of expected shortfall regression in estimating temperature and precipitation distributions and characterizing changes in the tails. Significance Statement This study employs expected shortfall (ES) regression to analyze the tails of temperature and precipitation distributions across the United States, focusing on how these tail behaviors vary over time, especially in relation to El Niño–Southern Oscillation (ENSO). ES regression provides insights into the events beyond high quantile levels, such as intense heat waves and heavy rainfall, which are critical for understanding the risks associated with climate change. The findings underscore the importance of incorporating tail behavior when analyzing climate variability, which has direct implications for policy decisions and societal adaptation strategies in the face of global warming.

中文摘要

摘要：全球变暖导致局地温度和降水分布发生变化。这些变化改变了均值、方差及极端气候事件频率等关键统计属性，使得精确预测变得更加复杂。本研究利用美国国家海洋和大气管理局（NOAA）二十世纪再分析项目提供的1950年至2015年美国大陆地区温度和降水数据，采用预期短缺（ES）回归方法分析温度和降水随时间及厄尔尼诺-南方涛动（ENSO）的变化趋势。与仅关注特定条件分位数（如中位数）的分位数回归不同，ES回归可提供超过某分位数水平的平均值信息，从而更全面地描述分布尾部特征。研究结果表明，ES回归与均值回归及分位数回归结果存在显著差异，揭示了年代际至年际时间尺度上独特的时空变化趋势。具体而言，ES回归捕捉到美国南部和中部地区在年代际尺度上显著的增温趋势，尤其是分布上尾部分，这支持了近年来”全球变暖空洞”现象的消失。此外，ENSO事件（特别是厄尔尼诺）会加剧墨西哥湾沿岸地区冬季的降温效应，尤其对分布上尾部分影响显著。本研究证实了预期短缺回归在估算温度和降水分布及刻画尾部变化特征方面的实用价值。意义声明：本研究采用预期短缺（ES）回归分析美国全境温度和降水分布的尾部特征，重点探讨这些尾部行为随时间的变化规律，特别是与厄尔尼诺-南方涛动（ENSO）的关联。ES回归能够揭示超过高分位数水平的事件（如极端热浪和强降水）特征，这对理解气候变化相关风险至关重要。研究结果强调了分析气候变率时纳入尾部行为特征的重要性，为全球变暖背景下的政策制定和社会适应策略提供了直接参考依据。

9. JC — An Observational Study on the Eddy-Driven Dynamics of the Summer Arctic Jets

Abstract

Abstract During July and August, a secondary westerly jet exists near 70°N, collocated with a thermally direct circulation. This thermally driven jet is accompanied by intraseasonal variability of zonal-mean zonal wind 5°–10° north of its core, which exceeds that of the winter midlatitude jet. This Arctic jet variability is driven first by eddy momentum flux in the upper troposphere, followed by poleward heat flux near the surface. This sequence is opposite to that of the canonical baroclinic life cycle. During its westerly phase, this eddy-driven jet peaks at 76°N, and the climatological thermally driven jet disappears altogether. This transient jet is referred to here as the Arctic eddy-driven jet (AEJ). In this study, the dynamics of this AEJ is explored using observational analysis. At the initial stage of development, the zonal-mean flow satisfies the Rayleigh–Kuo criterion for barotropic instability. The region of negative potential vorticity (PV) gradient is located at the local jet minimum, centered at ∼60°N, between the midlatitude jet and the climatological thermally driven jet. Consistently, across the region of the negative PV gradient and the positive PV gradient to its north, the eddies tilt against the meridional shear of the zonal wind. This eddy tilt drives the AEJ. Once the AEJ is established, anomalously positive poleward heat fluxes emerge in the lower troposphere. A thermodynamic energy budget analysis reveals that the overturning circulation induced by the initial momentum forcing contributes to the formation of subsequent heat flux anomalies. The easterly phase follows a similar sequence with opposite signs but, during its development, lacks the signatures of barotropic instability.

中文摘要

摘要 在7月至8月期间，70°N附近存在一支次级西风急流，与热力直接环流相伴随。这支热力驱动的急流在其核心以北5°–10°范围内表现出纬向平均纬向风的季节内变率，其强度超过冬季中纬度急流。该北极急流变率首先由对流层上层的涡动动量通量驱动，随后由地表附近的向极热通量驱动。这一序列与经典斜压生命周期的顺序相反。在其西风位相期间，这支涡动驱动的急流在76°N达到峰值，而气候态的热力驱动急流则完全消失。这支瞬变急流在此被称为北极涡动驱动急流（AEJ）。本研究利用观测分析探讨了该AEJ的动力学机制。在发展初期，纬向平均流满足正压不稳定的瑞利-郭准则。负位势涡度（PV）梯度区域位于局地急流最小值处，中心约在60°N，介于中纬度急流与气候态热力驱动急流之间。一致地，在负PV梯度区域及其北侧的正PV梯度区域，涡动相对于纬向风的经向切变发生倾斜。这种涡动倾斜驱动了AEJ。一旦AEJ建立，对流层低层出现异常偏强的向极热通量。热力学能量收支分析表明，初始动量强迫引起的翻转环流对后续热通量异常的形成有所贡献。东风位相遵循类似的序列但符号相反，然而在其发展过程中缺乏正压不稳定的特征。

10. JC — Interannual Variability of Winter Strong and Weak Marine Cold-Air Outbreak Frequency in the Extratropical Northern Hemisphere: Observation and CMIP6 HighResMIP Simulation

Abstract

Abstract This study investigates the interannual variability of the winter strong and weak marine cold-air outbreak (MCAO) frequency in the extratropical Northern Hemisphere, using fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5) reanalysis and simulations from eight state-of-the-art CMIP6 High-Resolution Model Intercomparison Project (HighResMIP) models. In the ERA5 reanalysis, we found two distinct modes in the interannual variability of winter strong and weak MCAO frequency. The positive phase of the strong MCAO–empirical orthogonal function (EOF) 1 mode is characterized by an increased strong MCAO frequency in the northwestern North Pacific Ocean and a decrease in the North Atlantic Ocean south of Greenland. Conversely, the positive phase of the weak MCAO–EOF1 mode exhibits more frequent weak MCAOs in the central–northern North Pacific and North Atlantic Oceans, coinciding with fewer weak MCAOs in the northwestern Pacific Ocean. The positive phase of the strong MCAO–EOF1 mode is linked to the Scandinavian pattern and the Polar/Eurasia pattern but shows a weak connection to El Niño, implying limited potential for seasonal prediction. In contrast, the positive phase of the weak MCAO–EOF1 mode is not only influenced by the Pacific–North American pattern, the west Pacific pattern, and the east Atlantic pattern but also strongly modulated by El Niño. Further analysis indicates that El Niño conditions modulate convection anomalies in the central–eastern tropical Pacific Ocean and the Gulf of Mexico/Caribbean Sea. The convection anomalies, in turn, excite a stationary Rossby wave train with northward propagation, influencing midlatitude circulation anomalies over the North Pacific and North Atlantic Oceans and, consequently, MCAO frequency in these regions. Most HighResMIP models are also able to reproduce these observed features to some extent. Significance Statement Marine cold-air outbreaks (MCAOs) destabilize the lower troposphere, leading to convection, cloud formation, and high winds. However, prior research has largely overlooked the interannual variations in the occurrence frequency of strong and weak MCAOs across the Northern Hemisphere, in both observational studies and numerical simulations. This study addresses that gap, revealing distinct characteristics in the interannual frequency variations of strong and weak winter MCAOs in the extratropical Northern Hemisphere. Furthermore, CMIP6 HighResMIP models are shown to reproduce these observed features to a fair degree.

中文摘要

摘要 本研究利用欧洲中期天气预报中心第五代大气再分析资料（ERA5）及八个最先进的CMIP6高分辨率模式比较计划（HighResMIP）模式的模拟结果，探讨了北半球温带冬季强、弱海洋冷空气爆发（MCAO）频率的年际变率。在ERA5再分析资料中，我们发现冬季强、弱MCAO频率的年际变率存在两种显著模态。强MCAO经验正交函数（EOF）第一模态的正位相表现为西北太平洋强MCAO频率增加，而格陵兰以南的北大西洋强MCAO频率减少。相反，弱MCAO-EOF1模态的正位相则表现为北太平洋中北部和北大西洋弱MCAO更为频繁，同时西北太平洋弱MCAO减少。强MCAO-EOF1模态的正位相与斯堪的纳维亚遥相关型和极地/欧亚遥相关型有关，但与厄尔尼诺现象的联系较弱，表明其季节预测潜力有限。相比之下，弱MCAO-EOF1模态的正位相不仅受太平洋-北美遥相关型、西太平洋遥相关型和东大西洋遥相关型的影响，还受到厄尔尼诺现象的强烈调制。进一步分析表明，厄尔尼诺条件调节了热带中东太平洋和墨西哥湾/加勒比海的对流异常。这些对流异常进而激发向北传播的定常罗斯贝波列，影响北太平洋和北大西洋的中纬度环流异常，从而影响这些区域的MCAO频率。大多数HighResMIP模式也能在一定程度上再现这些观测特征。意义声明 海洋冷空气爆发（MCAO）使对流层低层失稳，导致对流、云形成和强风。然而，以往的研究在观测研究和数值模拟中均很大程度上忽略了北半球强、弱MCAO发生频率的年际变化。本研究填补了这一空白，揭示了北半球温带冬季强、弱MCAO频率年际变化的独特特征。此外，CMIP6 HighResMIP模式被证明能够较好地再现这些观测特征。

11. JC — Interdependent Extratropical Atmospheric Responses to Arctic Sea Ice Loss, QBO, and ENSO

Abstract

Abstract The quasi-biennial oscillation (QBO) and El Niño–Southern Oscillation (ENSO) both influence the strength of the stratospheric polar vortex, with weakening of the polar vortex during the easterly QBO and El Niño. The polar vortex is also thought to weaken in response to Arctic sea ice loss, related to an equatorward shift of the midlatitude jet stream. However, it is unclear how these factors impact the polar vortex in combination and whether their influences are linearly additive. Here, using atmospheric general circulation model experiments, we show that in our model, in the presence of Arctic sea ice loss, the polar vortex weakens significantly during easterly QBO, but not during westerly QBO and weakens significantly during neutral ENSO, but not during El Niño. This suggests that the polar vortex responses to sea ice loss, QBO, and ENSO are interdependent and nonadditive. This interdependence cannot be explained by the polar vortex background state, since the easterly QBO and El Niño both separately weaken the polar vortex but have an opposite-signed influence on the response to sea ice loss. Instead, we surmise the modulation is governed by how QBO and ENSO affect anomalous wave propagation into the stratosphere in response to sea ice loss. At the surface, sea ice loss enhances the Siberian high and causes cooling over Eurasia in QBO easterly phase (QBO-E) but not QBO westerly phase (QBO-W). Both QBO-W and El Niño damp the equatorward tropospheric jet shift in response to sea ice loss, relative to QBO-E or neutral ENSO, respectively. The existence of these nonlinearities has implications for subseasonal-to-interannual climate prediction. Significance Statement This work aims to understand how the atmospheric changes triggered by sea ice loss in the Arctic will differ depending on the background state of the atmosphere. We find that the response to sea ice loss is stronger under certain conditions, meaning sea ice loss is more impactful to humans in years where these conditions are present. The results of this paper have implications for accurate climate prediction, particularly on the expected impacts of climate change.

中文摘要

摘要 准两年振荡（QBO）和厄尔尼诺-南方涛动（ENSO）均影响平流层极涡强度，在QBO东风位相和厄尔尼诺事件期间极涡减弱。极涡也被认为会因北极海冰减少而减弱，这与中纬度急流向赤道偏移有关。然而，尚不清楚这些因素如何共同影响极涡，以及它们的影响是否具有线性可加性。本文利用大气环流模式实验表明，在我们的模式中，当存在北极海冰减少时，极涡在QBO东风位相期间显著减弱，但在QBO西风位相期间未出现显著减弱；在ENSO中性状态期间显著减弱，但在厄尔尼诺事件期间未出现显著减弱。这表明极涡对海冰减少、QBO和ENSO的响应是相互依赖且非可加的。这种相互依赖无法用极涡背景态解释，因为QBO东风位相和厄尔尼诺事件均单独导致极涡减弱，但对海冰减少响应的符号影响相反。相反，我们推测这种调制作用受控于QBO和ENSO如何影响海冰减少引发的异常波动向平流层的传播。在地表，海冰减少在QBO东风位相（QBO-E）期间增强西伯利亚高压并导致欧亚大陆降温，但在QBO西风位相（QBO-W）期间未出现此现象。与QBO-E或ENSO中性状态相比，QBO-W和厄尔尼诺事件均抑制了海冰减少引发的对流层急流向赤道偏移。这些非线性特征的存在对次季节至年际气候预测具有重要意义。意义声明 本研究旨在理解北极海冰减少所引发的大气变化如何因大气背景态不同而存在差异。我们发现，在特定条件下海冰减少的响应更强，这意味着在这些条件出现的年份，海冰减少对人类的影响更为显著。本文结果对准确的气候预测，特别是气候变化预期影响评估具有重要启示。

12. JC — A Winter Predictability Barrier in the Far-Eastern Pacific

Abstract

Abstract The far-eastern Pacific (FEP) sea surface temperature anomaly (SSTA) has sparked renewed interest among scientists after coastal Niño had a huge impact on Peru in 2017. However, its predictability and the way to improve its prediction remain unknown. Our research indicates that the predictability of FEP SSTA is characterized by a winter predictability barrier (WPB), as evidenced by linear inverse model (LIM), convolutional neural networks (CNNs), and seven dynamical models in the North American Multimodel Ensemble (NMME). Through the recharge oscillator model, we observe that the weakest influence of El Niño–Southern Oscillation (ENSO) in winter contributes to the existence of this barrier in FEP, which is caused by wind–evaporation–sea surface temperature (SST) feedback. By employing LIM, we find that the inclusion of South Pacific elements, especially the South Pacific meridional mode (SPMM), can improve the prediction of FEP SSTA (by 20%) and weaken the winter predictability barrier. Significance Statement This research seeks to investigate a newly identified winter predictability barrier (WPB) in sea surface temperature anomalies (SSTAs) of the far-eastern Pacific (FEP), which is different from the well-known spring predictability barrier associated with ENSO. The findings indicate that this WPB results from the seasonal variation in ENSO’s impact on FEP SSTA. Importantly, including climate variability from the South Pacific, especially the South Pacific meridional mode (SPMM), in forecasting models can improve the accuracy of FEP SSTA predictions and help reduce the effects of the WPB.

中文摘要

摘要 远东太平洋（FEP）海表温度异常（SSTA）在2017年沿岸厄尔尼诺对秘鲁造成巨大影响后，重新激发了科学家的研究兴趣。然而，其可预测性及改进预测的方法仍不明确。本研究表明，FEP SSTA的可预测性具有冬季可预测性障碍（WPB）特征，这一结论通过线性逆模型（LIM）、卷积神经网络（CNN）以及北美多模式集合（NMME）中的七个动力模式得到验证。通过充放电振荡模型，我们观察到厄尔尼诺-南方涛动（ENSO）在冬季对FEP的影响最弱，这导致了该障碍的存在，其成因与风-蒸发-海表温度（SST）反馈有关。利用LIM发现，纳入南太平洋要素（尤其是南太平洋经向模（SPMM））可将FEP SSTA的预测能力提升20%，并削弱冬季可预测性障碍。意义声明 本研究旨在探究远东太平洋（FEP）海表温度异常（SSTA）中新发现的冬季可预测性障碍（WPB），该障碍不同于ENSO相关的春季可预测性障碍。结果表明，这一WPB源于ENSO对FEP SSTA影响的季节变化。重要的是，在预测模型中纳入南太平洋气候变率（尤其是南太平洋经向模（SPMM））可提高FEP SSTA预测精度，并有助于削弱WPB的影响。

13. JC — Prediction and Optimal Seasonal Precursors of Marine Heatwaves off Western Australia

Abstract

Abstract Marine heatwaves (MHWs) off Western Australia (WA) can cause devastating ecological and socioeconomic impacts. Previous research has shown that WA MHWs are more or less likely to occur depending on the phase of interannual climate variabilities, such as El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD). However, the seasonal characteristics of WA MHW predictability and prediction skill associated with these climate modes remain unclear. To address this, we develop a cyclostationary linear inverse model (CS-LIM) using vertically averaged temperature (VAT) to ∼300-m depth as input, and VAT indices are computed for the WA region and ENSO and IOD domains. We investigate seasonal variations in WA MHW prediction skill and predictability by identifying their seasonally varying optimal initial conditions, evolutions, and the contributions of ENSO and IOD. The optimal initial conditions and evolutions typically feature ENSO and IOD patterns, though their phases, timing, flavors, and intensities vary seasonally. An empirical normal mode analysis identifies three dominant modes with coupled ENSO and IOD features. The first (∼4-yr period) features eastern Pacific (EP) ENSO with weak IOD, and its La Niña and negative IOD dominate MHW growth in austral autumn (∼12-month lead). The second (∼7.5-yr period) features central Pacific (CP) ENSO with IOD, and its La Niña with positive IOD influence growth in austral autumn and winter at both 5- and 20-month leads. The third (∼2.5-yr period) features ENSO and strong IOD, and its La Niña with negative IOD dominates austral winter–summer growth (∼5-month lead), while its El Niño and positive IOD dominate at ∼20-month leads. Significance Statement Marine heatwaves off Western Australia can occur in any season, damaging marine ecosystems. The climate patterns that precede these events, and may provide predictability, vary seasonally. This study uses a cyclostationary linear inverse model, based on Hasselmann’s stochastic climate framework but incorporating seasonality, to examine how two major climate modes, El Niño–Southern Oscillation and the Indian Ocean dipole, act as precursors to marine heatwaves in different seasons and at different lead times. We find that specific combinations of these modes, with different flavors, intensities, and periods, are linked to marine heatwaves in particular seasons, sometimes showing signs months or even more than a year in advance. These insights can help improve seasonal prediction of marine heatwaves off Western Australia.

中文摘要

摘要 西澳大利亚（WA）海域的海洋热浪（MHW）可能对生态和社会经济造成毁灭性影响。已有研究表明，WA海域的MHW发生概率与年际气候变率（如厄尔尼诺-南方涛动（ENSO）和印度洋偶极子（IOD））的相位有关。然而，与这些气候模态相关的WA海域MHW可预测性及预测技巧的季节特征仍不明确。为此，我们利用垂直平均温度（VAT）至约300米深度作为输入，构建了一个循环平稳线性逆模型（CS-LIM），并计算了WA区域以及ENSO和IOD区域的VAT指数。通过识别MHW的季节性最优初始条件、演变过程以及ENSO和IOD的贡献，我们研究了WA海域MHW预测技巧和可预测性的季节变化。最优初始条件和演变通常呈现ENSO和IOD模态，但其相位、时间、类型和强度随季节变化。经验正态模态分析识别出三个与ENSO和IOD耦合的主导模态。第一模态（约4年周期）表现为东太平洋（EP）ENSO伴随弱IOD，其拉尼娜和负IOD主导南半球秋季（约12个月超前）的MHW增长。第二模态（约7.5年周期）表现为中太平洋（CP）ENSO伴随IOD，其拉尼娜与正IOD在5个月和20个月超前时均影响南半球秋季和冬季的MHW增长。第三模态（约2.5年周期）表现为ENSO与强IOD，其拉尼娜与负IOD主导南半球冬季至夏季（约5个月超前）的MHW增长，而其厄尔尼诺与正IOD在约20个月超前时占主导。意义声明：西澳大利亚海域的海洋热浪可在任何季节发生，对海洋生态系统造成破坏。这些事件发生前的气候模态可能提供可预测性，且随季节变化。本研究基于Hasselmann的随机气候框架并引入季节性，利用循环平稳线性逆模型，探讨了厄尔尼诺-南方涛动和印度洋偶极子这两个主要气候模态如何在不同季节和不同超前时间作为海洋热浪的前兆。我们发现，这些模态的不同类型、强度和周期组合与特定季节的海洋热浪相关，有时甚至提前数月或一年以上显现迹象。这些见解有助于改进西澳大利亚海域海洋热浪的季节预测。

14. JC — The Impact of Zonally Symmetric and Asymmetric Climates on Environmental Favorability of Tropical Cyclone Genesis in Coupled Aqua and Ridge Planets

Abstract

Abstract Tropical cyclone (TC) genesis depends on the favorability of the large-scale environment. This study demonstrates how zonal asymmetry shapes tropical atmospheric and oceanic circulations and alters environmental favorability for TC genesis implied by the genesis potential index (GPI). Two idealized coupled climate models are examined, one with (Ridge) and one without (Aqua) an oceanic meridional boundary—Aqua (Ridge) has a zonally symmetric (asymmetric) climate. Ridge has a zonally asymmetric GPI distribution that peaks near the equator over the warm pool with high sea surface temperature (SST) and moves poleward near the cold tongue with low SST, resembling observed GPI pattern in the south Indian Ocean Basin and western South Pacific basin. Despite warmer SSTs near the warm pool, Ridge produces a less favorable environment for TC genesis than Aqua because of enhanced vertical wind shear associated with the Walker circulation and insufficient absolute vorticity due to the equatorward shift of intertropical convergence zone (ITCZ), in addition to overall unfavorable conditions near the cold tongue. In both configurations, the seasonal cycle of GPI follows the seasonal shift of low vertical wind shear. Composite anomalies of GPI during different phases of ENSO-like variability on Ridge are calculated separately to illustrate the change of environmental favorability for TC genesis induced by the interannual variability. GPI decreases (increases) and shifts equatorward (poleward) near the cold tongue during El Niño (La Niña) associated with a weaker (stronger) Walker circulation. Our results demonstrate the value of an idealized model hierarchy for exploring global circulation and TC interactions (including ENSO impacts) within climate models. Significance Statement The purpose of this study is to better understand how the east–west contrast in climates impacts the environmental conditions relevant to the rate and distribution of tropical cyclone formation. We create climate models with and without east–west contrasts by adding an idealized continent to an otherwise water-covered planet. Our results show that a climate with east–west contrasts provides a less favorable environment for tropical cyclone formation compared to a climate without such contrasts. The climate with east–west contrasts also supports tropical variability similar to El Niño, modulating the year-to-year fluctuation in tropical cyclone formation. This study highlights the fundamental role of tropical circulations rooted in east–west contrasts and offers insights into how these circulations affect the environmental favorability for tropical cyclone formation.

中文摘要

摘要 热带气旋（TC）的生成取决于大尺度环境的适宜性。本研究展示了纬向不对称性如何塑造热带大气和海洋环流，并改变由生成潜势指数（GPI）所隐含的TC生成环境适宜性。研究检验了两个理想化的耦合气候模式：一个包含海洋经向边界（Ridge模式），另一个不包含（Aqua模式）——Aqua（Ridge）模式具有纬向对称（不对称）气候。Ridge模式的GPI呈纬向不对称分布，在海表温度（SST）高的暖池附近赤道区域达到峰值，并在SST低的冷舌附近向极地方向移动，与南印度洋海盆和西南太平洋海盆观测到的GPI分布形态相似。尽管暖池附近SST更高，但Ridge模式产生的TC生成环境比Aqua模式更不适宜，原因在于与沃克环流相关的增强的垂直风切变，以及由于热带辐合带（ITCZ）向赤道偏移导致绝对涡度不足，此外冷舌附近整体条件也不利。在两种配置中，GPI的季节循环均随低垂直风切变的季节性移动而变化。分别计算了Ridge模式中类似ENSO变率不同相位期间的GPI合成异常，以说明年际变率引起的TC生成环境适宜性变化。在厄尔尼诺（拉尼娜）期间，与较弱（较强）的沃克环流相关，冷舌附近的GPI减小（增大）并向赤道（极地）偏移。我们的结果证明了理想化模式层级结构在探索气候模式中全球环流与TC相互作用（包括ENSO影响）方面的价值。意义声明 本研究的目的是更好地理解气候的东西向对比如何影响与热带气旋生成速率和分布相关的环境条件。我们通过在一个原本完全被水覆盖的行星上添加理想化大陆，创建了具有和不具有东西向对比的气候模式。结果表明，与没有这种对比的气候相比，具有东西向对比的气候为热带气旋生成提供了更不适宜的环境。具有东西向对比的气候还支持类似于厄尔尼诺的热带变率，从而调节热带气旋生成的年际波动。本研究强调了根植于东西向对比的热带环流的基础性作用，并揭示了这些环流如何影响热带气旋生成的环境适宜性。

15. JC — More Pronounced El Niño–like Warming in Boreal Autumn and Winter under CO2 Removal Scenario

Abstract

Abstract The seasonal sea surface temperature (SST) changes in the tropical Pacific have significant implications for regional climate under greenhouse warming. In a carbon dioxide removal (CDR) scenario, the change in equatorial Pacific SST displays a more pronounced El Niño–like warming pattern induced by a weakened ocean dynamical thermostat effect during CO 2 ramp-down period, but its seasonal variation is less well understood compared to the CO 2 ramp-up period. Through an idealized CDR experiment, we reveal that the seasonal variations in the El Niño–like warming pattern tend to be asymmetric between the CO 2 ramp-up and ramp-down periods, despite achieving the same level of warming specified by the 2°C target set by the Paris Agreement. The El Niño–like warming pattern is strongest in boreal spring during CO 2 ramp-up but stronger in boreal autumn and winter during CO 2 ramp-down. The different seasonal variations in the El Niño–like warming between CO 2 ramp-up and ramp-down arise from the seasonal variations in cross-equatorial northerly changes and corresponding changes in zonal oceanic overturning circulation. During CO 2 ramp-down, the intertropical convergence zone (ITCZ) significantly shifts southward and leads to cross-equatorial northerly wind change. The relatively strong northerly wind change in equatorial Pacific facilitates strong easterly wind changes, which offset the weakened equatorial trade winds in boreal spring and upper-level zonal overturning circulation. The overall weakening in oceanic upper-level zonal overturning circulation becomes strong in May and brings less cold water to the subsurface layer, finally resulting in the stronger El Niño–like SST warming in boreal autumn and winter.

中文摘要

摘要 热带太平洋海表温度（SST）的季节性变化对温室增暖背景下的区域气候具有重要影响。在二氧化碳移除（CDR）情景中，赤道太平洋SST变化呈现出更显著的类厄尔尼诺增暖模态，这是由于CO₂下降阶段海洋动力恒温器效应减弱所致，但其季节变化特征相较于CO₂上升阶段尚不明确。通过理想化CDR实验，我们发现尽管达到《巴黎协定》设定的2°C增暖目标所对应的相同升温水平，类厄尔尼诺增暖模态的季节变化在CO₂上升与下降阶段呈现非对称性：CO₂上升阶段该增暖模态在北半球春季最强，而CO₂下降阶段则在北半球秋季和冬季更为显著。这种季节差异源于跨赤道北风变化及其对应的纬向海洋翻转环流变化的季节特征。在CO₂下降阶段，热带辐合带（ITCZ）显著南移，导致跨赤道北风变化增强。赤道太平洋较强的北风变化有利于产生强东风异常，从而抵消了北半球春季赤道信风减弱及上层纬向翻转环流的削弱。海洋上层纬向翻转环流的整体减弱在5月达到峰值，导致次表层冷水输送减少，最终在北半球秋季和冬季形成更强的类厄尔尼诺SST增暖。

16. JC — Seasonality of Waveguide Teleconnections along the Summertime Polar Front Jet over Eurasia

Abstract

Abstract Waveguide teleconnections along the summertime polar front jet (PFJ) exert strong influences on Eurasian climate extremes, yet their dominant patterns exhibit pronounced subseasonal evolution. Using one-point correlation maps of interannual variability in 250-hPa meridional wind, we document a robust transition from a British–Okhotsk Corridor (BOC)-like pattern in June–July to a British–Baikal Corridor (BBC)-like pattern in August. Energetic diagnostics reveal that this transition reflects a regime change in the nature of the dominant variability. The June–July BOC-like pattern behaves as an internally supported, near-neutral (weakly damped) pattern, characterized by the highest efficiency in extracting and replenishing eddy energy from the basic-state flow. White-noise forcing experiments with an idealized baroclinic model show that the BOC-like structure emerges robustly among the leading low-frequency stochastic response patterns. In contrast, the August BBC-like pattern is less favored energetically but becomes dominant through preferential forcing. Source-region sensitivity analysis consistently points to the Atlantic jet-exit region as the most effective source for exciting the August BBC-like pattern, in line with the climatological peak of transient-eddy feedback there in August. Concurrently, the PFJ waveguide weakens through the season, relaxing the waveguide constraint and permitting enhanced equatorward leakage of wave activity toward the subtropical jet and expanding the teleconnection footprint into subtropical Eurasia, including the East Asian summer monsoon region. These results highlight how subseasonal changes in the mean flow and mean-flow–eddy feedback jointly control PFJ waveguide teleconnections, producing a systematic shift in teleconnection structure and impacts from early to late summer. Significance Statement In summer, stationary Rossby waves guided by the polar front jet (PFJ) can form persistent teleconnections that contribute to extreme weather across Eurasia. Yet these teleconnections do not affect the same regions throughout the season. Here, we show a robust transition in the dominant PFJ pattern from a British–Okhotsk Corridor–like structure in June–July to a British–Baikal Corridor–like structure in August, accompanied by an equatorward expansion of impacts that can reach the East Asian summer monsoon. This transition marks a shift in dynamical control from a near-neutral mode in June–July to a preferentially forced mode in August. It highlights how seasonal changes in internal dynamics reorganize summertime teleconnections and their climate impacts over northern Eurasia.

中文摘要

摘要 沿夏季极锋急流（PFJ）的波导遥相关对欧亚大陆气候极端事件具有显著影响，但其主导模态表现出明显的次季节演变特征。利用250 hPa经向风年际变率的一点相关图，我们揭示了从6-7月类似不列颠-鄂霍次克走廊（BOC）模态到8月类似不列颠-贝加尔走廊（BBC）模态的稳健转变。能量诊断表明，这一转变反映了主导变率性质的模态变化。6-7月的BOC类模态表现为内部维持的近中性（弱阻尼）模态，其特征是从基本态流中提取和补充涡动能量的效率最高。利用理想化斜压模式进行的白噪声强迫实验表明，BOC类结构在主导低频随机响应模态中稳健出现。相比之下，8月的BBC类模态在能量上较不占优，但通过优先强迫成为主导模态。源区敏感性分析一致指出，大西洋急流出口区是激发8月BBC类模态最有效的源区，这与该区域8月瞬变涡动反馈的气候学峰值相一致。同时，PFJ波导随季节减弱，波导约束松弛，使得波活动向副热带急流的赤道向泄漏增强，并将遥相关足迹扩展至包括东亚夏季风区在内的副热带欧亚大陆。这些结果揭示了平均流和平均流-涡动反馈的次季节变化如何共同控制PFJ波导遥相关，从而产生从夏初到夏末遥相关结构及其影响的系统性转变。意义声明 夏季，由极锋急流（PFJ）引导的定常罗斯贝波可形成持续性遥相关，进而导致欧亚大陆的极端天气。然而，这些遥相关在整个夏季并不影响相同区域。本文揭示了主导PFJ模态从6-7月类似不列颠-鄂霍次克走廊结构到8月类似不列颠-贝加尔走廊结构的稳健转变，同时伴随影响范围的赤道向扩展，可波及东亚夏季风区。这一转变标志着动力学控制从6-7月的近中性模态转变为8月的优先强迫模态，凸显了内部动力学的季节性变化如何重组夏季遥相关及其对欧亚大陆北部气候的影响。

17. JC — Attenuated AMOC Decadal Modulations on North Atlantic Upper-Ocean Heat Content under Global Warming in the CESM1-LE

Abstract

Abstract Decadal variability of the Atlantic meridional overturning circulation (AMOC-DV) serves as a key driver of low-frequency variability in meridional ocean heat transport, generating a characteristic dipole pattern in upper-ocean heat content (UOHC) between the subpolar gyre and Gulf Stream regions. This dynamical linkage underpins the predictability of the Atlantic multidecadal variability and its global climate impacts. However, by contrasting the historical (1920–2005) and representative concentration pathway 8.5 (RCP8.5; 2006–2100) experiments in the Community Earth System Model, version 1, Large Ensemble (CESM1-LE), we reveal a significant weakening of the correlation between AMOC-DV and North Atlantic UOHC under global warming, particularly in the subpolar gyre and Gulf Stream regions. The weaker correlation in a warmer future is primarily driven by a weakened AMOC-DV intensity and its related circulation anomalies, along with some climatological changes. For the subpolar gyre region, relative to the historical period, a positive AMOC-DV anomaly during the RCP8.5 period leads to less convergence of upper-ocean warm water, and a weaker mean AMOC further diminishes anomalous warm water transport into this region, both of which suppress AMOC-DV-associated warming. For the Gulf Stream region, a positive AMOC-DV anomaly during the RCP8.5 period, compared with the historical period, produces weaker deep western boundary current anomalies, a smaller southward shift of the Gulf Stream path, and consequently nearly no upper-ocean cooling. Our findings suggest a progressive disconnection between AMOC-DV and North Atlantic UOHC under global warming, challenging current frameworks that rely on AMOC initialization for North Atlantic decadal climate prediction. Significance Statement Previous studies have found that North Atlantic upper-ocean heat content is substantially influenced by decadal variability of the Atlantic meridional overturning circulation (AMOC-DV) during the historical period. Here, using a large ensemble of a model experiment, our study demonstrates that global warming is disrupting this connection seen in simulations over the historical period. This disconnection is attributed to a decline in AMOC-DV intensity, changes in AMOC-DV modulations on oceanic processes, and some climatological changes. Our study suggests significantly diminished AMOC-DV effects on North Atlantic upper-ocean heat content in a warmer future, with far-reaching implications for understanding regional and global climate change.

中文摘要

摘要 大西洋经向翻转环流的年代际变率（AMOC-DV）是经向海洋热输送低频变化的关键驱动因素，在副极地环流与湾流区域的上层海洋热含量（UOHC）中形成特征性偶极子模态。这一动力学联系支撑着大西洋多年代际变率及其全球气候影响的可预测性。然而，通过对比地球系统模型第一版大型集合（CESM1-LE）的历史时期（1920–2005）与代表性浓度路径8.5（RCP8.5；2006–2100）试验，我们发现全球变暖背景下AMOC-DV与北大西洋UOHC的相关性显著减弱，尤其在副极地环流和湾流区域。未来变暖情境下相关性的减弱主要由AMOC-DV强度及其相关环流异常的减弱，以及部分气候态变化共同驱动。对于副极地环流区域，相较于历史时期，RCP8.5时期正AMOC-DV异常导致上层暖水辐合减少，而平均AMOC减弱进一步削弱了进入该区域的异常暖水输送，两者共同抑制了AMOC-DV相关的增暖效应。对于湾流区域，相较于历史时期，RCP8.5时期正AMOC-DV异常产生更弱的深层西边界流异常、更小的湾流路径南移幅度，从而几乎不产生上层海洋冷却效应。我们的研究结果表明，全球变暖下AMOC-DV与北大西洋UOHC之间的关联逐渐脱钩，这对当前依赖AMOC初始化进行北大西洋年代际气候预测的框架构成挑战。意义陈述 前人研究发现历史时期北大西洋上层海洋热含量显著受大西洋经向翻转环流年代际变率（AMOC-DV）影响。本研究通过大型集合模式试验揭示，全球变暖正在破坏历史时期模拟中观测到的这种关联。这种脱钩归因于AMOC-DV强度下降、AMOC-DV对海洋过程调控的改变以及部分气候态变化。研究表明，未来变暖情境下AMOC-DV对北大西洋上层海洋热含量的影响显著减弱，这对理解区域及全球气候变化具有深远意义。

18. JC — The Silk Road Pattern on Intraseasonal Time Scales

Abstract

Abstract This study investigates the characteristics of Silk Road pattern (SRP), a teleconnection pattern embedded in the Asian jet during summer, on intraseasonal time scales. The teleconnection is depicted by the upper-tropospheric meridional wind variability, which is dominated by 10–30-day oscillations, and thus is named biweekly SRP (bSRP) in this paper. Using the basepoints at various longitudes along 40°N, the one-point correlation analysis demonstrates that the bSRP exhibits high consistency for both the intensity and spatial structure, i.e., the bSRP has no preferred locations in the zonal direction. Therefore, we merge the teleconnection patterns for various basepoints to highlight the common features of bSRP. The merged bSRP is characterized by a cyclonic/anticyclonic anomaly on the west/east side of basepoint, with an equivalent barotropic structure. The wave energy propagates eastward at a group velocity of 25° longitude per day, but the phase speed is only about 2° longitude per day, suggesting that the bSRP might be regarded as quasi-stationary waves. The energy analysis shows that the bSRP obtains energy from basic flows mainly through baroclinic energy conversion, which is much more effective compared to barotropic energy conversion. Finally, the bSRP-related climate anomalies are explored, and the results indicate that warmer/cooler temperatures correspond to anticyclonic/cyclonic anomalies, while more/less precipitation tends to correspond to southerly/northerly anomalies. A diagnosis on the quasigeostrophic omega equation suggests that the vorticity advection, caused by the Asian jet and bSRP-related vorticity anomalies, plays a dominant role in inducing vertical velocity and resultant precipitation anomalies.

中文摘要

摘要 本研究探讨了夏季嵌入亚洲急流中的遥相关型——丝绸之路型（SRP）在季节内时间尺度上的特征。该遥相关由上层对流层经向风变率描述，其主导周期为10–30天振荡，因此本文将其称为双周丝绸之路型（bSRP）。利用沿40°N不同经度的基点，单点相关分析表明，bSRP在强度和空间结构上均表现出高度一致性，即bSRP在纬向方向上无特定偏好位置。因此，我们合并不同基点的遥相关型以突出bSRP的共同特征。合并后的bSRP表现为基点西/东侧的气旋/反气旋异常，具有等效正压结构。波能以每天25°经度的群速度向东传播，但相速度仅为每天约2°经度，表明bSRP可被视为准定常波。能量分析显示，bSRP主要通过斜压能量转换从基本流获取能量，其效率远高于正压能量转换。最后，探讨了bSRP相关的气候异常，结果表明：暖/冷温度对应反气旋/气旋异常，而多/少降水倾向于对应南风/北风异常。对准地转ω方程的诊断表明，由亚洲急流和bSRP相关涡度异常引起的涡度平流，在诱导垂直速度及由此产生的降水异常中起主导作用。

19. JC — Deus Ex Machina Long-Term Cooling of the Eastern Pacific Cold Tongue in Ocean Reanalysis Data

Abstract

Abstract The emergence of an observed distinctive, meridionally confined surface cooling trend in the tropical Pacific cold tongue over recent decades contrasts sharply with the rapid warming simulated by most climate models, representing a key unresolved feature of climate change. Ocean-only simulations, even when forced with observed atmospheric conditions, likewise fail to reproduce the observed long-term absence of surface-layer warming over the eastern Pacific cold tongue. Here, we examine the long-term heat budget of the surface layer in the equatorial Pacific using atmospheric and oceanic reanalysis data, quantifying contributions from surface heat fluxes, ocean advection, and vertical diffusion inferred through Richardson number–based diffusivity estimates. In the Ocean Reanalysis System 5 (ORAS5), the observed cold tongue cooling cannot be reproduced by the model’s intrinsic dynamics alone; instead, it depends on a surface heat flux adjustment imposed during data assimilation. A reduction in the warming effect associated with this adjustment in the eastern Pacific cold tongue over time emerges as the dominant contributor to the long-term cooling in the reanalysis data, a deus ex machina obscuring the actual physical drivers of change in the real ocean. We discuss potential origins of this deus ex machina cooling effect, including the influence of analysis increments, uncertainties in surface forcing, and possible problems in the representation of oceanic processes, particularly subsurface turbulent heat flux induced by oceanic mixing processes. This work emphasizes that reanalysis-based assessments remain subject to inherent biases from the ocean models on which they are built. Resolving the discrepancy between observed and simulated Pacific trends will require confronting the structural limitations of models.

中文摘要

摘要 近几十年来，热带太平洋冷舌区域出现了一种独特的、经向受限的观测海表冷却趋势，这与大多数气候模式模拟的快速变暖形成鲜明对比，成为气候变化研究中一个尚未解决的关键特征。仅基于海洋的模拟，即使使用观测到的大气条件进行强迫，也无法再现东太平洋冷舌区域观测到的长期海表层无增温现象。本文利用大气和海洋再分析数据，研究了赤道太平洋海表层的长期热量收支，量化了海表热通量、海洋平流以及基于理查森数估算的垂直扩散系数的贡献。在海洋再分析系统5（ORAS5）中，观测到的冷舌冷却无法仅通过模式的内在动力学机制再现；相反，它依赖于数据同化过程中施加的海表热通量调整。东太平洋冷舌区域这种调整所伴随的增温效应随时间减弱，成为再分析数据中长期冷却的主要贡献者，这是一种“机械降神”式的机制，掩盖了真实海洋中变化的实际物理驱动力。我们讨论了这种“机械降神”冷却效应的潜在来源，包括分析增量的影响、表面强迫的不确定性，以及海洋过程表征中可能存在的问题，特别是海洋混合过程引起的次表层湍流热通量。本研究强调，基于再分析的评估仍受其构建所依赖的海洋模式固有偏差的影响。要解决观测与模拟的太平洋趋势差异，必须直面模式的结构性局限。

20. GRL — Oceanic Spatio‐Temporal Patterns of Vertical Velocities in the Cape Basin and Agulhas Current Retroflection From Two Years of SWOT Altimetry

Abstract

Abstract The Surface Water and Ocean Topography (SWOT) satellite provides a groundbreaking view of sea surface height (SSH) across a 120‐km‐wide swath (20‐km nadir gap), opening new opportunities to reconstruct vertical velocities . Vertical motions play a central role in redistributing properties, influencing climate and ecosystems. Using the effective surface quasigeostrophic framework in the eddy‐rich Agulhas Current Retroflection region, we reconstruct down to 1,000 m. We assess its realism against the 1/60 (∼2 km) INALT60 ocean model, finding a spatial correlation of 0.6. SWOT‐derived reveal pronounced high‐frequency variability, with events lasting several days to one week during which variance more than doubles. The Agulhas Retroflection emerges as a hotspot of enhanced (∼300 m ), driven by strong horizontal strain. This work provides the first quantitative reconstruction of from SWOT in the region and highlights the mission’s potential to quantify vertical exchanges linking the ocean surface and interior.

中文摘要

摘要 地表水与海洋地形（SWOT）卫星提供了横跨120公里宽幅（20公里星下点间隙）的海面高度（SSH）开创性观测视角，为重建垂直流速开辟了新机遇。垂直运动在物质再分布过程中发挥核心作用，深刻影响气候与生态系统。本研究在涡旋活跃的阿古拉斯回流区，基于有效表面准地转框架重建了深达1000米的垂直流速，并通过1/60°（约2公里）分辨率的INALT60海洋模式评估其真实性，发现空间相关系数达0.6。SWOT反演结果揭示了显著的高频变率特征，存在持续数日至一周的事件，期间方差增幅超过两倍。阿古拉斯回流区因强水平应变驱动，成为增强型垂直流速（约300米/天）的热点区域。本研究首次实现了该区域基于SWOT的垂直流速定量重建，凸显了该任务在量化连接海洋表层与内部的垂直交换过程方面的潜力。

21. GRL — Formation and Arrest of a Surface Density Front via Strain‐Driven Frontogenesis

Abstract

Abstract Ocean fronts play a key role in the vertical transport of heat, energy and biogeochemical tracers, but their behavior and life cycle is not well‐understood, especially at smaller scales. We present a large‐eddy simulation of mixed layer frontogenesis capturing the onset of a submesoscale regime from a larger scale, rotation‐dominated front. Frontogenesis shifts the balance between vertical mixing and restratification driven by frontal ageostrophic secondary circulation and the final state is a combination of a small, turbulent arrested region and the restratified remainder of the front, which sits above an unmixed, stable region. The transition to this state is marked by the appearance of down‐front symmetric cells, which coalesce to form a circulation that entrains fluid from the mixed layer base. We describe the results in the context of submesoscale instability and potential vorticity transport and discuss the implications for frontogenesis and frontal arrest in the ocean mixed layer.

中文摘要

摘要 海洋锋面在热量、能量及生物地球化学示踪物的垂直输运中起着关键作用，但其行为与生命周期，尤其是小尺度锋面的特征，尚未得到充分理解。我们通过大涡模拟研究了混合层锋生过程，捕捉了从大尺度、旋转主导的锋面向亚中尺度状态的转变。锋生过程改变了由锋面地转次级环流驱动的垂直混合与再层化之间的平衡，最终状态表现为一个受湍流抑制的小区域与锋面再层化剩余部分的组合，后者位于未混合的稳定区域之上。这一转变的标志是顺锋对称涡胞的出现，这些涡胞合并形成环流，从混合层底部卷吸流体。我们结合亚中尺度不稳定性与位势涡度输运的框架描述了上述结果，并讨论了其对海洋混合层锋生与锋面抑制的启示意义。

22. JC — Climatic Impacts of a Warmer Mediterranean Sea Simulated by the Fully-Coupled Community Earth System Model version 2 (CESM2)

Abstract

Abstract This study presents a set of process-oriented sensitivity experiments using the state-of-the-art fully-coupled Community Earth System Model version 2 (CESM2) for the first time to isolate the role of Mediterranean Sea Surface Temperature (MedSST) anomalies from regional to global scales. Ten-member ensembles of historical simulations (Control) and two Mediterranean Pacemaker experiments (MedP and MedP3) are performed for the 1980–2014 period. MedP aims to achieve an accurate representation of MedSST evolution by applying bias corrections to the model-simulated fields, while MedP3 introduces a +3 °C perturbation to MedP as an idealized experiment to explore the sensitivity of the climate to substantially warmer MedSSTs. The impacts of the bias correction are evaluated by comparing MedP and Control with observational-based data, while the climatic impacts of a warmer Mediterranean are assessed by comparing MedP3 with MedP. MedP improves the representation of surface temperatures over large parts of the Euro-Mediterranean region. Relatedly, there are improvements in precipitation patterns over Anatolia, the Balkans, and Gibraltar, but also degradations in central Europe and the southern Mediterranean Basin. In MedP3, warmer MedSSTs enhance upward-motion and induce anomalous cyclonic surface winds, increasing atmospheric instability and intensifying precipitation. This precipitation enhancement is largely confined to the Mediterranean Sea and adjacent northern land areas, particularly the Anatolian, Italian, and Balkan peninsulas. At the hemispheric scale, MedP3 produces a Northern Hemisphere warming response. The associated interhemispheric thermal contrast shifts the Intertropical Convergence Zone slightly northward, resulting in increased precipitation in the northern tropics. Overall, our study shows that changes in MedSSTs could have climatic impacts on both regional and global scales.

中文摘要

摘要 本研究首次利用最先进的完全耦合社区地球系统模型第二版（CESM2）开展了一系列面向过程的敏感性实验，以单独探究地中海海表温度（MedSST）异常从区域到全球尺度的影响。针对1980–2014年期间，进行了十成员集合的历史模拟（控制实验）以及两个地中海起搏器实验（MedP和MedP3）。MedP实验通过对模型模拟场进行偏差校正，旨在准确再现MedSST的演变过程；而MedP3实验则在MedP基础上引入+3°C扰动，作为理想化实验以探索气候对显著变暖的MedSST的敏感性。通过对比MedP和控制实验与基于观测的数据，评估了偏差校正的影响；而通过对比MedP3与MedP，评估了更暖地中海的气候影响。MedP实验改善了欧亚-地中海地区大部分区域地表温度的模拟表现。相应地，安纳托利亚、巴尔干半岛和直布罗陀地区的降水格局有所改善，但中欧和地中海盆地南部地区的模拟效果出现退化。在MedP3实验中，更暖的MedSST增强了上升运动并诱发异常气旋性地面风，增加了大气不稳定性并加剧了降水。这种降水增强主要局限于地中海及其邻近的北部陆地区域，特别是安纳托利亚、意大利和巴尔干半岛。在半球尺度上，MedP3实验产生了北半球的增温响应。相关的半球间热力对比使热带辐合带略微北移，导致北热带降水增加。总体而言，本研究表明MedSST的变化可能对区域和全球尺度均产生气候影响。

23. GRL — Reduced Distinctiveness of Extreme El Niño Teleconnections in Warmer Climates

Abstract

Abstract In today’s climate, extreme El Niño events (e.g., 1982–1983, 1997–1998) generate stronger and eastward‐shifted teleconnections relative to moderate El Niño and La Niña events, leading to distinct North American impacts such as enhanced rainfall over California and warming over northeastern North America. A multi‐model, multi‐member, multi‐scenario CMIP6 analysis shows that as warming exceeds +2°C, extreme El Niño teleconnections shift even farther eastward (by 20°), weaken (by 33% at +3.5°C over North America) and develop a negative North Atlantic Oscillation–like response, echoing the changes seen in moderate El Niño–Southern Oscillation (ENSO) phases. Extreme El Niño North American impacts become progressively closer to those of moderate events, with little distinctiveness left beyond +3.5°C. Although future teleconnection changes are much stronger for extreme El Niños, their increased frequency and altered future patterns contribute only modestly to the overall change in ENSO teleconnections.

中文摘要

摘要 在当前气候条件下，极端厄尔尼诺事件（如1982–1983年、1997–1998年）相比中等强度厄尔尼诺和拉尼娜事件，会产生更强且向东偏移的遥相关，导致北美地区出现显著影响，例如加利福尼亚州降水增强和北美东北部增暖。基于多模式、多成员、多情景的CMIP6分析表明，当增温超过+2°C时，极端厄尔尼诺遥相关将进一步向东偏移（幅度达20°），强度减弱（在+3.5°C增温下北美地区减弱33%），并发展出类似负北大西洋涛动的响应，这与中等强度厄尔尼诺-南方涛动（ENSO）相位中观测到的变化一致。极端厄尔尼诺对北美的影响将逐渐趋近于中等强度事件的影响，在+3.5°C增温以上时几乎不再具有独特性。尽管未来极端厄尔尼诺的遥相关变化远强于其他事件，但其频率增加和未来格局改变对ENSO遥相关整体变化的贡献仅占较小部分。

24. JC — The Role of Internal Variability in Springtime Arctic Amplification from 1980 to 2022

Abstract

Abstract Arctic amplification (AA) refers to the enhanced warming of the Arctic relative to the global average due to rising greenhouse gases, measured as the ratio of Arctic-mean to global-mean surface air temperature (SAT) trends. From 1980 to 2022, annual-mean AA reached 4.2 (Arctic defined as north of 70°N). Climate models simulate AA but fail to reproduce its magnitude. Sweeney et al. attributed much of this model–observation discrepancy to internal variability. AA shows seasonality and so does the discrepancy. Spring (March–May) shows the largest gap: Observed AA is 4.2, while the multimodel mean is 2.7. This raises several questions: 1) What role does internal variability play in observed spring AA? 2) How does simulated spring AA compare to observations when internal variability is removed? 3) If internal variability is significant, what mechanisms drive it? To address these, we adapted the machine learning algorithm from Sweeney et al., training on simulated multidecadal spring SAT and sea level pressure (SLP) trend maps. Our results show that internal variability enhanced spring Arctic warming by 37% and reduced global warming by 10%. Removing internal variability reconciles the spring AA discrepancy. The estimated internal contribution to Arctic spring warming is supported by an independent dynamical adjustment approach. We identify an atmospheric circulation pattern in observations associated with this internal warming. Observed internal Siberian SAT and SLP trends follow the simulated SAT–SLP relationship but lie at the distribution’s extreme, suggesting models generally underestimate internal variability unless the observed configuration reflects a rare real-world realization. Significance Statement Climate models tend to underestimate how much faster the Arctic is warming compared to the globe, especially in spring. We show that this discrepancy is due to internal variability. Using a machine learning approach, we isolate the effect of internal variability on observed Arctic and global spring temperature trends. Once removed, the difference between observed and modeled Arctic amplification in spring largely disappears. We also identify an observed atmospheric circulation pattern linked to this springtime internal warming, but its anomaly exceeds typical model simulations, indicating underestimated internal variability in the models or a rare real-world realization. This highlights the need to better understand the mechanisms behind this internal variability to improve both future projections and model evaluation.

中文摘要

摘要：北极放大效应（AA）指因温室气体增加导致的北极相对于全球平均的增温增强现象，以北极与全球平均地表气温（SAT）趋势之比衡量。1980至2022年间，年平均AA值达4.2（北极定义为70°N以北区域）。气候模式虽能模拟AA，但无法再现其量级。Sweeney等人将模式与观测的差异主要归因于内部变率。AA具有季节性特征，其差异亦呈现季节性。春季（3-5月）差异最大：观测AA为4.2，而多模式均值为2.7。这引发以下问题：1）内部变率在观测春季AA中起何作用？2）去除内部变率后，模拟春季AA与观测结果如何比较？3）若内部变率显著，其驱动机制为何？为解答这些问题，我们借鉴Sweeney等人的机器学习算法，基于模拟的多年代春季SAT和海平面气压（SLP）趋势图进行训练。结果表明，内部变率使春季北极增温增强37%，同时使全球增温减弱10%。去除内部变率后，春季AA差异得以消除。独立动力调整方法验证了内部变率对北极春季增温贡献的估算结果。我们识别出与此次内部增温相关的观测大气环流模式：观测中内部西伯利亚SAT与SLP趋势遵循模拟的SAT-SLP关系，但处于分布极端，这表明除非观测构型反映罕见的现实世界实现，否则模式普遍低估内部变率。意义声明：气候模式倾向于低估北极相对于全球的增温速率，尤其在春季。我们证明该差异源于内部变率。采用机器学习方法，我们分离了内部变率对观测北极及全球春季温度趋势的影响。去除该影响后，观测与模拟的春季北极放大效应差异基本消失。我们还识别出与春季内部增温相关的观测大气环流模式，但其异常幅度超出典型模式模拟范围，表明模式低估了内部变率或反映了罕见的现实世界实现。这凸显了需深入理解该内部变率背后的机制，以改进未来预估与模式评估。

25. JC — Co-occurrence of Marine Heat Waves in the Northern South China Sea and Dry/Wet Events in Southern China

Abstract

Abstract Compared with individual events, marine heat waves (MHWs) and their co-occurrence with biogeochemical extremes have more severe effects on ecosystems, on which some studies have been done. Most MHWs are controlled by anomalous high pressure systems, which are also key drivers of dry/wet spells. This implies the potential for co-occurrence between MHWs and terrestrial dry/wet events; however, such investigations remain insufficient. In this study, the co-occurrences of MHWs in the northern South China Sea and dry/wet events in southern China are investigated using both observational data and model experiments. The results revealed that 24% of the MHWs coincide with dry events (MHW-Dry), 35% coincide with wet events (MHW-Wet), and 41% occur independently. These co-occurring events are simultaneously driven by atmospheric forcings, with the primary linked to the western North Pacific subtropical high (WNPSH). MHWs under different types of co-occurring events are modulated by atmospheric forcing, with only some differences in the relative importance of shortwave radiation and latent heat flux. During MHW-Dry events, the West Ridge Point (WRP) of the WNPSH is located west of Luzon Island, and dry events occur due to enhanced moisture flux divergence and evapotranspiration. During MHW-Wet events, the WRP of the WNPSH moves to southern Vietnam, and the wet events are attributed to stronger moisture convergence. Further model experiments suggest that the different sea surface temperature anomalies in the tropical Pacific and Indian Oceans contribute to the WRP of the WNPSH during co-occurring events through the Gill response. This study provides new insights into co-occurring land–ocean events and will be helpful for extreme climate prediction. Significance Statement Co-occurring extreme events often lead to more severe or widespread socioeconomic impacts than individual events. This study focuses on co-occurring land–ocean events, providing new insights into understanding the co-occurrence of extreme events across different underlying surfaces. The research clarifies that marine heat waves (MHWs) in the northern South China Sea tend to co-occur with dry/wet events in southern China (SC), with only a 41% probability of occurring independently. Co-occurring land–ocean extreme events are usually driven by one common driving factor, and the western North Pacific subtropical high (WNPSH) and its east–west displacements are identified as the most important factors in this study. Our work not only expands the understanding of the co-occurrence of abnormal MHW-terrestrial events but also offers valuable references for extreme climate prediction in SC.

中文摘要

摘要 与单一事件相比，海洋热浪及其与生物地球化学极端事件的共同发生对生态系统的影响更为严重，已有部分研究对此进行了探讨。大多数海洋热浪受异常高压系统控制，而高压系统也是干/湿期的关键驱动因素，这表明海洋热浪与陆地干/湿事件存在共同发生的可能性；然而，相关研究仍不充分。本研究利用观测数据和模式实验，探讨了南海北部海洋热浪与中国南方干/湿事件的共同发生关系。结果表明，24%的海洋热浪与干旱事件同时发生（MHW-Dry），35%与湿润事件同时发生（MHW-Wet），41%独立发生。这些共同发生事件同时受大气强迫驱动，其中主要与西北太平洋副热带高压（WNPSH）相关。不同类型共同发生事件下的海洋热浪均受大气强迫调制，仅在短波辐射和潜热通量的相对重要性上存在差异。在MHW-Dry事件期间，WNPSH的西脊点（WRP）位于吕宋岛以西，干旱事件因水汽通量辐散增强和蒸散发增加而发生。在MHW-Wet事件期间，WNPSH的西脊点移至越南南部，湿润事件归因于更强的水汽辐合。进一步的模式实验表明，热带太平洋和印度洋不同的海表温度异常通过吉尔响应影响了共同发生事件期间WNPSH的西脊点。本研究为陆地-海洋共同发生事件提供了新见解，并有助于极端气候预测。意义声明 共同发生的极端事件往往比单一事件造成更严重或更广泛的社会经济影响。本研究聚焦于陆地-海洋共同发生事件，为理解不同下垫面极端事件的共同发生提供了新视角。研究阐明了南海北部的海洋热浪倾向于与中国南方的干/湿事件共同发生，仅有41%的概率独立发生。陆地-海洋极端事件的共同发生通常由一个共同的驱动因素主导，本研究确定西北太平洋副热带高压及其东西位移是最重要的因素。我们的工作不仅拓展了对异常海洋热浪-陆地事件共同发生的理解，也为中国南方极端气候预测提供了有价值的参考。

边缘相关条目

命中物理海洋学关键词，但同时涉及其他学科领域，仅供参考。

  • GRL — Eastern Pacific Corals Track Robust ENSO Variability and Stronger La Niña Events 4,000 Years Before Present（DOI: https://doi.org/10.1029/2025gl119006）
    • 命中: ENSO
    • 排除: coral
  • GRL — Seismic Evidence for Slab Tearing Beneath the Indo‐Myanmar Subduction Zone（DOI: https://doi.org/10.1029/2026gl123151）
    • 命中: upwelling
    • 排除: seismic

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  • JPO — Journal Information and Table of Contents
    • 缺失项: 摘要缺失或过短; 作者列表缺失
    • 链接: https://doi.org/10.1175/jpo-567cover