Atmospheric and Oceanic Science Letters最新文献

This paper proposes a global sea surface temperature (SST) bias correction and downscaling unifying model based on the generative adversarial network. The generator of the model uses a bias correction module to correct the numerical model forecasting results. Then it uses a reusable shared downscaling module to improve the resolution of the corrected data gradually. The discriminator of the model evaluates the quality of the bias correction and downscaling results as a criterion for adversarial training. And a physics-informed dynamics penalty term is included in the adversarial loss function to improve the performance of the model. Based on the 1°-resolution SST forecasting results of the GFDL SPEAR (Seamless System for Prediction and Earth System Research) model, the authors select the Remote Sensing System observations as the refined targets and carry out validation experiments for three typical events at different scales and regions (ENSO, Indian Ocean dipole, and oceanic heatwave events). The model reduces the forecasting error by about 90.3% while increasing the resolution to 0.0625°×0.0625°, breaking the limitation of the resolution of the observation data, and the structural similarity with the observation results is as high as 96.46%.

摘要

本文提出了一种基于生成对抗网络的全球海表面温度(sea surface temperature, SST)偏差订正及降尺度整合模型. 该模型的生成器使用偏差订正模块将数值模式预测结果进行校正, 再用可复用的共享降尺度模块将订正后的数据分辨率逐次提高. 该模型的判别器可鉴别偏差订正及降尺度结果的质量, 以此为标准进行对抗训练. 同时, 在对抗损失函数中含有物理引导的动力学惩罚项以提高模型的性能. 本研究基于分辨率为1°的GFDL SPEAR模式的SST预测结果, 选择遥感系统(Remote Sensing System)的观测资料作为真值, 面向月尺度ENSO与IOD事件以及天尺度海洋热浪事件开展了验证试验: 模型在将分辨率提高到0.0625°×0.0625°的同时将预测误差减少约90.3%, 突破了观测数据分辨率的限制, 且与观测结果的结构相似性高达96.46%.

A La Niña condition in the equatorial Pacific began in the early summer of 2020 and has lasted more than two and a half years (referred to as the 2020 La Niña hereafter). Predicting its temporal evolution had attracted a lot of attention. Considering the possible phase-locked impact of the 11-year solar cycle on the tropical Pacific variability, in this study the authors present the possible modulations by the solar cycle 25 (SC25) started from December 2019, on the future temporal evolution of the 2020 La Niña. Based on statistical features of historical solar cycles, the authors propose three possible scenarios of the timing of the SC25 maximum year and discuss its possible impacts on the temporal evolution of the 2020 La Niña in the next two years. The ongoing ascending phase of SC25 dampens the development of a super El Niño condition to some extent in 2023.

摘要

自2020年初夏, 赤道太平洋地区出现拉尼娜现象并持续两年半多(以下简称2020拉尼娜), 对其未来演变的预测引起了很多关注, 考虑到11年太阳周期活动对热带太平洋SST异常可能存在锁相影响, 本研究分析了当前太阳活动周(即第25太阳周(SC25))对目前热带太平洋ENSO现象未来演变的调节作用, 基于历史太阳周的统计特征, 作者对第25太阳周达到其最大值的时间提出三种可能的情景, 并讨论了不同情景下的太阳活动对未来两年ENSO演变的可能影响, 第25太阳周的持续上升阶段在一定程度上抑制了当前2023厄尔尼诺现象发展为超级事件.

The Eurasian surface air temperature (SAT) is experiencing decadal variations against the background of global warming. The prediction skill for the seasonal mean SAT in CMIP6 Decadal Climate Prediction Project (DCPP) models is investigated in this study. The large decadal variations of winter and autumn Eurasian SAT are barely predicted by the CMIP6 models. IPSL-CM6A-LR and the multimodel ensemble have skill in predicting the variations of spring Eurasian SAT, with significant anomaly correlation coefficients, but not for the amplitude, with negative mean-square skill scores. Significant skill is apparent for the summer SAT over Mongolia and North China, with the CMIP6 models showing their best skill for the summer Eurasian SAT. Compared to external forcing, model skills for Eurasian SAT may derive more from the initialization. It should be noted that there are model system errors in the form of false strong relationships of SAT between winter and other seasons when in fact the variations of other seasons’ SATs are independent of the winter SAT in observations.

摘要

评估CMIP6年代际预测试验对季节平均SAT的预测技巧的结果表明: 模式不能有效预测冬季和秋季SAT的年代际变率. IPSL-CM6A-LR和多模式集合平均对于春季SAT展现了预测技巧, 其中对于变率的预测技巧好于振幅的结果. 基于蒙古和我国华北地区的显著预测技巧, 模式对于夏季SAT表现出最佳的预测水平. 与外部强迫相比, 模式对于SAT的预测技巧可能来自初始化. 模式中的一个明显系统性误差值得注意, 即模式中冬季SAT的变率可以持续到其他季节, 而在观测中其他季节的SAT变化与冬季SAT相对独立.

Recent advances in the bridging roles played by the Tibetan Plateau (TP) are reviewed in terms of the remote influence of circulation anomalies over the North Atlantic Ocean on Asian monsoon and El Niño-Southern Oscillation (ENSO) events, and in a clear link between the tropical oceans and Asian climate anomalies. The authors firstly introduce how the winter and spring anomalies in the North Atlantic Ocean affect the seasonal transition over the South Asian monsoon region and subsequent ENSO events on the interannual timescale. A distinct negative sensible heating-baroclinic structure in May over the TP is found to provide an intermediate bridging effect in this Atlantic-Asian-Pacific connection. In summer, the North Atlantic Oscillation is significantly correlated with the variations of East China summer rainfall, and it is the TP's latent heating that plays the bridging role within. On the other hand, such a TP bridging effect also exists in the connection from the tropical oceans to extreme precipitation events over eastern China in summer, and from the midlatitude wave train to the biweekly oscillation of South China rainfall in spring.

摘要

本文回顾了青藏高原桥梁作用方面的最新研究进展, 涉及北大西洋气候异常对春, 夏亚洲季风和厄尔尼诺-南方涛动 (ENSO) 事件的遥相关影响, 热带海洋异常和中国东部极端气候异常之间的联系以及华南春雨的季节内变化等. 介绍了年际时间尺度上, 冬-春季北大西洋海表温度强迫如何影响南亚季风的季节性转变以及随后ENSO事件的触发. 5月份青藏高原上空显著的负感热斜压结构, 为北大西洋影响亚洲季风和ENSO提供了桥梁效应. 夏季北大西洋涛动与华东夏季降水变化显著相关, 高原潜热在这一关系中起着桥梁作用. 另一方面, 这种高原桥梁效应也存在于从热带海洋异常到东亚夏季极端降水事件的连接中, 以及从中纬度波列到华南春雨准双周振荡的联系中.

It has been well documented that the interannual variation of atmospheric convection over the tropical western North pacific (WNP) affects the East Asian climate in summer significantly, and can be influenced by the preceding winter ENSO. However, there is also a large portion of WNP convection variability that cannot be explained by the preceding ENSO. This study suggests that, particularly in July, the WNP convection anomalies are closely associated with a teleconnection pattern of upper-tropospheric circulation anomalies over the Eurasian continent, which is characterized by an anomalous cyclone over Europe, an anticyclone over Central Asia, and a zonally elongated cyclone over East Asia. This teleconnection pattern can also be detected by the first leading mode of upper-tropospheric circulation in July. The authors conclude, based on the present results and those of previous studies, that the teleconnection pattern induces WNP convection anomalies through Rossby wave breaking near the Asian jet exit region, and this impact is comparable to that of the preceding winter ENSO.

摘要

热带西北太平洋大气对流的年际变化对东亚夏季气候有着显著影响, 而且受到前冬ENSO的影响. 然而, 还有相当多的西北太平洋对流年际变化不能由前冬ENSO解释. 本文表明, 7月西北太平洋对流受到欧亚大陆对流层上层遥相关型的显著影响, 且这一影响与前冬ENSO的影响程度相当. 该遥相关型表现为位于欧洲的气旋式环流异常, 中亚的反气旋式环流异常和东亚带状延伸的气旋式环流异常, 并表现为7月对流层上层环流的第一主模态. 基于本文的结果并结合前人的研究, 作者认为这一遥相关型能通过亚洲急流出口区附近的罗斯贝波破碎引起西北太平洋对流异常.

Tropopause folds represent a primary mechanism for stratosphere-troposphere exchange. This study employs a 3D labeling method with ERA5 reanalysis data spanning from 1979 to 2020 to elucidate the spatiotemporal variations of tropopause folds. The results reveal distinct seasonal and regional variations in trends of tropopause folds. Notably, tropopause folds exhibit an increasing trend, with the magnitude varying seasonally. Significant increasing trends of tropopause folds are observed in northern spring, summer, and winter, primarily along subtropical jets. Further analysis reveals that the increase in tropopause folds is related to the strengthening of frontogenesis due to enhanced atmospheric baroclinicity, while the intensification of meridional potential temperature gradients enhances secondary circulations and may further promote an increase in folds activities.

摘要

对流层顶折卷是平流层-对流层物质交换的主要机制. 本研究采用三维标记方法, 利用1979-2020年间的ERA5再分析数据, 分析了对流层顶折卷的时空变化特征及机理. 研究结果表明, 全球对流层顶折卷的多年变化趋势存在明显的季节性和区域性差异. 总体上, 对流层顶折卷呈增加趋势, 其中北半球的春季,夏季和冬季, 对流层顶折卷主要沿副热带急流区呈现明显增加的趋势. 进一步分析表明, 对流层顶折卷发生频率的增加与大气斜压性增大导致的锋生增强有关, 而经向位温梯度的增大使得次级环流增强, 也可能促进了对流层顶折卷活动的增多.

By introducing a linear diagnostic equation to compute perturbation pressure, the vertical momentum equation of the WRF model in the η coordinate is rederived, which constructs a direct relationship between vertical acceleration and physical factors we concern in the deep convection initiation (DCI) process. Important physical processes to the rapid growth of convective cloud are studied, aiming to fully understand the DCI process in the model. It is found that the DCI process is highly related to a cloud-core vertical acceleration. Due to this acceleration, the updraft is strengthened and the cloud is able to develop higher. Based on the diagnostic results of the vertical momentum equation, some different processes contributing to the high-level cloud-core accelerations in the model are found. A divergent pattern of the three-dimensional wind field is favorable for vertical acceleration. An inner physical process is that the horizontally convergent mass should be pumped up instantly by the vertical updraft to sustain a strong vertical acceleration. Second-order vertical inhomogeneity of perturbation geopotential also has an impact. Because of geopotential changes by vertical velocity (geopotential equation), this factor implies larger vertical motions will induce larger accelerations. The effects of the vertical gradient of perturbation potential temperature and moisture may be cancelled out since phase transitions can heat the convective air, but simultaneously decrease the water vapor content. Moisture makes a direct contribution to vertical acceleration, but is mostly cancelled out by the drag of cloud hydrometeors. Clearly understanding the direct impact of the basic prognostic variables on convection may help to identify the reason why DCI predictions within the model fail.

摘要

本文将扰动气压利用一个线性诊断关系代替, 重新推导了WRF模式框架地形追随坐标系下的垂直动量方程, 建立了垂直加速与对流触发 (DCI) 影响因子 (如温度, 水汽等) 的直接联系. 研究发现, DCI过程与对流核垂直加速相关, 三维副散, 扰动位势在垂直方向的二阶非均匀性, 扰动位温垂直梯度, 比湿及其垂直梯度, 水凝物拖曳, 均是能够直接影响垂直加速和对流触发的物理因子, 这些量与模式基本预报量相关, 通过解析基本预报量对对流发展的直接影响, 可能有助于理解模式对DCI过程预测失败的原因.

This study comprehensively assesses the model performance in simulating the variation of the Pacific Decadal Oscillation (PDO) in the winter time (November to March) during the historical period of 1870–2014 using 40 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). Its future change is also investigated under four Shared Socioeconomic Pathway scenarios on the basis of 17 CMIP6 models. Results show that CMIP6 models can reasonably reproduce the observed sea surface temperature anomaly mode associated with the PDO, with high spatial correlation coefficients of above 0.7. However, CMIP6 models generally perform poorly in simulating the variability of the PDO, with low correlation coefficients for most models, except FGOALS-g3 (0.57), GISS-E2-1-H (0.42), and NESM3 (0.37), which present a relatively greater correlation. The multi-model ensemble (MME) outperforms the individual models and can capture the dominant periodicity of the PDO (∼50 years), but it fails to capture the periodicity of ∼20 years. Additionally, the MME result underestimates the variability of the PDO. In response to future warming, the PDO is expected to transfer from a negative to positive phase around the 2050s. The 50-year periodicity of the PDO is projected to decrease compared to the historical period.

摘要

本文基于40个CMIP6模式输出结果, 系统评估了模式对历史时期太平洋年代际振荡(PDO)的模拟性能, 并利用其中17个模式的4种共享社会经济路径情景数据预估了PDO未来可能变化趋势. 结果表明, CMIP6模式能够合理再现PDO相关海表温度异常的空间模态, 但模式模拟PDO位相演变的能力普遍较弱. 多模式集合能够合理再现PDO的50年左右周期, 但无法模拟出其20年左右周期, 并且低估了PDO的变化幅度. 在未来变暖情景下, PDO可能在2050左右出现由负位相向正位相的转变, 同时其50年左右周期也将明显缩短.

The impact of the Atlantic multidecadal variability (AMV) on the East Asian summer climate is analyzed using a set of idealized simulations performed by CESM1. The results show that the AMV exerts a remote impact on the East Asian summer climate via two pathways: a midlatitude Rossby wave train and equatorial Kelvin waves. Specifically, the positive phase of the AMV can enhance the land–sea pressure contrast between the Asian continent and western North Pacific Ocean through the midlatitude Rossby wave train, and induce an anomalous anticyclone in the Northwest Pacific through exciting an equatorial Kelvin wave. These anomalies in atmospheric circulation in turn enhance the East Asian summer monsoon, leading to a northern-wet–southern-dry and warm summer climate in East Asia.