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1.
Spatially and temporally accurate event detection is a precondition for exploring the mechanisms of climate extremes. To achieve this, a classical unsupervised machine learning method, the DBSCAN (Density-Based Spatial Clustering of Applications with Noise) clustering algorithm, was employed in the present study. Furthermore, the authors developed a 3D (longitude–latitude–time) DBSCAN-based workflow for event detection of targeted climate extremes and associated analysis of parameter sensitivity. The authors applied this 3D DBSCAN-based workflow in the detection of the 2022 summertime Yangtze extreme heatwave and drought based on the ERA5 reanalysis dataset. The heatwave and drought were found to have different development and migration patterns. Synoptic-scale heatwave extremes appeared over the northern Pacific Ocean at the end of June, extended southwestwards, and covered almost the entire Yangtze River Basin in mid-August. By contrast, a seasonal-scale drought occurred in mid-July over the continental area adjacent to the Bay of Bengal, moved northeastwards, and occupied the entire Yangtze River Basin in mid-September. Event detection can provide new insight into climate mechanisms while considering patterns of occurrence, development, and migration. In addition, the authors also performed a detailed parameter sensitivity analysis for better understanding of the algorithm application and result uncertainties.摘要极端气候事件的精准识别是机理分析的重要前提. 本研究借助无监督机器学习中经典的DBSCAN密度聚类算法, 发展了在三维 (经度-纬度-时间) 空间内进行目标事件识别和参数敏感性分析的研究方案. 在2022年长江全域高温伏秋旱事件识别中的应用表明, 本次天气尺度极端热浪和季节尺度重旱事件的产生发展, 空间传播模式不同. 天气尺度热浪信号自6月底从北太平洋向西南方向延伸, 直至8月中旬覆盖长江全域; 季节重旱信号于7月中旬从孟加拉湾陆面区域向东北向延伸, 直至9月中旬覆盖长江全域. 同时, 本研究中亦进行了相关参数敏感性的详细分析, 对算法应用, 结果理解亦有帮助.  相似文献   

2.
The Arctic stratospheric polar vortex was exceptional strong, cold and persistent in the winter and spring of 2019–2020. Based on reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research and ozone observations from the Ozone Monitoring Instrument, the authors investigated the dynamical variation of the stratospheric polar vortex during winter 2019–2020 and its influence on surface weather and ozone depletion. This strong stratospheric polar vortex was affected by the less active upward propagation of planetary waves. The seasonal transition of the stratosphere during the stratospheric final warming event in spring 2020 occurred late due to the persistence of the polar vortex. A positive Northern Annular Mode index propagated from the stratosphere to the surface, where it was consistent with the Arctic Oscillation and North Atlantic Oscillation indices. As a result, the surface temperature in Eurasia and North America was generally warmer than the climatology. In some places of Eurasia, the surface temperature was about 10 K warmer during the period from January to February 2020. The most serious Arctic ozone depletion since 2004 has been observed since February 2020. The mean total column ozone within 60°–90°N from March to 15 April was about 80 DU less than the climatology.摘要2019-2020冬季北极平流层极涡异常并且持续的偏强,偏冷.利用NCEP再数据和OMI臭氧数据, 本文分析了此次强极涡事件中平流层极涡的动力场演变及其对地面暖冬天气和臭氧低值的影响.此次强极涡的形成是由于上传行星波不活跃.持续的强极涡使得2020年春季的最后增温出现时间偏晚.平流层正NAM指数向下传播到地面, 与地面AO指数和NAO指数相一致, 欧亚大陆和北美地面气温均比气候态偏暖, 在欧亚大陆的一些地区, 2020年1月和2月的气温甚至偏高了10K.2020年2月以来北极臭氧出现了2004年以来的最低值, 2020年3-4月60°–90°N的平均臭氧柱总量比气候态偏低了80DU.  相似文献   

3.
Decadal–centennial hydroclimate variability over eastern China during the last millennium is investigated using the product of Paleo Hydrodynamics Data Assimilation (PHYDA). Results reveal that the PHYDA depicts a more homogeneous temporal pattern during the early part of the Little Ice Age with other reconstructions than those during the other periods, and could also identify the droughts of 1352–90 AD, 1445–98 AD, 1580–94 AD, and 1626–65 AD during this period. On centennial time scales, the PHYDA shows that the linkage between the Palmer drought severity index over eastern China and the Atlantic Multidecadal Oscillation (AMO) index is more marked than that with the El Niño–Southern Oscillation and the location of the intertropical convergence zone over the Asian–Australian monsoon area during the period after the 1350s. For the decadal droughts, the PHYDA suggests most of the drought events during the last millennium were linked to the El Niño–like mean states and the negative AMO states.摘要利用古水文动力同化数据 (PHYDA) 研究了过去千年中国东部年代际-百年尺度干湿变化特征.结果表明, 对比其它重建数据PHYDA在百年尺度上对小冰期前期中国东部干湿变化的再现能力最好, 其对这一时期发生的年代际干旱事件包括1352–90年,1445–98年,1580–94年和1626–65年干旱事件的再现能力也最强.通过与强迫因子的对比和回归分析, 发现1350年后中国东部百年尺度干事变化主要受北大西洋年代际振荡影响, 而年代际干旱事件的主导因子则是厄尔尼诺和负位相的北大西洋年代际振荡.  相似文献   

4.
The quasi-biennial oscillation (QBO), a dominant mode of the equatorial stratospheric (~100–1 hPa) variability, is known to impact tropospheric circulation in the middle and high latitudes. Yet, its realistic simulation in general circulation models remains a challenge. The authors examine the simulated QBO in the 69-layer version of the Institute of Atmospheric Physics Atmospheric General Circulation Model (IAP-AGCML69) and analyze its momentum budget. The authors find that the QBO is primarily caused by parameterized gravity-wave forcing due to tropospheric convection, but the downward propagation of the momentum source is significantly offset by the upward advection of zonal wind by the equatorial upwelling in the stratosphere. Resolved-scale waves act as a positive contribution to the total zonal wind tendency of the QBO over the equator with comparable magnitude to the gravity-wave forcing in the upper stratosphere. Results provide insights into the mechanism of the QBO and possible causes of differences in models.摘要平流层准两年振荡 (QBO) 是赤道平流层 (~100–1 hPa) 变率的主要模态, 可对中高纬地区的环流产生重要影响, 但目前利用通用大气环流模式 (GCM) 对其进行准确模拟仍然是一个挑战.本文利用IAP大气环流模式 (IAP-AGCM) 的中高层大气模式版本 (IAP-AGCML69) 对QBO进行模拟, 并对其动量收支情况进行分析.研究发现, QBO主要是由对流活动引起的重力波强迫 (参数化) 引起的, 但该动量强迫被平流层赤道上升流所引起的平流过程显著削弱.模式可分辨尺度的波动强迫对赤道上空的QBO的总纬向风倾向有正贡献, 在上平流层, 其量值大小与参数化的重力波强迫相当.以上结果提供了对QBO形成机制以及模式模拟差异可能原因的认识.  相似文献   

5.
降水日变化受大气热力,动力过程以及复杂地形影响,演变特征复杂且区域差异显著.本文采用中国气象局发布的中国地面与CMORPH融合逐小时降水产品(2008-2019年),分析了新疆省暖季降水日变化特征.研究结果表明:(1)新疆大部分地区降水主峰值发生在清晨;(2)持续时间超过三小时的降水事件是新疆地区主要降水事件,贡献了南...  相似文献   

6.
The stratospheric polar vortex (SPV), which is an important factor in subseasonal-to-seasonal climate variability and climateprediction, exhibited a remarkable transition from weak in early winter to strong in late winter in 1987/88 (most significant on the interannual timescale during 1979–2019). Therefore, in this study, the subseasonal predictability of this transition SPV case in 1987/88 was investigated using the hindcasts from a selected model (that of the Japan Meteorological Agency) in the Subseasonal-to-Seasonal Prediction project database. Results indicated that the predictability of both weak and strong SPV stages in winter 1987/88, especially near their peak dates, exhibited large sensitivity to the initial condition, which derived mainly from the sensitivity in capturing the 100-hPa eddy heat flux anomalies. Meanwhile, the key tropospheric precursory systems with respect to the occurrence and predictability of this transition SPV case were investigated. The Eurasian teleconnection wave trains might have been a key precursor for the weak SPV stage, while significant tropospheric precursors for the strong SPV stage were not found in this study. In addition, positive correlation (r = 0.41) existed between the forecast biases of the SPV and the NAO in winter 1987/88, which indicates that reducing the forecast biases of the SPV might help to improve the forecasting of the NAO and tropospheric weather.摘要平流层极涡作为冬季次季节尺度上一个重要的可预测性来源, 其强度在1987/88年冬季表现为1979–2019年最显著的转折, 即在前 (后) 冬极端偏弱 (强). 因此在本文中选取这一个例研究了该年冬季平流层极涡在次季节尺度上的可预测性. 结果表明弱极涡和强极涡事件的预测与模式能否准确预测上传行星波的强度紧密相关. 同时, 发现前期对流层欧亚遥相关波列可能是弱极涡事件发生的关键预兆信号. 此外, 模式对平流层极涡强度和北大西洋涛动预测误差之间存在显著正相关关系, 表明模式减少平流层极涡的预测误差可能可以提高北大西洋涛动及相关对流层气候预测.  相似文献   

7.
本文通过对1979-2017年夏季925 hPa经向风异常进行经验正交函数(EOF)分解,研究了亚澳季风区内越赤道气流的年际变化特征.结果表明,越赤道气流的第一模态表现为亚澳季风区内不同通道间的同相变化,即一致加强或减弱;第二模态表现为孟加拉湾和澳大利亚越赤道气流的反相变化,其中新几内亚和孟加拉湾越赤道气流的反相变化最...  相似文献   

8.
China has implemented a series of emission reduction policies since 2013, and the concentration of air pollutants has consequently decreased significantly. However, PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 µm) pollution still occurs in China in relation to the interannual variations in meteorological conditions. Considering that El Niño–Southern Oscillation (ENSO) is the strongest signal modulating the interannual variation in the atmosphere–ocean system, in this study the authors investigate the variations in PM2.5 concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021. Results show that the wintertime PM2.5 concentrations in the Beijing–Tianjin–Hebei and Fenwei Plain regions during El Niño years are higher than those during La Niña years, which can be explained by the anomalous southerly (northerly) winds during El Niño (La Niña) favoring PM2.5 accumulation (diffusion). In the Pearl River Delta region, PM2.5 concentrations decrease in El Niño relative to La Niña years owing to the enhanced water vapor flux and precipitation, removing more PM2.5 from the atmosphere. The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM2.5 over the Yangtze River Delta region, which should be analyzed case by case.摘要2013年以来中国实施了一系列减排政策, 大气污染物浓度明显下降, 但由于气象条件的年际变化, 中国PM2.5 (空气动力学直径小于2.5 µm的颗粒物) 污染仍然存在. 厄尔尼诺–南方涛动 (ENSO) 是调节大气–海洋系统年际变化的最强信号. 本文研究了2014–2021年四次ENSO事件期间, 中国四个特大城市群冬季PM2.5浓度的变化. 结果表明, 在京津冀和汾渭平原地区, 由于厄尔尼诺 (拉尼娜) 期间的偏南风 (偏北风) 异常有利于 PM2.5 的积累 (扩散), 冬季PM2.5浓度在厄尔尼诺年高于拉尼娜年. 在珠三角地区, 由于厄尔尼诺冬季水汽通量和降水的增加有利于大气中PM2.5的湿清除, 冬季PM2.5浓度在厄尔尼诺年低于拉尼娜年. 在环流和降水异常的综合作用下, ENSO对长三角地区PM2.5浓度的影响难以预测, 应逐案分析.  相似文献   

9.
This study investigates whether and how the Madden–Julian Oscillation (MJO) influences persistent extreme cold events (PECEs), a major type of natural disaster in boreal winter, over Northeast China. Significantly increased occurrence probabilities of PECEs over Northeast China are observed in phases 3 and 5 of the MJO, when MJO-related convection is located over the eastern Indian Ocean and the western Pacific, respectively. Using the temperature tendency equation, it is found that the physical processes resulting in the cooling effects required for the occurrence of PECEs are distinct in the two phases of the MJO when MJO-related convection is consistently located over the warm pool area. The PECEs in phase 3 of the MJO mainly occur as a result of adiabatic cooling associated with ascending motion of the low-pressure anomaly over Northeast Asia. The cooling effect associated with phase 5 is stronger and longer than that in phase 3. The PECEs associated with phase 5 of the MJO are linked with the northwesterly cold advection of a cyclonic anomaly, which is part of the subtropical Rossby wave train induced by MJO-related convection in the tropical western Pacific.摘要 本文利用高分辨率气温数据和热带季节内振荡 (MJO) 实时指数, 研究了1979–2015年冬季MJO活动对中国东北持续性极端低温事件 (PECE) 的影响特征和机理.结果表明:当MJO对流分别位于暖池地区的东印度洋 (位相3) 和西太平洋 (位相5) 时, 中国东北PECE的发生频率显著增加.利用温度方程诊断分析发现MJO两个位相所导致的冷却过程不同: 当 MJO处于位相3时, 中国东北地区为低压异常, 上升运动引起绝热冷却作用; 而位相5所形成的气旋性环流为中国东北地区带来西北风冷平流, 降温过程更强且持续更长时间.  相似文献   

10.
A deep-learning method named U-Net was applied to improve the skill in forecasting summer (June–August) precipitation for at a one-month lead during the period 1981–2020 in China. The variables of geopotential height, soil moisture, sea level pressure, sea surface temperature, ocean salinity, and snow were considered as the model input to revise the seasonal prediction of the Climate Forecast System, version 2 (CFSv2). Results showed that on average U-Net reduced the root-mean-square error of the original CFSv2 prediction by 49.7% and 42.7% for the validation and testing set, respectively. The most improved areas were Northwest, Southwest, and Southeast China. The anomaly same sign percentages and temporal and spatial correlation coefficients did not present significant improvement but maintained the comparable performances of CFSv2. Sensitivity experiments showed that soil moisture is the most crucial factor in predicting summer rainfall in China, followed by geopotential height. Due to its advantages in handling small training dataset sizes, U-Net is a promising deep-learning method for seasonal rainfall prediction.摘要本研究应用了名为U-Net的深度学习方法来提高中国夏季 (6–8月) 降水的预报技能, 预报时段为1981–2020年, 预报提前期为一个月. 将位势高度场, 土壤湿度, 海平面气压, 海表面温度, 海洋盐度和青藏高原积雪等变量作为模型输入, 本文对美国NCAR气候预报系统第2版 (CFSv2) 的季节性预报结果进行了修正. 结果显示, 在验证集和测试集上, U-Net平均将原CFSv2预测的均方根误差分别减少了49.7%和42.7%. 预报结果改善最大的地区是中国的西北,西南和东南地区. 然而, 同号率和时空相关系数没有得到明显改善, 但仍与CFSv2的预测技巧持平. 敏感性实验表明, 土壤湿度是预测中国夏季降雨的最关键因素, 其次是位势高度场. 本研究显示了U-Net模型在训练小样本数据集方面的优势, 为我国汛期季节性降雨预测提供了一种有效的深度学习方法.  相似文献   

11.
Many coupled models are unable to accurately depict the multi-year La Niña conditions in the tropical Pacific during 2020–22, which poses a new challenge for real-time El Niño–Southern Oscillation (ENSO) predictions. Yet, the corresponding processes responsible for the multi-year coolings are still not understood well. In this paper, reanalysis products are analyzed to examine the ocean–atmosphere interactions in the tropical Pacific that have led to the evolution of sea surface temperature (SST) in the central-eastern equatorial Pacific, including the strong anomalous southeasterly winds over the southeastern tropical Pacific and the related subsurface thermal anomalies. Meanwhile, a divided temporal and spatial (TS) 3D convolution neural network (CNN) model, named TS-3DCNN, was developed to make predictions of the 2020/21 La Niña conditions; results from this novel data-driven model are compared with those from a physics-based intermediate coupled model (ICM). The prediction results made using the TS-3DCNN model for the 2020–22 La Niña indicate that this deep learning–based model can capture the two-year La Niña event to some extent, and is comparable to the IOCAS ICM; the latter dynamical model yields a successful real-time prediction of the Niño3.4 SST anomaly in late 2021 when it is initiated from early 2021. For physical interpretability, sensitivity experiments were designed and carried out to confirm the dominant roles played by the anomalous southeasterly wind and subsurface temperature fields in sustaining the second-year cooling in late 2021. As a potential approach to improving predictions for diversities of ENSO events, additional studies on effectively combining neural networks with dynamical processes and mechanisms are expected to significantly enhance the ENSO prediction capability.摘要2020–22年间热带太平洋经历了持续性多年的拉尼娜事件, 多数耦合模式都难以准确预测其演变过程, 这为厄尔尼诺-南方涛动(ENSO)的实时预测带来了很大的挑战. 同时, 目前学术界对此次持续性双拉尼娜事件的发展仍缺乏合理的物理解释, 其所涉及的物理过程和机制有待于进一步分析. 本研究利用再分析数据产品分析了热带东南太平洋东南风异常及其引起的次表层海温异常在此次热带太平洋海表温度(SST)异常演变中的作用, 并构建了一个时空分离(Time-Space)的三维(3D)卷积神经网络模型(TS-3DCNN)对此次双拉尼娜事件进行实时预测和过程分析. 通过将TS-3DCNN与中国科学院海洋研究所(IOCAS)中等复杂程度海气耦合模式(IOCAS ICM)的预测结果对比, 表明TS-3DCNN模型对2020–22年双重拉尼娜现象的预测能力与IOCAS ICM相当, 二者均能够从2021年初的初始场开始较好地预测2021年末 El Niño3.4区SST的演变. 此外, 基于TS-3DCNN和IOCAS ICM的敏感性试验也验证了赤道外风场异常和次表层海温异常在2021年末赤道中东太平洋海表二次变冷过程中的关键作用. 未来将神经网络与动力 模式模式间的有效结合, 进一步发展神经网络与物理过程相结合的混合建模是进一步提高ENSO事件预测能力的有效途径.  相似文献   

12.
China has been frequently affected by severe snowstorms in recent years that have particularly large economic and human impacts. It is thus of great importance to increase our understanding of the underlying mechanisms of and future changes in snowfall occurrences over China. In this study, the effects of anthropogenic influences on snowfall and the associated future changes are explored using new simulations from CMIP6 (phase 6 of the Coupled Model Intercomparison Project) models. Observational evidence reveals a decrease in the annual total snowfall days and an increase in intense snowfall days over the snowfall-dominated regions in China during recent decades. Fingerprints of anthropogenic influences on these changes are detectable, especially the impacts of increased greenhouse gas emissions. During the winter seasons, low temperatures still cover the regions of northern China, and the associated precipitation days show an increase due to anthropogenic warming, which substantially benefits the occurrence of snowfall over these regions, particularly for intense snowfall events. This is also true in the future, despite rapid warming being projected. By the end of this century, approximately 23% of grids centered over northern China are projected to still experience an increase in daily intense snowfall events in winters. Additionally, the length of the snowfall season is projected to narrow by nearly 41 days compared to the current climate. Thus, in the future, regions of China, especially northern China, are likely to experience more intense snowfall days over a more concentrated period of time during the winter seasons.摘要近年来, 中国部分地区频繁遭遇极端降雪事件袭击, 造成巨大经济损失和人员伤亡. 因此, 亟需深入理解中国地区极端降雪变化的物理机制及其未来演变趋势, 为国家防灾减灾及气候变化应对措施制定提供科学依据. 本文基于CMIP6模式结果, 深入开展人类活动对中国地区降雪变化的影响及其未来演变趋势预估研究. 观测显示, 过去几十年在中国降雪频发区, 其年降雪日数呈现减少趋势但强降雪日数增加; 在这些变化中能够检测到人类活动的痕迹, 尤其是温室气体排放的影响. 对于冬季, 全球变暖背景下中国北方地区降水日数明显增加, 但北方地区仍为低温控制, 这有利于降雪尤其是强降雪事件的发生; 到了本世纪末, 中国仍有约23%的区域 (主要集中在北方地区) 其冬季强降雪日数呈现增加趋势. 此外, 中国地区降雪季长度相比当前气候减少了约41天. 因此, 在未来持续变暖背景下, 中国北方部分地区冬季将经历更多更为集中的强降雪事件.  相似文献   

13.
This study investigated the distinct responses of western North Pacific (WNP) tropical cyclone (TC) activity during different decaying El Niño summers. The El Niño events were classified into two types according to the periodicity of the ENSO cycle, with positive SST anomalies in the equatorial central-eastern Pacific maintaining positive values into the following summer as the slow decaying (SD) cases, but transforming to negative values in the following summer as the rapid decaying (RD) cases. Compared with that in SD El Niño summers, the TC occurrence frequency over the WNP is significantly lower in RD El Niño summers, led by a much weaker WNP monsoon trough with more unfavorable environmental factors for TC genesis and development. Further examination showed that the apparent warming over the tropical Indian Ocean basin and cooling over the equatorial central-eastern Pacific contribute together to an enhanced lower-tropospheric anticyclone through modulation of the descending branch of the large-scale Walker circulation over the WNP, which may play a crucial role in suppressing the TC activity during the decaying summer of RD El Niño cases. In contrast, the warming equatorial central-eastern Pacific and remote western Indian Ocean induce a weakening WNP anticyclone and less suppressed deep convection during the decaying summer of SD El Niño cases. Thus, the different evolution of SST anomalies associated with different paces of El Niño decay results in the linkage between the preceding winter El Niño and the decreased WNP TC frequency in summer being more (less) robust for RD (SD) El Niño cases.摘要本文分析了El Niño事件衰减速度的差异对衰退年夏季西北太平洋热带气旋 (tropical cyclone, TC) 频数的不同影响. 按照El Niño事件衰减速度不同, 将其划分为迅速衰减 (rapid decaying, RD) 和缓慢衰减 (slow decaying, SD) 的El Niño事件. SD (RD) El Niño事件的衰退年夏季, 赤道中东太平洋海温仍维持正异常 (衰减为负异常) . 与SD El Niño事件相比, RD El Niño事件衰退年夏季西北太平洋TC频数显著减少. 进一步的分析揭示了导致TC频数差异的大尺度环境要素, 指出热带印度洋-太平洋海温异常密切相关的西北太平洋低层反气旋异常在其中起到了关键作用.  相似文献   

14.
胡桂芳  高理 《气象科技》2010,38(Z1):24-28
利用1951—2009年北半球500hPa高度、北太平洋海温、环流特征量、降水等资料,采用相关分析、合成分析、经验函数正交分解(EOF)、子波分析等多种统计技术,对影响山东2009年10月降水趋势的各种因素进行分析和研究。结果表明:山东10月降水大致存在3种降水分布型;在不同时间尺度的气候背景上,2009年10月山东基本处于一个少雨或由少雨向多雨转换的气候阶段;2009年春季加利福尼亚冷流的减弱,2009年6月开始的厄尔尼诺事件及6月起西太平洋副高持续的偏强、偏西、正常或偏南状态,各种指标均指示山东10月降水偏少的可能性大,预测与实况基本吻合。  相似文献   

15.
The Southern Annular Mode (SAM) is the leading mode of atmospheric variability in the mid–high latitudes of the Southern Hemisphere, representing large-scale variations in pressure and the polar front jet (PFJ). In SAM events, the combination of the SAM and other modes may result in different atmospheric patterns. In this study, a neural-network-based cluster technique, the self-organizing map, was applied to extract the distinct patterns of SAM events on the monthly time scale based on geopotential height anomalies at 500 hPa. Four pairs of distinguishable patterns of positive and negative SAM events were identified, representing the diversity in spatial distribution, especially the zonal symmetry of the center of action at high latitudes—that is, symmetric patterns, split-center patterns, West Antarctica patterns, and a tripole pattern. Although the SAM is well known to be belt-shaped, within the selected SAM events, the occurrence frequency of symmetric patterns is only 23.8%—less than that of West Antarctica patterns. Diverse PFJ variations were found in the symmetric and asymmetric patterns of SAM events. The more asymmetric the spatial distribution of the pressure anomaly, the more localized the adjusted zonal wind anomaly. The adjusted PFJ varied in meridional displacement and strength in different patterns of SAM events. In addition, the entrance and exit of the jet changed in most of the patterns, especially in the asymmetric patterns, which might result in different climate impacts of the SAM.摘要南半球环状模 (SAM) 是南半球中–高纬度地区大气变化的主导模态, 表现为气压和极锋急流 (PFJ) 的大尺度变动, 形成强烈的气候影响. 当SAM事件发生时, 气压场异常可呈现出不同的空间结构. 本文利用自组织映射网络方法对月尺度的SAM事件进行分类, 可识别出四对具有显著差异的正, 负SAM事件类型, 包括对称型, 中心分裂型, 西南极洲型和一种三极型分布. 气压异常的空间分布越不对称, 调整后的纬向风异常越局地化. PFJ的经向位移和强度变化入口和出口的变化, 可能导致了SAM的不同气候影响.  相似文献   

16.
过去几十年,气候变化和极端气候事件造成的经济损失和灾害显著增加.虽然全球的科学家在理解和预测气候变异方面做出了巨大的努力,但当前在气候预测领域仍然存在几个重大难题.2020年,依托于国家自然科学基金基础科学中心项目的气候系统预测研究中心(CCSP)成立了,该中心旨在应对和处理气候预测领域的三大科学难题:厄尔尼诺-南方涛动(ENSO)预测,延伸期天气预报,年际-年代际气候预测,并为更加准确的气候预测和更加有效的灾害防御提供科学依据.因此,本文介绍了CCSP的主要目标和面对的科学挑战,回顾了CCSP在季风动力过程,陆-气相互作用和模式开发,ENSO变率,季节内振荡,气候预测等方面已取得的重要研究成果.未来CCSP将继续致力于解决上述领域的关键科学问题.  相似文献   

17.
Changes in the water cycle on the Tibetan Plateau (TP) have a significant impact on local agricultural production and livelihoods and its downstream regions. Against the background of widely reported warming and wetting, the hydrological cycle has accelerated and the likelihood of extreme weather events and natural disasters occurring (i.e., snowstorms, floods, landslides, mudslides, and ice avalanches) has also intensified, especially in the high-elevation mountainous regions. Thus, an accurate estimation of the intensity and variation of each component of the water cycle is an urgent scientific question for the assessment of plateau environmental changes. Following the transformation and movement of water between the atmosphere, biosphere and hydrosphere, the authors highlight the urgent need to strengthen the three-dimensional comprehensive observation system (including the eddy covariance system; planetary boundary layer tower; profile measurements of temperature, humidity, and wind by microwave radiometers, wind profiler, and radiosonde system; and cloud and precipitation radars) in the TP region and propose a practical implementation plan. The construction of such a three-dimensional observation system is expected to promote the study of environmental changes and natural hazards prevention.摘要青藏高原的水循环变化对于高原及其下游区域人类的生产生活具有举足轻重的影响. 在高原暖湿化的背景下, 其水文循环加快, 极端天气和自然灾害事件概率增大, 比如, 雪灾, 洪水, 滑坡, 泥石流, 冰崩在山区频发. 因此, 如何准确的估算青藏高原水循环各分量的大小及变化幅度是评估高原环境变化影响亟需解决的科学问题. 根据水在各圈层间转换过程, 我们提出了建立第三极地区 (尤其是复杂山区) 的三维立体多圈层地气相互作用综合观测系统(包括涡动相关系统, 行星边界层塔, 微波辐射计, 风廓线仪和无线电探空系统观测的风温湿廓线及云雨雷达等)的紧迫性和具体方案, 进而为研究青藏高原环境变化和山区灾害预测服务.  相似文献   

18.
Observational data from satellite altimetry were used to quantify the performance of CMIP6 models in simulating the climatological mean and interannual variance of the dynamic sea level (DSL) over 40°S–40°N. In terms of the mean state, the models generally agree well with observations, and high consistency is apparent across different models. The largest bias and model discrepancy is located in the subtropical North Atlantic. As for simulation of the interannual variance, good agreement can be seen across different models, yet the models present a relatively low agreement with observations. The simulations show much weaker variance than observed, and bias is apparent over the subtropics in association with strong western boundary currents. This nearshore bias is reduced considerably in HighResMIP models. The underestimation of DSL interannual variance is at least partially due to the misrepresentation of ocean processes in the CMIP6 historical simulation with its relatively low resolution. The results identify directions for future model development towards a better understanding of the mean and interannual variability of DSL.摘要本研究采用卫星测高数据与第六次国际耦合模式比较计划 (CMIP6) 海平面动力进行对比, 重点针对40°S–40°N地区的动力海平面 (DSL) , 评估了模式对其平均态与年际变率的综合模拟能力. 结果表明, 对于DSL平均态的模拟, 模式与观测结果非常吻合, 模式之间的差异较小. 其中, 副热带北大西洋是模拟偏差和模式间差异较为显著的区域. 对于DSL年际变率的模拟, 模式之间保持较高的一致性, 但是, 模式与观测结果存在明显差异, 模式普遍低估了DSL的年际方差; 其中, 误差大值区域出现在副热带西边界流附近. 模式分辨率会影响CMIP6对中小尺度海洋过程的重现能力, 这可能是导致CMIP6历史模拟出现误差的原因之一.  相似文献   

19.
Based on reanalysis data from 1979 to 2016, this study focuses on the sea surface temperature (SST) anomaly of the tropical North Atlantic (TNA) in El Niño decaying years. The TNA SST exhibits a clear warm trend during this period. The composite result for 10 El Niño events shows that the TNA SST anomaly reaches its maximum in spring after the peak of an El Niño event and persists until summer. In general, the anomaly is associated with three factors—namely, El Niño, the North Atlantic Oscillation (NAO), and a long-term trend, leading to an increase in local SST up to 0.4°C, 0.3°C, and 0.35°C, respectively. A comparison between 1983 and 2005 indicates that the TNA SST in spring is affected by El Niño, as well as the local SST in the preceding winter, which may involve a long-term trend signal. In addition, the lead–lag correlation shows that the NAO leads the TNA SST by 2–3 months. By comparing two years with an opposite phase of the NAO in winter (i.e., 1992 and 2010), the authors further demonstrate that the NAO is another important factor in regulating the TNA SST anomaly. A negative phase of the NAO in winter will reinforce the El Niño forcing substantially, and vise versa. In other words, the TNA SST anomaly in the decaying years is more evident if the NAO is negative with El Niño. Therefore, the combined effects of El Niño and the NAO must be considered in order to fully understand the TNA SST variability along with a long-term trend.摘要基于1979年到2016年多种再分析资料, 本文分析了El Niño衰减年热带北大西洋的海温异常. 结果表明, 热带北大西洋海温在此期间呈显著变暖趋势. 10次El Niño事件的合成结果表明热带北大西洋海温异常在El Niño事件峰值之后的春季达到最大值, 并持续到夏季. 一般而言, 这种异常与三个因子有关, 即El Niño, 北大西洋涛动和长期趋势, 能分别导致局地海温上升0.4°C, 0.3°C和0.35°C. 1983年和2005年的对比分析表明, 尽管El Niño强度对春季北大西洋海温起到决定性作用, 与长期趋势密切相关的前冬海温也很重要. 此外, 超前-滞后相关结果表明北大西洋涛动超前海温约2–3个月. 比较两个冬季相反位相北大西洋涛动的年份 (即1992年和2010年) , 表明北大西洋涛动也能调制北大西洋海温异常. 冬季负位相北大西洋涛动能显著增强El Niño的强迫影响, 反之亦然. 换言之, 如果北大西洋涛动与El Niño位相相合, 衰减年北大西洋海温异常才更为显著. 因此, 为全面理解热带北大西洋海温变化, 除长期趋势外, 还必须考虑El Niño和北大西洋涛动的综合影响.  相似文献   

20.
高质量和高分辨率的降水产品在天气预报,数值模式模拟和气象防灾减灾方面起着重要的作用.本文利用四川地区高密度的地面降水传感器观测数据,比较CMPAS四种不同时空尺度的降水实况分析产品,评估CMPAS的融合准确性与在四川地区的适用性.研究表明:四种CMPAS降水产品都在四川盆地内精度较高,攀西地区和川西高原次之.随着降水量...  相似文献   

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