The North American summer monsoon (NASM) and the North African summer monsoon (NAFSM) are two vital subsystems of the global monsoon. To date, the potential inter-monsoon relationship between the NASM and NAFSM has not been fully understood. To fill this gap, we investigate the NASM-NAFSM relationship on the interannual timescale during the period of 1979-2022. Based on statistical methods (including correlation, empirical orthogonal function and cross wavelet analyses), we identify a noteworthy interannual covariation of the NASM and NAFSM. This observed NASM-NAFSM covariation can be explained by atmospheric circulation anomalies associated with sea surface temperature (SST) anomalies in the tropical central-eastern Pacific and tropical Atlantic, suggesting the critical roles of tropical Pacific-Atlantic SST anomalies in shaping the NASM-NAFSM covariation. The results of Coupled Model Intercomparison Project Phase 6 (CMIP6) models indicate that a model's ability to simulate the NASM-NAFSM covariation tends to be related to its ability to reproduce the modulating effects of the tropical Pacific-Atlantic SST anomalies. These results have potential implications for seasonal forecasts of the NASM and NAFSM variations, suggesting that the NASM and NAFSM can be considered simultaneously in climate predictions. This study identifies a noteworthy interannual covariation of the North American summer monsoon (NASM) and the North African summer monsoon (NAFSM). The NASM-NAFSM covariation can be explained by atmospheric circulation anomalies associated with trans-Atlantic-Pacific dipole-like sea surface temperature (SST) anomalies.image

Variations of the North American summer monsoon (NASM) and North Atlantic tropical cyclone (NATC) activities strongly influence climate anomalies in North America, with serious potential risk to life and property. Despite the scientific importance of this topic, the possible linkage between the NASM and the NATC genesis frequency remains unexplored. Here, we aim to examine the relationship between interannual variations of the NASM intensity and the NATC genesis frequency based on observations and Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Our results show a strong association between the NASM intensity and the NATC genesis frequency during the extended boreal summer, with a good synchronization between their interannual variations. In years with stronger (weaker) NASM intensity, the NATC genesis frequency tends to be higher (lower). The observed NASM–NATC synchronization may be explained by two pathways: tropical-ocean-driven pathway and monsoon-heating-driven pathway. In the tropical-ocean-driven pathway, the tropical Pacific and Atlantic interbasin sea surface temperature (SST) anomalies play a critical role in bridging the NASM and NATC, by modulating the cross-Central American wind. Simulations of the tropical Pacific–Atlantic interbasin SST anomalies are critical for CMIP6 models to capture the observed linkage between the NASM and the vertical wind shear over the NATC main development region (MDR). In the monsoon-heating-driven pathway, the heating source due to the rainfall anomalies associated with the NASM can trigger atmospheric circulation anomalies through the Gill-type response, thereby affecting the NATC by changing the vertical wind shear over the MDR. This study demonstrates a connection between interannual variations of the NASM and the NATC genesis frequency, results of which can be used to advance our understanding of the monsoon–TC relationship and increase research focus on the interannual NASM–NATC synchronization in climate prediction.

为了培养海洋科学与大气科学交叉复合型人才,文章首先说明了"海洋气象学"课程教学目标及教学存在的问题,然后对"海洋气象学"课程教学知识点进行了设计,最后论述了"海洋气象学"课程教学实践.

对比了1979-2020年全球8个主要季风区湿季和干季降雨的长期变化趋势、变率和偏度特征.主要结果如下:(1)在长期变化趋势方面,东亚、西北太平洋和北非季风的湿季降雨以及印度季风的干季降雨呈现显著的增加趋势,而北美和南美季风的干季降雨和南美季风的湿季降雨呈现显著的下降趋势.东亚和北非季风(南美季风)的湿季—干季降雨差值呈现显著的增加(下降)趋势.(2)在变率方面,北美和北非季风湿季和干季降雨的方差在2000-2020年(P2时期)要小于1979-1999年(P1时期);南非和澳洲季风湿季和干季降雨的方差在P2时期要大于P1时期;东亚、西北太平洋和南美季风降雨方差的变化在湿季和干季存在不一致性,湿季(干季)降雨的方差在P2时期增加(减小).(3)在偏度方面,东亚、印度、澳洲和南非季风干季降雨和东亚季风湿季降雨的偏度值在P2时期增加;而西北太平洋季风干季降雨和北非季风湿季降雨的偏度值在P2时期减小.

The western North Pacific summer monsoon (WNPSM) is an important subcomponent of the Asian summer monsoon. The equatorial zonal wind (EZW) in the lower troposphere over the western Pacific may play a critical role in the evolution of the El Niño-Southern Oscillation (ENSO). The possible linkage between the EZW over the western Pacific and the off-equatorial monsoonal winds associated with the WNPSM and its decadal changes have not yet been fully understood. Here, we find a non-stationary relationship between the WNPSM and the western Pacific EZW, significantly strengthening their correlation around the late 1980s/early 1990s. This observed shift in the WNPSM–EZW relationship could be explained by the changes in the related sea surface temperature (SST) configurations across the tropical oceans. The enhanced influence from the springtime tropical North Atlantic, summertime tropical central Pacific, and maritime continent SST anomalies may be working together in contributing to the recent intensified WNPSM–EZW co-variability. The observed recent strengthening of the WNPSM–EZW relationship may profoundly impact the climate system, including prompting more effective feedback from the WNPSM on subsequent ENSO evolution and bolstering a stronger biennial tendency of the WNPSM–ENSO coupled system. The results obtained herein imply that the WNPSM, EZW, ENSO, and the tropical North Atlantic SST may be closely linked within a unified climate system with a quasi-biennial rhythm occurring during recent decades, accompanied by a reinforcement of the WNPSM–ENSO interplay quite possibly triggered by enhanced tropical Pacific–Atlantic cross-basin interactions. These results highlight the importance of the tropical Atlantic cross-basin influences in shaping the spatial structure of WNPSM-related wind anomalies and the WNPSM–ENSO interaction.

The western Pacific subtropical high (WPSH) substantially affects the climate in the Pacific and East Asia. Previous studies have revealed that the springtime Indo‐Pacific warm pool (IPWP) sea surface temperature zonal gradient (SSTG) could be used as a predictor of the subsequent summertime WPSH's intensity. Here, we find that the interannual variability of the springtime IPWP SSTG has greatly decreased after the late 1990s, accompanied by the weakened relationship between the springtime IPWP SSTG and the following summertime WPSH, which may reduce the efficiency of the springtime IPWP SSTG as a key predictor for the summertime WPSH in recent decades. This observed recent weakening IPWP SSTG–WPSH relationship could be largely contributed by the decadal shift of the El Niño–Southern Oscillation (ENSO) and the WPSH around the late 1990s. The ENSO regime shift from the eastern Pacific (EP) type to the central Pacific (CP) type could alter the spatial pattern of the springtime IPWP sea surface temperature (SST) dipole and further weaken the local air–sea interaction between the underlying IPWP SST and the WPSH. From another perspective of the WPSH decadal shift, the WPSH‐related first leading mode before (after) the late 1990s, characterized by a large‐scale uniform (dipole) pattern with an oscillating period of ~4–5 year (~2–3 year), tended to promote a stronger (weaker) linkage with the springtime IPWP SSTG. In addition, the recent enhancement of the tropical Atlantic SST influences is considered to possibly promote the decadal shifts of the ENSO and the WPSH‐related leading mode. After the springtime tropical Atlantic SST was added as a predictor, the predicting skills of the empirical equation for the summertime WPSH could be substantially improved. The results herein have important implications for the further improvement of the seasonal WPSH prediction, which is of great practical significance in the prevention and mitigation of climate disasters.

The monsoon and tropical cyclone (TC) are principal components of global climate variability. The relationship between the monsoon intensity and the TC genesis frequency (TCGF) in different major monsoon regions has not been fully studied. Here, we compared the relationship of monsoon intensity and TCGF during the extended boreal summer between the western and eastern North Pacific, results of which revealed different monsoon–TC relationships (with opposite-sign correlations) in these two regions. A significant positive correlation could be found between the western North Pacific summer monsoon (WNPSM) index and the TCGF over the western North Pacific (WNP). In contrast, a significant negative correlation was identified between the North American summer monsoon (NASM) index and the TCGF over the eastern North Pacific (ENP). The observed different monsoon–TC relationships could be explained by the monsoon-associated changes in the environmental factors over the regions where TCs were formed and the influences from sea surface temperature (SST) anomalies across tropical ocean basins. By comparing the environmental factors in the TC genesis potential index (GPI), the mid-level relative humidity (vertical wind shear) was the factor to make the largest contribution to the monsoon-associated TC genesis changes over the WNP (ENP). In strong (weak) WNPSM years, the high (low) atmospheric mid-level relative humidity could promote (inhibit) the TCGF over the WNP, resulting in a significant positive monsoon–TC correlation. In contrast, in strong (weak) NASM years, the strong (weak) vertical wind shear could inhibit (promote) the TCGF over the ENP, thus leading to a significant negative monsoon–TC correlation. In addition, the WNPSM and the TCGF over the WNP could be modulated by the similar tropical Pacific–Atlantic SST anomalies jointly, thus leading to a significant positive correlation between the WNPSM and the WNP TCGF. In contrast, the signs of tropical Pacific–Atlantic SST anomalies influencing the NASM were almost opposite to those affecting the TCGF over the ENP, thus resulting in a significant negative correlation between the NASM and the ENP TCGF. The results obtained herein highlight the differences of the monsoon–TC relationship between the WNP and the ENP, which may provide useful information for the prediction of monsoon intensity and TC formation number over these two regions.

季风区降雨可以对农业活动产生重要的影响,研究和预测季风区降雨的变异对农业具有重要的意义.对比了全球各主要季风区降雨与El Ni?o-Southern Oscillation(ENSO)之间关系的差异(包括相关关系的年代际变异以及季风—ENSO准两年关系),旨在更好地理解全球季风降雨的演变规律和季风—ENSO之间的关系.结果表明,全球各个主要季风降雨量与同时期Ni?o3.4指数之间相关关系的年代际变异存在显著的差异.西北太平洋季风、东亚季风和南非季风存在季风降雨—ENSO的相关系数在考察的时间范围内出现正负符号转变的现象.印度夏季风降雨与Ni?o3.4指数的负相关关系在2000年以后增强;与之相反,北非夏季风降雨与Ni?o3.4指数的负相关关系在2000年以后则减弱.澳洲夏季风和北美夏季风降雨与同时期Ni?o3.4指数的相关关系比较稳定.相比较全球其他季风,西北太平洋夏季风降雨与ENSO具有更强的准两年关系.

基于3种灾害指数(风灾害指数、雨灾害指数和风雨联合灾害指数)对比了 1970-2018年登陆广东与登陆我国的热带气旋灾害指数的特征.结果表明:登陆广东的热带气旋所造成的雨灾害指数略高于我国平均值,而风灾害指数略低于我国平均值,风雨联合指数与我国平均值相当.在长期变化趋势方面,与登陆我国的热带气旋灾害指数的平均值比较,登陆广东热带气旋的平均雨灾害指数和风雨联合灾害指数均呈现更强的增加趋势.尽管登陆广东和登陆我国的热带气旋的总数量在最近时期存在减少的趋势,但是由于平均单个热带气旋引起的雨灾害指数及风雨联合灾害指数均呈现增加的趋势,从而导致相应的年累计总灾害指数并没有出现减少的趋势.登陆广东的平均单个热带气旋的雨灾害指数及风雨联合灾害指数的上升趋势均较登陆我国的单个热带气旋的平均值更强.灾害等级强的热带气旋数量的增加趋势是造成平均单个热带气旋的雨灾害指数及风雨联合灾害指数增加的重要原因.

热带云团(Tropical Cloud Cluster,TCC)和热带气旋(Tropical Cyclone,TC)是热带地区的重要天气系统,对热带地区的农业活动可以产生重要的影响.TCC是TC的初始胚胎状态,可以在适宜的环境条件下发展为TC,TCC的发展率可以用来定量地表征能够发展为TC的TCC所占的比例.东北太平洋和北大西洋是西半球TCC和TC活动活跃的海域.利用1982—2018年的TCC和TC数据,对东北太平洋和北大西洋海域TCC发展率的变异特征进行了对比.结果显示:在季节变化方面,东北太平洋的TCC发展率在7月份达到最大值(13.22％),北大西洋的TCC发展率在9月份达到最大值(16.09％);在年际变化方面,东北太平洋和北大西洋海域TCC发展率时间序列的相关性并不显著;在长期变化趋势方面,东北太平洋TCC发展率呈显著的减少趋势,而北大西洋TCC发展率呈不显著的减少趋势.这些研究结果有助于更好地认识东北太平洋和北大西洋海域TCC发展率的变异特征.

对2021年春季影响西太副高的3种春季环境因子(热带印度洋与西北太平洋海域海表面温度异常(SSTA)的差值、赤道中太平洋5月与3月SSTA的差值、北大西洋涛动指数)的特征进行了分析.结果显示:2021年春季热带印度洋与西北太平洋海域SSTA的差值表现为负异常(-0.32℃)、赤道中太平洋5月与3月的SSTA差值表现为弱的正异常(0.02℃)、北大西洋涛动指数则出现负异常(-0.79).利用3个春季环境因子构建的预报方程对2021年夏季西太副高指数的预报值为-0.44,这与2021年夏季西太副高指数的实测值(0.28)存在一些偏差.春季热带印度洋与西北太平洋的SSTA差值在3个环境因子中对2021年西太副高的预报结果有着最大的贡献,西北太平洋海域SSTA的暖异常可能是引起2021年夏季西太副高预报强度偏弱的重要原因.通过对比2021年夏季各月的西太副高指数观测值发现,8月与7月的西太副高指数存在较大差异,夏季各月之间差异的增大可能是导致预报结果不理想的原因.在西太副高的预报方面,需要进一步针对夏季各月之间差异较大的情况改进预报方法.