热带MJO和ENSO对西北太平洋热带气旋影响研究综述

对西北太平洋热带气旋的活动规律作了综合评述,简单回顾了热带季节内振荡（MJO）特征和厄尔尼诺/南方涛动（ENSO）特征以及两者间关系,较系统地总结了近年来国内外学者关于MJO和ENSO对西北太平洋海域热带气旋活动影响和机理等方面的研究成果。讨论的热带气旋活动特征包括源地、频数、路径、强度、生命期和登陆等几个方面,并简单讨论了目前该领域存在的科学问题和未来可能的研究方向。     

Patterns of Pacific decadal variability recorded by Indian Ocean corals

We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral δ¹⁸O series from La Réunion and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies, we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance patterns of the coral time series with sea surface temperature (SST) and sea level pressure (SLP) of the Indian and Pacific Oceans. In addition, the empirical orthogonal functions of the filtered SST and SLP fields (single and coupled) are related to the filtered coral times series. The covariance maps show the typical PDO pattern for SST and SLP, confirming the coupling between the Indian and Pacific Oceans. Both corals show the strongest signal in boreal summer. The La Réunion (Ifaty) coral better records SST (SLP) than SLP (SST) pattern variability. We suggest that the filtered La Réunion coral δ¹⁸O represents δ¹⁸O of seawater that varies with the South Equatorial Current, which, in turn, is linked with the SST PDO. The filtered Ifaty coral δ¹⁸O represents SST and is remotely linked with the SLP PDO variability. A combined coral record of the Ifaty and La Réunion boreal summer δ¹⁸O series explains about 64% of the variance of the coupled SST/SLP PDO time series. AGU OS06 special issue “Ocean’s role in climate change—a paleo perspective”.     

Genesis of the Assif El Mal Zn–Pb (Cu,Ag) vein deposit. An extension-related Mesozoic vein system in the High Atlas of Morocco. Structural,mineralogical, and geochemical evidence

The Assif El Mal Zn–Pb (Cu–Ag) vein system, located in the northern flank of the High Atlas of Marrakech (Morocco), is hosted in a Cambro-Ordovician volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered with minor tuff and mudstone. Intrusion of synorogenic to postorogenic Late Hercynian peraluminous granitoids has contact metamorphosed the host rocks giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, amphibole, chloritoid, and garnet. The Assif El Mal Zn–Pb (Cu–Ag) mineralization forms subvertical veins with ribbon, fault breccia, cockade, comb, and crack and seal textures. Two-phase liquid–vapor fluid inclusions that were trapped during several stages occur in quartz and sphalerite. Primary inclusion fluids exhibit T _h mean values ranging from 104°C to 198°C. Final ice-melting temperatures range from −8.1°C to −12.8°C, corresponding to salinities of ∼15 wt.% NaCl equiv. Halogen data suggest that the salinity of the ore fluids was largely due to evaporation of seawater. Late secondary fluid inclusions have either Ca-rich, saline (26 wt.% NaCl equiv.), or very dilute (3.5 wt.% NaCl equiv.) compositions and homogenization temperatures ranging from 75°C to 150°C. The δ¹⁸O and δD fluid values suggest an isotopically heterogeneous fluid source involving mixing between connate seawater and black-shale-derived organic waters. Low δ¹³C_VPDB values ranging from −7.5‰ to −7.7‰ indicate a homogeneous carbon source, possibly organic matter disseminated in black shale hosting the Zn–Pb (Cu–Ag) veins. The calculated δ³⁴S_H2S values for reduced sulfur (22.5‰ to 24.3‰) are most likely from reduction of SO₄ ²⁻ in trapped seawater sulfate or evaporite in the host rocks. Reduction of sulfate probably occurred through thermochemical sulfate reduction in which organic matter was oxidized to produce CO₂ which ultimately led to precipitation of saddle dolomite with isotopically light carbon. Lead isotope compositions are consistent with fluid–rock interaction that leached metals from the immediate Cambro-Ordovician volcaniclastic and metasedimentary sequence or from the underlying Paleo-Neoproterozoic crustal basement. Geological constraints suggest that the vein system of Assif El Mal formed during the Jurassic opening of the central Atlantic Ocean.     

基于IPCC AR4耦合模式的南极涛动和北极涛动的模拟及未来变化预估

评估了参加政府间气候变化委员会第4次评估报告(IPCCAR4)的耦合模式对南极涛动和北极涛动的模拟能力。分析了24个模式对1970—1999年南极涛动和北极涛动的模拟效能,并与两套再分析资料ERA-40和NCEP-1进行了对比分析。结果表明,模式的模拟能力具有一定的季节依赖性,冬季模拟能力最好。大多数模式对南极涛动空间结构和时间序列趋势的模拟好于北极涛动。根据Taylor图选出具有较好模拟能力的模式并做集合分析,发现经过选取的模式集合可以明显改善模式的模拟能力。分析SRESA1B情景下的南极涛动和北极涛动的模拟、预估结果表明:1970—2099年,南极涛动和北极涛动指数均呈持续上升趋势,北极涛动指数增长略显平稳。相对于1970—1999年、2060—2089年两半球的海平面气压场均呈现极区气压降低、中纬度气压升高的形态,同样表明南、北极涛动在后一时段更强。因此,在气候变暖背景下,南、北极涛动将持续增强,21世纪中期的臭氧恢复可能不会显著影响这种趋势。     

两类El Niño事件赤道洋流的异常对东太平洋SST的影响

Based on the Simple Ocean Data Assimilation (SODA) from 1970 to 2001, equatorial currents and their association with the warm water propagation mechanism during two patterns of El Niño events are studied. In this study, the middle-pattern of El Ni?o (ME) and the eastern-pattern of El Niño (EE) events are defined as anomalous warm water originating first to the west and the east of 120°W, respectively. It is pointed out that the westerly and eastward anomalous currents in the western Pacific are stronger during the ME event than the EE event, which is conducive to the eastward migration of warm water from western Pacific by zonal advection of temperature. In contrast, the weaker westerly and the westward anomalous currents east of the dateline would be unfavorable for the eastward migration of warm water during EE events. More importantly, another propagation mechanism of the warm water is attributed to the anomalous convergence of the surface currents, as well as the anomalous divergence of the subsurface currents, which obstruct the upwelling of colder water from the deep ocean. Meanwhile, the anomalous convergence of the surface currents and the anomalous divergence of the subsurface currents maintain eastward migration, which plays an important role in the eastward migration of the warm water during ME events. Although there is anomalous convergence in the upper ocean and anomalous divergence in the subsurface ocean during EE events, they appear quasi-stationary in the western Pacific. The warm water over the eastern Pacific during EE events is caused by the local anomalous convergence of surface currents and the anomalous divergence of subsurface currents.     

Warming in the Northwestern Indian Ocean Associated with the El Nio Event

This paper investigates possible warming effects of an El Nino event on the sea surface temperature anomaly (SSTA) in the northwestern Indian Ocean. Most pure positive Indian Ocean dipole (IOD) events (without an El Nino event co-occurring) have a maximum positive SSTA mainly in the central Indian Ocean south of the equator, while most co-occurrences with an El Nino event exhibit a northwest-southeast typical dipole mode. It is therefore inferred that warming in the northwestern Indian Ocean is closely related to the El Nino event. Based on the atmospheric bridge theory, warming in the northwestern Indian Ocean during co-occurring cases may be primarily caused by relatively less latent heat loss from the ocean due to reduced wind speed. The deepened thermocline also contributes to the warming along the east coast of Africa through the suppressed upwelling of the cold water. Therefore, the El Nino event is suggested to have a modulating effect on the structure of the dipole mode in the tropical Indian Ocean.     

强潮汐激发地震火山活动的新证据

强潮汐与火山地震活动密切相关. 天文资料表明, 2000年6月到8月日本Izu半岛最活跃的火山地震活动正好处于天文大潮时期和日长变化最小值时期. 在厄尔尼诺事件和拉尼娜事件发生前后,东西太平洋海面高度分别升降40cm, 水均衡作用使洋壳反向升降13cm. 由此形成的东西太平洋地壳跷跷板运动加强了强潮汐对地震火山活动的激发作用.     

Impacts of El Niño–southern oscillation on global runoff: Characteristic signatures and potential mechanisms

Runoff signatures, including low flow, high flow, mean flow and flow variability, have important implications on the environment and society, predominantly through drought, flooding and water resources. Yet, the response of runoff signatures has not been previously investigated at the global scale, and the influencing mechanisms are largely unclear. Hence, this study makes a global assessment of runoff signature responses to the El Niño and La Niña phases using daily streamflow observations from 8217 gauging stations during 1960–2015. Based on the Granger causality test, we found that ~15% of the hydrological stations of multiple runoff signatures show a significant causal relationship with El Niño–southern oscillation (ENSO). The quantiles of all runoff signatures were larger during the El Niño phase than during the La Niña phase, implying that the entire flow distribution tends to shift upward during El Niño and downward during La Niña. In addition, El Niño has different effects on low and high flows: it tends to increase the low and mean flow signatures but reduces the high flow and flow variability signatures. In contrast, La Niña generally reduces all runoff signatures. We highlight that the impacts of ENSO on streamflow signatures are manifested by its effects on precipitation (P), potential evaporation (PET) and leaf area index (LAI) through ENSO-induced atmospheric circulation changes. Overall, our study provides a comprehensive picture of runoff signature responses to ENSO, with valuable insights for water resources management and flood and drought disaster mitigation.     

A diatom‐based reconstruction of summer sea‐surface salinity in the Southern Okinawa Trough,East China Sea,over the last millennium

A high‐resolution diatom record from site MD05‐2908 in the Southern Okinawa Trough, East China Sea, reveals pronounced multidecadal‐ to centennial‐scale palaeoceanographic changes throughout the last millennium. Summer sea‐surface salinity (SSS) was reconstructed using a weighted averaging partial least squares diatom‐based training set. The reconstructed SSS shows slightly decreasing values during the period AD 905–1930 with considerable fluctuations superimposed on this general trend. Relatively high‐salinity conditions during the interval AD 905–1450 probably suggest a low flood frequency in north‐eastern Taiwan. Furthermore, the high SSS values are associated with a strong and stable influence of the Kuroshio Current on the Southern Okinawa Trough during the Medieval Climate Anomaly. The period AD 1450–1930 is characterized by three low‐salinity intervals (AD 1450–1500, AD 1625–1725 and AD 1770–1880) separated by periods of relatively high salinity. The low SSS intervals indicate increased freshwater discharge into the Southern Okinawa Trough during the Little Ice Age, probably as a result of higher flood frequencies in north‐eastern Taiwan. Spectral and wavelet analyses suggest that this pattern was linked to multidecadal variations in summer SSS, presumably associated with the Pacific Decadal Oscillation. Copyright © 2012 John Wiley & Sons, Ltd.     

The implications of regional variations in rainfall for reconstructing rainfall patterns using tree rings

In Australia, multidecadal periods of floods and droughts have major economic consequences. Due to the short duration of Australian instrumental precipitation records, it is difficult to determine the patterns of these multidecadal periods. Proxy records can be used to create long‐term rainfall reconstructions for regions that are lacking instrumental data. However, the spatial extent over which single‐site proxy records can be applied is poorly understood. Southeast Queensland (SEQ) is an area where tree rings can be used to reconstruct long‐term rainfall patterns, but their regional representation is unknown. In this study, the spatial variability in rainfall across SEQ is investigated from 1908 to 2007 using 140 instrumental rainfall stations. Pearson correlation analysis between stations is used to create groups at the r = 0.80, 0.85, and 0.90 correlation levels, and then annual deviations from the mean are determined. These patterns indicate that rainfall is not uniform across SEQ but can be broken into 2 main spatially consistent groups. Each of these groups is broken down into several subgroups with higher correlation levels. Long‐term streamflow records are found to be correlated to rainfall patterns local to the streamflow stations, indicating that analysis of extreme events should consider spatial precipitation variability. Finally, the only currently available proxy rainfall reconstruction for the region, a 140‐year Toona ciliata tree ring width record from Lamington National Park, is compared to rainfall groups at different correlation levels across all of SEQ. The correlation between the reconstruction and the rainfall station groupings is best for the groups within which the tree‐ring record is spatially located, and this correlation improves as rainfall group correlation increases. Correlation is nearly nonexistent for groupings located at a distance from the tree‐ring site. These results demonstrate the importance of assessing the spatial variability of precipitation so that the spatial applicability of proxy records can be assessed.