Interannual variations of sea water parameters and chlorophyll a concentration in the Japan Sea in autumn

Studied are the interannual variations of physical (temperature, salinity, and relative density) and chemical (dissolved oxygen and biogenic elements) parameters of sea water and chlorophyll a concentration in the Japan Sea in autumn. It is demonstrated that the increase in the water flow from the East China Sea through the Korea (Tsushima) Strait leads to the temperature rise and decrease in salinity and dissolved oxygen content in the surface water layer of the Japan Sea. It is revealed that in the central part of the Japan Sea from 1978 to 2012 trends were observed towards the increase in the content of dissolved inorganic nitrogen N, decrease in the content of inorganic phosphorus, and decrease in the concentration of chlorophyll a at the level of 50 m and its increase in the layer of 0–30 m. The observed trends are explained by the intensification of the effect of coastal water of the East China Sea subjected to the significant anthropogenic load on the water of the central part of the Japan Sea.     

Interannual variability of water transport by the East Kamchatka and East Sakhalin Currents and their influence on dissolved oxygen concentration in the Sea of Okhotsk and subarctic pacific

The influence of interannual variability of water transport by the East Kamchatka Current, the Oyashio, and the East Sakhalin Current on the dissolved oxygen concentration in the western subarctic Pacific and the Sea of Okhotsk is considered for studying climate change impact on sea water chemical parameters. It is shown that statistically significant relation is observed between the calculated with the Sverdrup equation interannual variations in water transport with the East Kamchatka Current, the Oyashio, and the East Sakhalin Current and changes in mean sea water level at coastal stations in winter. It is found that the main reason of interannual variability of the dissolved oxygen concentration at isopycnic surfaces in the intermediate water layer (100–800 m) of the Sea of Okhotsk and in the western subarctic Pacific is caused by variations in water transport by the East Kamchatka Current, the Oyashio, and the East Sakhalin Current.     

Intercomparison of Air–Sea Interface Fluxes over the Yellow Sea and Korea Strait: Impact of Tsushima Warm Current

Surface-layer meteorological observations obtained from oceanic buoys over the Korean Strait and the Yellow Sea are used to estimate surface-layer turbulent fluxes of heat, moisture and momentum over the East-Asian Marginal Seas. Special emphasis is paid towards explanation of the impact of the Tsushima warm current flowing through the Korean Strait on air–sea interface fluxes. During the active phase of the Tsushima warm current, when the difference in sea surface temperature and air temperature becomes as large as 8°C, the sensible heat flux increases to a value of about 135 W m⁻², while the latent heat flux is around 200 W m⁻². The study attempts to broaden our understanding on the air-sea interaction processes over the Yellow Sea and Korean Strait.     

Variability of Fram Strait sea ice export: causes, impacts and feedbacks in a coupled climate model

Analyses of a 500-year control integration of the global coupled atmosphere–sea ice–ocean model ECHAM5.0/MPI-OM show a high variability in the ice export through Fram Strait on interannual to decadal timescales. This variability is mainly determined by variations in the sea level pressure gradient across Fram Strait and thus geostrophic wind stress. Ice thickness anomalies, formed at the Siberian coast and in the Chukchi Sea, propagate across the Arctic to Fram Strait and contribute to the variability of the ice export on a timescale of about 9 years. Large anomalies of the ice export through Fram Strait cause fresh water signals, which reach the Labrador Sea after 1–2 years and lead to significant changes in the deep convection. The associated anomalies in ice cover and ocean heat release have a significant impact on air temperature in the Labrador Sea and on the large-scale atmospheric circulation. This affects the sea ice transport and distribution in the Arctic again. Sensitivity studies, simulating the effect of large ice exports through Fram Strait, show that the isolated effect of a prescribed ice/fresh water anomaly is very important for the climate variability in the Labrador Sea. Thus, the ice export through Fram Strait can be used for predictability of Labrador Sea climate up to 2 years in advance.     

东亚冬季风综合指数及其表达的东亚冬季风年际变化特征

本文通过多变量经验正交函数展开 (multivariate EOF, 简称 MV-EOF) 研究了东亚冬季风各系统成员的协同关系, 再运用单变量EOF定义单个系统的强度系数。从而给出能够反映东亚冬季风各主要特征及其年际变化、同时包含西伯利亚高压、东亚大槽和纬向风经向切变信息的强度指数 (EAWMII)。分析表明, 这个新指数EAWMII能够很好地反映东亚冬季风在20世纪80年代中期的减弱信号, 并且与大气环流场以及东亚冬季表面温度的变化均显著相关, 能够在很大程度上表征东亚冬季风的综合特征。此外, EAWMII与北极涛动 (Arctic Oscillation, 简称AO) 指数、北太平洋涛动 (North Pacific Oscillation, 简称NPO) 指数和Nio3.4指数相关显著。分析还表明AO和NPO影响东亚冬季气候的区域有所不同: AO主要影响欧亚大陆中、高纬、我国东北以及日本北部等地区, NPO则主要影响华南、华东、朝鲜、韩国以及日本中南部及其附近海域。并且, AO很可能可以通过影响NPO进而影响东亚冬季风。     

关于东亚夏季风变化及其成因的最近研究进展

东亚夏季风变化是中国、日本和韩国的重要研究课题。回顾了关于东亚季风(尤其是东亚夏季风)的季节内变化、年际和年代际变化及其这些变化成因的最近研究进展,特别是系统地回顾了厄尔尼诺、南方涛动(ENSO)循环、西太平洋暖池、青藏高原和陆面过程对东亚夏季风的季节内变化、年际和年代际变化的作用。     

Impacts of the South China Sea Throughflow on seasonal and interannual variations of the Indonesian Throughflow

Impacts of the South China Sea Throughflow (SCST) on seasonal and interannual variations of the Indonesian Throughflow are studied by comparing outputs from ocean general circulation model (OGCM) experiments with and without the SCST. The observed subsurface maximum in the southward flow through the Makassar Strait is simulated only when the SCST, which is driven by the large-scale wind, is allowed in the model. The mean volume and heat transport by the Makassar Strait Throughflow are reduced by 1.7 Sv and 0.19 PW, respectively, by the existence of the SCST in the model. The difference is particularly remarkable during boreal winter when the SCST reaches its seasonal maximum. Furthermore, the SCST is strengthened during El Niño, leading to the weakening in the southward volume and heat transport through the Makassar Strait by 0.37 Sv and 0.05 PW, respectively. These findings from the OGCM experiments suggest that the SCST may play an important role in climate variability of the Indo-Pacific Ocean.     

近50a东北冷涡暴雨水汽源地分布及其水汽贡献率分析

用HYSPLIT v4.9轨迹追踪模式,以分辨率为2.5°×2.5°的再分析资料驱动模式,对东北地区308例冷涡暴雨过程中的目标气块,进行后向轨迹追踪模拟。结果显示东北冷涡暴雨主要有4个水汽源地,(Ⅰ)西太平洋及相邻海域(包括鄂霍次克海、日本海、黄海、渤海和东海)水汽贡献率最大,平均水汽贡献率达39.8%;依次是(Ⅱ)孟加拉湾—南海海域为32.1%;(Ⅲ)欧亚大陆,尤其是贝加尔湖附近为20.9%;(Ⅳ)东北地区的水汽贡献率最小,仅为7.2%。欧亚大陆主要输送700 hPa高度附近的干冷气团,而各海域则输送800 hPa高度以下的暖湿气团。     

Interannual and interdecadal variations of the South Asian and western Pacific subtropical highs and their relationships with Asian-Pacific summer climate

In this study, interdecadal and interannual variations of the South Asian high (SAH) and the western Pacific subtropical high (WPSH), as well as their relationships with the summer climate over Asian and Pacific regions, are addressed. The variations of SAH and WPSH are objectively measured by the first singular value decomposition (SVD) mode of geopotential heights at the 100- and 500-hPa levels. The first SVD mode of summertime 100- and 500-hPa geopotential heights represents well the relationship between the variations of SAH and WPSH. Both SAH and WPSH exhibit large interannual variability and experienced an apparent long-term change in 1987. The WPSH intensifies and extends westward when SAH intensifies and extends eastward, and vice versa. The India?CBurma trough weakens when WPSH intensifies. The changes in SAH and WPSH at various levels are linked to broad-scale increases in tropical tropospheric temperature and geopotential height. When SAH and WPSH strengthen, monsoon flow becomes weaker over eastern Asia. In the meantime, precipitation decreases over eastern South China Sea, Philippines, the Philippine Sea and northeastern Asia, but increases over China, Korea, Japan and the ocean domain east of Japan. Similar features are mostly found on both interdecadal and interannual timescales, but are more evident on interannual timescale.     

A Study of the Impact of the Fukushima Nuclear Leak on East China Coastal Regions

ABSTRACT

The nuclear leak in Fukushima, Japan, which occurred on 11 March 2011, had disastrous impacts in many regions of the northern hemisphere. In this study, a highly resolved, one-way nesting model incorporating tides is set up with the Regional Ocean Modeling System (ROMS) to simulate and predict the potential impact of the disaster on the East China Sea (ECS), with the large domain covering the entire North Pacific. Of the four main waterways, namely Taiwan Strait, the waterway east of Taiwan, Tokara Strait, and Tsushima Strait, the first two have net fluxes of radionuclides into the ECS, while the other two have net outward transport during the entire 14-year period of the simulation (2011–2025). Differing from previous studies, we have taken into account background radionuclides in this model; the results agree well with available observations. Based on the simulation, the radioactive material has arrived in the ECS. The amount will reach its peak in 2019 and late in 2021 will return to its original state before the accident. Temporally it has a clear seasonal variability, with peaks usually appearing during winter. Spatially it is not homogeneously distributed, and the concentration has local maxima along the coasts of Jiangsu and Zhejiang, which are the most populous regions of China; a conspicuous feature is the Subei Bank high in summer. This study is expected to help form policy for rapid response to such disasters.     

A model-based study of ice and freshwater transport variability along both sides of Greenland

We investigate some aspects of the variability of the Arctic freshwater content during the 1965–2002 period using the DRAKKAR eddy admitting global ocean/sea-ice model (12 km resolution in the Arctic). A comparison with recent mooring sections shows that the model realistically represents the major advective exchanges with the Arctic basin, through Bering, Fram and Davis Straits, and the Barents Sea. This allows the separate contributions of the inflows and outflows across each section to be quantified. In the model, the Arctic freshwater content variability is explained by the sea-ice flux at Fram and the combined variations of ocean freshwater inflow (at Bering) and outflow (at Fram and Davis). At all routes, except trough Fram Strait, the freshwater transport variability is mainly accounted for by the liquid component, with small contributions from the sea-ice flux. The ocean freshwater transport variability through both Davis and Fram is controlled by the variability of the export branch (Baffin Island Current and East Greenland Current, respectively), the variability of the inflow branches playing a minor role. We examine the respective role of velocity and salinity fluctuations in the variability of the ocean freshwater transport. Fram and Davis Straits offer a striking contrast in this regard. Freshwater transport variations across Davis Strait are completely determined by the variations of the total volume flux (0.91 correlation). On the other hand, the freshwater transport through Fram Strait depends both on variations of volume transport and salinity. As a result, there is no significant correlation between the variability of freshwater flux at Fram and Davis, although the volume transports on each side of Greenland are strongly anti-correlated (−0.84). Contrary to Davis Strait, the salinity of water carried by the East Greenland Current through Fram Strait varies strongly due to the ice-ocean flux north of Greenland.     

Climatic Changes in Thermal Conditions of Marginal Seas in the Western Pacific

Observational data from the Roshydromet hydrometeorological stations for 1978–2017, global meteorological network, and objective analysis and reanalysis (NOAA) are used to study the interannual variability of sea surface temperature and air temperature in the coastal and marine areas of the Okhotsk, Japan, Yellow, East China, and South China seas at the modern stage of the warming. Based on the EOF, cluster, and correlation analysis, the spatiotemporal pattern of temperature variations is analyzed and the zoning of sea areas according to the features of modern climate change is performed. The possible cause-and-effect relationships between these changes and the variations in wind components and climate indices are investigated. The studies revealed, specified, and quantified the modern trends and regional features of interannual variability of thermal conditions in the distinguished areas.     

Simulation of the interannual variability of the wind-driven Arctic sea-ice cover during 1958–1998

A thermodynamic-dynamic sea-ice model based on a granular material rheology developed by Tremblay and Mysak is used to study the interannual variability of the Arctic sea-ice cover during the 41-year period 1958–98. Monthly wind stress forcing derived from the National Centers for Environmental Prediction (NCEP) Reanalysis data is used to produce the year-to-year variations in the sea-ice circulation and thickness. We focus on analyzing the variability of the sea-ice volume in the Arctic Basin and the subsequent changes in sea-ice export into the Greenland Sea via Fram Strait. The relative contributions of the Fram Strait sea-ice thickness and velocity anomalies to the sea-ice export anomalies are first investigated, and the former is shown to be particularly important during several large export events. The sea-ice export anomalies for these events are next linked to prior sea-ice volume anomalies in the Arctic Basin. The origin and evolution of the sea-ice volume anomalies are then related to the sea-ice circulation and atmospheric forcing patterns in the Arctic. Large sea-ice export anomalies are generally preceded by large volume anomalies formed along the East Siberian coast due to anomalous winds which occur when the Arctic High is centered closer than usual to this coastal area. When the center of this High relocates over the Beaufort Sea and the Icelandic Low extends far into the Arctic Basin, the ice volume anomalies are transported to the Fram Strait region via the Transpolar Drift Stream. Finally, the link between the sea-ice export and the North Atlantic Oscillation (NAO) index is briefly discussed. The overall results from this study show that the Arctic Basin and its ice volume anomalies must be considered in order to fully understand the export through Fram Strait. Received: 27 January 1999 / Accepted: 8 July 1999     

1960～2011年江淮地区夏季极端高温日数的特征及成因分析

基于江淮地区气象站1960~2011年逐日最高气温资料,分析了江淮地区在北半球夏季极端高温日数的年际变化及其与大气环流场和海温的关系。结果表明在江淮流域极端高温日偏多(少)时,其上空对流层中上层出现了具有正压结构的异常反气旋(气旋)环流,以及热成风涡度平流导致的下沉(上升)运动;亚洲西风急流的位置偏北(南),并且200 h Pa经向风场有明显的类似丝绸之路遥相关型的波列结构。在江淮地区极端高温日数偏多(少)的年份,前期的赤道太平洋中部,中国南海、孟加拉湾以及阿拉伯海海温呈现显著的正(负)异常,同期的中国东部海区、南日本海的海温呈现显著的正(负)异常。利用耦合模式比较计划第五阶段(CMIP5)中的8个模式的结果,评估了CMIP5模式对中国江淮地区夏季年平均极端高温的模拟效果,在此基础上,对未来极端高温的变化进行了预估。模式结果表明,在RCP(Representative Concentration Pathway)2.6情景下,21世纪末江淮地区夏季极端高温日数将可能达20 d左右;在RCP4.5情景下,21世纪末极端高温日数可能达40 d左右;在RCP8.5情景下,21世纪末极端高温日数将可能达约70 d。     

涡分辨率全球海洋环流模式LICOM模拟的吕宋海峡流场的季节变化

分析了一个1/10°的涡分辨率全球环流模式LICOM(LASG/IAP Climate system Ocean Model)对吕宋海峡附近海洋环流的模拟能力。结果表明,模拟的吕宋海峡附近上层环流及输运具有明显的季节变化特征,除6月是东向净流出外,其余月份均为西向流入,冬季流量最大。年平均流量在-3.76 Sv(1 Sv=106 m3/s),其中上层(600 m以上)流量起主要贡献,为-3.60 Sv,与目前已有的研究结果基本一致。南海通过6个海峡完成与外界的水交换,其中吕宋海峡和巴拉巴克海峡是大洋水进入南海的主要通道,其余海峡均以流出为主,流出量最大的是台湾海峡(1.99 Sv),其次是卡里玛塔海峡(1.03 Sv)。进一步分析表明,由季风引起的埃克曼输送量约占吕宋海峡流量的11%,而由季风引起的吕宋海峡压力梯度形成的西向的地转流对吕宋海峡的输运起支配作用。作为黑潮源头的太平洋北赤道流流量对吕宋海峡输运的季节变化也有一定影响。     

东亚夏季PJ遥相关型的年际及年代际变化机理

利用夏季东亚地区500 h Pa高度场和菲律宾附近的降水场进行SVD分析,将东亚500 h Pa高度场对应的时间序列定义为PJ指数,该指数不仅清楚地反映PJ型的年际变化,而且反应出PJ型的年代际变化,即500 h Pa高度场型态在20世纪70年代末由"气旋、反气旋、气旋"型突变为"反气旋、气旋、反气旋"型。本文研究表明PJ指数的年际变化与ENSO事件有密切的联系:El Ni1o事件通过电容器充电效应使印度洋海温增暖,而增暖的印度洋海温在菲律宾海附近强迫出异常反气旋,并沿东亚沿岸激发出PJ遥相关型。而PJ型态的年代际变化与热带印度洋SST的持续增暖有关。虽然许多学者认为是菲律宾附近海温异常引起对流异常,并沿东亚沿岸激发出PJ遥相关型,但我们认为该区域的海温变化并不是造成PJ型年际和年代际变化的原因,而是由于该区域有反气旋(或者气旋)异常,从而辐射增加(减少),蒸发减弱(增加),温跃层下降(上升),SST变暖(变冷),该区域的海温变暖意味着对流是减弱的。本文进一步利用大气环流模式ECHAM5.4进行数值试验,结果表明:当热带印度洋增暖时,在菲律宾海附近强迫出反气旋,并沿东亚激发出"反气旋、气旋、反气旋"PJ遥相关型。     

Seasonal surface ocean circulation and dynamics in the Philippine Archipelago region during 2004–2008

The dynamics of the seasonal surface circulation in the Philippine Archipelago (117°E–128°E, 0°N–14°N) are investigated using a high-resolution configuration of the Regional Ocean Modeling System (ROMS) for the period of January 2004–March 2008. Three experiments were performed to estimate the relative importance of local, remote and tidal forcing. On the annual mean, the circulation in the Sulu Sea shows inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the southern basin. A strong jet with a maximum speed exceeding 100 cm s⁻¹ forms in the northeast Sulu Sea where currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the surface water of the western Pacific (WP) from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry the surface water from the WP near the San Bernardino Strait into the Sulu Sea via the Tablas Strait.These surface currents exhibit strong variations or reversals from winter to summer. The cyclonic (anticyclonic) circulation during winter (summer) in the Sulu Sea and seasonally reversing currents within the Archipelago region during the peak of the winter (summer) monsoon result mainly from local wind forcing, while remote forcing dominates the current variations at the Mindoro Strait, western Sulu Sea and Sibutu passage before the monsoons reach their peaks. The temporal variations (with the mean removed), also referred to as anomalies, of volume transports in the upper 40 m at eight major Straits are caused predominantly by remote forcing, although local forcing can be large during sometime of a year. For example, at the Mindoro Strait, the correlation between the time series of transport anomalies due to total forcing (local, remote and tides) and that due only to the remote forcing is 0.81 above 95% significance, comparing to the correlation of 0.64 between the total and local forcing. Similarly, at the Sibutu Passage, the correlation is 0.96 for total versus remote effects, comparing to 0.53 for total versus local forcing. The standard deviations of transports from the total, remote and local effects are 0.59 Sv, 0.50 Sv, and 0.36 Sv, respectively, at the Mindoro Strait; and 1.21 Sv, 1.13 Sv, and 0.59 Sv at the Sibutu Passage. Nonlinear rectification of tides reduces the mean westward transports at the Surigao, San Bernardino and Dipolog Straits, and it also has non-negligible influence on the seasonal circulation in the Sulu Sea.     

The onset and cessation of the “long rains” in eastern Africa and their interannual variability

Summary ?Thirty years (1958–1987) of daily rainfall data for Kenya and north eastern Tanzania are analysed with the aim to characterize the interannual variability of the onset and cessation of the East African “long rains” (boreal spring). The leading principal component (PC1) depicts consistent rainfall variations over much of the region. Cumulative PC1 scores for each year serve to identify onset and cessation dates. The robustness of the dates derived from this method is demonstrated through the use of an independent sample of stations. Their spatial representativity is assessed by daily rainfall composites. Average onset occurs on March 25^th, and cessation on May 21^st. The interannual variability of the onset (standard deviation of 14.5 days) is larger than that of the withdrawal (10.3 days), but the onset is also spatially much more consistent. Mean dates and dates in selected anomalous years agree well with previous studies. The relationship between onset time-series and large-scale atmospheric and oceanic fields is analysed. On a monthly time-scale, interannual variations in “long rains” onset are associated with sea-surface temperature (SST) and sea-level pressure (SLP) patterns that have a different sign for the Atlantic and Indian Oceans. A warm South Atlantic and a cool Indian Ocean are associated with low and high SLP anomalies, respectively. These patterns are conducive to enhanced equatorial easterlies and surface divergence over East Africa. This maintains the meridional branch (north–south orientated) of the Intertropical Convergence Zone (ITCZ) further west, and the net result is a delayed onset of the “long rains”. Some of the South Atlantic features are already present during January–February, suggesting some potential for monitoring interannual variations in the wet season onset, based on SST and SLP patterns. Additional signals are found over Europe and the Mediterranean Sea in terms of the interaction between the Northern Hemisphere extratropics and equatorial eastern Africa. A surge in the mid-tropospheric northerlies at this time induces instability that may lead to an early onset event. Received July 3, 2002; revised November 28, 2002; accepted December 7, 2002 Published online March 17, 2003     

1951—2015年进入东海的台风频数及登陆点的变化

利用日本气象厅提供的西北太平洋台风最佳路径观测资料,选取东海海区为研究范围,统计处理1951—2015年台风各要素资料,研究进入东海海区的台风频数、台风登陆点位置、台风频数及登陆点位置与太平洋年代际振荡（Pacific Decadal Oscillation,PDO）及ENSO的关系、影响台风生成和移动的因素等。结果表明：1）每年的7—9月为东海海区的台风高发季,其中8月最高,登陆台风也有相似趋势。2）进入东海海域的台风频数存在较明显的年际和年代际变化趋势。当PDO处于暖位相时,台风频数较小且有上升趋势,反之亦然。El Niño年进入东海海区的台风频数较常年减少,反之亦然。Niño3.4指数与台风频数整体上为负相关关系,相关系数为-0.32且通过90%置信度检验。3）进入东海海域的台风登陆点纬度变化较大,处于24~36°N之间,且有年代际变化特征。当PDO处于暖（冷）位相时,台风登陆点偏北（偏南）且有向北（南）移动的趋势。而登陆点纬度与ENSO的关系较为复杂。4）西北太平洋副热带高压的位置和强度是引起台风频数及登陆点位置变化的主要原因之一。当PDO处于冷位相时,西北太平洋副热带高压强度偏弱,且副高中心向东向北方向移动,导致进入东海的台风频数偏多,且台风登陆点偏北,反之亦然。     

Effects of El Ni?o Modoki on winter precipitation in Korea

This study compares the impacts of El Ni?o Modoki and El Ni?o on precipitation over Korea during the boreal winters from 1954 to 2009. Precipitation in Korea tends to be equal to or greater than the normal level during an El Ni?o Modoki winter, whereas there is no significant change during an El Ni?o winter. Greater than normal precipitation during El Ni?o Modoki was also found over the lower reaches of the Yangtze River, China and much of southern Japan. The latitudes of these regions are 5–10° further north than in southern China, where precipitation increases during El Ni?o. The following two anomalous atmospheric circulations were found to be causes that led to different precipitation distributions over East Asia. First, an atmospheric wave train in the lower troposphere, which propagated from the central tropical Pacific (cyclonic) through the southern Philippine Sea (anticyclonic) to East Asia (cyclonic), reached the southern China and northern Philippine Sea during El Ni?o, whereas it reached Korea and southern Japan during El Ni?o Modoki. Second, an anomalous local meridional circulation, which consists of air sinking in the tropics, flowing poleward in the lower troposphere, and rising in the subtropics, developed between the southern Philippine Sea and northern Philippine Sea during El Ni?o. During El Ni?o Modoki, however, this circulation expanded further to the north and was formed between the southern Philippine Sea and regions of Korea and southern Japan.