青藏高原热状况和海温异常对亚洲季风季节转换年际变化的影响

本文根据季节转换前后副高脊面附近经向温度梯度变号的本质，利用相关分析和合成分析等方法研究了季节转换年际变化与外部影响因子的联系. 结果表明，冬春季青藏高原热状况和ENSO（El Nio/Southern Oscillation，厄尔尼诺/南方涛动）是决定亚洲季风区季节转换年际变化的主要因素. 当冬、春季海温呈现El Nio异常时，Walker环流减弱，于是西太平洋暖池区对流活动受到抑制，而赤道东太平洋对流活动加强则强迫赤道印度洋地区产生绝热下沉运动，使得印度洋地区大气偏暖，结果增大了南北向温度梯度，季节转换往往偏晚. 反之，季节转换偏早. 初春高原上空对流层中高层的气温异常对于判断季节转换迟早有很好的指示意义.     

Variability in Solomon Sea circulation derived from altimeter sea level data

The Solomon Sea is a key region in the Pacific Ocean where equatorial and subtropical circulations are connected. The region exhibits the highest levels in sea level variability in the entire south tropical Pacific Ocean. Altimeter data was utilized to explore sea level and western boundary currents in this poorly understood portion of the ocean. Since the geography of the region is extremely intricate, with numerous islands and complex bathymetry, specifically reprocessed along-track data in addition to standard gridded data were utilized in this study. Sea level anomalies (SLA) in the Solomon Sea principally evolve at seasonal and interannual time scales. The annual cycle is phased by Rossby waves arriving in the Solomon Strait, whereas the interannual signature corresponds to the basin-scale ENSO mode. The highest SLA variability are concentrated in the eastern Solomon Sea, particularly at the mouth of the Solomon Strait, where they are associated with a high eddy kinetic energy signal that was particularly active during the phase transition during the 1997–1998 ENSO event. Track data appear especially helpful for documenting the fine structure of surface coastal currents. The annual variability of the boundary currents that emerged from altimetry compared quite well with the variability seen at the thermocline level, as based on numerical simulations. At interannual time scales, western boundary current transport anomalies counterbalance changes in western equatorial Pacific warm water volume, confirming the phasing of South Pacific western boundary currents to ENSO. Altimetry appears to be a valuable source of information for variability in low latitude western boundary currents and their associated transport in the South Pacific.     

赤道MJO活动对南海夏季风爆发的影响

利用1979—2013年NCEP/DOE再分析资料的大气多要素日平均资料、美国NOAA日平均向外长波辐射资料和ERSST月平均海温资料,分析赤道大气季节内振荡(简称MJO)活动对南海夏季风爆发的影响及其与热带海温信号等的协同作用.结果表明,赤道MJO活动与南海夏季风爆发密切联系,MJO的湿位相(即对流活跃位相)处于西太平洋位相时,有利于南海夏季风爆发,而MJO湿位相处于印度洋位相时,则不利于南海夏季风爆发.赤道MJO活动影响南海夏季风爆发的物理过程主要是大气对热源响应的结果,当MJO湿位相处于西太平洋位相时,一方面热带西太平洋对流加强使潜热释放增加,导致处于热源西北侧的南海—西北太平洋地区对流层低层由于Rossby响应产生气旋性环流异常,气旋性环流异常则有利于西太平洋副热带高压的东退,另一方面菲律宾附近热源促进对流层高层南亚高压在中南半岛和南海北部的建立,使南海地区高层为偏东风,从而有利于南海夏季风建立;当湿位相MJO处于印度洋位相时,热带西太平洋对流减弱转为大气冷源,情况基本相反,不利于南海夏季风建立.MJO活动、孟加拉湾气旋性环流与年际尺度海温变化协同作用,共同对南海夏季风爆发迟早产生影响,近35年南海夏季风爆发时间与海温信号不一致的年份,基本上是由于季节转换期间的MJO活动特征及孟加拉湾气旋性环流是否形成而造成,因此三者综合考虑对于提高季风爆发时间预测水平具有重要意义.     

Aspects of Low Frequency Oscillation During the Northern Winter as Inferred From Nonlinear Energy Interactions

— The work deals with the computation and analysis of spectral energetics in the frequency domain at 850?hPa and 200?hPa over the tropics (20°S–20°N) and extratropics (20°N–60°N). The data for the winter months, i.e., November, December and January of 1995, 1996 and 1997 are selected for this purpose. The results suggest that much of the low frequency variability of the Northern Hemisphere wintertime general circulation is associated with disturbances which derive their energy from the time-mean flow through barotropic instability. Low frequency fluctuations tend to be larger in horizontal scale and their kinetic energy is largely confined to the upper troposphere. At 850?hPa, strong energy interaction south of 5°N is noticed due to a southward shift of major inflow channel, originating from the Bay of Bengal and entering the ITCZ from the western Arabian Sea. The energy balances in the tropics and the extratropics during winter have different characteristics from those during summer. In contrast to the summer circulation, instead of a downscale decascade as in the case of the extratropics, kinetic energy is transferred in an opposite sense, namely from transients of shorter to those of longer time scales in the tropics during winter. The strong nonlinear energy interactions associated with low frequency waves over the Indian Ocean (5°N–5°S) during winter is the manifestation of the deep convection due to warm water coupled with the crossequatorial low level flow along the ITCZ over this region. Forcing from this region readily excites a large response in terms of nonlinear energy interaction over the extratropical northeast Pacific.     

The behavior of deep convective clouds over the warm pool and connection to the Walker circulation

As the deep convective clouds (DCCs) over the western Pacific and Indian Ocean warm pool may play different roles in the climate system, variations in DCC properties over these two sectors are investigated and compared. The DCC intensity and area varies more significantly in the Indian Ocean than the western Pacific sector, while the DCC frequency is comparable in both sectors at the seasonal scale. Although the Indian Ocean sector is strongly dominated by the seasonal evolution, the interannual variations in the two sectors are comparable for all three DCC properties (frequency, intensity, and area). Besides, Walker circulation is closely correlated with the interannual variability of DCCs in both sectors. The Walker circulation strengthens (weakens) as the DCCs shift eastward (westward) over the Indian Ocean sector and westward (eastward) over the western Pacific sector. When more or stronger DCCs occur over the Indian Ocean sector (western Pacific sector), the Walker circulation becomes stronger (weaker) and shifts westward (eastward). Interestingly, the response of the Walker circulation to DCC variability over the warm pool is asymmetry. The asymmetry response of the Walker circulation to the negative and positive DCC anomaly may be related to the non-linearity internal variability of the atmosphere. DCCs over the Indian Ocean sector have a much weaker nonlinear correlation with the Walker circulation than DCCs over the western Pacific sector.     

Role of Ocean in the Variability of Indian Summer Monsoon Rainfall

Asian summer monsoon sets in over India after the Intertropical Convergence Zone moves across the equator to the northern hemisphere over the Indian Ocean. Sea surface temperature (SST) anomalies on either side of the equator in Indian and Pacific oceans are found related to the date of monsoon onset over Kerala (India). Droughts in the June to September monsoon rainfall of India are followed by warm SST anomalies over tropical Indian Ocean and cold SST anomalies over west Pacific Ocean. These anomalies persist till the following monsoon which gives normal or excess rainfall (tropospheric biennial oscillation). Thus, we do not get in India many successive drought years as in sub-Saharan Africa, thanks to the ocean. Monsoon rainfall of India has a decadal variability in the form of 30-year epochs of frequent (infrequent) drought monsoons occurring alternately. Decadal oscillations of monsoon rainfall and the well-known decadal oscillation in SST of the Atlantic Ocean (also of the Pacific Ocean) are found to run parallel with about the same period close to 60 years and the same phase. In the active–break cycle of the Asian summer monsoon, the ocean and the atmosphere are found to interact on the time scale of 30–60 days. Net heat flux at the ocean surface, monsoon low-level jetstream (LLJ) and the seasonally persisting shallow mixed layer of the ocean north of the LLJ axis play important roles in this interaction. In an El Niño year, the LLJ extends eastwards up to the date line creating an area of shallow ocean mixed layer there, which is hypothesised to lengthen the active–break (AB) cycle typically from 1 month in a La Niña to 2 months in an El Niño year. Indian monsoon droughts are known to be associated with El Niños, and long break monsoon spells are found to be a major cause of monsoon droughts. In the global warming scenario, the observed rapid warming of the equatorial Indian ocean SST has caused the weakening of both the monsoon Hadley circulation and the monsoon LLJ which has been related to the observed rapid decreasing trend in the seasonal number of monsoon depressions.     

华南前汛期降水异常与太平洋海表温度异常的关系

利用近50年华南地区站点逐日降水观测资料和全球大气、海洋分析资料,分析了华南前汛期降水异常的变化特征及其与太平洋海温异常的联系.结果表明,近50年来华南前汛期降水总体呈现减少趋势.影响华南前汛期降水异常的太平洋海温异常型是一个类似于ENSO的西太平洋暖池模态,即显著海温异常区域位于西太平洋暖池.西太平洋暖池区域(120°E-180°E,20°S-20°N)前期冬季海温异常同华南前汛期降水存在显著的负相关关系,是具有预报意义的海温关键区.该关键区海温异常影响华南前汛期降水的可能物理过程是:当前期冬季暖池异常偏暖时,菲律宾周围地区对流活动加强,导致Walker环流及东亚太平洋中低纬局地Hadley环流增强;该异常通过影响东亚－太平洋遥相关波列,使前汛期期间西太平洋副高加强西伸,脊线位置偏北,同时副热带西风急流减弱北退.随着Hadley环流上升支的增强,东亚副热带地区下沉运动也增强了,华南地区对流活动受到抑制.而且由于副高的增强,经过其北侧向华南地区的西南水汽输送辐合也减弱了,因此前汛期降水偏少.冷海温年的情形则相反,华南前汛期降水偏多.近50年来华南前汛期降水总体呈现趋势性减少正是由于前冬西太平洋暖池趋势性增暖所致.     

Three-dimensional distributions of sewage markers in Tokyo Bay water--fluorescent whitening agents (FWAs)

Three-dimensional distributions of fluorescent whitening agents (FWAs: more specifically, DSBP and DAS1), which are sewage-derived water-soluble markers, were observed in Tokyo Bay water through multi-layer sampling of water at 20 locations. In summer, FWAs predominated in the surface layers, with trace but significant concentration of FWAs in bottom water due to stratification of seawater. In winter, on the other hand, FWAs were extensively mixed into the bottom layers because of the vertical mixing of seawater. In the surface layer, FWA concentrations and the DSBP/DAS1 ratio (the concentration ratio of DSBP to DAS1) were lower in summer than in winter, suggesting more efficient photodegradation of FWAs in euphotic zones during the summer due to stronger solar radiation. Horizontally, FWAs were widely distributed over the surface layer of Tokyo Bay. Surface water with DSBP concentrations above 50ng/L, corresponding to <200 times dilution of sewage effluent, was found to have spread up to 10km from the coastline. In addition, an offshore decline in FWA concentrations was observed, showing a half-distance of 10-20km. The decrease was caused by dilution by seawater of fresh water containing FWAs. The eastern part of the bay was different with respect to surface layers, with higher concentrations seen in northeastern parts. Furthermore, dispersion of combined sewer overflow (CSO)-derived water mass was observed in Tokyo Bay after heavy rain.     

Modeling the East Asian climate during the last glacial maximum

Climatologists have been paying much attention to the global and regional climatic charac-teristics during the LGM. A lot of paleodata were obtained in East Asia during the LGM[1—5] and laid the firm foundation of reconstructing East Asian paleoclimate t…     

夏季西北太平洋大气环流异常及其与热带印度洋-太平洋海温变化的关系

本文分析了夏季西北太平洋大气环流异常特征及其与海温变化的关系,发现夏季西北太平洋异常反气旋/气旋(WNPAC/WNPC)是西北太平洋地区对流层中低层存在的重要大气环流异常现象,与东亚-西北太平洋低纬度至高纬度的经向PJ波列及欧亚中高纬度东西纬向波列的变化有关,通过与中高纬度环流变化的联系,对东亚及欧亚中高纬度气候有重要影响.夏季WNPAC/WNPC与热带海温变化的关系存在明显的不对称性,显著的WNPAC一般出现在El Niño衰减年夏季,与前期El Niño成熟年冬季的赤道东太平洋暖海温异常和El Niño衰减年春夏季印度洋海盆尺度的暖海温异常有明显的正相关关系,进一步表明了WNPAC在El Niño事件影响夏季气候中的重要桥梁作用;而夏季显著的WNPC与前期和同期热带海温变化的关系存在明显的不确定性,主要与夏季热带印度洋和赤道中东太平洋之间东暖西冷的热力差异异常引起的孟加拉湾-赤道西太平洋西风异常有关.进一步分析WNPAC/WNPC与海温变化关系不对称的可能原因,发现El Niño和La Niña衰减年夏季热带印度洋和太平洋海温变化所引起的印-太之间海温(热力)差异的一致性特征可能是导致WNPAC/WNPC与海温变化关系不对称的主要原因.     

南海夏季风爆发与南大洋海温变化之间的联系

利用1979-2009年NCEP第二套大气再分析资料和ERSST海温资料,分析南海夏季风爆发时间的年际和年代际变化特征,考察南海夏季风爆发早晚与南大洋海温之间的联系.主要结果为:(1)南海夏季风爆发时间年际和年代际变化明显,1979-1993年与1994-2009年前后两个阶段爆发时间存在阶段性突变;(2)南海夏季风爆发时间与前期冬季(12-1月)印度洋-南大洋(0-80°E,75°S-50°S)海温、春季(2-3月)太平洋-南大洋(170°E -80°W,75°S-50°S)海温都存在正相关关系,当前期冬、春季南大洋海温偏低(高)时,南海夏季风爆发偏早(晚).南大洋海温信号,无论是年际还是年代际变化,都对南海夏季风爆发具有一定的预测指示作用;(3)南大洋海温异常通过海气相互作用和大气遥相关影响南海夏季风爆发的迟早.当南大洋海温异常偏低(偏高)时,冬季南极涛动偏强(偏弱),同时通过遥相关作用使热带印度洋-西太平洋地区位势高度偏低(偏高)、纬向风加强(减弱),热带大气这种环流异常一直维持到春季4、5月份,位势高度和纬向风异常范围逐步向北扩展并伴随索马里越赤道气流的加强(减弱),从而为南海夏季风爆发偏早(偏晚)提供有利的环流条件.初步分析认为,热带大气环流对南大洋海气相互作用的遥响应与半球际大气质量重新分布引起的南北涛动有关.     

孟加拉湾夏季风爆发的判断指标及其年际特征

利用高低层大气环流、OLR（向外长波辐射）、CMAP降水、SST（海表温度）等资料分析了孟加拉湾地区3—5月多年气候平均大气环流及不同要素的演变特征,定义了一个新的孟加拉湾夏季风（BOBSM,下同）爆发指标为孟加拉湾地区（5°N—15°N,90°E—97.5°E）850 hPa和200 hPa纬向风区域平均的变化同时满足U850 > 3 m·s^-1和U200 < -5 m·s^-1,并持续5天的第一天即作为BOBSM爆发日期.该季风指数有明确的天气学意义,可以反映孟加拉湾低层西南风持续稳定和南亚高压在青藏高原建立早晚的特征.文章进一步分析了BOBSM爆发的年际特征及其前兆海洋信号特征,结果表明：1981—2010年BOBSM爆发的平均日期为5月10日,季风爆发有显著的年际波动,爆发最早在1999年（4月11日）和最晚在1968年（6月1日）,年代际尺度上表现为由爆发偏晚至偏早的变化趋势;BOBSM爆发早（晚）与热带印度洋地区850 hPa的越赤道气流和西风异常加强（减弱）,以及200 hPa青藏高原南亚高压的季节性建立偏早（晚）等密切联系;前期冬季赤道西太平洋的海温冷（暖）变化对BOBSM爆发早（晚）有很好的指示意义,前期冬季海温偏高（低）有利于季风偏早（晚）,其影响的主要途径是通过热源变化激发纬向垂直环流及其热带印度洋和太平洋低层环流异常,进而影响季风爆发早晚.     

Wind-forced circulation model and water exchanges through the channel in the Bay of Toulon

A hydrodynamic model of the Bay of Toulon has been developed for use as a post-accident radionuclide dispersion simulation tool. Located in a Mediterranean urban area, the Bay of Toulon is separated into two basins by a 1.4-km long seawall. The Little Bay is semi-enclosed and connected to the Large Bay by a fairway channel. This channel is the site of significant water mass exchange as a result of both wind-driven currents and bathymetry. It is therefore a focal point for marine contamination. As part of the model calibration and validation process, the first step consisted of studying the water mass exchange between the two basins. An Acoustic Doppler Current Profiler was moored in the channel for 1 year. The present study analyses in situ data to determine the current intensity and direction, and also to better understand the vertical current profile, which is highly correlated with meteorological forcing. Comparisons of model-generated and measured data are presented, and various atmospheric forcing datasets are used to enhance computed results. It appears that accurate meteorological forcing data is needed to enhance the accuracy of the hydrodynamic model. This channel is an important location for water mass renewal in the Bay of Toulon, and model results are used to quantify these exchanges. The mean calculated annual water exchange time is approximately 3.4 days. However, this duration is strongly wind dependent and shortens during windy winter months. It ranges from 1.5 days during strong wind periods to 7.5 days during calm weather. Residence time values calculated through tracer dispersion modelling after release at the back of the Little Bay are found to be comparable to the mean exchange time values, especially for windy conditions.     

北太平洋海表面高度的年际变化及其机制

利用15年（1993～2007年）月平均的海表面高度（SSH）异常资料,分析了北太平洋海表面高度的年际变化的时空结构,并研究了热通量和风应力两个因子对其的强迫作用.结果表明,北太平洋年际时间尺度SSH变化的大值区在黑潮延伸区和西太平洋暖池区.EOF分解第一模态的空间结构沿纬向呈带状分布,第二模态为沿经向呈带状分布.热通量强迫作用在中纬度的东北太平洋可以解释SSH年际变化40%以上.风应力对SSH的作用包括正压和斜压两个方面.正压Sverdrup平衡模型模拟的SSH年际变化较弱,仅能解释高纬度副极地环流西部的20%~40%.由大尺度风应力强迫的第一阶斜压Rossby波模型可以解释热带地区的20%~60%,中纬度中部的20%~40%,以及阿拉斯加环流东部和副极地环流西部的20%~60%.风应力强迫的一阶斜压Rossby波模型对SSH的强迫机理又可分为局地风应力强迫和西传Rossby波作用.其中,风应力的局地强迫作用（Ekman抽吸）在东北太平洋、白令海以及热带中部有显著的预报技巧,可以解释SSH年际变异的40%以上.Rossby波的传播作用在中纬度海域的副热带环流中西部和夏威夷岛以东起着重要作用,可解释20%~60%.     

厄尔尼诺持续时间与大气环流异常形势

针对不同持续时间的El Nio事件,进行了大尺度大气环流及其演变的合成分析研究.其结果清楚地表明,不同持续时间的El Nio事件的发生、发展和消亡过程,对流层低层风场和对流层高层速度势场的距平都有极为显著差异.分析得到了对El Nio事件的发生和消亡起着重要作用的大气环流异常形势.还发现对于持续时间较长的El Nio事件,东北太平洋上850hPa异常气旋性环流减弱和西北太平洋上异常反气旋性环流增强较慢,因此赤道太平洋异常西风维持的时间也较长,而与澳大利亚冬季风加强相关联的南半球西太平洋的速度势正距平的维持,对El Nio的持续也起一定作用;对应持续时间较短的El Nio事件,西太平洋上200hPa速度势正距平的迅速东移,对El Nio的迅速消亡起重要作用.     

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.     

Progressive change of tidal wave characteristics from the eastern Yellow Sea to the Asan Bay,a strongly convergent bay in the west coast of Korea

Although there have been studies on the tide in convergent bay (or estuary), the tide change in terms of phase speed, amplitude, and phase difference between elevation and tidal current from a coastal ocean to a convergent bay has not been clearly shown so far. This study systematically examines the change of tidal wave characteristics from the eastern Yellow Sea to the Asan Bay, a strongly convergent bay on the west coast of Korea, using observations and an analytical model. As the tidal wave propagates from the eastern Yellow Sea into the Asan Bay, the phase speed, amplitude, and phase difference between elevation and tidal current increase along the channel. Such a phenomenon represents a unique example of tide change from a coastal ocean to a convergent bay, indicating dominance of convergence over friction in the Asan Bay. Both analytically computed tidal amplitude and travelling time compare well with observations. In the Asan Bay, the influence of the reflected wave is only felt in the upper one fifth of the bay and is almost unperceivable in the rest of the bay. The analytical analyses presented in this paper are particularly useful for understanding the relative importance of channel convergence, bottom friction, and reflected wave on the tidal characteristics change along the channel and the proposed method could be applicable to other estuaries.     

Grain-size records at ODP Site 1146 from the northern South China Sea: Implications on the East Asian monsoon evolution since 20 Ma

273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling algorithm (EMMA) in order to investigate the evolution of the East Asian monsoon since about 20 Ma. 10–19 μm/1.3–2.4 μm, the ratio of two grain-size populations with the highest variability through time was used to indicate East Asian winter monsoon intensity relative to summer monsoon. The mass accumulation rate of the coarsest end member EM1 (eolian), resulting from EMMA, can be used as a proxy of winter monsoon strength and Asian inland aridity, and the ratio of EM1/(EM2 EM3) as a proxy of winter monsoon intensity relative to summer monsoon. The combined proxies show that a profound enhancement of East Asian winter monsoon strength and winter monsoon intensity relative to summer monsoon occurred at about 8 Ma, and it is possible that the summer monsoon simultaneously intensified with winter monsoon at 3 Ma. Our results are well consistent with the previous studies in loess, eolian deposion in the Pacifc, radiolarians and planktonic foraminifera in the SCS. The phased uplift of the Himalaya-Tibetan Plateau may have played a significant role in strengthening the Asian monsoon at 8 Ma and 3 Ma.     

Energy Decay of the 2004 Sumatra Tsunami in the World Ocean

The catastrophic Indian Ocean tsunami generated off the coast of Sumatra on 26 December 2004 was recorded by a large number of tide gauges throughout the World Ocean. This study uses gauge records from 173 sites to examine the characteristics and energy decay of the tsunami waves from this event in the Indian, Atlantic and Pacific oceans. Findings reveal that the decay (e-folding) time of the tsunami wave energy within a given oceanic basin is not uniform, as previously reported, but depends on the absorption characteristics of the shelf adjacent to the coastal observation site and the time for the waves to reach the site from the source region. In general, the decay times for island and open-ocean bottom stations are found to be shorter than for coastal mainland stations. Decay times for the 2004 Sumatra tsunami ranged from about 13 h for islands in the Indian Ocean to 40–45 h for mainland stations in the North Pacific.     

Sea-floor fissures, biological communities and sediment fatty acids of the Northern Okushiri Ridge, Japan Sea: Implications for possible methane seepage

A biological community was discovered in the Northern Okushiri Ridge, northeastern Japan Sea. The community was closely associated with sea-floor fissures, and presumed to be supported by methanotrophic and/or thiotrophic bacterial production. Sediments inside of and in the vicinity of the fissures were collected, and the short-chain (C_9–20) sediment fatty acids were analyzed for amounts and compositions. The fatty acid compositions were compared with those from a known methane seep and a submarine volcano in the Sagami Bay, central Japan, and from a whale skeleton at the Torishima Seamount, northwestern Pacific Ocean. As a result, a close relationship between the sediments from the Northern Okushiri Ridge, the known methane-seep, and the whale skeleton was found. This finding represents the first discovery of methane seepage and associated biological communities in the Japan Sea. This also supports the hypothesis that the eastern margin of the northern Japan Sea is at the early stage of new subduction.