环境同位素记录中共生碳酸盐氧同位素分馏差值的影响

湖泊化学沉积碳酸盐δ18O是研究区域气候演变的重要环境指标之一。青海湖等闭流湖泊的研究结果证实,在对δ18O环境记录进行共生碳酸盐氧同位素分馏效应校正时,应依据具体情况,采用0-1‰的分馏差值。由高温实验结果推断出的常温分馏差值(4‰-7‰)不能被应用到自然条件下湖泊共生碳酸盐氧同位素分馏效应的校正。     

西太平洋暖池对西北太平洋季风槽和台风活动影响过程及其机理的最近研究进展

本文回顾和综述了近年来关于西太平洋暖池对西北太平洋热带气旋和台风（TCs）活动影响过程及其机理的研究进展。文中首先简单回顾了近年来关于西太平洋暖池热状态和菲律宾周围对流活动变化特征及其对与TCs活动有关的南海夏季风爆发和西太平洋副热带高压的季节内、年际变异的影响过程和机理的研究;然后,本文系统地回顾了近年来关于西太平洋暖池热状态通过西北太平洋季风槽影响TCs活动年际和年代际变化的影响过程及其机理的研究。此外,文中还指出了关于西太平洋暖池对西北太平洋上空季风槽和TCs活动变异的热力和动力作用需进一步深入研究的科学问题。     

On the oceanic impact of a data-assimilation method in a coupled ocean-land-atmosphere model

 Based on the Kalman filter theory, a new data-assimilation method has been used to improve the 3-D oceanic temperature field of the Center for Ocean-Land-Atmosphere Studies (COLA) coupled general circulation model. This method is applied to assimilate surface and subsurface temperature of in situ measurements from the Pilot Research Moored Array in the Tropical Atlantic project (PIRATA). The assimilation of the PIRATA data produces an improved representation of the thermal state of the ocean and allows a better estimation of other oceanographic quantities, like meridional heat fluxes and zonal currents. The present paper focuses on the tropical Atlantic and, in particular, it contains new reconstructed temperature profiles. One-month forecast experiments during 1999 were performed and the impact of the assimilation is discussed. Received: 24 April 2001 / Accepted: 8 March 2002     

Seep mounds on the Southern Vøring Plateau (offshore Norway)

Multidisciplinary study of seep-related structures on Southern Vøring Plateau has been performed during several UNESCO/IOC TTR cruises on R/V Professor Logachev. High-resolution sidescan sonar and subbottom profiler data suggest that most of the studied fluid discharge structures have a positive relief at their central part surrounded by depression. Our data shows that the present day fluid activity is concentrated on the top of these “seep mounds”. Number of high hydrocarbon (HC) gas saturated sediment cores and 5 cores with gas hydrate presence have been recovered from these structures. δ¹³C of methane (between −68 and −94.6‰ VPDB) and dry composition of the gas points to its biogenic origin. The sulfate depletion generally occurs within the upper 30–200 cm bsf and usually coincides with an increase of methane concentration. Pore water δ¹⁸O ranges from 0.29 to 1.14‰ showing an overall gradual increase from bottom water values (δ¹⁸O ∼ 0.35‰). Although no obvious evidence of fluid seepage was observed during the TV surveys, coring data revealed a broad distribution of living Pogonophora and bacterial colonies on sea bottom inside seep structures. These evidences point to ongoing fluid activity (continuous seepage of methane) through these structures. From other side, considerable number and variety of chemosynthetic macro fauna with complete absence of living species suggest that present day level of fluid activity is significantly lower than it was in past. Dead and subfossil fauna recovered from various seep sites consist of solemyid (Acharax sp.), thyasirid and vesicomyid (cf. Calyptogena sp.) bivalves belonging to chemosymbiotic families. Significant variations in δ¹³C (−31.6‰ to −59.2‰) and δ¹⁸O (0.42‰ and 6.4‰) of methane-derived carbonates collected from these structures most probably related to changes in gas composition and bottom water temperature between periods of their precipitation. This led us to ideas that: (1) seep activity on the Southern Vøring Plateau was started with large input of the deep thermogenic gas and gradually decries in time with increasing of biogenic constituent; (2) authigenic carbonate precipitation started at the near normal deep sea environments with bottom water temperature around +5 °C and continues with gradual cooling up to negative temperatures recording at present time.     

不同强度热带气旋对中国降水变化的影响

基于1960—2017年2 000多个气象台站逐日降水数据和中国气象局热带气旋(TC)最佳路径资料集,采用客观天气图分析法(OSAT)识别得到TC降水。研究表明,中国TC降水总体呈显著下降趋势,较12年前的研究结果下降趋势变缓;TC盛期(7~9月)降水占到TC总降水的78.5%,TC盛期降水和TC非盛期降水均呈显著下降趋势。TC降水气候趋势在空间分布上以减少为主要特征,并表现出明显的地域差异,自南向北呈"减少—增多—减少"的分布型,减少趋势中心位于广东和海南。按TC影响期最大强度分级(弱TC、中等强度TC和强TC)研究不同强度TC降水的变化,结果显示,强TC降水表现出显著减少趋势,主要决定着TC总降水的影响范围和趋势等主要特征。进一步分析发现,影响TC频数在1960—2017年呈显著减少趋势,并在1995年发生突变;对1995年前后2个时期的对比研究显示,与前一时期(1960—1994年)相比,后一时期(1995—2017年)影响TC活动频次在20°N以南的海域呈现出显著的减少趋势,减少大值中心位于南海北部,而且这一特征也主要由影响TC中的强TC所决定;强TC的这一变化趋势导致了华南地区尤其是广东和海南TC降水日数的减少,进而使得TC降水减少。     

亚洲夏季风季节内振荡对云南主汛期降水的影响Ⅱ:云南主汛期季节内振荡活动过程及其对MJO活动的响应

利用NCEP OLR、风场再分析资料和日本APHRO_MA_V1003R1降水资料,针对云南主汛期季节内振荡(ISO)活跃年分析了对应低频对流场、环流场和降水的异常特征,以及热带印度洋大尺度振荡MJO分别激发孟加拉湾西南季风ISO和南海热带季风ISO,从而对云南主汛期ISO和降水产生的影响.在云南主汛期ISO活跃年,低频对流场和环流场在云南ISO波动的1～3位相和4～6位相呈反位相特征,这主要由热带印度洋低频对流东传、北传和副热带西太平洋低频对流西传造成的.热带印度洋的低频对流在发展过程中,一方面沿孟加拉湾西岸向西南-东北方向传播,激发了孟加拉湾西南季风ISO活跃并继续向云南传播;另一方面沿孟加拉湾以南继续东传到南海,激发了南海热带季风ISO活跃并北传到副热带中国东部地区,再沿副热带西传至云南,越过云南后与沿孟加拉湾西岸从东北方向传来的低频对流在孟加拉湾以北地区交汇,完成了一个经纬向接力传播的周期.云南主汛期降水在1～3位相由于副热带低频对流西传和孟加拉湾低频对流东北向传播而处于正距平(第2位相降水最多);在4～6位相,由于副热带低频对流抑制区西传和孟加拉湾低频对流抑制区东北向传播而降水减少(第5位相降水最少),云南主汛期降水与当地低频对流有较好的对应关系.当热带印度洋MJO较强时,4-7月以两条路径向云南的三次传播增强和提前,使得云南主汛期ISO活动也加强,对应产生三次低频对流活跃期,这种MJO由热带印度洋向云南的传播需要30～40天的时间.因此,正是热带印度洋MJO分别对孟加拉湾西南季风ISO和南海热带季风ISO的激发,使得东亚夏季风和南亚夏季风这两个亚洲夏季风系统共同作用于云南主汛期ISO,影响当地降水.     

非绝热加热对热带气旋径向非均匀结构的影响

利用平面极坐标系下无摩擦有外源(非绝热加热)的正压无辐散方程,将热带气旋的物理量分解成环境场和扰动,进而求出了热带气旋扰动的行波解,并分析了风场(切向、径向)和重力位势扰动场的径向非均匀松紧结构.表明:这种松紧结构与热带气旋所在纬度的科氏参数(f)、热带气旋的强度(Ω)、热带气旋扰动的圆频率(ω)、热带气旋扰动在θ方向的角波数(m)有关,且不同要素的松紧结构不尽相同;同时还受非绝热加热(Q₁)的影响,这种影响主要表现在使风场(切向、径向)呈内紧外松的非均匀分布.     

夏季亚洲-太平洋涛动与中国近海热带气旋活动的关系

采用联合台风警报中心的台风最伟路径资料和NCEP/NCAR再分析资料,分析了夏季亚洲-太平洋涛动(Asian-Pacif-ic Oscillation,简称APO)与东亚近海-西北太平洋大气环流的关系,并进一步探讨了APO与中国近海热带气旋(tropical cy-clone,简称TC)活动的关系.研究表明:(1)夏季APO强弱与同期西北太平洋及中国东部近海TC活动存在密切关系,即在APO强(弱)年,西北太平洋TC活动偏西(东)和偏北(南),中国东部近海TC明显增多(减少);(2)当APO偏强(弱)时,中国东部近海大气环流有(不)利于TC的维持和发展,表现为低层存在异常气旋性(反气旋性)环流,对流层高低层纬向风垂直切变减小(增大),且对流加强(减弱);(3)APO强弱也影响着TC引导气流的方向:在APO强(弱)年,西北太平洋副热带高压(以下简称副高)偏北和偏东(偏南和偏西),副高南侧偏东气流减弱(加强),有利于TC的向西北行或在偏北(南)纬度西行,进入中国东部近海的TC增多(减少);(4)APO强弱也影响着南海-热带西太平洋TC源地上空的大气环流,在APO强(弱)年,南海-热带西太平洋季风槽偏北、偏西(偏南、偏东),热带西太平洋TC活动偏北和偏西(偏南和偏东),有利于进入中国东部近海TC的增多(减少).     

用赤道东太平洋海温预报西太平洋热带气旋年际变化的探讨

根据实际应用中统计预报对相关系数的基本要求,利用相关分析探讨了用赤道东太平洋海温预测西太平洋热带气旋年际变化的可行性。同时,利用谱分析方法探讨了这种预报的有效性和局限性。主要结论是:用区域(5°N—5°S,90—150°W)的平均海温预测西太平洋热带气旋的年际变化,效果比使用赤道东太平洋海温好,用前者可预测西太平洋中区各类热带气旋的年际变化,用后者只能预测西太平洋全区及中区热带气旋总体的年际变化,对达到热带风暴或台风的热带气旋的年际变化则分别是勉强能或不能预测;用赤道东太平洋海温无法预测南海热带气旋的年际变化;用赤道东太平洋海温预测西太平洋热带气旋活动实际上只对年际变化中的ENSO(3—5年)周期及准二年周期有效。     

Tropical Deforestation and Climate Change: What Does the Record Reveal?

Tropical deforestation is widely believed to directly influence the climate at a number of scales. Yet while much has been written about the tropical forest-climate relationship, there is little empirical evidence showing if and how local and regional climates are modified by deforestation. This study presents the results of an analysis of deforestation and climate change in a rain forest in southern Mexico. Records from 18 climate stations in the Selva Lacandona of Chiapas, Mexico were examined and related to an analysis of deforestation based on Landsat images. The area surrounding some stations has been deforested since the stations were established, while the area surroundings others has remained forested. Strong climatic trends were generally evident at the deforested stations, including decreases in the average daily maximum temperature and temperature range. No precipitation changes were observed. A comparison of the results with microclimatic experiments and modeling studies suggests that the climatic impacts of deforestation are overgeneralized at the local scale. Landscape heterogeneity appears to influence the biophysical mechanisms linking tropical forests and climate, and should be explicitly represented in modeling studies.