风应力桥梁作用下热带太平洋和热带大西洋相互作用的数值试验

利用中等复杂程度热带大气和海洋模式研究了热带太平洋和大西洋SST通过风应力桥梁的相互作用.利用1958～1998年NCEP分析的海表面温度场（SST）强迫大气模式得到的表面风应力与NCEP分析的同期热通量共同驱动海洋模式,作为控制试验;和控制试验平行,但强迫大气模式的SST在某一海盆取为多年气候平均值的试验作为敏感性试验;比较控制试验与敏感性试验模拟,则可反映风应力桥梁作用下热带某海盆SST异常对其他海盆的影响.结果表明,热带某一海盆SST暖（冷）异常总是引起局地海盆表面西部西（东）风异常和东部东（西）风异常;热带太平洋SST暖（冷）异常导致的该海盆东部表面东（西）风异常可以扩展到热带大西洋,从而导致热带大西洋SST冷（暖）异常;热带大西洋SST暖（冷）异常导致的该海盆西部表面西（东）风异常可以扩展到热带太平洋,从而导致热带太平洋SST暖（冷）异常.     

Towards a high-resolution,global, deep-sea chronology for the last 750,000 years

Variations in the ratio of¹⁸O/¹⁶O as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume; hence these variations provide a set of global time lines in deep-sea sediments. It is likely that the timing of major changes in oxygen isotope values is strongly influenced, if not controlled, by variations in the geometry of the Earth's orbit. Since the variation of orbital parameters can be accurately calculated, the opportunity exists for transforming this orbital chronology into a geological chronology.Through careful correlation of oxygen isotope records in a set of deep-sea cores from the sub-Antarctic, South Atlantic and equatorial Pacific, we have assembled a composite isotopic section spanning the last 750,000 years with an average sedimentation rate of 2.3 cm/1000 years. A new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300,000 years to the entire 750,000-year record. Previously identified difficulties in phase locking precession with the filtered isotopic signal between 365,000 and 465,000 years B.P. have been resolved with the recognition that precessional variations have an average period of 19,000 years and not 23,000 years during this interval. Since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record, we believe that it presents the most accurate chronology yet developed for deep-sea sediments.With this new age model providing the time control, power spectral analyses of South Atlantic and sub-Antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of ～ 100,000, 41,000 and 23,000 years.     

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.     

火山活动的周期性及其在若干气候要素中的反映

根据六百多年全球VEI 5级以上火山活动资料分析和谱分析以及与北半球地面气温、西太平洋高压SLP、北大西洋高压SLP和北大西洋西风漂流区SSTA对比分析得知:(1)全球强火山活动存在显著的88年左右和100年左右世纪尺度周期循环,二者对于VEI(i)原序列方差贡献率达到21.64%.还存在33年左右年代际尺度周期循环以...     

Mitigating parameter bias in hydrological modelling due to uncertainty in covariates

The uncertainty in hydrological model covariates, if ignored, introduces systematic bias in the parameters estimated. We introduce here a method to determine the true value of parameters given uncertainty in model inputs. This method, known as simulation extrapolation (SIMEX) operates on the basis of an empirical relationship between parameters and the level of input noise (or uncertainty). The method starts by generating a series of alternate model inputs by artificially adding white noise in increasing multiples of the known error variance. The resulting parameter sets allow us to formulate an empirical relationship between their values and the level of noise present. SIMEX is based on theory that the trend in alternate parameters can be extrapolated back to the notional error free zone.

We illustrate the strength of SIMEX in improving skills of predictive models that use uncertain sea surface temperature anomaly (SSTA) data over the NINO3 region as predictor to the southern oscillation index (SOI), an alternate measure of the strength of the El Nino southern oscillation. Our hypothesis is that the higher magnitude of noise in the pre 1960 data period introduces bias to model parameters where SSTA is the input variable. The relatively error invariant southern oscillation index (SOI) is regressed over SSTA and calibrated using a subset of the series from 1900 to 1960. We validate the resulting models using the less erroneous 1960–2003 data period. Overall the application of SIMEX is found to reduce the residual predictive errors during the validation period.     

全球海洋碳循环模式MOM4_L40对碳和营养物自然分布的模拟

本文介绍了国家气候中心发展的一个全球海洋碳循环环流模式,并分析评估了该模式的基本性能.该模式是在美国地球物理流体动力学实验室(GFDL,Geophysical Fluid Dynamics Laboratory)的全球海洋环流模式MOM4(Modular Ocean Model Version 4)基础上发展的一个垂直方向40层、包含生物地球化学过程的全球三维海洋碳循环环流模式,简称为MOM4_L40(Modular Ocean Model Version 4 With 40Levels).该模式在气候场强迫下长期积分1000年,结果分析表明,与观测相比,模式较好地模拟了海洋温度、盐度、总二氧化碳、总碱、总磷酸盐的表面和垂直分布特征.模拟的海洋总二氧化碳分布与观测基本相符,表层为低值区,其下为高值区,高值区域位于10°S—60°N之间,但2000m以上模拟值较观测偏小,2000m以下模拟值较观测偏大.总体来说,MOM4_L40模式是一个可信赖的海洋碳循环过程模拟研究工具.     

The Rio Grande fracture zone in the western South Atlantic and its tectonic implications

A broad zone of linear, mappable basement structures is observed north and northeast of the Rio Grande Rise in the South Atlantic Ocean. These structures lie along the same flow line as the Sa?o Paulo Ridge, the Florianopolis High, and onshore lineaments, suggesting that they all comprise the same tectonic trend: the Rio Grande fracture zone. The morphology developed along this fracture zone during the early opening of the South Atlantic Ocean formed a barrier to open ocean circulation during the Aptian and allowed the formation of extensive evaporite deposits to the north of it.     

Wind-induced subduction at the South Atlantic subtropical front

The South Atlantic Subtropical Front, associated with the eastward-flowing South Atlantic Current, separates the colder, nutrient-rich waters of the subpolar gyre from the warmer, nutrient-poor waters of the subtropical gyre. Perturbations to the quasi-geostrophic, eastward flow generate meanders and filaments which induce cross-frontal exchange of water properties. Down-front winds transport denser waters from the South over warm waters from the North, inducing convective instability and subduction. Such processes occur over spatial scales of the order of 1 km and thus require high horizontal spatial resolution. In this modeling study, a high-resolution (4 km) regional grid is embedded in a basin-wide configuration (12 km) of the South Atlantic Ocean in order to test the importance of submesoscale processes in water mass subduction along the subtropical front. Stronger and more numerous eddies obtained in the high-resolution run yield more intense zonal jets along the frontal zone. Such stronger jets are more susceptible to instabilities, frontogenesis, and the generation of submesoscale meanders and filaments with \(\mathcal {O}(1)\) Rossby number. As a consequence, vertical velocities larger than 100 md ¹ are obtained in the high-resolution run, one order of magnitude larger than in the low-resolution run. Wind-driven subduction occurs along the frontal region, associated with negative Ertel potential vorticity in the surface layer. Such processes are not observed in the low-resolution run. A passive tracer experiment shows that waters with density characteristics similar to subtropical mode waters are preferentially subducted along the frontal region. The wind-driven buoyancy flux is shown to be much larger than thermal or haline fluxes during the wintertime, which highlights the importance of the frictional component in extracting PV from the surface ocean and inducing subduction, a process that has been overlooked in subtropical mode water formation in the region.     

Sensitivity of cosmic ray trajectory calculations to geomagnetic field model representations

Cosmic ray vertical cutoff rigidities at sea level have been calculated, using the trajectory-tracing method, for a number of different epochs. These calculations have been carried out for a world-wide grid of locations, and, in an effort to locate the cosmic ray equator, for a fine grid in the equatorial region. Comparison of the vertical cutoff rigidity values obtained using the International Geomagnetic Reference Field model for 1980.0 with those obtained from previous models shows systematic significant changes in the Atlantic Ocean region and over South America. The differences are greater than those predicted utilizing the older field models with their predicted secular change. The cutoff rigidity values calculated using the new IGRF 1980.0 field model appear to be in better agreement with data from cosmic ray latitude surveys in the Atlantic Ocean region. The changes in the cosmic ray equator are asymmetrical with essentially no changes in the equator position in the Asian and Pacific region, but with significant changes in the South American, Atlantic Ocean and West African regions. Calculations have also been undertaken for different directions of arrival for a satellite orbiting at 400 km altitude using the predicted 1980 field model and the interim 1980 field model adopted in 1981. Some differences have been found.     

Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors

~~Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors@马宗晋 @任金卫 @张进~~     

A magnetotelluric study of the Damara Belt in Namibia: 1. Regional scale conductivity anomalies

The Namibian margin is dominated by the late Proterozoic to early Cambrian fold belts of the Damara Orogen, which wrap around and separate the Congo and Kalahari Cratons. This mosaic of relatively ‘soft’ fold belts and ‘hard’ cratons apparently controlled the path for the opening of the South Atlantic in the early Cretaceous. The continents split along the coast-parallel fold belts of the Damara Orogen while the inland fold belt (Damara Belt) was effected by extension and widespread igneous intrusion but never developed to the rift stage. This paper is concerned with the interpretation of magnetotelluric (MT) data along a 200 km NW-SE profile across the Damara Belt in NW Namibia. The regional, two-dimensional electrical resistivity model and the induction vector data exhibit three distinctive zones: (i) a generally very resistive upper crust which is typical for the granites and metasediments of the Damara Belt, (ii) two subvertical conductors in upper to mid-crustal levels which correlate with major tectonic zone boundaries and (iii) a highly conductive middle to lower crust in the southern part of the profile. The geometry of the conductive structures could reflect a regional shear system in which upper crustal listric faults pass into a detachment zone in the middle crust. We interpret the high electrical conductivity in terms of graphite (or other forms of mineralization) enrichment along the shear planes. This zone of crustal weakness may have originated in Pre-Damara times and had probably experienced several episodes of crustal reactivation before the intrusion of basaltic dike swarms during the Cretaceous rifting and magmatism associated with the opening of the South Atlantic.     

Global atmospheric response to specific linear combinations of the main SST modes. Part I: numerical experiments and preliminary results

This article investigates through numerical experiments the controversial question of the impact of El NinCo-Southern Oscillation (ENSO) phenomena on climate according to large-scale and regional-scale interhemispheric thermal contrast. Eight experiments (two considering only inversed Atlantic thermal anomalies and six combining ENSO warm phase with large-scale interhemispheric contrast and Atlantic anomaly patterns) were performed with the Météo-France atmospheric general circulation model. The definition of boundary conditions from observed composites and principal components is presented and preliminary results concerning the month of August, especially over West Africa and the equatorial Atlantic are discussed. Results are coherent with observations and show that interhemispheric and regional scale sea-surface-temperature anomaly (SST) patterns could significantly modulate the impact of ENSO phenomena: the impact of warm-phase ENSO, relative to the atmospheric model intercomparison project (AMIP) climatology, seems stronger when embedded in global and regional SSTA patterns representative of the post-1970 conditions [i.e. with temperatures warmer (colder) than the long-term mean in the southern hemisphere (northern hemisphere)]. Atlantic SSTAs may also play a significant role.     

Water and nutrient fluxes off Northwest Africa

A historical data set is used to describe the coastal transition zone off Northwest Africa during spring 1973 and fall 1975, from 17° to 26°N, with special emphasis on the interaction between subtropical (North Atlantic Central Waters) and tropical (South Atlantic Central Waters) gyres. The near-surface geostrophic circulation, relative to 300 m, is quite complex. Major features are a large cyclonic pattern north of Cape Blanc (21°N) and offshore flow at the Cape Verde front. The large cyclone occurs in the region of most intense winds, and resembles a large meander of the baroclinic southward upwelling jet. The Cape Verde frontal system displays substantial interleaving that may partly originate as mesoscale features at the coastal upwelling front. Property–property diagrams show that the front is an effective barrier to all properties except temperature. The analysis of the Turner angle suggests that the frontal system is characterized by large heat horizontal diffusion as a result of intense double diffusion, which results in the smoothing of the temperature horizontal gradients. Nine cross-shore sections are used to calculate along-shore geostrophic water-mass and nutrient transports and to infer exchanges between the coastal transition zone and the deep ocean (import: deep ocean to transition zone; export: transition zone to deep ocean). These exchanges compare well with mean wind-induced transports and actual geostrophic cross-shore transport estimates. The region is divided into three areas: southern (18–21°N), central (21–23.5°N), and northern (23.5–26°N). In the northern area geostrophic import is roughly compensated with wind-induced export during both seasons. In the central area geostrophic import is greater than wind-induced export during spring, resulting in net import of both water (0.8 Sv) and nitrate (14 kmol s⁻¹), but during fall both factors again roughly cancel. In the southern area geostrophy and wind join to export water and nutrients during both seasons, they increase from 0.6 Sv and 3 kmol s⁻¹ during fall to 2.9 Sv and 53 kmol s⁻¹ during spring.     

前冬南半球环状模对春季华南降水的影响及其机理

利用相关、合成、奇异值分解等统计诊断和数值模拟方法,分析了前冬(12—2月)南半球环状模(SAM)对春季(3—5月)中国华南降水的可能影响及其机理.诊断分析的结果表明,前冬南半球环状模与春季华南降水存在显著的负相关关系,也即前冬SAM偏强(弱),对应春季华南降水偏少(多).为了探讨这种南半球中高纬信号影响滞后一个季节的华南降水的物理机制,需要考虑下垫面海洋的桥梁作用.诊断分析的结果表明,当前冬SAM偏强时,南半球中高纬海洋的潜热释放受到海表风速影响发生变化,导致30°S—45°S海温偏高, 45°S—70°S海温偏低,并且异常的海温信号可以持续到次年春季.这种前冬SAM偏强时的春季海温异常信号,对应着春季西北太平洋副热带高压位置偏东且强度偏弱,西北太平洋上盛行异常气旋式环流,华南地区上空对流层低层有异常东北风和风场辐散,西南水汽输送较常年减弱,为春季降水偏少提供了有利的条件.前冬SAM偏弱时,南半球中高纬的海温异常及其引起的华南区域大气环流异常相反,有利于华南降水偏多.利用CAM3进行海温敏感性试验,也证明了上述南半球中高纬海温异常对应的环流异常.模拟结果表明,SAM偏强时的海温异常,对应着华南上空对流层低层的东北风异常、风场辐散、以及下沉运动,不利于华南降水生成;SAM偏弱时的海温异常,对应的环流异常相反,有利于华南降水增多,验证了资料诊断的结论.综上,在前冬SAM影响春季华南降水的过程中,体现了海气耦合桥的作用,即:海洋储存了冬季SAM的异常信号并在春季释放,通过影响春季大气环流,进一步影响华南春季降水.因此,前冬SAM为华南春季降水预测提供了一个有意义的前期信号.     

Analysis of the Energetic Particles Around the Chili Earthquake of M8.8

Based on the IDP data from the French DEMETER satellite,global distribution is shown,which corresponds to three precipitation zones:the aural precipitation zone,the mid-high latitude precipitation zone and the South Atlantic precipitation zone.Then the Chili earthquake with M8.8 which occurred on February 27,2010 is taken as an example.The IDP fluxes from repeat orbits are compared and the results show that there is a clear enhancement on February 26,2010,just one day ahead of the Chili earthquake.In the south zone with L=2.1～2.7,the flux on February 26 is higher than that on previous days.However in the north zone with L=2.1～2.7,there is no clear change during the day but great enhancement during the night,which is close to the time of the earthquake.At the same time,the flux on February 26 near the equator is far lower than that on previous days.     

Blocking Episodes in the Southern Hemisphere: Impact on the Climate of Adjacent Continental Areas

This work presents an updated climatology of blocking episodes for the Southern Hemisphere between 1960 and 2000, based on data from NCEP/NCAR reanalysis. Five contiguous areas of blocking activity are considered; Southeastern Pacific, Southwestern Pacific, Atlantic, Indian and Oceania. The impact of the three most important areas of onset blocking episodes (Southeastern Pacific, Atlantic and Oceania) upon the climate of the adjacent continental areas (South America and Australia) was evaluated. Composites of the meteorological variables (temperature and precipitation) were obtained for periods of diagnosed blockings. The impact of the blocking episodes over the climate of South America and Australia is highlighted whenever anomaly fields of temperature and precipitation are significant at the 5% and 10% levels, respectively. Impacts of Southeastern Pacific and Atlantic blockings are observed on the temperature field over several regions of South America. Significantly higher (lower) temperatures than climatology occur in southern Brazil, northern Argentina, Uruguay and Paraguay, and lower (higher) than climatology in the extreme south of South America for the Southeastern Pacific (Atlantic) blocking episodes. Precipitation over South America is also affected by the Southeastern Pacific and Atlantic blockings in different ways. The Southeastern Pacific blocking has higher impact on precipitation in summer (dry conditions in northeast Brazil) and spring (wet conditions in central and southern Brazil), while the Atlantic blocking affects precipitation in autumn and winter (wet conditions in parts of central and southern Brazil). The blocking cases over Oceania affect southeastern Australia with normal to higher than climatological precipitation and with negative temperature anomalies in that region. Finally we provide a detailed analysis of a South Atlantic blocking episode, which occurred between the 4^th and the 8^th of June 1997. This event shows clearly the split of the jet stream into two branches (subtropical and polar) surrounding the anticyclonic sector, and satellite imagery revealed the presence of transient systems in the periphery of the blocking anticyclone responsible for high values of precipitation in the southeastern sector of South America.     

Measurement of aerosol optical thickness over the Atlantic Ocean and in West Antarctica, 2006–2007

In this paper, optical measurements of aerosol properties made during a ship cruise from Poland to Antarctic Station in September and October 2006, and during the cruise back to Gdynia in April and May 2007 are described. A large gradient of pollution between the clear South Atlantic and the dusty North Atlantic was observed. The maximum of aerosol optical thickness at a wavelength of 500 nm reached 0.4 at 20°N in September 2006 and 0.3 at 40°N in May 2007, respectively. Strong Saharan dust transport is suggested as an explanation for the small values of Ångström exponent observed (values of 0.2 and 0.4 on these respective dates). On the Southern Hemisphere the aerosol optical thickness at 500 nm ranged from 0.05 to 0.2. Significant increases of the aerosol optical thickness were associated with strong wind and sea salt production. Good agreement was found when the in situ measurements of aerosol optical thickness were compared to satellite retrievals and modelling results.     

Modelling the Gibraltar Strait/Western Alboran Sea ecohydrodynamics

The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological database. A high-resolution model (~1 km) of the Gibraltar/Western Alboran region embedded within a coarse-resolution model of the West Mediterranean (~5 km) is implemented. The model seasonal climatology of the 3-D circulation and the flow characteristics at the Gibraltar Strait and the Alboran Sea are discussed, and their impact on the plankton ecosystem evolution is explored. An important ecohydrodynamic feature produced by the model is a permanent upwelling zone in the northwestern part of the Alboran Sea in agreement with observations. Model results show that both horizontal and vertical current intensity of the Atlantic Jet increases progressively at the strait to obtain maximum values in the northeastern Mediterranean entrance, inducing an upward displacement of the nitracline. The nutrient-rich water transport through the strait along with the generation of cyclonic vorticity in the northwestern Alboran Sea result in the accumulation of nutrients there and thus induce a permanent fertilisation of this area.     

Impact of warm ENSO events on atmospheric circulation and convection over the tropical Atlantic and West Africa

Empirical studies have shown that warm El Nino/Southern Oscillation (ENSO) episodes are associated during northern summer with, first, a southward location of the intertropical convergence zone (ITCZ) over the tropical Atlantic, and, second, a weakened convection over West Africa where the ITCZ is near its mean latitude. A modelling experiment presented here is used to help explain this apparent contradiction. In simulated ENSO conditions, the ITCZ is located southwards over the tropical Atlantic. Over West Africa the intertropical front is also displaced southwards, but more slightly; the ITCZ is located at its climatological latitude and the vertical development of convective clouds over West and Central Africa is reduced due to dynamical subsidence in the upper levels.