Interannual Variation of Freshwater in the Yellow and East China Seas: Roles of the Changjiang Discharge and Wind Forcing

The interannual variation of the behavior of Changjiang freshwater has been investigated using the Princeton Ocean Model (POM). Five experiments are described in this study. Three basic experiments (Exps. B1, B2 and B3) were performed to examine the freshwater behavior in response to annual variations of the Changjiang discharge in normal, wet and dry years, respectively. Thereafter, the freshwater variation was investigated with the model forced by primary-interannual variations of river discharge with an 8-year period (Exp. I1) and a wind field with a 3.6-year period (Exp. I2). In Exp. B1, the average residence time of freshwater is roughly estimated to be 681.4 days in the Yellow Sea (YS) and 353.4 days in the combined area of the East China Sea (ECS) and the Chinese Coast (CC). This difference is attributed to the current pattern in each region and freshwater exchange among the regions. The interannual variation of freshwater volume in Exp. I1 has a large amplitude and long phase lag in the YS (38 km³ and 1.6-year against primary-interannual discharge variation), while there are relatively small amplitudes and short phase lags in the ECS (18 km³ and 0.7-year) and the CC (14 km³ and 0.5-year). It is concluded that the difference in the freshwater behavior results from the difference in the average residence time in each region.     

Modelling Thermohaline Properties in an Estuarine Upwelling Ecosystem (Ría de Vigo: NW Spain) Using Box-Jenkins Transfer Function Models

Since 1987, twice weekly, hydrological variables have been monitored at a fixed station in the Ría de Vigo (NW Spain), aiming to examine the time scales of variability and the relationships to meteorological conditions. The present paper analyses: (1) the advantage of Box-Jenkins transfer function (TF) models (single output–multiple input), a type of linear stochastic model, to describe the dynamic behaviour of the system; and (2) the coupling between the Ría and meteorological events at the time scale of autonomy of this coastal inlet affected by the Iberian coastal upwelling, approximately a fortnightly period. In order to achieve these objectives, thermohaline properties have been used to characterize the estuarine ecosystem (output variables), while wind regime, runoff in the drainage basin and incoming solar radiation have been considered as the main forcing variables (input variables). The use of the amplitude time series, derived from principal component analysis (PCA) applied to the deseasonalized meteorological variables, is also explored as a different set of input variables.When compared with standard regression models, all TF models built to describe thermohaline behaviour had reduced residual variance. Similar TF models, as well as percentage of explained variance, were also obtained when meteorological variables or the amplitude time series were used as input variables. The fitted TF models provided an insight into the ‘ inertial ’ behaviour of the system and the time scales of coupling of the system with the forcing variables. The plausible physical mechanisms which link the response of the system with the observed meteorological variability are also discussed. As could be expected, bottom thermohaline properties show a stronger inertial behaviour than the surface ones, which is particularly marked for bottom temperature. Besides, the shelf domain, by means of upwelling-downwelling events, strongly influences surface and bottom temperature, as well as bottom salinity; by contrast, surface salinity is mainly influenced by the effect of wind along the main axis of the Ría and runoff. In relation to the time scales of coupling between the system and the forcing variables, thermohaline properties show a dependance with the meteorological conditions in, at least, the immediately preceding fortnight period. It was concluded that: (1) TF models that incorporate meteorological information described the dynamic behaviour of the system adequately; and (2) this type of model can be useful as a first approximation to develop more sophisticated (deterministic) models, since, with the purpose of modelling any state variable of the system, both the coupling between different domains and the time scales of the interactions must be taken into account.     

Zonally asymmetric response of the Japan Sea to synoptic pressure forcing

We investigated the sea level response of the Japan Sea to changes in atmospheric pressure using barotropic shallow water models driven by idealized synoptic pressure forcing. The regional response lags behind the synoptic pressure forcing because the adjustment is slowly established by water exchange through narrow, shallow straits. The sea level response of the realistic Japan Sea to the idealized forcing varies with geographical location and shows zonally asymmetric variations in amplitude and phase. The simulated response is in good agreement with the observed response of sea level recorded at Japanese coastal tide gauges. The results of a simple one-dimensional model indicate that the zonally asymmetric pattern, with an eastward-propagating pressure system, is essentially caused by bottom friction in shallow straits. This asymmetry arises if the typical wavelength of the synoptic pressure system is slightly larger than the spatial scale of the Japan Sea.     

Spatio-temporal structure of diatom assemblages in a temperate estuary. A STATICO analysis

This study examines the spatio-temporal structure of diatom assemblages in a temperate estuary (Ria de Aveiro, Western Portugal). Eighteen monthly surveys were conducted, from January 2002 to June 2003, at three sampling sites (at both high and low tide) along the estuarine salinity gradient. The relationship of diatom assemblages and environmental variables was analysed using the STATICO method, which has been designed for the simultaneous analysis of paired ecological tables. This method allowed examination of the stable part of the environment-diatom relationship, and also the variations of this relationship through time. The interstructure factor map showed that the relationship between the 11 environmental variables and the abundance of the 231 diatom species considered was strongest in the months May and September 2002 and January, February and May 2003. The stable part of the species–environment relationships mainly consisted of a combined phosphate, chlorophyll a and salinity gradient linked to a freshwater-marine species gradient. A more pronounced gradient was observed in January, February and May 2003. Diatom assemblages showed clear longitudinal patterns due to the presence of both marine and freshwater components. May and September 2002 had the least structured gradients with marine-estuarine species appearing in the freshwater side of the gradient. The most complete gradient in February 2003 could be considered, in terms of bio-ecological categories, as the most structured period of the year, with a combination of strong marine influence in the lower zone and freshwater influence in the upper. The best-structured gradients were during periods of a diatom bloom. Stable diatom assemblages (with a strong structure and a good fit between the diatoms and environment) are described and characterized. This study shows the efficiency of the STATICO analysis. The inclusion of space-time data analysis tools in ecological studies may therefore improve the knowledge of the dynamics of species–environmental assemblages.     

RESPONSE OF THE OCEAN UPPER MIXED LAYER TO ATMOSPHERIC FORCING

Using a one-dimension Turbulence Kinetic Energy(TKE)mixed layer model based on a simple eddyKinetic energy parameterization of the ocean upper mixed layer,some numerical examinations are intro- duced in this paper.These examination results show that the TKE ocean mixed layer model can respondwell to the effect of atmospheric forcing on the ocean upper mixed layer.The joint effect of wind stressand heat exchange on the ocean upper layer has nonlinear characteristics.The adjustment time of the re-sponse of the ocean upper mixed layer to the atmospheric forcing is about 12 hours in this model.     

基于遥感影像的大气辐射校正和反射率反演方法

应用1995年7月在法国La Crau辐射校正场进行的遥感实验获得的SPOT HRV数据,在DOS方法的基础上,合理分析假设暗体反射率值,并结合Lowtran-7、6S、Modtran-3大气辐射传输模型进行大气模拟,研究并发展基于遥感影像信息的快速、经济、有效的大气辐射校正和反射率反演方法。通过La Crau场的反射率反演值与实时测量反射率值相比较,分析评价了该研究方法的有效性。     

过去2 000年中国东南地区气温与降水的集成重建与分析

筛选和利用中国东南地区（大致范围为105o E以东、30o N以南）16个站点的多种气候代用指标序列,重建了东南地区过去2 000年以来的气温与降水变化过程,并探讨了其可能的影响机制。研究发现,东南地区气温集成序列与其他学者重建的中国温度序列、北半球温度序列等均具有较好的可比性,一些百年尺度的典型特征气候时期,如黑暗时代冷期、中世纪暖期、近代小冰期以及20世纪现代暖期等均有显著的体现;降水集成序列显示东南地区在过去2 000年中干湿阶段性变化较为明显,特别是在中世纪暖期时降水整体上较为偏多,而在小冰期的前半段降水偏少、后半段降水偏多。总体来看,近2 000年来我国东南地区的气温与降水变化经历了较为多样的水热组合过程。值得指出地是,东南地区降水集成序列与已有的中国北方地区多条降水重建序列相互间可比性较弱,反映了中国东部季风区由南到北降水变化及其影响机制具有很大的区域性差异。分析认为,大尺度海—气相互作用、火山活动以及太阳辐射量变化等对我国东南地区过去2 000年的气候环境变化具有显著影响。     

Water vapor abundance in Venus' middle atmosphere from Pioneer Venus OIR and Venera 15 FTS measurements

The Pioneer Venus Orbiter Infrared Radiometer and Venera 15 Fourier Transform Spectrometer observations of thermal emission from Venus' middle atmosphere between 10° S and 50° N have been independently re-analyzed using a common method to determine global maps of temperature, cloud optical depth, and water vapor abundance. The spectral regions observed include the strong 15 μm carbon dioxide band and the 45 μm fundamental rotational water band. The different spatial and spectral resolutions of the two instruments have necessitated the development of flexible analysis tools. New radiative transfer and retrieval models have been developed for this purpose based on correlated-k absorption tables calculated with up-to-date spectral line data. The common analysis of these two sets of observations has hence been possible for the first time. From the PV OIR observations, the cloud-top unit optical depth pressure showed a minimum of ∼110±10 mbars in the evening equatorial region and a maximum of ∼160±12 mbars in the morning mid-latitude regions. From the Venera 15 FTS spectra, the cloud-top pressure was found to increase from morning values of ∼120±10 to 200±30 mbars in the late afternoon/early evening region. The cloud-top water vapor abundances observed by the PV OIR instrument were found to fluctuate from 10±5 ppm at night up to 90±15 ppm in the equatorial cloud-top region shortly after the sub-solar point. The mean Venera 15 FTS water vapor abundances were found to be 12±5 ppm with only a slight enhancement over the equatorial latitude bands and no clear day-night distinction. The common analysis of these two sets of observations broadly validates previously published individual findings. The differences in the retrieved atmospheric state can no longer be attributed to radiative transfer modeling bias and suggest significant temporal variability in the middle atmosphere of Venus.     

Study on Physical Mechanism of Influence on Atmospheric Boundary Layer Depth in the Arid Regions of Northwest China

Using the sounding data of wind, temperature, and humidity in the boundary layer and micrometeorological data on the earth's surface observed in the same period in Dunhuang arid region of Northwest China,this paper researches characteristics of potential temperature, wind, and humidity profiles, confirms the structure and depth of thermodynamic boundary layer in Dunhuang region, and analyzses the relationship of depth of thermodynamic boundary layer with surface radiation, buoyancy flux as well as wind speed and wind direction shear in the boundary layer. The results show that the maximum depth of diurnal convective boundary layer is basically above 2000 m during the observational period, many times even in excess of 3000 m and sometimes up to 4000 m; the depth of nocturnal stable boundary layer basically maintains within a range of 1000-1500 m. As a whole, the depth of atmospheric boundary layer is obviously bigger than those results observed in other regions before. By analyzing, a preliminary judgement is that the depth of atmospheric thermodynamic boundary layer in Dunhuang region may relate to local especial radiation characteristics, surface properties (soil moisture content and heat capacity) as well as wind velocity shear of boundary layer, and these properties have formed strong buoyancy flux and dynamic forcing in a local region which are fundamental causes for producing a super deep atmospheric boundary layer.     

Particle size and abundance of HC3N ice in Titan’s lower stratosphere at high northern latitudes

Up to now, there has been no corroboration from Cassini CIRS of the Voyager IRIS-discovery of cyanoacetylene (HC₃N) ice in Titan’s thermal infrared spectrum. We report the first compelling spectral evidence from CIRS for the ν₆ HC₃N ice feature at 506 cm⁻¹ at latitudes 62°N and 70°N, from which we derive particle sizes and column abundances in Titan’s lower stratosphere. We find mean particle radii of 3.0 μm and 2.3 μm for condensed HC₃N at 62°N and 70°N, respectively, and corresponding ice phase molecular column abundances in the range 1-10 × 10¹⁶ mol cm⁻². Only upper limits for cloud abundances can be established at latitudes of 85°N, 55°N, 30°N, 10°N, and 15°S. Under the assumption that cloud tops coincide with the uppermost levels at which HC₃N vapor saturates, we infer geometric thicknesses for the clouds equivalent to 10-20 km or so, with tops at 165 km and 150 km at 70°N and 62°N, respectively.