两次副高边缘特大暴雨对比分析

利用常规资料、地面加密自动观测资料、NCEP/NCAR的1°×1°每6h再分析资料及多普勒雷达资料,对2011年6月16日（简称6.16过程）及2008年7月31日（简称7.31过程）发生在粤东南两次副高边缘特大暴雨进行对比分析。结果表明：6.16过程主要是受高空短波槽和偏南风急流共同影响而产生的,较厚的暖云层、深厚的湿层等使该过程降水范围更广;7.31过程主要是受对流中层扰动诱发产生的,为局地性强降水。雷达回波均表现为强的反射率因子,回波发展迅速且移动缓慢;6.16过程回波图上出现有界弱回波区（BWER）等超级单体风暴特征。     

斜压罗斯贝变形半径优化的误差相关尺度及其对最优插值效果的改进

利用最优插值方法进行三维温盐场重构时,如何正确估算背景场误差协方差至关重要。针对背景场误差协方差主要取决于误差相关尺度的问题,本文提出了用中国东部海域及其附近海域的最新的高分辨率气候态数据进行斜压罗斯贝变形半径优化其误差相关尺度计算的研究方案和技术途径;对比分析了均一化相关尺度方案和法国ISAS系统尺度方案,讨论了变形半径对最优插值的影响。结果表明:均一化相关尺度方案的均方根误差小于ISAS方案,但温度场过于平滑,难以刻画一些重要的物理现象;相比而言,本文提出的基于变形半径的相关尺度方案在取2倍变形半径时,不仅均方根误差在各水平层较小,且温度场能够更好地刻画四国海盆海域涡旋及黑潮影响的温度场三维结构。由于实际海洋中各层物理过程的尺度存在差异,实际应用时各层的最优尺度设置也应有所不同。     

基于城市内涝仿真模型的天津风暴潮灾害评估

基于城市内涝仿真模型,根据天津沿海地区的地形、地貌特征以及排水系统等对城市内涝仿真模型进行改进,在沿海边界和河口设置时变水位,使得模型拓展到既能模拟暴雨产生的内涝,也能模拟由于风暴潮侵袭造成的淹没情景。该模型对天津沿海地区历史上典型风暴潮个例以及10年、20年、50年、100年一遇重现期风暴潮产生的积水范围和积水深度进行了模拟,并对2012年8月3日台风达维 (1210) 造成的天津沿海风暴潮进行了业务试应用。将历史风暴潮个例模拟结果以及2012年8月3日的评估结果与实际灾情进行对比,结果显示模型具有较好的模拟能力,可应用于风暴潮灾害的评估和预估业务中,为相关部门和行业提供决策参考。     

Climatological study of ionospheric irregularities over the European mid-latitude sector with GPS

High-frequency variability of the ionosphere, or irregularities, constitutes the main threat for real-time precise positioning techniques based on Global Navigation Satellite Systems (GNSS) measurements. Indeed, during periods of enhanced ionospheric variability, GNSS users in the field—who cannot verify the integrity of their measurements—will experience positioning errors that can reach several decimeters, while the nominal accuracy of the technique is cm-level. In the frame of this paper, a climatological analysis of irregularities over the European mid-latitude region is presented. Based on a 10 years GPS dataset over Belgium, the work analyzes the occurrence rate (as a function of the solar cycle, season and local time) as well as the amplitude of ionospheric irregularities observed at a single GPS station. The study covers irregularities either due to space weather events (solar origin) or of terrestrial origin. If space weather irregularities are responsible for the largest effects in terms of ionospheric error, their occurrence rate highly depends on solar activity. Indeed, the occurrence rate of ionospheric irregularities is about 9 % during solar maximum, whereas it drops to about 0 % during medium or low solar activity periods. Medium-scale ionospheric disturbances (MSTIDs) occurring during daytime in autumn/winter are the most recurrent pattern of the time series, with yearly proportions slightly varying with the solar cycle and an amplitude of about 10 % of the TEC background. Another recurrent irregularity type, though less frequent than MSTIDs, is the noise-like variability in TEC observed during summer nighttime, under quiet geomagnetic conditions. These summer nighttime irregularities exhibit amplitudes ranging between 8 and 15 % of the TEC background.     

The roles of different mechanisms related to the tide-induced fronts in the Yellow Sea in summer

In summer, the Yellow Sea Cold Water Mass （YSCWM） is a stable water mass of low temperature lying at the bottom of the central Yellow Sea （YS）. It is fringed by some typical tidal fronts, which separate deep, stratified water on the offshore side from the well-mixed, shallow water on the inshore side. Three striking fronts--Subei Bank Front （SBF）, Shandong Peninsula Front （SPF）, and Mokpo Front （MKF; a front off the southwestern tip of the Korean Peninsula）--have been iden- tified by various studies from both satellite observations and model results. Tide plays an important role in the formation and maintenance of these fronts. However, it is still a matter of debate as to the roles these two kinds of mechanisms of upwelling and tidal mixing play, and how importance they are in the maintenance processes of the above three fronts. Basing a nested high-resolution model HYCOM （the Hybrid Coordinate Ocean Model）, this study focuses on the different mechanisms of tidal effects on the thermal fronts in the YS in summertime. Through comparative experiments with and without tidal forcing, the results indicate that the MKF is mainly driven by tide-induced upwelling. For the SPF, tidal mixing is the dominant factor, when lower cold water is stirred upwards along the sloping topography of the western YS. Meanwhile, the combined effect of upwelling and tidal mixing is the main cause of the formation of the SBF. Diagnostic analysis of thermal balance shows that horizontal nonlinear advection induced by strong tidal currents also contributes to the thermal balance of frontal areas.     

Present and projected degree days in China from observation,reanalysis and simulations

Degree days are usually defined as the accumulated daily mean temperature varying with the base temperature, and are one of the most important indicators of climate changes. In this study, the present-day and projected changes of four degree days indices from daily mean surface air temperature output simulated by Max Planck Institute, Earth Systems Model of low resolution (MPI-ESM-LR) model are evaluated with the high resolution gridded-observation dataset and two modern reanalyses in China. During 1979–2005, the heating degree days (HDD) and the numbers of HDD (NHDD) have decreased for observation, reanalyses (ERA-Interim and NCEP/NCAR) and model simulations (historical and decadal experiments), consistent with the increasing cooling degree days (CDD) and the numbers of CDD (NCDD). These changes reflect the general warming in China during the past decades. In most cases, ERA-Interim is closer to observation than NCEP/NCAR and model simulations. There are discrepancies between observation, reanalyses and model simulations in the spatial patterns and regional means. The decadal hindcast/forecast simulation performance of MPI-ESM-LR produce warmer than the observed mean temperature in China during the entire period, and the hindcasts forecast a trend lower than the observed. Under different representative concentration pathway (RCP) emissions scenarios, HDD and NHDD show significant decreases, and CDD and NCDD consistently increase during 2006–2100 under RCP8.5, RCP4.5 and RCP2.6, especially before the mid-21 century. More pronounced changes occur under RCP8.5, which is associated with a high rate of radiative forcing. The 20th century runs reflect the sensitivity to the initial conditions, and the uncertainties in terms of the inter-ensemble are small, whereas the long-term trend is well represented with no differences among ensembles.     

Investigating soil thermodynamic parameters of the active layer on the northern Qinghai-Tibetan Plateau

The soil thermodynamic parameters, including thermal conductivity, diffusivity and volumetric capacity within the active layer on the northern Tibetan Plateau, were calculated using the measured data of soil temperature gradient, heat flux, and moisture at four stations from October 2003 to September 2004. The results showed that the soil thermodynamic parameters exhibited clear seasonal fluctuation. The thermal conductivity and diffusivity in summer and autumn at Beiluhe, Kexinling, and Tongtianhe were larger than those in winter. The volumetric thermal capacity causes an opposite change; it was larger in autumn and winter than in summer. In spring, the soil thermal conductivity at the Kekexili station was larger than that in summer. Generally, fine-grained soils and lower saturation degrees in the topsoil might be a reason for the lower soil thermal conductivity in winter. For a given soil, soil moisture was the main factor influencing the thermodynamic parameters. The unfrozen water content that existed in frozen soils greatly affected the soil thermal conductivity, whose contribution rate was estimated to be 55 %. The thermodynamic parameters of frozen soils could be expressed as a function of soil temperature, volumetric ice content and soil salinity, while for the unfrozen ground the soil moisture content is the dominant factor for those thermal parameters. As for the soil thermal diffusivity, there exists a critical value of soil moisture content. When the soil moisture content becomes less than a critical value, the soil thermal diffusivity increases as the soil moisture content rises.     

Field characterization and data integration to define the hydraulic heterogeneity of a shallow granular aquifer at a sub-watershed scale

Providing a sound basis for aquifer management or remediation requires that hydrogeological investigations carried out to understand groundwater flow and contaminant transport be based on representative data that capture the heterogeneous spatial distribution of aquifer hydraulic properties. This paper describes a general workflow allowing the characterization of the heterogeneity of the hydraulic properties of granular aquifers at an intermediate scale of a few km². The workflow involves characterization and data integration steps that were applied on a 12-km² study area encompassing a decommissioned landfill emitting a leachate plume and its main surface water receptors. The sediments composing the aquifer were deposited in a littoral–sublittoral environment and show evidence of small-scale transitional heterogeneities. Cone penetrometer tests (CPT) combined with soil moisture and electrical resistivity (SMR) measurements were thus used to identify and characterize spatial heterogeneities in hydraulic properties over the study area. Site-specific statistical relationships were needed to infer hydrofacies units and to estimate hydraulic properties from high-resolution CPT/SMR soundings distributed all over the study area. A learning machine approach was used due to the complex statistical relationships between colocated hydraulic and CPT/SMR data covering the full range of aquifer materials. Application of this workflow allowed the identification of hydrofacies units and the estimation of horizontal hydraulic conductivity, vertical hydraulic conductivity and porosity over the study area. The paper describes and discusses data acquisition and integration methodologies that can be adapted to different field situations, while making the aquifer characterization process more time-efficient and less labor-intensive.     

Thermal simulation of basic volcanic fluid influence on different source rocks

Based on thermal simulation experiment, interactions between volcanic fluids and source rocks were studied. Gas generations in the dry system and fluid system under different temperatures were analyzed. The results showed that the various types of source rocks are similar in composition, containing gaseous C1-C5 hydrocarbons, H2 and CO2 whose gas yields increase with increasing temperature. The gas yield of source rocks of type I is the high- est, followed by type II, and that of source rocks of type III is the lowest, indicating that the yield of hydrocarbon gases is related to their hydrocarbon generating potential. Although the generating potential of type III is the lowest, it can still be regarded as a useful gas source when it is buried deeply enough. The basic volcanic fluid restrains the generation of gaseous hydrocarbons in different types of source rocks, but promotes the generation of inorganic gases.     

夏季黄海冷水团海域的丙烯酸分布与海洋环境因子和叶绿素a变化之间的关系

海水中主要含硫化合物β-二甲基巯基丙酸内盐(DMSP)降解可产生丙烯酸(AA)和活性气体二甲基硫(DMS)。2011年8月对黄海冷水团海域的AA及相关参量的分布特征进行了研究。结果表明,该海域表层海水中AA的浓度为0~0.208μmol/L,平均值为(0.081±0.075)μmol/L。AA的高值区出现在海域的东南部,可能是受到长江冲淡水的影响。AA的浓度总体上呈现出由南到北递增的趋势,与Chl-a较为一致,表明该海域的AA主要是由DMSP裂解产生的。表层海水中AA与温度表现出明显的负相关性。AA的垂直分布表现为:中层底层表层,这可能是产生AA的浮游植物与消耗AA的细菌共同作用的结果。海域中AA浓度与DMSP或DMS无明显的相关性。AA浓度远高于DMS,AA/DMS平均为106∶1,初步估算出DMSP降解产生的AA约为66.5%。AA/Chl-a平均为126.6 mmol/g,比DMSP/Chl-a高1个数量级,比DMS/Chl-a高2个数量级。