2003年江淮梅雨期一次特大暴雨的研究——中尺度对流和水汽条件分析

本文对2003年7月4日-5日江淮梅雨期间的一次特大暴雨过程进行了多尺度的详细分析.环流背景、中尺度对流云团和水汽条件分析表明,这次特大暴雨是在典型梅雨的有利环境背景形势下,由梅雨锋上的中尺度对流系统造成的,地面低压、低层切变线及西南低空急流与这次特大暴雨过程有着密切的关系.强降水中心与中尺度对流云团的关系十分密切,中β尺度云团的生成合并增强,和其中中γ降水系统的存在,导致了降水强度的局地性差异.江淮流域主要表现为经向水汽通量的辐合区,强水汽通量舌与低层高θse的舌区一致,暴雨过程中水汽的快速集中主要是通过风场散度项造成的,局地风场的辐合在水汽快速集中起主要作用.低层充沛的水汽则通过气旋性涡度柱中的强上升气流输送到对流层的中高层.     

煤体结构差异的吸附响应及其控制机理

为了研究不同煤体结构煤的吸附行为差异和作用机理, 以焦作煤田为研究区, 对煤体破坏严重的糜棱煤和原生结构煤的岩石学组成、吸附性和孔隙性进行了测试, 结果表明: 煤体破坏后, 吸附、解吸能力增大; 温度增加, 煤的吸附能力均为下降, 解吸能力增加.相比于原生结构煤, 随着温度增加, 糜棱煤吸附能力下降趋势和解吸能力增大趋势比原生结构煤更为明显.研究认为: 煤体破坏后, 不同孔径段的孔隙数量均有增大, 使得煤样容纳气体的能力增大.特别是大中孔含量的增大, 导致了糜棱煤样更容易发生解吸.另外, 煤体破坏后的煤级增高、镜质组含量增大和惰质组含量减小也对吸附能力增大具有重要作用, 而灰分含量不是决定两类煤吸附性差异的主要因素.      

南海中尺度涡研究进展

近20年以来,南海环流及中尺度涡的研究得到了国内外海洋学家相当的重视,取得了许多研究成果。随着高度计资料的广泛应用以及涡分辨率数值模式的发展,南海中尺度涡的研究越趋活跃。简要介绍南海大尺度环流的主要工作,并着重分析南海多涡结构观测以及形成机理研究方面的主要进展。     

A nested pre-operational model for the Egyptian shelf zone: Model configuration and validation/calibration

We explored the variability of the Egyptian shelf zone circulation connected to atmospheric forcing by means of a numerical simulation of the general circulation. A high resolution model grid was used at 1/60° horizontal resolution and 25 sigma layers. The simulation was carried out using the most recent version of the Princeton Ocean Model (POM). The initialised model was run the whole year of 2006 using the analysis forcing data for the same year obtained from ECMWF and MFS (Mediterranean Forecasting System, Pinardi et al., 2003). The model skills were evaluated by means of the root mean square error (RMSE) and correlations. The Egyptian Shelf Model (EGYSHM) simulation suggests the presence of an Egyptian Shelf Slope Current (ESSC), which is flowing eastward at different depths in the domain. We found that the maximum velocity of the ESSC [0.25 m/s] is located near the continental slope during the summer time, while in winter the velocity of ESSC is weaker [0.12 m/s] in the same location. The ESSC appears to be directly affected by Mersa-Matruh gyre system. EGYSHM reproduced the main region circulation patterns, especially after adding the Nile River outflow. We found that wind stress is crucial to force the circulation of the Egyptian shelf zone. EGYSHM SST was significantly correlated to satellite SST in all months at a 95% confidence limit, with a maximum of 0.9743 which was obtained in May 2006. The RMSE between EGYSHM and Argo floats salinity data was about 0.09. We compared our results with satellite altimetry to verify the positions and shapes of mesoscale features.     

Analysis of the effect of the coastal discontinuity on near-surface flow

Conditional sampling is used herein to examine the effect of fetch, stability, and surface roughness changes on wind speeds in the coastal zone. Using data from an offshore wind farm it is shown that at a distance of 1.2–1.7 km from the coast, up to a height of 20 m above the surface, differences in wind speed distributions from onshore and offshore masts are statistically significant for flow moving offshore under all stability conditions. In contrast, differences between the distribution of wind speeds at 38 and 48 m at masts located at the coast and in the coastal zone are not significant for flow moving offshore, indicating that flow at these heights is not fully adjusted to the change in surface roughness (land to sea). These findings are in accordance with calculations of the internal boundary layer (IBL) height which indicate that the IBL would frequently be below the two upper measurement heights at 1.2–1.6 km from the coast. The analyses presented here indicate that the wind speed distribution at a potential offshore wind farm site is not solely dependent on fetch (distance from the coast) but also depends on the stability climate.     

一次强烈发展西南低涡的中尺度结构分析

通过对1989年7月8～10日发生于四川盆地东部的西南低涡的诊断分析,揭示了西南低涡成熟期的三维结构。结果表明,成熟阶段的西南低涡正涡度可伸展到100 hPa以上,中心轴线垂直;其流场和高度场表现为贯穿对流层的中尺度气旋和低压;涡区内动量、层结、垂直运动等呈非对称分布,是一个准圆形而非对称的中尺度系统。     

一次影响山东强暴雨过程的中尺度分析

利用１９９０年华北区域中尺度暴雨监测联防业务试验期间的获得的较为稠密的地面观测资料,卫星云图及常规天气图资料,对１９９０年８月中旬的一次影响山东强暴雨天气过程作了初步的天气学分析和中尺度分析,指出了直接造成这场大暴雨的中尺度系统和有利于它们发展的环境条件,文中重点讨论了中尺度天气系统及云团与雨团的关系。     

New Approaches in Two-equation Turbulence Modelling for Atmospheric Applications

The turbulence closure in atmospheric boundary-layer modelling utilizing Reynolds Averaged Navier–Stokes (RANS) equations at mesoscale as well as at local scale is lacking today a common approach. The standard kɛ model, although it has been successful for local scale problems especially in neutral conditions, is deficient for mesoscale flows without modifications. The k–ɛ model is re-examined and a new general approach in developing two-equation turbulence models is proposed with the aim of improving their reliability and consequently their range of applicability. This exercise has led to the replacement of the ɛ-transport equation by the transport equation for the turbulence inverse length scale (wavenumber). The present version of the model is restricted to neutrally stratified flows but applicable to both local scale and mesoscale flows. The model capabilities are demonstrated by application to a series of one-dimensional planetary boundary-layer problems and a two-dimensional flow over a square obstacle. For those applications, the present model gave considerably better results than the standard k–ɛ model.     

Monsoon-driven biogeochemical processes in the Arabian Sea

Although it is nominally a tropical locale, the semiannual wind reversals associated with the Monsoon system of the Arabian Sea result annually in two distinct periods of elevated biological activity. While in both cases monsoonal forcing drives surface layer nutrient enrichment that supports increased rates of primary productivity, fundamentally different entrainment mechanisms are operating in summer (Southwest) and winter (Northeast) Monsoons. Moreover, the intervening intermonsoon periods, during which the region relaxes toward oligotrophic conditions more typical of tropical environments, provide a stark contrast to the dynamic biogeochemical activity of the monsoons. The resulting spatial and temporal variability is great and provides a significant challenge for ship-based surveys attempting to characterize the physical and biogeochemical environments of the region. This was especially true for expeditions in the pre-satellite era.Here, we present an overview of the dynamical response to seasonal monsoonal forcing and the characteristics of the physical environment that fundamentally drive regional biogeochemical variability. We then review past observations of the biological distributions that provided our initial insights into the pelagic system of the Arabian Sea. These evolved through the 1980s as additional methodologies, in particular the first synoptic ocean color distributions gathered by the Coastal Zone Color Scanner, became available. Through analyses of these observations and the first large-scale physical–biogeochemical modeling attempts, a pre-JGOFS understanding of the Arabian Sea emerged. During the 1990s, the in situ and remotely sensed observational databases were significantly extended by regional JGOFS activities and the onset of Sea-viewing Wide Field-of-View Sensor ocean color measurements. Analyses of these new data and coupled physical–biogeochemical models have already advanced our understanding and have led to either an amplification or revision of the pre-JGOFS paradigms. Our understanding of this complex and variable ocean region is still evolving. Nonetheless, we have a much better understanding of time–space variability of biogeochemical properties in the Arabian Sea and much deeper insights about the physical and biological factors that drive them, as well as a number of challenging new directions to pursue.     

Operational Altimeter Data Processing for Mesoscale Monitoring

Since 1996, global, near-real-time maps of mesoscale anomalies derived from tandem sampling provided by altimeters aboard the TOPEX/Poseidon and ERS-2 satellites have been posted on web pages hosted at the Colorado Center for Astrodynamics Research. The original, near-real-time processing system was based on a quick-look analysis that referenced the data to a high-resolution gridded mean sea surface available at the time. Recently, state-of-the-art mean sea surfaces have been derived that are based on a more complete record of altimeter observations. An updated mesoscale monitoring system based on a new mean surface is described and shown to provide improved mesoscale monitoring to the successful system implemented in 1996.