京津冀地区一次严重霾天气过程及其影响因素分析

利用大气污染监测资料、常规气象观测资料及NCEP再分析资料,对2013年1月9—17日京津冀地区一次严重霾天气过程的特征及其与气象条件的关系进行分析。结果表明：此次霾天气过程京津冀地区6个城市（北京、天津、石家庄、保定、邯郸、唐山）的PM10、SO2和NO2污染物日平均浓度均较高,变化趋势基本相同,其中PM10日平均浓度的变化幅度最大,峰值出现在11—13日之间;石家庄、保定和邯郸市的污染最严重,PM10日平均浓度最大值分别为0.94 mg·m－3、0.95 mg·m－3和0.82 mg·m－3。SO2和NO2日平均浓度的变化幅度较小,但浓度值均较大,基本为0.10 mg·m－3以上。影响此次霾天气过程的大范围环流形势为纬向型,存在较强的逆温层,弱下沉运动使近地层大气处于静稳状态,不利于污染物扩散,而近地面较小的风速和低层相对湿度小于90％为霾的形成提供了有利条件。另外,后向轨迹分析表明,此次污染过程京津冀地区的气团主要来自新疆地区,路径主要是从西北气流转为西南气流,携带南方的湿空气和污染物向京津冀地区输送。     

Doppler Lidar Measurements of Vertical Velocity Spectra in the Convective Planetary Boundary Layer

We utilized a Doppler lidar to measure spectra of vertical velocity w from 390m above the surface to the top of the daytime convective boundary layer (CBL). The high resolution 2μm wavelength Doppler lidar developed by the NOAA Environmental Technology Laboratory was used to detect the mean radial velocity of aerosol particles. It operated continuously during the daytime in the zenith-pointing mode for several days in summer 1996 during the Lidars-in-Flat-Terrain experiment over level farmland in central Illinois, U.S.A. The temporal resolution of the lidar was about 1 s, and the range-gate resolution was about 30m. The vertical cross-sections were used to calculate spectra as a function of height with unprecedented vertical resolution throughout much of the CBL, and, in general, we find continuity of the spectral peaks throughout the depth of the CBL. We compare the observed spectra with previous formulations based on both measurements and numerical simulations, and discuss the considerable differences, both on an averaged and a case-by-case basis. We fit the observed spectra to a model that takes into account the wavelength of the spectral peak and the curvature of the spectra across the transition from low wavenumbers to the inertial subrange. The curvature generally is as large or larger than the von Kármán spectra. There is large case-to-case variability, some of which can be linked to the mean structure of the CBL, especially the mean wind and the convective instability. We also find a large case-to-case variability in our estimates of normalized turbulent kinetic energy dissipation deduced from the spectra, likely due for the most part to a varying ratio of entrainment flux to surface flux. Finally, we find a relatively larger contribution to the low wavenumber region of the spectra in cases with smaller shear across the capping inversion, and suggest that this may be due partly to gravity waves in the inversion and overlying free atmosphere.     

2008年河南黄淮地区暴雨过程个例分析

利用常规气象资料和NCEP资料对2008年7月22日河南黄淮地区的暴雨过程进行了分析.结果表明:这次过程是在500 hPa槽前西南气流引导下,高低空急流耦合区内西南涡沿切变线移出,弱冷空气侵入暖倒槽触发不稳定能量释放造成的.垂直螺旋度计算结果显示:中低层正垂直螺旋度中心与降水落区有很好的对应关系,大暴雨中心位于正垂直螺旋度中心附近.湿位涡演变分析发现,这次过程有"干侵入"发生,暴雨区中低层对流不稳定和对称不稳定共存,有利于降水增幅.水汽条件分析表明:这次过程的水汽源地在孟加拉湾和南海,主要是低层和近地层的水汽辐合.     

一次突发性特大暴雨的中尺度分析和诊断

利用常规探测资料、TBB资料和NCEP分析资料,对2008年5月27日发生在沅陵西北部的一次突发性特大暴雨天气过程进行了中尺度分析和诊断.结果表明:这次特大暴雨是在有利的大尺度环流背景下发生的,低空西南急流为暴雨区带来了丰富的水汽和不稳定能量;产生暴雨的中βCS云团由两个对流云团合并而成,具有椭圆形结构特征,长时间维持少动,强降水出现在中BCS云团发展最旺盛的地方;在尺度分离的流场上,特大暴雨出现在850 hPa和700 hPa的两条中尺度辐合线之间的低层辐合区内;这次暴雨与暴雨区上空对流层中低层正垂直螺旋度、高层负垂直螺旋度中心的分布和增大减小变化密切相关;非地转湿Q矢量激发的次级环流的存在有利于不稳定能量的释放,促进暴雨发生发展;暴雨区特殊的地形对这次特大暴雨过程有明显的增幅作用.     

Effects of vertical wind shear on convective development during a landfall of severe tropical storm Bilis (2006)

Effects of vertical wind shear on convective development during the landfall of tropical storm Bilis (2006) are investigated with a pair of sensitivity experiments using a two-dimensional cloud-resolving model. The validated simulation data from Wang et al. [Wang, D., Li, X., Tao, W.-K., Liu, Y., Zhou, H., 2009: Torrential rainfall processes associated with a landfall of severe tropical storm Bilis (2006): A two-dimensional cloud-resolving modeling study. Atmos. Res., 91, 94–104.] are used as the control experiment. The difference between the control and sensitivity experiments is that vertically varying zonal winds in the control experiment are replaced by their mass-weighted means in the sensitivity experiment. The imposed vertical velocity with ascending motion in the upper troposphere and descending motion in the lower troposphere is responsible for dominant stratiform rainfall on 15 July. The vertical wind shear does not have important impacts on development of stratiform rainfall. One day later, imposed upward motion extends to the lower troposphere. The inclusion of negative vertical wind shear produces well-organized convection and strong convective rainfall because it causes kinetic energy transfer from large-scale forcing to perturbation circulations.     

中国大地测量科学发展的若干问题

概述了大地测量学作为测绘基准、提供地理信息系统的基础框架作用。回顾了我国大地测量在建立国家平面基准、国家高程基准、国家重力基准等方面的情况。论述介绍了大地测量学当前发展的国际背景，提出了对我国大地测量学今后发展，如建立现代大地坐标框架和现代重力基准的目标和任务，以及改善国家高程基准等方面的考虑。     

用四维反演方法研究地震活动的深部环境

导出了用重力和水准重复测量资料反演地壳界面密度和垂直形变随时间变化的四维反演公式，并对甘肃河西地区（包括祁连山地区）和滇西北地区的重力和水准重复测量资料进行了计算。根据计算结果，分析了2个地区莫霍西密度变化速率和垂直形变速率与地震的关系。结果表明：甘肃河西地区和滇西北地区莫霍面密度大规模减小和莫霍面大范围隆起可作为1年尺度的地震预报的深部判据。地震往往发生在莫霍面隆起区与沉降区、密度减小区与增长区的过渡地带。     

Water budget and vertical conductance for Lowry (Sand Hill) Lake in north-central Florida, USA

Water-budget components and the vertical conductance were determined for Lowry (Sand Hill) Lake in north-central Florida, USA. In this type of lake, which interacts with both the surface-water and groundwater systems, the inflow components are precipitation, surface-water inflow, groundwater inflow, and direct runoff (i.e. overland flow), and the outflow components are evaporation, groundwater outflow, and surface-water outflow. In a lake and groundwater system that is typical of many karst lakes in Florida, a large part of the groundwater outflow occurs by means of vertical leakage through an underlying confining unit to a deeper, highly transmissive aquifer called the upper Floridan aquifer. The water-budget component that represents vertical leakage to the upper Floridan aquifer was calculated as a residual using the water-budget equation. For the 13 month period from August 1994 to August 1995, relative to the surface area of the lake, rainfall at Lowry Lake was 1.55 m yr⁻¹, surficial aquifer inflow was 0.79 m yr⁻¹, surface-water inflow was 1.92 m yr⁻¹, and direct runoff was 0.01 m yr⁻¹. Lake evaporation was 1.11 m yr⁻¹, and surface-water outflow was 1.61 m yr⁻¹. The lake stage increased 0.07 m yr⁻¹, and the vertical leakage to the upper Floridan aquifer was 1.48 m yr⁻¹. Surficial aquifer outflow from the lake was negligible. At Lowry Lake, vertical leakage is a major component of the water budget, comprising about 35% of the outflow during the study period. The vertical conductance (K_V/b), a coefficient that represents the average of the vertical conductances of the hydrogeologic units between the bottom of a lake and the top of the upper Floridan aquifer, was determined to be 2.51 × 10⁻⁴ day⁻¹ for Lowry Lake.     

The response of coastal marshes to sea-level rise: Survival or submergence?

In order to maintain an elevation in the intertidal zone at which marsh vegetation can survive, vertical accretion of the marsh surface must take place at a rate at least equal to the rate of relative sea-level rise. Net vertical accretion of coastal marshes is a result of interactions between tidal imports, vegetation and depositional processes. All of these factors are affected, directly or indirectly, by alterations in marsh hydrology which might occur as a result of sea-level rise. The overall response of coastal marshes to relative sea-level rise depends upon the relative importance of the inorganic and organic components of the marsh soil and the impact of increased hydroperiod on net accumulation. The varied combination of factors contributing to sediment supply, and their complexity at the scale of individual marshes, means that predicting the response of suspended sediment concentration in marsh floodwater to any changes which may occur as a result of sea-level rise, at anything other than the local scale is unlikely to be accurate. The impact of sea-level rise on net below-ground production is also complex. The sensitivity of certain species to waterlogging and soil chemical changes could result in a change in species composition or the migration of vegetation zones. Consequently, predicting the net impact of sea-level rise on organic matter accumulation is fraught with difficulties and requires improved understanding of interactions between vegetation, soil and hydrologic processes.     

单部多普勒天气雷达对降水中垂直流场结构的探测研究

该文提出用单部多普勒天气雷达距离高度扫描（RHI）的探测资料，从大气运动连续方程出发，在实际流场的二维假设下，反演雷达探测区域内的垂直剖面流场结构。通过个例试验表明，反演结果比较合理。该方法可供多普勒天气雷达探测研究应用。