一次特大暴雨(雪)天气过程的微物理模拟

利用非静力中尺度模式MM5(V3.7)模拟了2007年3月3-5日发生在辽宁地区的一次特大暴雨(雪)天气过程.分析在相同的天气形势背景下,不同降水类型中心各种水成物的相态分布特点,重点对各种水成物的源项进行详细分析.结果表明:雨水碰并雪成雨是雨水产生的主要云微物理过程,雪、霰和云水的碰并对雨水的形成起着非常重要的作用,...     

Recovery of macrobenthos in defaunated tropical estuarine sediments

In the estuarine environment, hypoxia and/or anoxia have become a major cause of benthic defaunation and are strongly associated with increased eutrophication. Mesoscale field experiments were carried out to examine the recolonization and recovery time of macrobenthos after defaunation. Azoic sediments were achieved by covering four areas with polyethylene sheeting. Temporal changes and depth distribution of macrobenthos within the defaunated sediments were compared with those in undisturbed natural sediments at the same site. Within 3 days, annelids appeared as the first immigrants. After 153 days, the process of recovery had not yet been completed in terms of species richness. Whereas diversity and evenness showed no significant differences between treatments during the entire experiment, multivariate analyses proved that differences between treatments were still significant 93 days after the start of the experiment.     

Characteristics and vertical structure of oceanic mesoscale eddies in the Bay of Bengal

The signatures of mesoscale eddies induced surface and subsurface changes have not been comprehensively quantified for the Bay of Bengal (BoB) region. This study quantifies the statistical properties and three-dimensional (3D) eddy structures in the BoB. To accomplish this, the satellite altimetry data combined with automated eddy detection and tracking algorithm is used. Horizontal distribution of surface characteristics of eddies is analyzed by using 24 years (1993–2016) of AVHRR infrared satellite sea surface temperature (SST) and 7 years (2010–2016) of sea surface salinity (SSS) of SMOS satellite data. Surface eddy centric composite analysis reveals the existence of warm (cold) and diverse SSS anomalies for anticyclonic (cyclonic) eddies. During winter, it is important to note that the eddy induced SST and SSS anomalies show the dipole patterns show opposite phases for the cyclonic and anticyclonic eddies. Observed diploe structures are consistent with the eddy rotation and background large-scale meridional gradient of temperature and salinity fields. The 3D structure of eddies is investigated by using the ARMOR3D and Argo float profiles. The horizontal distribution of temperature and salinity anomalies from ARMOR3D signify the monopole structure of eddies in the subsurface layers. Further, the analysis of composite averages of 241 (200) Argo temperature profiles indicates the core of anticyclonic (cyclonic) eddies centered at about ∼140 m (∼100 m). However, salinity profiles depict the existence of core at ∼65 m (∼50 m). This study have practical relevance to a variety of stakeholders and finds profound importance in the validation of eddy-resolving ocean models for the BoB region.     

2×CO2 Eastern Asia regional responses in the RSM/CCM3 modeling system

A global to regional modeling system has been developed to evaluate precipitation under doubled CO₂. The National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) is initialized and forced by current and doubled CO₂ simulations from the NCAR community climate model (CCM3). Three RSM simulations, RSM0, RSM1, and RSM2, with resolution of 280, 50 and 15 km, are examined. The RSM0 setup resolution matches the T42 CCM3 simulations. The RSM2 simulation is centered over Taiwan. Due to incompatibility of the model physics, noticeable differences between RSM0 and CCM3 are found, especially in wintertime, which suggests that simulation from RSM0, rather than CCM3, should be used to contrast high-resolution regional variations produced by RSM1 or RSM2 simulations.While the spatial distributions of RSM1 and RSM2 simulations over Taiwan are greatly improved over the CCM3 simulation, the intensity of the unique wintertime drizzle is overestimated, especially in RSM2. There is also a spurious northward extension of the precipitation pattern from the subtropical warm-pool region. Thus the regional response to doubled CO₂, which consists of more summerlike wintertime precipitation characteristics over the northeastern and eastern sides of Taiwan, with increased intensity mostly in the extreme events, is still in doubt and must be examined with improved global and regional models.     

中尺度涡影响下目的层地震成像的畸变与影响因素分析

将PE方法与地震数值模拟方法相结合研究了中尺度涡影响下目标地层成像的畸变.模拟了不同声源频率、不同水深条件下的地震波场.计算结果发现,中尺度涡的存在使得真实地形结构无法在地震成像中反映,而且地震成像畸变随着海水深度、震源频率的增加而增大.机理分析表明,中尺度涡所带来的水体温度梯度变化是产生地震成像畸变的主要因素.为了便于工程应用,本文还推导了有效涡强度、温度差与地形畸变率的关系式.本文的研究结果将对提高深海地震成像精度有一定的指导意义.     

一次降雪过程持续原因分析

利用多种观测资料和中尺度数值模拟资料,对2011年2月14日发生在江淮地区的一次预报失误的持续性降雪过程进行较为全面的分析.结果表明:前期的降水导致近地面维持较大湿度,补充南下的冷平流促使低层大气接近饱和,降雪持续期间,水汽集中在对流层低层浅薄的层次中;对流层中层发展和维持的强冷平流导致降水区上空迅速降温减湿,从而在对流层中低层,逐渐建立起弱对流不稳定层结.而叠置其上的稳定层则将对流活动和水汽的向上输送限制在对流层低层内,使得水汽和能量得以在一定范围内集中;不断补充南下的冷空气强迫近地层风场发生扰动,形成的中尺度切变线,为这种浅薄层次下的弱对流活动提供了触发条件.尽管辐合抬升较弱,但与其它季节相比,气温较低的冬季,在抬升凝结高度较低的大气中,水汽易凝结成云致降水.造成这次预报失误的原因,是忽略了近地层系统的变化.另外,对补充冷空气的影响作用考虑不充分.     

中尺度模式积云参数化方案的改进及其在暴雨模拟中的应用

本文针对中国暴雨发生发展天气特征,改进和发展了一种适合于描述东亚暴雨的中尺度积云参数化方案.首先基于近年来(1990—2010)江淮流域汛期降水合成分析的基础上,诊断出组织化对流降水环境的动力参数;其次利用该动力参数作为动力控制条件,改进了Kain-Fritsch Eta中尺度积云对流参数化方案;最后利用改进的中尺度积云参数化方案对梅雨期暴雨、华南前汛期暴雨过程进行了数值模拟,结果表明:改进后的中尺度积云参数化方案对上述两次暴雨过程的落区及强度的模拟,均有明显改进.     

Satellite-observed variability of phytoplankton size classes associated with a cold eddy in the South China Sea

Ocean-color remote sensing has been used as a tool to detect phytoplankton size classes (PSCs). In this study, a three-component model of PSC was reparameterized using seven years of pigment measurements acquired in the South China Sea (SCS). The model was then used to infer PSC in a cyclonic eddy which was observed west of Luzon Island from SeaWiFS chlorophyll-a (chla) and sea-surface height anomaly (SSHA) products. Enhanced productivity and a shift in the PSC were observed, which were likely due to upwelling of nutrient-rich water into the euphotic zone. The supply of nutrients promoted the growth of larger cells (micro- and nanoplankton), and the PSC shifted to greater sizes. However, the picoplankton were still important and contributed ∼48% to total chla concentration. In addition, PSC time series revealed a lag period of about three weeks between maximum eddy intensity and maximum chlorophyll, which may have been related to phytoplankton growth rate and duration of eddy intensity.     

豫西地形对一次强降水过程的影响分析

利用中尺度模式WRF 3.3.1模拟了2007年7月29日豫西山区强对流天气过程,并进行了地形高度敏感性试验。结果表明：模式能够很好地再现此次强对流降水过程,模拟降水范围与强降雨中心均与实况较一致。分析对比控制试验和地形敏感性试验结果可知,地形的改变能够在水平和垂直方向上影响环流形势,进而影响降水的落区和中心量级。地形升高和迎风坡梯度增大使近地面层水平风场辐合增强,中层上升运动明显增大,且低层的水汽通量增大,导致雨带横向范围和降水中心量级明显增大;而地形降低和迎风坡梯度减小使山脉对近地面层气流的阻挡作用明显减弱,低层水汽通量显著降低,中层辐合抬升运动明显减弱,迎风坡前强降水中心减弱甚至消失,而山脉下游降水则有所增强。分析地形高度与山前降水的定量关系可知,降水中心量级随着地形升高或降低相应地增大或减小,但二者并非完全的线性正相关。     

辽宁黑山突发性局地特大暴雨中尺度对流条件和特征

利用常规和加密自动气象站观测资料、卫星和雷达探测资料以及NCEP再分析资料（1°×1°,6h）, 对2013年8 月15-16日辽宁黑山地区特大暴雨的中尺度对流条件和对流系统特征进行探讨。结果表明: 此次强降水由中-β尺度系统引起,短时大暴雨发生在能量舌边缘,地面偏东风和地形强迫抬升作用造成对流单体沿着山脉东侧生成、发展和移动,最终导致持续性对流性强降雨。东北低压冷锋前所激发的中尺度切变和涡旋触发了局地大暴雨。黑山地区上游有两个对流单体生成,向东移动合并影响该地区,移动方向前侧的斜升气流和低质心回波提高了降水效率。