城市热岛与海风锋叠加作用对一次局地强降水的影响

利用常规观测资料、天津255 m气象塔资料、多普勒雷达资料和VDRAS反演资料及中尺度TJ WRF模式输出资料,对2010年8月16日天津城区出现的一次局地强降水过程进行分析,重点分析了城市热岛与海风锋叠加作用对此次局地强降水的触发机制。结果表明：此次局地强降水发生在低层槽后弱的反环流条件下,具有明显的γ中尺度对流降水特征;城市热岛效应能造成局地的热力不均匀,这对形成地面中尺度辐合线非常有利。海风锋由岸边向市区移动中与中尺度辐合线相遇,能激发局地不稳定能量的释放,从而产生强对流天气。城市热岛对海风锋的移动有明显阻挡作用;当海风锋移到城市热岛效应明显区域附近时,其后侧气流会出现明显分支绕流和爬升现象,而且两者相遇处的辐合上升运动会迅速加强,这为该地不稳定能量的释放及雷暴的发生发展提供了有利的动力热力条件。中尺度TJ WRF模式可以很好地模拟出这一现象。     

江西夏季高温天气期间副高特征与预报方法

利用1959-2010年资料对江西夏季高温的气候分布概况进行分析,利用1970-2009年常规资料对江西夏季高温期间500hPa副高特征进行分析,以揭示江西夏季高温与副高的关系.利用2001-2008年资料进行的统计相关分析结果表明,850hPa和925hPa气温以及500hPa高度与日最高气温相关较高,采用统计回归模...     

海风锋导致雷暴生成和加强规律研究

应用雷达和地面自动气象站资料结合订正的天津探空资料,分三种类型统计分析了2004—2009年雷达监测到的50次由渤海湾海风锋导致雷暴生成和加强的规律及对应的天气背景;应用VDRAS系统资料分析了第三种类型（在不稳定环境下,沿海风锋直接触发雷暴）的热力、动力结构特征。结果表明:（1）强对流不稳定环境下,沿海风锋可以直接触发雷暴并沿海风锋移动的同时发展加强;（2）不同的类型在雷暴生成的位置、发展加强的速度、强度等方面都有明显的不同;（3）Ⅰ型对应背景场的动力条件更为有利,强对流天气更为剧烈,Ⅲ型对应背景场的热力、动力条件和水汽条件更为有利,对流抑制指数（CIN）小;（4）海风锋使得低层形成中尺度辐合线,沿海风锋垂直上升速度从地面一直延伸至3 km高度,强中心出现在1.5～3.0 km高度,最大风速达1.9 m·s^-1。     

2007年夏季两次强雷电过程的气象卫星资料分析

利用FY2一C、FY2一D高时空分辨率可见光云图和FY2一C云顶亮温资料,选取了2007年6月24—25日和7月10一11日2次强雷电过程,对雷电时空分布与强雷暴云团（MCS）演变特征的相关性进行了分析。结果表明：（1）对于不同MCS来说,落雷次数和落雷密度都与MCS的强度密切相关,即MCS强度越大,对流越强,落雷次数越多,落雷密度越大。（2）落雷集中的时段主要都出现在MCS成熟之前、水平尺度为中口尺度的时段内。（3）对于同一MCS来说,在MCS成熟之前,当前以及未来1h的落雷密集区都不是位于当前大范围较低亮温区所覆盖的区域,而是位于MCS移动方向前方和最低云顶亮温中心前方TBB梯度最大的区域内,未来1h的落雷密集区比当前的落雷密集区偏东30—50km。在MCS成熟之后,落雷密集区位于MCS主体外新生的尺度小、生命史短的雷暴云团附近TBB的密集区内。     

Improving WRF-Hydro runoff simulations of heavy floods through the sea surface temperature fields with higher spatio-temporal resolution

This study investigates the impact of the spatio-temporal accuracy of four different sea surface temperature (SST) datasets on the accuracy of the Weather Research and Forecasting (WRF)-Hydro system to simulate hydrological response during two catastrophic flood events over the Eastern Black Sea (EBS) and the Mediterranean (MED) regions of Turkey. Three time-variant and high spatial resolution external SST products (GHRSST, Medspiration and NCEP-SST) and one coarse-resolution and time-invariant SST product (ERA5- and GFS-SST for EBS and MED regions, respectively) already embedded in the initial and the boundary conditions datasets of WRF model are used in deriving near-surface atmospheric variables through WRF. After the proper event-based calibration is performed to the WRF-Hydro system using hourly and daily streamflow data in both regions, uncoupled model simulations for independent SST events are conducted to assess the impact of SST-triggered precipitation on simulated extreme runoff. Some localized and temporal differences in the occurrence of the flood events with respect to observations depending on the SST representation are noticeable. SST products represented with higher cross-correlations (GHRSST and Medspiration) revealed significant improvement in flood hydrographs for both regions. The GHRSST dataset shows a substantial improvement in NSE (~70%), RMSE reduction up to 20%, and an increase in correlation from 0.3 to 0.8 with respect to the invariable SST (ERA5) in simulated runoffs over the EBS region. The use of both GHRSST and Medspiration SST data characterized with high spatio-temporal correlation resulted in runoff simulations exactly matching the observed runoff peak of 300 m³/s by reducing the overestimation seen in invariable SST (GFS) in the MED region. Improved precipitation simulation skills of the WRF model with the detailed SST representation show that the hydrographs of GHRSST and Medspiration simulations show better performance compared to the simulated hydrographs by observed precipitation.     

Total Hg concentrations in stream and lake sediments: Discerning geospatial patterns and controls across Canada

This article presents an analysis of Geological Survey of Canada (GSC) open-file data for total Hg concentrations (THg) in stream and lake sediments at 142,028 sampling locations. This analysis was done for select survey zones across Canada, with emphasis on discerning THg-relevant geographic, geological, atmospheric and topographic controls. THg was generally highest in areas affected by mining and smelting, followed by areas with high metallogenic source locations. Background levels for THg were elevated in the more populated areas along the south, but dropped toward the remote and coldest locations in the east, north and west. This trend was correlated (R² = 0.74; P < 0.0001) with the 2005 GRAHM projections (Global/Regional Atmospheric Heavy Metals Model) for atmospheric Hg deposition (zones and locations with major geogenic sources and mining activities removed). Mean THg was higher for upland lakes (100.9 ± 0.5 SE, ppb) and streams (71.7 ± 0.6 SE, ppb) than for lowland lakes (94.4 ± 0.86 SE, ppb) and streams (64.2 ± 1.26 SE, ppb). The east-central portion of the Yukon Territory (Selwyn Basin) was analyzed in further detail. Here, THg within the sediments increased with increasing loss-on-ignition and increasing trace-element concentrations, and decreased with an increasing wet-area component per catchment above the sediment sampling locations. The characterization and quantification of these Hg trends is important for modeling and mapping health risks to ecosystems and communities across Canada and elsewhere.     

2013年3月19日江西省冰雹天气成因分析

利用常规观测资料和卫星、雷达、自动站等非常规观测资料以及NCEP再分析资料,对2013年3月19日江西省大范围冰雹天气过程形成原因进行分析。结果表明,该过程是在有利的环境条件下发生的：对流层中低层强热力不稳定和强动力不稳定为冰雹生成和增长提供了不稳定机制;暖湿边界层偏南风急流和低层西南急流以及中层“干”西南急流对热力不稳定和动力不稳定机制发展有重要贡献;适宜的0℃层和-20℃层高度有利于冰雹增长。江西北部冰雹天气是在边界层有锋面逆温的条件下发生的,为“高架雷暴”类对流,南部冰雹天气是在边界层有较强暖平流的条件下发生的,为非“高架雷暴”类对流,两类对流的边界层温度层结分布差异明显。与历史同类个例比较发现,假相当位温垂直变化不仅能表征条件不稳定发展程度,对雷雨大风类强对流天气的判断也有一定参考意义。     

Generation of isoprenoid compounds,notably prist-1-ene,via photo- and autoxidative degradation of vitamin E

In order to mimic the photodegradation of vitamin E during phytoplankton senescence and study the behaviour of the resulting photoproducts during cell lysis, vitamin E dispersed in seawater was irradiated with solar light in the presence of hematoporphyrin as sensitizer. Under these conditions, singlet oxygen-mediated photooxidation and free radical oxidation (autoxidation) acted simultaneously on the substrate, affording 4,8,12-trimethyltridecanal, 4,8,12-trimethyltridecanoic acid, 6,10,14-trimethylpentadecan-2-one, α-tocopherylquinone, 4,8,12,16-tetramethylheptadecan-4-olide, 2,3-epoxy-α-tocopherylquinone and 5,6-epoxy-α-tocopherylquinone as minor products. Different mechanisms were proposed to explain the formation of these different isoprenoids. The main products (85% of the degraded substrate) appeared to be previously described diastereoisomeric trimeric oxidation products of vitamin E, whose pyrolysis during gas chromatography–mass spectrometry (GC–MS) afforded 2,6,10,14-tetramethylpentadec-1-ene (prist-1-ene). On the basis of their greater ability to produce prist-1-ene during pyrolysis than intact vitamin E and their highly favoured production in phytoplanktonic cells, these trimers are proposed as likely sources of this isoprenoid alkene, previously identified in many pyrolysates from immature kerogens.