一次台风变性并入东北冷涡过程的动力诊断分析

台风北移变性并入东北冷涡是造成东北地区夏季大范围暴雨的主要形式之一, 但其中的热动力结构变化特征及其物理机制尚不清晰。本文利用美国国家环境预报中心(NCEP)的再分析资料对一次台风变性并入东北冷涡过程进行动力诊断分析, 分析结果显示:冷涡冷空气的不断侵入以及台风移动形成的相对冷平流使得台风暖心结构消亡, 其低层低压辐合和高层高压辐散结构消失, 变性并入东北冷涡后气旋整层偏冷, 低层出现冷中心。台风变性并入东北冷涡过程中, 冷涡中心附近高空急流南侧的反气旋切变抑制气旋直接往高空发展, 而急流轴左侧的热动力分布特征有利于垂直涡度的发展, 变性后的气旋环流向冷涡的移近有利于急流轴维持倾斜, 从而促进气旋向高空冷涡倾斜发展。同时, 冷空气在气旋低层附近堆积导致等假相当位温线发生倾斜, 造成垂直涡度在气旋中层倾斜发展。台风变性并入东北冷涡后, 高空冷涡槽底的正垂直涡度平流促进气旋由中层直接向高层发展, 而高空冷涡槽底急流促进正垂直涡度平流的维持。气旋高空环流的发展反过来削弱了东北冷涡的高层环流, 导致高空冷涡中心出现北撤。     

甘肃武威市一次局地大到暴雨天气成因分析

利用常规天气图、FY-2D卫星云图、单站地面资料、NCEP再分析物理量场资料,对2013年8月6日发生在甘肃武威市对流性强降雨天气成因进行了诊断分析。结果表明:强降雨是在一定的大尺度环流背景下高低层天气系统共同作用下发生的,地面气象要素的剧烈变化是强对流天气能量的释放过程;湿度条件和水汽在本地辐合为大到暴雨提供了充沛的水汽;高层辐散、低层辐合以及强烈的上升气流是大到暴雨发生的动力条件;强烈的不稳定能量和不稳定层结是对流增强、雨强较大的必要条件;对流云团的发展和加强是降雨强度较大的直接原因。     

The total operating characteristic to measure diagnostic ability for multiple thresholds

The relative operating characteristic (ROC) is a popular statistical method to measure the association between observed and diagnosed presence of a characteristic. The diagnosis of presence or absence depends on whether the value of an index variable is above a threshold. ROC considers multiple possible thresholds. Each threshold generates a two-by-two contingency table, which contains four central entries: hits, misses, false alarms, and correct rejections. ROC reveals for each threshold only two ratios, hits/(hits + misses) and false alarms/(false alarms + correct rejections). This article introduces the total operating characteristic (TOC), which shows the total information in the contingency table for each threshold. TOC maintains desirable properties of ROC, while TOC reveals strictly more information than ROC in a manner that makes TOC more useful than ROC. We illustrate the concepts with an application to land change science.     

低层偏南气流对一次暴雨过程的动力作用分析和数值模拟

利用常规观测资料和NCEP再分析资料,对2010年7月22-25日四川盆地西部出现的一次暴雨过程进行了诊断分析.结果表明:暴雨出现在对流层低层南海至四川盆地一直维持偏南气流的环流背景下,暴雨与这支偏南气流的风速演变密切相关,降雨强度随南风气流的增强而增强,南风气流增强所形成的风速辐合及正涡度平流是暴雨的主要动力触发因子,暴雨与低层辐合和正涡度平流区域有很好的对应关系.WRF数值模拟试验进一步表明:850 hPa层3h风速演变对中尺度对流系统的发展具有很好的指示意义,在3h风速增大区域的下风方,未来3h对流云团将迅速发展;盆地西部形成的气流辐合与其西侧的高原地形密切相关.     

Assessing cause and effect of multiple stressors on marine systems

An operational framework is developed to serve as a guideline for investigating causal relationships between environmental stressors and effects on marine biota. Because of the complexity and variability of many marine systems, multiple lines of evidence are needed to understand relationships between stressors and effects on marine resources. Within this framework, a weight of evidence approach based on multiple lines of evidence are developed and applied in a sequential manner by (1) characterizing the study system which involves determining if target biota are impaired, assessment of food and habitat availability, and measuring contaminant levels in the environment, (2) assessing direct effects of contaminant exposure on target biota using biomarkers and assessing indirect effects of exposure using suites of bioindicators, and (3) applying standard causal criteria based on epidemiological principles and diagnostic health profiling techniques to assess potential causes. Use of multiple lines of evidence should also reduce the risk of false positives (Type I error or falsely concluding that there is a causal relationship when there is none) and false negatives (Type II error or falsely concluding there is not a causal relationship when there actually is). Understanding causal relationships and the mechanistic processes between environmental stressors and effects on biota is important in the effective management and restoration of impaired marine ecosystems.     

NCEP/CFS模式对东亚夏季延伸预报的检验评估

利用NCEP的气候预报系统（Climate Forecast System, CFS）所提供的1981—2004年历史回报试验结果,检验和评估了该系统对夏季东亚地区大气环流的预报技巧和系统误差;在此基础上通过提取模式预报和观测的10~20 d及30~60 d低频振荡分量,重点对我国南方3次典型持续性暴雨过程的预报技巧进行检验和诊断分析。结果表明:CFS系统对东亚整体大气环流逐日预报的可靠时效为5 d左右,60°N以北的对流层中高层高度场预报系统性偏低,而在40°~60°N则为系统性偏高。系统性误差随预报时间的延长而增加,但10 d以上预报的系统性误差大小和空间分布逐渐趋于稳定;CFS系统对低频分量的延伸期预报技巧好于对其整体大气环流的预报技巧,并且在典型持续性暴雨过程中,CFS系统对影响强降水过程的主要环流系统低频振荡特征有一定预报能力。     

Possible Sources of Forecast Errors Generated by the Global/Regional Assimilation and Prediction System for Landfalling Tropical Cyclones. Part Ⅱ: Model Uncertainty

This paper investigates the possible sources of errors associated with tropical cyclone (TC) tracks forecasted using the Global/Regional Assimilation and Prediction System (GRAPES). In Part I, it is shown that the model error of GRAPES may be the main cause of poor forecasts of landfalling TCs. Thus, a further examination of the model error is the focus of Part II. Considering model error as a type of forcing, the model error can be represented by the combination of good forecasts and bad forecasts. Results show that there are systematic model errors. The model error of the geopotential height component has periodic features, with a period of 24 h and a global pattern of wavenumber 2 from west to east located between 60°S and 60°N. This periodic model error presents similar features as the atmospheric semidiurnal tide, which reflect signals from tropical diabatic heating, indicating that the parameter errors related to the tropical diabatic heating may be the source of the periodic model error. The above model errors are subtracted from the forecast equation and a series of new forecasts are made. The average forecasting capability using the rectified model is improved compared to simply improving the initial conditions of the original GRAPES model. This confirms the strong impact of the periodic model error on landfalling TC track forecasts. Besides, if the model error used to rectify the model is obtained from an examination of additional TCs, the forecasting capabilities of the corresponding rectified model will be improved.     

BCC S2S模式对亚洲夏季风准双周振荡预报评估

利用1994-2013年ERA-Interim及NCEP/NCAR再分析数据,对国家气候中心（BCC）次季节到季节尺度模式（S2S）1994-2013年的回报试验数据进行亚洲季风区准双周振荡（QBWO）预报能力评估,并诊断模式预报误差来源。结果表明:BCC S2S模式对QBWO的预报能力随着预报提前时间的增长而降低,9 d后预报技巧明显减弱,其周期、传播特征和强度出现误差;在提前9 d预报中,印度洋地区QBWO对流-环流系统结构松散,信号偏弱,对流向东传播,这与印度洋平均态的预报误差有关,夏季对流平均态低层水汽场在西太平洋和阿拉伯海较强,而东印度洋、孟加拉湾一带偏弱;西北太平洋地区QBWO具有向西北传播的特征,但强度偏弱,可能原因是预报低估了QBWO对流西北侧低层涡度的超前信号,经涡度方程诊断发现,地转涡度平流正贡献微弱,相对涡度平流在对流西北侧引发负涡度,从而减弱了对流西北侧由低层正涡度引发的有利条件。     

CINRAD/SA(B)发射机触发器芯片级故障诊断流程

发射机触发放大器主要为调制器中SCR开关管提供放电触发脉冲,同时兼具调制组件的保护功能。发射机触发器芯片级故障诊断流程将触发器故障定位到芯片级,大大降低了触发器故障维修成本,同时为雷达测试平台中触发器故障自动诊断建模提供了技术支持。在发射机触发器信号流程基础上,依据发射机触发器关键点波形或关键点电平,通过触发器故障树图了解故障因果关系,研究出规范化的触发器芯片级故障诊断流程。列举了依据触发器芯片级故障诊断流程,修复了由于单稳态触发器无触发信号输出,导致无-200V放电触发信号的单稳态触发器故障个例。结果表明:芯片级触发器故障诊断流程可以快速定位发射机触发器故障点到最小可更换芯片。具有操作方法简洁、诊断思路清晰、操作规范,基层雷达站技术人员容易掌握的特点,可有效提高新一代天气雷达技术保障水平,保证雷达观测数据的可靠性。     

NMC第二代中期数值预报系统误差的动力诊断

利用国家气象中心第二代中期数值预报模式计算了１月和７月的预报诊断量。计算结果表明,新一代模式在动力外强迫作用、辐射通量和对流参数化等物理过程方面的改进,使该模式的预报比第一代模式有了较大的改善,模式预报的系统误差明显减小。通过对角动量、热量和水汽的经向输送和收支平衡的分析,认为该模式在地形处理、陆面过程、云辐射和积云对流参数化等物理过程还有待进一步改进。