X波段双线偏振天气雷达双通道一致性测试及分析

对房山X波段双线偏振天气雷达的天线性能、接收动态范围、噪声系数、系统定标能力以及接收双通道一致性进行测试分析,结果表明:天线增益和交叉极化隔离度最小值分别为44.73dB和36.1dB、双通道差分反射率ZDR和差分传播相位ΦDP标准差分别为0.02dB和0.26°、双通道的噪声系数最大平均值为2.02dB,均满足该雷达系统相应的指标设计要求;双通道的动态曲线特征和回波强度定标性能一致性存在差异,会对雷达系统探测数据质量造成不利影响。同时对该雷达系统的差分反射率ZDR标定方法进行了探讨,对雷达探测降水个例数据进行了分析。     

双线偏振雷达标定技术应用

正随着双线偏振雷达技术的成熟和广泛应用,对双偏振量标定方法、精度和稳定性提出了更高的要求。使用双偏振标定技术可以全面检查雷达系统的状态,实时在线校正雷达系统偏差,提高双线偏振雷达数据质量。随着双线偏振天气雷达技术不断成熟和部署,对雷达数据质量和数据稳定性提出了更高的要求。双线偏振雷达较传统的单偏振雷达新增的三个基本物理量分别为水平和垂直线极化幅度差异差分反射率(ZDR)、相位差异差分传播相移(φDP)和两通道     

X波段双线偏振多普勒雷达资料质量评估

以山东省首部X波段全固态双线偏振多普勒天气雷达724XSP观测的几次降水过程资料为例,与济南站多普勒天气雷达(CINRAD/SA)资料进行对比分析,并利用XSP雷达观测的层状云降水资料进行偏振参量的质量分析。结果表明:XSP雷达波束在穿越层状云云体时的衰减比较均匀,与SA雷达探测的云体结构比较接近,但XSP雷达对45 dBZ以上强回波的探测能力较差,尤其探测冰雹云云体结构时二者差别较大。对偏振参量分析发现,当SNR10 dB时,Z_(DR)、CC、Φ_(DP)和K_(DP)等偏振参量受噪声影响明显,误差较大不可信;当SNR位于15~23 dB时,Z_(DR)和CC的测量值有明显波动,质量较差;XSP雷达的Z_(DR)测量值较理论值偏低0.5 dB;Φ_(DP)和K_(DP)资料受衰减影响较小,当SNR10dB时,质量比较可靠。     

CINRAD/SA雷达双偏振升级数据质量分析评估

广州CINRAD/SA雷达完成双偏振升级改造后,本文评估分析了其探测灵敏度、地物抑制能力以及差分反射率ZDR,差分相移Φ_(DP)、差分相移率K_(DP)及相关系数的数据质量,结果表明:双偏振升级后雷达灵敏度与升级前基本一致,地物杂波抑制效果有明显改善;ZDR系统偏差变化稳定,随Z的增长趋势与经验值一致,测量误差不超过0.2dB;Φ_(DP)的初始相位具有较好的稳定性,K_(DP)对强降水敏感,与强降水有很好的对应关系;相关系数能够很好地区分气象和非气象回波。     

国产双偏振天气雷达差分反射率测量性能分析

双偏振天气雷达对气象目标差分反射率(Z_(DR))的精确测量是我国新一代天气雷达双偏振升级过程中的一个重要环节。本文介绍了采用机外仪表、机内测试信号、太阳、小雨等方法对双偏振天气雷达系统引入的Z_(DR)偏差进行测量的原理,分析了影响Z_(DR)测量精度的关键因素,即发射机、接收机和方位旋转关节引入的Z_(DR)动态偏差。比较了各种标定方法的优点和局限性。以南京大学C波段双偏振雷达为例,给出了采用机外仪表、太阳、小雨方法对雷达系统引入的Z_(DR)偏差的实测结果,并对测量结果进行了比较分析,发现3种方法的测量结果具有较好的一致性;且Z_(DR)测量值随方位角的变化具有一定的规律,因此随着双偏振雷达的长期运转,方位旋转关节的影响不可忽略。本文对未来我国双偏振雷达的业务运行和组网观测具有一定的参考价值。     

车载X波段双线偏振多普勒天气雷达及其数据处理系统

文章介绍了车载X波段双线偏振多普勒天气雷达及其数据处理系统,并对其资料质量和应用问题进行了分析和讨论。该雷达采用的单发双收的工作机制,实现对Z_H、Z_(DR)、Φ_(DP)、K_(DP)、ρ_(HV)(0)以及L_(DR)等参数的探测。这些信息反映了云和降水粒子的范围、大小和运动变化等特征,是研究云和降水特别是灾害性天气的形成机制及其物理过程变化的有效工具。基于该雷达的数据处理系统是在利用这些测量参数的基础上,可以实现降水处理和降水粒子相态识别功能,为用户提供有效的气象服务。     

双线偏振雷达双通道一致性及测试方法研究

从偏振天气雷达通道一致性的重要性出发,分析了雷达系统本身特性(天线、接收机、旋转铰链和馈线)对双通道一致性的影响。结合目前国内外偏振雷达所能达到的指标,提出了双通道一致性的测试内容和方法,并给出性能指标要求。根据上述方法,获得了北京市气象局C波段双线偏振天气雷达天线和双通道的测试结果,对如何提高双线偏振雷达的性能及评估性能好坏具有一定的参考意义。     

广州S波段双线偏振天气雷达双通道一致性测试及分析

双线偏振天气雷达双通道的一致性,是新一代天气雷达双线偏振升级的技术关键。本文分别采用机外仪表和机内测试信号,测试分析了广州CINRAD/SA-D双线偏振雷达接收机双通道的一致性。结果表明:①接收机双通道的动态范围、噪声系数、强度定标等满足设计指标,但测试结果也存在一定的差异,导致偏振参量差分反射率因子ZDR和差分相移ΦDP产生误差,需要对这种差异进行定期检查和修正,以确保双通道一致性;②旋转关节对整个接收链路的信号幅度和相位一致性有影响,这种影响随着方位的变化呈现出一定的周期变化规律,因此随着双线偏振雷达的长期运行,方位旋转关节的影响不可忽略。     

CINRAD/SA-D雷达差分反射率金属球标定试验

目前我国新一代天气雷达正升级为双偏振体制,CINRAD/SA-D双偏振天气雷达对气象目标差分反射率(Z_(DR))的精确测量是参数标定的重要环节。对徐州双偏振雷达配置VCP-sect扫描模式,采用目标方位±5°的扇扫组合,且关闭地物等所有雷达滤波算法,用无人机分别携带2种标准金属球开展Z_(DR)标定试验。分析试验结果,发现采用40cm金属球,控制无人机与金属球间隔为68m时,Z_(DR)平均值为-0.265dB,最小为-0.125dB,最大为-0.375dB,满足雷达定标Z_(DR)的技术要求。研究结果为业务雷达开展双偏振雷达定标Z_(DR)提供了技术方案。     

双线偏振天气雷达天线性能要求及其检测方法

双线偏振天气雷达天线性能的优劣将直接影响雷达探测能力和气象目标定量测量的精度。双线偏振雷达主要采用交替发射和双发双收两种模式,即水平和垂直线偏振波交替发射同时接收和同时发射同时接收两种形式。本文基于双线偏振天气雷达天线误差对气象目标探测精度影响的研究和分析,提出了双线偏振天气雷达天线性能要求及其检测方法,特别对如何在雷达工作现场利用太阳和专用信号源检测评估双线偏振天气雷达天线性能的方法进行了说明。     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on     

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正AIMS AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.SUBMISSIONAll submitted     

A Brief Introduction to Marine Meteorological Science Experiment Base at Bohe Town,Maoming City,Guangdong Province

<正>With the support of specialized funds for national science institutions,the Guangzhou Institute of Tropical and Marine Meteorology,China Meteorological Administration set up in October 2008 an experiment base for marine meteorology and a number of observation systems for the coastal boundary layer,air-sea flux,marine environmental elements,and basic meteorological elements at Bohe town,Maoming city,Guangdong province,in the northern part of the South China Sea.     

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AIMS AND SCOPE
Atmospheric and Oceanic Science Letters （AOSL） publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.     

Information for Authors

AIMS AND SCOPE Atmospheric and Oceanic Science Letters （AOSL） pub- lishes short research letters on all disciplines of the atmos- phere sciences and physical oceanography. Contributions from all over the world are welcome.