新一代多普勒天气雷达强度定标研究

天气雷达回波强度的强弱直接影响预报员对降水强度的判断,在重大气象灾害天气过程中,回波强度偏差有可能导致漏报而产生无法挽回的损失,中国气象局提出“到2022年底全国新一代天气雷达反射率因子标准偏差平均值从4.5dB降低到3.5dB”的目标,就是为了提高雷达监测均一性,降低客观因子对预报质量的影响。本文对岳阳、长沙、湘潭、益阳雷达产品对比分析,利用数据平均偏差方法计算雷达回波强度的扩散特征,得出岳阳雷达回波强度较其他三部雷达均偏弱约4dB以上的结论,并采用“对点测量”方法对岳阳雷达进行重新标定,将平均偏差降低至2.5dB以内,降低了中尺度区域内不同雷达之间的平均偏差,有效增强了回波强度一致性,对提高雷达业务可用性具有十分现实的意义。     

GPM/DPR雷达与CINRAD雷达降水探测对比

通过对比星载DPR雷达与地基CINRAD雷达的降雨测量值,评估星地雷达联合应用的潜力。为了提高对比的准确性,在尽可能高的时空分辨率下,以几何匹配与格点匹配相结合的方式,提取星地雷达降水样本数据。2015年6月30日降水过程的对比分析结果表明:泰州、常州CINRAD雷达反射率因子在两站中分剖面的平均值偏差0.94 dB,地基雷达之间有很好的一致性;在DPR雷达与常州、泰州CINRAD雷达同时覆盖的降雨区域,星地之间雷达反射率因子的平均值偏差分别为-1.2 dB和-1.6 dB,显示星地雷达也有较好的一致性;现有DPR雷达陆上衰减订正算法在缩小星地雷达偏差方面起到一定作用,平均订正量0.4 dB,只要回波覆盖充分,匹配样本的高度以及其到地基雷达的距离对对比结果没有明显影响,而衰减订正和匹配样本区回波覆盖率是影响星地雷达对比结果的重要因素。     

双偏振雷达水凝物相态识别算法的参数改进

双偏振雷达的水凝物相态识别算法基于模糊逻辑方法建立,针对方法的可靠性和稳定性问题,利用2016—2017年暖季广州S波段双偏振雷达数据,从3个方面找出影响识别效果的关键因素并改进。使用模糊逻辑的累加值为检验依据,找出不合理的模糊规则,通过相态特征统计和权重矩阵修改加以改进。使用误差敏感性检验法系统,评估误差对识别效果的影响,发现反射率因子的误差在-0.5~+0.5 dBZ、差分反射率因子的误差在-0.1~+0.1 dB、雷达相关系数的误差在0~0.02、差分相移率的误差在-0.3~+0.9 dB的范围内,识别结果稳定性较好。此外,相态时空分布统计中发现底层冰雹面积异常增加,通过空间一致性检验可订正异常结果。     

基于雷达回波概率特征的雷达部分遮挡区域识别算法

部分遮挡是影响雷达观测资料质量的重要误差源之一。基于雷达回波的概率特征,本文提出一种不依赖高精度地形信息的雷达部分遮挡区域识别算法。该算法无须以人工方式建立样本数据库,只需直接检测实际业务应用中雷达连续观测的反射率因子,统计雷达探测范围内的每个格点出现大于某一反射率因子阈值(定义为Z阈值)的概率,并通过设置适当的概率阈值(定义为C阈值)来确定不同遮挡性质的雷达探测区域。应用该算法,使用2012年5-10月金华、衢州及上饶雷达连续探测资料,识别得到金华、衢州和上饶三部雷达距离地面3 km高度层上CAPPI的完全遮挡区域、部分遮挡区域和无遮挡区域;同时,通过对比2013年4月29日金华、衢州、杭州、上饶、黄山雷达3 km高度重叠探测区域的雷达反射率因子,检验了雷达部分遮挡区域识别结果的有效性,并分析了算法阈值的敏感性;最后,结合剔除部分区域弱回波的方案,对雷达组网拼图算法进行优化改进。结果表明:通过选择适当的Z阈值和C阈值算法,可以有效识别雷达部分遮挡区域;算法阈值的设置是识别部分遮挡区域的关键,较为适中的Z阈值有利于C阈值的选择;优化后的组网拼图算法可以有效解决部分遮挡问题,有效地提高了组网拼图数据的质量。     

基于空间一致性的双套站数据选取方法探索

国家级台站自动气象站双套运行后,将双套站产生的多套数据处理为一套数据的算法成为双套站投入业务运行前必须解决的重要问题。文章从数据"热备份"角度提出了基于空间一致性的主备法,在此基础上进一步从统计学基本原理以及保证数据连续角度提出了基于空间一致性的差值订正合成法两种数据处理算法。利用安徽省休宁站逐小时气温资料对两种算法结果的完整性和差异性进行了评估,评估使用的方法包括缺测率、差值均值、差值标准差、差值的一致率、超差率和粗差率等。评估结果表明:算法均能很好地保证数据的完整性;算法结果均与"真值"较为接近,基本能够反映大气真实情况,基于差值订正的"合成法"结果更优。最后利用新疆库车、安徽安庆等5个台站资料对算法涉及到的空间一致性方法进行了评估,结果表明该方法总体效果较好,尤其在相对湿度、气压和气温上具有很好的判别效果,而风速可能受局地地形或参考站选取影响效果略差。     

基于单站CAPPI格点数据的相邻天气雷达均一性评估系统研究

基于经过严格质量控制后的单站CAPPI格点数据,对相邻天气雷达观测重叠区域内等距离线上的回波强度一致性状况进行研究,根据雷达不同探测距离、不同海拔高度、不同降水强度等因素编制相邻雷达自动配对程序和等高面自动选择程序,建立了相邻天气雷达均一性算法。制定了适合我国天气雷达回波观测差异特征的均一性评估的3类标准(可信、可疑和疑误),并给出了评估标准的满足条件,从而建立了全国天气雷达均一性实时评估系统。从评估效果来看,均一性评估系统能够实时高效检测出全国不同波段、不同型号以及不同省份相邻雷达之间的回波一致性状况,并给出评估结果;对浙江、福建、广东3省雷达一次降水过程的均一性评估,发现参与评估的27部S波段雷达整体可信率为85.19%,可疑率为11.11%,疑误率为3.7%,成功检测出雷达回波强度偏低、波束阻挡以及电磁干扰等问题;对临沂站雷达回波均一性分析,评估系统能及时报警,检测出该站雷达回波位置指向存在偏差,天线方位顺时针偏移16.88°,缩短了故障发现时间。     

基于TRMM/PR的长江下游地基雷达一致性订正

我国有近200部地基多普勒天气雷达,已经积累了近20年的观测数据,这些数据对雷达气候学研究非常重要。但由于不同雷达的标定误差不同,雷达之间存在观测值不一致性的现象（与美国的地基雷达类似）,有的反射率因子差异超过了3 dB。这种不一致影响了多雷达联合降水估计的精度和雷达组网临近预报的效果。为此,采用筛选比较法对地基雷达与TRMM/PR（Tropical Rainfall Measuring Mission/Precipitation Radar）进行空间匹配和异常数据剔除,以TRMM/PR为参照计算并订正地基雷达偏差。对2013年5—9月长江下游7部S波段雷达数据订正后,结果表明:订正后7部雷达之间的平均反射率因子差异从1.8 dB降至0.5 dB,任意两部雷达之间的差异均小于1.0 dB,多雷达的观测一致性和空间连续性有明显改善。与传统的几何匹配法比较,筛选比较法订正结果相对稳定,不存在过量订正的问题。     

济南双偏振多普勒天气雷达在线自动标定数据质量分析评估

阐述了CINRAD/SA-D双偏振多普勒天气雷达（简称“双偏振雷达”）标定技术,统计分析了济南双偏振雷达试运行以来在线自动标定数据和该时间段内的维护维修情况,从雷达几十个标定状态性能参数中,遴选对雷达探测数据质量影响最大的发射峰值功率Pt、相位噪声σφ、噪声系数NF、反射率标定系数SYSCAL、差分反射率因子ZDR、差分传播相移ΦDP等性能参数,分析评估在线自动标定数据质量。结果表明：1）峰值功率维持在679.68 kW,H（水平）和V（垂直）双通道的峰值功率长期运行吻合一致性较好。2）H和V双通道噪声系数均值分别维持在1.66 dB和1.73 dB,双通道数据总体分布稳定,且具有较好的一致性;标定数据的异常来源于外界干扰,占0.39%,受外界干扰H通道多于V通道,干扰造成接收机灵敏度降低了1.5 dB,导致雷达产品异常。3）反射率标定ΔSYSCAL最小值为-0.46 dB,最大值为0.25 dB,满足±2 dB的技术指标要求。4）I/Q相角法标定相位噪声均值为0.051 3°,实物对消能力60 dB与估测地物杂波抑制能力61.36 dB结果基本吻合,证实了雷达系统具有较好的地物杂波抑制能力。5）采用机内CW、TS双信号源标定法,接收双通道幅度和相位的标准差：ZDR-CW和ΦDP-CW分别为0.025 dB和0.735,ZDR-TS和ΦDP-TS分别为0.044 dB和1.116°,满足接收双通道一致性的技术指标,但CW信号标定结果明显小于TS信号标定结果,表明双路方位旋转关节对接收链路信号幅度和相位的一致性有影响,导致ZDR-TS和ΦDP-TS标定结果比ZDR-CW和ΦDP-CW出现更大的偏差,因此随着双偏振雷达的长期运行,对方位旋转关节带来的幅度和相位固有偏差进行测试和订正非常重要。     

广东天气雷达覆盖现状的评估

利用广东省10部天气雷达2010—2016年的观测基数据,对雷达的国土覆盖、地形遮挡现状进行评估,结果表明:珠三角地区覆盖密集,大部分区域覆盖都达到4～5部雷达重叠,海岸线连续性覆盖良好;粤东地区覆盖均匀,大部地区覆盖达到3～4部雷达重叠;粤西部覆盖较好,大部分地区达到2～3部雷达覆盖重叠;粤北等人口较少的地区雷达覆盖差、遮挡严重。     

雷达波束部分遮挡识别应用及效果评估

雷达波束部分遮挡是雷达定量降水估测(QPE)算法的重要误差源。利用4次大范围的天气过程,联合上饶、黄山、杭州、金华、宁波、衢州、温州和台州8部天气雷达和浙江省2047个雨量计观测资料,应用金华、衢州和上饶雷达的部分遮挡区域识别结果,从定性和定量分析两个角度,将雷达组网拼图数据划分为部分遮挡区域、无遮挡区域和总数据区域,验证分析了部分遮挡回波订正方案在提高雷达组网拼图质量和提高雷达QPE精度方面的作用。结果表明:剔除部分遮挡回波的回波订正方案,在不同天气过程中均可以(1)有效地增强部分遮挡区域内雷达组网拼图和雷达QPE数据场的连续性;(2)显著提高了部分遮挡区域内雷达QPE数据场的精度,降低了因部分遮挡导致的雷达QPE误差,并间接提高了无遮挡区域以及总的数据区域内的雷达QPE的精度;(3)改善了Z-R关系拟合方案和最优插值校准方案的有效性,这是剔除部分遮挡回波后,雷达QPE数据场精度提高的重要原因。     

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.     

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.     

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.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

VARIABILITY OF INTER-ANNUAL RELATIONSHIP BETWEEN INDIAN OCEAN DIPOLE AND HUAXI REGION’S AUTUMN PRECIPITATION

The moving-window correlation analysis was applied to investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the synchronous autumn precipitation in Huaxi region, based on the daily precipitation, sea surface temperature (SST) and atmospheric circulation data from 1960 to 2012. The correlation curves of IOD and the early modulation of Huaxi region’s autumn precipitation indicated a mutational site appeared in the 1970s. During 1960 to 1979, when the IOD was in positive phase in autumn, the circulations changed from a “W” shape to an ”M” shape at 500 hPa in Asia middle-high latitude region. Cold flux got into the Sichuan province with Northwest flow, the positive anomaly of the water vapor flux transported from Western Pacific to Huaxi region strengthened, caused precipitation increase in east Huaxi region. During 1980 to 1999, when the IOD in autumn was positive phase, the atmospheric circulation presented a “W” shape at 500 hPa, the positive anomaly of the water vapor flux transported from Bay of Bengal to Huaxi region strengthened, caused precipitation ascend in west Huaxi region. In summary, the Indian Ocean changed from cold phase to warm phase since the 1970s, caused the instability of the inter-annual relationship between the IOD and the autumn rainfall in Huaxi region.     

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     

全球贸易隐含碳变化及其影响分析

基于最新的GTAP8 (Global Trade Analysis Project）数据库,使用投入产出法,分析了2004年到2007年全球贸易变化下南北集团贸易隐含碳变化及对全球碳排放的影响。结果显示,随着发展中国家进出口规模扩张,全球贸易隐含碳流向的重心逐渐向发展中国家转移。2004年到2007年,发达国家高端设备制造业和服务业出口以及发展中国家资源、能源密集型行业及中低端制造业出口的趋势加强,该过程的生产转移导致全球碳排放增长4.15亿t,占研究时段全球贸易隐含碳增量的63%。未来发展中国家的出口隐含碳比重还将进一步提高。贸易变化带来的南北集团隐含碳流动变化对全球应对气候变化行动的影响日益突出,发达国家对此负有重要责任。     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

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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