利用新一代天气雷达资料反演云体含水量

利用多普勒天气雷达探测的反射率因子Z与含水量M的Z-M经验关系式,反演云体含水量。计算域定为以雷达站为中心、水平边长为150 km的正方形格点域,垂直高度为30 km,分辨率是1 km×1 km×1 km。通过对2006年4月11日发生在湖南长沙的一次飑线过程的分析,利用反演软件计算该飑线云体的含水量分布,构建了CAPPI和VCS及整层VIL(垂直累积液态含水量)3种显示方式。反演结果与实测的雷达基本反射率产品、雷达CAPPI反射率产品、垂直积分液态含水量产品对比分析表明,反演的含水量分布及中心位置与雷达产品结果吻合,且利用Z-M经验关系式反演的含水量M反映了含水量的三维分布,较雷达VIL产品更能显示真实的含水量状况。     

一次强对流的三维数值模拟分析

利用中国科学院大气物理研究所的完全弹性三维雹云数值模式（IAP—CSM3D）,对2007年7月21日发生在湛江的一次强对流进行数值模拟,分析了强对流的气流结构、垂直涡度、雷达回波及含水量分布变化特征。结果表明,模拟的回波最大强度与雷达实测结果较吻合。模拟的强对流发展阶段气流结构的典型特征为下层水平辐合,上层水平辐散,气流在5km高度发生转向;处于成熟阶段的底层辐合比发展阶段的更强。随着时间的推移,近地层气流先辐合后辐散,下沉辐散气流一直持续到冰雹云消散。模拟的风暴云高含水量中心与强回波中心相对应,出现在上升气流最大区域附近,这说明该风暴云的动力场与物质场配合较好。     

双多普勒雷达反演强风暴三维风场的数值试验

两部雷达测得的径向速度再加上质量连续方程可以求解大气风场，利用这一原理，以1996年6月29日发生在北京东北部京冀交界处的一次强风暴过程为例，用模式反演出风暴体的三维风场结构，误差分析表明和实况基本一致。利用模式输出的三维风场，先模拟两部多普勒雷达扫描的数据，在此基础上，进行三维风场反演，结果表明，反演得到的流场和模拟的流场总体趋势完全一致，风暴的中心位置吻合较好，上升气流和下沉气流的分布也很接近，水平速度分量反演的误差很小，基本上可以反映三维风场的真实情况。垂直速度的平均离差在各个高度上都较小，反演结果较好。     

淮河流域东北部一次异常特大暴雨的数值模拟研究 Ⅰ: 结果检验和 β 中尺度对流系统的特征分析

在2000年12号台风(Prapiroon)影响期间,其外围对淮河流域东北部造成了一次罕见的特大暴雨,暴雨中心响水24 h降水量达到800 mm.文中所用的模式是俄克拉荷马大学风暴分析和预测中心研制的一个三维非静力可压缩数值区域预报模式ARPS(V5.2).采用了3层单向嵌套网格,Domain1中心取为(27.5°N,117.5°E),格距45 km,格点数为75×75;Domain2中心取为(31.5°N,119.5°E),格距15 km,格点数为140×140;Domain3中心取为(33.5°N,119.5°E),格距5 km,格点数为180×180;垂直方向分为35层,垂直格距为625 m.所利用的资料为:2000年8月29-31日每日4个时次(00、06、12、18时) 1°×1°的NCEP/ NCAR再分析资料及713雷达资料、GMS-5红外云图、探空报、地面加密资料.物理过程选用简单冰相方案,Kain和Fritsch 积云参数化方案.对逐时的卫星云图、713雷达图像进行数值反演,结合探空资料反演出暴雨中深对流系统的水汽三维分布情况,通过三维同化系统ADAS处理,同化初始场和侧边界条件,再用ARPS模式进行数值积分,从8月29日08时开始到31日08 时结束,积分48 h.并结合雷达资料、红外云图、探空报、地面加密资料等对数值模拟结果进行了对比分析.结果表明:ARPS较好地模拟了在台风移动的左前方、在高空槽与副高之间出现的中尺度强暴雨区,模拟降水区及暴雨中心位置与实况较为一致.利用模拟大气中的水物质模拟了雷达回波,与实际雷达回波进行了对比分析,揭示了该过程中β中尺度对流系统的演变特征,4条对流带的交汇点在响水附近.并将模式模拟的T-lgp图与实际T-lgp图进行了对比分析,揭示了该次暴雨过程的不稳定性.持续的高空风垂直切变为对流系统的发展提供动能,造成对流系统斜压发展,有利于降水集中在某一固定的地点.由于模拟结果与实况较为接近,因此可以利用模拟结果作为对该暴雨过程作进一步研究的基础.     

环北京地区八月风暴云的气候分布特征

基于2006—2008年8月北京新一代天气多普勒雷达资料,在TITAN(Thunderstorm Identifi-cation Tracking Analysis and Nowcasting)三维风暴识别、跟踪、分析算法的基础上,客观分析了北京地区8月的风暴气候特征。结果表明:(1)风暴初生的日变化特征表现为典型的双峰型,峰值分别在凌晨06~08时和傍晚18~20时;西南—东北走向的山脉附近风暴云初生频次明显高于其它地区,且迎风坡大于背风坡,表明地形对风暴触发的重要作用,同时地形对风暴移速、降水的分布等产生重要影响;(2)环北京地区8月50%的对流风暴云持续时间30 min,绝大部分风暴云体积400 km3,平均风暴云顶高度为6.9 km;(3)反射率因子阈值为35 dBz的风暴体积、面积、高度的频率近似呈对数正态分布;(4)通过尺度分析发现8月主要为D尺度风暴云,其平均组合面积较低纬度偏大,平均回波顶高比低纬偏高。     

北京一次强单体雹暴的三维数值模拟

利用中国科学院大气物理研究所建立的完全弹性三维雹云数值模式,模拟了1996年6月29日发生在北京东北部京冀交界地区的一次强单体雹暴过程,并结合多普勒雷达探测资料,分析了风暴的流场结构、雷达回波结构特征、含水量场等宏微观物理量的分布及其演变.模式模拟出了超级单体风暴云的一些典型特征,如悬垂回波、弱回波区、回波墙等.同时,模拟分析了冰雹形成的微物理过程,结果表明,本个例模拟雹云中,冰雹粒子主要由冻滴(CNfh)和霰(CNgh)转化形成,但冻滴对冰雹形成的贡献比霰大得多,冰雹含水量中心的发展演变与冻滴含水量中心的发展演变相一致,冰雹主要是通过撞冻过冷水过程(CLch、CLrh)而进一步长大的.     

2009年7月20日承德龙卷多普勒天气雷达特征

为了研究2009年7月20日发生在河北省承德市龙卷过程的多普勒天气雷达特征,利用承德CINRAD/CB多普勒天气雷达结合天气图、风廓线雷达、自动气象站等实况观测资料,对该次龙卷过程进行了详细的分析。结果表明:龙卷出现前低层大气相对暖湿,受高空冷涡影响,在对流层中层有较强的干冷空气下传,中高层有较强的垂直风切变。龙卷风出现过程中,在多普勒天气雷达径向速度产品上自低层到6.8 km都存在强烈的气旋性涡旋,风暴单体顶高、最大反射率因子高度、风暴质心高度等位置较高。垂直积分液态含水量产品显示在龙卷风出现前VIL数值产生了跃增,但40kg·m~(-2)以上维持时间短。定位分析表明,受风暴运动和结构影响,雷达龙卷涡旋特征位置位于实际龙卷风的东南侧。     

华南一次强飑线过程的三维变分风场反演效果分析

利用三维变分方法对2014年3月30—31日华南一次强飑线过程进行风场反演,经与风廓线雷达探测结果、双多普勒天气雷达反演结果、原始径向速度数据等对比分析,得到如下结论：三维变分方法反演的中低层水平风场与风廓线雷达探测到的结果较为一致,且能很好地表现飑线过境时的风向切变;通过与双多普勒雷达风场反演结果对比发现,两种方法得到的风场空间分布十分相似,均能很好地表现2 km高度上系统内部强带状回波前缘的辐合线以及5 km高度上较弱的辐散;三维变分方法反演的水平风场与径向速度场有较好的一致性,2 km高度强回波带前缘阵风锋处的辐合线位置以及5 km和8 km高度上辐散区的位置均与径向速度场十分吻合;三维变分方法反演的垂直速度能较好地反映该飑线过程中气流的上升和下沉运动,平行于飑线方向的气流变化较小,而系统气流变化主要沿垂直于飑线的方向。三维变分方法反演的飑线系统的三维风场结构合理,反演结果可靠。     

河北张家口一次超级单体龙卷雷达回波特征分析

利用ERA5 再分析资料、雷达资料以及北京VDRAS资料，对2021年7月1日发生在张家口的一次与超级单体伴随的龙卷天气特征进行分析。结果表明：①此次龙卷天气发生在高空冷涡的东南象限、低空切变线前侧暖区及地面辐合线附近。②雷达资料分析显示在超级单体的南侧产生了此次龙卷，龙卷过程中超过50 dBz的高度在6 km以下，强核中心在3 km以下，为低质心的对流系统，反演的风场上在低层1 km高度存在闭合的气旋性环流。③北京VDRAS资料分析表明低层强辐合与高层强辐散配置、中低层强的正风暴相对螺旋度为龙卷发生提供了有利的环境条件；垂直速度分布显示龙卷生成地存在强上升运动，其两侧均存在下沉运动；扰动温度的垂直分布表明4 km以下存在负中心，4 km以上存在正中心。     

三雷达、双雷达反演降雹超级单体风暴三维风场结构特征研究

为研究降雹超级单体风暴的三维结构特征,利用厦门、龙岩、梅州3部新一代天气雷达（CINRAD/SA）基数据,采用基于动态地球坐标系的双雷达和三雷达三维风场反演技术,分析了2016年4月8日傍晚福建省南部漳州地区出现的一次冰雹过程的回波强度、三维风场及相关物理量分布变化。主要结果为：（1）冰雹云初生、发展阶段,低层水平流场出现气旋性辐合,云体内部形成较强的上升运动。（2）冰雹云强盛阶段,回波顶高度达16 km,其中大于60 dBz的回波高度由5.3 km发展至9 km,最强回波达74.5 dBz,伴随出现最长达25 km的三体散射长钉回波和32.7 km的旁瓣回波。低层水平维持气旋性流场的同时,高层出现反气旋性流场。4-8 km高度内,大于20 m/s的强上升气流持续近37 min。最大垂直速度达51.06 m/s,出现在超级单体悬垂部（约7.5 km高度处）。（3）降雹时段,出现明显的下沉气流。降雹超级单体的三维流场结构表现为：风暴移向前沿低层气旋性气流进入风暴后逐渐倾斜上升,到达风暴顶形成反气旋性气流,并逐渐向下形成下沉气流。（4）系统减弱阶段,出现系统性下沉气流,强回波底及地。双雷达和三雷达能较好地反演降雹超级单体的三维风场精细结构,有助于加深对冰雹云结构的认识进而提高冰雹预报能力。     

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.     

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.     

IMPACT OF ATMOSPHERIC LOW-FREQUENCY OSCILLATION ON THE IMMIGRATION OF NILAPARVATA LUGENS(STL) IN HUNAN AND JIANGXI PROVINCES

Various features of the atmospheric environment affect the number of migratory insects, besides their initial population. However, little is known about the impact of atmospheric low-frequency oscillation(10 to 90 days) on insect migration. A case study was conducted to ascertain the influence of low-frequency atmospheric oscillation on the immigration of brown planthopper, Nilaparvata lugens(Stl), in Hunan and Jiangxi provinces. The results showed the following:(1) The number of immigrating N. lugens from April to June of 2007 through 2016 mainly exhibited a periodic oscillation of 10 to 20 days.(2) The 10-20 d low-frequency number of immigrating N. lugens was significantly correlated with a low-frequency wind field and a geopotential height field at 850 h Pa.(3) During the peak phase of immigration, southwest or south winds served as a driving force and carried N. lugens populations northward, and when in the back of the trough and the front of the ridge, the downward airflow created a favorable condition for N. lugens to land in the study area. In conclusion, the northward migration of N. lugens was influenced by a low-frequency atmospheric circulation based on the analysis of dynamics. This study was the first research connecting atmospheric low-frequency oscillation to insect migration.     

A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIO EVENTS

The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o.     

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.     

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