Using typhoon data from the Shanghai Typhoon Institute of the China Meteorological Administration, the Japan Meteorological Agency’s annual Pacific decadal oscillation (PDO) index, and NCEP/NCAR reanalysis data from 1951 to 2021, correlation and composite analyses were carried out to study the relationship between the variability among tropical cyclones of different magnitudes affecting South China and the PDO. The results show that there is an obvious out-of-phase relationship between the proportion of tropical cyclones reaching a typhoon-level intensity or above in South China and the PDO index. When the PDO is in a cold (warm) phase, the sea surface temperature in the eastern and central equatorial Pacific is cold (warm), similar to the eastern Pacific La Niña (El Niño) phenomenon, and the SST in the eastern and western tropical Pacific Ocean shows a negative (positive) gradient; the subtropical high in the western Pacific Ocean is weaker (stronger) than normal, with the western ridge point to the east (west), and the 500 hPa geopotential height in the South China Sea and the area east of the Philippines is weaker (stronger), which is conducive to (unfavorable to) the formation of a monsoon trough; and the westerly (easterly) winds at high altitudes and the southwesterly (northeasterly) winds at low altitudes from the South China Sea to the Philippines are abnormally strong, and a positive (negative) vorticity at low altitudes, a low (high) sea level pressure, and strong (weak) convection are shown. These conditions are favorable (unfavorable) for the intensification of typhoons affecting South China, and as a result, the number of tropical cyclones reaching the level of typhoons or above account for a greater (smaller) proportion of those affecting South China.

基于广西91个国家地面气象观测站降水数据和ERA5逐日再分析资料,分析2022年5月21日至6月21日广西"龙舟水"过程的天气气候成因.结果表明:(1)"龙舟水"期间冷空气南下活跃,西太平洋副热带高压位置偏西,南支槽伸至孟加拉湾,水汽条件充沛,冷暖空气交汇导致锋面降水频繁.(2)南海夏季风提前爆发,前期偏强后期减弱,利于雨带滞留广西.(3)200hPa西风急流偏强位置偏南,利于上升运动的维持和加强.(4)基于结构化自组织神经网络聚类的延伸期降水过程预测模型,较好预测出"龙舟水"期间暴雨过程的空间类型和出现时段.

Prolonged low temperature significantly threatens transportation and planting in populous areas and is closely linked to slowly varying forcing such as sea surface temperature (SST). In this study, we reveal the impact of the north–south dipole pattern in extra-tropical North Atlantic SST (DNA) anomaly on surface air temperature (SAT) over southern China in February. The positive phase of the DNA is favorable for a positive North Atlantic Oscillation-like pattern at the troposphere via synoptic eddy vorticity forcing and triggers a southeastward-propagating Rossby wave train associated with the deepened East Asian trough and the strengthened Siberian high, which are conducive to enhancement of the East Asian winter monsoon. A stronger monsoon leads to lower-than-normal SAT over southern China by intensifying southward cold air outbreaks. Considerably, the extremely low temperature over southern China in February 2022 is explainable by this physical mechanism. Furthermore, experiments with a linear baroclinic model verify that the proposed downstream propagating Rossby wave train is mainly associated with the midlatitude North Atlantic SST anomaly. These results emphasize that the extra-tropical North Atlantic SST anomaly should be focused when interpreting and predicting the late winter SAT over southern China.

主要综述和回顾近30a来国内外关于华南"龙舟水"暴雨的天气气候研究进展,包括高空槽、切变线、低涡、急流、副热带高压等天气系统的影响,低频振荡、季风等大尺度环流背景,及其对高原积雪、海温等外强迫信号的响应.总结了"龙舟水"暴雨精细化预报中主要存在的问题,对提高"龙舟水"暴雨预报预测能力提出了展望.

Tropical cyclones entering coastal areas adversely affect southern China. However, changes in the frequency of tropical cyclones affecting the west of southern China remain unclear. Our study reveals the possible impact of the thermal forcing anomaly over the southeast Tibetan Plateau (TP) on the frequency of tropical cyclones affecting Guangxi formed within the west of 120° E during boreal summer. Further analysis indicates that the cooling over the southeast TP is accompanied by local descending motions over southeastern TP and compensating ascending motions over eastern Indochina Peninsula and results in a reduced 850–200 hPa vertical wind shear over the north of 15° N in South China Sea (SCS), which is conducive to the westward development of tropical cyclones and favorable conditions for the formation of TCs affecting Guangxi over the SCS. Finally, the results from a linear baroclinic model experiment also verify that the changes in the 850–200 hPa vertical wind shear over southern SCS and compensating vertical motions over eastern Indochina Peninsula are associated with the thermal forcing anomaly over the southeast TP. Our results imply that in summer the thermal forcing anomaly over TP should be emphasized when interpreting and predicting the frequency of tropical cyclones affecting local areas in southern China.

以2020年广西91个国家地面气象观测站2m气温资料作为基准,对中国第一代陆面再分析资料CMA-RA/Land及目前广泛使用的ERA5/Land、CFSR等3套再分析气温资料在广西的适用性进行初步对比评估.结果表明,3套资料均能重现气温时空分布特征,但存在不同程度的冷偏差,CMA-RA/Land与观测值最接近,ERA5/Land在桂北冷偏差较明显,CFSR整体冷偏差较大.CMA-RA/Land在站点上的各项评估指标均表现良好,相关系数高,均方根误差、绝对误差、相对误差均较小.总体来看,CMA-RA/Land在广西适用性最好.

利用FNL 1° ×1°再分析资料、FY-2F卫星TBB资料及常规气象观测资料,对2020年9月14日发生在贵州安顺的1次罕见秋季暴雨天气过程进行分析.结果表明:副热带高压东退,引导短波槽东移和低涡切变线南压,为暴雨的发生提供了有利的天气尺度背景条件;强水汽辐合中心稳定维持在安顺,暴雨中心与水汽辐合中心相对应;暴雨区上空低层暖平流和中层冷平流的叠加,利于上升运动的发展,为能量和潜热的释放提供有利条件;中尺度对流云团在生成阶段发展迅速,成熟以后减弱缓慢,并在安顺上空稳定少动,是导致全市范围出现暴雨到特大暴雨的主要原因,且暴雨区与TBB≤55℃的区域对应较好;在对流云团生成的区域,其水汽、能量和抬升条件均较好,在对流云团东移影响的区域,大气层结不稳定,湿层深厚,但能量条件较差,导致此次暴雨过程的对流性不是很强,在降水最强时段,小时雨强大多在20～40 mm·h-1之间.

利用1961-2021年广西东兴国家地面气象观测站逐日降水量资料,采用气候趋势分析、小波分析等数理统计方法,对东兴近61a不同等级的暴雨日数气候特征进行了研究分析.结果表明,东兴暴雨总日数及不同等级暴雨日数具有明显的年际和年代际变化特征,近61a东兴暴雨总日数存在2～4a、6～9a的准周期振荡.暴雨总日数在20世纪90年代为最多,20世纪60年代为最少;全年各个季节和月份均有暴雨发生,主要发生在5-9月,暴雨总日数年内呈单峰型分布,峰值出现在7月,后汛期暴雨明显多于前汛期.持续性暴雨过程主要出现在夏季,最长过程持续时间为8d.

使用1991-2021年7-9月广西90个地面气象观测站降水量、NCEP/NCAR月再分析资料和国家气候中心BCC_CSM1.1气候模式回报资料,研究建立基于粒子群-神经网络、随机森林算法的广西后汛期降水气候预测模型,并对2016年—2021年预测进行应用试验.结果表明,基于粒子群-神经网络、随机森林算法的后汛期降水预测Ps得分比逐步回归方法分别提高了 2.78分、2.5分,比气候模式分别提高了 29.22分、28.94分,预测能力有明显的提升.

利用FNL 1° ×1°再分析资料、FY-2F卫星TBB资料及常规气象观测资料,对2019年5月24—26日发生在贵州的1次连续性暴雨天气过程进行分析.结果表明:此次连续性暴雨过程地面维持热低压影响,无冷空气影响,是典型的暖区暴雨;高空槽和中低层切变线为暴雨的产生提供了天气尺度背景,地面辐合线是触发对流的重要因子;暴雨发生前大气呈现动力和热力不稳定的结构特征;24日夜间地面辐合线在贵州中部地区稳定维持,触发中β尺度对流单体生成,并发展形成中α尺度系统,对流发展旺盛,伸展高度较高,影响范围广.25日夜间辐合线移动较快,触发的中β尺度对流单体组织性较弱,没有形成中α尺度系统,造成的暴雨局地性强;暴雨与水汽通量散度梯度的大值区、TBB≤-52℃的冷云区和TBB梯度大值区对应较好,TBB≤-65℃的区域有利于大暴雨产生.

基于2002-2013年广西南宁、桂林、北海3市二氧化硫(SO2)、二氧化氮(N02)和可吸入颗粒物(PM10)等3种大气污染物的逐日监测值,计算3种大气污染物的空气污染指数,研究3个城市空气质量、首要污染物及其月际变化特征及其与气象要素的相关关系,并利用百分位法确定2、3级空气质量过程的阈值,分析南宁市6次长时间污染过程的大气环流特征.结果表明,3个城市中南宁市空气质量相对最差;3市首要污染物均以PM10为主,占66.37％-100％,污染主要发生在秋冬春季;影响各市空气质量的主要气象要素及其2、3级对应的气象要素阈值呈现差异性;南宁市出现污染天气的主要大气环流特征是850hPa广西受东北气流影响,水汽输送条件差,无降雨产生.

使用广西90个地面气象观测站逐日降水资料、NCEP/NCAR再分析资料等,研究了广西持续性暴雨气候特征及其对热带季节内振荡(Madden-Julian Oscillation,MJO)的响应特征.结果 表明,沿海地区暴雨过程持续天数历史最长、持续性暴雨过程次数最多;前汛期持续性区域暴雨发生前期MJO多处于上游地区,随时间变化向东逐渐增多,暴雨发生时MJO处于印度洋中东部次数最多,此时副热带高压西伸到南海区域,广西处于副热带高压边沿,索马里越赤道气流夹带着水汽穿过印度洋,源源不断给广西送来丰富的水汽;后汛期持续性区域暴雨发生前期MJO位于海洋性大陆次数随时间临近增多,暴雨发生时MJO位于海洋性大陆西部次数偏多,此时副热带高压偏弱,广西上空为气旋性环流,越赤道水汽输送带明显比前汛期第3位相时宽大、偏强,在西南风引导下向广西移动,利于持续性区域暴雨维持.

全球气候变化背景下,广西强降水事件趋于频繁,加上社会经济的高速发展和人类活动影响范围不断扩大,使得水土流失防御工作面临着严峻考验.本文在分析广西水土流失成因、特征和危害的基础上,从水土流失监测预测、气象预警和保障服务、应急管理等方面提出减缓水土流失对策和建议.

利用常规气象观测资料、多普勒雷达资料和FNL再分析资料等,对2020年4月17日发生在贵州省安顺市的一次局地性冰雹天气过程进行分析.结果表明:高原短波槽、中低层切变线、低空急流和地面辐合线是导致此次局地性强冰雹天气的主要影响系统,冰雹出现在850 hPa湿舌的顶端和地面高温中心附近;C波段雷达的反射率因子图上TBSS和前侧入流缺口共同出现,表征了大冰雹的产生,风暴单体具有明显的强回波悬垂和低层弱回波区,且大于50 dBz的强回波伸展高度明显超过-20℃层高度,表明了风暴在垂直方向强烈发展;VIL值在降雹前后有明显的变化,降雹前1～2个体扫VIL有跃增现象,降雹期间VIL≥30 kg·m-2,且在出现大冰雹时VIL≥50 kg·m-2,而在降雹结束后,VIL值迅速减小.