华南近五百年气候变化特征

本文根据方志时期的历史记载及近代的气候资料,建立了华南近五百年(1470—1988)的冬温等级序列,订正增补了旱涝等级序列,根据上述气候序列研究华南的气候变化特征。结果表明,华南冷暖、旱涝有10—12、19—22、31—37、40—45、80、100及120—140年等主要周期;近五百年经历了4次冷暖期的交替;旱涝方面则有3次旱期、4次涝期。      

ASCAT反演风场与华南及南海站点观测对比分析

利用2014—2017年华南沿海及南海的浮标站、海岛站、石油平台站、沿海自动站等277个自动站风场数据,与ASCAT反演风场进行了对比分析。结果表明,当观测风速小于5 m/s(大于15 m/s)时,ASCAT反演风速的平均绝对误差在3 m/s左右(存在2级左右的高(低)估);当风速介于5～10 m/s时,平均绝对误差在2 m/s左右(多数ASCAT有1～2级的高估);介于10～15 m/s时,ASCAT反演结果相对最好,风速、风向准确率能够达到60%以上。ASCAT对风速的反演结果受陆地影响较大,与观测风速的相关系数从高到低可分为三类:(1)浮标、平台站;(2)西沙、南沙自动站;(3)广东沿海自动站及海岛站、海南海岛站。ASCAT反演风场在风向的应用较风速更优,其中,东北风样本数最多,其次分别为西南风、东南风和西北风。浮标站、平台站、西沙自动站的风向反演质量相对较好;所有测站风向偏差主要由5 m/s以下的弱风贡献。单站多年月平均风速变化显示,ASCAT反演风速相对测站主要为正偏差,且秋冬季比春夏季偏差更大,这可能与大气稳定度有关。     

THE CHARACTERISTICS OF TEMPORAL AND SPATIAL DISTRIBUTION OF TROPICAL CYCLONE FREQUENCIES OVER THE SOUTH CHINA SEA AND ITS AFFECTING OCEANIC FACTORS IN THE PAST 50 YEARS

The characteristics of temporal and spatial distribution of tropical cyclone frequencies over the South China Sea areas and its affecting factors in the past 50yrs are analyzed based on typhoon data that provided by CMA and Simple Ocean Data Assimilation (SODA). The results show that the tropical cyclone frequencies from June to October show concentrated geographic distribution, for they mainly distribute over the SCS area from 15 - 20 °N. The characteristics present significant interdecadal changes. The impact of oceanic factors on the tropical cyclone frequencies in the SCS area is mainly realized by La Ni(n)a and La Ni(n)a-like events before 1975 but mainly by El Ni(n)o and El Nifo-like events after 1975.     

SEASONAL VARIATIONS OF CONVECTIVE ACTIVITIES OVER THE SOUTH CHINA SEA AND ITS NEIGHBORHOOD AND THEIR COMPARATIVE ANALYSES IN THE STRONG AND WEAK CONVECTION YEARS

The seasonal variations of convective activities over the South China Sea(SCS)and itsneighborhood.as well as the similarities and differences of convection in the different key regionsduring the strong and weak convection years are analyzed by using the pentad data of TBB from1980 to 1993.The results show that in winter and summer the seasonal variations of the convectiveactivities are synchronous over the SCS and its neighborhood,the anomalous convection amplitudesare obviously different in different regions.The significant extents of convective activities havesomewhat seasonal differences in the strong and weak convection years.In the strong convectionyears,it is in winter,spring and autumn that the convection anomaly is more evident than that inthe normal years,however,after the summer monsoon onset the convection is sustained.stableand similar to that in the normal years.In the weak convection years.the convection weakensgreatly in each season.but the primary weakening occurs in spring.summer and autumn.Nomatter in the strong or the weak convection years.the convective activities are somewhat ofdifference in the Bay of Bengal.the Indochina Peninsula.the SCS and the Philippines.In addition.the convective activities are also different over the south and the north parts of the SCS.theconvection variation in the strong year is similar to that in the weak year over the north part of theSCS.but over the south part there are great differences.     

STUDY ON VARIATION CHARACTERISTICS OF SST OBSERVED IN THE PAST 40 YEARS IN THE COASTAL REGION OF SOUTH CHINA

To study the variation characteristics of SST in coastal south China, observed SST was analyzed for the past 44 years. The results show that the monthly and yearly averaged SST have rising trends, the yearly averaged SST's linearity rising rate is 0.12-0.19 ℃/decade in the years, the rising extents in winter are higher than those in summer. The variability in winter is larger than that in summer, with the largest in February and March. A majority of significant cold or warm events occurred in winter. A wavelet multiresolution method was used to analyze periodical characteristics of SST in coastal south China, all timescale decomposition series are very similar, and high-frequency decompositions within the year are dominant. Low-frequency decompositions show rising trends since the mid-1970.     

VARIABILITY IN THE WESTERN PACIFIC SUBTROPICAL HIGH AND ITS RELATIONSHIP WITH SEA TEMPERATURE VARIATION CONSIDERING THE BACKGROUND OF CLIMATE WARMING OVER THE PAST 60 YEARS

By adopting characteristic index data for the Western Pacific Subtropical High (WPSH) from the National Climate Center of China, U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, and the National Oceanic and Atmospheric Administration (NOAA) sea surface temperature (SST) data, we studied the WPSH variability considering the background of climate warming by using a Gaussian filter, moving averages, correlation analysis, and synthetic analysis. Our results show that with climate warming over the past 60 years, significant changes in the WPSH include its enlarged area, strengthened intensity, westward extended ridge point and southward expanded southern boundary, as well as enhanced interannual fluctuations in all these indices. The western ridge point of the WPSH consistently varies with temperature changes in the Northern Hemisphere, but the location of the ridgeline varies independently. The intensity and area of the WPSH were both significantly increased in the late 1980s. Specifically, the western ridge point started to significantly extend westward in the early 1990s, and the associated interannual variability had a significant increase in the late 1990s; in addition, the ridgeline was swaying along the north-south-north direction, and the corresponding variability was also greatly enhanced in the late 1990s. With climate warming, the SST increase becomes more weakly correlated with the WPSH intensity enhancement but more strongly correlated with the westward extension of the ridge point in the equatorial central and eastern Pacific Ocean in winter, corresponding to an expanding WPSH in space. In the northern Pacific in winter, the SST decrease has a weaker correlation with the southerly location of the ridgeline but also a stronger correlation with the westward extension of the ridge point. In the tropical western Pacific in winter, the correlations of the SST decrease with the WPSH intensity enhancement, and the westward extension of the ridge point is strengthened. These observations can be explained by strengthened Hadley circulations, the dominant effects of the southward shift, and additional effects of the weakened ascending branch of the Walker circulation during warm climatological periods, which consequently lead to strengthened intensities, increased areas, and southward expansions of the WPSH in summer.     

华南近海近40年的实测SST变化特征

使用实测月平均海表温度（SST）资料序列研究华南近海区域的变化特征,得出：华南近海的月和年平均SST皆以上升趋势为主,年平均SST最近44年的线性增长率为0.12～0.19℃/10年,冬半年的上升幅度普遍高于夏半年。其变率冬半年远大于夏半年,最大为2、3月份,显著的冷暖事件也多发生于冬半年;冬半年东部变率较小,而夏半年则以东部较大。运用小波多分辨分析方法进行周期特征分析,华南近海各站SST的各尺度的分量序列十分相近,其中低频分量显示华南近海SST始于1970年代中期的上升趋势延续至今,其变化以年内变化为主。华南近海SSTA与Ni？o4指数同期相关很好,与Ni？o3,4区超前4个月时相关最显著。Ni？o各海区SSTA与华南近海SSTA的小波多分辨分析所得平滑成分、2.3～4.6年成分间的相关最为显著,其他年以上尺度的相关也高于SSTA序列间的相关,可见华南近海SST年际以上时间尺度的变化与ENSO变化有密切关系。     

西南季风爆发前后南海SST变化特征及影响因子分析

利用1982～2001年NCEP/NCAR再分析的周平均SST场、逐日表面热通量场及近地层10米高度风场资料,分析了南海地区季风爆发前后几周南海多年平均SST随时间的变化和空间分布特征及其影响因子.结果表明,南海季风爆发前,SST急剧升高,季风爆发后,SST的变化呈现比较明显的空间差异,南海北部SST继续上升,而南部SST持续下降.南海季风爆发前,海面净得热,这是季风爆发前南海SST上升的主要原因.季风爆发后几周,海面净得热减少,此时的海表净热通量收支与SST无显著相关.而季风爆发期和爆发后几周,南海SST变化的不均匀性与西南气流具有很好的相关性,南海的降温区呈东北-西南走向,与低层西南气流的方向一致.因而,在季风爆发后的一段时间内,近地层风场导致的海洋表面及内部动力过程是影响南海SST变化的另一重要因子.     

近70年不同路径的南海热带气旋的统计特征

为进一步认识南海热带气旋(SCSTC)的基本特征规律,利用中国气象局上海台风研究所(CMA-ATI)整编的“热带气旋最佳路径数据集”等资料,对1949—2019年不同移动路径的SCSTC的频数、源地、强度变化等特征进行统计分析。(1) 近70年的SCSTC的频数呈现递减的趋势,其中东北走向的SCSTC频数相对较少,其峰值集中在5月、6月,西/西北走向的SCSTC频数相对较多,约占总数的76%,其峰值集中在8月、9月,且西/西北走向的SCSTC频数变化趋势与西太平洋副热带高压(“副高”)脊线位置的移动趋势相匹配,即当副高脊线逐渐向北(南)移动时,SCSTC频数随月份逐渐增多(减少)。(2) 东北走向的SCSTC平均强度比西/西北走向的SCSTC强,生命史也更长,并且在5种SCSTC强度等级中,东北走向的台风和强台风的强度二次加强的现象相比西/西北走向的更显著。(3) 两种路径走向的SCSTC的源地位置随着季节的变化都有一个先北抬后南撤的过程,与副高脊线的移动规律一致,东北走向SCSTC源地位置整体比西/西北走向的SCSTC更偏北2~3个纬距。      

1986年东海与南海的海-气界面热量交换

采用实测资料计算1986年7—12月东海和南海观测海域海-气界面热量交换。结果表明：7—9月上旬,大气向观测海域输送热量是主要现象,因为这时的气温比水温高,潜热通量与感热通量出现反相变化,天气晴好,海洋大量吸热;9月中旬—12月,观测海域向大气输送热量是主要现象,东海表现得比南海更为明显,主要贡献来自潜热通量和感热通量。受冷空气影响时,感热通量重要;在热带辐合带和热带气旋系统内海-气界面热量交换强烈,大气对海洋的响应为主。