南海和南亚大气季节内振荡月异常对夏季风活动及中国东部夏季降水的影响

利用ECMWF逐日再分析资料(1961—2000年),中国气象局国家气候中心提供的1961—2000年中国160个站降水资料,探讨了夏季逐月南海和南亚ISO的强弱对南海和南亚夏季风及中国东部降水的影响。研究表明,夏季各月南海和南亚ISO异常对夏季风活动及中国东部降水的影响存在显著的差异,有分月进行讨论的必要。夏季各个月南海大气ISO的异常对南海和南亚夏季风活动的影响在6、7月有些相似,都表现为ISO强(弱)与南海地区和南亚地区气旋性(反气旋性)环流相对应,而8月截然相反,ISO强(弱)与仍南海地区气旋性(反气旋性)环流对应,而南亚地区表现为反气旋性(气旋性)环流。南亚大气ISO异常对夏季风活动的影响与南海地区有较大差异,6月和8月南亚大气ISO强(弱)与南亚地区气旋性(反气旋性)环流对应,而7月ISO的强(弱)对应于南亚地区反气旋性(气旋性)环流。6月南亚大气ISO强(弱)对应于南海地区气旋性(反气旋性)环流,而7、8月无论是南亚大气ISO强年还是弱年,南海地区都表现为反气旋性异常环流。从降水来看,夏季6、7月南海大气ISO偏强(弱)年,长江以南大部分为正(负)距平而江淮流域降水基本上为负(正)距平。而8月南海大气ISO强弱年,长江以南与江淮流域这种反相的降水特征并不明显。7月南亚大气ISO强(弱)年,长江以南降水大部分为负(正)距平而江淮流域为正(负)距平,而6月和8月南亚大气ISO的强弱对中国东部降水的影响并不如7月表现明显。     

IMPACTS OF MONTHLY ANOMALIES OF INTRASEASONAL OSCILLATION OVER SOUTH CHINA SEA AND SOUTH ASIA ON THE ACTIVITY OF SUMMER MONSOON AND RAINFALL IN EASTERN CHINA

The impact of strong (weak) intraseasonal oscillation (ISO) over South China Sea (SCS) and South Asia (SA) in summer on the SCS and SA summer monsoon and the summer rainfall in Eastern China are studied by using the NCEP-NCAR analysis data and the rainfall data of 160 stations in China from 1961 to 2010. It is found that the impacts are significantly different in different months of summer. The study shows that in June and July cyclonic (anticyclonic) atmospheric circulation over SCS and SA corresponds to strong (weak) ISO over SCS. In August, however, strong (weak) ISO over SCS still corresponds to cyclonic (anticyclonic) atmospheric circulation over SA. In June and August cyclonic (anticyclonic) atmospheric circulation over South Asia corresponds to strong (weak) ISO over SA while a strong (weak) ISO corresponds to anticyclonic (cyclonic) atmospheric circulation over SA in July. Besides, in June the strong (weak) ISO over SA corresponds to cyclonic (anticyclonic) atmospheric circulation over SCS, while in July and August the atmospheric circulation is in the same phase regardless of whether the ISO over SA is strong or weak. The impacts of the strong（weak）ISO over SCS on the rainfall of eastern China are similar in June and July, which favors less (more) rainfall in Yangtze-Huaihe Rivers basin but sufficient (deficient) rainfall in the south of Yangtze River. However, the impacts are not so apparent in August. In South Asia, the strong (weak) ISO in July results in less (more) rainfall in the south of Yangtze River but sufficient (deficient) rainfall in Yangtze-Huaihe Rivers basin. The influence on the rainfall in eastern China in June and August is not as significant as in July.     

SURFACE OBSERVATIONS IN THE TROPICAL CYCLONE ENVIRONMENT OVER THE SOUTH CHINA SEA

In this paper,the observational data from Marine and Meteorological Observation Platform(MMOP)at Bohe,Maoming and buoys located in Shanwei and Maoming are used to study the characteristics of air-sea temperature and specific humidity difference and the relationship between wind and wave with the tropical cyclones over the South China Sea(SCS).The heat and momentum fluxes from eddy covariance measurement(EC)are compared with these fluxes calculated by the COARE 3.0 algorithm for Typhoon Koppu.The results show that at the developing and weakening stages of Koppu,both these differences between the sea surface and the near-surface atmosphere from the MMOP are negative,and data from the buoys also indicate that the differences are negative between the sea surface and near-surface atmosphere on the right rear portion of tropical cyclones(TCs)Molave and Chanthu.However,the differences are positive on the left front portion of Molave and Chanthu.These positive differences suggest that the heat flux is transferred from the ocean to the atmosphere,thus intensifying and maintaining the two TCs.The negative differences indicate that the ocean removes heat fluxes from the atmosphere,thus weakening the TCs.The wind-wave curves of TCs Molave and Chanthu show that significant wave height increases linearly with 2-min wind speed at 10-m height when the wind speed is less than 25 m/s,but when the wind speed is greater than 25 m/s,the significant wave height increases slightly with the wind speed.By comparing the observed sensible heat,latent heat,and friction velocity from EC with these variables from COARE 3.0 algorithm,a great bias between the observed and calculated sensible heat and latent heat fluxes is revealed,and the observed friction velocity is found to be almost the same as the calculated friction velocity.     

IMPACT OF CONVECTION OVER THE SOUTH CHINA SEA ON TROPICAL CYCLONE MOTION OVER THE WESTERN NORTH PACIFIC DURING SUMMER MONSOON

The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows.(1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active(inactive), the SCS-WNP monsoon trough stretches eastward(retreats westward) due to the activity(inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward(stretches westward), which enhances(suppresses) the monsoon circulation.(2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases.(3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase.(4) Simulation results show that the steering flow associated with the active(inactive)phases is in favor of straight-moving(recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.     

近50年南海热带气旋时空分布特征及其海洋影响因子

用中国气象局组织整编的《台风年鉴》资料和全球近表层简易海洋数据同化(SODA)资料,研究了近50年南海海域生成和经过的热带气旋位置点频数的时空分布特征及其海洋影响因子。结果表明,6～10月的热带气旋位置点频数表现出明显的地理分布集聚性特征,主要分布在南海15～22°N海域,并有明显的年代际变化特征。在1975年以前,海洋因子对南海海域生成和经过的热带气旋位置点频数的影响主要以La Nia和类La Nia事件为主,1975年之后以El Nio和类El Nio事件为主。     

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.     

南海热带气旋路径集合预报试验

利用3种不同模式的初始资料,通过它们生成得到16个不同的初始场,分别对2004年南海及其周边地区9个热带气旋个例进行集合预报试验,最后筛选得到了7个南海热带气旋初值集合成员,由此初步探讨了南海热带气旋初值集合成员的生成方法。结果表明,采用不同模式的初始资料生成得到初值集合成员的方法用于集合预报,对南海热带气旋路径预报有一些明显的改进。     

PRELIMINARY STUDY OF RELATIONSHIP BETWEEN INTERANNUAL VARIATIONS OF SST IN SOUTH CHINA SEA AND TROPICAL INDIAN OCEAN AND SOUTH CHINA SEA MONSOON OUTBREAK

Conclusions are divided regarding the role of the variations of thermodynamics in the monsoon activity for the South China Sea region. In this study, primary eigenvectors are studied for the SSTA from East Asia to the tropical eastern Indian Ocean in May. The results show that temperature anomalies that center on Sumatra are closely related with the outbreak of the South China Sea monsoon. When the SST is warmer (cooler) than average year, it is likely that the monsoon set in late (early). It may be caused by the changes in meridional difference in thermodynamics between the Indochina Peninsula and its southern tropical oceans. Studying the temporal and spatial evolution of primary eigenvector distribution of the SSTA in the South China Sea-tropical eastern Indian Ocean from winter to summer, we find that the temperature anomalies that center around Sumatra in late spring and early summer can be traced back to the variations of the SST fields in the South China Sea in the preceding winter. Being well associated with the outbreak of the South China Sea monsoon, the latter is a signifi-cant index for it. The work helps understanding the atmospheric and oceanic background against which the South China Sea monsoon breaks out and behaves.     

夏季西北太平洋热带气旋生成频次与热带海温关系的年代际变化

探讨了夏季(6—8月)西北太平洋(Western North Pacific,WNP)热带气旋生成频次(Tropical Cyclone Genesis Frequency,TCGF)与热带海温关系的年代际变化,发现影响WNP TCGF的热带海温型在1991/1992年发生了年代际变化。在1990年代初之前,TCGF正异常对应的热带海温异常(Sea Surface Temperature Anomaly,SSTA)呈现东部型La Ni?a衰减位相,前冬至春季WNP局地暖SSTA在其西北侧激发气旋异常,夏季时由热带印度洋冷SSTA继续维持。在1990年代初之后,TCGF正异常对应的热带SSTA呈现东部型La Ni?a向中部型El Ni?o快速转换的位相,夏季中太平洋暖SSTA在其西北侧激发气旋异常,同时热带东印度洋至海洋性大陆以及热带大西洋的冷SSTA通过垂直环流圈加强中太平洋的辐合上升运动,进一步维持其西北侧气旋异常。由于激发气旋异常的暖SSTA在第二个年代相较第一个年代明显偏南偏东,气旋异常和TCGF正异常在第二个年代也整体偏南且向东扩展至更远的区域。WNP TCGF与热带海温关系的年代际变化与1990年代初之后厄尔尼诺-南方涛动演变速率加快有关。      

THE CHARACTERISTICS OF LOW-FREQUENCY OSCILLATIONS OVER THE SOUTH CHINA SEA

Using 1975-1993 (with 1978 missing) data of the outgoing longwave radiation (OLR), characteristics of seasonal variation of low-frequency oscillations in the South China Sea and its relation to the establishment and activity of the summer monsoon there are studied. As is shown in the result, the low-frequency oscillation in the South China Sea is much stronger in the period of summer monsoon than in that of winter monsoon and the summer monsoon there usually begins to set up in a negative phase of the first significant low-frequency oscillation for the early summer. The study also reveals that the circulation for the low-frequency oscillation during the summer monsoon in the Sea is embodied as north-south fluctuations of the ITCZ and east-west shifts of western ridge point of the West Pacific subtropical high, suggesting close correlation between the low-frequency oscillation and the active and break (decay) of the South China Sea monsoon. In the meantime. the work illustrates how the low-frequency oscillation in the South China Sea are superimposed with the seasonal variation of the general circulation. so that the summer inonsoon covers the establishment of the I^st, intensification of the 2^nd and 3^rd the low-frequency oscillations and decay of the 4^th oscillation.     

南海地区OLR变化与华南汛期降水的联系

用奇异值分解的方法逐月分析了华南汛期（4-9月）降水与南海地区OLR变化的关系，并用合成分析的方法对OLR异常年份的降水进行对比分析，结果表明两者确实有一定的相关关系，后汛期（特别是7、8月）两者的相关程度比前汛期大，但每个月的情况各有不同。     

STUDY ON THE AIR-SEA INTERACTION ON THE INTERANNUAL TIME SCALE IN THE SOUTH CHINA SEA

In this paper we document the correlationship between sea surface temperature (SST) and lowlevel-winds such as sea level wind and 850 hPa wind in the South China Sea (SCS) based onCOADS (1958—1987) and ECMWF objective analysis data (1973—1986).Further statisticalanalyses tell us that there is a fixed SCS basin mode for variations both of SST and low-level windsin the region on the interannual time scale due to air-sea interactions.A simplified,coupled model that is designed following the McCreary and Anderson's (1985)model and includes the feedback between the upper ocean and the circulation of East Asianmonsoon demonstrates an interannual oscillation in the coupled air-sea system,which is similar tothe observations in the SCS.     

用卡尔曼滤波预报南海热带气旋路径的试验

利用卡尔曼滤波方法预报南海热带气旋路径，发现采用卡尔曼滤波可以大大地降低预报误差，提高预测模型的预报能力。     

影响华东地区热带气旋年频数与热带对流场的关系

利用由美国NOAA系列卫星观测的OLR资料研究了影响华东地区热带气旋年频数（记为ATC）与热带对流场的关系，结果表明两者存在密切的联系：（1）当华东地区热带气旋年频数ATC为异常偏多（少）时，ITCZ位置累积距平为正（负）值，即ITCZ位置异常偏北（南）；（2）利用OLR设计了Walker综合指数WI，该指数的强弱可以反映ATC的异常情况，即当ATC为异常偏多（少）时，walker环流圈异常强（弱）；（3）OLR距平累积量场能较好的表征ATC异常年份所对应的低纬度及中高纬地区大气环流的配置，其可以作为预测影响华东地区热带气旋年频数的强信号。     

南海-西北太平洋季风槽强度的变化特征及其与热带气旋活动的关系

利用1979—2005年NCEP/DOE AMIP-Ⅱ再分析逐日平均资料,根据西北太平洋季风槽的特点,研制了能较好表征季风槽活动的强度指数和位置指数,并分三段描述不同区域季风槽的活动特征及其对生成于南海-西北太平洋季风槽的热带气旋（MTTC）活动的影响,结果表明：（1） 季风槽强度指数和位置指数呈正相关关系,季风槽强度越强,其位置越偏北。（2） 季风槽强度存在明显的年际变化,1994年前以4～5年的变化周期较为显著,1994年后2～3年的周期较明显。（3） 不同区域季风槽强度的影响因子不同。前期海温场的异常将导致大气环流异常,致使不同区域的季风槽强度异常。（4） 季风槽强度与MTTC频数异常密切相关,3个不同区域的季风槽以南海季风槽强度与MTTC频数异常的关系最为密切。MTTC异常偏少年大多出现在季风槽总体偏弱,各区域季风槽也偏弱的年份;MTTC异常偏多年可能出现在季风槽偏强的年份,也可能出现在季风槽总体偏弱但南海季风槽偏强的年份,且后者出现的概率更大一些。（5） 季风槽强度的季节内变化能为TC的生成和发展提供有利条件,季风槽同时处于30～60天振荡和准双周10～20天振荡的活跃期时,有利于MTTC的生成。     

8014号热带气旋发生发展过程的能量学诊断研究

利用动能和总位能收支方程，对８０１４号强热带风暴过程进行了能量学诊断研究。结果表明，地转作用是该热带气旋中辐散风动能向旋转风动能转换的主要物理机制；非绝热加热是热带气旋发展的主要能源，其对总位能的制造大部分用于次网格耗散和侧边界输出，只有一小部分被转化为辐散风动能；两个转换函数Ｃ（Ｐ，Ｋｘ）和Ｃ（Ｋｘ，Ｋφ）在时空分布上具有很好的一致性；该热带气旋与周围环境场有明显的能量交换，在高层有总位能和旋转风动能输出，在低层有辐散风动能输入；在总动能收支中，辐散风作功是主要的功能产生项，旋转风作功主要是消耗动能。     

THE RELATIONSHIP BETWEEN TROPICAL PACIFIC SEA SURFACE TEMPERATURE AND SUMMER RAINFALL OVER NORTHWEST CHINA

In this paper,the data of summer precipitation in Northwest China were expanded by means of EOF.According tomajor eigenvectors in expansion the area of Northwest China was divided into four natural rainfall regions.Amongthem the region of greatest precipitation variability is found over the East Qinghai-North Shaanxi region,includingEast Qinghai,Central and East Gansu,Ningxia and North Shaanxi.There is apparent teleconnection between the firstand second time-dependent coefficients in EOF expansion and the tropical Pacific SST in the corresponding period andearlier months.The variation of the east tropical Pacific SST in winter and spring is able to predict precipitation trend ofNorthwest China next summer.Moreover,in the El Nino years precipitation trend is opposite to the following year,andthe region from East Qinghai to North Shaanxi is most sensitive.     

THE RELATIONSHIP BETWEEN GLOBAL WARMING AND THE VARIATION IN TROPICAL CYCLONE FREQUENCY OVER THE WESTERN NORTH PACIFIC

The relationship between global warming and the variation in tropical cyclone (TC) genesisfrequency is analyzed using the data of the Tropical Cyclone Year Book by the China MeteorologicalAdministration and the National Centers for Environmental Prediction (NCEP) reanalysis data from 1949to 2007. The observational results indicate that the average sea surface temperature (SST) in theIntertropical Convergence Zone (ITCZ) region (10°N – 20°N, 100°E – 140°E) increases by 0.6°C againstthe background of global warming, while the frequency of tropical cyclone geneses in this region decreasessignificantly. Generally, the rise of SSTs is favorable for the genesis of tropical cyclones, but it is nowshown to be contrary to the normal effect. Most of the tropical cyclones in the western North Pacific (WNP)are generated in the ITCZ. This is quite different from the case in the Atlantic basin in which the tropicalcyclones are mostly generated from the easterly wave. Our research results demonstrate that the ITCZ has aweakening trend in strength, and it has moved much more equatorward in the past 40 years; both aredisadvantageous to the formation of tropical cyclones. Furthermore, our study also found that the ridge ofthe subtropical high tends to shift slightly equatorward, which is another adverse mechanism for theformation of tropical cyclones.     

云凝结核浓度对不同强度南海热带气旋强度影响的个例模拟研究

利用云分辨天气研究和预报模式(CR-WRF)模拟在清洁大气和污染大气下,气溶胶的云凝结核作用对不同强度南海热带气旋(TC)的强度变化影响,对比分析了动力结构和微物理结构的变化。(1)在污染大气环境中,更多气溶胶能进入到弱TC内部云带区,并充当凝结核作用,TC内部各相态水凝物含量都有明显增多,释放潜热有利于TC内部的对流发展,弱TC中心海平面气压下降,强度加强。(2)在污染大气环境中,气溶胶主要影响强TC的外部螺旋云带区;外部云带区各相态水凝物增多,释放潜热有利于该处对流的发展;外部云带区对流与云墙区内对流形成竞争,导致入流减弱,云墙区内上升运动减弱,强TC中心海平面气压上升,强度减弱。     

QBO 与南海夏季风爆发的关系

利用1979—2001 年ECMWF 再分析资料和NOAA 海温资料,通过相关分析和合成分析等统计方法,分析了平流层准两年周期振荡(QBO)与南海夏季风建立时间的关系。结果表明,QBO 位相与南海夏季风爆发时间有显著的相关关系:超前南海夏季风爆发约18 个月的QBO 西(东)风位相对应着季风爆发时间偏早(晚)。QBO 与南海夏季风爆发的联系要比ENSO 与南海夏季风爆发的联系更密切。