ANALYSIS ON THE SOURCE AND SINK OF KINETIC ENERGY OF ATMOSPHERIC 30-60 DAY PERIOD OSCILLATION AND THE PROBABLE CAUSES*

Based on ECMWF daily grid point data in summer(May-August),1981,the distribution features of the source and sink of kinetic energy of atmosphere 30-60 day oscillation,including its horizontal distribution characteristics and its vertical structure characteristics,are investigated systematically with diagnostic analysis methods over a latitude belt between 80°N and 60°S.Also,the probable reasons for the existence of the source and sink of low frequency kinetic energy(LFKE) are discussed preliminarily.Results show that the horizontal distribution of the sources and sinks of kinetic energy of atmospheric 30-60 day oscillation is extremely different.The significant sources and sinks of LFKE mainly exist in the oceans and the coastal regions of continents or islands in the mid-high latitudes.It is also found that,in the vertical direction,the sources and sinks of kinetic energy of 30-60 day oscillation display barotropic structure in the mid-high latitudes of both hemispheres,but dispaly baroclinic structure in the equtorial region,and in the horizontal direction,the sources and sinks mainly display zonal wave-like distribution.The source and sink of LFKE are determinded by ageostrophic wind effect,frictional effect,interaction between sub-grid-scale systems,nonlinear interaction,and the flux-divergence of LFKE transported by transient wind.There are some regional reasons for the generation of sources and sinks which are not completely identical in different areas.     

Interactions between the 30－60 Day Oscillation，the Walker Circulation and the Convective Activities in the Tropical Western Pacific and Their Relations to the Interannual Oscillation

Ｉｎｔｅｒａｃｔｉｏｎｓｂｅｔｗｅｅｎｔｈｅ３０－６０ＤａｙＯｓｃｉｌｌａｔｉｏｎ，ｔｈｅＷａｌｋｅｒＣｉｒｃｕｌａｔｉｏｎａｎｄｔｈｅＣｏｎｖｅｃｔｉｖｅＡｃｔｉｖｉｔｉｅｓｉｎｔｈｅＴｒｏｐｉｃａｌＷｅｓｔｅｒｎＰａｃｉｆｉｃａｎｄＴｈｅｉｒＲｅ...     

Relationships between the North Pacific Oscillation and the typhoon/hurricane frequencies

Relationships between the North Pacific Oscillation (NPO) and the typhoon as well as hurricane fre-quencies are documented. The correlation between NPO index in June-July-August-September and the annual typhoon number in the western North Pacific is 0.37 for the period of 1949―1998. The NPO is correlated with the annual hurricane number in the tropical Atlantic at -0.28 for the same period. The variability of NPO is found to be concurrent with the changes of the magnitude of vertical zonal wind shear, sea-level pressure patterns, as well as the sea surface temperature, which are physically asso- ciated with the typhoons and hurricanes genesis. The NPO associated atmospheric circulation vari- ability is analyzed to explain how NPO is linked with variability of the tropical atmospheric circulation in the western Pacific and the tropical Atlantic, via the atmospheric teleconnection.     

1950～2010年PDO 对北太平洋地区海平面变化影响的量化与评估

本文研究和估计了1950～2010年不同太平洋年代际涛动(Pacific decadal oscillation, PDO)事件对北太平洋地区的海平面上升趋势所造成的影响。研究使用了SODA(Simple Ocean Data Assimilation)的海表面高度(sea surface height, SSH)数据资料, 通过多元线性回归方法, 分离了由PDO事件所引起的海表面高度变化(PDO-SSH), 以此分析PDO事件对海平面变化所造成的影响。结果表明, PDO-SSH所引起的海表面变化趋势的空间分布, 及其对区域海平面变化的遮掩效果, 和对应时期内PDO信号的振幅和周期有着紧密的关系。进一步的分析表明, PDO事件对北太平洋地区SSH变化所造成的影响是不均匀的, 在东西太平洋有着相反的变化趋势。1960～1989年, 具有较长数据时间长度的PDO信号对海平面变化的影响, 要强于高度计投入使用后的时期的表现, 而受其影响最重的海域出现在赤道西太平洋海域、阿留申群岛及北美沿岸地区, PDO-SSH在上述地区SSH的占比甚至高达60%。     

上海梅汛期候降水异常的低频信号及延伸期预报

提高汛期降水过程的延伸期预报能力是目前天气预报和气候预测发展的重要方向。本文以上海梅汛期降水为例,利用非传统滤波方法提取多变量季节内分量,分析了梅汛期季节内候降水异常及其相联系的延伸期关键低频信号,进一步综合多变量低频信号建立了梅汛期候降水异常延伸期预报方法,并开展了多年的回报和试报检验。结果表明:①梅汛期候降水异常季节内分量具有显著的40～60d低频振荡周期,与降水异常实况具有显著的正相关和较高的符号一致率;②梅汛期季节内候降水异常与超前10～35d的热带及中高纬低频信号有关,主要包括:热带MJO(Madden Julian Oscillation)自阿拉伯海的向东传播、西太平洋副热带高压季节内活动的西北向传播、PNA(Pacific-North American)遥相关型的季节内位相转换以及东北亚冷空气的持续性异常影响;③综合上述多变量低频信号建立了延伸期候降水异常预报模型,对提前10～35d的延伸期候降水异常的季节内分量具有预报技巧,也能较好地预报实际的候降水异常趋势。     

兰州气温变化长期倾向和振荡的检测及预报试验

用奇异谱分析检测兰州最近６４年气温的长期倾向和周斯振荡得到其总倾向是增暖的,年代际振荡振幅较大,１９４６－１９６７年降温约１℃,１９６８年至９０年代前期升温约１．３℃。年际和月际振荡主要有７．５年、３．３年、７．６９月和３．３８月。１９７６年起季节循环有明显变化,冬季变暖夏季变凉,月平均气温的年较差比前４３年减小１．７℃。用ＳＳＡ－ＭＥＭ可以做４个月的月平均气温距平预报。     

Computation of Long-Term Statistical Properties of Wave Agitation in Harbors

In this paper,the long-term statistical properties of wave height in an idealized square harborwith a partial opening are studied.The incident waves are propagated into the harbor numerically by the fi-nite/infinite element method using three different wave models:(1)monochromatic wave train,(2)long-crested random wave train,and(3)short-crested random wave train.This study shows that for a giv-en incident wave,the wave height in the harbor is affected by the wave model used.For long-term estima-tion of wave height exceedance probability,it is recommended that the waves be propagated into the har-bor using the random wave model,and that wave heights be computed by use of the Rayleigh probabilitydistribution.     

福建前汛期持续性强降水的大气低频特征分析

本文采用福建1979—2010年66个气象站逐日降水资料和NCEP再分析资料和OLR资料,揭示了福建前汛期降水的低频特征,分析了福建前汛期持续性强降水同期的大气低频特征以及前期低频信号的演变特征,结果表明:(1)福建前汛期降水存在显著的低频周期,出现频率较高的前三个低频周期分别为:10~20、30~60和20~30 d;约63%的年份出现两种以上显著的低频周期;10~90 d低频变化占前汛期降水总方差的20%~30%;(2)前汛期总雨量与降水低频信号的强度呈显著正相关关系,持续性强降水的强度和持续时间与降水的低频特征关系密切,以BWO(ISO)为主的年份,持续性强降水的持续时间较短(长)。(3)福建前汛期持续性强降水期间日本以东、索马里以东和南海三个关键区皆为低频反气旋,日本至渤海湾南下的冷空气与索马里越赤道气流、南海南部越赤道气流在福建上空持续相遇形成低频气旋,导致福建上空低层低频辐合、高层低频辐散,对流活跃。(4)福建前汛期持续性强降水与热带及副热带大气低频变化密切相关,热带MJO的东传以及东亚西北太平洋地区低频信号的北传对福建持续性强降水过程的延伸期预报具有一定的指示意义。     

2008年广东强龙舟水与准10天振荡

采用小波分析、相关分析、Lanczos时间滤波器等方法分析了2008年广东强龙舟水与大气低频振荡的关系.结果表明,强龙舟水期间广东逐日降水存在显著的准7～12天周期振荡即准10天振荡,广东上空的逐日500 hPa高度场存在显著的8～13天周期振荡、南海北部平均的逐日850 hPa纬向风场存在显著的准12天周期振荡.广东...     

贺兰山过去196年降水的树轮宽度重建及降水变率

贺兰山属于中国北方的半干旱地区,位于东亚夏季风的西北缘。应用贺兰山南段、中段和北段的3组树轮宽度差值年表合成贺兰山树轮宽度年表,应用邻近采样点的贺兰山东坡、山顶和西坡的气象站资料合成贺兰山气象数据。通过贺兰山树轮宽度年表和贺兰山气象数据的线性回归分析,重建了1802—1997年2—7月降水标准化序列,重建方程的方差解释量是46%。计算重建序列的11年滑动平均标准差后,发现存在着3次标准差的突然变化:1908年标准差由前年的0.38增加到当年的0.56,1942年标准差由两年前的0.57增加到当年的0.70,1956年标准差由前年的0.74降低到当年的0.63。小波分析表明,1908年到1949年之间存在显著的11年准周期,1942年出现2年准周期,该2年准周期到1959年彻底消失。1965—1997年,存在由8年向3年过渡的准周期。11年周期对应着太阳活动周期,2年周期对应“准两年脉动”,8年到3年周期与ENSO周期比较一致。故此认为,当太阳活动、“准两年脉动”或ENSO活动增强时,贺兰山地区降水变率一般比较大,年际间降水变得不稳定。