大气对外强迫低频遥响应的数值模拟 Ⅰ:对赤道东太平洋SSTA的响应   总被引：3，自引：0，他引：3  

肖子牛  李崇银 《大气科学》1992,(6)

本文通过在IAP-GCM上实现的数值模拟,研究了大气对赤道东太平洋地区暖SSTA的响应,着重讨论了大气遥响应的性质和演变过程. 数值模拟清楚地表明,大气对异常外源的响应主要是一种具有30—60天周期的低频遥响应.分析不同地区和不同季节这种强迫响应的30—60天低频振荡的结构及活动,可以清楚看到它与大气中实际存在着的30—60天振荡极为相似.因此也可以认为,大气对海温异常的强迫遥响应是激发产生全球大气30—60天振荡的重要机制.  相似文献   

中国南方夏季低频雨型特征及其年代际变化研究   总被引：1，自引：0，他引：1  

张玉洁  刘寿东  任宏利  李维京  陈丽娟  张培群  左金清 《气象学报》2014,72(6):1205-1217

为了揭示南方低频降水的季节内及年代际变化规律,利用1961—2011年夏季中国南方逐日降水资料和大气环流再分析资料,运用经验正交函数分解(EOF)与聚类分析相结合方法,将南方地区10 d以上的低频尺度降水划分为5个异常雨型.分析表明,各雨型具有较好的持续性,与同期的环流场有很好的对应关系,彼此间水汽异常输送特征有明显差别.通过对雨型的统计特征进行分析,指出不同于以往的季节平均雨型,低频雨型可在季节内交替出现,反映了大尺度异常降水的低频演变特征.进一步研究发现,近50年来各低频雨型的多项统计特征存在显著的年代际变化:20世纪80—90年代各多雨型均相继出现峰值,进入21世纪偏旱型的各项统计特征存在明显上升趋势,而大部分低频多雨型出现次数减少,这可能预示着中国南方地区正在进入一个季节内尺度降水减少的阶段.  相似文献   

淮河流域6—7月涝年降水的10~30d低频振荡特征   总被引：1，自引：1，他引：0  

韩世茹  王黎娟  于波  庞玥 《气象科学》2014,34(6):629-637

利用1981—2010年全国753站逐日降水资料,NCEP/NCAR逐日再分析资料和NOAA向外长波辐射资料,通过小波分析和Lanczos滤波的方法,得到淮河流域6—7月涝年降水的10~30 d低频振荡特征并进行了分析。结果表明:(1)淮河流域6—7月涝年降水具有明显的10~30 d周期变化。(2)位于高、低空的低频(10~30 d)反气旋和气旋分别影响南亚高压和西太平洋副热带高压的东西进退,从而影响淮河流域的低频降水强度。(3)在850 h Pa上,南海上空的低频反气旋(气旋)和日本海地区的低频气旋(反气旋)使得淮河流域有(无)冷暖气流交汇,并随着低频反气旋和气旋向东北方向移动,造成淮河地区低频降水发展为活跃(中断)期。(4)在低频降水过程中,低频OLR负(正)值区域发展加强对应淮河流域降水过程加强(减弱),当负(正)值区到达淮河流域时,淮河流域降水到达极端活跃(中断)期。随后低频OLR负(正)值区向东移动,淮河流域低频降水过程向过渡期转变。  相似文献   

南沙与暖池海域SST的长期振荡及其耦合过程   总被引：6，自引：2，他引：4  

谢强  鄢利农  侯一筠  胡基福 《海洋与湖沼》1999,30(1):88-96

利用多项式函数分析了南沙和暖池海温的长期变化,发现两海域的海面温度（ＳＳＴ）１９３４－１９８９年５６年来有明显地增温趋势,并且存在着ＳＳＴ变化的周期的突变现象,根据交叉谱分析特征,两海区ＳＳＴ之间存在不同频率的耦合振荡,可分为两种主要类型,周期约为１６．６年的同相低频耦合振荡和周期约为２年的反应相耦合振荡。  相似文献   

热带海洋SST与北半球大气环流的低频振荡特征   总被引：6，自引：2，他引：4  

李永平  端义宏  刘秦玉  秦曾灏 《海洋与湖沼》1999,30(1):97-103

采用复经验正交函数展开（ＣＥＯＦ）等方法研究了热带海洋海表温度异常（ＳＳＴＡ）和北半球５００ｈＰａ高度场异常（Ｈ５００）的甚低频（ＬＦ）和准两年（ＱＢ）两种低频振荡空间振幅和位相变化,发现ＳＳＴＡ变化信号在热带西太平洋最先出现,其后是热带中东太平洋,最后是热带中东太平洋,最后是热带印度洋和南海。副热带中西太平洋Ｈ５００滞后于中东太平洋ＳＳＴＡ １￣２月,Ｈ５００的ＬＦ分量从副热带中西太平洋经西北太  相似文献   

江苏省汛期强降水过程的延伸期预报试验   总被引：1，自引：1，他引：0  

蒋薇  孙国武  陈伯民  项瑛  陶玫 《气象科学》2012,32(S1):24-30

针对汛期延伸期降水预报问题,根据大气低频振荡特性,运用低频天气图预报方法,通过分析关键区低频天气系统(低频气旋和低频反气旋)的活动特征,建立低频系统与强降水过程间的对应关系,通过低频系统的活动特征来预报降水过程。在2011年7—9月江苏省延伸期强降水过程预报试验中,低频天气图预报方法的预报效果较好,且预报时效为10~30 d,可以在延伸期业务预报中加以应用。此外,还运用模式统计降尺度方法预报降水落区,为强降水过程的发生提供背景依据和参考信息,具有一定的实用意义。  相似文献   

Characteristics of Large Low-frequency Debris Flow Hazards and Mitigation Strategies     

WANGShige 《山地科学学报》2005,2(1):50-58

A low-frequency debris flow took place in the north coastal range of Venezuela on Dec. 16, 1999,and scientists all over the world paid attention to this catastrophe. Four characteristics of low-frequency debris hazard are discussed: long return period and extreme catastrophe, special rare triggering factors,difficulty in distinguishing and a series of small hazards subsequent to the catastrophe. Different measures, such as preventing, forecast - warning,engineering, can be used for mitigating and controlling the catastrophe. In engineering practice, it is a key that large silt-trap dams are used to control rare large debris flow. A kind of low dam with cheap cost can be used to replace high dam in developing countries. A planning for controlling debris flow hazard in Cerro Grande stream of Venezuela is presented at the end of this paper.  相似文献   

冬季北太平洋大气低频环流的年际和年代际变化特征及其与大气环流和海温异常的联系     

秦润天  朱益民  陈晓颖  谢倩  钱景 《气象科学》2018,38(3):293-301

利用1979—2015年ECMWF逐日再分析资料,通过EOF分解和回归分析研究了冬季北太平洋大气低频环流的年际和年代际变化特征及其与海表面温度异常(SSTA)和大气环流异常之间的联系。研究结果表明:冬季中纬度北太平洋地区850 h Pa低频尺度环流存在3个明显的变化模态:第一模态为海盆尺度的单极型异常气旋(反气旋)式环流,同期太平洋SSTA呈现El Ni1o(La Ni1a)以及PDO暖位相(冷位相)空间分布,阿留申低压强度增强(减弱),对流层中高层是正位相(负位相)的PNA型遥相关,北太平洋天气尺度风暴轴中东部南压(北抬);第二模态为在白令海峡和副热带地区呈气旋式与反气旋式环流南北向偶极型变化,同时中纬度北太平洋SSTA呈现NPGO(North Pacific Gyre Oscillation)正位相(负位相)的空间分布,黑潮区域SSTA偏暖(偏冷),北太平洋SSTA经向梯度加大(减小),对流层中高层为负位相(正位相)的WP型遥相关,北太平洋天气尺度风暴轴整体偏北(偏南),强度增强(减弱);第三模态为北太平洋中西部和北美西岸呈气旋式与反气旋式环流东西向偶极型异常,黑潮区域SSTA偏冷(偏暖)而北太平洋东部SSTA偏暖(偏冷),SSTA纬向梯度加大(减弱),同时赤道东太平洋出现类似La Ni1a(El Ni1o)的SSTA分布,北太平洋天气尺度风暴轴中东部明显减弱(加强)而西部略有加强(减弱)。  相似文献   

Laboratory study of wave and turbulence velocities in a broad-banded irregular wave surf zone     

Francis C. K. Ting   《Coastal Engineering》2001,43(3-4)

The characteristics of wave and turbulence velocities created by a broad-banded irregular wave train breaking on a 1:35 slope were studied in a laboratory wave flume. Water particle velocities were measured simultaneously with wave elevations at three cross-shore locations inside the surf zone. The measured data were separated into low-frequency and high-frequency time series using a Fourier filter. The measured velocities were further separated into organized wave-induced velocities and turbulent velocity fluctuations by ensemble averaging. The broad-banded irregular waves created a wide surf zone that was dominated by spilling type breakers. A wave-by-wave analysis was carried out to obtain the probability distributions of individual wave heights, wave periods, peak wave velocities, and wave-averaged turbulent kinetic energies and Reynolds stresses. The results showed that there was a consistent increase in the kurtosis of the vertical velocity distribution from the surface to the bottom. The abnormally large downward velocities were produced by plunging breakers that occurred from time to time. It was found that the mean of the highest one-third wave-averaged turbulent kinetic energy values in the irregular waves was about the same as the time-averaged turbulent kinetic energy in a regular wave with similar deep-water wave height to wavelength ratio. It was also found that the correlation coefficient of the Reynolds stress varied strongly with turbulence intensity. Good correlation between u′ and w′ was obtained when the turbulence intensity was high; the correlation coefficient was about 0.3–0.5. The Reynolds stress correlation coefficient decreased over a wave cycle, and with distance from the water surface. Under the irregular breaking waves, turbulent kinetic energy was transported downward and landward by turbulent velocity fluctuations and wave velocities, and upward and seaward by the undertow. The undertow in the irregular waves was similar in vertical structure but lower in magnitude than in regular waves, and the horizontal velocity profiles under the low-frequency waves were approximately uniform.  相似文献   

Observations of volcanic tremor during the January–February 2005 eruption of Mt. Veniaminof,Alaska     

Silvio De Angelis  Stephen R. McNutt 《Bulletin of Volcanology》2007,69(8):927-940

Mt. Veniaminof, Alaska Peninsula, is a stratovolcano with a summit ice-filled caldera containing a small intracaldera cone and active vent. From January 2 to February 21, 2005, Mt. Veniaminof erupted. The eruption was characterized by numerous small ash emissions (VEI 0 to 1) and accompanied by low-frequency earthquake activity and volcanic tremor. We have performed spectral analyses of the seismic signals in order to characterize them and to constrain their source. Continuous tremor has durations of minutes to hours with dominant energy in the band 0.5–4.0 Hz, and spectra characterized by narrow peaks either irregularly (non-harmonic tremor) or regularly spaced (harmonic tremor). The spectra of non-harmonic tremor resemble those of low-frequency events recorded simultaneously with surface ash explosions, suggesting that the source mechanisms might be similar or related. We propose that non-harmonic tremor at Mt. Veniaminof results from the coalescence of gas bubbles while low-frequency events are related to the disruption of large gas pockets within the conduit. Harmonic tremor, characterized by regular and quasi-sinusoidal waveforms, has duration of hours. Spectra containing up to five harmonics suggest the presence of a resonating source volume that vibrates in a longitudinal acoustic mode. An interesting feature of harmonic tremor is that frequency is observed to change over time; spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained. Factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and variations of the effective size of the resonator.  相似文献