Mooring observations of internal solitary waves in the deep basin west of Luzon Strait

A total of 137 internal solitary waves （ISWs） are captured during a field experiment conducted in the deep basin west of the Luzon Strait （LS） from March to August, 2010. Mooring observations reveal that a fully developed ISW owns a maximum westward velocity of more than 1.8 m/s and an amplitude of about 200 m. The ISWs in the South China Sea （SCS） are most active in July, which may be due to the strong stratification in summer. Most of the ISW episodes are detected around and after the 1st or 15th lunar day, indicating that the ISW in the SCS is triggered by astronomic tides. Half part of the observed ISWs were detected around 19：00 local time, which can be explained by the fact that type-a ISWs emerged in the evening at roughly the same time each day. The propagation direction of the ISWs and the astronomic tides in the LS show that the area south of the Batan Island is probably the main source region of the type-a ISWs, while the area south of Itbayat Island and south of the Batan Island is likely the main source region of the type-b ISWs observed at the mooring. Moreover, for the resonance of semidiurnal internal tides emitting from the double ridges in the LS, the underwater ridge south of the Itbayat Island and south of the Batan Island is believed to favor the generation of the energetic ISWs.     

THE NORTH-SOUTH ANTI-PHASE DISTRIBUTION OF RAINFALL IN MEIYU PERIODS AND ITS RELATIONSHIP WITH QUASI-BIWEEKLY OSCILLATION IN THE ATMOSPHERE

Based on the daily rainfall datasets from 740 stations in China from 1954 to 2005 and the NCEP/NCAR reanalysis data, the relationship between the north-south anti-phase distribution(APD) of rainfall during Meiyu periods and the Quasi-Biweekly Oscillation(QBWO) in the atmosphere was analyzed. Diagnostic results are as follows:(1) there was significant north-south oscillation of Meiyu rainfall during the 16 years from 1954 to 2005. Since the 1990 s, the APD enhanced significantly and showed 2- and 4-6-year period. In the region with more rainfall, the QBWO was always more active.(2) The APD of Meiyu and north-south movements of precipitation in eastern China belong to the same phase.(3) The 10-25 day filtered water vapor flux could spread to the area north of 30°N in 1991. The divergence of the water vapor flux which propagated from middle- and higher- latitudes to the of Yangtze-Huaihe River Basins(YHRB) was significant in 1991, but the latitudes that the water vapor flux could reach were further southward and there was no southward propagation of divergence in 1993.(4) The locations of Western Pacific Subtropical High(WPSH) and 10-25 day anti-cyclone, which modulated WPSH's advancement in and out of the South China Sea, were relatively northward in 1991. Furthermore, the vertical circulation showed north-south deviation between 1991 and 1993, just as other elements of the circulation did.     

中国东南部与川渝陕甘地区夏季降水 30～60天CISO的反相现象

利用1979～2010年NCEP/NCAR逐日再分析资料和我国753站逐日降水资料,研究了中国东南部和川渝陕甘地区夏季降水30～60天气候季节内振荡（Climatological IntraSeasonal Oscillation,CISO）的反相现象。结果显示两个区域夏季降水CISO在7月中旬之前存在显著的反相关系,且在传播特征上有明显差异。川渝陕甘地区降水局地低频振荡显著,中国东南部降水CISO北传特征清晰。低频环流分析表明,对流层低层低频槽、脊的更替形成了川渝陕甘地区降水CISO的“驻相”振荡,低频气旋式、反气旋式环流位置的移动则产生了中国东南部降水CISO的北传。CISO垂直环流显示上升支与下沉支正好处于川渝陕甘地区与中国东南部,较好地反映了低频降水在两区域的相反变化。中国东南部、长江中下游与川渝陕甘地区三者之间存在动力学上的关联,这可部分地解释川渝陕甘地区和中国东南部之间降水CISO的反相关系。这种反相关系的形成还与气候态下的西太平洋副热带高压和贝加尔湖附近大陆高压脊的季节内变化有关。揭示中国东南部与川渝陕甘地区之间降水CISO的反相现象对于丰富人们对我国夏季风区低频振荡局地特征的认识和理解降水季节内振荡产生机制有重要意义。     

首都机场浓雾中的能见度突发性振荡及其演变规律

利用2000—2011年北京首都机场每分钟的自动观测资料,对影响首都机场的52次浓雾过程进行分析,发现浓雾的形成、发展和消散过程中能见度演变具有突发性和振荡性的特征。浓雾中的能见度振荡可分为前导振荡、中间振荡和后位振荡,三者所占比例分别为86.5%、62.5%和79.2%。冷季浓雾比暖季浓雾具有更明显的温度振荡,在影响首都机场的34次冷季浓雾中,有61.8%的个例具有温度的振荡。辐射雾中温度振荡超前于能见度振荡,而平流雾来临前有温度振荡,雾发生时温度振荡不明显。根据统计结果本文定义了浓雾振荡指数DFOI,并发现DFOI为±0.2可以作为首都机场浓雾临近预报的阈值,使用该阈值可以将首都机场2000—2011年的浓雾预警平均提前1~2 h。根据2012年1月的实际预警测试,发现单独使用该指数无法区分浓雾、降雪和霾过程,今后在雾的预警过程中还需要引入其他指数。     

基于模糊干扰观测器的抗饱和自适应反步控制

针对一类输入受限的非匹配不确定非线性系统,提出了一种抗饱和自适应反步控制方法.利用模糊干扰观测器在线逼近系统的未知非匹配不确定及干扰,采用反步控制方法设计自适应控制器.控制系统设计中引入限幅滤波器,有效降低了控制输入饱和对系统稳定性的影响,并且控制器设计无需对虚拟控制律进行重复求导.利用李亚普诺夫稳定性定理,证明了闭环系统渐近稳定.仿真结果表明了该方法的有效性.     

星敏感器/GNSS定姿系统的联合非线性预测滤波算法

提出一种联合式非线性预测滤波算法,解决该系统在姿态动力学模型误差非高斯分布条件下的多敏感器信息融合问题。从算法结构和估计准则两个方面证明非线性预测滤波(NPF)与Kalman滤波的等效性,分析联合式NPF的算法流程,讨论模型误差方差矩阵的计算方法,给出加权系数矩阵的设计准则;介绍星敏感器和全球卫星导航系统(GNSS)的定姿原理,推导星敏感器/GNSS组合姿态确定系统的联合式NPF滤波模型,分析系统的算法实现流程;进行数值仿真试验,结果表明联合式NPF算法融合NPF与联邦滤波的优良品质,可有效解决姿态动力学模型误差非高斯分布条件下无陀螺姿态确定系统的多敏感器信息融合问题。     

一种利用扩展磁偏角数据自动计算磁偏角的方法

提出一种基于扫描磁偏角地磁图自动计算磁偏角的方法,把一维磁偏角数据扩展到二维数据,将有关图像校正的方法用在磁偏角的求取上,即在扫描磁偏角地磁图中以图上的地理坐标、扩展磁偏角等值线坐标以及扩展磁偏角等变线坐标所对应的像素坐标为媒介,通过非线性变换,最终建立起地理坐标、磁偏角等值线以及磁偏角等变线之间的相互对应关系,以解决...     

2006年夏季川渝地区伏旱与低频大气热源的关系

利用NCEP/NCAR再分析资料和中国地面观测站的逐日降水资料,研究了2006年夏季中国川渝地区的伏旱与亚洲地区大气低频振荡的联系.结果表明,2006年夏季中国川渝地区降水低频振荡的主要周期约为60 d;在川渝严重干旱期的7月下旬至8月上旬,经向上由于川渝地区上空低频热汇、广西和海南及其以西地区上空低频热源的影响,在1...     

平稳随机激励下随机结构非线性动力响应分析

为了在结构强震灾变过程模拟中正确反映结构参数的随机性并准确界定结构失效模式,提出一种平稳随机激励下随机结构非线性动力响应分析的简化方法.首先运用点估计法将复合非线性随机系统转化为一系列平稳随机激励下的确定性非线性结构,然后再应用成熟的等效线性化方法计算出平稳随机激励下非线性结构动力响应的各阶矩.文末进行了算例分析与验证...     

利用体应变观测智利8.8级大地震激发的地球球型自由振荡

用河北省体应变的数字化观测资料,利用功率谱密度估计方法,在没有对资料进行处理的情况下,准确获得了2010年2月27日智利8.8级大地震激发的0S5-0S35摹频球型自由振荡,并与地球初步参考模型(PREM)的理论自由振荡频率进行对比,发现实测振荡频率与PREM预测的振荡频率基本符合.河北省体应变的数字化观测资料的确可以...