华西秋雨的气候特征及成因分析   总被引：41，自引：4，他引：37  

白虎志  董文杰 《高原气象》2004,23(6):884-889

在分析华西秋雨气候特征的基础上,设计了综合考虑秋季降水量和降水日数的秋雨指数,并进行了EOF和REOF分解以及秋雨主要影响因素分析。结果表明：第一模态反映了长江中上游以北地区与以南地区降水相反的形势,第二模态反映了华西降水的一致性;REOF将华西秋雨可分为6个气候区。华西秋雨的变化趋势表明,1960年代到1970年代初期、1980年代初期为相对多秋雨期,1970年代中后期、1980年代中后期到20世纪末华西秋雨相对较少。21世纪开始又出现了较明显的华西秋雨现象。西太平洋副热带高压、印缅槽、贝加尔湖低槽是华西秋雨的主要影响系统,当贝加尔湖、印缅槽深且副热带高压强时,有利于华西多秋雨;反之,则秋雨不明显。  相似文献   

Depression and elevation internal solitary waves in a two-layer fluid and their forces on cylindrical piles   总被引：1，自引：0，他引：1  

徐振华  尹宝树  杨红卫  齐继峰 《中国海洋湖沼学报》2012,30(4):703-712

Both large amplitude depression and elevation internal solitary waves (ISWs) were observed on the continental shelf of the northwest South China Sea (SCS) during the Wenchang Internal Wave Experiment. In this study, we investigate the characteristics of depression and elevation ISWs based on comparisons between observational results and internal wave theories. It is suggested that the large amplitude depression wave is better represented by the extended Korteweg-de Vries (EKdV) theory than by the KdV model, whereas the large amplitude elevation wave is in better agreement with the KdV equation than with the EKdV theory. Wave-induced forces on a supposed small-diameter cylindrical pile by depression and elevation waves are also estimated using the internal wave theory and Morison formula. The wave-induced force by elevation ISWs is rarely reported in the literature. It is found that the force induced by the elevation wave differs significantly from that by the depression wave, and the elevation wave generally produces greater force on the pile in the lower water column than the depression wave. These results show that ISWs in the study area can present a serious threat to ocean engineering structures, and should not be ignored in the design of oil platforms and ocean operations.  相似文献   

Comparison of remote sensing data with in-situ wind observation during the development of the South China Sea monsoon     

李健  王东晓  陈举  杨磊 《中国海洋湖沼学报》2012,30(6):933-943

Wind measurements derived from QuikSCAT data were compared with those measured by anemometer on Yongxing Island in the South China Sea (SCS) for the period from April 2008 to November 2009. The comparison confirms that QuikSCAT estimates of wind speed and direction are generally accurate, except for the extremes of high wind speeds (>13.8m/s) and very low wind speeds (<1.5m/s) where direction is poorly predicted. In-situ observations show that the summer monsoon in the northern SCS starts between May 6 and June 1. From March 13, 2010 to August 31, 2010, comparisons of sea surface temperature (SST) and rainfall from AMSR-E with data from a buoy located at Xisha Islands, as well as wind measurements derived from ASCAT and observations from an automatic weather station show that QuikSCAT, ASCAT and AMSR-E data are good enough for research. It is feasible to optimize the usage of remote-sensing data if validated with in-situ measurements. Remarkable changes were observed in wind, barometric pressure, humidity, outgoing longwave radiation (OLR), air temperature, rainfall and SST during the monsoon onset. The eastward shift of western Pacific subtropical high and the southward movement of continental cold front preceded the monsoon onset in SCS. The starting dates of SCS summer monsoon indicated that the southwest monsoon starts in the Indochinese Peninsula and forms an eastward zonal belt, and then the belt bifurcates in the SCS, with one part moving northeastward into the tropical western North Pacific, and another southward into western Kalimantan. This largely determined the pattern of the SCS summer monsoon. Wavelet analysis of zonal wind and OLR at Xisha showed that intra-seasonal variability played an important role in the summer. This work improves the accuracy of the amplitude of intra-seasonal and synoptic variation obtained from remote-sensed data.  相似文献   

直接同化卫星辐射数据的黄海海雾数值试验研究     

李冉  高山红  王永明 《中国海洋大学学报(自然科学版)》2012,42(3):10-20

基于中尺度大气模式WRF及其3DVAR.模块,采用循环3DVAR数据同化方案,针对6次明显的黄海海雾过程,实施了一系列直接同化ATOVS卫星辐射数据数值试验.在试验中设计了不同化任何观测数据、仅同化GTS常规数据、仅直接同化辐射数据,同时同化二者,以及同化不同疏密程度辐射数据的对比研究方案.利用地面水平能见度与卫星云图对模拟的海雾雾区进行了评估,并比较了各种同化方案所形成初始场的差异.对试验结果的统计分析表明:同化试验较好地再现了影响海雾的天气系统,模拟雾区与实际观测较为吻合,并且初始温度场和湿度场对比不同化任何观测数据的试验有明显的改善;仅同化辐射数据的结果略优于仅同化常规数据的结果,疏化或者只同化海上辐射数据几乎不影响模拟的雾区,但却可以大幅节约计算资源;同时同化常规数据与辐射数据的结果为单独同化它们所得结果的综合体现,总体效果最好.  相似文献   

跨海高程传递三角高程数据处理及质量分析     

方明  武威 《海洋测绘》2012,32(5):53-55

对跨河水准测量和跨海高程传递三角高程测量的观测方法和数据处理进行了比较.简单介绍了4处跨海高程传递测区的概况,并提出一种针对“光段差互差”的评估方法.对4处跨海点三角高程实测数据进行质量分析和平差计算,结果表明:除实验区外,跨海三角高程测量的偶然中误差可以达到二等水准测量的精度;数据质量分析结果表明,满足二等水准限差的外业观测数据的有效率为50％左右;满足三等水准限差的数据有效率为90％左右.  相似文献   

Freshening of the intermediate water of the South China Sea between the 1960s and the 1980s     

刘长建  王东晓  陈举  杜岩  谢强 《中国海洋湖沼学报》2012,30(6):1010-1015

Variation in intermediate water salinity in the South China Sea (SCS) between the 1960s and 1980s was studied using historical hydrographic data. The results demonstrate that the water was significantly fresher in the 1980s than in the 1960s, indicating that vertical mixing at intermediate water depth was reduced in the 1980s. This was partially because of the change of the SCS meridional overturning circulation (MOC) connecting local intermediate water with deep water. Data assimilation showed a 0.5Sv (1 Sv=10 6m 3/s) reduction in the strength of the MOC, which is about one third of the mean SCS MOC. Because the SCS MOC is linked to the Pacific Ocean, such an interdecadal variation in the intermediate water SCS may reflect anthropogenic climate change in the world ocean.  相似文献   

不同水化状态下的压实膨胀土应力-应变-强度特征     

周葆春  孔令伟  郭爱国 《岩土力学》2012,33(3):641-651

为探讨水化状态对饱和压实膨胀土应力-应变-强度特征的影响,以压实度为95%的荆门弱膨胀土为研究对象,开展了2种典型水化状态下的固结与三轴试验,其中第1种水化状态采用常规饱和方法,第2种水化状态为试样自由膨胀至稳定状态。结果表明：（1）受变形约束条件与渗径的影响,不同水化状态下体膨胀率有较大差别;（2）第2种水化状态下的饱和压实膨胀土具有更大的硬化指数λ与膨胀指数κ、较小的弹性剪切模量,其有效内摩擦角为第1种水化状态下的77.2%,体现出膨胀土饱和强度的变动性;（3）2种水化状态下的固结曲线均呈现出明显的屈服现象,其屈服应力分别为123.2 kPa与94.5 kPa;（4）第1种水化状态下,低围压下试样应变软化与剪胀,高围压下应变强化与剪缩;第2种水化状态下试验围压范围内均发生剪缩和轻微的应变软化;（5）2种水化状态下试样在固结与剪切过程中均表现出超固结性,这种超固结性并非完全由先期固结压力所致,而是试样受荷过程中膨胀受到约束造成的;（6）不同水化饱和状态下初始孔隙比不同,膨胀势也不同,膨胀势与外部约束条件、排水条件、应力状态相互作用,造成其应力-应变-强度特征的差异性。  相似文献   

ENSO 与中国东部夏季降水的关联   总被引：8，自引：1，他引：7  

张礼平  张乐飞  曾凡平 《热带气象学报》2012,(2):177-186

计算1 月减6 月El Niño 3.4 指数与6—8 月平均200、850 hPa 风场的相关矢量,分析中等或强ElNiño/La Niña 事件后的夏季(6—8 月)中国东部降水异常分布、西太平洋副热带高压异常特征。结果表明,对ENSO 的响应,无论高、底层大气环流还是西太平洋副热带高压,1970 年代中期气候突变后变为更敏感。主要表现在:对衰减的El Niño 的响应,夏季南亚高压偏东,西太平洋副热带高压偏强、偏西、偏南,印度季风、南海季风减弱,黄河下游以南副热带季风增强。黄河中下游及以南形成异常环流辐合带,由El Niño 导致的降水正异常最有可能出现在这一西南-东北的带状区域。对衰减的La Niña 响应大致相反。   相似文献   

国产遥感传感器大气层外波段平均太阳光谱辐照度计算     

张璐  施润和  徐永明  李龙  高炜 《地球信息科学学报》2014,16(4):621-627

目前,我国大部分遥感传感器的大气层外波段平均太阳光谱辐照度(Mean solar exoatmospheric irradiances over band b,简称ESUN_b)尚未公布,这给遥感图像表观反射率的计算带来了不便,在一定程度上影响了数据资料的应用和推广。本文基于已有官方ESUN_b值的EO1/ALI、Terra/ASTER、QuickBird等多种中、高空间分辨率传感器,对9条常见的太阳光谱曲线进行比较分析。结果表明,WRC太阳光谱曲线最合适计算中分辨率传感器的ESUN_b,而Wehrli太阳光谱曲线最合适计算高分辨率传感器的ESUN_b。基于WRC太阳光谱曲线和Wehrli太阳光谱曲线计算,得到了ZY-1 02C/PMS相机、ZY-3/TLC相机和MUX相机,以及GF-1/WFV相机和PMS相机各波段ESUN_b值,并对ESUN_b值的不确定性进行了分析。结果显示,太阳光谱选取的不同,对ESUN_b的取值会产生-1.94%至1.48%的偏差。本文使用多种卫星传感器交叉比较的方式确定了最佳的太阳光谱,给出了ZY-1 02C、ZY-3和GF-1等卫星搭载的遥感传感器各波段的ESUN_b值,为这些国产卫星遥感数据的广泛应用提供便利。此外,本文所用方法简便易行,在其他新的遥感传感器上具有推广应用价值。  相似文献   

南海土台风和非局地台风的对比研究     

程撼  梁楚进  董昌明  刘正礼 《海洋学研究》2014,32(1):19-30

利用1951—2012年日本气象厅(JMA)热带气旋(TC)最佳路径资料,分析了影响南海的土台风和非局地台风62 a间的时空分布特征,比较了二者在时空分布上的差异性,得到以下主要结果:土台风源地位置与热带季风性气候有关,夏季风时主要在15°N以北,冬季风时向15°N以南移动;土台风与非局地台风相比,活动范围更广,但强度比后者弱;土台风在南海的强度发展过程呈对称曲线形式,非局地台风则是一条递减曲线;土台风和非局地台风的登陆位置都具有季风期规律,夏季风时登陆的TC比冬季风时登陆的多得多,同纬度的非局地台风比土台风移动速度大。  相似文献