Relationship between North Pacific SST anomalies and the atmospheric circulation anomalies in January 2008     

Jianbo Wang  Lei Fan  Qinyu Liu 《中国海洋大学学报(英文版)》2010,9(1):11-15

Based on the NCEP (National Centers for Environmental Prediction) data, the relationship between the Sea Surface Temperature Anomalies (SSTAs) in the North Pacific and the atmospheric circulation anomalies in January 2008 is analyzed in this study. The SSTA mode most correlated with the Geopotential Height anomalies (GHAs) in January 2008 in the North Pacific exhibited a basin-wide horseshoe pattern with a warm center in November 2007. This persistent SSTA pattern would induce positive GHAs in the Aleutian Low area and East Asia and the northward extension of the West Pacific Subtropical High in January 2008 by maximum diabatic heating in the atmosphere over the Kuroshio Oyashio Extension (KOE) area, leading to the occurence of the circumpolar trough-ridge wave train anomaly in January 2008.  相似文献   

中国北方春季沙尘暴频数与北半球500hPa高度场的SVD分析   总被引：10，自引：7，他引：3  

唐红玉  翟盘茂  常有奎 《中国沙漠》2005,25(4):570-576

选取1957-2000年中国北方地区春季沙尘暴发生次数资料和北半球500hPa秋、冬、春季的平均高度场资料,对沙尘暴和高度场作SVD分析。结果表明,我国北方春季沙尘暴次数各地具有比较一致的变化趋势,表明可能与大尺度气候背景的变化有联系。变化的最敏感区域为内蒙古中西部地区、新疆西部、青海西部和东北地区。我国北方春季沙尘暴发生次数与同期及前期500hPa高度场有较好的相关关系,前期环流形势对春季沙尘暴频数有一定的指示和预测意义,冬季环流场尤其具有预报指示意义,因为前一年冬季北大西洋涛动对我国春季北方沙尘暴发生次数有影响。  相似文献   

黄土高原春季降水对青藏高原感热异常的响应   总被引：1，自引：0，他引：1  

叶燕华  李栋梁  陈晓光 《中国沙漠》2007,27(2):315-319

利用1961—2000年黄土高原56站的春季降水和NCEP/NCAR再分析资料,采用SVD方法分析了黄土高原春季降水与青藏高原地面感热的关系。结果表明,黄土高原春季降水量与青藏高原地面感热的前两个模态代表了两场间的主要耦合特征,具有高度的时空相关。青藏高原感热对黄土高原降水影响最显著的区域在西部和南部、北部。前期高原感热场的第一、二模态对黄土高原春季干旱的预测具有指示意义。  相似文献   

顾及基准站坐标动态特性与稳定性的区域框架构建     

蒋光伟  王斌  王延伟  李康  孙洋洋 《地球物理学进展》2020,(1):8-15

基准站受构造运动与非线性因素的影响,如何构建高精度、现势性强的精细区域框架是位置服务与形变分析的的关键.笔者提出顾及基准站坐标动态特性与稳定性的区域框架构建方法.以我国西部与东部某城市的多年连续运行基准站数据为例进行试算比对,试验结果表明:该方法是可行的,较好地顾及了基准站的坐标特性与非线性影响,考虑了基准站的垂直运动规律,可构建高精度的区域基准,可发现区域基准的微动态变化.  相似文献   

Crop characterization using an improved scattering power decomposition technique for compact polarimetric SAR data     

《International Journal of Applied Earth Observation and Geoinformation》2020

Crop characterization using Compact-Pol Synthetic Aperture Radar (CP-SAR) data is of prime interest with the rapid advancements of SAR systems towards operational applications. It is noteworthy that as a good compromise between the dual and quad-polarized SAR systems, the CP-SAR offer advantages in terms of the larger swath and lower data rate. The m − χ CP decomposition considers two out of the three Stokes child parameters: degree of polarization (m), ellipticity (χ), and orientation angle (ψ) to describe the polarized part of the quasi-monochromatic partially polarized wave. An improvement in the scattering powers was proposed in the S − Ω decomposition, which takes into accounts both the transmitted and received wave ellipticities (χ_t, χ_r) and the orientation angles (ψ_t, ψ_r). In this decomposition, S denotes the Stokes vector and Ω is the polarized power fraction. However, it may be noted that the S − Ω decomposition intrinsically ignores dominance in the target scattering mechanism while calculating the powers. In this work, improvement is proposed for the S − Ω decomposition by utilizing the degree of dominance in the scattering mechanism. The improved S − Ω (named as iS − Ω) decomposition powers are first compared with the existing m − χ and S − Ω powers for elementary (viz., trihedral and dihedral corner reflectors) and distributed targets using simulated CP-SAR data from quad-pol RADARSAT-2 data. An increase of ∼2% for odd and even-bounce powers obtained from the iS − Ω decomposition is observed for the trihedral and dihedral corner reflectors respectively. The analysis of the scattering powers for distributed targets shows that an increase of 15% and 12% in the even and odd-bounce powers is observed from iS − Ω for urban and bare soil areas respectively as compared to the m − χ and S − Ω decompositions. Besides, temporal variations in the scattering powers obtained from the iS − Ω decomposition are also analyzed for rice, cotton, and sugarcane crops at different growth stages.  相似文献   

The Role of Changes in the Annual Cycle in Earlier Onset of Climatic Spring in Northern China   总被引：2，自引：0，他引：2  

QIAN Cheng  FU Congbin  Zhaohua WU  YAN Zhongwei 《大气科学进展》2011,28(2):284-296

Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature (SAT) dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle (MAC). The results show that spring at Beijing has arrived significantly earlier by about 2.98 d (10 yr)-1, of which about 1.85 d (10 yr)-1 is due to changes in the annual cycle and 1.13 d (10 yr)-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia (55°–80°N, 50°–110°E), an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.  相似文献   

氮沉降和水位下降对湿地生态系统的影响     

李里  刘伟 《湿地科学与管理》2011,7(4):48-52

介绍了湿地生态系统及其氮沉降和水位下降的概况,综述了全球变化背景下的氮沉降和水位下降对湿地生态系统的具体影响。氮沉降能够在一定范围内提高生产力,具体表现在植物的地上生物量、净初级生产力、植株高度等方面,氮沉降还影响植被组成,使苔藓类植物向维管植物过渡;氮沉降通过两种方式促进微生物分解,一是解除微生物代谢的限制因素,二是改变微生物分解底物的质量;此外,氮沉降还影响温室气体(甲烷、二氧化碳、氧化亚氮)的通量。水位下降后,植被的光合速率降低,生长降低,促进微生物的分解,使温室气体二氧化碳、氧化亚氮的通量增加,使甲烷通量降低。  相似文献   

全波形激光雷达回波分解方法     

李洪鹏  李国元  蔡志坚  吴冠豪 《遥感学报》2019,23(1):89-98

全波形激光雷达的回波中携带了被测目标的距离与特征信息,为了获取这些信息,本文提出了一种回波分解方法。本方法将原始的全波形回波分解为几个独立的高斯脉冲,并得到其函数表达式,从而提取出被测目标的距离等信息。分解过程中,首先,采用可变阈值的经验模态分解滤波法(EMD-soft)对原始波形进行滤波和噪声水平评估;其次,采用一套应对多种波形组成的初始参数估计方法,获取后续拟合所需的初始参数;最后,采用LM(Levenberg-Marquardt)优化算法对回波进行拟合优化,从而获取全波形回波中包含的独立高斯脉冲及其函数表达式。仿真波形的分解实验表明,分解误差在0.1 ns量级,换算成距离误差为15 mm,通过实验室自制的全波形激光雷达实验系统获取的回波的分解实验表明,分解的距离误差小于0.1 m。对比另外两种高斯分解方法对于相同仿真与实验数据的分解结果可以看出,本方法在分解成功率与精度上都有较大的提高。回波分解后的独立高斯脉冲中,除距离外还含有被测目标的反射率、粗糙度、面型等丰富的信息,回波分解方法作为回波分析的基础,将在遥感、测绘等生产与科研领域中发挥非常重要的作用。  相似文献   

1993—2016年中国近海海平面时空变化趋势          下载免费PDF全文

张成卓  郭景松  曹小群  薛宇欢 《海洋科学进展》2021,39(2):187-196

区域海平面变化是目前气候变化研究的热点问题。海平面变化具有时间和空间的异质性,分析海平面变化,应充分考虑时间和空间的差异。基于集合经验模态分解(Ensemble Empirical Mode Decomposition,EEMD)、最小二乘法,利用卫星高度计、验潮站数据,分析了1993—2016年间中国近海及周边海域海平面的时空变化规律。利用EEMD,计算了1993—2016年中国近海海平面变化空间结构的时间变化规律。结果表明中国近海海平面持续升高,但海平面变化在空间分布和时间上的变化并不均匀。空间结构大致分三个部分:大陆沿岸海平面持续上升且上升速率逐年增加,近海海区升高速率逐年降低,而研究区域内的西太平洋西部海区先减速升高又加速降低。分别利用EEMD分解和线性最小二乘拟合算法计算了1993—2016年中国近海海平面平均上升速率的空间分布,结果表明两种方法得到的海平面升高速率的空间分布大致吻合。两种方法均显示沿海地区的上升速率远大于近海海区,沿海地区上升速率大约为6 mm/a,近海海区上升速率大约为2 mm/a。但EEMD方法显示在广东沿岸和靠近赤道部分区域的上升速率更大。分别计算了大陆沿岸、近海及西太平洋西部海区三个海区内空间平均的海平面时间变化的线性及非线性趋势。非线性趋势显示大陆沿岸海区海平面加速上升,上升速率由1993年的3.65 mm/a,增加到2016年的5.03 mm/a;近海地区海平面上升速率逐年变小,由1993年的4.51 mm/a,减缓至2016年的3.8 mm/a;西太平洋西部海区海平面先减速上升,后加速下降,从1993年的上升率为9.5 mm/a,逐渐变化到2016年的下降率为2.27 mm/a。利用验潮站数据分析了大连、坎门、香港的水位变化,除大连海平面上升速率降低外,其余均显示海平面上升速度逐年升高,和卫星高度计的结果吻合。  相似文献   

青藏高原感热与黄土高原春季降水异常关系研究   总被引：6，自引：1，他引：5  

叶燕华王平鲁  李栋梁 《干旱气象》2005,23(1):21-25

利用1961～2000年黄土高原56站的春季降水、气温资料,用SVD方法分析了其与青藏高原感热场的关系。结果表明,降水量与青藏高原感热场的前两模态代表了两场间的主要耦合特征;上年冬季和秋季青藏高原感热场的异常通过影响大气环流,能够导致次年黄土高原春季降水异常;青藏高原感热对黄土高原西部和南部、北部的部分地区影响较显著,而对陕西北部、山西中部影响不明显。前期高原感热场SVD第一、二模态的变化,可以作为黄土高原春季降水异常的预测信号。  相似文献