Analysis of the regional spectral properties in northwestern South China Sea based on an empirical orthogonal function

This study presents an analysis of the spectral characteristics of remote sensing reflectance(Rrs)in northwestern South China Sea based on the in situ optical and water quality data for August 2018.Rrswas initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole Rrs were characterized using the empirical orthogonal function(EOF)analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95%of the variances of Rrs are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of Rrs(A-D Rrs-EOF1)significantly contributed to the total variances of each Rrs class.In addition,the correlation coefficients between the amplitude factors of class A-D Rrs-EOF1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class ARrs-EOF1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B Rrs-EOF1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(ag(λ)),whereas the spectral shape of class C Rrs-EOF1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D Rrs-EOF1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape.

Jacobi-Sobolev Orthogonal Polynomialsand Spectral Methods for Elliptic Boundary Value Problems

Generalized Jacobi polynomials with indexes α,β∈ R are introduced and some basic properties are established. As examples of applications,the second- and fourth-order elliptic boundary value problems with Dirichlet or Robin boundary conditions are considered,and the generalized Jacobi spectral schemes are proposed. For the diagonalization of discrete systems,the Jacobi-Sobolev orthogonal basis functions are constructed,which allow the exact solutions and the approximate solutions to be represented in the forms of infinite and truncated Jacobi series. Error estimates are obtained and numerical results are provided to illustrate the effectiveness and the spectral accuracy.

斯里兰卡极端降水时空演变特征及趋势预测

斯里兰卡是中国“一带一路”倡议的重要节点国家,极端降水对当地社会经济威胁较大,极易引发灾害。选取当地10个气象站2008—2020年的逐日降水资料,基于RClimDex模型计算斯里兰卡6个极端降水指标,利用经验正交函数分析、Morlet小波分析和重标极差法(R/S分析)等,分析极端降水事件的时空演变特征。结果表明:极端降水指数在时间分布上,除持续干旱指数(CDD)呈减少趋势外,其他各指数均为上升趋势;极端降水指数空间差异表现为北部沿海平原地带的极端降水强度高于南部沿海平原,拉特纳普勒市以西地区为斯里兰卡降水事件的多发区;极端降水指数周期性明显,绝大多数极端降水指数以6~7 a为第一主周期。R/S分析表明当地极端降水事件未来持续可能性较大。研究成果可为斯里兰卡极端气候预测、生态环境保护、防灾减灾工作等提供决策支持。

青海省多年地表感热通量的时空变化特征

选取青海省35个气象站观测数据,基于CHEN-WENG感热系数方案,计算了1980—2017年青海省地表感热通量。利用小波分析、Mann-Kendall突变检验和经验正交函数法(Empirical Orthogonal Function,EOF),对感热通量的时空变化特征及其影响因子进行分析。结果表明:(1)1980年以来,青海省全年和各季节感热通量总体上均呈上升趋势,并具有28 a的主周期和约18 a的副周期,冬季的周期变化较为复杂;(2)全年和各季节感热通量与地气温差存在显著相关性,2004—2017年受地气温差增大的影响上升;(3)全年、春季和秋季感热通量与风速存在显著相关性,1980—2004年受风速减小的影响感热通量下降;(4)夏季降水与感热通量呈显著负相关;(5)从空间上看,全年以及春季感热通量呈现出显著的东西分异,秋、冬季表现出一定程度的南北分异。

基于REOF分析的山东省年降水区域特征及趋势分析

[目的]探究山东省不同气候分区年降水量的时空特征,为该地区气候分析、防灾减灾提供更加区域性的参考依据。[方法]根据山东省95个国家地面气象观测站1991—2020年降水年值数据,首先对山东省年降水场进行气候分区,然后通过相关统计方法分析各分区降水的时空变化特征。[结果](1)山东省各降水模态降水偏少的年份更多,降水偏多的年份降水强度更大,年代际变化均较为明显,但各模态降水偏多偏少的年份分布及强度变化有所不同。(2)山东省年降水量大致由东南向西北递减,年降水场划分为东南沿海区(Ⅰ区)、西北平原区(Ⅱ区)和中部山地区(Ⅲ区)3个区域,各降水分区年降水均呈不显著增加趋势,趋势率各不相同,突变均不明显。(3)山东省各降水分区年降水量均具有较为明显的周期性特征,东南沿海区年降水场存在2个较为明显的能量中心,中心尺度均为2~3 a,未来变化具有强持续性;西北平原区年降水场存在3个较为明显的能量中心,中心尺度分别为5~7 a, 3 a和2~3 a,未来变化具有持续性;中部山地区年降水场存在2个较为明显的能量中心,中心尺度分别为2~3 a, 6 a,未来变化具有强持续性。[结论]山东省降水偏少的年份更多,降水偏多的年份降水强度更大,年降水场大致可分为3个分区,各分区年降水量均呈不显著增加趋势,均具有较为明显的周期性特征,且未来变化均具有持续性。

反向传播神经网络的太平洋海域温跃层反演

温跃层是反映海洋温度场的重要指标。针对太平洋中东部海域复杂多变的水文情况以及传统温跃层分析模式的局限性,该文基于BOA_Argo历史网格,通过BP神经网络,建立温度剖面的经验正交系数与海面遥感数据、少量深度处海水温度之间的非线性映射关系,实现海洋垂向温度剖面的实时反演,最后利用垂向梯度法获得海洋温跃层的相关参数。实验结果表明,相比于传统方法,该方法反演得到的跃层深度与测量值更加吻合,其中上层深度平均反演误差从10.3 m下降到5.7 m,下层深度平均反演误差从16.8 m下降到8.8 m。

基于相对湿润指数的浙江省茶叶气象干旱特征分析

【目的】研究浙江省茶叶气象干旱的演变规律,为茶叶安全生产优化布局提供科学依据。【方法】利用浙江省68个地面气象观测站50 a(1971—2020年)的逐日气温、降水量、日照时数等数据,基于相对湿润指数、正交经验函数和小波分析法等分析浙江省茶叶气象干旱的时空分布规律。【结果】浙江省茶叶生产夏季干旱的强度和发生频率高于秋季,且均呈现西高东低的分布,中西部尤其金衢盆地的干旱强度和频率为全省最强,浙北地区次之,沿海地区最小。茶叶夏季干旱站次比呈逐年下降的趋势,秋季则呈现先升后降的趋势,2000年以后夏秋两季出现极端大范围茶叶气象干旱的年份增多。茶叶夏季和秋季干旱强度的正交经验函数第一模态表现为全省变化一致性,第二模态中沿海局部地区和内陆呈反相位变化,夏秋两季干旱强度的主模态时间序列分别存在2-6、2-4、6-10 a的振荡周期。【结论】浙江省在夏季和秋季出现茶叶气象干旱的频率在下降,但出现极端干旱的概率在增加,应重点加强茶叶主产区干旱监测预警能力建设,提升防旱抗旱能力。

Spatio-temporal variability of surface chlorophyll a in the Yellow Sea and the East China Sea based on reconstructions of satellite data of 2001-2020

Chlorophyll-a(Chl-a)concentration is a primary indicator for marine environmental monitoring.The spatio-temporal variations of sea surface Chl-a concentration in the Yellow Sea(YS)and the East China Sea(ECS)in 2001-2020 were investigated by reconstructing the MODIS Level 3 products with the data interpolation empirical orthogonal function(DINEOF)method.The reconstructed results by interpolating the combined MODIS daily+8-day datasets were found better than those merely by interpolating daily or 8-day data.Chl-a concentration in the YS and the ECS reached its maximum in spring,with blooms occurring,decreased in summer and autumn,and increased in late autumn and early winter.By performing empirical orthogonal function(EOF)decomposition of the reconstructed data fields and correlation analysis with several potential environmental factors,we found that the sea surface temperature(SST)plays a significant role in the seasonal variation of Chl a,especially during spring and summer.The increase of SST in spring and the upper-layer nutrients mixed up during the last winter might favor the occurrence of spring blooms.The high sea surface temperature(SST)throughout the summer would strengthen the vertical stratification and prevent nutrients supply from deep water,resulting in low surface Chl-a concentrations.The sea surface Chl-a concentration in the YS was found decreased significantly from 2012 to 2020,which was possibly related to the Pacific Decadal Oscillation(PDO).

Feature analysis of stratospheric wind and temperature fields over the Antigua site by rocket data

The wind and temperature fields at 20 to 55 km above the Antigua launch site(17°N,61°W)were analyzed by using sounding rocket data published by the research organization on Stratosphere-Troposphere Processes and their Role in Climate(SPARC).The results showed distinct variations in the wind and temperature fields at different heights from the 1960s to the 1990s.The overall zonal wind speed showed a significant increasing trend with the year,and the overall change in meridional wind speed showed a falling trend from 1976 to 1990,whereas the temperature field showed a significant cooling trend from 1964 to 1990.The times the trends mutated varied at different levels.By taking the altitudes at 20,35,and 50 km as representatives,we found that the zonal wind speed trend had mutated in 1988,1986,and 1986,respectively;that the meridional wind speed trend had mutated in 1990,1986,and 1990,respectively;and that the temperature trend had mutated separately in 1977,1973,and 1967,respectively.Characteristics of the periodic wind and temperature field variations at different heights were also analyzed,and obvious differences were found in time scale variations across the different layers.The zonal and meridional wind fields were basically characterized as having a significant periodic variation of 5 years across the three layers,and each level was characterized as having a periodic variation of less than 5 years.Temperature field variation at the three levels was basically characterized as occurring in 10-year and 5-year cycles.

ROTATED COMPLEX EMPIRICAL ORTHOGONAL FUNCTION(RCEOF)ANALYSIS—PART Ⅱ:THEORY AND EXAMPLES

The numerical solving and the program designing of the rotated complex empirical orthogonal function(RCEOF)are discussed.Some examples of RCEOF are also presented.

COMPARISONS OF EOF AND CCA METHODS IN EXPERIMENTS WITH TYPHOON TRACK

A predictive model for 24-120 h track of the tropical cyclone over the South ChinaSea is set upusing the predictors of CLIPER and with reference to those 0f EOF and CCA. This EOF-and CCA-basedmodel is compared with dependent and independent samples in veritring forecasts’Analpees appltwg themeth0ds to 500-hPa geopotential heights have shown that the CCA method is able toconcentrate moreoriginal information of variable fleld that has the best global correlation withtropical cycl0ne track andthus reduces more efficiently error arisen in forecast,despite that can0nicaldistribution of weighted vari-able coefficients derived by it is less well-defined or smoothed 0f a spacialpattern as is done by eigenvec-tor in the EOF method. The verification indicates a certain degree of skill inb0th track predictive model,though better results are yielded in the CCA-based one, whose mean vector err0rare 159. 27, 314. 84,524. 12, 813. 03, and 987. 12 km, respectively for periods of 24, 48, 72, 96, and120 h. The modelmakes an objective approach for prediction of short-and medium-range track of tropical cyclone in theSouth China Sea.

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR-SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.

Statistical analysis of surface hydrography and circulation variations in northern South China Sea

To study the variations in surface hydrography and circulation in northern South China Sea (NSCS), rotated empirical orthogonal function (REOF) and extended associate pattern analysis (EAPA) are used with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets cover- ing 1 126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in this paper. Results show that in summer, the SCS Diluted Water Expansion (SDWE) is the most dominant factor con- trolling SSS variations in the NSCS. The remarkable SDWE usually begins in early July, reaches its maximum in middle August and weakens in late September. In summer flourishing period, its low saline core is just limited between 21°N and 22°N because of strong surface anomalous anticyclonic circulation in the NSCS. In early or late stage, the anomalous anticyclonic circulation becomes weak or turns into cyclonic one, thus the weak SCS diluted water can disperse. And its influence on the SSS variations has obviously decreased. The Kuroshio intrusion is the second controlling factor, and it has the almost opposite seasonal or intraseasonal oscillations and spatial charac- teristics to the SDWE. Winter Kuroshio Intrusion (WKI) begins in early November and lasts about three months. Intraseasonal Kuroshio Intrusion (IKI) takes place at any seasons. The westward Ekman transport produced by the north anomaly of East Asia Monsoon (EAM) pushes warmer and more saline seawater into the NSCS through the Bashi Strait and seems to decide the intensity of seasonal and intraseasonal Kuroshio intrusions.

山西省地表温度时空变化及其与地质灾害的关系分析

利用山西省107个国家气象站1981—2018年0 cm地表温度及崩塌、滑坡地质灾害的资料,采用线性回归、M-K检验、滑动t检验和经验正交函数(EOF)时空分离等方法,对山西省0 cm地表温度时空变化以及与地质灾害的相关性分析得出:山西省年际及四季地温均呈增温上升趋势;地温在1999年春季、2002和2004年夏季、2004年秋季、1993年冬季分别发生由冷转暖的突变,年均地温无突变。利用EOF经验正交分析得出:年和四季第一模态空间变化具有较好的一致性特征,时间序列年和四季都是从2004年之后一致表现为以正位相为主;第二模态南部和北部具有反位向变化的特征。春季崩塌、滑坡地质灾害与年、春季和秋季地温呈正相关(通过95%的检验),即年、春季和秋季地表温度由冷变暖时,春季地质灾害的发生会由少变多。夏季降水量与年和夏秋季地质灾害呈正相关(通过90%和95%的检验),但年和夏秋季地质灾害的发生略滞后于夏季降水的发生,由此也可推断夏季降水是年、夏秋季崩塌和滑坡地质灾害的主要诱发因素。

基于SPEI的陕西省干旱特征及其对玉米产量的影响

基于陕西省1971-2020年32个气象站实测气象资料,计算不同尺度玉米生育期标准化降水蒸散指数(SPEI),利用旋转正交经验函数法、趋势分析法和小波分析法分析玉米不同生育期的干旱时空特征。结合陕西省9地区1990-2020年玉米单产数据,借助HP滤波法分离出玉米气象产量,采用交叉小波分析和线性回归法分析了干旱对玉米气象产量的影响。结果表明:①研究区干湿空间分布在玉米生育期可划分出关中、延安、榆林和陕南西南部4个干旱敏感区域;②在1971-2020年内,全生育期关中、榆林和延安地区呈干-湿交替变化,1990s末陕西大部分地区干旱较严重;③铜川、宝鸡、咸阳和渭南地区玉米气象产量与花丝期干湿状况密切相关,其余地区受全生育期干湿状况影响最大。玉米气象产量与干旱状况呈显著的正相关,且在1994-2000年存在1~4 a的共振周期;④榆林、铜川和渭南地区玉米气象产量随SPEI值增大而增加,而延安、宝鸡、咸阳、安康、汉中和商洛当SPEI值大于1.6或小于-0.4时会发生轻度及以上程度的减产。

2001―2021年东亚地区CTP时空模态特征分析

基于2001年1月至2021年12月期间MODIS和AIRS遥感反演数据,利用经验正交函数(EOF)、MK趋势分析、最小二乘法等方法研究了东亚地区近21年的云顶气压(CTP)时空模态特征及变化趋势。结果表明:东亚地区CTP从东北到西南呈逐渐递减趋势;四季变化差异性较大,呈现“√”字型变化,表现为冬季气压值最高、夏季最低;受地理位置和纬度带影响,CTP的高值区在一年四季均分布在东北地区上空,低值区始终位于青藏高原地区。在中国的广西、广东和缅甸、印度等地属于热带季风区,在冬季受干冷气流的影响,容易形成CTP高值区。东亚地区主要以中云分布为主,低云区主要集中在中国东北、京津冀、朝鲜半岛和中纬度海洋地区,在中国中原地区、南方地区(广西、广东和长江中下游各省地区)以及新疆部分地区以中云为主,高云主要出现在中国青藏高原和塔克拉玛干沙漠。通过趋势分析发现,在2001年至2021年间,CTP在中国的新疆、印度半岛、缅甸、蒙古和贝加尔湖等区域呈现较高的增长趋势,而在中国的青藏高原、南部沿海等部分区域以及东部海域均呈较明显的下降趋势。东亚地区部分区域的CTP与地表温度、湿度、水汽和云量均呈现较为显著的相关性,因此CTP的变化可以在一定程度上反应区域性天气变化情况。

长江口南槽最大浑浊带表层沉积物动态变化研究

河口最大浑浊带表层沉积物的动态变化在很大程度上反映径潮流交汇作用影响的悬底沙交换过程,直接关联最大浑浊带区域的拦门沙冲淤整治。利用2013年6月在长江口南槽最大浑浊带小潮至大潮期间定点持续采集的共9 d逐时水文资料及表层沉积物等数据,分析了南槽最大浑浊带表层沉积物沉积动力过程。主要结果包括:(1)南槽最大浑浊带表层沉积物颗粒较细,以粉砂为优势粒级,沉积物分选性较差,平均粒径、分选系数及偏态自小潮到大潮呈逐渐减小的特征。落潮时水体悬浮泥沙易发生絮凝沉降,表层沉积物较细,以极细粉砂为主;涨潮期间,受涨潮顶托作用,以细砂为主的水体粗颗粒泥沙易于沉降,表层沉积物较粗。(2)沉积物组分存在2种变化模式:主要模式为潮流作用及盐水絮凝引起细颗粒悬沙沉降,以粗黏土及极细粉砂为主的沉积模式;次要模式为径流作用下,细颗粒泥沙被冲刷,细砂比重增加,导致表层沉积物变粗,以中粉砂为主的沉积特征;其中径流主导了表层沉积物的短时间内变化,而盐度的变化决定了表层沉积物整体的粗细转换。

基于时空分解的汾河流域植被净初级生产力的变异性及驱动因子分析

汾河流域生态环境脆弱,且水土流失问题较为严重,易受自然及人为因素的影响。基于1982—2019年汾河流域的植被净初级生产力(NPP),利用趋势分析、经验正交分解(EOF)和结构方程模型(SEM)研究汾河流域NPP的时空演变特征及其驱动因素,旨在为汾河流域生态环境建设和保护提供理论依据。结果表明,汾河流域NPP由流域中心向边缘增加,整体呈波动上升趋势,NPP显著增加的面积远大于退化面积;从2003年开始,汾河流域尤其是东北部地区植被NPP明显提高,中北部区域的NPP呈现退化趋势,并表现出较强的时间变异性。人类活动、气候变化和基础自然环境因子对汾河流域NPP空间结构的总效应分别为0.50、0.20、0.03,表明了人类活动是影响NPP空间结构最主要的因素;基础自然环境对NPP变化有显著的直接和间接效应,并且容易在小尺度范围内形成潜在的时空格局。温度和相对湿度是影响流域NPP空间结构和时间变异最主要的气候因素。

Characteristics of the dynamic changes in active accumulated temperature in Sichuan,China in the last 51 years against the background of climate change

It is of utmost necessity to understand the dynamics of regional active accumulated temperature(AAT)to cope with the negative impacts of global warming on agroforestry development and food security and to provide a real-time and effective reference basis for regional agroforestry planning.The daily temperature data from 30 meteorological stations in Sichuan Province from 1970 to 2020,and sea surface temperature(SST)index data from the Atlantic Multiphase Oscillation(AMO)and Pacific Decadal Oscillation(PDO)were used for the study.Sichuan Province was divided into the western region(WS)and the eastern region(ES),considering 1000 m above sea level as the boundary.The spatiotemporal characteristics of≥0℃ and≥10℃ active accumulated temperature(AAT0,AAT10)in WS and ES were analyzed comprehensively using 5-day average sliding,empirical orthogonal function(EOF),ensemble empirical mode decomposition(EEMD),and multiple mutation tests.The results show that(1)AAT0 and AAT10 of WS ranged from 3034℃ to 3586℃ and 1971℃ to 2636℃,respectively,while the AAT0 and AAT10 of ES ranged from 5863℃ to 6513℃ and 4847℃ to 5875℃,respectively.The period around 1997 was a significant abrupt change,and the AAT in the province generally increased during the subsequent time period(2)AAT in the study area is mainly driven by the fluctuations of AMO,as reflected by the low-to-high variation of AAT coinciding with the jump of the cold-to-warm phase of AMO.Considering different time scale fluctuations in the past 51 years,the major cycle for both AAT0 and AAT10 in WS is 3.40 a,while the major cycles in ES are 3.64 a and 3.19 a,respectively with a sub-cycle of 7.29 a.AAT fluctuation has an insignificant periodic characteristic of 25.50 a on the interdecadal scale(3)The spatial heterogeneity of AAT in WS is prominent and is mainly reflected by the significantly warm conditions in the south of the WS region and relatively slight warm conditions in the north,as well as by the isolated cooling area in the form of"freezing point",i.e.,Xiaojin county.In contrast,the spatial variability of AAT in ES is more or less consistent,with the warming areas concentrated in the foothills of the western edge of the basin and a slight increase in AAT observed in the central part of the basin.

磨刀门枯季咸潮上溯归因分析与响应规律研究

在气候变化和人类活动影响下,磨刀门咸潮上溯显著加剧,极大地威胁了粤港澳大湾区的供水安全。基于2004-2016年磨刀门水道7个站点的日超标时间数据,与日最大潮差、径流量、平均海平面、跨岸风和沿岸风进行了经验正交函数分析(EOF)和一元及多元线性回归分析,探究磨刀门咸潮上溯与各影响因素的响应关系,量化各影响因素的作用大小。结果表明:对磨刀门咸潮上溯的贡献最大的是潮差,其次是径流,两者分别能解释超标时间日变化的30%和28%,风的作用略大于平均海平面,两者对咸潮上溯的贡献分别为12%和11%,其中跨岸风作用略大于沿岸风作用。磨刀门咸潮峰值出现在小潮潮差最小后的3.2 d,而高要站流量增大,1.8 d后才能抑制磨刀门河口咸情。该研究可为流域调度及咸潮预报提供理论支撑。