青藏高原近地层及北侧气压系统的季节性振荡变化

基于ERA-Interim逐日4次600 h Pa位势高度再分析资料,以及青藏高原和周边地区75个气象站日平均温度、降水和相对湿度资料,对高原近地层及北侧气压系统的季节性振荡变化进行了分析.结果表明:高原近地层及北侧气压系统强度在围绕中心点顺时针运动时不断加强,逆时针运动时不断减弱.两气压系统呈明显的跷跷板式变化,在600 h Pa上表现为高度场空间结构沿经向上的调整;低高压差负值的开始和结束时间与高原季风起讫时间吻合.高原夏季降水的起讫不仅与高原及北侧气压系统结构密切相关,而且与高原东南或南部水汽输送条件息息相关.

基于SSO多扰动输入机理分析的DFIG-GSC功率振荡抑制策略研究

电网次同步振荡(SSO)已成为桎梏新能源发展的主要问题之一,针对SSO下双馈感应发电机(DFIG)中网侧变流器(GSC)的功率振荡问题展开研究。首先,建立SSO对GSC的多扰动输入数学模型,探究不同扰动输入的性质以及其对GSC系统的影响,明确了针对物理量扰动以及信号扰动分别采用补偿与滤除两种不同的抑制方法。其次,针对锁相环(PLL)输出误差经过坐标变换产生耦合振荡的问题,建立PLL输出误差角度的频域数学模型,并通过设计一种改进PLL消除其输出误差对GSC的信号扰动影响。同时,设计一种准谐振控制器的自适应算法,并提出基于自适应准谐振控制器的DFIG-GSC功率振荡抑制策略,消除SSO对GSC的物理扰动影响;最后,通过搭建具有SSO模拟环境的DFIG实验平台,验证本文所提控制策略的有效性。

中国北方夏半年极端干期的时空变化特征

利用1951—2004年我国北方348个测站的夏半年逐日降水资料,首先整理出各站点的极端干期日数和无雨总日数两个序列,得到极端干期日数的空间分布,并将北方划分为A、B、C 3个区,其中A、B 2个区相对湿润,C区则相对干旱和半干旱,这种分布与地理环境有密切的联系。然后建立这3个区夏半年极端干期以及无雨总日数的时间序列,采用经验模态分解(EMD)方法,分析极端干期序列的多尺度振荡结构以及多年变化的总趋势。结果显示,北方各区夏半年极端干期变化主要由前2个较高频的本征模态函数(IMF)分量构成,这表明3～4年和6～7年的变化对整个极端干期的变化起主要作用。对较低频分量和总趋势的分析表明,近54年来东北和华北大部分相对湿润的地区极端干期延长,有变干的趋势;北方主要干旱半干旱地区的极端干期变短,干旱有所缓解。近10～20年来整个北方极端干期日数增加,干旱化加剧,但西北局部干旱地区的极端干期在缩短,干旱有所缓解。这说明,分析的时—空尺度不同,得到的结果会有所不同。

基于EMD方法的我国年气温和东部年降水量序列的振荡模态分析

基于经验模态分解（EMD）方法，探讨了近百年来全国年平均气温序列以及东部地区年降水量序列的振荡模态结构特征。结果表明：全国年气温序列的振荡变化主要由第1，2，4本征模态分量构成，3～5年、8～10年的振荡以及百年内的升-降-升的年代际变化对整个气温变化起主要作用，近几年处于暖期。东部年降水量序列的振荡变化主要由第1，2本征模态分量构成，3～5年的振荡起主要作用，百年中有3个高值期，近几年处于多雨期。气温和降水原序列都没有明显的周期性，但其内在振荡分量却有某些周期性。

夏季副热带大气系统的多尺度振荡分析

应用经验模态分析方法(经验模态分解(EMD)和Hilbert谱),对夏季副热带大气系统在周期态和振荡态下的流函数数值解序列进行本征模态函数(IMF)及其Hilbert谱的分析。结果表明:(1)周期态下的流函数分量时间序列一般由1个IMF构成,而且其周期就是该流函数的周期。对周期性的IMF分量使用Hilbert变换得到的瞬时频率和振幅都不随时间变化。(2)振荡态下的流函数分量时间序列一般由2个以上的IMF构成,其中有的IMF分量具有显著的周期性,相应的瞬时频率和振幅都不随时间变化;有的IMF分量则没有显著的周期性,相应的瞬时频率和振幅有变化,而且随着振荡态复杂程度的增大,瞬时频率和振幅的变化也趋于复杂。(3)瞬时振幅有明确的物理意义,表示IMF振荡的能量;振幅的局部相对大值对应着原序列(IMF)的强振荡,小值则对应着弱的变化。瞬时频率的显著增大,表示原序列有大的变化。

波流相互作用的大气系统中振荡模态的分析

把经验模态分解(EMD)方法用于波流相互作用的大气动力系统,对不同系统状态的流函数解序列求其本征模态函数(IMF)分量,分析系统状态与IMF之间的关系,揭示流函数的振荡结构。结果表明:随着系统的复杂性增大,构成解序列的IMF分量的个数相应增多。对于系统的定常态(Hadley流),每个流函数Ψ分量的各个IMF分量都趋于零均值线;对于周期态(Rossby流),Ψ分量由1个周期性的高频IMF分量构成;对于振荡态,Ψ分量主要由2—3个较高频IMF分量构成;对于非周期流,Ψ分量由多个非周期的IMF分量构成;对于周期-非周期状态,其本征模态有的有周期性,有的没有周期性。低频IMF分量表现Ψ序列的长时间尺度的变化。

基于反步自适应准谐振控制的双馈风机次同步振荡抑制策略

随着电力系统容量和规模的不断扩大,常采取串补电容的方式提升输电线路的输电能力,但这加剧了电力系统中出现次同步振荡(SSO)的风险。SSO的产生会影响双馈感应发电机(DFIG)转子侧变流器(RSC)的控制,进而引起定子电流的振荡发散,严重时将会导致风机解列脱网。因此,为解决SSO对RSC控制产生扰动的问题,该文提出了基于自适应准谐振控制的RSC反步次同步振荡抑制策略。首先对SSO在RSC控制系统中的传播路径及其频率变化对控制的影响等内容展开研究;然后通过反步控制器与自适应准谐振控制器的协同控制,对DFIG定子中宽频带SSO电流进行抑制,避免发电系统输出受到SSO的影响;最后通过搭建仿真模型与实验平台,验证所提理论与控制策略的有效性。该文分别对在10 Hz、20 Hz、30 Hz及频率变化时SSO影响下的DFIG定子振荡电流抑制效果进行验证。实验结果表明,所提策略对DFIG系统中宽频带SSO具有良好的抑制效果。

Interannual variability of boreal summer intraseasonal oscillation over the northwestern Pacific influenced by the Pacific Meridional Mode

During the boreal summer,intraseasonal oscillations exhibit significant interannual variations in intensity over two key regions:the central-western equatorial Pacific(5°S-5°N,150°E-150°W)and the subtropical Northwestern Pacific(10°-20°N,130°E-175°W).The former is well-documented and considered to be influenced by the ENSO,while the latter has received comparatively less attention and is likely influenced by the Pacific Meridional Mode(PMM),as suggested by partial correlation analysis results.To elucidate the physical processes responsible for the enhanced(weakened)intraseasonal convection over the subtropical northwestern Pacific during warm(cold)PMM years,the authors employed a moisture budget analysis.The findings reveal that during warm PMM years,there is an increase in summer-mean moisture over the subtropical northwestern Pacific.This increase interacts with intensified vertical motion perturbations in the region,leading to greater vertical moisture advection in the lower troposphere and consequently resulting in convective instability.Such a process is pivotal in amplifying intraseasonal convection anomalies.The observational findings were further verified by model experiments forced by PMM-like sea surface temperature patterns.

深部洞室开挖卸荷分区破裂机制的动力分析

随着地下工程开挖深度的增加,深部岩体将处于高应力和复杂的地质环境中,产生与浅埋洞室破坏模式迥异的分区破裂现象。深部洞室在动力卸荷作用下,基于应变梯度理论和损伤软化模型,建立了弹塑性损伤软化动力模型,推导了含有应变梯度项的运动方程、平衡方程和边界条件,提出相应的破坏判据,采用Runge-Kutta方法和Matlab数值软件求得不同卸载时刻围岩附加位移场、应力场和开挖后围岩总位移场、应力场,得到深部洞室围岩分区破裂的动态形成过程和发展规律。由理论计算值与地质力学模型试验实测值对比分析得知,围岩的径向位移、径向应力和切向应力出现波峰和波谷交替振荡的变化规律,理论计算得到的破裂区和非破裂区的宽度和数量与试验实测值有很好的一致性,证实了该模型分析分区破裂现象的适用性,对以后深部地下工程围岩变形破坏和支护设计提供理论支持。

井下地电阻率观测异常核实实例

针对2015年12月17—19日甘肃省陇南市汉王台地电阻率井下观测三道同步出现的振荡变化,通过现场核实,并对观测数据进行对比分析后得到:此次垂向观测记录到的扰动变化不是来自深部地下介质的电性变化,而是浅部的干扰,可能因素是台站高压电扰动(或变压器漏电)与台站测区草坪浇水导致地表湿润易于传导有关;通过这次异常核实,对井下地电阻率观测有了较为完整的认识,为资料突变核实步骤和分析方法积累了一定经验,也为探讨深井地电阻率变化是否是地震前兆增添了佐证。

低能离子注入对大豆酯酶同功酶活性的影响

利用 30KeV低能氮离子在 3× 10 15～ 3× 10 17N+ ·cm-2 剂量范围内对大豆进行了离子注入 ,并用电泳结合薄层扫描的方法对其酯酶同功酶的相对活性进行了测定 .结果表明 ,其变化为升 降 升 降的振荡型变化趋势 .真空对照样品的电泳结果显示 。

Long-term changes in wintertime persistent heavy rainfall over southern China contributed by the Madden-Julian Oscillation

During the boreal winter,abundant persistent heavy rainfall(PHR)amount and significant rainfall variability at subseasonal timescale are generally observed over the southern sector of East China,where the large-scale circulation and moisture transport are tightly connected with the equatorial Madden-Julian Oscillation(MJO).As the MJO convections occur over the equatorial Indian Ocean(MJO phases 1-4),the low-level moisture convergence is enhanced over southern China(SC,108°-120°E,21°-26°N)with the divergence to the north.Thus,a positive anomaly of PHR amount appears in SC but a negative anomaly of PHR amount is seen in the Yangtze River valley(YR,113°-122°E,28°-30°N).In contrast,the divergence(convergence)of moisture flux anomalies in the SC(YR)associated with the western equatorial Pacific MJO convections(phases 5-8)limits(benefits)the occurrence of PHR in the SC(YR).The wintertime PHR over southern China is found to undergo a long-term change over the past three decades(1979-2011)with a decreasing(an increasing)trend of PHR amount in the SC(YR).The change in PHR amount occurs consistently with the decadal change in MJO activity.In the earlier decade(1979-1994,E1),the active Indian Ocean(western Pacific)MJO events appeared more frequently while they became less frequent in the recent decade(1995-2011,E2).Accordingly,the Indian Ocean(western Pacific)MJO-related moisture convergence(divergence)anomalies in the SC tend to be weakened(enhanced),contributing to the decrease in PHR amount over the SC in the recent decade.

Influence of the Pacific Decadal Oscillation on regional sea level rise in the Pacific Ocean from 1993 to 2012

The rate of regional sea level rise （SLR） provides important information about the impact of human activities on climate change. However, accurate estimation of regional SLR can be severely affected by sea surface height （SSH） change caused by the Pacific Decadal Oscillation （PDO-SSH）. Here, the PDO- SSH signal is extracted from satellite altimeter data by multi-variable linear regression, and regional SLR in the altimeter era is calculated, before and after removing that signal. The results show that PDO-SSH trends are rising in the western Pacific and falling in the eastern Pacific, with the strongest signal confined to the tropical and North Pacific. Over the past 20 years, the PDO-SSH accounts for about 30%/-400% of altimeter-observed SLR in the regions 8° 15°N, 130°-160°E and 30°-40°N, 170°-220°E. Along the coast ＆North America, the PDO-SSH signal dramatically offsets the coastal SLR, as the sea level trends change sign from falling to rising.

CLIMATE CHANGE:LONG-TERM TRENDS AND SHORT-TERM OSCILLATIONS

Identifying the Northern Hemisphere （NH） temperature reconstruction and instrumental data for the past 1000 years shows that climate change in the last millennium includes long-term trends and varioas oscillations. Two long-term trends and the quasi-70-year oscillation were detected in the global temperature series tbr the last 140 years and the NH millennium series. One important feature was emphasized that temperature decreases slowly but it increases rapidly based on the analysis of different series. Benefits can be obtained of climate change from understanding various long-term trends and oscillations. Millennial temperature proxies from the natural climate system and time series of nonlinear model system are used in understanding the natural climate change and recognizing potential benefits by using the method of wavelet transform analysis. The results from numerical modeling show that major oscillations contained in numerical solutions on the interdecadal timescale are consistent with that of natural proxies. It seems that these oscillations in the climate change are not directly linked with the solar radiation as an external tbrcing. This investigation may conclude that the climate variability at the interdecadal timescale strongly depends on the internal nonlinear effects in the climate system.

Possible contribution of the PDO to the eastward retreat of the western pacific subtropical high

Previous studies have demonstrated that the western Pacific subtropical high(WPSH)has experienced an eastward retreat since the late 1970s.In this study,the authors propose that this eastward retreat of the WPSH can be partly attributed to atmospheric responses to the positive phase of the Pacific decadal oscillation(PDO),based on idealized SST forcing experiments using the Community Atmosphere Model,version 4.Associated with the positive phase of the PDO,convective heating from the Indian Peninsula to the western Pacific and over the eastern tropical Pacific has increased,which has subsequently forced a Gill-type response to modulate the WPSH.The resulting cyclonic gyre over the Asian continent and the western Pacific in the lower troposphere is favorable for the eastward retreat of the WPSH.Additionally,the resulting anticyclonic gyre in the upper troposphere is favorable for the strengthening and southward expansion of the East Asian westerly jet,which can modulate the jet-related secondary meridional-vertical circulation over the western Pacific and promote the eastward retreat of the WPSH.

Effects of air-sea coupling on the eastward propagating boreal winter intraseasonal oscillation over the tropical Indian Ocean

The effects of air-sea coupling over the tropical Indian Ocean（TIO） on the eastward propagating boreal winter intraseasonal oscillation（MJO） are investigated by comparing a fully coupled and a partially decoupled Indian Ocean experiment using the SINTEX-F coupled model.Air-sea coupling over the TIO significantly enhances the intensity of the eastward propagations of the MJO along the5°-10°S zonal areas.The zonal asymmetry of the SST anomaly（SSTA） is responsible for the enhanced eastward propagation.A positive SSTA appears to the east of the MJO convection,which results in the boundary layer moisture convergence and positively feeds back to the MJO convection.In addition,the air-sea interaction effect on the eastward propagation of the MJO is related to the interannual variations of the TIO.Air-sea coupling enhances（reduces） the eastward-propagating spectrum during the negative Indian Ocean dipole mode and positive Indian Ocean basin mode.Such phase dependence is attributed to the role of the background mean westerly in affecting the wind-evaporation-SST feedback.Air-sea coupling（decoupling） enhances（reduces） the zonal asymmetry of the low-level specific humidity,and thus the eastward propagation spectrum of the MJO.

Intraseasonal variability of summer monsoon rainfall over the lower reaches of the Yangtze River basin

This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global precipitation data.The ISV of the summer monsoon rainfall over the LYRB is mainly dominated by the lower-frequency 12–20-day variability and the higher-frequency 8–12-day variability.The lower-frequency variability is found to be related to the northwestwardpropagating quasi-biweekly oscillation(QBWO)over the western North Pacific spanning the South China Sea(SCS)and Philippine Sea,while the higher-frequency variability is related to the southeastward propagating midlatitude wave train(MLWT).Moreover,not each active QBWO(MLWT)in the SCS(East Asia)can generate ISV components of the precipitation anomaly over the LYRB.The QBWO can change the rainfall significantly with the modulation of mean state precipitation,while the quasi-11-day mode mainly depends on the intensity of the MLWT rather than the mean precipitation change.These findings should enrich our understanding of the ISV of the East Asian summer monsoon and improve its predictability.

Oscillation in Evolution of Cooperation for Addressing Climate Change

Climate protection is a problem of sustaining a public resource. All countries of the world should take action to deal with climate change. However, such an action is actually a game process where each country chooses to cooperate or defect under constrained condition. Here we study the group behavior of countries in dealing with climate change. In our study, the countries of the world are considered as players who are distributed on an assumed spatial network. A new evolution rule is proposed to model the game process among the players. Our extensive experiments demonstrate that under constrained condition, the local psychology of players possibly results in the formation of local group. Some local and global oscillations can be found where part or all of the players change their choices periodically.

Distinct intensity of 10-30-day intraseasonal waves over the North Pacific between early and late summers

The authors’previous study identified the wave trains of intraseasonal oscillations,which are mainly in the band of 10–30 days,over the North Pacific during summer.The wave trains are zonally oriented and trapped along the upper-tropospheric westerly jet,and accordingly gain energy mainly through baroclinic energy conversion.In this study,the authors investigate the distinct features of the wave trains between early summer(1 June to 7 July)and late summer(8 July to 31 August),considering that the westerly jet experiences a remarkable subseasonal variation over the North Pacific during summer—that is,the jet is much stronger in early summer than late summer.The results indicate that the wave trains are stronger in early summer compared with late summer.Further analysis suggests that,in early summer,the wave trains can obtain energy more efficiently from the basic flow;or more exactly,stronger westerlies through baroclinic energy conversion.

Analytic Expansion for Ground-State Wavefunction of Time-Dependent Strong-Coupling Schrodinger Equation

The new method proposed recently by Friedberg, Lee, and Zhao is extended to obtain an analytic expansion for the ground-state wavefunction of a time-dependent strong-coupling Schroedinger equation. Two different types of the time-dependent harmonic oscillators are considered as examples for application of the time-dependent expansion. It is show that the time-dependent strong-coupling expansion is applicable to the time-dependent harmonic oscillators with a slowly varying time-dependent parameter.