Recent Enhancement in Co-Variability of the Western North Pacific Summer Monsoon and the Equatorial Zonal Wind

The western North Pacific summer monsoon(WNPSM)is an important subcomponent of the Asian summer monsoon.The equatorial zonal wind(EZW)in the lower troposphere over the western Pacific may play a critical role in the evolution of the El Niño-Southern Oscillation(ENSO).The possible linkage between the EZW over the western Pacific and the offequatorial monsoonal winds associated with the WNPSM and its decadal changes have not yet been fully understood.Here,we find a non-stationary relationship between the WNPSM and the western Pacific EZW,significantly strengthening their correlation around the late 1980s/early 1990s.This observed shift in the WNPSM–EZW relationship could be explained by the changes in the related sea surface temperature(SST)configurations across the tropical oceans.The enhanced influence from the springtime tropical North Atlantic,summertime tropical central Pacific,and maritime continent SST anomalies may be working together in contributing to the recent intensified WNPSM–EZW co-variability.The observed recent strengthening of the WNPSM–EZW relationship may profoundly impact the climate system,including prompting more effective feedback from the WNPSM on subsequent ENSO evolution and bolstering a stronger biennial tendency of the WNPSM–ENSO coupled system.The results obtained herein imply that the WNPSM,EZW,ENSO,and the tropical North Atlantic SST may be closely linked within a unified climate system with a quasi-biennial rhythm occurring during recent decades,accompanied by a reinforcement of the WNPSM–ENSO interplay quite possibly triggered by enhanced tropical Pacific–Atlantic cross-basin interactions.These results highlight the importance of the tropical Atlantic cross-basin influences in shaping the spatial structure of WNPSM-related wind anomalies and the WNPSM–ENSO interaction.

Zonal displacement of western Pacific warm pool and zonal wind anomaly over the Pacific Ocean

The thermal condition anomaly of the western Pacific warm pool and its zonal displacement have very important influences on climate change in East Asia and even the whole world. However, the impact of the zonal wind anomaly over the Pacific Ocean on zonal displacement of the warm pool has not yet been analyzed based on long-term record. Therefore, it is important to study the zonal displacement of the warm pool and its response to the zonal wind anomaly over the equatorial Pacific Ocean. Based on the NCDC monthly averaged SST (sea surface temperature) data in 2°×2° grid in the Pacific Ocean from 1950 to 2000, and the NCEP/NCAR global monthly averaged 850 hPa zonal wind data from 1949 to 2000, the relationships between zonal displacements of the western Pacific warm pool and zonal wind anomalies over the tropical Pacific Ocean are analyzed in this paper. The results show that the zonal displacements are closely related to the zonal wind anomalies over the western, central and eastern equatorial Pacific Ocean. Composite analysis indicates that during ENSO events, the warm pool displacement was trigged by the zonal wind anomalies over the western equatorial Pacific Ocean in early stage and the process proceeded under the zonal wind anomalies over the central and eastern equatorial Pacific Ocean unless the wind direction changes. Therefore, in addition to the zonal wind anomaly over the western Pacific, the zonal wind anomalies over the central and eastern Pacific Ocean should be considered also in investigation the dynamical mechanisms of the zonal displacement of the warm pool.

Impact of the central Pacific zonal wind divergence and convergence on the central Pacific El Nio event

The central Pacific（CP） zonal wind divergence and convergence indices are defined, and the forming mechanism of CP El Nio（La Nia） events is discussed preliminarily. The results show that the divergence and convergence of the zonal wind anomaly（ZWA） are the key process in the forming of CP El Nio（La Nia） events. A correlation analysis between the central Pacific zonal wind divergence and convergence indices and central Pacific El Nio indices indicates that there is a remarkable lag correlation between them. The central Pacific zonal wind divergence and convergence indices can be used to predict the CP events. Based on these results, a linear regression equation is obtained to predict the CP El Nio（La Nia） events 5 months ahead.

Effect of the westward-propagating zonal wind anomaly on the initial development of quasi-biweekly oscillation over the South China Sea during early summer

The characteristics of quasi-biweekly oscillation（QBWO） over the South China Sea during early summer are investigated.Composite results demonstrate that QBWO convection and the meridional wind anomaly exhibit local variation,while the zonal wind anomaly displays zonal propagation.Besides,emergence of the zonal wind anomaly precedes the enhancement of QBWO convection,suggesting the zonally propagating zonal wind anomaly may play a key role in initiating the development of QBWO convection.Diagnostics of the convergence of moisture flux and divergence tendency indicate that QBWO convection is primarily modulated by eddy divergence.Among the contributing factors in the divergence tendency,the β effect associated with the zonally-propagating zonal wind anomaly makes an appropriate phase difference with the eddy divergence,which can contribute to the convergence tendency in the initial stage of QBWO.As a result,QBWO convection and the meridional wind anomaly are enhanced,thus facilitating the initial development of QBWO convection over the SCS during early summer.

Distribution of the tropical Pacific surface zonal wind anomaly and its relation with two types of El Nio

E1 Nino events with an eastern Pacific pattern （EP） and central Pacific pattern （CP） were first separated using rotated empirical orthogonal functions （REOF）. Lead/lag regression and rotated singular value decomposition （RSVD） analyses were then carried out to study the relation between the surface zonal wind （SZW） anomalies and sea surface temperature （SST） anomalies in the tropical Pacific. A possible physical process for the CP E1 Nifio was proposed. For the EP E1 Nino, strong westerly anomalies that spread eastward continuously produce an anomalous ocean zonal convergence zone （ZCZ） centered on about 165°W. This SZW anomaly pattern favors poleward and eastward Sverdrup transport at the equator. For the CP E1Nino, westerly anomalies and the ZCZ are mainly confined to the western Pacific, and easterly anomalies blow in the eastern Pacific. This SZW anomaly pattern restrains poleward and eastward Sverdrup transport at the equator; however, there is an eastward Sverdrup transport at about 5°N, which favors the wanning of the north-eastern tropical Pacific. It is found that the slowness of eastward propagation of subsurface warm water （partly from the downwelling caused by Ekman convergence and the ZCZ） is due to the slowdown of the undercurrent in the central basin, and vertical advection in the central Pacific may be important in the formation and disappearance of the CP E1 Nifio.

Quasi-biennial oscillation signal detected in the stratospheric zonal wind at 55–65°N

To investigate the impacts of the quasi-biennial oscillation （QBO） on high-latitude circulation and the Arctic vortex, stratospheric zonal wind at 55-65°N is analyzed. The seasonal cycle, solar cycle, and linear trend in the zonal wind at these latitudes are analyzed and removed, and the QBO signal is retrieved from the monthly zonal wind for the period 1979-2014. The zonal wind has a strong decreasing trend in winter, with a maximum decrease （less than -0.35 m s-1 yr-1） occurring within 70-100°E. The zonal wind has an in-phase response of 1.6 m s-1 to the solar cycle, with a maximum within 100-140°E. A clear QBO signal is detected in the zonal wind during the period 1979-2014, with an amplitude of 2.5 m s-1 and a period of 30 months. The latitudinal distribution of the QBO signal is inhomogeneous, with a maximum within 120-180°E and a minimum within 25-45°E.

Evaluation of the zonal wind stress response to SST in the CMIP5 AMIP simulations

Zonal wind stress plays an important role in the evolution of El Ni（n）o-Southern Oscillation （ENSO） events;however,a comprehensive comparison and analysis in terms of model performance and related bias in the interannual variability of zonal wind stress across the tropical Pacific has yet to be performed.In this study,the authors evaluate how well the individual atmospheric models participating in phase 5 of the Coupled Model Intercomparison Project simulate zonal wind stress.It is found that the wind stress anomalies simulated by the multi-model ensemble are weaker than those in the observation in both El Ni（n）o and La Ni（n）a events,with a larger bias in the former.Further analysis indicates that the bias associated with El Ni（n）o events may be mainly attributable to the weaker negative precipitation anomalies in the AMIP simulations,compared with observations,over the eastern Indian Ocean.Through the Gill-like responses in atmospheric circulation,the rainfall bias over the eastern Indian Ocean results in an easterly wind stress anomaly in the western and central equatorial Pacific,which to some extent offsets the westerly wind stress anomalies associated with El Ni（n）o events.Consequently,the responses of zonal wind stress anomalies to warm SST anomalies are much underestimated in AMIP simulations during El Niffo events.

RELATIONSHIPS BETWEEN ZONAL WIND ANOMALIES IN HIGH AND LOW TROPOSPHERE AND ANNUAL FREQUENCY OF NW PACIFIC TROPICAL CYCLONES

Relationships between large-scale zonal wind anomalies and annual frequency of NW Pacific tropical cyclones and possible mechanisms are investigated with the methods of correlation and composition. It is indicated that when A U2oo- A U850 〉0 in the eastern tropical Pacific and A U2oo- A U850 〈0 in western tropical Pacific, the Walker cell is stronger in the Pacific tropical region and the annual frequency of NW Pacific tropical cyclone are above normal. In the years with zonal wind anomalies, the circulation of high and low troposphere and the vertical motions in the troposphere have significant characteristics. In the time scale of short-range climate prediction, zonal wind anomalies in high and low troposphere are useful as a preliminary signal of the annual frequency prediction of NW Pacific tropical cyclones.

Variation of Zonal Winds in the Upper Troposphere and Lower Stratosphere in Association with Deficient and Excess Indian Summer Monsoon Scenario

The Indian summer monsoon is one of the most dominant tropical circulation systems in the general circulation of the atmosphere. The country receives more than 80% of the annual rainfall during a short span of four months (June to September) of the southwest monsoon season. Variability in the quantum of rainfall during the monsoon season has profound impacts on water resources, power generation, agriculture, economics and ecosystems in the country. The inter annual variability of Indian Summer Monsoon Rainfall (ISMR) depends on atmospheric and oceanic conditions prevailed during the season. In this study we have made an attempt to understand the variation of the of zonal winds in the tropical Upper Troposphere and Lower Stratosphere (UT/LS) region during deficient and Excess rainfall years of Indian summer monsoon and its relation to Indian Summer Monsoon Rainfall (ISMR). It is found that in the equatorial Upper Troposphere zonal winds have westerly anomalies during deficient rainfall year’s and easterly anomaly during excess rainfall years of Indian summer monsoon and opposite zonal wind anomaly is noted in the equatorial Lower Stratosphere during the deficient and excess rainfall years of Indian summer monsoon. It is also found that the June to September upper troposphere zonal winds averaged between 15°N and 15°S latitudes have a long-term trend during 1960 to 1998. Over this period the tropical easterlies and the tropical jet stream have weakened with time.

An Idealized Numerical Study of the Effects of Uniform Zonal Winds on Tropical Cyclogenesis

The effect of uniform zonal winds on tropical cyclone(TC)genesis is examined on a beta plane using an idealized mesoscale model.The simulation results show that uniform easterly and westerly flows are both favorable for TC genesis.However,uniform easterly flows result in a faster TC genesis rate compared with uniform westerly flows.It is found that faster TC genesis is associated with greater surface heat fluxes and convection during the early stage.The superposition of uniform easterly flows and the beta effect results in greater surface heat fluxes and convection around the TC center compared with uniform westerly flows.Meanwhile,TC genesis is closely associated with the size and intensity of a mid-level circulation.The joint greater convection induced by the easterly flows and beta effect results in enhancement of the vertical temperature gradient,which is associated with the intensification of mid-level circulation.The strong and compact mid-level circulation is more favorable for efficient conversion of latent heat energy to the kinetic energy of the lower-level cyclonic winds.Thus,uniform easterly flows are more favorable for TC genesis than uniform westerly flows.

Possible modulation of migrating diurnal tide by latitudinal gradient of zonal wind observed by SABER/TIMED

Temperature data from SABER/TIMED and Empirical Orthogonal Function （EOF） analysis are taken to examine possible modulations of the temperature migrating diurnal tide （DW1） by latitudinal gradients of zonal mean zonal wind （ ζ ）. The result shows that ζ increases with altitudes and displays clearly seasonal and interannual variability. In the upper meso- sphere and lower thermosphere （MLT）, at the latitudes between 20°N and 20°S, when ζ strengthens （weakens） at equinoxes （solstices） the DW1 amplitude increases （decreases） simultaneously. Stronger maximum in March-April equinox occurs in both ζ and the DW1 amplitude. Besides, a quasi-biennial oscillation of DW1 is also found to be synchronous with ζ. The resembling spatial-temporal features suggest that ζ in the upper tropic MLT probably plays an important role in modulating semiannual, annual, and quasi-biennial oscillations in DW1 at the same latitude and altitude. In addition, ζ in the meso- sphere possibly affects the propagation of DW1 and produces SAO of DW1 in the lower thermosphere. Thus, SAO of DW1 in the upper MLT may be a combined effect of ζ both in the mesosphere and in the upper MLT, which models studies should determine in the future.

Structure of the Indian Ocean Meridional Overturning Circulation and its relationship with the zonal wind stress

We studied the structure of the Indian Ocean(IO)Meridional Overturning Circulation(MOC)by applying a nonlinear inertia theory and analyzed the coupled relationship between zonal wind stress and MOC anomalies.Our results show that the inertia theory can represent the main characteristics of the IO MOC:the subtropical cell(STC)and cross-equator cell(CEC).The stream function in equatorial and northern IO changes a sign from winter to summer.The anomalies of the zonal wind stress and stream function can be decomposed into summer monsoon mode,winter monsoon mode,and abnormal mode by using the singular vector decomposition(SVD)analysis.The first two modes correlate with the transport through 20°S and equator simultaneously whereas the relationship obscures between the third mode and transports across 20°S and equator,showing the complex air-sea interaction process.The transport experiences multi-time scale variability according to the continuous power spectrum analysis,with major periods in inter-annual and decadal scale.

Southern Hemisphere mean zonal wind in upper troposphere and East Asian summer monsoon circulation

Rlationship between the Southern Hemisphere upper troposphere zonal wind variability and the East Asian summer monsoon was studied. The mean zonal wind difference in 150 hPa between 60°S and 30°S is defined as an index (ISH). The re- search reveals that ISH is negatively correlated with the East Asian summer monsoon (EASM) circulation in the interannual scale. It is also suggested that the meridional teleconnection in the zonal wind field, with the main part in Eastern Hemisphere, from mid-and- high latitudes in the Southern Hemisphere to the tropical region is responsible for the ISH-EASM link- age. The teleconnection may result in changes of the wind fields and pressure system changes causing variability of the East Asian monsoon. In addition, the anomalous teleconnection pattern in Eurasia is likely to be another mechanism. ISH and EASM circulation are found to have both simultaneous and lag correla- tions, thus, the relationship has implications for sea- sonal climate prediction over East Asia.

Impact of winter thermal condition of the Tibetan Plateau on the zonal wind anomaly over equatorial Pacific

Using the improved CCM1 dynamic climate model, the impact of abnormal heat source and sink over the Tibetan Plateau in winter on the abnormal zonal wind over the Pacific Ocean is studied in this paper. The following new-findings are obtained: (1) When the atmospheric cold source during January-March on the Tibetan Plateau gets intensified, an abnormal anticyclone around the Tibetan Plateau will appear in lower troposphere. Abnormal northerly wind at the coastal area of the mainland of China and an abnormal cyclone will appear on the West Pacific in the following months. Then, abnormal west wind will appear over the equator of the West Pacific and extends to the East Pacific. (2) When the atmospheric cold source during January-March over the Tibetan Plateau is unusually weak, an abnormal cyclone around the Tibetan Plateau will appear at lower levels first, then abnormal anticyclone will appear on the West Pacific and move to the south and result in abnormal easterly wind over the equator of the West Pacific, which will extend to the east. Furthermore, abnormal changes of zonal wind on equatorial Indian Ocean can be caused by the intensity change of atmospheric cold source in winter and early spring over the Tibetan Plateau.

Dynamical impact of anomalous East-Asian winter monsoon on zonal wind over the equatorial western Pacific

Zonal wind anomaly over the equatorial west- ern Pacific plays an important role in the occurrence of ENSO. The mechanism to produce zonal wind anomaly over the equatorial western Pacific is studied in this paper. It is shown clearly that zonal wind anomaly over the equatorial western Pacific is closely related to the anomaly of East- Asian winter monsoon. Anomalous strong (weak) East-Asian winter monsoon can excite not only the westerly (easterly) anomaly over the equatorial western Pacific but also a cyc- lonic (an anticyclonic) circulation over the east of the Philip- pines. The above anomalous circulation results from dy- namical impacts of anomalous pressure pattern due to the East-Asian winter monsoon. Because there is westward (eastward) pressure gradient over the equatorial western Pacific, i.e. there is ?? xp <0(> 0), during strong (weak) East-Asian winter monsoon.

The Relationship between the Meridional Profile of Zonal- mean Geostrophic Wind and Station Wave at 500 hPa

The sea-level pressure (SLP), 500 hPa height, zonal-mean 500 hPa height ([Z(500)]), stationary wave eddy component of the 500 hPa height (Z(500)*) and zonal-mean 500 hPa geostrophic wind [U-g] fields poleward of 20 degreesN are examined for the period 1958-1997, with emphasis on the winter season. The relationships between the Arctic Oscillation (AO)index and algebraic difference of the zonal-mean wind in 55 degreesN and 35 degreesN (Ut) index were investigated, making use the Monte Carlo procedure, Singular Value Decomposition (SVD), Empirical orthogonal function (EOF) and regression method. The leading modes of empirical orthogonal function (EOF's) of SLP are more robust than the 500 hPa height EOF's. not only in the ratio of the two largest eigenvalues, but in more zonally symmetric. Comparing the meridional profiles of zonal-mean wind amplitude associated with the AO and Ut index, the profiles for the two indexes are very similar, both with respect to amplitude and the placement of the maximum and minimum. Comparing the station wave component of 500 hPa height field regressed upon the AO and Ut index. there is one-to-one correspondence between all the major centers of action in the two maps, especially in the North Atlantic and Eurasian continent. The pattern is unlike the prominent teleconnection patterns, they have hemispheric extent and cannot be interpreted in term of the individual wavetrains.

考虑模糊多目标优化的风电场无功电压分区控制

为提升双馈风电场的无功功率补偿和电压稳定能力,提出了一种考虑模糊多目标优化的风电场无功电压分区控制方法。基于有功功率数据对风电场进行分区降维,并计算获得了各分区的无功优化限值;定义了分区无功裕度指标用以描述风电场电压运行的安全裕度,综合考虑运行安全性和稳定性,建立了风电场无功电压的模糊多目标优化模型;提出了一种可大范围全局快速寻优的自适应遗传禁忌算法,通过重新定义交叉与变异概率提升了寻优的全局时效性,通过引入禁忌算法改善了寻优准确性。最后,以某双馈风电场为例进行了仿真验证。结果表明:所提方法能够为风电场预留充足的无功裕度,显著降低系统内部的电压波动。

The Circum-Pacific Teleconnection Pattern in Meridional Wind in the High Troposphere

The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR re-analysis data. The CPTP is found to be composed of the North Pacific-North American teleconnection pattern (PNA), the South Pacific-South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.

Observational Zonal Mean Flow Anomalies:Vacillation or Poleward Propagation?

North-south displacements and meridional vacillations of the eddy-driven jet are widely accepted as the dominant cause of variability of the observational zonal-mean zonal wind anomalies(denoted [u]').In this study,a new idea regarding the primary variability of the observational [u]' in the middle latitude troposphere is presented.It is hypothesized that there are two different classes of primary variability of the observational [u]':the poleward propagation of the [u]'(abbreviated as PP) and meridional vacillations.To validate this hypothesis,one-point correlation maps of [u]' at 200-hPa during the boreal cold season(November-April) of every year from 1957-2002 are used as a criterion.Twelve PP years,in which the PP events are dominant in the variability of [u]',and 15 no_PP years,in which the PP events are recessive and the meridional vacillations are dominant in the variability of [u]',are examined.The results show that the variabilities of [u]' are different in the chosen PP and no_PP years.In the PP years,the PP events dominate the variability of [u]';however,the meridional vacillations are prevalent in the no_PP years.

风电功率预测的新兴技术与发展趋势综述

介绍了风电功率预测技术的新兴技术与发展趋势,分析了分区建模、Koopman算子深度神经网络、DBN与多元线性回归结合等方法;探讨了未来研究的方向,强调了对算法的改进和多领域应用的重要性。