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 a...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.展开更多
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 decom...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.展开更多
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 converg...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.展开更多
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 e...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.展开更多
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 ...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.展开更多
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 linea...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.展开更多
Based on the ERA5 reanalysis datasets during 1980-2019,a total of eleven zonal shear lines(ZSLs)that caused heavy precipitation and lasted more than 60 hours over the Tibetan Plateau in summer are selected for composi...Based on the ERA5 reanalysis datasets during 1980-2019,a total of eleven zonal shear lines(ZSLs)that caused heavy precipitation and lasted more than 60 hours over the Tibetan Plateau in summer are selected for composite analysis.By decomposing the kinetic energy(K)near the ZSL into divergent and rotational kinetic energies(K_(D)and K_(R))and the kinetic energy of interaction between the divergent wind and the rotational wind(K_(R)D),the influence of the rotational and divergent winds on the evolution of the ZSL intensity is investigated from the perspective of K_(D)and K_(R).The main results are as follows.The ZSL is a comprehensive reflection of rotation and convergence.The intensity evolution of ZSL is essentially synchronized with those of K,K_(R),and K_(RD)but lags behind K_(D)by about three hours.The enhancement of K is mainly contributed by K_(R),which is governed by the conversion from K_(D)to K_(R).Furthermore,the increase in the conversion from K_(D)to K_(R)is controlled by the geostrophic effect term Af,which is determined by the joint enhancement of the zonal rotational and meridional divergent wind components(u_(R)and v_(D)).Therefore,the joint enhancement of u_(R)and v_(D)controls the increase of the ZSL intensity,leading to increased precipitation.展开更多
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 stud...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.展开更多
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 inte...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.展开更多
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 tha...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.展开更多
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 ...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.展开更多
The interannual variability of tropical zonal wind and the relationship between ENSO and the Asian / Australian monsoon in different phases are discussed. Results show that the tropical zonal wind strongly couples wit...The interannual variability of tropical zonal wind and the relationship between ENSO and the Asian / Australian monsoon in different phases are discussed. Results show that the tropical zonal wind strongly couples with the central-eastern Pacific SST on a quasi-four-year scale. During the period of El Nino, the East Asian winter (summer) monsoon is weaker (stronger) and the South Asian summer monsoon is weaker than normal. Conversely, the East Asian winter (summer) monsoon is stronger (weaker) and the South Asian summer monsoon is stronger than normal during the period of La Niña. The anomalous northerly over East Asia induces an anomalous westerly over the western equatorial Pacific, which favors the appearance of positive SST anomalies in the central-eastern Pacific. The development of El Niño requires the persistence of a westerly over the central-eastern Pacific. The convergence between anomalous northerlies from the central North Pacific (not from the East Asian continent) and anomalous southerlies from Northeast Australia favors the persistence of a westerly over the central-eastern Pacific. In particular, the anomalous southerlies from Northeast Australia play a key role in the onset of strong westerly anomalies over the tropical central-eastern Pacific.展开更多
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 al...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.展开更多
The quasi-biennial oscillation(QBO),a dominant mode of the equatorial stratospheric(~100–1 hPa)variability,is known to impact tropospheric circulation in the middle and high latitudes.Yet,its realistic simulation in ...The quasi-biennial oscillation(QBO),a dominant mode of the equatorial stratospheric(~100–1 hPa)variability,is known to impact tropospheric circulation in the middle and high latitudes.Yet,its realistic simulation in general circulation models remains a challenge.The authors examine the simulated QBO in the 69-layer version of the Institute of Atmospheric Physics Atmospheric General Circulation Model(IAP-AGCML69)and analyze its momentum budget.The authors find that the QBO is primarily caused by parameterized gravity-wave forcing due to tropospheric convection,but the downward propagation of the momentum source is significantly offset by the upward advection of zonal wind by the equatorial upwelling in the stratosphere.Resolved-scale waves act as a positive contribution to the total zonal wind tendency of the QBO over the equator with comparable magnitude to the gravity-wave forcing in the upper stratosphere.Results provide insights into the mechanism of the QBO and possible causes of differences in models.展开更多
The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocea...The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocean（SPO） in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.展开更多
The present work reports the development of nonlinear time series prediction method of genetic algorithm（GA） with singular spectrum analysis（SSA） for forecasting the surface wind of a point station in the South Ch...The present work reports the development of nonlinear time series prediction method of genetic algorithm（GA） with singular spectrum analysis（SSA） for forecasting the surface wind of a point station in the South China Sea（SCS） with scatterometer observations.Before the nonlinear technique GA is used for forecasting the time series of surface wind,the SSA is applied to reduce the noise.The surface wind speed and surface wind components from scatterometer observations at three locations in the SCS have been used to develop and test the technique.The predictions have been compared with persistence forecasts in terms of root mean square error.The predicted surface wind with GA and SSA made up to four days（longer for some point station） in advance have been found to be significantly superior to those made by persistence model.This method can serve as a cost-effective alternate prediction technique for forecasting surface wind of a point station in the SCS basin.展开更多
Tropical Cyclones (TCs) are among the atmospheric events which may trigger/enhance the occurrence of disasters to the society in most world basins including <span style="font-family:Verdana;">the </...Tropical Cyclones (TCs) are among the atmospheric events which may trigger/enhance the occurrence of disasters to the society in most world basins including <span style="font-family:Verdana;">the </span><span style="font-family:;" "=""><span style="font-family:Verdana;">Southwestern Indian Ocean (SWIO). This study analyzed the dynamics and the impacts of the Tropical Cyclone (TC) Idai (4</span><sup><span style="font-family:Verdana;">th</span></sup><span style="font-family:Verdana;">-21</span><sup><span style="font-family:Verdana;">st</span></sup><span style="font-family:Verdana;"> March, 2019) which devastated most of the SWIO countries. The study used the Reanalysis 1 products of daily zonal (u) and meridional (v) winds, Sea Surface Temperatures (SSTs), amount of Precipitable Water (PRW), </span></span><span style="font-family:Verdana;">and relative humidity</span><span style="font-family:Verdana;"> (Rh). The dynamics and movements of Idai w</span><span style="font-family:Verdana;">ere</span><span style="font-family:Verdana;"> analyzed using the wind circulation at 850, 700, 500 and 200 mb, where the TC dynamic variables like vertical wind shear, vorticity, and the mean zonal wind were calculated using u and v components. Using the open Grid Analysis and Display System (GrADS) software the data was processed into three</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">time epochs of pre, during and post;and then analyzed to feature the state of the atmosphere before (pre), during and post TC Idai using all datasets. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">amount of precipitable water was used to map the rainfall on pre, during, and post Idai as well as during its landfall. The results revealed that dynamics of TC Idai was intensifying the weather (over Mozambique) and clearing the weather equatorward or southward of 12<span style="white-space:nowrap;">°</span>S, with low vertical wind shear over the landfall areas (</span><span style="white-space:nowrap;font-family:Verdana;">-</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">3 to 3 m/s) and higher shear values (10 - 40 m/s) northward and southward of the Mozambican channel. Higher moisture content (80 - 90%) and higher PRW (40 - 60 mm/day) mapped during Idai over the lowland areas of Mozambique propagating westward. Higher low</span></span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">level vorticity values were also mapped over the landfall areas. More results revealed that countries laying equatorward of 12<span style="white-space:nowrap;">°</span>S</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> e.g.</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the northern coastal areas of Kenya (Turkana and Baringo) and Tanzania, Idai disrupted the 2019 March to May (MAM) seasonal rainfall by inducing long dry spell which accelerated the famine over the northeastern Kenya (Turkana). Moreover, results revealed that the land falling of Idai triggered intensive flooding which affected </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">wide spectrum of socio</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">economic livelihoods including significant loss of lives, injuries, loss of material wealth, infrastructure;indeed, people were forced to le</span><span style="font-family:Verdana;">ave</span><span style="font-family:Verdana;"> their houses for quite </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">longtime;water</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">born</span><span style="font-family:Verdana;">e</span><span style="font-family:Verdana;"> diseases like malaria, cholera among others were experienced. Furthermore, results and reports revealed that </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">large amount of funds were raised to combat the impacts of Idai. For instance, USAID/OFDA used about $14,146,651 for human aid and treatment of flood</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">prone diseases like Cholera in Mozambique ($13,296,651), Zimbabwe ($100,000), and Malawi ($280,000), respectively. Also a death toll of about 602 in Mozambique and 344 in Zimbabwe, and more than 2500 cases of injured people were reported</span><span style="font-family:Verdana;">.</span><span style="font-family:Verdana;"> Conclusively the study has shown that TCs including Idai and other are among the deadliest natural phenomenon which great affects the human and his environments, thus extensive studies on TCs frequency, strength, tracks as well </span><span style="font-family:Verdana;">as </span><span style="font-family:Verdana;">their coast benefit analysis should be conducted to reduce the societal impacts of these TCs.</span>展开更多
The Cape Verde archipelago is located between 14。N - 18。N and 22。W - 28。W in the Atlantic Ocean. Previous studies associated Cape Verde’s rainfall regime with ITCZ and African squall lines. This hypothesis is rev...The Cape Verde archipelago is located between 14。N - 18。N and 22。W - 28。W in the Atlantic Ocean. Previous studies associated Cape Verde’s rainfall regime with ITCZ and African squall lines. This hypothesis is revisited here using rainfall time series?of the 4 Santiago Island station network of Cape Verde National Institute of Meteorology and Geophysics. Rainfall monthly totals are standardized to produce indices in the 1981-2009 period. Time section plots of zonal and meridional wind components anomalies are made using reanalysis data from ESRL/PSD/NOAA website. Daily outgoing long wave radiation and sea level pressure time section plots are also made as proxies for weather systems propagation. Results show that Santiago presents a seasonal rainfall regime characterized by dry (November-June) and wet (July-October) seasons, with short transition period. In general, rainfall totals increase with altitude. Weather systems within a wet year rainy season were associated with positive anomalies of zonal and meridional wind components of relative short duration, while negative anomalies dominated in dry years. These results suggest that winds coming from southwestern quadrant over warm Atlantic Ocean, associated with frontal systems traveling eastward, are the rain-producing events in wet years, not ITCZ or African squall lines. Winds coming from the northeastern quadrant produce dry years. Apparently, decadal-long wet periods are related to PDO cold phase. In the current PDO cold phase, there is only one year (2002) slightly dry. Considering that each PDO phases lasts 25 to 30 years and the current PDO cold phase started in 1999, it is possible that wet years predominate in the next 10 to 15 years.展开更多
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 z...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.展开更多
基金Supported by Key Project of International Co-operative Department, Ministry of Science and Technology, PRC (No. 2002CB714001)Key Project of National Natural Science Foundation of China (No. 90411013)Open Fund of State Key Laboratory of Satellite Ocean Environment Dynamics (Second Institute of Oceanography, State Oceanic Administration. (No. 2004010).
文摘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.
基金Supported by the National Natural Science Foundation of China(Nos.41076010,41206017)the National Basic Research Program of China(973 Program)(No.2012CB417402)
文摘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.
基金The National Basic Research Program(973 Program)of China under contract No.2012CB417402the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11010102
文摘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.
基金This work was supported by the National Natural Science Foundation of China(Grant No:41776031)the National Key Research and Development Program of China(Grant 2018YFC1506903)+1 种基金the team project funding of scientific research innovation for universities in Guangdong province(Grant 2019KCXTF021)the program for scientific research start-up funds of Guangdong Ocean University(Grant R17051).
文摘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.
基金supported financially by the National Basic Research Program of China[grant number 2014CB953902]the National Natural Science Foundation of China[grant numbers 41275001 and 41475074]
文摘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.
基金supported by the Special Fund for Meteorological Research in the Public Interest[grant number GYHY201206041]the projects entitled‘Comprehensive Evaluation of Polar Areas in Global and Regional Climate Changes’[grant number CHINARE2015–2019]‘Polar Environment Comprehensive Investigation and Assessment’[grant number CHINARE2015–2019]
文摘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.
基金the Key Program of the National Science Foundation of China(Grant No.42030611)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0105)+1 种基金the Integration Project of Major Research Program of the National Natural Science Foundation of China(Grant No.91937301)the General Program of the National Science Foundation of China(Grant No.42175008).
文摘Based on the ERA5 reanalysis datasets during 1980-2019,a total of eleven zonal shear lines(ZSLs)that caused heavy precipitation and lasted more than 60 hours over the Tibetan Plateau in summer are selected for composite analysis.By decomposing the kinetic energy(K)near the ZSL into divergent and rotational kinetic energies(K_(D)and K_(R))and the kinetic energy of interaction between the divergent wind and the rotational wind(K_(R)D),the influence of the rotational and divergent winds on the evolution of the ZSL intensity is investigated from the perspective of K_(D)and K_(R).The main results are as follows.The ZSL is a comprehensive reflection of rotation and convergence.The intensity evolution of ZSL is essentially synchronized with those of K,K_(R),and K_(RD)but lags behind K_(D)by about three hours.The enhancement of K is mainly contributed by K_(R),which is governed by the conversion from K_(D)to K_(R).Furthermore,the increase in the conversion from K_(D)to K_(R)is controlled by the geostrophic effect term Af,which is determined by the joint enhancement of the zonal rotational and meridional divergent wind components(u_(R)and v_(D)).Therefore,the joint enhancement of u_(R)and v_(D)controls the increase of the ZSL intensity,leading to increased precipitation.
基金sponsored by the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)the National Basic Research Program of China (973 Program,Grant No. 2010CB950401)+1 种基金the National Nature Science Foundation of China (Grant Nos. U0833602 and 40805023)the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Free Exploration Fund
文摘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.
基金supported by the National Natural Science Foundation of China[grant number 41530426]
文摘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.
基金Research on predictive signals and methods for short-short climate of annual frequency oftyphoons, a project from the research fund on typhoons of 2003 – 2004 at Shanghai Typhoon Institute
文摘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.
基金This study was jointly supported by the Chinese Academy of Sciences Key Program under Grant No.KZCX3-SW-221the National Natural Science Foundation of China under contract 40125014.
文摘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.
基金Acknowledgments. The work was supported by the National Natural Science Foundation of China under GrantNo.49775270.
文摘The interannual variability of tropical zonal wind and the relationship between ENSO and the Asian / Australian monsoon in different phases are discussed. Results show that the tropical zonal wind strongly couples with the central-eastern Pacific SST on a quasi-four-year scale. During the period of El Nino, the East Asian winter (summer) monsoon is weaker (stronger) and the South Asian summer monsoon is weaker than normal. Conversely, the East Asian winter (summer) monsoon is stronger (weaker) and the South Asian summer monsoon is stronger than normal during the period of La Niña. The anomalous northerly over East Asia induces an anomalous westerly over the western equatorial Pacific, which favors the appearance of positive SST anomalies in the central-eastern Pacific. The development of El Niño requires the persistence of a westerly over the central-eastern Pacific. The convergence between anomalous northerlies from the central North Pacific (not from the East Asian continent) and anomalous southerlies from Northeast Australia favors the persistence of a westerly over the central-eastern Pacific. In particular, the anomalous southerlies from Northeast Australia play a key role in the onset of strong westerly anomalies over the tropical central-eastern Pacific.
基金This work was supported by the National Natural Science Foundation of China[grant numbers 42130504 and 41721004].
文摘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.
基金This research was supported by the National Major Research High Performance Computing Program of China[grant number 2016YFB0200800]the National Natural Science Foundation of China[grant numbers 41630530 and 41706036]the National Key Scientific and Technological Infrastructure project“Earth System Science Numerical Simulator Facility”(EarthLab).
文摘The quasi-biennial oscillation(QBO),a dominant mode of the equatorial stratospheric(~100–1 hPa)variability,is known to impact tropospheric circulation in the middle and high latitudes.Yet,its realistic simulation in general circulation models remains a challenge.The authors examine the simulated QBO in the 69-layer version of the Institute of Atmospheric Physics Atmospheric General Circulation Model(IAP-AGCML69)and analyze its momentum budget.The authors find that the QBO is primarily caused by parameterized gravity-wave forcing due to tropospheric convection,but the downward propagation of the momentum source is significantly offset by the upward advection of zonal wind by the equatorial upwelling in the stratosphere.Resolved-scale waves act as a positive contribution to the total zonal wind tendency of the QBO over the equator with comparable magnitude to the gravity-wave forcing in the upper stratosphere.Results provide insights into the mechanism of the QBO and possible causes of differences in models.
基金jointly supported by the Special Fund for Public Welfare Industry (meteorology) (Grant No. GYHY201306026)the National Natural Science Foundation of China (Grant Nos. 41421004 and 41522503)
文摘The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocean（SPO） in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.41230421 and 41605075)the National Basic Research Program of China(Grant No.2013CB430101)
文摘The present work reports the development of nonlinear time series prediction method of genetic algorithm（GA） with singular spectrum analysis（SSA） for forecasting the surface wind of a point station in the South China Sea（SCS） with scatterometer observations.Before the nonlinear technique GA is used for forecasting the time series of surface wind,the SSA is applied to reduce the noise.The surface wind speed and surface wind components from scatterometer observations at three locations in the SCS have been used to develop and test the technique.The predictions have been compared with persistence forecasts in terms of root mean square error.The predicted surface wind with GA and SSA made up to four days（longer for some point station） in advance have been found to be significantly superior to those made by persistence model.This method can serve as a cost-effective alternate prediction technique for forecasting surface wind of a point station in the SCS basin.
文摘Tropical Cyclones (TCs) are among the atmospheric events which may trigger/enhance the occurrence of disasters to the society in most world basins including <span style="font-family:Verdana;">the </span><span style="font-family:;" "=""><span style="font-family:Verdana;">Southwestern Indian Ocean (SWIO). This study analyzed the dynamics and the impacts of the Tropical Cyclone (TC) Idai (4</span><sup><span style="font-family:Verdana;">th</span></sup><span style="font-family:Verdana;">-21</span><sup><span style="font-family:Verdana;">st</span></sup><span style="font-family:Verdana;"> March, 2019) which devastated most of the SWIO countries. The study used the Reanalysis 1 products of daily zonal (u) and meridional (v) winds, Sea Surface Temperatures (SSTs), amount of Precipitable Water (PRW), </span></span><span style="font-family:Verdana;">and relative humidity</span><span style="font-family:Verdana;"> (Rh). The dynamics and movements of Idai w</span><span style="font-family:Verdana;">ere</span><span style="font-family:Verdana;"> analyzed using the wind circulation at 850, 700, 500 and 200 mb, where the TC dynamic variables like vertical wind shear, vorticity, and the mean zonal wind were calculated using u and v components. Using the open Grid Analysis and Display System (GrADS) software the data was processed into three</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">time epochs of pre, during and post;and then analyzed to feature the state of the atmosphere before (pre), during and post TC Idai using all datasets. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">amount of precipitable water was used to map the rainfall on pre, during, and post Idai as well as during its landfall. The results revealed that dynamics of TC Idai was intensifying the weather (over Mozambique) and clearing the weather equatorward or southward of 12<span style="white-space:nowrap;">°</span>S, with low vertical wind shear over the landfall areas (</span><span style="white-space:nowrap;font-family:Verdana;">-</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">3 to 3 m/s) and higher shear values (10 - 40 m/s) northward and southward of the Mozambican channel. Higher moisture content (80 - 90%) and higher PRW (40 - 60 mm/day) mapped during Idai over the lowland areas of Mozambique propagating westward. Higher low</span></span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">level vorticity values were also mapped over the landfall areas. More results revealed that countries laying equatorward of 12<span style="white-space:nowrap;">°</span>S</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> e.g.</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the northern coastal areas of Kenya (Turkana and Baringo) and Tanzania, Idai disrupted the 2019 March to May (MAM) seasonal rainfall by inducing long dry spell which accelerated the famine over the northeastern Kenya (Turkana). Moreover, results revealed that the land falling of Idai triggered intensive flooding which affected </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">wide spectrum of socio</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">economic livelihoods including significant loss of lives, injuries, loss of material wealth, infrastructure;indeed, people were forced to le</span><span style="font-family:Verdana;">ave</span><span style="font-family:Verdana;"> their houses for quite </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">longtime;water</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">born</span><span style="font-family:Verdana;">e</span><span style="font-family:Verdana;"> diseases like malaria, cholera among others were experienced. Furthermore, results and reports revealed that </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">large amount of funds were raised to combat the impacts of Idai. For instance, USAID/OFDA used about $14,146,651 for human aid and treatment of flood</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">prone diseases like Cholera in Mozambique ($13,296,651), Zimbabwe ($100,000), and Malawi ($280,000), respectively. Also a death toll of about 602 in Mozambique and 344 in Zimbabwe, and more than 2500 cases of injured people were reported</span><span style="font-family:Verdana;">.</span><span style="font-family:Verdana;"> Conclusively the study has shown that TCs including Idai and other are among the deadliest natural phenomenon which great affects the human and his environments, thus extensive studies on TCs frequency, strength, tracks as well </span><span style="font-family:Verdana;">as </span><span style="font-family:Verdana;">their coast benefit analysis should be conducted to reduce the societal impacts of these TCs.</span>
基金Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior—CAPES for the financial support.
文摘The Cape Verde archipelago is located between 14。N - 18。N and 22。W - 28。W in the Atlantic Ocean. Previous studies associated Cape Verde’s rainfall regime with ITCZ and African squall lines. This hypothesis is revisited here using rainfall time series?of the 4 Santiago Island station network of Cape Verde National Institute of Meteorology and Geophysics. Rainfall monthly totals are standardized to produce indices in the 1981-2009 period. Time section plots of zonal and meridional wind components anomalies are made using reanalysis data from ESRL/PSD/NOAA website. Daily outgoing long wave radiation and sea level pressure time section plots are also made as proxies for weather systems propagation. Results show that Santiago presents a seasonal rainfall regime characterized by dry (November-June) and wet (July-October) seasons, with short transition period. In general, rainfall totals increase with altitude. Weather systems within a wet year rainy season were associated with positive anomalies of zonal and meridional wind components of relative short duration, while negative anomalies dominated in dry years. These results suggest that winds coming from southwestern quadrant over warm Atlantic Ocean, associated with frontal systems traveling eastward, are the rain-producing events in wet years, not ITCZ or African squall lines. Winds coming from the northeastern quadrant produce dry years. Apparently, decadal-long wet periods are related to PDO cold phase. In the current PDO cold phase, there is only one year (2002) slightly dry. Considering that each PDO phases lasts 25 to 30 years and the current PDO cold phase started in 1999, it is possible that wet years predominate in the next 10 to 15 years.
基金supported by the National Natural Science Foundation of China(Grant Nos.41274153&41331069)the National Important Basic Research Project of China(Grant No.2011CB811405)+2 种基金the Chinese Academy of Sciences(Grant No.KZZD-EW-01-2)supported by the Specialized Research Fund for State Key Laboratoriesperformed by Numerical Forecast Modelling R&D and VR System of State Key Lab.of Space Weather and Special HPC work stand of Chinese Meridian Project
文摘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.
