The daily outgoing longwave radiation(OLR)field in boreal summer shows significant power spectrum peaks on quasi-biweekly(10–20-day)and intraseasonal(20–80-day)timescales over the Indo–western Pacific warm pool,esp...The daily outgoing longwave radiation(OLR)field in boreal summer shows significant power spectrum peaks on quasi-biweekly(10–20-day)and intraseasonal(20–80-day)timescales over the Indo–western Pacific warm pool,especially over the South China Sea and Bay of Bengal.The quasi-biweekly oscillation(QBWO)originates from offequatorial western North Pacific,and is characterized by a northwest–southeast oriented wave train pattern,propagating northwestward.The intraseasonal oscillation(ISO),on the other hand,originates from the equatorial Indian Ocean and propagates eastward and northward.Why the equatorial mode possesses a 20–80-day periodicity while the off-equatorial mode favors a 10–20-day periodicity is investigated through idealized numerical experiments with a 2.5-layer atmospheric model.In the off-equatorial region,the model simulates,under a realistic three-dimensional summer mean flow,the most unstable mode that has a wave train pattern with a typical zonal wavelength of 6000 km and a period of 10–20 days,propagating northwestward.This is in contrast to the equatorial region,where a Madden–Julian oscillation(MJO)like mode with a planetary(wavenumber-1)zonal scale and a period ranging from 20 to 80 days is simulated.Sensitivity experiments with different initial conditions indicate that the QBWO is an intrinsic mode of the atmosphere in boreal summer in the off-equatorial Indo–western Pacific region under the summer mean state,while the MJO is the most unstable mode in the equatorial region.展开更多
The atmospheric intraseasonal oscillation(ISO)and its interannual variability are simulated by the atmospheric general circulation model,which was developed at the Institute of Atmospheric Physics.Two numerical experi...The atmospheric intraseasonal oscillation(ISO)and its interannual variability are simulated by the atmospheric general circulation model,which was developed at the Institute of Atmospheric Physics.Two numerical experiments were performed,corresponding to the AMIP-Ⅰ and AMIP-Ⅱ simulations,respectively.The model reasonably reproduces the major aspects of the intraseasonal oscillation,including the propagating property and the seasonal differences in the tropics,the wavenumber structure of ISO in the globe,and the global coincidence in the interannual variation of ISO.Comparison of the results between the two experiments suggests that improvement of the boundary forcing or considering the air-sea interaction may help to improve the simulation on the ISO and its interannual variability.展开更多
The intraseasonal oscillation（ISO） in the South China Sea summer monsoon（SCSSM） and its influence on regionally persistent heavy rain（RPHR） over southern China are examined by using satelhte outgoing long wave r...The intraseasonal oscillation（ISO） in the South China Sea summer monsoon（SCSSM） and its influence on regionally persistent heavy rain（RPHR） over southern China are examined by using satelhte outgoing long wave radiation,NCEP/NCAR reanalysis,and gridded rainfall station data in China from 1981 to 2010.The most important feature of the ISO in SCSSM,contributing to the modulation of RPHR,is found to be the fluctuation in the western Pacific subtropical high（WPSH）,along with a close link to the Madden-Julian oscillation（MJO）.Southern China is divided into three regions by using rotated empirical orthogonal functions（REOFs）for intraseasonal rainfall,where the incidence rate of RPHR is closely linked to the intraseasonal variation in rainfall.It is found that SCSSM ISOs are the key systems controlling the intraseasonal variability in rainfall and can be described by the leading pair of empirical orthogonal functions（EOFs） for the 850-hPa zonal wind over the SCS and southern China.Composite analyses based on the principal components（PCs） of the EOFs indicate that the ISO process in SCSSM exhibits as the east-west oscillation of the WPSH,which is coupled with the northward-propagating MJO,creating alternating dry and wet phases over southern China with a period of 40 days.The wet phases provide stable and lasting circulation conditions that promote RPHR.However,differences in the ISO structures can be found when RPHR occurs in regions where the WPSH assumes different meridional positions.Further examination of the meridional-phase structure suggests an important role of northward-propagating ISO and regional air-sea interaction in the ISO process in SCSSM.展开更多
Based on the NCEP/NCAR reanalysis I daily data from 1958 to 2002,climatic characteristics of the 30-60-day intraseasonal oscillations（ISOs） of the zonal wind（u）,meridional wind（v）,and geopotential height（h） ov...Based on the NCEP/NCAR reanalysis I daily data from 1958 to 2002,climatic characteristics of the 30-60-day intraseasonal oscillations（ISOs） of the zonal wind（u）,meridional wind（v）,and geopotential height（h） over global areas and especially the ISO of v over the subtropical northern Pacific are analyzed using the space-time spectrum analysis and wavelet transform methods.The results show that the ISO of v is very different from those of u and h,with the former representing the meridional low-frequency disturbances,which are the most active in the subtropics and mid-high latitudes,but very weak in the tropics.In the subtropical Northern Hemisphere,the energies of the ISOs of u and h are both concentrated on the waves with wave number of 1 and periods of 30-60 days,while the main energy of the ISO of v is concentrated on the waves with wave numbers of 4-6 and periods of 30-60 and 70-90 days.The westward propagating energies for the 30-60-day oscillations of u,v,and h are all stronger than the eastward propagating energies in the subtropics.In addition,the ISO of v is the strongest（weakest） in summer （winter） over the subtropics of East Asia and northwestern Pacific,while the situation is reversed over the subtropical northeastern Pacific,revealing a ＂seesaw＂ of the ISO intensity with seasons over the subtropics from the northwestern to northeastern Pacific.In the subtropical northwestern Pacific,the interannual and interdecadal changes of the ISO for v at 850 hPa indicate that its activities are significantly strong during 1958-1975,while obviously weak during 1976-1990,and are the strongest during 1991-2000,and its spectral energy is obviously abnormal but ruleless during the ENSO periods.However,in the 2-7-yr bandpass filtering series,the interannual changes of the v ISO over the subtropical northwestern Pacific contain distinct ENSO signals.And in the 9-yr low-pass filtering series,the v ISO changes over the subtropical northwestern Pacific are significantly out of phase with the chang展开更多
The relationship between the tropical intra-seasonal oscillation(ISO) and tropical cyclones(TCs) activities over the South China Sea(SCS) is investigated by utilizing the National Centers for Environmental Prediction/...The relationship between the tropical intra-seasonal oscillation(ISO) and tropical cyclones(TCs) activities over the South China Sea(SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009.The main conclusions are:(1)A new ISO index is designed to describe the tropical ISO activity over the SCS,which can simply express ISO for SCS.After examining the applicability of the index constructed by the Climate Prediction Center(CPC),we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories.Consequently,the CPC index can't replace the function of the new ISO index;(2)The eastward spread process of tropical ISO is divided into eight phases using the new ISO index,the phase variation of which corresponds well with the TCs activities over the SCS.TCs generation and landing are significantly reduced during inactive period(phase 4-6) relative to that during active period(phase 7-3);(3)The composite analyses indicate distinct TCs activities over the SCS,which is consistent with the concomitant propagation of the ISO convective activity.During ISO active period,the weather situations are favorable for TCs development over the SCS,e.g.,strong convection,cyclonic shear and weak subtropical high,and vice versa;(4)The condensation heating centers,strong convection and water vapor flux divergence are well collocated with each other during ISO active period.In addition,the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period,and vice versa.Thus,the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.展开更多
The influences of basic flow fields on the unstable excitation of the intraseasonal atmosphericoscillation in the mid-high latitudes are studied by using a simple nonlinear dynamical model.The results showthat the wes...The influences of basic flow fields on the unstable excitation of the intraseasonal atmosphericoscillation in the mid-high latitudes are studied by using a simple nonlinear dynamical model.The results showthat the westerly profile has an important effect on unstable modes in the atmosphere;the growth rates andspectrum distributions of the excited unstable modes are different for the different profiles.For the usualwesterly profile patterns in the real atmosphere,the most unstable mode is in the intraseasonal(30—60 d)frequency band.The local intensity and meridional gradient of the westerlies also clearly affect unstablemodes.The consistency of the results in observational data analyses with that in dynamical theory proved thecorrectness and rationalization of the above-mentioned results.展开更多
This study investigates how the El Nino-Southern Oscillation(ENSO)modulates the intraseasonal variability(ISV)of Pacific-Japan(PJ)teleconnection pattern.The PJ index during boreal summer is constructed from the empiri...This study investigates how the El Nino-Southern Oscillation(ENSO)modulates the intraseasonal variability(ISV)of Pacific-Japan(PJ)teleconnection pattern.The PJ index during boreal summer is constructed from the empirical orthogonal function(EOF)of the 850-hPa zonal wind(U850)anomalies.Distinct periods of the PJ index are found during El Nino and La Nina summers.Although ISV of the PJ pattern is significant during 10-25 days for both types of summers,it peaks on Days 30 and 60 in El Nino and La Nina summers respectively.During El Nino summers,the 30-day ISV of PJ pattern is related to the northwestward propagating intraseasonal oscillation(ISO)over the western North Pacific(WNP),which is originated from the tropical Indian Ocean(IO).During La Nina summers,the 60-day ISV of PJ pattern is related to the northeastward propagating ISO from the tropical IO.The low-frequency ISV modes in both El Nino and La Nina summers are closely related to the boreal summer ISO(BSISO),and the high-frequency ISV modes over WNP are related to the quasi-biweekly oscillation.The underlying mechanisms for these different evolutions are also discussed.展开更多
Based on daily precipitation observation data in China,the intraseasonal oscillation(ISO)features of summer precipitation over southern China in 2019 have been investigated by wavelet and band-pass filtering analyses....Based on daily precipitation observation data in China,the intraseasonal oscillation(ISO)features of summer precipitation over southern China in 2019 have been investigated by wavelet and band-pass filtering analyses.The results show that enhanced(suppressed)precipitation occurred over southern China during early(late)boreal summer2019.The signals of both 10-20-and 30-60-day ISO in southern China are remarkable,with the amplitude of the10-20-day ISO larger than the 30-60-day ISO in boreal summer 2019.The synergistic effect of the 10-20-and 30-60-day ISO wet phases was found to exert a tremendous influence on persistent heavy precipitation in July 2019,when the amount of precipitation reached its maximum in southern China since 1981.The atmospheric circulation and convection evolution characteristics of both 10-20-and 30-60-day ISO are further investigated.An anomalous low-level anticyclone over the South China Sea is prominently linked to the wet phase of the 10-20-day ISO,whereas an anomalous low-level cyclone over southern China is dominantly associated with the wet phase of the 30-60-day ISO.Both events enhance the water vapor convergence and ascending motion over southern China.Thus,the atmospheric circulation that accompanied the synergism of the wet phases of the 10-20-and 30-60-day ISO resulted in persistent heavy precipitation over southern China in July 2019.展开更多
The authors explore the intraseasonal oscillation(ISO)of rainfall anomalies in South China,the related circulation regimes,and discuss the possible causes of the large variability of the positive rainfall anomalies ov...The authors explore the intraseasonal oscillation(ISO)of rainfall anomalies in South China,the related circulation regimes,and discuss the possible causes of the large variability of the positive rainfall anomalies over South China during the winter of the 1982/83,1997/98 and 2015/16 super EI Nino events.Case-by-case analysis shows that the 10–20-day ISO associated with the successive heavy rainfall events lead to the positive anomalies of winter rainfall in the three winters.Meanwhile,the 20–50-day ISO is relatively stronger in the winter of 1982/83 and 2015/16 but weaker in the winter of 1997/98.Except for a different speed,the anomalies of the 200-hPa wave train associated with the two ISOs both propagate eastward along the westerly jet between 20 N and 30 N.In the winter of 1982/83 and 2015/16,when the upper-level subseasonal wave trains in different periods pass through South China,the in-phase enhancement of upper-level divergences and the pumping effect could induce the persistent heavy rainfall events,which facilitate the stronger seasonal-mean rainfall.Although the 10–20-day ISO alone in the winter of 1997/98 could cause the higher-frequency rainfall events,the weaker 20–50-day ISO attenuates the anomalies of the South China winter rainfall.Therefore,the joint effects of the 10–20-and 20–50-day ISOs are critical for the larger amount of above-normal rainfall over South China during the mature phase of super EI Nino events.展开更多
基金Supported by the National Key Research and Development Program of China(2018YFC1505805)US NOAA(NA18OAR4310298)+2 种基金US NSF(AGS-1643297)National Natural Science Foundation of China(41875069,41575052,and 41575043)Fund for Collaborative Innovation of Meteorological Science in East China(QYHZ201608).
文摘The daily outgoing longwave radiation(OLR)field in boreal summer shows significant power spectrum peaks on quasi-biweekly(10–20-day)and intraseasonal(20–80-day)timescales over the Indo–western Pacific warm pool,especially over the South China Sea and Bay of Bengal.The quasi-biweekly oscillation(QBWO)originates from offequatorial western North Pacific,and is characterized by a northwest–southeast oriented wave train pattern,propagating northwestward.The intraseasonal oscillation(ISO),on the other hand,originates from the equatorial Indian Ocean and propagates eastward and northward.Why the equatorial mode possesses a 20–80-day periodicity while the off-equatorial mode favors a 10–20-day periodicity is investigated through idealized numerical experiments with a 2.5-layer atmospheric model.In the off-equatorial region,the model simulates,under a realistic three-dimensional summer mean flow,the most unstable mode that has a wave train pattern with a typical zonal wavelength of 6000 km and a period of 10–20 days,propagating northwestward.This is in contrast to the equatorial region,where a Madden–Julian oscillation(MJO)like mode with a planetary(wavenumber-1)zonal scale and a period ranging from 20 to 80 days is simulated.Sensitivity experiments with different initial conditions indicate that the QBWO is an intrinsic mode of the atmosphere in boreal summer in the off-equatorial Indo–western Pacific region under the summer mean state,while the MJO is the most unstable mode in the equatorial region.
基金This work was supported jointly by the Chinese Academy of Sciences Key Program KZCX2-203the National Natural Science Foundation of China Programs under contracts 49735160 and 49805004.
文摘The atmospheric intraseasonal oscillation(ISO)and its interannual variability are simulated by the atmospheric general circulation model,which was developed at the Institute of Atmospheric Physics.Two numerical experiments were performed,corresponding to the AMIP-Ⅰ and AMIP-Ⅱ simulations,respectively.The model reasonably reproduces the major aspects of the intraseasonal oscillation,including the propagating property and the seasonal differences in the tropics,the wavenumber structure of ISO in the globe,and the global coincidence in the interannual variation of ISO.Comparison of the results between the two experiments suggests that improvement of the boundary forcing or considering the air-sea interaction may help to improve the simulation on the ISO and its interannual variability.
基金Supported by the National Science and Technology Support Program of China(2009BAC51B04)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406022)
文摘The intraseasonal oscillation（ISO） in the South China Sea summer monsoon（SCSSM） and its influence on regionally persistent heavy rain（RPHR） over southern China are examined by using satelhte outgoing long wave radiation,NCEP/NCAR reanalysis,and gridded rainfall station data in China from 1981 to 2010.The most important feature of the ISO in SCSSM,contributing to the modulation of RPHR,is found to be the fluctuation in the western Pacific subtropical high（WPSH）,along with a close link to the Madden-Julian oscillation（MJO）.Southern China is divided into three regions by using rotated empirical orthogonal functions（REOFs）for intraseasonal rainfall,where the incidence rate of RPHR is closely linked to the intraseasonal variation in rainfall.It is found that SCSSM ISOs are the key systems controlling the intraseasonal variability in rainfall and can be described by the leading pair of empirical orthogonal functions（EOFs） for the 850-hPa zonal wind over the SCS and southern China.Composite analyses based on the principal components（PCs） of the EOFs indicate that the ISO process in SCSSM exhibits as the east-west oscillation of the WPSH,which is coupled with the northward-propagating MJO,creating alternating dry and wet phases over southern China with a period of 40 days.The wet phases provide stable and lasting circulation conditions that promote RPHR.However,differences in the ISO structures can be found when RPHR occurs in regions where the WPSH assumes different meridional positions.Further examination of the meridional-phase structure suggests an important role of northward-propagating ISO and regional air-sea interaction in the ISO process in SCSSM.
基金Supported jointly by the National Basic Research Program of China(2006CB403606)the National Natural Science Foundation of China(Grant Nos.40575027 and 40905035)the National Non-Profit Public-Interest Research Project(Grant No. GYHY200806004)
文摘Based on the NCEP/NCAR reanalysis I daily data from 1958 to 2002,climatic characteristics of the 30-60-day intraseasonal oscillations（ISOs） of the zonal wind（u）,meridional wind（v）,and geopotential height（h） over global areas and especially the ISO of v over the subtropical northern Pacific are analyzed using the space-time spectrum analysis and wavelet transform methods.The results show that the ISO of v is very different from those of u and h,with the former representing the meridional low-frequency disturbances,which are the most active in the subtropics and mid-high latitudes,but very weak in the tropics.In the subtropical Northern Hemisphere,the energies of the ISOs of u and h are both concentrated on the waves with wave number of 1 and periods of 30-60 days,while the main energy of the ISO of v is concentrated on the waves with wave numbers of 4-6 and periods of 30-60 and 70-90 days.The westward propagating energies for the 30-60-day oscillations of u,v,and h are all stronger than the eastward propagating energies in the subtropics.In addition,the ISO of v is the strongest（weakest） in summer （winter） over the subtropics of East Asia and northwestern Pacific,while the situation is reversed over the subtropical northeastern Pacific,revealing a ＂seesaw＂ of the ISO intensity with seasons over the subtropics from the northwestern to northeastern Pacific.In the subtropical northwestern Pacific,the interannual and interdecadal changes of the ISO for v at 850 hPa indicate that its activities are significantly strong during 1958-1975,while obviously weak during 1976-1990,and are the strongest during 1991-2000,and its spectral energy is obviously abnormal but ruleless during the ENSO periods.However,in the 2-7-yr bandpass filtering series,the interannual changes of the v ISO over the subtropical northwestern Pacific contain distinct ENSO signals.And in the 9-yr low-pass filtering series,the v ISO changes over the subtropical northwestern Pacific are significantly out of phase with the chang
基金Characteristics Analysis of Typhoon Wind and Wave Field in the South China Sea(SOEDZZ1519)Multi-Source Environmental Data Analysis and Atlas Compilation in the Indian Ocean(JT1506)Special Fund of Chinese Academy of Meteorological Sciences(41575055)
文摘The relationship between the tropical intra-seasonal oscillation(ISO) and tropical cyclones(TCs) activities over the South China Sea(SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009.The main conclusions are:(1)A new ISO index is designed to describe the tropical ISO activity over the SCS,which can simply express ISO for SCS.After examining the applicability of the index constructed by the Climate Prediction Center(CPC),we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories.Consequently,the CPC index can't replace the function of the new ISO index;(2)The eastward spread process of tropical ISO is divided into eight phases using the new ISO index,the phase variation of which corresponds well with the TCs activities over the SCS.TCs generation and landing are significantly reduced during inactive period(phase 4-6) relative to that during active period(phase 7-3);(3)The composite analyses indicate distinct TCs activities over the SCS,which is consistent with the concomitant propagation of the ISO convective activity.During ISO active period,the weather situations are favorable for TCs development over the SCS,e.g.,strong convection,cyclonic shear and weak subtropical high,and vice versa;(4)The condensation heating centers,strong convection and water vapor flux divergence are well collocated with each other during ISO active period.In addition,the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period,and vice versa.Thus,the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.
文摘The influences of basic flow fields on the unstable excitation of the intraseasonal atmosphericoscillation in the mid-high latitudes are studied by using a simple nonlinear dynamical model.The results showthat the westerly profile has an important effect on unstable modes in the atmosphere;the growth rates andspectrum distributions of the excited unstable modes are different for the different profiles.For the usualwesterly profile patterns in the real atmosphere,the most unstable mode is in the intraseasonal(30—60 d)frequency band.The local intensity and meridional gradient of the westerlies also clearly affect unstablemodes.The consistency of the results in observational data analyses with that in dynamical theory proved thecorrectness and rationalization of the above-mentioned results.
基金Supported by the National Natural Science Foundation of China(41420104002)National Key Research and Development Program of China(2018YFC1505804)。
文摘This study investigates how the El Nino-Southern Oscillation(ENSO)modulates the intraseasonal variability(ISV)of Pacific-Japan(PJ)teleconnection pattern.The PJ index during boreal summer is constructed from the empirical orthogonal function(EOF)of the 850-hPa zonal wind(U850)anomalies.Distinct periods of the PJ index are found during El Nino and La Nina summers.Although ISV of the PJ pattern is significant during 10-25 days for both types of summers,it peaks on Days 30 and 60 in El Nino and La Nina summers respectively.During El Nino summers,the 30-day ISV of PJ pattern is related to the northwestward propagating intraseasonal oscillation(ISO)over the western North Pacific(WNP),which is originated from the tropical Indian Ocean(IO).During La Nina summers,the 60-day ISV of PJ pattern is related to the northeastward propagating ISO from the tropical IO.The low-frequency ISV modes in both El Nino and La Nina summers are closely related to the boreal summer ISO(BSISO),and the high-frequency ISV modes over WNP are related to the quasi-biweekly oscillation.The underlying mechanisms for these different evolutions are also discussed.
基金Supported by the National Key Research and Development Program of China(2018YFC1505603)National Natural Science Foundation of China(41975088 and 41575074)+1 种基金China Meteorological Administration Special Public Welfare Research Fund(GYHY201306024)State Oceanic Administration International Cooperation Program(GASI-IPOVAI-03)。
文摘Based on daily precipitation observation data in China,the intraseasonal oscillation(ISO)features of summer precipitation over southern China in 2019 have been investigated by wavelet and band-pass filtering analyses.The results show that enhanced(suppressed)precipitation occurred over southern China during early(late)boreal summer2019.The signals of both 10-20-and 30-60-day ISO in southern China are remarkable,with the amplitude of the10-20-day ISO larger than the 30-60-day ISO in boreal summer 2019.The synergistic effect of the 10-20-and 30-60-day ISO wet phases was found to exert a tremendous influence on persistent heavy precipitation in July 2019,when the amount of precipitation reached its maximum in southern China since 1981.The atmospheric circulation and convection evolution characteristics of both 10-20-and 30-60-day ISO are further investigated.An anomalous low-level anticyclone over the South China Sea is prominently linked to the wet phase of the 10-20-day ISO,whereas an anomalous low-level cyclone over southern China is dominantly associated with the wet phase of the 30-60-day ISO.Both events enhance the water vapor convergence and ascending motion over southern China.Thus,the atmospheric circulation that accompanied the synergism of the wet phases of the 10-20-and 30-60-day ISO resulted in persistent heavy precipitation over southern China in July 2019.
基金jointly supported by the Special Fund for Public Welfare Industry[grant number GYHY20140619]the National Natural Science Foundation of China[grant numbers41475057,41775052 and 41505049]the Basic Scientific Research and Operation Foundation of CAMS[grant numbers2015Z001 and 2017R001]
文摘The authors explore the intraseasonal oscillation(ISO)of rainfall anomalies in South China,the related circulation regimes,and discuss the possible causes of the large variability of the positive rainfall anomalies over South China during the winter of the 1982/83,1997/98 and 2015/16 super EI Nino events.Case-by-case analysis shows that the 10–20-day ISO associated with the successive heavy rainfall events lead to the positive anomalies of winter rainfall in the three winters.Meanwhile,the 20–50-day ISO is relatively stronger in the winter of 1982/83 and 2015/16 but weaker in the winter of 1997/98.Except for a different speed,the anomalies of the 200-hPa wave train associated with the two ISOs both propagate eastward along the westerly jet between 20 N and 30 N.In the winter of 1982/83 and 2015/16,when the upper-level subseasonal wave trains in different periods pass through South China,the in-phase enhancement of upper-level divergences and the pumping effect could induce the persistent heavy rainfall events,which facilitate the stronger seasonal-mean rainfall.Although the 10–20-day ISO alone in the winter of 1997/98 could cause the higher-frequency rainfall events,the weaker 20–50-day ISO attenuates the anomalies of the South China winter rainfall.Therefore,the joint effects of the 10–20-and 20–50-day ISOs are critical for the larger amount of above-normal rainfall over South China during the mature phase of super EI Nino events.
