Unusual Rainfall in Southern China in Decaying August during Extreme El Niño 2015/16: Role of the Western Indian Ocean and North Tropical Atlantic SST

2018 ◽  
Vol 31 (17) ◽  
pp. 7019-7034 ◽  
Author(s):  
Jiepeng Chen ◽  
Xin Wang ◽  
Wen Zhou ◽  
Chunzai Wang ◽  
Qiang Xie ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South China ◽  
El Niño ◽  
North Pacific ◽  
Yangtze River ◽  
Western North Pacific ◽  
El Nino ◽  
Southern China ◽  
The Yangtze River ◽  
Extreme El Niño

Previous research has suggested that the anomalous western North Pacific anticyclone (WNPAC) can generally persist from an El Niño mature winter to the subsequent summer, influencing southern China precipitation significantly, where southern China includes the Yangtze River valley and South China. Since the late 1970s, three extreme El Niño events have been recorded: 1982/83, 1997/98, and 2015/16. There was a sharp contrast in the change in southern China rainfall and corresponding atmospheric circulations in the decaying August between the 2015/16 extreme El Niño event and the earlier two extreme El Niño events. Enhanced rainfall in the middle and upper reaches of the Yangtze River and suppressed rainfall over South China resulted from basinwide warming in the tropical Indian Ocean induced by the extreme El Niño in August 1983 and 1998, which was consistent with previous studies. However, an anomalous western North Pacific cyclone emerged in August 2016 and then caused positive rainfall anomalies over South China and negative rainfall anomalies from the Yangtze River to the middle and lower reaches of the Yellow River. Without considering the effect of the long-term global warming trend, in August 2016 the negative SST anomalies over the western Indian Ocean and cooling in the north tropical Atlantic contributed to the anomalous western North Pacific cyclone and a rainfall anomaly pattern with opposite anomalies in South China and the Yangtze River region. Numerical experiments with the CAM5 model are conducted to confirm that cooler SST in the western Indian Ocean contributed more than cooler SST in the north tropical Atlantic to the anomalous western North Pacific cyclone and anomalous South China rainfall.

Changing impact of ENSO events on the following summer rainfall in eastern China since the 1950s

2021 ◽  
pp. 1-55
Author(s):  
Linyuan Sun ◽  
Xiu-Qun Yang ◽  
Lingfeng Tao ◽  
Jiabei Fang ◽  
Xuguang Sun
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Yangtze River ◽  
El Nino ◽  
East Asian ◽  
Eastern China ◽  
Summer Rainfall ◽  
The Yangtze River ◽  
Enso Events

AbstractThe El Niño-Southern Oscillation (ENSO) events which generally mature in winter profoundly affect the following summer rainfall in eastern China (ECSR), but such an impact can change significantly with decadal background. This study examines how the impact changes since the 1950s by running correlation and regression analyses. It is found that the ENSO’s impact on ECSR has undergone two decadal shifts in the late 1970s and 1990s, respectively. Sequentially, three distinct ENSO-induced ECSR anomaly patterns are categorized, which exhibit both robust and changeable sides. The robust side manifests generally more precipitation in the Yangtze River basin affected by the anomalous tropical western North Pacific anticyclone (WNPAC) in the post-El Niño summer. The changeable side is reflected in the more variable ENSO-induced rainfall anomalies north of the Yangtze River, due to the ENSO-induced different East Asian midlatitude circulation anomalies. Meanwhile, the El Niño-induced drought in South China is enhanced since the late 1970s with the intensification of the anomalous WNPAC. The ENSO’s changing impact on the ECSR stems from the changes of ENSO-induced tropical and midlatitude circulation anomalies over East Asia, which are associated with different zonal (from tropical Pacific to Indian Ocean) and meridional (from tropical Pacific to Midlatitude North Pacific) teleconnections of ENSO-induced SST anomalies. The former affects the intensity and location of the anomalous WNPAC by affecting Indian Ocean capacitor effect and convection anomalies over the tropical Indo-western Pacific. The latter modulates the ocean-to-atmosphere feedback in the midlatitude North Pacific, contributes to different local geopotential anomaly sources, and then directly or indirectly through Rossby wavetrain affects the East Asian midlatitude circulation.

scholarly journals Weakened Anomalous Western North Pacific Anticyclone during an El Niño–Decaying Summer under a Warmer Climate: Dominant Role of the Weakened Impact of the Tropical Indian Ocean on the Atmosphere

2018 ◽  
Vol 32 (1) ◽  
pp. 213-230 ◽  
Author(s):  
Chao He ◽  
Tianjun Zhou ◽  
Tim Li
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Tropospheric Temperature ◽  
Coupled Models ◽  
Subtropical Anticyclone ◽  
Mean State

Abstract The western North Pacific subtropical anticyclone (WNPAC) is the most prominent atmospheric circulation anomaly over the subtropical Northern Hemisphere during the decaying summer of an El Niño event. Based on a comparison between the RCP8.5 and the historical experiments of 30 coupled models from the CMIP5, we show evidence that the anomalous WNPAC during the El Niño–decaying summer is weaker in a warmer climate although the amplitude of the El Niño remains generally unchanged. The weakened impact of the sea surface temperature anomaly (SSTA) over the tropical Indian Ocean (TIO) on the atmosphere is essential for the weakened anomalous WNPAC. In a warmer climate, the warm tropospheric temperature (TT) anomaly in the tropical free troposphere stimulated by the El Niño–related SSTA is enhanced through stronger moist adiabatic adjustment in a warmer mean state, even if the SSTA of El Niño is unchanged. But the amplitude of the warm SSTA over TIO remains generally unchanged in an El Niño–decaying summer, the static stability of the boundary layer over TIO is increased, and the positive rainfall anomaly over TIO is weakened. As a result, the warm Kelvin wave emanating from TIO is weakened because of a weaker latent heating anomaly over TIO, which is responsible for the weakened WNPAC anomaly. Numerical experiments support the weakened sensitivity of precipitation anomaly over TIO to local SSTA under an increase of mean-state SST and its essential role in the weakened anomalous WNPAC, independent of any change in the SSTA.

scholarly journals Summertime Moisture Sources and Transportation Pathways for China and Associated Atmospheric Circulation Patterns

2021 ◽  
Vol 9 ◽  
Author(s):  
Ruonan Zhang ◽  
QuCheng Chu ◽  
Zhiyan Zuo ◽  
Yanjun Qi
Keyword(s):  
South China ◽  
North Pacific ◽  
Moisture Transport ◽  
Northeast China ◽  
Yangtze River ◽  
Western North Pacific ◽  
North China ◽  
Yangtze River Valley ◽  
The Yangtze River ◽  
Moisture Sources

Based on the Lagrangian particle dispersion model, HYSPLIT 4.9, this study analyzed the summertime atmospheric moisture sources and transportation pathways affecting six subregions across China. The sources were: Midlatitude Westerly (MLW), Siberian-Arctic regions (SibArc), Okhotsk Sea (OKS), Indian Ocean (IO), South China Sea (SCS), Pacific Ocean (PO), and China Mainland (CN). Furthermore, the relative contributions of these seven moisture sources to summertime precipitation in China were quantitatively assessed. Results showed that the CN precipitation source dominates the interannual and interdecadal variation of precipitation in most subregions, except Southwest and South China. The Northeast China vortex and Pacific–Japan (PJ) teleconnection, which transport water vapor from the MLW, OKS and PO sources, are crucial atmospheric systems and patterns for the variation of precipitation in Northeast China. The interannual variation of precipitation in Northwest and North China is mainly dominated by mid–high-latitude Eurasian wave trains, which provide the necessary dynamical conditions and associated moisture transport from the MLW and SibArc sources. In addition, an enhanced western North Pacific subtropical high (WNPSH) accompanied by the East Asian–western North Pacific summer monsoon and PJ teleconnection, transports extra moisture to North China from the SCS and PO sources, as well to the Yangtze River Valley and South China. The Indian summer monsoon (ISM) is also critically important for the interdecadal change in precipitation over the Yangtze River Valley and South China, via the southwesterly branch of moisture transport from the IO source. The interdecadal changes in precipitation over Southwest China are determined by the IO and SCS sources, via enhanced WNPSH coupling with a weakened ISM. These results suggest that the interdecadal and interannual variations of moisture sources contribute to the attendant variation of summertime precipitation in China via large-scale circulation regimes in both the mid–high and lower latitudes.

scholarly journals Modulation of Boreal Summer Intraseasonal Oscillations over the Western North Pacific by ENSO

2016 ◽  
Vol 29 (20) ◽  
pp. 7189-7201 ◽  
Author(s):  
Fei Liu ◽  
Tim Li ◽  
Hui Wang ◽  
Li Deng ◽  
Yuanwen Zhang
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Boreal Summer ◽  
Maritime Continent ◽  
La Nina

Abstract The authors investigate the effects of El Niño and La Niña on the intraseasonal oscillation (ISO) in the boreal summer (May–October) over the western North Pacific (WNP). It is found that during El Niño summers, the ISO is dominated by a higher-frequency oscillation with a period of around 20–40 days, whereas during La Niña summers the ISO is dominated by a lower-frequency period of around 40–70 days. The former is characterized by northwestward-propagating convection anomalies in the WNP, and the latter is characterized by northward- and eastward-propagating convective signals over the tropical Indian Ocean/Maritime Continent. The possible mechanisms through which El Niño–Southern Oscillation (ENSO)-induced background mean state changes influence the ISO behavior are examined through idealized numerical experiments. It is found that enhanced (weakened) mean moisture and easterly (westerly) vertical wind shear in the WNP during El Niño (La Niña) are the main causes of the strengthened (weakened) 20–40-day northwestward-propagating ISO mode, whereas the 40–70-day ISO initiated from the Indian Ocean can only affect the WNP during La Niña years because the dry (moist) background moisture near the Maritime Continent during El Niño (La Niña) suppresses (enhances) the ISO over the Maritime Continent, and the ISO propagates less over the Maritime Continent during El Niño years than in La Niña years.

scholarly journals Asymmetric Relationship between Indian Ocean SST and the Western North Pacific Summer Monsoon

2015 ◽  
Vol 28 (4) ◽  
pp. 1383-1395 ◽  
Author(s):  
Riyu Lu ◽  
Shu Lu
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Summer Precipitation ◽  
La Niña ◽  
La Nina ◽  
Precipitation Anomalies ◽  
Sst Anomalies

Abstract The summer precipitation anomalies over the tropical western North Pacific (WNP), which greatly affect East Asian climate, are closely related to Indian Ocean (IO) SST anomalies, and this WNP–IO relationship is widely assumed to be linear. This study indicates that the IO SST–WNP precipitation relationship is generally linear only when the IO SST anomalies are positive and not when the IO SST anomalies are negative, that is, a strongly cooler IO, in comparison with a moderately cooler IO, does not correspond to stronger precipitation enhancement over the WNP. Further analysis suggests that the phases of ENSO play a crucial role in modifying the impacts of IO SSTs on WNP anomalies. The reverse IO SST–WNP precipitation relationship, which exists without apparent ENSO development/decay, is intensified by El Niño decay through the enhancement of IO SST anomalies, but weakened by El Niño development and La Niña decay through the concurrence of SST anomalies in the tropical central and eastern Pacific. After removing El Niño developing and La Niña decaying cases, the IO SST and WNP precipitation anomalies show a clear linear relationship. Because of the effects of the phases of ENSO, the years of negative precipitation or anticyclonic anomalies over the WNP are highly concentrated over strongly warmer IO and El Niño decaying years, which is consistent with previous studies. However, the years of positive precipitation anomalies are scattered over cooler IO and moderately warmer IO years, implying a complexity of tropical SST forcing on positive WNP precipitation anomalies.

scholarly journals Impact of Preceding El Niño and the Indian Ocean Dipole on the Southern China Precipitation in Early Summer

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Yan Li ◽  
Yafei Wang ◽  
Lin Mu ◽  
Qingyuan Wang ◽  
Jun Song ◽  
...  
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
Yangtze River ◽  
El Nino ◽  
Southern China ◽  
The Philippines ◽  
Early Summer ◽  
Single Event ◽  
The Indian Ocean

Delayed impacts of El Niño and the Indian Ocean Dipole in positive phase (P-IOD) on the South China early monsoon were investigated by observations and simulations. The most significant correlation between IOD index (IODI) and NINO3 appeared in boreal autumn. A new index (IODN3) related to the intensity of El Niño and IOD was created. Three indexes in boreal autumn were positively well correlated with the rainfall over the Yangtze River and its southern area (rain-YRBS) in next June. The most significant correlation appeared between IODN3 and rain-YRBS. Positive rain-YRBS anomalies in June tend to occur after P-IOD or El Niño solely matured in previous boreal autumn. However, when both events matured in boreal autumn, rain-YRBS anomalies tended to be more enhanced, which suggests that a delayed combined influence of both events on rain-YRBS in June was larger than that of either event alone. There was a low level anticyclonic circulation around the Philippines (PSAC) that developed in boreal autumn and was maintained until the following June when the single event occurred. However, a much stronger PSAC tended to occur when both events matured. The stronger PSAC could transport more water vapor to YRBS and cause more rainfall there in June.

Relative Contributions of the Indian Ocean and Local SST Anomalies to the Maintenance of the Western North Pacific Anomalous Anticyclone during the El Niño Decaying Summer*

2010 ◽  
Vol 23 (11) ◽  
pp. 2974-2986 ◽  
Author(s):  
Bo Wu ◽  
Tim Li ◽  
Tianjun Zhou
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Late Summer ◽  
Kelvin Waves ◽  
Relative Role ◽  
Local Forcing ◽  
Anomalous Anticyclone

Abstract To investigate the relative role of the cold SST anomaly (SSTA) in the western North Pacific (WNP) or Indian Ocean basin mode (IOBM) in maintaining an anomalous anticyclone over the western North Pacific (WNPAC) during the El Niño decaying summer, a suite of numerical experiments is performed using an atmospheric general circulation model, ECHAM4. In sensitive experiments, the El Niño composite SSTA is specified in either the WNP or the tropical Indian Ocean, while the climatological SST is specified elsewhere. The results indicate that the WNPAC is maintained by the combined effects of the local forcing of the negative SSTA in the WNP and the remote forcing from the IOBM. The former (latter) contribution gradually weakens (enhances) from June to August. The negative SSTA in the WNP is crucial for the maintenance of the WNPAC in early summer. However, because of a negative air–sea feedback, the negative SSTA gradually decays, as does the local forcing effect. Enhanced local convection associated with the IOBM stimulates atmospheric Kelvin waves over the equatorial western Pacific. The impact of the Kelvin waves on the WNP circulation depends on the formation of the climatological WNP monsoon trough, which does not fully establish until late summer. Therefore, the IOBM plays a crucial role in late summer via the Kelvin wave induced anticyclonic shear and boundary layer divergence.

scholarly journals Extremely Early Summer Monsoon Onset in the South China Sea in 2019 Following an El Niño Event

2020 ◽  
Vol 148 (5) ◽  
pp. 1877-1890 ◽  
Author(s):  
Peng Hu ◽  
Wen Chen ◽  
Shangfeng Chen ◽  
Yuyun Liu ◽  
Ruping Huang
Keyword(s):  
South China Sea ◽  
Summer Monsoon ◽  
South China ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Monsoon Onset ◽  
El Niño Event ◽  
Preceding Winter

Abstract The El Niño–Southern Oscillation (ENSO) is regarded as one of the most important factors for onset of the South China Sea summer monsoon (SCSSM). Previous studies generally indicated that an El Niño event tends to result in a late onset of the SCSSM monsoon. However, this relationship has not been true in recent years, particularly when an extremely early SCSSM onset (1 May 2019) occurred following the 2018/19 El Niño event in the preceding winter. The processes of the second earliest SCSSM onset in the past 41 years were investigated using NCEP–DOE reanalysis, OLR data, and ERSST. A negative sea surface temperature and associated anticyclonic anomalies were absent over the western North Pacific in the late spring of 2019 following an El Niño event in the preceding winter. Thus, the mean circulation in the late spring of 2019 does not prevent SCSSM onset, which is in sharp contrast to the composited spring of the El Niño decaying years. The convective active and westerly phases of a 30–60-day oscillation originating from the Indian Ocean provided a favorable background for the SCSSM onset in 2019. In addition, the monsoon onset vortex over the Bay of Bengal and the cold front associated with a midlatitude trough over East Asia also played important roles in triggering the early onset of the SCSSM in 2019. No tropical cyclone appeared over the western North Pacific during April and May, and the enhancement of quasi-biweekly oscillation mainly occurs after the SCSSM onset; thus, these two factors contribute little to the SCSSM onset in 2019.

scholarly journals Impact of the mean state on El Niño induced western North Pacific anomalous anticyclone during its decaying summer in AMIP models

2021 ◽  
pp. 1-49
Author(s):  
Xieyuan Wang ◽  
Tim Li ◽  
Chao He
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Cp El Niño ◽  
Anomalous Anticyclone ◽  
The Mean ◽  
Mean State

AbstractThrough the diagnosis of 29 Atmospheric Model Inter-comparison Project (AMIP) experiments from the CMIP5 inter-comparison project, we investigate the impact of the mean state on simulated western North Pacific anomalous anticyclone (WNPAC) during El Niño decaying summer. The result indicates that the inter-model difference of the JJA mean precipitation in the Indo-western Pacific warm pool is responsible for the difference of the WNPAC. During the decaying summer of an Eastern Pacific (EP) type El Niño, a model that simulates excessive mean rainfall over the western North Pacific (WNP) reproduces a stronger WNPAC response, through an enhanced local convection-circulation-moisture feedback. The intensity of the simulated WNPAC during the decay summer of a Central Pacific (CP) type El Niño, on the other hand, depends on the mean precipitation over the tropical Indian Ocean. The distinctive WNPAC-mean precipitation relationships between the EP and CP El Niño result from different anomalous SST patterns in the WNP. While the local SST anomaly plays an active role in maintaining the WNPAC during the EP El Niño, it plays a passive role during the CP El Niño. As a result, only the mean-state precipitation/moisture field in the tropical Indian Ocean modulates the circulation anomaly in the WNP in the latter case.

Sign in / Sign up

Export Citation Format

Share Document