East Asia-Pacific Pattern Research Articles

Dominant modes and mechanisms of atmospheric rivers in East Asia

Atmospheric rivers (ARs), the long and narrow conveyors of intense moisture transport, are a unique mover of moisture from the low latitudes to the mid to high latitudes and have a considerable impact on hydrometeorological events (i.e., extreme precipitation). Using the top-hat by reconstruction (THR) algorithm and ERA5 reanalysis data, this study analyzes the climatological characteristics of ARs over East Asia (EA) in summer (June to August) during 1979–2020. According to the four leading modes of EOF analysis, ARs events occur mainly in the Yangtze River valley, the Huaihe River valley, and the coastal region of South China. The sea surface temperature anomalies (SSTAs) related to the first EOF mode (EOF1) show the warming of the central and eastern Pacific and Indian Oceans. The northward movement of the westerly jet stream maintains the western North Pacific subtropical high (WNPSH) and guides water vapor transport to China. EOF2 corresponds to the positive phase of EAP (East Asia-Pacific) pattern. SSTAs related to EOF2 show an El Niño recession-like pattern, which modulates precipitation over southern China through anticyclones over the western North Pacific. SSTAs related to EOF3 show a La Niña-like pattern, which regulates the precipitation in the Yangtze-Huaihe valley through upper-level convective heating on the north side of the WNPSH. For EOF4, the circulation system affecting ARs is dispersed, resulting in smaller scale ARs. ARs of EOF4 are associated with cyclones, mainly showing the characteristics of coastal landing ARs. These results can provide a new forecasting source for EA summer precipitation.

Weakened Connection between East China Summer Rainfall and the East Asia-Pacific Teleconnection Pattern

The interdecadal change in the relationship between the East Asia-Pacific (EAP) teleconnection pattern and rainfall over East China during boreal summer (June–August) was investigated using observation and reanalysis datasets during 1951–2018. As proposed in a previous study, summer rainfall in the Yangtze-Huaihe River (YH-R) valley is below (above) normal when a positive (negative) EAP event occurs. Based on the close relationship with the rainfall anomalies, the EAP teleconnection pattern has been widely used in the prediction of summer rainfall variations in the YH-R valley. However, we found that the rainfall anomalies in the YH-R basin associated with the EAP pattern were weaker and less evident after the late 1980s. This finding indicates a decreased relationship between the EAP pattern and YH-R basin summer rainfall after the late 1980s, and a decrease in the quality and skill of seasonal predictions of YH-R basin summer rainfall related to the EAP pattern. This pronounced weakening in the YH-R summer rainfall-EAP pattern connection is attributed to the northeastward displacement of the Japanese action center of the EAP pattern after the late 1980s, which caused weaker anomalous vertical motion and moisture transportation over the YH-R valley. The present research reveals that the interdecadal expansion in the size of the Indo-Pacific warm pool in the late 1980s is likely responsible for the northeastward shift in the Japanese action center of the EAP teleconnection pattern by modulating anomalous convective activities and the northward propagation of the EAP pattern.

Characteristics of atmospheric circulation patterns over East Asia and their impacts on precipitation in summer

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 78:117-133 (2019) - DOI: https://doi.org/10.3354/cr01544 Characteristics of atmospheric circulation patterns over East Asia and their impacts on precipitation in summer Shuping Li1, Guolin Feng2,3,*, Wei Hou3, Jianbo Cheng4 1College of Hydraulic Science and Engineering, Yangzhou University, Yangzhou 225000, PR China 2College of Physical Science and Technology, Yangzhou University, Yangzhou 225000, PR China 3National Climate Center, China Meteorological Administration, Beijing 100081, PR China 4College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, PR China *Corresponding author: fenggl@cma.gov.cn ABSTRACT: We investigated 3 summer atmospheric circulation patterns over the mid-latitudes of East Asia—the monopole (MOP), East Asia-Pacific (EAP) and southeast-northwest out-of-phase dipole (EWD)—and their impacts on precipitation in eastern China. Our results show that an increase in the frequency of the positive MOP pattern enhances precipitation in northeastern China, while a longer persistence of this pattern induces above-average precipitation in the mid-to-lower reaches of the Yangtze River valley (MLRYR). For the negative MOP pattern, a higher frequency of this pattern leads to below-average precipitation in northeastern and southern China, while its persistence has insignificant influences on precipitation in eastern China. Increases in the frequency and persistence of the positive EAP pattern intensify precipitation in the MLRYR. For the negative EAP pattern, increases in the frequency and persistence of the pattern reduce precipitation in the MLRYR, and a higher frequency of this pattern markedly intensifies precipitation in northern China. Regarding the positive EWD pattern, an increase in its frequency favors below-average precipitation in northern China, and an increase in its persistence clearly intensifies precipitation in the MLRYR. Increases in the frequency and persistence of the negative EWD pattern produce below- (above-)average precipitation in the MLRYR (northeastern China), with a longer persistence of this pattern especially reducing precipitation in the MLRYR. These results indicate that the frequency and persistence of each pattern have different impacts on precipitation in eastern China. KEY WORDS: Eastern China · Atmospheric circulation patterns · Summer precipitation Full text in pdf format PreviousNextCite this article as: Li S, Feng G, Hou W, Cheng J (2019) Characteristics of atmospheric circulation patterns over East Asia and their impacts on precipitation in summer. Clim Res 78:117-133. https://doi.org/10.3354/cr01544 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 78, No. 2. Online publication date: July 11, 2019 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2019 Inter-Research.

Structural Changes in the Pacific–Japan Pattern in the Late 1990s

AbstractThe Pacific–Japan (PJ) pattern, also known as the East Asia–Pacific pattern, is a teleconnection that significantly influences the East Asian summer climate on various time scales. Based on several reanalysis and observational datasets, this study suggests that the PJ pattern has experienced a distinct three-dimensional structural change in the late 1990s. Compared with those during 1979–98, the PJ pattern shifts eastward by approximately 20° during 1999–2015, and the intensity of its barotropic structure in the extratropics weakens significantly. As a result, its influences on the summer rainfall along the mei-yu band are weakened after the late 1990s. These observed changes can be attributed to three reasons. First, the location where the PJ pattern is excited shifts eastward. Second, the easterly shear of the background wind is very weak around the source region of the PJ pattern after the late 1990s, which prevents the convection-induced baroclinic mode from converting into barotropic mode and thereby from propagating into the extratropics. Third, the PJ pattern–induced rainfall anomalies are weak along the mei-yu band after the late 1990s. As a result, their feedbacks to the PJ pattern become weak and play a considerably reduced role in maintaining the structure of the PJ pattern in the midlatitudes. In contrast, the eddy energy conversion from the basic flow efficiently maintains the PJ pattern before and after the late 1990s and thereby contributes little to the observed change.

Predictable and Unpredictable Components of the Summer East Asia–Pacific Teleconnection Pattern

The East Asia–Pacific (EAP) teleconnection pattern is the dominant mode of circulation variability during boreal summer over the western North Pacific and East Asia, extending from the tropics to high latitudes. However, much of this pattern is absent in multi-model ensemble mean forecasts, characterized by very weak circulation anomalies in the mid and high latitudes. This study focuses on the absence of the EAP pattern in the extratropics, using state-of-the-art coupled seasonal forecast systems. The results indicate that the extratropical circulation is much less predictable, and lies in the large spread among different ensemble members, implying a large contribution from atmospheric internal variability. However, the tropical–mid-latitude teleconnections are also relatively weaker in models than observations, which also contributes to the failure of prediction of the extratropical circulation. Further results indicate that the extratropical EAP pattern varies closely with the anomalous surface temperatures in eastern Russia, which also show low predictability. This unpredictable circulation–surface temperature connection associated with the EAP pattern can also modulate the East Asian rainband.

Evolution mechanism of synoptic-scale EAP teleconnection pattern and its relationship to summer precipitation in China

Using ERA-Interim reanalysis daily data and gridded precipitation dataset, the evolution mechanism of East Asia-Pacific (EAP) teleconnection pattern and its relationship to summer precipitation in China were investigated on synoptic timescales based on EOF analysis, composite analysis, and significance test. The results demonstrate that the evolution of synoptic-scale EAP pattern is identified as having a significant relationship with the energy propagation represented by the wave-activity flux (WAF). Such EAP-related WAFs show various features in different levels of the troposphere. In the lower troposphere, the WAF primarily points poleward from the Philippines, playing a vital role in triggering and maintaining the synoptic-scale EAP pattern. A middle tropospheric zonally distributed ridge/trough/ridge wave train provides a favorable westerly waveguide for the southeastward (eastward) energy propagation, converging with a relatively weak poleward WAF over mid-latitude (high-latitude) East Asia. Moreover, the upper-level EAP-related anomalies are partly influenced by two conspicuous eastward WAFs. One may favor the development of Okhotsk anticyclonic (positive) anomaly, and the other one related to the Silk-Road (SR) wave train along the Asian jet converges into the cyclonic (negative) anomaly to greatly strengthen it. Particularly, the highly efficient baroclinic energy conversion responsible for the self-maintenance of SR pattern is also crucial for reinforcing and maintaining this cyclonic anomaly for a prolonged period by extraction of available potential energy from basic flow. In addition, during EAP pattern lifetime, due to the strong moisture flux convergence and upper-level divergence, the long-lasting strong ascents of moist/warm air along a moist and thick layer, therefore induce the summer consecutive extreme precipitation in the middle and lower reaches of Yangtze River.

Atmospheric Circulation Patterns over East Asia and Their Connection with Summer Precipitation and Surface Air Temperature in Eastern China during 1961–2013

Based on the NCEP/NCAR reanalysis data and Chinese observational data during 1961–2013, atmospheric circulation patterns over East Asia in summer and their connection with precipitation and surface air temperature in eastern China as well as associated external forcing are investigated. Three patterns of the atmospheric circulation are identified, all with quasi-barotropic structures: (1) the East Asia/Pacific (EAP) pattern, (2) the Baikal Lake/Okhotsk Sea (BLOS) pattern, and (3) the eastern China/northern Okhotsk Sea (ECNOS) pattern. The positive EAP pattern significantly increases precipitation over the Yangtze River valley and favors cooling north of the Yangtze River and warming south of the Yangtze River in summer. The warm sea surface temperature anomalies over the tropical Ind-ian Ocean suppress convection over the northwestern subtropical Pacific through the Ekman divergence induced by a Kelvin wave and excite the EAP pattern. The positive BLOS pattern is associated with below-average precipitation south of the Yangtze River and robust cooling over northeastern China. This pattern is triggered by anomalous spring sea ice concentration in the northern Barents Sea. The anomalous sea ice concentration contributes to a Rossby wave activity flux originating from the Greenland Sea, which propagates eastward to North Pacific. The positive ECNOS pattern leads to below-average precipitation and significant warming over northeastern China in summer. The reduced soil moisture associated with the earlier spring snowmelt enhances surface warming over Mongolia and northeastern China and the later spring snowmelt leads to surface cooling over Far East in summer, both of which are responsible for the formation of the ECNOS pattern.

Potential Influence of the East Asia–Pacific Teleconnection Pattern on Persistent Precipitation in South China: Implications of Atypical Yangtze River Valley Cases

Abstract In this study, cases of the East Asia–Pacific (EAP) teleconnection pattern not responsible for persistent precipitation processes in the Yangtze River valley (YRV) have been investigated. The results suggest that such a type of EAP pattern has some linkage with persistent precipitation processes in south China (SC) with the following properties: 1) in response to the negative SSTAs and anticyclone near the Philippines, the meridional energy propagates from the low latitudes over the north of the Philippines; 2) the western Pacific subtropical high (WPSH) then intensifies and extends westward; 3) a meridional triple structure of the EAP teleconnection pattern is established; 4) at the same time, the cyclonic circulation over northeastern China introduces cold and dry air to the lower latitudes, merging with the water vapor into SC and leading to heavy precipitation from the fringe of the WPSH, the South China Sea, and the Bay of Bengal and the combination of systems persists for at least 3 days, leading to the persistent precipitation processes in SC; and 5) compared with the EAP teleconnection responsible for the precipitation in YRV, the positions of the three centers in the mid- and low latitudes are more southerly located than the YRV EAP centers. Further study indicates that the ocean surface heat conditions in the areas near the Philippines seem to be important in affecting the EAP teleconnection pattern for persistent precipitation processes in SC. Finally, all of the cases with persistent precipitation in SC during 1961–2010 linked with the EAP pattern have been investigated; the results are consistent with the above conclusions.

Low-frequency oscillations of the East Asia–Pacific teleconnection pattern and their impacts on persistent heavy precipitation in the Yangtze–Huai River valley

Based on the daily reanalysis data from NCEP–NCAR and daily precipitation data from the China National Meteorological Information Center, an ensemble empirical mode decomposition method is employed to extract the predominant oscillation modes of the East Asia–Pacific (EAP) teleconnection pattern. The influences of these low-frequency modes on persistent heavy precipitation in the Yangtze–Huai River (YHR) valley are investigated. The results indicate that the EAP pattern and rainfall in YHR valley both exhibit remarkable 10–30- and 30–60-day oscillations. The impacts of the EAP pattern on the YHR persistent heavy precipitation can be found on both the 10–30- and 30–60-day timescales—the 10–30-day scale for most cases. Composite analysis indicates that, on the 10–30-day timescale, formation of the EAP pattern in the lower and middle troposphere is determined by convective systems near the tropical western Pacific; whereas in the middle troposphere, the phase transition is jointly contributed by both the dispersion of zonal wave energies at higher latitudes and convective systems over the South China Sea. In the context of the 10–30-day EAP pattern, the anomalously abundant moisture is transported by an anomalous subtropical anticyclone system, and strong moisture convergence results from that anomalous anticyclone system and a cyclonic system in the midlatitude East Asia. Such a combination of systems persists for at least three days, contributing to the formation of persistent heavy precipitation in the YHR valley.

Synoptic‐scale precursors of the East Asia/Pacific teleconnection pattern responsible for persistent extreme precipitation in the Yangtze River Valley

Synoptic‐scale precursors of the typical East Asia/Pacific (EAP) teleconnection pattern responsible for persistent extreme precipitation events (PEPEs) in the Yangtze River Valley (YRV) are investigated, based on a composite analysis. The results reveal that, about one week prior to PEPEs, a blocking high develops near the Sea of Okhotsk owing to an eastward energy dispersion and further strengthens markedly due to poleward energy dispersion from low latitudes. Subsequently, a meridional tripole structure of the typical EAP pattern becomes well established by this blocking, along with a westward‐migrated strong negative anomaly at midlatitudes/positive anomaly at lower latitudes. In the lower troposphere, a westward‐progressive anomalous anticyclone–cyclone pair can be identified up to about a week prior to PEPEs, contributing to greatly enhanced moisture transport towards the YRV with a magnitude anomaly over three standard deviations above normal. A midlatitude anomalous cyclone associated with the EAP pattern evolution and the eastward‐extended South Asia High combine to provide favourable upper‐level divergence. Correspondingly, strong ascent of low‐level warm/moist air along a quasi‐stationary front leads to PEPEs in the YRV. A contrastive analysis between evolution of typical wet and dry EAP regimes indicates that EAP‐induced PEPEs are more likely to occur in the YRV, with the ridge of the western Pacific subtropical high typically staying around the northeastern quadrant of the South China Sea. This contrasting analysis also highlights the importance of the upstream pre‐existing ridge to early strengthening of the Okhotsk blocking.

An Introduction to the Integrated Climate Model of the Center for Monsoon System Research and its simulated influence of El Niño on East Asian-western North Pacific climate

This study introduces a new global climate model—the Integrated Climate Model (ICM)—developed for the seasonal prediction of East Asian-western North Pacific (EA-WNP) climate by the Center for Monsoon System Research at the Institute of Atmospheric Physics (CMSR, IAP), Chinese Academy of Sciences. ICM integrates ECHAM5 and NEMO2.3 as its atmospheric and oceanic components, respectively, using OASIS3 as the coupler. The simulation skill of ICM is evaluated here, including the simulated climatology, interannual variation, and the influence of El Nino as one of the most important factors on EA-WNP climate. ICM successfully reproduces the distribution of sea surface temperature (SST) and precipitation without climate shift, the seasonal cycle of equatorial Pacific SST, and the precipitation and circulation of East Asian summer monsoon. The most prominent biases of ICM are the excessive cold tongue and unrealistic westward phase propagation of equatorial Pacific SST. The main interannual variation of the tropical Pacific SST and EA-WNP climate—El Nino and the East Asia-Pacific Pattern—are also well simulated in ICM, with realistic spatial pattern and period. The simulated El Nino has significant impact on EA-WNP climate, as in other models. The assessment shows ICM should be a reliable model for the seasonal prediction of EA-WNP climate.

Predictability of the western North Pacific summer climate demonstrated by the coupled models of ENSEMBLES

The Asian monsoon system, including the western North Pacific (WNP), East Asian, and Indian monsoons, dominates the climate of the Asia-Indian Ocean-Pacific region, and plays a significant role in the global hydrological and energy cycles. The prediction of monsoons and associated climate features is a major challenge in seasonal time scale climate forecast. In this study, a comprehensive assessment of the interannual predictability of the WNP summer climate has been performed using the 1-month lead retrospective forecasts (hindcasts) of five state-of-the-art coupled models from ENSEMBLES for the period of 1960–2005. Spatial distribution of the temporal correlation coefficients shows that the interannual variation of precipitation is well predicted around the Maritime Continent and east of the Philippines. The high skills for the lower-tropospheric circulation and sea surface temperature (SST) spread over almost the whole WNP. These results indicate that the models in general successfully predict the interannual variation of the WNP summer climate. Two typical indices, the WNP summer precipitation index and the WNP lower-tropospheric circulation index (WNPMI), have been used to quantify the forecast skill. The correlation coefficient between five models’ multi-model ensemble (MME) mean prediction and observations for the WNP summer precipitation index reaches 0.66 during 1979–2005 while it is 0.68 for the WNPMI during 1960–2005. The WNPMI-regressed anomalies of lower-tropospheric winds, SSTs and precipitation are similar between observations and MME. Further analysis suggests that prediction reliability of the WNP summer climate mainly arises from the atmosphere–ocean interaction over the tropical Indian and the tropical Pacific Ocean, implying that continuing improvement in the representation of the air–sea interaction over these regions in CGCMs is a key for long-lead seasonal forecast over the WNP and East Asia. On the other hand, the prediction of the WNP summer climate anomalies exhibits a remarkable spread resulted from uncertainty in initial conditions. The summer anomalies related to the prediction spread, including the lower-tropospheric circulation, SST and precipitation anomalies, show a Pacific-Japan or East Asia-Pacific pattern in the meridional direction over the WNP. Our further investigations suggest that the WNPMI prediction spread arises mainly from the internal dynamics in air–sea interaction over the WNP and Indian Ocean, since the local relationships among the anomalous SST, circulation, and precipitation associated with the spread are similar to those associated with the interannual variation of the WNPMI in both observations and MME. However, the magnitudes of these anomalies related to the spread are weaker, ranging from one third to a half of those anomalies associated with the interannual variation of the WNPMI in MME over the tropical Indian Ocean and subtropical WNP. These results further support that the improvement in the representation of the air–sea interaction over the tropical Indian Ocean and subtropical WNP in CGCMs is a key for reducing the prediction spread and for improving the long-lead seasonal forecast over the WNP and East Asia.