Summer climate in the Northwestern Pacific (NWP) displays large year-to-year variability, affecting densely populated Southeast and East Asia by impacting precipitation, temperature, and tropical cyclones. The Pacific–Japan (PJ) teleconnection pattern provides a crucial link of high predictability from the tropics to East Asia. Using coupled climate model experiments, we show that the PJ pattern is the atmospheric manifestation of an air–sea coupled mode spanning the Indo-NWP warm pool. The PJ pattern forces the Indian Ocean (IO) via a westward propagating atmospheric Rossby wave. In response, IO sea surface temperature feeds back and reinforces the PJ pattern via a tropospheric Kelvin wave. Ocean coupling increases both the amplitude and temporal persistence of the PJ pattern. Cross-correlation of ocean–atmospheric anomalies confirms the coupled nature of this PJIO mode. The ocean–atmosphere feedback explains why the last echoes of El Nino–Southern Oscillation are found in the IO-NWP in the form of the PJIO mode. We demonstrate that the PJIO mode is indeed highly predictable; a characteristic that can enable benefits to society.

Origin of Seasonal Predictability for Summer Climate over the Northwestern Pacific

The South China Sea Monsoon Experiment (SCSMEX) is an international field experiment with the objective to better understand the key physical processes for the onset and evolution of the Asian summer monsoon in relation to fluctuation of the regional hydrologic cycle over Southeast Asian, southern East Asia, aiming at improving monsoon prediction. In this article, we present a description of the major meteorological observation platforms during the Intensive Observing Periods (IOP) of SCSMEX. We also provide highlights of early results and discussions of the role of SCSMEX in providing valuable in-situ data for calibration of satellite rainfall estimate from the Tropical Rainfall Measuring Mission (TRMM). Preliminary results indicate that there are distinctive stages in the onset of the South China Sea monsoon including possibly strong influences from extratropical systems as well as from convection over the Indian Ocean and the Bay of Bengal. There are some tantalizing evidence of complex interactions between the supercloud cluster development over the Indian Ocean, advancing southwest monsoon flow over the South China Sea, midlatitude disturbances and the western Pacific subtropical high, possibly contributing to the disastrous flood over Yangtze River Basin in China during June 1998.

The Field Operations and Early Results of the South China Sea Monsoon Experiment (SCSMEX)

The East Asian trough (EAT) is a distinct component of the boreal winter circulation whose strength corresponds to the amplitude of the Northern Hemispheric stationary waves. In this study, the mechanism and climatic impacts of the intraseasonal variations of the EAT’s strength are investigated through composite analysis and dynamical diagnostics. The significant roles played by the low-frequency Rossby wave (RW) and synoptic transient eddy (TE) are revealed. Before the peaks of strong EAT events, an upper-tropospheric RW train propagates across northern Eurasia and interacts with preexisting surface cold anomalies over central Siberia. This pattern intensifies the Siberian high and causes RW convergence toward the EAT, leading to 30% of the EAT’s amplification directly via the RW-induced feedback forcing. Meanwhile, RW weakens the background baroclinicity and reduces TE activities near the entrance region of the North Pacific storm track. The TE-induced feedback forcing leads to another 30% of th...

Intraseasonal Variation of the Strength of the East Asian Trough and Its Climatic Impacts in Boreal Winter

把数据基于 NCEP/ NCAR 分析东方亚洲冬季季风(EAWM ) 的 interannual 可变性与一个最新定义的 EAWM 紧张索引被学习。显著特征为一强壮(弱)冬季季风包括强壮(弱)沿着沿海的东亚的在北方的风，冷(温暖)东方亚洲大陆和包围的海并且温暖(寒冷)从副热带的中央太平洋的海洋到热带西方的太平洋，高(低)在东方亚洲大陆的压力并且低(高度)在邻近的海洋并且深迫使(弱)在 500 hPa 的东方亚洲马槽。这些 interannual 变化被显示仔细在热带太平洋，被连接到 SST 异例两个在西方、东方的太平洋。结果建议 EAWM 的力量被在热带太平洋上与 SST 异例联系的过程主要影响。当在热带东方太平洋有一个积极 SST 异例时， EAWM 通常变得弱(El Ni ? o ) ，并且当有一个否定 SST 异例时，它变得强壮(La Ni ? 一) 。而且，在华南海的 SST 异例被发现是仔细与 EAWM 有关并且可以坚持到下列夏天。两在在中国的 850 hPa 和降雨的发行量证实在 EAWM 和下列东方亚洲人之间的连接夏天季风。可能的原因为最近在中国的 1998 夏天洪水也简短被讨论。关键词东方亚洲冬季季风 - Interannual 可变性 - SST - 夏天季风这研究被鈥 ? 公民钥匙计划，并且由中国科学院的关键工程(KZ 952-S1-404 ) 为开发第 1 部分基本科学鈥 ? G1998040900 支持。

The Interannual Variability of East Asian Winter Monsoon and Its Relation to the Summer Monsoon

. Atmospheric pollution has become a serious environmental and social problem in China. Over the past 30 years, the number of winter (December–February) haze days over the North China Plain (WHDNCP) was greatest in 2014. In addition to anthropogenic influence, climate anomalies also played a role. Thus, it is necessary to analyze the anomalous atmosphere circulations associated with haze pollution of this year in detail. Near the surface, the weaker East Asian winter monsoon pattern, causing southerly winds over the North China Plain, could aggravate the situation of haze. In the lower and middle troposphere, taking the anticyclone circulation over North China as an intermediate system, the positive phases of the eastern Atlantic/western Russia (EA/WR), the western Pacific (WP), and the Eurasia (EU) patterns led to a worse air pollution dispersion condition that contributed to a larger number of WHDNCP. In 2014, these three patterns could be recognized from the wind anomalies in the lower troposphere. The preceding autumn (September–November) Arctic sea ice (ASI) anomalies over the eastern Hemisphere and the warmer winter surface over Eurasia might have induced or intensified the positive EA/WR pattern in 2014. These two external forcings, together with the pre-autumn sea surface temperature anomalies in the Pacific, might have also stimulated or enhanced the positive EU-like patterns. The anomalous surface temperature in autumn 2014 was efficient in intensifying anomalous circulations such as the positive phase of the WP pattern. The opposite case of minimum WHDNCP in 2010 further supports the mechanism of how EA/WR and WP patterns and associated external factors altered the local climate conditions to impact the WHDNCP.

/pdf/understanding-severe-winter-haze-events-in-the-north-china-589npu4rro.pdf

Understanding severe winter haze events in the North China Plain in 2014: roles of climate anomalies

The Eurasian (EU) pattern is a distinct teleconnection pattern observed in boreal winter. Since the EU pattern was first identified, three types have been reported in the literature: the conventional EU pattern; the type 1 EU pattern, or Scandinavian (SCAND) pattern; and the type 2 EU pattern, or East Atlantic/West Russia (EATL/WRUS) pattern. Based on several reanalysis and observational datasets, the three EU patterns are extracted using the rotated empirical orthogonal function method. In order to provide a further distinction and understanding of the three EU patterns, a comprehensive side-by-side comparison is performed among them including their temporal variability, horizontal and vertical structure, related stationary Rossby wave activity, impact on climate, and possible driving factors associated with external forcing. The results reveal that all three EU patterns are characterised by a clear quasi-barotropic wave-train structure, but each has a distinct source and centre of action. Accordingly, their impacts on the precipitation and surface air temperature also differ from one other. Further evidence suggests that the conventional EU pattern is likely driven by anomalous sea surface temperatures (SST) over the North Atlantic, in which process the transient eddies are actively involved. The SCAND pattern is partly maintained by the vorticity source over Western Europe, which arises from the anomalous convergence/divergence over the Mediterranean and is efficiently driven by the tropical and southern Indian Ocean SST via divergent circulation. The EATL/WRUS pattern shows some linkage to the North American snow cover, and the involved process remains unclear and needs further investigation.

Three Eurasian teleconnection patterns: spatial structures, temporal variability, and associated winter climate anomalies

The 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...

/pdf/structural-changes-in-the-pacific-japan-pattern-in-the-late-47h372ghu2.pdf

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

The Eurasian (EU) pattern was shown to be closely linked to the North Atlantic sea surface temperature (SST) in boreal winter, and this study suggest that such linkage varies with time and that the structure of the EU pattern also changes accordingly. During the period with strong EU-SST linkage (1961–1977 and 1993–2013, denoted as HIGH epoch), the EU pattern is a well-defined barotropic wave train stretching from the North Atlantic towards East Asia-western North Pacific, and it facilitates cooling and slight reduction of precipitation over East Asia and enhanced precipitation over Europe in its positive phase. During the period with weak EU-SST linkage (1948–1960 and 1978–1992, denoted as LOW epoch), in contrast, its centre over Northern Europe weakens sharply, and the wave-like structure of the EU pattern is not well established. In this case, its influences on precipitation over Europe almost vanish, but its influences on both the surface air temperature and precipitation over East Asia amplify significantly. The Atlantic centre of the EU pattern forms from different mechanism during the two epochs. It can be excited by the underlying North Atlantic SST via eddy-mediated processes during the HIGH epoch, while it is likely generated by an incoming Rossby wave train from upstream region during the LOW epoch. Nevertheless, its location and intensity remain similar during the two epochs. Numerical experiments with a barotropic model suggest that the contrasting structure of the EU pattern is mainly attributed to the changes of the atmospheric mean flow.

Time-varying structure of the wintertime Eurasian pattern: role of the North Atlantic sea surface temperature and atmospheric mean flow

https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/asl.964

The record-breaking heat wave of June 2019 in Central Europe

The El Nino–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 a...

Yuyun Liu

Papers

Three Eurasian teleconnection patterns: spatial structures, temporal variability, and associated winter climate anomalies

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

Time-varying structure of the wintertime Eurasian pattern: role of the North Atlantic sea surface temperature and atmospheric mean flow

The record-breaking heat wave of June 2019 in Central Europe

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