Interdecadal Weakening of the East Asian Winter Monsoon in the Mid-1980s: The Roles of External Forcings

2018 ◽  
Vol 31 (21) ◽  
pp. 8985-9000 ◽  
Author(s):  
Jiapeng Miao ◽  
Tao Wang ◽  
Huijun Wang ◽  
Yali Zhu ◽  
Jianqi Sun
Keyword(s):  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Monsoon Circulation ◽  
Jet Stream ◽  
Anthropogenic Aerosols ◽  
Coupled Models ◽  
East Asian Trough ◽  
Asian Winter Monsoon ◽  
External Forcings

Observations show that the East Asian winter monsoon (EAWM) experienced an interdecadal weakening in the mid-1980s. This is evident for all members of the EAWM system (i.e., East Asian trough, upper-tropospheric jet stream, and lower-tropospheric monsoon circulation). Here, we investigate the relative contributions of natural (volcanic aerosols and solar variability) and anthropogenic [greenhouse gases (GHGs) and anthropogenic aerosols] forcings to this interdecadal weakening using multiple coupled models within phase 5 of the Coupled Model Intercomparison Project (CMIP5). The results indicate that in the midtroposphere, the increased GHG concentrations play an important role in weakening the East Asian trough (EAT) by increasing the sea surface temperatures (SSTs) over the North Pacific. In the upper troposphere, natural external forcings contribute to the observed weakening of the meridional shear of the East Asian jet stream (EAJS) by regulating the meridional temperature gradient (MTG) over the East Asian region. In the lower troposphere, both anthropogenic and natural forcings can weaken the Siberian high during this period. Overall, based on the present analysis of the CMIP5 output, GHGs and natural forcings play key roles in shaping the observed interdecadal weakening of the EAWM during the mid-1980s. Additionally, contributions from internal variability cannot be neglected and require further investigation.

Changes in the relationship between the East Asian winter monsoon and ENSO under global warming

2020 ◽  
Author(s):  
Zixuan Jia ◽  
Massimo Bollasina ◽  
Chaofan Li ◽  
Ruth Doherty ◽  
Oliver Wild
Keyword(s):  
Global Warming ◽  
East Asian Winter Monsoon ◽  
Southern Oscillation ◽  
East Asian ◽  
Winter Monsoon ◽  
Pacific Region ◽  
Anthropogenic Aerosols ◽  
Asian Winter Monsoon ◽  
Asian Pacific Region ◽  
Asian Pacific

<p>The East Asian winter monsoon (EAWM) is a prominent feature of the northern hemisphere atmospheric circulation during boreal winter, which has a large influence on weather and climate of the Asian-Pacific region. At interannual time scales, the strength of the EAWM is strongly influenced by the El Niño-Southern Oscillation (ENSO), while the ENSO-EAWM relationship displays pronounced interdecadal variations associated with changes in the ENSO teleconnection pathways to East Asia. Using future transient simulations from the Max Planck Institute-Grand Ensemble (MPI-GE), changes in the ENSO-EAWM relationship are examined at various global warming levels during the 21<sup>st</sup>-century. Results indicate that this relationship will enhance from present-day to +1.5°C, and then weaken until +3°C, strongly impacted by changes in anthropogenic forcing with internal variability playing a negligible role. The ENSO-EAWM relationship is strongly related to the background mean state of both the EAWM and ENSO under global warming. Both the climatological EAWM strength and the ENSO-related anomalies across the Asian-Pacific region contribute to changes in the ENSO-EAWM relationship. Furthermore, anthropogenic aerosols are also found to play a major role in influencing the ENSO-EAWM relationship under moderate warming (up to 1.5°C).</p>

Roles of Intraseasonal Disturbances and Diabatic Heating in the East Asian Jet Stream Variabilities Associated with the East Asian Winter Monsoon

2018 ◽  
Vol 31 (7) ◽  
pp. 2871-2887 ◽  
Author(s):  
Nagio Hirota ◽  
Mai Ohta ◽  
Yousuke Yamashita ◽  
Masaaki Takahashi
Keyword(s):  
Diabatic Heating ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Low Frequency ◽  
Winter Monsoon ◽  
Jet Stream ◽  
Mean Flow ◽  
Asian Winter Monsoon ◽  
Frequency Components ◽  
East Asian Jet Stream

This study evaluates the relative importance of diabatic heating and intraseasonal disturbances with regard to the variabilities of the East Asian jet stream (EAJS) associated with the East Asian winter monsoon (EAWM). First, strong and weak monsoon years are selected based on the EAWM index of Jhun and Lee, which is highly correlated with the monsoon northerlies between the Eurasian continent and the Pacific. The EAJS is stronger and narrower in strong monsoon years and weaker and wider in weak monsoon years. Model experiments were performed to investigate the atmospheric response to the diabatic heating and the eddy–mean flow feedback from the intraseasonal disturbances. The diabatic heating is closely related to the convective activities. The intraseasonal disturbances include high-frequency components with periods of 3–10 days and low-frequency components with periods of 10–90 days. The model results indicate that the diabatic heating plays a major role maintaining the stronger and weaker EAJS in the strong and weak monsoon years, respectively, whereas the impacts of the eddy feedback are relatively small.

scholarly journals Change in Relationship between the East Asian Winter Monsoon and the East Asian Jet Stream during the 1998–99 Regime Shift

2019 ◽  
Vol 32 (18) ◽  
pp. 6163-6175 ◽  
Author(s):  
Se-Yong Song ◽  
Sang-Wook Yeh ◽  
Jae-Heung Park
Keyword(s):  
East Asian Winter Monsoon ◽  
East Asian ◽  
Hadley Circulation ◽  
Winter Monsoon ◽  
Jet Stream ◽  
Decadal Change ◽  
Reanalysis Dataset ◽  
Asian Winter Monsoon ◽  
East Asian Jet Stream ◽  
The Relationship

Abstract A composite analysis was conducted on the reanalysis dataset for 1979–2016, along with an idealized model experiment to show that the relationship between the East Asian jet stream (EAJS) and the East Asian winter monsoon (EAWM) is nonstationary. The relationship between EAWM and the EAJS weakened during the late 1990s. This decadal change in the EAJS–EAWM relationship was mainly due to a change in the secondary circulation across the EAJS between two contrasting periods, induced by the northward shift of the EAJS. A possible mechanism associated with the decadal change in meridional displacement of the EAJS is proposed. The enhanced convective activity in the western tropical Pacific after the late 1990s results in stronger Hadley circulation that could have contributed to the northward displacement of the Hadley circulation boundary latitude. Subsequently, this leads to the northward shift of the EAJS. Therefore, it is necessary to define a new EAJS index to account for the EAWM variability based on the change in the oceanic and atmospheric mean state across the late 1990s.

scholarly journals Distinct Modes of the East Asian Winter Monsoon

2006 ◽  
Vol 134 (8) ◽  
pp. 2165-2179 ◽  
Author(s):  
Bingyi Wu ◽  
Renhe Zhang ◽  
Rosanne D’Arrigo
Keyword(s):  
East Asia ◽  
Atmospheric Circulation ◽  
East Asian Winter Monsoon ◽  
Southern Oscillation ◽  
East Asian ◽  
Winter Monsoon ◽  
The Arctic ◽  
East Asian Trough ◽  
Siberian High ◽  
Asian Winter Monsoon

Abstract Two distinct modes of the East Asian winter monsoon (EAWM) have been identified, and they correspond to real and imaginary parts of the leading mode of the EAWM, respectively. Analyses of these modes used the National Centers for Environment Prediction (NCEP) and National Center for Atmospheric Research (NCAR) monthly mean reanalysis datasets for the period 1968–2003, as well as the Southern Oscillation index (SOI), North Atlantic Oscillation index, and eastern equatorial Pacific sea surface temperature (SST) data. Results were obtained by resolving a complex Hermite matrix derived from 850-hPa anomalous wind fields, and determining the resulting modes’ associations with several climate variables. The first distinct mode (M1) is characterized by an anomalous meridional wind pattern over East Asia and the western North Pacific. Mode M1 is closely related to several features of the atmospheric circulation, including the Siberian high, East Asian trough, East Asian upper-tropospheric jet, and local Hadley circulation over East Asia. Thus, M1 reflects the traditional EAWM pattern revealed in previous studies. The second distinct EAWM mode (M2), which was not identified previously, displays dominant zonal wind anomalies over the same area. Mode M2 exhibits a closer relation than M1 to sea level pressure anomalies over the northwestern Pacific southeast of Japan and with the SOI and equatorial eastern Pacific SST. Unlike M1, M2 does not show coherent relationships with the Siberian high, East Asian trough, and East Asian upper-tropospheric jet. Since atmospheric circulation anomalies relevant to M2 exhibit a quasi-barotropic structure, its existence cannot simply be attributed to differential land–sea heating. El Niño events tend to occur in the negative phase of M1 and the positive phase of M2, both corresponding to a weakened EAWM. The Arctic Oscillation does not appear to impact the EAWM on interannual time scales. Although the spatial patterns for the two modes are very different, the two distinct modes are complementary, with the leading EAWM mode being a linear combination of the two. The results herein therefore demonstrate that a single EAWM index may be inappropriate for investigating and predicting the EAWM.

scholarly journals The Linkage between Upper-Level Jet Streams over East Asia and East Asian Winter Monsoon Variability

2015 ◽  
Vol 28 (22) ◽  
pp. 9013-9028 ◽  
Author(s):  
Xiao Luo ◽  
Yaocun Zhang
Keyword(s):  
East Asia ◽  
Barents Sea ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
The Arctic ◽  
The Tibetan Plateau ◽  
East Asian Trough ◽  
Asian Winter Monsoon ◽  
Upper Level

Abstract This study investigates the linkage between East Asian winter monsoon (EAWM) variability and upper-level jets, with particular focus on the East Asian polar front jet (PJ) and its concurrent variation with the subtropical jet located to the south of the Tibetan Plateau (TSJ). The winter upper-level zonal wind variations over the Asian landmass (70°–120°E) are dominated by two principal modes (i.e., meridional displacement of the PJ and out-of-phase variation in the intensity of the TSJ and PJ) and they are closely linked to the EAWM northern mode and southern mode, respectively. Southward shifting of the PJ concurs with northwestward displacement of the Siberian high (SH), an enhanced northern East Asian trough, leading to cold winter in northern East Asia. Meanwhile the simultaneous TSJ intensification and PJ weakening is linked to an amplified SH, a southward shift of the Aleutian low (AL), a strengthened southern East Asian trough, and a wavelike anomaly pattern extending from western Barents Sea downstream to East Asia at the 500-hPa level. Equatorward shift of the PJ is associated with La Niña conditions in the tropics and sea ice anomalies over the Arctic. An intensified TSJ and weakened PJ are preceded by autumn warming over the central and eastern Pacific Ocean and are linked to circulation anomalies induced by the extensions of stationary Rossby waves, as well as synoptic-scale transient eddy activity anomalies. Therefore, a combination of external forcing and internal atmospheric dynamics plays a role in driving the variations of two leading EOFs, and there is potential for seasonal forecasting of both modes.

Ice-Volume Forcing of East Asian Winter Monsoon Variations in the Past 800,000 Years

1995 ◽  
Vol 44 (2) ◽  
pp. 149-159 ◽  
Author(s):  
Zhongli Ding ◽  
Tungsheng Liu ◽  
Nat W. Rutter ◽  
Zhiwei Yu ◽  
Zhengtang Guo ◽  
...  
Keyword(s):  
Grain Size ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Continuous Process ◽  
Loess Soil ◽  
Winter Monsoon ◽  
Monsoon Circulation ◽  
Asian Winter Monsoon ◽  
Ice Volume ◽  
The Past

AbstractParticle-size measurements of some typical loess-soil samples taken in different localities of the Chinese Loess Plateau demonstrate that the grain size ratio of <2 μm/>10 μm (%) can be used as an indicator of variations in intensity of the East Asian winter monsoon winds. Grain-size curves of the Baoji and Weinan sections show that this proxy indicator is very sensitive to loess-soil alterations. Analytical results also suggest that during soil-forming periods, eolian dust accumulation was still substantial and, hence, loess deposition can be regarded as a nearly continuous process during the Quaternary period. In this study we compared the Baoji grain-size time series with the SPECMAP marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation. Both records show good agreement at both time and frequency domains. In particular, the winter monsoon variations are also dominated by a 100,000 yr period over the past 800,000 yr. It is thus inferred that direct local insolation forcing could be less important in driving the East Asian winter monsoon variability, and, alternatively, variations in glacial-age boundary conditions may have played a key role in modulating and pacing its strength and timing.

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