Interannual Meridional Displacement of the Upper-Tropospheric Westerly Jet over Western East Asia in Summer

The interannual meridional displacement of the upper-tropospheric westerly jet over the eastern portion of East Asia in summer has been well documented.This study,however,investigates the interannual meridional displacement of the westerly jet over the western portion of East Asia in summer,which is distinct from its eastern counterpart.The results show that the meridional displacement of the western East Asian jet shows a clear asymmetric feature;that is,there are remarkable differences between the southward and northward displacement of the jet.The southward displacement of the jet corresponds to suppressed convection in the tropical western North Pacific and Maritime Continent and enhanced convection in the equatorial Pacific,which can be explained by the warmer sea surfaces found in the northern Indian Ocean and equatorial eastern Pacific.These tropical anomalies somewhat resemble those associated with the eastern East Asian jet variability.However,the northward displacement of the western East Asian jet does not correspond to significant convection and SST anomalies in the entire tropics;instead,the northward displacement of the jet corresponds well to the positive phase of the Arctic Oscillation.Furthermore,the meridional displacement of the western jet has asymmetric impacts on rainfall and surface air temperatures in East Asia.When the western jet shifts northward,more precipitation is found over South China and Northeast China,and higher temperatures appear in northern China.By contrast,when the jet shifts southward,more precipitation appears over the East Asian rainy belt,including the Yangtze River valley,South Korea,and southern and central Japan and warmer temperatures are found South and Southeast Asia.

Interannual Meridional Displacement of the East Asian Upper-tropospheric Jet Stream in Summer

On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-July-August, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.

Weakening of Interannual Variability in the Summer East Asian Upper-tropospheric Westerly Jet since the Mid-1990s

In this study,we found that the intensity of interannual variability in the summer upper-tropospheric zonal wind has significantly weakened over Northeast Asia and the subtropical western North Pacific（WNP） since the mid-1990s,concurrent with the previously documented decrease of the westerly jet over North China and Northwest China.Corresponding to this weakening of zonal wind variability,the meridional displacement of the East Asian westerly jet（EAJ） manifested as the leading mode of zonal wind variability over the WNP and East Asia（WNP-EA） before the mid-1990s but not afterward.The energetics of the anomalous pattern associated with the meridional displacement of the EAJ suggests that barotropic energy conversion,from basic flow to anomalous patterns,has led to the weakening of the variability in the EAJ meridional displacement and to a change in the leading dominant mode since the mid-1990s.The barotropic energy conversion efficiently maintained the anomalies associated with the variability in the EAJ meridional displacement during 1979-1993 but acted to dampen the anomalies during 1994-2008.A further investigation of the energetics suggests that the difference in the patterns of the circulation anomaly associated with either the first leading mode or the meridional displacement of the EAJ,i.e.,a southwest-northeast tilted pattern during 1979-1993 and a zonally oriented pattern during 1994-2008,has contributed greatly to the change in barotropic energy conversion.

Predictability of the Summer East Asian Upper-Tropospheric Westerly Jet in ENSEMBLES Multi-Model Forecasts

The interannual variation of the East Asian upper-tropospheric westerly jet （EAJ） significantly affects East Asian climate in summer. Identifying its performance in model prediction may provide us another viewpoint, from the perspective of uppertropospheric circulation, to understand the predictability of summer climate anomalies in East Asia. This study presents a comprehensive assessment of year-to-year variability of the EAJ based on retrospective seasonal forecasts, initiated from 1 May, in the five state-of-the-art coupled models from ENSEMBLES during 1960-2005. It is found that the coupled models show certain capability in describing the interannual meridional displacement of the EAJ, which reflects the models＇ performance in the first leading empirical orthogonal function （EOF） mode. This capability is mainly shown over the region south of the EAJ axis. Additionally, the models generally capture well the main features of atmospheric circulation and SST anomalies related to the interannual meridional displacement of the EAJ. Further analysis suggests that the predicted warm SST anomalies in the concurrent summer over the tropical eastern Pacific and northern Indian Ocean are the two main sources of the potential prediction skill of the southward shift of the EAJ. In contrast, the models are powerless in describing the variation over the region north of the EAJ axis, associated with the meridional displacement, and interannual intensity change of the EAJ, the second leading EOF mode, meaning it still remains a challenge to better predict the EAJ and, subsequently, summer climate in East Asia, using current coupled models.

Meridional Displacement of the East Asian Upper-tropospheric Westerly Jet and Its Relationship with the East Asian Summer Rainfall in CMIP5 Simulations

As the first leading mode of upper-tropospheric circulation in observations, the meridional displacement of the East Asian westerly jet (EAJ) varies closely with the East Asian rainfall in summer. In this study, the interannual variation of the EAJ meridional displacement and its relationship with the East Asian summer rainfall are evaluated, using the historical simulations of CMIP5 (phase 5 of the Coupled Model Intercomparison Project). The models can generally reproduce the meridional displacement of the EAJ, which is mainly manifested as the first principal mode in most of the simulations. For the relationship between the meridional displacement of the EAJ and East Asian rainfall, almost all the models depict a weaker correlation than observations and exhibit considerably large spread across the models. It is found that the discrepancy in the interannual relationship is closely related to the simulation of the climate mean state, including the climatological location of the westerly jet in Eurasia and rainfall bias in South Asia and the western North Pacific. In addition, a close relationship between the simulation discrepancy and intensity of EAJ variability is also found: the models with a stronger intensity of the EAJ meridional displacement tend to reproduce a closer interannual relationship, and vice versa.

Impacts of Two Types of Northward Jumps of the East Asian Upper-tropospheric Jet Stream in Midsummer on Rainfall in Eastern China

The East Asian upper-tropospheric jet stream （EAJS） typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types： the first type corresponds to the enhanced westerly to the north of the EAJS＇s axis （type A）, while the second type is related to the weakened westerly within the EAJS＇s axis （type B）. In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A （B） jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast （North） China when the EAJS＇s axis jumps from 40~N to 55~N （50~N）. Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.

Experimental study on temperature fluctuations on plate surface induced by coaxial-jet flow

In nuclear reactors,temperature fluctuations of fluids may cause fatigue damage to adjacent structures;this is referred to as thermal striping.Research on thermal striping in the upper plenum has mainly focused on fluid fields.Few experimental studies have been reported on solid structures in a fluid field with a coaxial jet.This study entailed an experimental study of the temperature fluctuations in the fluid and on a plate surface caused by a coaxial jet.The temperature fluctuations of the fluid and plate surfaces located at different heights were analyzed.The cause of the temperature fluctuation was analyzed using a transient temperature distribution.The results show that the mixing of the hot and cold fluids gradually becomes uniform in the positive axial direction.The average surface temperatures tended to be consistent.When the jet reaches the plate surface,the swing of the jet center,contraction and expansion of the cold jet,and changes in the jet shape result in temperature fluctuations.The intensity of the temperature fluctuation was affected by the position.More attention should be paid when the plate is located at a lower height,and between the hot and cold-fluid nozzles.

Anomalous Midsummer Rainfall in Yangtze River-Huaihe River Valleys and Its Association with the East Asia Westerly Jet

In this study, the interannual and interdecadal relationship between midsummer Yangtze River-Huaihe River valley （YHRV） rainfall and the position of the East Asia westerly jet （EAWJ） were investigated. The midsummer YHRV rainfall was found to significantly increase after the 1980s. Moreover, the location of the EAWJ was found abnormally south of the climatic mean during 1980–2008 （ID2） compared to 1951–1979 （ID1）. During ID2, associated with the southward movement of the EAWJ, an anomalous upper-level conver-gence occurred over middle-high latitudes （35° –55° N） and divergence occurred over lower latitudes （～30°N） of East Asia. Correspondingly, anomalous descending and ascending motion was observed in middle-high and lower latitudes along 90°–130° E, respectively, favoring more precipitation over YHRV. On an interan-nual time scale, the EAWJ and YHRV rainfall exhibited similar relationships during the two periods. When the EAWJ was centered abnormally southward, rainfall over YHRV tended to increase. However, EAWJ-related circulations were significantly different during the two periods. During ID1, the circulation of the southward-moving EAWJ exhibited alternating positive–negative–positive distributions from low to middle– high latitudes along the East Asian coast; the most significant anomaly appeared west of the Okhotsk Sea. However, during ID2 the EAWJ was more closely correlated with the tropical and subtropical circulations. Significant differences between ID1 and ID2 were also recorded sea surface temperatures （SSTs）. During ID1, the EAWJ was influenced by the extratropical SST over the northern Pacific; however, the EAWJ was more significantly affected by the SST of the tropical western Pacific during ID2.

Seasonal Variation of the East Asian Subtropical Westerly Jet and Its Association with the Heating Field over East Asia

The structure and seasonal variation of the East Asian Subtropical Westerly Jet （EAWJ） and associations with heating fields over East Asia are examined by using NCEP/NCAR reanalysis data. Obvious differences exist in the westerly jet intensity and location in different regions and seasons due to the ocean-land distribution and seasonal thermal contrast, as well as the dynamic and thermodynamic impacts of the Tibetan Plateau. In winter, the EAWJ center is situated over the western Pacific Ocean and the intensity is reduced gradually from east to west over the East Asian region. In summer, the EAWJ center is located over the north of the Tibetan Plateau and the jet intensity is reduced evidently compared with that in winter. The EAWJ seasonal evolution is characterized by the obvious longitudinal inconsistency of the northward migration and in-phase southward retreat of the EAWJ axis. A good correspondence between the seasonal variations of EAWJ and the meridional differences of air temperature （MDT） in the mid-upper troposphere demonstrates that the MDT is the basic reason for the seasonal variation of EAWJ. Correlation analyses indicate that the Kuroshio Current region to the south of Japan and the Tibetan Plateau are the key areas for the variations of the EAWJ intensities in winter and in summer, respectively. The strong sensible and latent heating in the Kuroshio Current region is closely related to the intensification of EAWJ in winter. In summer, strong sensible heating in the Tibetan Plateau corresponds to the EAWJ strengthening and southward shift, while the weak sensible heating in the Tibetan Plateau is consistent with the EAWJ weakening and northward migration.

The Effect of Transient Eddy on Interannual Meridional Displacement of Summer East Asian Subtropical Jet

Using ERA-40 reanalysis daily data for the period 1958-2002, this study investigated the effect of tran- sient eddy （TE） on the interannual meridional displacement of summer East Asian subtropical jet （EASJ） by conducting a detailed dynamical diagnosis. The summer EASJ axis features a significant interannual coherent meridional displacement. Associated with such a meridional displacement, the TE vorticity forcing anomalies are characterized by a meridional dipole pattern asymmetric about the climatological EASJ axis. The TE vorticity forcing anomalies yield barotropic zonal wind tendencies with a phase meridionally lead- ing the zonal wind anomalies, suggesting that they act to reinforce further meridional displacement of the EASJ and favor a positive feedback in the TE and time-mean flow interaction. However, The TE thermal forcing anomalies induce baroclinic zonal wind tendencies that reduce the vertical shear of zonal wind and atmospheric baroclinicity and eventually suppress the TE activity, favoring a negative feedback in the TE and time-mean flow interaction. Although the two types of TE forcing tend to have opposite feedback roles, the TE vorticity forcing appears to be dominant in the TE effect on the time-mean flow.

Has the East Asian Westerly Jet Experienced a Poleward Displacement in Recent Decades?

Previous studies have suggested a poleward shift of the zonally averaged jet stream due to rapid warming over continents.However,the regional characteristics of the change in the jet stream are not yet understood.Here,we present evidence suggesting that the East Asian westerly jet did not shift poleward in past decades（1980-2004 relative to 1958-1979）,both in winter and summer.Rather,the jet axis has moved southward in summer,but its meridional position is steady in winter.The main change of the jet stream in winter is the enhancement of its intensity.These changes in both summer and winter are consistent with the corresponding changes in the large meridional tropospheric temperature-gradient zone.Based on these results,we suggest that the changes of the jet stream over East Asia are unique and are different from the zonal mean jet stream over the Northern Hemisphere and over the North Atlantic region.

Simulations of the East Asian Subtropical Westerly Jet by LASG/IAP AGCMs

Performances of two LASG/IAP （State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics） Atmospheric General Circulation Models （AGCMs）, namely GAMIL and SAMIL, in simulating the major characteristics of the East Asian subtropical westerly jet （EASWJ） in the upper troposphere are examined in this paper. The mean vertical and horizontal structures and the correspondence of the EASWJ location to the meridional temperature gradient in the upper troposphere are well simulated by two models. However, both models underestimate the EASWJ intensity in winter and summer, and are unable to simulate the bimodal distribution of the major EASWJ centers in mid-summer, relative to the observation, especially for the SAMIL model. The biases in the simulated EASWJ intensity are found to be associated with the biases of the meridional temperature gradients in the troposphere, and furthermore with the surface sensible heat flux and condensation latent heating. The models capture the major characteristics of the seasonal evolution of the diabatic heating rate averaged between 30°-45°N, and its association with the westerly jet. However, the simulated maximum diabatic heating rate in summer is located westward in comparison with the observed position, with a relatively strong diabatic heating intensity, especially in GAMIL. The biases in simulating the diabatic heating fields lead to the biases in simulating the temperature distribution in the upper troposphere, which may further affect the EASWJ simulations. Therefore, it is necessary to improve the simulation of the meridional temperature gradient as well as the diabatic heating field in the troposphere for the improvement of the EASWJ simulation by GAMIL and SAMIL models.

Intermodel Diversity in the Zonal Location of the Climatological East Asian Westerly Jet Core in Summer and Association with Rainfall over East Asia in CMIP5 Models

The East Asian westerly jet(EAJ), an important midlatitude circulation of the East Asian summer monsoon system,plays a crucial role in affecting summer rainfall over East Asia. The multimodel ensemble of current coupled models can generally capture the intensity and location of the climatological summer EAJ. However, individual models still exhibit large discrepancies. This study investigates the intermodel diversity in the longitudinal location of the simulated summer EAJ climatology in the present-day climate and its implications for rainfall over East Asia based on 20 CMIP5 models. The results show that the zonal location of the simulated EAJ core is located over either the midlatitude Asian continent or the western North Pacific(WNP) in different models. The zonal shift of the EAJ core depicts a major intermodel diversity of the simulated EAJ climatology. The westward retreat of the EAJ core is related to a warmer mid–upper tropospheric temperature in the midlatitudes, with a southwest–northeast tilt extending from Southwest Asia to Northeast Asia and the northern North Pacific, induced partially by the simulated stronger rainfall climatology over South Asia. The zonal shift of the EAJ core has some implications for the summer rainfall climatology, with stronger rainfall over the East Asian continent and weaker rainfall over the subtropical WNP in relation to the westward-located EAJ core.

An Assessment of the Predictability of the East Asian Subtropical Westerly Jet Based on TIGGE Data

The predictability of the position,spatial coverage and intensity of the East Asian subtropical westerly jet （EASWJ） in the summers of 2010 to 2012 was examined for ensemble prediction systems （EPSs） from four representative TIGGE centers,including the ECMWF,the NCEP,the CMA,and the JMA.Results showed that each EPS predicted all EASWJ properties well,while the levels of skill of all EPSs declined as the lead time extended.Overall,improvements from the control to the ensemble mean forecasts for predicting the EASWJ were apparent.For the deterministic forecasts of all EPSs,the prediction of the average axis was better than the prediction of the spatial coverage and intensity of the EASWJ.ECMWF performed best,with a lead of approximately 0.5-1 day in predictability over the second-best EPS for all EASWJ properties throughout the forecast range.For probabilistic forecasts,differences in skills among the different EPSs were more evident in the earlier part of the forecast for the EASWJ axis and spatial coverage,while they departed obviously throughout the forecast range for the intensity.ECMWF led JMA by about 0.5-1 day for the EASWJ axis,and by about 1-2 days for the spatial coverage and intensity at almost all lead times.The largest lead of ECMWF over the relatively worse EPSs,such as NCEP and CMA,was approximately 3-4 days for all EASWJ properties.In summary,ECMWF showed the highest level of skill for predicting the EASWJ,followed by JMA.

Responses of the East Asian Jet Stream to the North Pacific Subtropical Front in Spring

This study concerns atmospheric responses to the North Pacific subtropical front （NPSTF） in boreal spring over the period 1982-2014. Statistical results show that a strong NPSTF in spring can significantly enhance the East Asian jet stream （EAJS）. Both transient eddy activity and the atmospheric heat source play important roles in this process. The enhanced atmospheric temperature gradient due to a strong NPSTF increases atmospheric baroclinicity, resulting in an intensification of transient eddy and convection activities. On the one hand, the enhanced transient eddy activities can excite an anomalous cyclonic circulation with a quasi-baraotropical structure in the troposphere to the north of the NPSTF. Accordingly, the related westerly wind anomalies around 30°N can intensify the component of the EAJS over the Northeast Pacific. On the other hand, an enhanced atmospheric heat source over the NPSTF, which is related to increased rainfall, acts to excite an anomalous cyclonic circulation system in the troposphere to the northwest of the NPSTF, which can explain the enhanced component of the EAJS over the Northwest Pacific. The two mechanisms may combine to enhance the EAJS.

WINTERTIME MIDDLE EAST SUBTROPICAL WESTERLY JET STREAM INTERANNUAL VARIATION CHARACTERISTICS AND ITS POSSIBLE PHYSICAL FACTORS

Using National Centers for Environmental Prediction/Department of Energy(NCEP/DOE) monthly reanalysis data and an extended reconstruction of the sea surface temperature data provided by National Oceanic and Atmospheric Administration, the basic characteristics of the interannual variation in the wintertime Middle East subtropical westerly jet stream(MEJ) and its possible physical factors are studied. The results show that the climatological mean MEJ axis extends southwestward-northeastward and that its center lies in the northwest part of the Arabian Peninsula. The south-north shift of the MEJ axis and its intensity show obvious interannual variations that are closely related to the ElNio-Southern Oscillation(ENSO) and the mid-high latitude atmospheric circulation. The zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing causes the MEJ axis shift, and the Arctic Oscillation(AO)causes the middle-western MEJ axis shift. Due to the influences of both the zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing and the dynamical role of the AO, an east-west out-of-phase MEJ axis shift is observed. Furthermore, the zonal asymmetric response to the ENSO-related tropical convective forcing can lead to an anomalous Mediterranean convergence(MC) in the high troposphere. The MC anomaly excites a zonal wave train along the Afro-Asian jet, which causes the middle-western MEJ axis shift. Under the effects of both the zonal symmetric response to the ENSO-related tropical convective forcing and the wave train along the Afro-Asian jet excited by the MC anomaly, an east-west in-phase MEJ axis shift pattern is expressed. Finally, the AO affects the MEJ intensity, whereas the East Atlantic(EA) teleconnection influences the middle-western MEJ intensity. Under the dynamical roles of the AO and EA, the change in the MEJ intensity is demonstrated.

Different Configurations of Interannual Variability of the Western North Pacific Subtropical High and East Asian Westerly Jet in Summer

This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH)and the East Asian westerly jet(EAJ)in summer on interannual timescales.The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward)extension of the WNPSH and the southward(northward)shift of the EAJ,which is consistent with the general correspondence between their variations.The out-of-phase configuration includes the residual cases.We find that the in-phase configuration manifests itself as a typical meridional teleconnection.For instance,there is an anticyclonic(cyclonic)anomaly over the tropical western North Pacific and a cyclonic(anticyclonic)anomaly over the mid-latitudes of East Asia in the lower troposphere.These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ.By contrast,for the out-of-phase configuration,the mid-latitude cyclonic(anticyclonic)anomaly is absent,and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension.Correspondingly,significant rainfall anomalies move northward to North China and the northern Korean Peninsula.Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO,with strong and significant sea surface temperature(SST)anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter.This is sharply different from the in-phase configuration,for which the tropical SSTs are not a necessity.

STUDY ON THE MAIN CLIMATE MODES OF SHANDONG PRECIPITATION AND THEIR RELATIONS WITH THE EAST ASIAN WESTERLY JET

Summer precipitation patterns of Shandong Province are relatively independent with regard to the whole eastern China region.To study the rules and causes of precipitation variations,three main climate modes-on the annual,seasonal,and climatic intra-seasonal oscillation(CISO) scales-are extracted using a harmonic analysis method based on daily precipitation of Shandong during 1965-2009 and multi-year averaged pentad precipitation at 722 stations in China during 1971-2000.Among the three precipitation climate modes,the annual mode is closely related to the annual cycle of Earth-Atmosphere thermal system,which is characterized by the periodic dry and wet seasons.The seasonal mode reflects the monsoon effect on precipitation and the main flood season's contribution to annual precipitation variations.As an important climatic signal,the CISO mode is more evident during summer monsoon.The gradual modulations of the CISO mode,seasonal mode,and annual mode control the annual variation of precipitation.To study the relationship between precipitation climate modes and atmospheric circulations,an East Asian Westerly Jet Index(EAWJI) is defined in this paper.It is revealed that precipitation of Shandong is closely related to EAWJI in all climate modes.A wet or dry phase of each climate mode corresponds to a specific atmospheric circulation pattern.The phase of the annual mode is reverse to that of EAWJI.During the wet phase of the seasonal mode(weak phase of EAWJI),the atmospheric circulation in and around Shandong is characterized by upper-level divergence and low-level convergence.A reversed atmospheric circulation exists for the dry phase(strong phase for EAWJI).In the summer wet phase of CISO mode(strong phase of EAWJI),Shandong is controlled by upper-level divergence and low-level convergence.Again,the dry phase is corresponding to a reversed circulation structure.The methodology employed in this research,i.e.studying the precipitation climatic variations in terms of independent components of different temporal scales,provides a new approach for annual and seasonal precipitation prediction.

Simulation of the East Asian Subtropical Westerly Jet Stream with GFDL AGCM (AM2.1)

The present study validated the capability of the AM2.1,a model developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL),in reproducing the fundamental features of the East Asian Subtropical Westerly Jet Stream (EASWJ).The main behaviors of the EASWJ are also investigated through the reanalysis of observational NCEP/NCAR data.The mean state of the EASWJ,including its intensity,location,structure,and seasonal evolution is generally well-portrayed in the model.Compared with the observation,the model tends to reproduce a weaker jet center.And,during summer,the simulated jet center is northward-situated.Results also demonstrate the model captures the variability of EASWJ during summer well.The results of the empirical orthogonal function (EOF) applied on the zonal wind at 200 hPa (U200) over East Asia for both the observation and simulation indicate an inter-decadal shift around the late 1970s.The correlation coefficient between the corresponding principle components is as great as 0.42 with significance at the 99% confidence level.

The Relationship between the East Asian Subtropical Westerly Jet and Summer Precipitation over East Asia as Simulated by the IAP AGCM4.0

Based on a 30-year Atmospheric Model Intercomparison Project(AMIP) simulation using IAP AGCM4.0, the relationship between the East Asian subtropical westerly jet(EASWJ) and summer precipitation over East Asia has been investigated, and compared with observation. It was found the meridional displacement of the EASWJ has a closer relationship with the precipitation over East Asia both from model simulation and observation, with an anomalous southward shift of EASWJ being conducive to rainfall over the Yangtze-Huaihe River Valley(YHRV), and an anomalous northward shift resulting in less rainfall over the YHRV. However, the simulated precipitation anomalies were found to be weaker than observed from the composite analysis, and this would be related to the weakly reproduced mid-upper-level convergence in the mid-high latitudes and ascending motion in the lower latitudes.