Relationships Between Perturbation Kinetic Energy Anomaly Along East Asian Westerly Jet and Subtropical High in Summer

Yang Lianmei; Zhang Qingyun

Vol.18, NO.4, 2007

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Yang Lianmei, Zhang Qingyun. Relationships between perturbation kinetic energy anomaly along East Asian westerly jet and subtropical high in summer. J Appl Meteor Sci, 2007, 18(4): 452-459.

Citation:

Yang Lianmei, Zhang Qingyun. Relationships between perturbation kinetic energy anomaly along East Asian westerly jet and subtropical high in summer. J Appl Meteor Sci, 2007, 18(4): 452-459.

Yang Lianmei, Zhang Qingyun. Relationships between perturbation kinetic energy anomaly along East Asian westerly jet and subtropical high in summer. J Appl Meteor Sci, 2007, 18(4): 452-459.

Citation:

Yang Lianmei, Zhang Qingyun. Relationships between perturbation kinetic energy anomaly along East Asian westerly jet and subtropical high in summer. J Appl Meteor Sci, 2007, 18(4): 452-459.

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Relationships Between Perturbation Kinetic Energy Anomaly Along East Asian Westerly Jet and Subtropical High in Summer

Yang Lianmei^1,2,3,
Zhang Qingyun¹

1.
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
2.
Institute of Desert Meteorology, China Meteorological Administration, Urumqi 830002
3.
Graduate University, Chinese Academy of Sciences, Beijing 100039

Received Date: 2006-03-03
Rev Recd Date: 2007-01-09
Publish Date: 2007-08-31

Abstract

Abstract

In summer, upper level subtropical westerly jet stream along 40°N over East Asia is one of the most important large-scale circulation systems which influence weather and climate change over east China. At the same time, it is also a wave-guide along Rossby wave activity.Thus, it is necessary to define an objective and quantitive perturbation kinetic energy (E_k) index along East Asian westerly jet (EAWJ), and E_k annual variation and anomalies are investigated.Moreover, the relationships between E_k and EAWJ intensity and EAWJ position are examined, lastly the configuration and connection processes between E_k variability along EAWJ and South Asia high (SAH) and western pacific subtropical high (WPSH) in summer are confirmed by NCEP/NCAR reanalysis dataset from 1979 to 2003.u basic and v basic are defined by wave number k < 3 based on wind u and v in 200 hPa calculated by Fourier expressions, the perturbation kinetic energy of Rossby wave along EAWJ is defined by k≥3 wave activity, and Rossby wave perturbation (u′, v′)=(u, v)-(u_b v_b), E_k=(u′·u′+v′·v′)/2 which is averaged in the area of latitude with maxima zonal wind shifted±5°and in 100°—140°E, so normal E_k is defined as Rossby wave activity index along EAWJ which also includes meridional displacement variability of EAWJ.EAWJPI (East Asian westerly jet position index) is defined by the difference of zonal wind in 200 hPa between 35°—40°N, 100°—140°E and 40°—45°N, 100°—140°E, and EAWJII (East Asian westerly jet intensity index) is defined by the summation of zonal wind in 200 hPa averaged by 35°—45°N, 100°—140°E.The results show that EAWJ is southward (northward) than the normal and its intensity becomes stronger (weaker) while E_k strengthened (weakened). Not only E_k variations are associated with EAWJ intensity and steady Rossby wave perturbation along westerly jet in summer, but also south—north wave train anomaly in East Asia. Height anomaly in Asia mid-latitude area is most remarkable.When E_k appears stronger (weaker) than normal, center position of circumglobal wave train wave in mid-latitude zone moves to southern (northern). The correlation coefficient is 0.56 between E_k and SAH intensity, 0.66 between E_k and SAH eastward ridge point position, and-0.52 between E_k and WPSH ridge line position during 1979—2003 summer respectively, all are over 99% level.While E_k appears stronger (weaker) than normal, SAH moves to eastward (westward) and stronger (weaker) than the normal.At the same time, WPSH is southward (northward) than the normal.It is found that the response of WPSH to E_k anomaly is going with the change of divergence-convergence over East Asia in 200 hPa and vertical motion in tropic and subtropical zone from surface to upper air.
- East Asian westerly jet stream;
- perturbation kinetic energy;
- subtropical high

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References(15)

Figures and Tables

图 1 1958—2003年夏季 (6—8月) 200 hPa纬向风的标准差分布

(单位: m/s; 阴影区表示置信度大于95%)

Fig. 1 The climatology standard deviation of 200 hPa zonal wind in summer (JJA) averaged over 1958—2003

(unit : m/s; shaded areas denote exceeding the test of 95% level)

DownLoad: Full-Size Img PowerPoint

图 2 1979—2003年6—8月东亚 (100°~140°E) 急流扰动动能E_K标准化序列

Fig. 2 The interannual variations of normalized Rossby wave perturbation kinetic energy E_k along 100°—140°E westerly jet in summers during 1958—2003

DownLoad: Full-Size Img PowerPoint

图 3 夏季东亚200 hPa纬向风EOF方差最大的前二个特征模态

(a) 第一模态, (b) 第二模态

Fig. 3 The patterns of the eigenvectors of the first two gravest EOF modes of 200 hPa over East Asia in summer

(a) the first mode, (b) the second mode

DownLoad: Full-Size Img PowerPoint

图 4 夏季200 hPa高度距平场

(单位: gpm; 阴影区表示纬向风速大于25 m/s) (a) 扰动强年, (b) 扰动弱年

Fig. 4 Geopotential height anomalies at 200 hPa in summer of the strong E_k(a) and weak E_k(b) years

(unit: gpm; shade areas indicate zonal winds larger than 25 m/s)

DownLoad: Full-Size Img PowerPoint

图 5 夏季15°~30°N位势高度纬向-高度剖面图

(单位: gpm)(a) 扰动强年, (b) 扰动弱年

Fig. 5 Zone-height cross section (averaged over 15°—30°N) of geopotential height in summer of the strong E_k(a) and weak E_k(b) years (unit : gpm)

DownLoad: Full-Size Img PowerPoint

图 6 夏季500 hPa高度距平场

(单位: gpm)(a) 扰动强年, (b) 扰动弱年

Fig. 6 Geopotential height anomalies at 500 hPa in summer of the strong E_k(a) and weak E_k(b) years (unit : gpm)

DownLoad: Full-Size Img PowerPoint

图 7 夏季200 hPa散度场 (单位: 10^-6s^-1)

(a) 气候平均场, (b) 扰动强年距平场, (c) 扰动弱年距平场

Fig. 7 Divergence at 200 hPa in summer (unit : 10^-6s^-1)

(a) climate mean, (b) anomalies for strong E_k yeas, (c) anomalies for weak E_k years

DownLoad: Full-Size Img PowerPoint

图 8 夏季垂直速度距平合成经向-高度剖面图 (110°~130°E平均)

(单位: Pa·s^-1, ω>0表示下沉运动, ω<0表示上升运动) (a) 扰动强年, (b) 扰动弱年

Fig. 8 Meridian-height cross section (averaged over 110°—130°E) of anomalous vertical velocity in summer of the strong E_k(a) and weak E_k(b) years

(unit : Pa/s, ω>0 indicates subsidence, ω<0 indicates ascending)

DownLoad: Full-Size Img PowerPoint

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