Interannual Variation of Summer Precipitation in Xinjiang and Asian Subtropical Westerly Jet Stream

Yang Lianmei; Zhang Qingyun

Vol.19, NO.2, 2008

Article Contents

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Yang Lianmei, Zhang Qingyun. Interannual variation of summer precipitation in Xinjiang and Asian subtropical westerly jet stream. J Appl Meteor Sci, 2008, 19(2): 171-179.

Citation:

Yang Lianmei, Zhang Qingyun. Interannual variation of summer precipitation in Xinjiang and Asian subtropical westerly jet stream. J Appl Meteor Sci, 2008, 19(2): 171-179.

Yang Lianmei, Zhang Qingyun. Interannual variation of summer precipitation in Xinjiang and Asian subtropical westerly jet stream. J Appl Meteor Sci, 2008, 19(2): 171-179.

Citation:

Yang Lianmei, Zhang Qingyun. Interannual variation of summer precipitation in Xinjiang and Asian subtropical westerly jet stream. J Appl Meteor Sci, 2008, 19(2): 171-179.

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Interannual Variation of Summer Precipitation in Xinjiang and Asian Subtropical Westerly Jet Stream

Yang Lianmei^1,2,
Zhang Qingyun²

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

Received Date: 2006-10-25
Rev Recd Date: 2007-07-10
Publish Date: 2008-04-30

Abstract

Abstract

The relationships between Asian subtropical westerly jet stream (ASWJS) and summer precipitation in Xinjiang are examined using the NCEP/NCAR reanalysis dataset and 75 stations monthly precipitation data in Xinjiang from 1960 to 2003. Summer precipitation in Xinjiang is closely related to meridional displacement of west Asian jet stream and quasi-stationary wave activity along ASWJS. It is confirmed by Eliasson-Palm flux diagnoses that stationary waves propagation over Scandinavian Peninsulan-middle Europe has important impacts on stationary waves activity along ASWJS. It is found that anomalous summer more (less) rainfall in Xinjiang is related to the West Asian Westerly Jet axis moving to Southern (Northern) rather than normal, and subtropical westerly front also migrates southward (northward) over the whole troposphere. As a result, anomalous convergence and divergence occur over Xinjiang. The composite plots show the troposphere atmospheric steady wave weakens or strengthens over West Asia and strengthens or weakens over Xinjiang which are associated with more or less rainfall in Xinjiang. It is investigated that the horizontal wave vector propagation is obviously different between more and less rainfall years. During more (less) rainfall years, it is found that horizontal wave activity flux divergence center over Scandinavian Peninsula-middle Europe is favorable for moving eastward (westward and southward), and horizontal wave activity propagation strengthens (weakens) toward eastward leading to turning to southeastward near Ural mountain and entering ASWJS at Aral Sea-Xinjiang and the wave propagation strengthens (weakens). In the meantime, the direct wave propagation toward southeastward enters ASWJS in the east Mediterranean and Black Sea and weakens (strengthens) because of which quasi-stationary wave activity along West Asian westerly jet stream weakens (strengthens). Xinjiang summer rainfall is closely related to wave activity and propagation over Scandinavian Peninsula-middle Europe-ASWJS. Furthermore, the meridional wave train along 60°E connecting the two hemispheres is revealed, and this wave train which propagates meridionally upward from lower-troposphere in polar region to low-latitude tropopause and continues turning downward to mid-latitude in northern hemisphere is associated with west Asian jet variation. This wave train EP flux divergence performs opposite the variation near the south and north along 40°N, leading to different west Asian westerly jet stream intense variation near the south and north along 40°N for drought/flood years. EP flux divergence to the south (north) of 40°N and convergence to the north (south) of 40°N enhances (weakens) in flood (drought) years leading to the enhanced (weakened) upper level westerly to the south of 40°N and weakens (enhances) upper level westerly to the north of 40°N.
- West Asian westerly jet stream;
- quasi-stationary wave propagation;
- summer precipitation anomaly in Xinjiang

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References(25)

Figures and Tables

图 1 新疆75站夏季降水量标准化序列EOF方差最大的前两个特征模态 (a, b) 及对应的主分量正规化时间序列 (c, d)

Fig. 1 The patterns of the eigenvectors of the first two gravest EOF modes (a, b) and corresponding time series (c, d) of 75 stations normalized rainfall over Xinjiang in summer

DownLoad: Full-Size Img PowerPoint

图 2 夏季200 hPa纬向风 (单位:m·s^-1)(a) 气候平均, (b) 降水偏多年, (c) 降水偏少年

Fig. 2 Zonal winds at 200 hPa in summer (unit:m·s^-1)(a) climate mean, (b) in more rainfall years, (c) in less rainfall years

DownLoad: Full-Size Img PowerPoint

图 3 新疆夏季降水第一主分量时间序列与夏季200 hPa纬向风的相关分布

(阴影区表示通过0.05显著性检验)

Fig. 3 Linear correlation between first mode of Xinjiang summer rainfall EOF and zonal winds in summer

(shaded areas indicate the level exceeding 0.05)

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图 4 同图 2, 但为经向风

(阴影区表示通过0.05显著性检验)

Fig. 4 Same as in Fig.2, but for meridional winds

(shaded areas indicate the level exceeding 0.05)

DownLoad: Full-Size Img PowerPoint

图 5 同图 3, 但为经向风

Fig. 5 Same as in Fig. 3, but for meridional winds

DownLoad: Full-Size Img PowerPoint

图 6 夏季70°~100°E散度经向-高度分布 (单位:10^-6s^-1; 阴影为地形高度)(a) 气候平均, (b) 降水偏多年距平, (c) 降水偏少年距平

Fig. 6 Meridion-height cross section averaged over 70°—100°E of divergence in summer (unit:10^-6s^-1; shaded areas indicate topography)(a) climate mean, (b) anomaly in more rainfall years, (c) anomally in less rainfall years

DownLoad: Full-Size Img PowerPoint

图 7 夏季200 hPa水平波活动通量 (矢量, 单位:m ²·s ^-2) 和通量散度 (等值线, 单位:10^-6m·s^-2)(a) 气候平均, (b) 降水偏多年, (c) 降水偏少年

Fig. 7 The horizontal wave activity flux (vectors, unit:m²·s^-2) and its divergence (contours, unit:10^-6m·s^-2) at 200 hPa in summer (a) climeate mean, (b) in more rainfall years, (c) in less rainfall years

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图 8 沿60°E夏季EP通量散度剖面图 (单位:10 ^-6m·s ^-2, 阴影部分表示地形高度)(a) 气候平均, (b) 降水偏多年距平, (c) 降水偏少年距平

Fig. 8 Cross section of EP flux divergence (unit:10 ^-6m·s ^-2, shadings indicate topography) along 60°E (a) climate mean, (b) anomaly in more rainfall years, (c) anomaly in less rainfall years

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