Influence of the East Asia Subtropical Westerly Jet on Spring Drought in Northwest China

doi:10． 11755/j． issn． 1006 －7639(2014) －02 －0184

Abstract

Abstract:

Based on daily average wind and height fields data at 2． 5° ×2． 5° spatial resolution from NCEP/NCAR and daily precipitati-
on of 136 stations in spring in Northwest China during 1980 －2009，the temporal and spatial distribution of spring drought and the a-
nomalies characteristics of East Asia Subtropical Westerly Jet (EASWJ) in Northwest China were studied by defining the percentage of
precipitation anomaly as the drought index and the average latitude of largest westerly wind scanning region with 25°N －50°N and 70°
E －120°E at 200 hPa as the position index of EASWJ，firstly． Then，the correlations between the drought index and the position index
of prophase and synchronous EASWJ were analyzed to reveal the influence of EASWJ on spring drought in Northwest China． The results
showed that the spring drought in Northwest China was firstly weak and then strong from 1980 to 2009． However，the positions of the
EASWJ whether in spring or winter had a trend with moving northwards on the whole from 1980 to 2009，and the moving rate in spring
and winter was 0． 4 °N/10 a and 0． 276 °N/10 a，respectively． Moreover，the correlation analysis showed the spring drought in North-
west China had significant negative correlation with winter EASWJ in last year． When the position of EASWJ in winter was to the north，
the area of Northeast China in spring next year was controlled by strong high pressure，and the dry and cold northwest airflow in the
front of the ridge would be very likely to cause the drought． On the contrary，when the position of EASWJ in winter is to the south，
high pressure controlling the region of Northwest China was relatively weak，the southerly airflow carrying water vapor moved to the
north and converged with the northerly airflow，and thus precipitation increased accordingly，the spring drought didn’t occur easily in
Northwest China．

Key words: East Asian Subtropical Westerly Jet (EASWJ), Northwest China, spring drought, influence mechanism

摘要：

利用 1980 ～2009 年 NCEP/NCAR 逐日平均风速场、高度场资料和中国西北地区 136 个台站春季逐日降水量资料，通过定义干旱指数和东亚副热带急流位置指数，研究我国西北春季干旱事件的时空分布特征以及东亚副热带急流的异常特征，揭示副热带急流对西北春季干旱的影响。结果表明，1980 ～2009 年西北地区的春旱表现出前 15 a 稍减轻、后 15 a 再次加重的趋势;东亚副热带西风急流的位置无论是冬季还是春季都有向北移动的趋势。相关分析表明，西北地区的春旱与前一年冬季东亚副热带西风急流的位置呈显著负相关，冬季急流位置偏北的年份，次年春季西北地区为强大的高压控制，脊前干冷的西北气流使得干旱容易发生;而急流位置偏南的年份，控制西北地区的高压相对较弱，西北气流偏北，偏南气流能够携带水汽北上与偏北气流交汇，导致降水相应的增多，从而春旱不易发生。

关键词: 副热带西风急流, 西北地区, 春季干旱, 影响机理

CLC Number:

P442

DONG Ting，LI Yan. Influence of the East Asia Subtropical Westerly Jet on Spring Drought in Northwest China[J]. Journal of Arid Meteorology, DOI: 10． 11755/j． issn． 1006 －7639(2014) －02 －0184.

董婷，李艳. 东亚副热带急流对我国西北春季干旱的影响[J]. 干旱气象, DOI: 10． 11755/j． issn． 1006 －7639(2014) －02 －0184.

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