Abrupt Northward Jump of the East Asian Upper-Tropospheric Jet Stream in MidSummer
Abrupt Northward Jump of the East Asian Upper-Tropospheric Jet Stream in MidSummer
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DOI：
10.2151/jmsj.86.857
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发表时间：
2008-12
影响因子：
3.1
通讯作者：
Zhongda Lin;R. Lu
中科院分区：
文献类型：
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作者：
Zhongda Lin;R. Lu
本文利用1958-2002年NCEP/NCAR再分析资料，记录了盛夏东亚沿海地区东亚对流层高空急流(EAJS)的季节突变。在气候学方面，EAJS在7月下旬突然向北跳跃。通过对总共45年中的每一年的考察，发现有27年的东亚夏季风在盛夏出现了突然的北跳，大约一半的跳跃发生在7月下旬，表明了与日历年的位相锁定特征。对东亚沿岸对流层高空纬向风异常的经向变化与东亚夏季风的北跳进行了聚类分析，结果表明东亚夏季风的北跳主要由两种类型主导，即东亚对流层高空纬向风强度增强和东亚对流层高空纬向风强度减弱。对于这两种类型，都有一对西风和东风异常位于EAJS轴的北部和南部。然而，这些西风和东风异常在两种类型之间表现出明显的时间变化：第一种类型的西风和东风异常对从高纬度向南移动到EAJS区，而第二种类型的西风和东风异常表现为准静止的经向偶极模式。
In this study we document the abrupt seasonal migration of the East Asian upper-tropospheric jet stream (EAJS) in boreal mid-summer over the East Asian coast, based on the NCEP/NCAR reanalysis data from 1958 to 2002. In climatology, an abrupt northward jump of the EAJS is identified in late July. By examining each of the total 45 years there are 27 years in which the EAJS exhibits an abrupt northward jump in mid-summer, and about half of the jump cases occur in late July, suggesting the characteristic of phase locking with the calendar year. A cluster analysis on the meridional variation of the upper-tropospheric zonal wind anomalies along the eastern Asian coast associated with the northward jump of the EAJS reveals that the northward jump of the EAJS is dominated by two categories, in which the intensity of the EAJS is enhanced and weakened, respectively. For both categories, there is a pair of westerly and easterly anomalies which are located to the north and south of the EAJS’s axis. However, these westerly and easterly anomalies exhibit distinct temporal variations between the two categories: The pair of westerly and easterly anomalies shifts southward from the high latitudes to the EAJS region for the first category, but appears as a quasi-stationary meridional dipole pattern for the second category.