Effects of Combined Teleconnection Patterns on the East Asian Summer Monsoon Circulation: Remote Forcing from Low- and High-Latitude Regions
Effects of Combined Teleconnection Patterns on the East Asian Summer Monsoon Circulation: Remote Forcing from Low- and High-Latitude Regions
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DOI：
10.2151/jmsj.86.491
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发表时间：
2008-12
影响因子：
3.1
通讯作者：
Takuya Ogasawara;R. Kawamura
中科院分区：
文献类型：
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作者：
Takuya Ogasawara;R. Kawamura
利用欧洲中期天气预报中心（ECMWF）再分析（ERA-40）数据，我们研究了两种夏季遥相关模式，即欧洲-日本（EJ）和太平洋-日本（PJ）模式，它们分别盛行于欧亚大陆北部和北太平洋西部，并强调了这两种模式的结合对东亚夏季风变化对高频（HF）分量（次月时间尺度）和低频（LF）分量（长于约一个月）。正 EJ 2 型（EJ2+）特别解释了两种类型 EJ 模式（EJ 1 型和 EJ 2 型）中 Okhotsk 高压的变化，与负 PJ（PJ-）模式的组合在东亚对流层中位势高度场中建立了一个明显的三极结构，其特征是鄂霍次克海上空有两个正异常以及菲律宾北部的北太平洋西部和日本上空的负异常。研究发现，EJ2+/PJ-两种模式的组合比单独的单一遥相关模式导致东亚东北部地表温度下降幅度更大，对东亚夏季风环流产生重大影响。低频组合还会在日本附近引起明显的凉爽海面温度异常。在HF组合情况下，鄂霍次克海上空正高度异常的时间演化与LF组合情况有很大不同。高频异常在高峰日几天后向东极度移位到阿留申群岛，并占据了横跨北太平洋中部新组织的波列模式的一部分。波列模式的进一步发展可能归因于与日本东部天气尺度扰动增强相关的异常对流加热。LF-EJ2+和LF-PJ-模式在1980年后时期往往频繁出现，因此，LF组合病例的数量在过去二十年可能有所增加。异常凉爽且降雨量大的夏季，特别是在日本，例如 1993 年和 2003 年的夏季，通常是由这种 LF 组合产生的。
Using the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-40) data, we examined two summertime teleconnection patterns, the Europe-Japan (EJ) and the Pacic-Japan (PJ) patterns, which prevail over northern Eurasia and the western North Pacic, respectively, and high lighted the effects of the combination of the two on the East Asian summer monsoon variability on a high frequency (HF) component (sub-monthly timescales) and a low-frequency (LF) component (longer than about one month).The combination of positive EJ type 2 (EJ2+), which particularly accounts for the variability of the Ok hotsk high among the two types of EJ pattern (EJ type 1 and EJ type 2), and negative PJ (PJ-) patterns establishes a noticeable tripole structure in the mid-tropospheric geopotential height eld of East Asia that is characterized by two positive anomalies over the Okhotsk Sea and the western North Paci c to the north of the Philippines and a negative anomaly over Japan. It is found that the combination of both pat terns, EJ2+/PJ-, leads to a larger surface temperature decrease in the northeastern part of East Asia than a single teleconnection pattern alone, having a substantial impact on the East Asian summer monsoon circulation. The LF-combination also induces signicant cool sea surface temperature anomalies in the vicinity of Japan. In the HF-combined case, the time evolution of a positive height anomaly over the Ok hotsk Sea considerably differs from that of the LF-combined one. The HF-anomaly is extremely displaced eastward to the Aleutian Islands a few days after the peak day and occupies part of a newly organized wavetrain pattern across the central North Pacic. Further development of the wavetrain pattern may be attributed to anomalous convective heating related to enhanced synoptic-scale disturbances to the east of Japan.Both the LF-EJ2+ and LF-PJ- patterns tend to appear frequently during the post-1980 period, and, as a result, the number of LF-combined cases may have increased in the last two decades. Exceptionally cool summers with signicant amounts of rainfall, particularly in Japan, such as the 1993 and 2003 summers, often arise from such an LF-combination.