Decadal change in the boreal summer intraseasonal oscillation
Decadal change in the boreal summer intraseasonal oscillation
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DOI：
10.1007/s00382-016-3247-8
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发表时间：
2017-05
期刊：
影响因子：
4.6
通讯作者：
T. Yamaura;Y. Kajikawa
中科院分区：
文献类型：
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作者：
T. Yamaura;Y. Kajikawa
在大尺度上确定了北方夏季季内振荡（BSISO）活动的年代际变化。这种变化在北方夏季的8 - 10月更为明显。1999-2008年（P2） BSISO活动显著大于1984-1998年（P1）。与P1相比，P2中BSISO对流增强，向北传播的对流相速度降低。在背景条件下，热带印度洋和热带西太平洋的暖海温（SST）异常明显。前者为BSISO对流活跃提供了有利条件，后者通过对流增强导致Walker环流增强。这导致热带印度洋上空出现下降异常。热对流往往受到下降异常的抑制，而一旦一个活跃的BSISO信号进入印度洋，对流就会因海温正异常而增强。在P2之后，2009-2014年BSISO活动减弱（P3）。与P2相比，P3在南热带印度洋上BSISO的对流活动趋于不活跃。向北传播的对流相速度加快。在P3背景条件下，海洋大陆海温异常变暖增强了对流，增强了热带西部太平洋和热带南部印度洋之间的局地Hadley环流。因此，南热带印度洋上的BSISO对流受到抑制。BSISO活动的年代际变化与热带亚洲季风区季节平均海温的变率相关，表明可以预测其年代际变化。
A decadal change in activity of the boreal summer intraseasonal oscillation (BSISO) was identified at a broad scale. The change was more prominent during August–October in the boreal summer. The BSISO activity during 1999–2008 (P2) was significantly greater than that during 1984–1998 (P1). Compared to P1, convection in the BSISO was enhanced and the phase speed of northward-propagating convection was reduced in P2. Under background conditions, warm sea surface temperature (SST) anomalies in P2 were apparent over the tropical Indian Ocean and the western tropical Pacific. The former supplied favorable conditions for the active convection of the BSISO, whereas the latter led to a strengthened Walker circulation through enhanced convection. This induced descending anomalies over the tropical Indian Ocean. Thermal convection tends to be suppressed by descending anomalies, whereas once an active BSISO signal enters the Indian Ocean, convection is enhanced through convective instability by positive SST anomalies. After P2, the BSISO activity was weakened during 2009–2014 (P3). Compared to P2, convective activity in the BSISO tended to be inactive over the southern tropical Indian Ocean in P3. The phase speed of the northward-propagating convection was accelerated. Under background conditions during P3, warmer SST anomalies over the maritime continent enhance convection, which strengthened the local Hadley circulation between the western tropical Pacific and the southern tropical Indian Ocean. Hence, the convection in the BSISO over the southern tropical Indian Ocean was suppressed. The decadal change in BSISO activity correlates with the variability in seasonal mean SST over the tropical Asian monsoon region, which suggests that it is possible to predict the decadal change.