Fundamental Mechanisms of Large-Scale Atmospheric Circulation Systems Related to the Decadal-Scale Climate Variability

与十年尺度气候变化相关的大尺度大气环流系统的基本机制

基本信息

批准号：
12640418
负责人：
NAKAMURA Hisashi
金额：
$ 2.5万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12640418/
关键词：
Decadal-scale climate variability Storm tracks Siberian High Subtropical jet stream East Asian winter monsoon Subtropical High Stationary Rossby wave train Blocking 移動性高低気圧傾圧不安定亜熱帯ジェット冬季極東モンスーンアリューシャン低気圧アイスランド低気圧定常ロスビー波 /

项目摘要

1) The presence of the two distinct modes of decadal-scale climate variability in the wintertime North Pacific has been confirmed, one of which is associated with the anomalous subtropical high. The anomalous high was found highly barotropic in its midlatitude portion, whereas its subtropical portion is distinctly baroclinic. This complex structure is found to be suited for the generation of anomalous subsidence, through which the surface and upper-level anomalous circulation can be tightly linked.2) The decadal-scale weakening of the Siberian High and the East Asian winter monsoon has been found to cause systematic enhancing of the storm track activity in the North Pacific despite the relaxed background baroclinicity. This enhancement is apparently opposite to what the linear theory of baroclinic instability predicts. In the presence of the excessively strong subtropical jet in association with the strong monsoon during the early through mid-1980s, synoptic-scale eddies propagating in … More to the North Pacific through the midlatitude tropopause over the Asian continent (9 km in altitude, 45°N) tend to be trapped into the jet core, while lifted up to 3 km and shifted equatorward by 1000 km away from the surface baroclinic zone at 40°N located along the boundary between the subpolar and subtropical oceanic gyres. The vertical coupling of the eddies with the surface baroclinic zone is thus weakened and thus unfavorable for the baroclinic growth of the eddies. In contrast, the eddy trapping has been less likely since the late 1980 s under the relaxed subtropical jet. The eddies were more likely to propagate through the midlatitude tropopause right above the surface baroclinic zone, resulting in their efficient baroclinic growth as observed. The decadal change observed in the eddy trapping is manifested as the structural changes of those eddies.3) A particular form of a wave-activity flux has been derived for the first time, which can represent three-dimensional group-velocity propagation of a Rossby wave packet, either stationary or migratory in the realistic westerlies. It has been revealed through our application of this flux that a stationary Rossby wave train emanated from each of the strong sub-seasonal tropospheric anomalies including blocking can reach into the lower stratosphere, forming a wave train along the polar-night jet. Those wave trains were found to contribute substantially to the observed sub-seasonal variability in the wintertime lower stratosphere. Less

1) 北太平洋冬季存在两种不同的十年尺度气候变率模式已被证实，其中一种与异常副热带高压有关。这种复杂的结构被发现适合于异常沉降的产生，通过它可以将地表和上层的异常环流紧密地联系起来。2)人们发现，尽管斜压背景宽松，西伯利亚高压和东亚冬季风的十年尺度减弱仍导致北太平洋风暴路径活动系统性增强，这种增强显然与斜压不稳定的线性理论相反。预测，在 20 世纪 80 年代初至中期，由于副热带急流与强季风有关，天气规模的涡流将向北传播。太平洋穿过亚洲大陆上空的中纬度对流层顶（海拔 9 公里，北纬 45°）往往会被困在急流核心中，同时被提升至 3 公里，并向赤道移动 1000 公里，远离北纬 40° 的地表斜压区位于副极地和副热带海洋环流的边界，涡流与表面斜压区的垂直耦合因此减弱，从而不利于海洋环流的形成。相比之下，自 20 世纪 80 年代末以来，在副热带急流松弛的情况下，涡流更有可能通过地表斜压区上方的中纬度对流层顶传播，从而产生有效的斜压。观察到的涡流捕获中观察到的年代际变化表现为这些涡流的结构变化。3) 涡流的一种特殊形式。首次导出了波活动通量，它可以代表罗斯贝波包的三维群速度传播，无论是在现实西风带中静止还是迁移。通过应用该通量，我们揭示了静止波包。罗斯贝波列从每个强烈的次季节对流层异常（包括阻塞）发出，可以到达平流层下部，沿着极夜急流形成波列，这些波列对观测到的波列有很大贡献。冬季低平流层的次季节变化较小。