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

(1)证实了北太平洋冬季存在两种不同的年代际气候变率模态，其中一种模态与副热带高压有关。异常高压在中纬度部分表现为高度正压，副热带部分表现为明显斜压。这种复杂的构造适合于异常沉降的产生，通过它可以将地面和高层异常环流紧密联系起来。(2)尽管背景斜压性减弱，但西伯利亚高压和东亚冬季风的年代际减弱导致了北太平洋风暴路径活动的系统增强。这种增强显然与斜压不稳定的线性理论所预测的相反。20世纪80年代初至中期，在与强季风相关的超强副热带急流存在的情况下，通过亚洲大陆（海拔9 km， 45°N）上空的中纬度对流层顶向北太平洋传播的天气尺度涡旋倾向于被困在急流核中。而上升至3 km，远离40°N的表面斜压区，沿亚极地和副热带海洋环流边界向赤道移动了1000 km。旋涡与表面斜压区的垂直耦合减弱，不利于旋涡的斜压生长。而自20世纪80年代末以来，在松弛的副热带急流下，涡旋捕获的可能性较小。涡旋更有可能通过地表斜压带上方的中纬度对流层顶传播，导致观察到的它们有效的斜压增长。涡旋捕获的年代际变化表现为涡旋的结构变化。3)首次导出了一种特殊形式的波活动通量，它可以表示实际西风带中静止或迁移的罗斯比波包的三维群速度传播。通过对这一通量的应用表明，从包括阻塞在内的每一个强烈的次季节对流层异常中发出的静止罗斯比波列可以到达平流层下层，沿着极夜急流形成波列。发现这些波列对观测到的冬季平流层下层的次季节变率有很大贡献。少

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