Dynamics of synoptic eddy and low-frequency flow interaction. Part II: A theory for low-frequency modes
Dynamics of synoptic eddy and low-frequency flow interaction. Part II: A theory for low-frequency modes
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DOI：
10.1175/jas3716.1
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发表时间：
2006-07-01
影响因子：
3.1
通讯作者：
Watanabe, M.
中科院分区：
文献类型：
--
作者：
Jin, F. -F.;Pan, L. -L.;Watanabe, M.
在暴风雨般的大气环流中，行星环流存在显着的周期性变化模式，例如南极涛动（AAO）、北极涛动（AO）或北大西洋涛动（NAO）以及太平洋-北美（PNA）模式。本文利用第一部分中提出的带 SELF 反馈的线性正压模型，研究了天气涡和低频流 (SELF) 反馈在这些主导低频模态形成中的作用。发现，线性动力系统的类 AO 和类 AAO 主导奇异模态是由于正 SELF 反馈的结果，从暴风雨背景流中出现的。在北方冬季的气候条件下，这种SELF反馈也更喜欢类PNA奇异向量。还使用具有基本平均流量和天气涡流活动理想化条件的模型以及原型模型来说明通过正SELF反馈对AAO和类AO模态存在自然尺度选择。大西洋（南印度洋）AO（AAO）局部特征的纬向范围在很大程度上与该地区风暴路径活动增强的纬向范围有关。由于尺度选择性正自反馈，AO 和类 AAO 低频模式的子午偶极子结构受到青睐，这可以通过倾斜槽机制启发式地理解。
Amidst stormy atmospheric circulation, there are prominent recurrent patterns of variability in the planetary circulation, such as the Antarctic Oscillation (AAO), Arctic Oscillation (AO) or North Atlantic Oscillation (NAO), and the Pacific-North America (PNA) pattern. The role of the synoptic eddy and low-frequency flow (SELF) feedback in the formation of these dominant low-frequency modes is investigated in this paper using the linear barotropic model with the SELF feedback proposed in Part I. It is found that the AO-like and AAO-like leading singular modes of the linear dynamical system emerge from the stormy background flow as the result of a positive SELF feedback. This SELF feedback also prefers a PNA-like singular vector as well among other modes under the climatological conditions of northern winters.A model with idealized conditions of basic mean flow and activity of synoptic eddy flow and a prototype model are also used to illustrate that there is a natural scale selection for the AAO-and AO-like modes through the positive SELF feedback. The zonal scale of the localized features in the Atlantic (southern Indian Ocean) for AO (AAO) is largely related to the zonal extent of the enhanced storm track activity in the region. The meridional dipole structures of AO- and AAO-like low-frequency modes are favored because of the scale-selective positive SELF feedback, which can be heuristically understood by the tilted-trough mechanism.