The Generation of Extratropical Low-Frequency Variability

该项目将利用简单的大气环流数值模式研究热带外大气低频变率的来源，并着重研究天气变率在产生低频运动中的作用。这些研究将使用球面上的两层原始方程模型进行，将包括以下内容：1)对在整个模式的长期积分期间产生的低频变率的动力学进行详细的诊断研究，无论有没有地形。这些模拟被指定为“控制”。2)研究排除产生高频变异性的尺度的“截断”模型。只包括从控制中计算的高频的平均效果。因此，这些模型中的低频行为将独立于大的空间和慢的时间尺度。3)包括天气变率对低频强迫的实验：根据控制和强迫的随机模式计算的线性和非线性随时间变化的正压响应。4)在控制模型和截断模型之间比较低频运动的可预测性损失。这项工作将有助于理解天气尺度如何有助于大气的低频变化，并将加强我们预测季节性气候的能力。

This project will study the sources of low-frequency variability in the extra-tropical atmosphere using simple numerical models of the general circulation and focusing on the role of synoptic variability in generating low-frequency motions. These investigations, to be carried out using the two-layer primitive equation model on the sphere, will comprise the following: 1) Detailed diagnostic studies of the dynamics of low-frequency variability generated during long integrations of the full model, with and without orography. These simulations are designated the "controls". 2) Studies of "truncated" models that exclude the scales at which high-frequency variability is generated. Only the average effects, computed from the controls, of the high-frequencies will be included. Low-frequency behavior in these models will, therefore, be autonomous to large spatial and slow time scales. 3) Experiments that include the forcing of low frequencies by synoptic variability: the linear and nonlinear time-dependent barotropic responses to the forcing calculated from the controls and to stochastic models of that forcing. 4) comparisons, between the control and truncated models, of the loss of predictability of low-frequency motions. This work will lead to an understanding of how synoptic scales contribute to low frequency variability of the atmosphere and will enhance our capability to predict seasonal climate.