ABSTRACT

Utilizing the Community Atmosphere Model, version 4 (CAM4), the influence of sudden Arctic sea-ice thinning on North Atlantic Oscillation (NAO) events is investigated on a sub-seasonal time scale. First, the control simulation with CAM4 using prescribed daily boundary conditions produces realistic descriptions for the frequency and evolution of NAO events. Second, sensitivity experiments are then conducted to investigate the impact of sudden Arctic sea-ice thinning on NAO events. Numerical results show that the NAO has obvious responses to sudden sea-ice thinning over 10 days. Finally, the NAO responses to sudden sea-ice thinning are related to the positions of the NAO event. Further diagnostic analysis reveals that when the poleward centre of a positive NAO event is located west (east) of Greenland, cold (warm) advection would be induced because of the sudden sea-ice thinning along with the northward (southward) wind. This cooling (warming) causes the air to contract (expand) and further results in a decrease (increase) in the geopotential height and sea level pressure fields, which corresponds to a positive NAO (negative NAO) response. The results of this investigation show that the response of atmospheric circulation to boundary conditions is determined by both boundary condition changes and the atmospheric circulation regime, which provides an understanding of the effect on an NAO event of sudden sea-ice thinning on a sub-seasonal time scale.

摘要

利用社区大气模型第4版（CAM4），在亚季节时间尺度上研究了北极海冰突然变薄对北大西洋涛动（NAO）事件的影响。首先，使用规定的每日边界条件使用CAM4进行的控制仿真可对NAO事件的发生频率和演变过程进行实际描述。其次，然后进行敏感性实验，以研究北极突然的海冰变薄对NAO事件的影响。数值结果表明，NAO对10天内海冰突然变薄有明显的响应。最后，NAO对海冰突然变薄的反应与NAO事件的位置有关。进一步的诊断分析表明，当NAO阳性事件的极点中心位于格陵兰岛的西部（东部）时，由于突然的海冰变薄以及北风（南风），会引起冷（热）平流。这种冷却（变暖）使空气收缩（膨胀），并进一步导致势能高度和海平面压力场减小（增加），这对应于NAO（负NAO）的正响应。这项调查的结果表明，大气环流对边界条件的响应是由边界条件的变化和大气环流状况共同决定的，这提供了对次季节内海冰突然变薄对NAO事件的影响的理解。时间尺度。这种冷却（变暖）使空气收缩（膨胀），并进一步导致势能高度和海平面压力场减小（增加），这对应于NAO（负NAO）的正响应。这项调查的结果表明，大气环流对边界条件的响应是由边界条件的变化和大气环流状况共同决定的，这提供了对次季节内海冰突然变薄对NAO事件的影响的理解。时间尺度。这种冷却（变暖）使空气收缩（膨胀），并进一步导致势能高度和海平面压力场减小（增加），这对应于NAO（负NAO）的正响应。这项调查的结果表明，大气环流对边界条件的响应是由边界条件的变化和大气环流状况共同决定的，这提供了对次季节内海冰突然变薄对NAO事件的影响的理解。时间尺度。