Ice albedo feedback on sea ice/ocean coupled system

首先，我们分析了几艘破冰船在整个南极海域收集的上层海洋/海冰数据，以及卫星微波辐射计数据。这些分析表明，通过开放水域的热量输入(主要是太阳辐射)，海冰主要在底部和侧面融化。在此基础上，发现退缩季节冰集中负(正)异常导致下一个进水季的负(正)异常，且相关性强，可视为冰-海洋耦合系统中的冰-反照率反馈。该模式很好地解释了南极夏季冰集中与上层海洋的关系。通过对模式结果和观测数据的拟合，可以确定上层海洋与海冰之间的拍动输送系数。利用该系数值，该模型可以较好地再现海冰的经向退缩，当模型在子午线方向扩展到二维并计入风流影响时，海冰退缩的再现将进一步进行。这个二维模式可以描述后续的冰反照率反馈效应；一旦散度风场降低了冰的浓度，输入到上层海洋的热量就会增加，导致冰的浓度进一步降低。这一机制可以部分解释南极海冰退缩的年际变化。然而，一些观测结果不能仅用冰-海耦合系统来解释，这需要了解包括大气在内的反馈系统。

First we analyze upper-ocean/sea-ice dataset collected by several icebreakers over the whole Antarctic Ocean, along with the satellite microwave radiometer data. These analyses suggest that sea ice melts mostly on the bottom and lateral faces by the heat input (mainly solar radiation) through the open water area. Further, it is found that the negative (positive) anomalies in ice concentration in the retreat season lead to the negative (positive) anomalies in the next advance season with strong correlation, which can be regarded as ice-albedo feedback in a coupled ice-ocean system.We propose a simple ice-upper ocean coupled model in which sea ice melts only by the ocean beet supplied from the air. The model well explains the relation between ice concentration and upper-ocean in the Antarctic summer. By fitting of the model result and observation, the beat transfer coefficient between upper-ocean and sea ice can be determined. With use of this coefficient value, the model can roughly reproduce meridional retreat of sea ice.When the model is extended to two-dimensional in the meridional direction with the inclusion of the wind-drift effects, reproduction of the sea ice retreat has further progressed. This two-dimensional model can describe the following ice albedo feedback effect ; once the ice concentration is decreased by the divergent wind field, the heat input to the upper ocean is enhanced, leading to further decrease of ice concentration. This mechanism can partly explain the year-to-year variation of the sea ice retreat in the Antarctic Ocean. However, some observed results cannot be explained only by the ice-ocean coupled system, which requires the understanding of the feedback system including the atmosphere.