水球世界气候态与经向热量输送的数值模拟试验

Mean Climate and Meridional Heat Transport in an Aqua-Planet

利用完全耦合的气候模式(FOAM),通过两组理想的水球试验,研究水球气候系统中的平均气候态和经向热量输送。两组水球试验分别是Aqua和Ridge,前者整个星球完全被水覆盖,没有任何陆地,后者与前者的唯一区别是从南极到北极有一道连续的地脊。相比于现实世界,水球世界的气候更加温暖,极地几乎没有海冰。北半球的经向温度梯度较现实世界弱,导致北半球的大气经向热量输送较小。这些差别主要来源于海陆分布改变造成的行星反照率的改变,而云量的增加部分抵消了这种改变。尽管在两个水球试验中海洋环流和平均温度场差别很大,但大气平均气候态差别不大。不同于Ridge,在Aqua中赤道区域出现"反"哈德雷环流,使得低纬度大气向赤道方向输送热量。尽管水球世界的海洋环流与现实世界相比发生了巨大改变,但总的经向热量输送及其在大气和海洋之间的分配依然保持稳定。中小尺度的涡旋和扩散引起的经向热量输送部分抵消了大尺度环流引起的经向热量输送,尤其在中纬度起着重要作用。

The mean climate and the meridional heat transport in a fully coupled aqua-planet are studied using the Fast Ocean Atmosphere Model （FOAM）. Two idealized configurations are considered： Aqua, where the whole planet is covered by the ocean; Ridge, the only difference from Aqua is a meridional barrier blocking zonal flow in the ocean. Much warmer climate relative to the real world with little sea ice is observed in both Aqua and Ridge. The meridional temperature gradient in the Northern Hemisphere （NH） is greatly reduced, which may be responsible to the decreased atmospheric heat transport in the NH. The warming results from the decrease in planetary albedo induced by the modification of the land-ocean distribution, though partly canceled by the increase in cloud amount. There is no significant difference between Aqua and Ridge in the atmosphere, except Reversed Hadley Ceils in Aqua. It is found that in general the meridional heat transport and its partitioning between the atmosphere and the ocean are robust features of the climate system, even under the significant modification in the ocean as in the aqua-planet. Diffusion induced heat transport is opposite to the mean advection induced component and is of vital importance in this robustness.