基于CESM1.2.2模拟的浪致混合对末次冰盛期和工业革命前气候的影响

The Effect of Wave-Induced Mixing on the Climates During the Last Glacial Maximum and Pre-Industrial Based on CESM1.2.2 Simulations

海洋上层垂向混合在模式中发挥重要的作用,以往的研究表明垂向混合的不足使得模拟的海洋温度和混合层深度与观测存在显著偏差。前人提出一种修正方案,考虑波浪产生的垂向混合,将由表面风作用下产生的波浪这样一个实际物理过程的湍混合进行参数化,其结果被证实能够显著提高模式模拟和预报的准确性。本文首次将浪致混合引入海气耦合的古气候模式,基于末次冰盛期和工业革命前2种不同的气候条件,探究浪致混合在海气耦合模式中的作用。在不同气候背景下,由于风场强度的不同,导致末次冰盛期浪致混合的强度小于工业革命前,但2个气候时期都体现出中纬度混合强度最大的特点。将浪致混合加入到气候模式中,模拟结果表明:中纬度海域2个时期都出现海表面降温而次表层升温的现象,但末次冰盛期的表面降温强度弱于工业革命前状态;不同月份下的模拟结果显示,在南北半球的夏季,海洋表层温度的降温最为显著。中纬度海域海洋上混合层深度在年平均条件下2个气候背景时期都出现加深现象,但末次冰盛期的加深程度弱于工业革命前;不同月份下的模拟结果显示,在南北半球的冬季,混合层加深的变化达到极值。另一方面,在高纬度海域,末次冰盛期的海表面温度出现了显著升高,这是由于浪致混合导致海冰的减少进而引发海洋表层升温。最后将末次冰盛期的模拟结果与代用资料进对比,发现浪致混合使得72%的数据点模拟结果与代用数据的差异减少。

Vertical mixing in the upper ocean plays an important role in the model,the lack of vertical mixing makes the simulated ocean temperature and mixing depth significantly deviate from the observation.A modification scheme is discussed a real physical process which the vertical mixing generated by waves.Previous researchers parameterized the turbulent mixing generated by waves under the action of surface wind,and named wave-induced vertical mixing(Bv).The preliminary model results show that Bv can significantly improve the accuracy of simulation and forecasting.Based on two different climatic conditions,the Last Glacial Maximum(LGM)and Pre-industrial(PI),for the first time in the world,this paper explores the effects of Bv in the Community Earth System Model version 1.2.2(CESM1.2.2).Because the LGM wind is weaker than that of PI,the Bv during LDM is weaker than that of PI.By including Bv to the coupled model,the simulation results show that sea surface cooling and subsurface surface warming occur in both background climate periods in mid-latitude regions,while the intensity of surface cooling during the LGM is weaker than that of PI.For seasonal variations,simulations show that surface cooling is coldest in summer in each hemisphere.The annual mean mixed layer depth in the two background periods is deepened in the middle latitude regions,and the deepening during LGM is weaker than that of PI.The simulation results show that the mixing layer deepening reaches the maximum in winter of each hemisphere.On the other hand,at high latitudes for LGM,sea surface temperature increased significantly,which is caused by the decrease of sea ice caused by the wave-induced mixing.Finally,by comparing the LGM simulations and the proxy data,it is found that the wave-induced mixing can improve the model simulation for data at 72%locations.