The effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments
The effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments
复制标题
平板海洋水生行星实验中海洋混合层深度对气候的影响
DOI：
10.1007/s00382-013-1843-4
复制
发表时间：
2013
期刊：
影响因子：
4.6
通讯作者：
D. Battisti
中科院分区：
文献类型：
--
作者：
A. Donohoe;D. Frierson;D. Battisti
在一套平板海洋水行星模拟中，探讨了海洋混合层深度对气候的影响，不同的混合层深度在全球均匀值50-2.4 m之间。除了随着海洋混合层深度的减小而预期的温度季节周期振幅的增加外，模拟的气候在几个不太直观的方面存在差异，包括年平均气候的基本变化。温度的季节周期相位随海洋混合层深度的增加呈非单调变化，在12 m厚板深度模拟中达到最大值。这一结果是整个模拟系统中季节性大气加热源变化的结果。在浅海流中，大气的季节性加热主要由地表能量通量主导，而在深海流中，季节性加热主要由大气柱内的直接短波吸收主导。随着海洋的加深，地表通量相对于日照的滞后越来越大，这说明了从浅层到中深度的相位滞后增加。短波的直接吸收与日照是同相的，因此随着海洋深度的加深，总加热与日照是同相的，短波的直接吸收主导了大气的季节性加热。热带辐合带随着季节变化的日照量和最高海表温度在浅海流进入夏季半球，而在深海流则相当接近赤道。因此，热带降水和行星反照率高的地区在浅海流的低纬度地区分布得更广，导致热带地区相对于深海流的明显扩张。结果，在浅海模拟中，全球和年平均行星反照率显著（20%）高，这导致全球和年平均表面温度较低（7℃）。浅海模拟中热带行星反照率的增加也导致吸收的短波辐射赤道到极点梯度的减小，并导致相对于深海运行的经向能量传输严重减少（≈50%）。结果，大气涡旋减弱并向极地移动（远离高反照率热带地区），涡旋驱动的急流也减少并相对于深海流向极地移动了15°。
The effect of ocean mixed layer depth on climate is explored in a suite of slab ocean aquaplanet simulations with different mixed layer depths ranging from a globally uniform value of 50–2.4 m. In addition to the expected increase in the amplitude of the seasonal cycle in temperature with decreasing ocean mixed layer depth, the simulated climates differ in several less intuitive ways including fundamental changes in the annual mean climate. The phase of seasonal cycle in temperature differs non-monotonically with increasing ocean mixed layer depth, reaching a maximum in the 12 m slab depth simulation. This result is a consequence of the change in the source of the seasonal heating of the atmosphere across the suite of simulations. In the shallow ocean runs, the seasonal heating of the atmosphere is dominated by the surface energy fluxes whereas the seasonal heating is dominated by direct shortwave absorption within the atmospheric column in the deep ocean runs. The surface fluxes are increasingly lagged with respect to the insolation as the ocean deepens which accounts for the increase in phase lag from the shallow to mid-depth runs. The direct shortwave absorption is in phase with insolation, and thus the total heating comes back in phase with the insolation as the ocean deepens more and the direct shortwave absorption dominates the seasonal heating of the atmosphere. The intertropical convergence zone follows the seasonally varying insolation and maximum sea surface temperatures into the summer hemisphere in the shallow ocean runs whereas it stays fairly close to the equator in the deep ocean runs. As a consequence, the tropical precipitation and region of high planetary albedo is spread more broadly across the low latitudes in the shallow runs, resulting in an apparent expansion of the tropics relative to the deep ocean runs. As a result, the global and annual mean planetary albedo is substantially (20 %) higher in the shallow ocean simulations which results in a colder (7C) global and annual mean surface temperature. The increased tropical planetary albedo in the shallow ocean simulations also results in a decreased equator-to-pole gradient in absorbed shortwave radiation and drives a severely reduced (≈50 %) meridional energy transport relative to the deep ocean runs. As a result, the atmospheric eddies are weakened and shifted poleward (away from the high albedo tropics) and the eddy driven jet is also reduced and shifted poleward by 15° relative to the deep ocean run.