Discrepancies in Simulated Ocean Net Surface Heat Fluxes over the North Atlantic

Abstract

The change in ocean net surface heat flux plays an important role in the climate system. It is closely related to the ocean heat content change and ocean heat transport, particularly over the North Atlantic, where the ocean loses heat to the atmosphere, affecting the AMOC (Atlantic Meridional Overturning Circulation) variability and hence the global climate. However, the difference between simulated surface heat fluxes is still large due to poorly represented dynamical processes involving multiscale interactions in model simulations. In order to explain the discrepancy of the surface heat flux over the North Atlantic, datasets from nineteen AMIP6 and eight highresSST-present climate model simulations are analyzed and compared with the DEEPC (Diagnosing Earth’s Energy Pathways in the Climate system) product. As an indirect check of the ocean surface heat flux, the oceanic heat transport inferred from the combination of the ocean surface heat flux, sea ice, and ocean heat content tendency is compared with the RAPID (Rapid Climate Change-Meridional Overturning Circulation and Heat flux array) observations at 26°N in the Atlantic. The AMIP6 simulations show lower inferred heat transport due to less heat loss to the atmosphere. The heat loss from the AMIP6 ensemble mean north of 26°N in the Atlantic is about 10 W m₋₂ less than DEEPC, and the heat transport is about 0.30 PW (1 PW = 10₁₅ W) lower than RAPID and DEEPC. The model horizontal resolution effect on the discrepancy is also investigated. Results show that by increasing the resolution, both surface heat flux north of 26°N and heat transport at 26°N in the Atlantic can be improved.

摘 要

海表净热通量变化在气候系统中起着重要作用. 它与海洋热含量变化以及海洋热能传输密切相关, 特别是在北大西洋, 海洋向大气散失热量, 影响 AMOC (大西洋经向翻转环流) 变化, 从而影响全球气候. 然而, 由于模式不能很好地模拟多尺度相互作用的动态过程, 模拟的海表热通量仍然有很大差异. 为了解释北大西洋海表热通量的差异, 本文分析了 19 个 AMIP6 和 8 个 highresSST 气候模式模拟资料, 并与 DEEPC (诊断气候系统中的地球能量流动) 产品进行了比较. 作为对海表热通量的间接检验, 把海表热通量、 海冰和海洋热含量趋势结合起来, 导出海洋热能传输, 并与 RAPID (快速气候变化-经向翻转环流和热通量阵列) 在大西洋 26°N 的观测结果进行了比较. AMIP6 模式模拟显示由于向大气散发的热量较少, 导出的热能传输较低. AMIP6 集合平均在大西洋 26°N 以北的热损失比 DEEPC 约低 10 W m^–2, 热能传输比 RAPID 和 DEEPC 约低 0.30 PW (1 PW = 10¹⁵ W). 还研究了模式水平分辨率对海表热通量差异的影响. 结果表明, 通过提高分辨率, 可以改进 26°N 以北的大西洋海表热通量和大西洋 26°N 处的热能传输.