Estimating Ocean Heat Uptake Using Boundary Green's Functions: A Perfect-Model Test of the Method.
Estimating Ocean Heat Uptake Using Boundary Green's Functions: A Perfect-Model Test of the Method.
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DOI：
10.1029/2022ms002999
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发表时间：
2022-12
影响因子：
6.8
通讯作者：
Gregory, Jonathan M.
中科院分区：
文献类型：
--
作者：
Wu, Quran;Gregory, Jonathan M.
海洋热吸收是由“多余的热量”通过海气通量添加到海洋表面，然后通过海洋运输带到深处引起的。估计海洋中多余热量的一种方法是使用海洋传输的绿色函数（GF）表示将观测到的海表温度（SST）异常向下传播。采用“完美模型”的方法，我们使用历史模拟来测试这种GF方法，其中诊断了真正的余热。我们从两种方法得到GFs：（a）使用理想化示踪剂模拟GFs，和（B）从模拟的CFCs和气候示踪剂推断GFs。在模型世界中，我们发现，将模拟的GF与SST异常相结合，重建了印度洋太平洋多余热量，深度积分变化的均方根误差为26%;推断的GF的相应数字为34%。模拟的GF是不准确的，因为它们在空间和时间上是粗粒度的，以减少计算成本。推断的GF是不准确的，因为观察是不充分的约束。这两种GF都忽略了随着海洋变暖，北大西洋热量吸收的减缓。SST边界条件包含南大洋的再分配冷却，这导致低估了那里的热量吸收。所有这些误差的大小都相当，并且往往会部分地相互补偿。推断出的过量热量对以下情况不敏感：（a）先前GF形状的微小变化，或（B）来自SF6和高压气瓶14 C的附加约束。绿色函数（GF）在历史模拟中受到模拟观测的约束时，广泛地重建了模拟的海洋热吸收。GF方法中的误差来自于观测约束不足和海洋输送的强迫变化。当使用海表面温度异常作为边界条件时，GF低估了南大洋的热吸收。
Ocean heat uptake is caused by “excess heat” being added to the ocean surface by air‐sea fluxes and then carried to depths by ocean transports. One way to estimate excess heat in the ocean is to propagate observed sea surface temperature (SST) anomalies downward using a Green's function (GF) representation of ocean transports. Taking a “perfect‐model” approach, we test this GF method using a historical simulation, in which the true excess heat is diagnosed. We derive GFs from two approaches: (a) simulating GFs using idealized tracers, and (b) inferring GFs from simulated CFCs and climatological tracers. In the model world, we find that combining simulated GFs with SST anomalies reconstructs the Indo‐Pacific excess heat with a root‐mean‐square error of 26% for depth‐integrated changes; the corresponding number is 34% for inferred GFs. Simulated GFs are inaccurate because they are coarse grained in space and time to reduce computational cost. Inferred GFs are inaccurate because observations are insufficient constraints. Both kinds of GFs neglect the slowdown of the North Atlantic heat uptake as the ocean warms up. SST boundary conditions contain redistributive cooling in the Southern Ocean, which causes an underestimate of heat uptake there. All these errors are of comparable magnitude, and tend to compensate each other partially. Inferred excess heat is not sensitive to: (a) small changes in the shape of prior GFs, or (b) additional constraints from SF6 and bomb 14C. Green's functions (GFs) broadly reconstruct simulated ocean heat uptake when constrained by simulated observations in a historical simulation Errors in the GF method arise from insufficient observational constraints and forced changes in ocean transports GFs underestimate the Southern Ocean heat uptake when using sea surface temperature anomalies as boundary conditions