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Attribution of Chemistry-Climate Model Initiative (CCMI) ozone radiative flux bias from satellites

机译：化学 - 气候模型倡议的归因（CCMI）臭氧辐射通量偏向卫星

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The top-of-atmosphere (TOA) outgoing longwave flux over the 9.6 μm ozone band is a fundamental quantity for understanding chemistry–climate coupling. However, observed TOA fluxes are hard to estimate as they exhibit considerable variability in space and time that depend on the distributions of clouds, ozone (O3), water vapor (H2O), air temperature (Ta), and surface temperature (Ts). Benchmarking present-day fluxes and quantifying the relative influence of their drivers is the first step for estimating climate feedbacks from ozone radiative forcing and predicting radiative forcing evolution. To that end, we constructed observational instantaneous radiative kernels (IRKs) under clear-sky conditions, representing the sensitivities of the TOA flux in the 9.6 μm ozone band to the vertical distribution of geophysical variables, including O3, H2O, Ta, and Ts based upon the Aura Tropospheric Emission Spectrometer (TES) measurements. Applying these kernels to present-day simulations from the Chemistry-Climate Model Initiative (CCMI) project as compared to a 2006 reanalysis assimilating satellite observations, we show that the models have large differences in TOA flux, attributable to different geophysical variables. In particular, model simulations continue to diverge from observations in the tropics, as reported in previous studies of the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP) simulations. The principal culprits are tropical middle and upper tropospheric ozone followed by tropical lower tropospheric H2O. Five models out of the eight studied here have TOA flux biases exceeding 100 mW m?2 attributable to tropospheric ozone bias. Another set of five models have flux biases over 50 mW m?2 due to H2O. On the other hand, Ta radiative bias is negligible in all models (no more than 30 mW m?2). We found that the atmospheric component (AM3) of the Geophysical Fluid Dynamics Laboratory (GFDL) general circulation model and Canadian Middle Atmosphere Model (CMAM) have the lowest TOA flux biases globally but are a result of cancellation of opposite biases due to different processes. Overall, the multi-model ensemble mean bias is -133±98 mW m?2, indicating that they are too atmospherically opaque due to trapping too much radiation in the atmosphere by overestimated tropical tropospheric O3 and H2O. Having too much O3 and H2O in the troposphere would have different impacts on the sensitivity of TOA flux to O3 and these competing effects add more uncertainties on the ozone radiative forcing. We find that the inter-model TOA outgoing longwave radiation (OLR) difference is well anti-correlated with their ozone band flux bias. This suggests that there is significant radiative compensation in the calculation of model outgoing longwave radiation.
机译：在9.6μm臭氧频段上的大气层（TOA）传出的长波通是理解化学气候偶联的基本数量。然而，观察到的TOA助焊剂很难估计，因为它们在依赖于云的分布，臭氧（O3），水蒸气（H2O），空气温度（TA）和表面温度（TS）上表现出相当大的空间和时间的可变性。基准测试当天的助势和量化其司机的相对影响是估算来自臭氧辐射强制和预测辐射强制进化的气候反馈的第一步。为此，我们在清晰的天空条件下构建了观测瞬时辐射核（Irks），代表了9.6μm臭氧带中TOA通量的敏感性，包括地球物理变量的垂直分布，包括O3，H2O，TA和TS基于TS在光环对流层发射光谱仪（TES）测量上。将这些内核应用于本日仿真从化学 - 气候模型计划（CCMI）项目相比，与2006年重新分析同化卫星观测相比，我们表明该模型对TOA通量具有很大的差异，可归因于不同的地球物理变量。特别地，正如在对热带地区的观察中，模型模拟继续分歧，如前所述的大气化学气候模型相互熟悉项目（ACCMIP）模拟。主要罪魁祸首是热带中部和上部对流层臭氧，然后是热带较低的对流层H2O。其中八种型号在这里研究的五个型号均具有超过100兆瓦的偏见偏差，其归因于对流层臭氧偏差。另一组五种模型由于H2O而导致50 MW MW的磁通量超过50毫米。另一方面，所有型号的TA辐射偏置可忽略不计（不超过30 MW MW？2）。我们发现地球物理流体动力学实验室（GFDL）通用循环模型和加拿大中大气模型（CMAM）的大气组分（AM3）具有全球最低的TOA通量偏差，而是由于不同的过程而取消相反偏差的结果。总的来说，多模型集合均值偏压为-133±98 mw m？2，表明它们过于大气不透明，因为通过高估热带的对流层O3和H2O捕获了大气中的太多辐射。在对流层中具有太多O3和H2O会对TOA通量对O3的敏感性产生不同的影响，并且这些竞争效应增加了更多对臭氧辐射强制的不确定性。我们发现，模型互波辐射（OLR）差异与其臭氧频带偏压良好的反相关。这表明在模型输出长波辐射计算中存在显着的辐射补偿。

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