Inverse modeling of methane sources and sinks using the adjoint of a global transport model
Inverse modeling of methane sources and sinks using the adjoint of a global transport model
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DOI：
10.1029/1999jd900428
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发表时间：
1999-11-20
影响因子：
4.4
通讯作者：
Heimann, M
中科院分区：
文献类型：
--
作者：
Houweling, S;Kaminski, T;Heimann, M
提出了一种反演大气甲烷源汇的方法。一个伴随版本的全球传输模式已被用来估计这些通量在一个相对较高的空间和时间分辨率。国家海洋和大气管理局在两次船只巡航期间从34个监测站和11个地点沿着获得的测量数据被用作投入。最近对甲烷来源的估计，包括一些次要来源，已被用作先验约束。对于目标期1993-1995年，我们的反演减少了先验假设的全球甲烷排放量528至505 Tg（CH 4）年（-1）后验。此外，北方半球来源的相对贡献从先验的77%降低到后验的67%。除了使排放量估计与测量更加一致外，反演还有助于减少源的不确定性，不确定性减少从全球尺度上的75%到网格尺度（8度x10度）上的1%不等，表明网格尺度的可变性不能通过测量来解决。大规模的功能，如半球间的甲烷浓度梯度是相对较好的解决，因此施加强有力的限制估计通量。该模型再现这种梯度的能力是严重依赖于半球间示踪剂交换和大规模的羟基自由基分布的精度表示。因此，反演得出的排放量估计是敏感的错误，在运输模型和计算的羟基自由基分布。事实上，这些模型误差的相当大的贡献是不可忽视的。这强调了通过逆向建模进行的源量化受到半球间转运速率和羟基自由基分布可以被验证的程度的限制。我们表明，使用的排放的时间和空间相关性可能会显着提高我们的结果，但是，目前缺乏这种相关性的实验支持。我们的研究结果进一步表明，在以前的甲烷逆研究报告的不确定性降低被高估。
An inverse modeling method is presented to evaluate the sources and sinks of atmospheric methane. An adjoint version of a global transport model has been used to estimate these fluxes at a relatively high spatial and temporal resolution. Measurements from 34 monitoring stations and 11 locations along two ship cruises by the National Oceanographic and Atmospheric Administration have been used as input. Recent estimates of methane sources, including a number of minor ones, have been used as a priori constraints. For the target period 1993-1995 our inversion reduces the a priori assumed global methane emissions of 528 to 505 Tg(CH4) yr(-1) a posteriori. Further, the relative contribution of the Northern Hemispheric sources decreases from 77% a priori to 67% a posteriori. In addition to making the emission estimate more consistent with the measurements, the inversion helps to reduce the uncertainties in the sources, Uncertainty reductions vary from 75% on the global scale to similar to 1% on the grid-scale (8 degrees x10 degrees), indicating that the grid scale variability is not resolved by the measurements. Large scale features such as the interhemispheric methane concentration gradient are relatively well resolved and therefore impose strong constraints on the estimated fluxes. The capability of the model to reproduce this gradient is critically dependent on the accuracy at which the interhemispheric tracer exchange and the large-scale hydroxyl radical distribution are represented. As a consequence, the inversion-derived emission estimates are sensitive to errors in the transport model and the calculated hydroxyl radical distribution. In fact, a considerable contribution of these model errors cannot be ignored. This underscores that source quantification by inverse modeling is limited by the extent to which the rate of interhemispheric transport and the hydroxyl radical distribution can be validated. We show that the use of temporal and spatial correlations of emissions may significantly improve our results; however, at present the experimental support for such correlations is lacking. Our results further indicate that uncertainty reductions reported in previous inverse studies of methane have been overestimated.