Estimating regional methane surface fluxes: the relative importance of surface and GOSAT mole fraction measurements
Estimating regional methane surface fluxes: the relative importance of surface and GOSAT mole fraction measurements
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DOI：
10.5194/acp-13-5697-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
Weiss, R. F.
中科院分区：
文献类型：
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作者：
Fraser, A.;Palmer, P. I.;Weiss, R. F.
我们使用集合卡尔曼滤波(EnKF)和GEOS-Chem化学输送模式，使用来自GOSAT(温室气体观测卫星)和/或NOAA ESRL(地球系统研究实验室)和CSIRO GASLAB(全球大气采样实验室)CH4表面摩尔分数测量的替代干空气柱平均甲烷(XCH4)来估计2009年6月至2010年12月期间的区域每月甲烷(CH4)通量。使用GOSAT和/或地面测量的全球后验估计在510-516Tg年(-1)之间，这低于先前529+/-25Tg年(-1)的全球通量，但在不确定性范围内。我们发现区域前后通量之间的差异较大，最大的月排放量变化(75TgYr(-1))发生在温带欧亚大陆。在非北部地区，使用GOSAT数据进行反演的误差降幅至少是仅同化地面数据时的三倍(高达45%)，这反映了GOSAT更大的空间覆盖范围，但与数据过滤器相关的纬度60度和欧洲上空的两个例外，即地面网络充分描述了我们模型空间和时间网格上的通量。我们使用CarbonTracker和GEOS-Chem XCO2模式输出研究了量化代理GOSAT XCH4(涉及模式XCO2)和从地表摩尔分数数据推断甲烷通量估计的模型误差，并显示了相似的结果通量，差异反映了代理值的初始差异。利用一系列观测系统仿真实验(OSSES)对GOSAT非均匀大气采样引入的后验通量误差进行了表征。我们表明，理论上，晴空测量可以在真实值的10%以内重现通量，但热带地区除外，在那里，由于云和气溶胶的测量数量有很大的季节性循环，通量在真实通量的15%以内。我们通过将它们合并到GEOS-Chem中，并在AGAGE(高级全球大气气体实验)网络的表面CH4测量和TCCON(总碳柱观测网络)的XCH4柱测量的位置和时间对模型进行采样，来评估我们的后方甲烷通量。与之前的通量相比，后方通量略微改善了与AGAGE和TCCON数据的模型一致性，相关系数(r(2))平均增加了0.04(范围：-0.17~0.23)，偏差平均降低了0.4 ppb(范围：-8.9~8.4 ppb)。
We use an ensemble Kalman filter (EnKF), together with the GEOS-Chem chemistry transport model, to estimate regional monthly methane (CH4) fluxes for the period June 2009-December 2010 using proxy dry-air column-averaged mole fractions of methane (XCH4) from GOSAT (Greenhouse gases Observing SATellite) and/or NOAA ESRL (Earth System Research Laboratory) and CSIRO GASLAB (Global Atmospheric Sampling Laboratory) CH4 surface mole fraction measurements. Global posterior estimates using GOSAT and/or surface measurements are between 510-516 Tg yr(-1), which is less than, though within the uncertainty of, the prior global flux of 529 +/- 25 Tg yr(-1). We find larger differences between regional prior and posterior fluxes, with the largest changes in monthly emissions (75 Tg yr(-1)) occurring in Temperate Eurasia. In non-boreal regions the error reductions for inversions using the GOSAT data are at least three times larger (up to 45 %) than if only surface data are assimilated, a reflection of the greater spatial coverage of GOSAT, with the two exceptions of latitudes >60 degrees associated with a data filter and over Europe where the surface network adequately describes fluxes on our model spatial and temporal grid. We use CarbonTracker and GEOS-Chem XCO2 model output to investigate model error on quantifying proxy GOSAT XCH4 (involving model XCO2) and inferring methane flux estimates from surface mole fraction data and show similar resulting fluxes, with differences reflecting initial differences in the proxy value. Using a series of observing system simulation experiments (OSSEs) we characterize the posterior flux error introduced by non-uniform atmospheric sampling by GOSAT. We show that clear-sky measurements can theoretically reproduce fluxes within 10% of true values, with the exception of tropical regions where, due to a large seasonal cycle in the number of measurements because of clouds and aerosols, fluxes are within 15% of true fluxes. We evaluate our posterior methane fluxes by incorporating them into GEOS-Chem and sampling the model at the location and time of surface CH4 measurements from the AGAGE (Advanced Global Atmospheric Gases Experiment) network and column XCH4 measurements from TCCON (Total Carbon Column Observing Network). The posterior fluxes modestly improve the model agreement with AGAGE and TCCON data relative to prior fluxes, with the correlation coefficients (r(2)) increasing by a mean of 0.04 (range: -0.17 to 0.23) and the biases decreasing by a mean of 0.4 ppb (range: -8.9 to 8.4 ppb).