Constraining regional fluxes of CO2 and CH4 over Canada by merging atmospheric and ground observations

对大气中二氧化碳（CO2）和甲烷（CH4）等温室气体浓度增加的担忧，使得进一步了解这些气体在陆地表面和大气之间交换的地点、原因和速率变得至关重要。关键的差距是我们无法将大气和地面的观测结果（具有不同时空尺度的特征）与过程级生物学知识相结合。本研究的目标如下：(1)建立一个能够吸收多时空尺度大气和地面观测数据的陆地-大气模拟系统。(2)确定加拿大上空两种主要温室气体CO2和CH4通量的位置、强度和原因。重点是解决大陆上空的区域尺度（10~1000公里）通量，由于建模系统无法解释大陆上空高度变化的大气观测数据，因此对这些通量的了解受到了阻碍。最先进的大气模型将与生物圈模型相结合，生物圈模型针对诸如CO2/CH4直接通量观测和森林清查分析等数据流进行优化，这些数据流以前在没有大气观测的情况下使用。因此，所提议的模拟系统吸收了大气和地面测量数据，从而产生了与大气和生物圈知识最优一致的“最佳猜测”通量。拟议中的研究计划将在气候科学方面取得进展：对当前温室气体的源/汇有更详细的了解，有助于提高预测未来气候的能力。此外，拟议的研究方案将为量化和监测温室气体排放奠定基础，从而有助于加拿大履行《京都议定书》规定的义务。

Concerns over increases in atmospheric concentrations of greenhouse gases such as CO2 (carbon dioxide) and CH4 (methane) make it critically important to improve understanding of where, why, and at what rates these gases are exchanged between the land surface and the atmosphere. The key gap is our inability to merge observations in the atmosphere and on the ground, characterizing diverse spatio-temporal scales, with process-level biological knowledge. The objectives of this study are as follows: (1) Develop a land-atmosphere modeling system that can ingest both atmospheric and ground-based observations at multiple spatial and temporal scales. (2) Determine the locations, strengths, and reasons for fluxes of CO2 and CH4, the two major greenhouse gases, over Canada. The focus is on resolving regional scale (10~1000 km) fluxes over the continent, knowledge of which have been hampered by modeling systems that cannot interpret the highly varying atmospheric observations over the continent. State-of-the-art atmospheric models will be combined with biospheric models that are optimized against such datastreams as direct CO2/CH4 flux observations and forest inventory analyses, previously used in absence of the atmospheric observations. Thus the proposed modeling system assimilates both atmospheric and ground-based measurements, thereby yielding "best-guess" fluxes that are optimally consistent with both atmospheric and biospheric knowledge. The proposed research program will make steps forward in climate science: a more detailed knowledge of sources/sinks of current greenhouse gases leads to enhanced capability to project future climate. Furthermore, the proposed research program will contribute towards Canada's obligations under the Kyoto Protocol by building the foundation for quantifying and monitoring emissions of greenhouse gases.