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Application and Advances in ground-based total column measurements for Earth System Science Studies

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Anthopogenic activities have caused considerable changes in the Earth's biogeochemistry. For example, fossil fuel burning has caused a 35% increase in atmospheric CO2, and 140% increase in CH4, which in turn affects the Earth's energy budget. These increases would be larger but for the response of the biosphere. A prerequisite to accurately predicting the future response of the Earth's systems, via prognostic modeling, is understanding the processes in the past. Such understanding can be reached via a combination of bottom-up and top-down approaches. Measurements of atmospheric composition play an important role for both approaches, as an independent validation of processed-based understanding, or as a primary input for top-down inverse studies. In situ point measurements provide excellent information on fine temporal and spatial scales, but are also extremely sensitive to the ability to model the transport of constituents. Total column measurements, on the other hand, provide complementary information. They are typically less precise, and sensitive to broader spatial and temporal scales, but as an integrated signal are less affected by the vertical distribution of the constituents. The Total Carbon Column Observing Network is a global network of ground-based sites measuring column-averaged CO2, CH4 and other gases with unprecedented precision. The network is extensively used as a transfer standard for calibration of satellite measurements. In addition, comparison of TCCON time series to model simulations has revealed errors in biospheric surface flux estimation, both in the northern and southern hemispheres. Furthermore, efforts are ongoing within the TCCON to improve current and develop additional products. These include retrievals of total column H2O, which show excellent agreement with independent balloon-borne sonde measurements across a range of sites. Retrievals of tropospheric CH4 based on an N2O proxy will also be introduced, along with their comparison to independent measurements and model simulations.