CHsub(4) concentrations over the Amazon from GOSAT consistent with in situ vertical profile data

Abstract

The Amazon Basin contains large wetland ecosystems which are important sources of methane (CH4). Space-borne observations of atmospheric CH4 provide constraints on emissions from these remote ecosystems, but lack of validation precludes robust estimates. We present the rst validation of CH4 columns in the Amazon from the Greenhouse gases Observing SATellite (GOSAT) using dedicated vertical pro le measurements of CH4 over ve sites across the Amazon Basin. These aircraft pro les, combined with the TOMCAT stratospheric model, are vertically integrated allowing direct comparison to the GOSAT measurements. The absolute columns agree within uncertainties or show no signi cant di erence at three of the aircraft sites (-1.9 2.2 ppb and 3.6 4.3 ppb at one site with two di erent campaigns; and 3.6 1.7 ppb, and 6.6 2.6 ppb at the other two), whilst at two sites GOSAT XCH4 is shown to be slightly higher than aircraft measurements, by up to approximately 10 ppb in the most di ering case (8.1 2.1 ppb and 9.7 2.8 ppb). The seasonality in XCH4 seen by the aircraft pro les is also well captured. GOSAT observes elevated concentrations in the north-west corner of South America in the dry season and enhanced concentrations elsewhere in the Amazon Basin in the wet season; with the strongest seasonal di erences coinciding with regions in Bolivia known to contain large wetlands. Our results are encouraging evidence that these GOSAT CH4 columns are in good agreement with in situ measurements and can be reliably used to provide new insights into tropical methane emissions