Detecting methane from thawing yedoma: an OSSE evaluating tall towers, TROPOMI, and MERLIN’s capabilities.  

Climate change is exerting severe impacts on the Northern high latitudes. Large quantities of carbon stored in Yedoma, a carbon and ice-rich permafrost soil, become catalysts for rapid degradation and subsequent carbon release as temperatures rise. The resulting radiative forcing, expected to be 40 to 70 percent in the form of CH4, necessitates accurate detection and quantification to properly account for these fluxes into the global carbon budget. Greenhouse gas observation systems monitor GHG concentrations to infer surface-atmosphere exchange processes. In this study The pan-Arctic tall tower network, passive TROPOMI, and active MERLIN satellites are considered as monitoring platforms. We employ an observing system simulation experiment (OSSE). Utilising a 4D atmospheric transport model, synthetic observations are generated through the Goddard Earth Observing System model (GEOS). To which established errors and biases are added. We simulate a disturbance scenario of enhanced methane release from anticipated Yedoma thaw. A nature run with 'natural' emissions serves as the basis when compared to an enhanced CH4 release run from Yedoma soils. The strength of the enhancement is scaled to establish lower detection limits Satellite systems demonstrate lowest detection limits when aggregating data over a 112-day period, requiring a 1.9 to 2.8 times increase in fluxes compared to current conditions for reliable change detection, which is increased by a factor 1.2 when considering transport modelling uncertainties. Tall tower networks exhibit varied detection limits, emphasising the influence of tower placement and transport errors. This research not only informs the development of a comprehensive methane observing system but also sheds light on the challenges and strengths of in situ and satellite-based monitoring in high latitude environments.