Environmental drivers constraining the seasonal variability in satellite-observed and modelled methane at northern high latitudes

Abstract

Methane emissions from Northern Hemisphere high-latitude wetlands are associated with large uncertainties, especially in the rapidly warming climate. Satellite observations of column-averaged methane concentrations (XCH4) in the atmosphere exhibit variability due to time-varying sources and sinks as well as atmospheric transport. In this study, we investigate how environmental variables, such as temperature, soil moisture, snow cover, and the hydroxyl radical (OH) sink of methane, explain the seasonal variability in XCH4 observed from space over Northern Hemisphere high-latitude wetland areas. We use XCH4 data obtained from the TROPOMI instrument aboard the Sentinel-5 Precursor satellite, retrieved using the Weighting Function Modified Differential Optical Absorption Spectroscopy (WFMD) algorithm. In addition, we perform the analysis using two atmospheric inversion model configurations: one based on non-optimized prior fluxes and another using fluxes optimized with in situ atmospheric observations. The aim was to assess the consistency between satellite-based and model-based results and to explore differences in how environmental variables drive the variability in XCH4. Environmental variables are derived primarily from meteorological reanalysis datasets, with satellite-based data used for snow cover and soil freeze–thaw dynamics and modelled data used for the OH sink. Our analysis focuses on five wetland-dominated case study regions over Northern Hemisphere high latitudes, including two in Finland and three in Russian Siberia, covering the period from 2018 to 2023. Our findings reveal that environmental variables have a systematic impact on satellite-based XCH4 variability. Seasonal variability is primarily driven by the OH sink and snow, particularly the snow water equivalent, while daily variability is most strongly affected by air temperature. The results are largely consistent with local in situ studies, although the role of snow appears more pronounced in our analysis. We observe interesting differences in the environmental drivers influencing satellite-based and model-based XCH4. The posterior results after in situ data assimilation were better aligned with the satellite-based results than the prior, suggesting that, while there remains room for improvement in model priors and configurations, there is already some consistency between the modelled and observed total-column methane dynamics. However, the prior fluxes used in the model could benefit from improved snow information. Overall, our results demonstrate how satellite-based XCH4 observations can be used to study the seasonal variability in atmospheric methane over large wetland regions. The results imply that satellite observations of atmospheric composition and other Earth observations and meteorological reanalysis data can be jointly informative with respect to the processes controlling emissions in Northern Hemisphere high latitudes.