cqvip:Seven operative thermal infrared(TIR)spectrometers launched at sun-synchronous polar orbits supply huge amounts of information about Arctic methane(CH4)year-round,day and night.TIR data are unique for estimating CH4 emissions from a warming Arctic,both terrestrial and marine.This report is based on publicly available CH4 concentrations retrieved by NOAA and NASA from spectra of TIR radiation delivered by EU IASI and US AIRS sounders.Data were filtered for high thermal contrast in the troposphere.Validation versus aircraft measurements at three US continental sites reveal a reduced,but still significant sensitivity to CH4 anomalies in the troposphere below 4 km of altitude.The focus area is the Barents and Kara seas(BKS).BKS is impacted with warm Atlantic water and mostly free of sea ice.It is a shelf area with vast deposits of oil and natural gas(~90%CH4),as well as methane hydrates and submarine permafrost.Although in summer AIRS and IASI observe no significant difference in CH4 between BKS and N.Atlantic,a strong,monthly positive CH4 spatial anomaly of up to 30 ppb occurs during late autumn–winter.One of explanations of this increase is a fall/winter pycnocline breakdown after a period of blocked mixing caused by a stable density seawater stratification in summer:enhanced mixing lets CH4 to reach the sea surface and atmosphere.
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