posted on 2015-04-15, 15:11authored byLaimonas Zubas
Space-borne methane observations provide increased spatial coverage and complement
the precise, but sparse network of in-situ measurement sites. In this study, a method
has been developed to investigate regional-scale methane budgets using space-borne
methane observations, utilising the UK Met Office Numerical Atmospheric Modelling
Environment (NAME). Lagrangian atmospheric dispersion models, such as NAME, allow
us to investigate fluxes at a lesser computational cost and potentially, a higher spatial
resolution.
An inversion algorithm was created and tested on synthetic ground measurement
data. The NAME based inversion algorithm was then developed to utilise column CH4
concentrations, with an intention of applying it to Greenhouse Gases Observing SATellite
(GOSAT) observations. A study utilising synthetic GOSAT-like observations was
carried out, as well as synthetic inversions quantifying the performance of future methane
sensing space-borne missions (CarbonSat and Sentinel-5 Precursor), when used to study
fluxes over the British Isles. The results were obtained for 2 months, January and July,
2011. Sentinel-5 Precursor can reduce the flux uncertainty over England by 30% over
England and Wales in July, with the remaining regions (Scotland, Republic of Ireland,
Northern Ireland and northern France) achieving a reduction of 8-14%. In contrast,
CarbonSat error reduction values are expected to range from 3% to 18%.
Finally, we used the forward model to relate bottom-up inventories to satellite observations
of atmospheric XCH4 from GOSAT. For selected regions, we have inferred
patterns in atmospheric XCH4 from the spatial distribution of the surface emissions, factoring
in the atmospheric transport using an atmospheric dispersion model. The forward
model was found to perform poorly over Western Europe (r=0.43) and North America
(r=0.48). The agreement between the observations and simulations of r=0.72 were calculated
over South America, r=0.60 over South East Asia and r=0.60 over Australasia.