Planetary boundary layer errors in mesoscale inversions of column‐integrated CO₂ measurements

Abstract

Observing platforms of greenhouse gas column mole fractions using remote sensing instruments have enhanced the capability of carbon data assimilation systems at large scales and helped improve our understanding of the underlying processes involved in the exchange of carbon at the surface of the globe. In this study, we quantify the additional information carried by these measurements at finer scales and consider the impact of vertical transport errors in current modeling systems, one of the main sources of uncertainties in regional inverse flux estimates. Surface-based column-integrated sensors are shown to be a significant source of information to constrain local surface fluxes at fine scales. Gain and error reduction are only about 20% lower than for in situ instruments. Column measurements show less dependence on near-field surface fluxes compared to in situ, with the error reduction being more homogeneously distributed. However, vertical transport errors still impact the flux retrievals, as with in situ measurements but to a lesser extent. Inverse fluxes from both types of measurements were affected by errors in vertical mixing and mean horizontal winds, with a larger impact on the inverse carbon balance using in situ measurements. The use of remote sensing measurements also appeared to constrain significantly the boundary concentrations, a critical limitation in current regional inversions. We finally performed a pseudo-data experiment combining both types of instruments, creating an optimal observing network with a lower impact of planetary boundary layer transport errors on the surface fluxes and the boundary concentrations, and a more widely distributed reduction of the errors over the boundaries.

Lower-tropospheric CO<sub>2</sub> from near-infrared ACOS-GOSAT observations

“…- Stephens et al (2007) show that vertical gradient in mole fraction determined from two points in the atmospheric column better constrains model transport and partitioning between northern extratropical land fluxes and land fluxes further south since vertical transport is an uncertainty in flux estimates Lauvaux and Davis, 2014;Stephens et al, 2007).…”

Intercomparison of open-path trace gas measurements with two dual-frequency-comb spectrometers

“…Point sensors provide valuable information about local sources, but their use for continuous regional measurements on sampling towers is complicated by local wind patterns, local sources, and mixing within the planetary boundary layer (PBL), especially at night (Lauvaux et al, 2008(Lauvaux et al, , 2012Ciais et al, 2010). Similarly, total-column measurements are particularly useful for sub-continental to global-scale measurements; however they are sensitive to atmospheric transport errors within the PBL (Lauvaux and Davis, 2014), are affected by clouds and aerosols, are primarily limited to daytime measurements, and lack either the revisit rates or mobility for regional flux measurements. Horizontal integrated path measurements are complementary to point sensors and satellites: they cover spatial scales from one to tens of kilometers, provide measurements on secondto-minute timescales with portable instruments, and are thus appropriate for regional studies.…”

Assimilation of satellite NO<sub>2</sub> observations at high spatial resolution using OSSEs

“…Current uncertainties in the surface NO 2 emission inventories in the US are thought to be of the order of 50 % (Krotkov et al, 2016;Travis et al, 2016). Comparable uncertainties affect estimates of the planetary boundary layer (PBL) height and mixing rates that redistribute emissions from the surface (Kretschmer et al, 2012(Kretschmer et al, , 2014Lauvaux and Davis, 2014).…”