A new look at spatial gradients in Xco2 from satellite and ground-based observations

We examine the relationship between surface fluxes of carbon dioxide and spatial and temporal gradients in total column CO2 (Xco2). Previously, we used data from the TCCON site at Park Falls, Wisconsin to examine the correlation between summer Xco2 and free tropospheric potential temperature. The correlation between these quantities was used as a proxy to estimate the north-south gradient in Xco2 during the growing season. In 2009, GOSAT was launched to observe Xco2 from space. The Atmospheric CO2 Observations from Space (ACOS) group, which was formed out of the OCO science team, has worked with the GOSAT Research Announcement (RA) office to retrieve Xco2 values from the GOSAT spectra. These new satellite data - as well as data from other sites in the growing TCCON network - allow us to examine the relationship between gradients in Xco2 and surface fluxes globally across all seasons. We compare the north-south gradient in GOSAT data to that estimated from TCCON data. We use a general circulation model, driven by a standard biospheric model (CASA) as well as optimized fluxes from CarbonTracker to better understand how the interaction between surface fluxes and atmospheric dynamics sets the north-south gradient in different seasons. Because temporal variations and spatial gradients in Xco2 are often dominated by the large scale atmospheric turbulence, we can use Xco2 data to draw conclusions regarding the phasing and strength of surface fluxes necessary to sustain the observed gradients.