Sources of variations in total column carbon dioxide

Abstract

Abstract.Observations of gradients in the total CO 2 column, CO 2 , are expected to provide improved constraints on surface fluxes of CO 2 . Here we use a general circulation model with a variety of prescribed carbon fluxes to investigate how variations in CO 2 arise. On diurnal scales, variations are small and are forced by both local fluxes and advection. On seasonal scales, gradients are set by the north-south flux distribution. On synoptic scales, variations arise due to large-scale eddy-driven disturbances of the meridional gradient. In this case, because variations in CO 2 are tied to synoptic activity, significant correlations exist between CO 2 and dynamical tracers. We illustrate how such correlations can be used to describe the north-south gradients of CO 2 and the underlying fluxes on continental scales. These simulations suggest a novel analysis framework for using column observations in carbon cycle science.

A method for colocating satellite <i>X</i><sub>CO<sub>2</sub></sub> data to ground-based data and its application to ACOS-GOSAT and TCCON

“…This colocation methodology is based on the one used in Inoue et al (2013), with the exception that we replace the lat-long circle with a great-distance circle to avoid warping near the poles. Wunch et al (2011b) refined the geographical method by adding midtropospheric temperature at 700 hPa as an extra threshold to take advantage of the correlation between X CO 2 and midtropospheric temperature (Keppel-Aleks et al, 2011, 2012. Their colocation methodology locates and averages all ACOS-GOSAT observations falling within ±30 • longitude, ±10 • latitude, ±5 days, and ±2 kelvin in T 700 .…”

“…Atmospheric variability of X CO 2 has been shown to be correlated to the free-tropospheric potential temperature, which can be considered as a proxy for equivalent latitude for X CO 2 in the Northern Hemisphere (Keppel-Aleks et al, 2011). In this paper, we follow Wunch et al (2011b) in making use of midtropospheric temperature as one of the covariates along with latitude, longitude, and time.…”

“…In this paper, we follow Wunch et al (2011b) in making use of midtropospheric temperature as one of the covariates along with latitude, longitude, and time. Specifically, we use the midtropospheric temperature field at 700 hPa from the National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis product, which uses a frozen state-of-the-art analysis/forecast system and performs data assimilation using past data (Kalnay et al, 1996). The midtropospheric temperature field at 700 hPa should be directly proportional to the potential temperature at 700 hPa for the range of temperature of interest, and its inclusion as a covariate should allow us to construct better colocation metrics.…”

Bias corrections of GOSAT SWIR XCO<sub>2</sub> and XCH<sub>4</sub> with TCCON data and their evaluation using aircraft measurement data

“…Therefore, several sophisticated methods were devised to obtain a sufficient number of co-located data. Following Keppel-Aleks et al (2011) who implied a relationship between meridional gradients of free-tropospheric potential temperature and CO 2 concentrations in mid-latitudes over the Northern Hemisphere, Wunch et al (2011b) used the distribution of potential temperature at 700 hPa when defining the co-location criteria in the Northern Hemisphere. Expansively, Nguyen et al (2014) utilized a modified Euclidean distance weighted average of distance, time, and temperature at 700 hPa.…”

Comparisons of the Orbiting Carbon Observatory-2 (OCO-2) <i>X</i><sub>CO<sub>2</sub></sub> measurements with TCCON

“…The X CO 2 quantity is useful for carbon cycle science, as it is used to directly infer surface fluxes of CO 2 , and is relatively insensitive to vertical mixing (Yang et al, 2007;Keppel-Aleks et al, 2011). In the remainder of this paper, a "measurement" refers to the entire process of producing the atmospheric abundances of X CO 2 .…”