## 1 Introduction  
The distribution of carbon dioxide (CO\({}_{2}\)) in the mid-troposphere is influenced by tropospheric weather and large-scale circulation patterns around the globe and interannual variability associated with the El Nino Southern Oscillation (ENSO) [1,2]. Areas with enhanced upward or downward motions associated with large-scale circulations can transport CO\({}_{2}\) between the free troposphere (FT) and the atmospheric boundary layer (ABL) on the timescale of a day [3]. If information related to CO\({}_{2}\) concentrations flows between synoptic systems and the ABL on a daily to subdaily timescale [3,4], changes in soil moisture, surface albedo, and temperature that drive biosphere-atmosphere interactions at short timescales may also influence mid-tropospheric CO\({}_{2}\). While observations of the vertically integrated CO\({}_{2}\) mixing ratio have been found to be influenced by continental-scale flux patterns [5], it is not yet understood how local fluxes from varying land-cover types relate to CO\({}_{2}\) concentrations in the mid-troposphere. How is the high-frequency variability of CO\({}_{2}\) in the ABL communicated to the FT, and how do CO\({}_{2}\) concentrations in the FT influence CO\({}_{2}\) concentrations in the ABL? In contrast to ABL CO\({}_{2}\) concentrations, FT CO\({}_{2}\) concentrations are governed exclusively by transport mechanisms, either large-scale ascent or descent associated with the Hadley/Walker circulation, other large-scale cells, or baroclinic/synoptic disturbances. [PERSON] _et al._[6] quantified \"venting\" of ABL air into the FT by cloud circulations of different scales and found that synoptic cyclones or mid-latitude baroclinic waves constitute the greatest contribution to ABL venting. One mesoscale modeling study demonstrated that 70\(\%\) of passive tracers initialized in the boundary layer are transported to the free troposphere over a period of three days [7]. [PERSON] _et al._[8] attributed this substantial exchange between ABL and FT to the warm conveyor belt, which provides substantial ascent from the ABL to the mid-troposphere. A detailed mass budget demonstrates the ventilation of ABL air into the FT over the warm sector, as well as the entrainment of FT air behind the cold front and near the high-pressure center [9]. Convective circulations can also promote exchanges between the ABL and FT. Isolated shallow and deep convective cells can ventilate the boundary layer over small areas in the span of a few hours [10,11]. Mesoscale convective systems (MCS), complexes of thunderstorms characterized by an organized mesoscale circulation, provide much of the warm-season rainfall over the central U.S. [12,13], and these systems contribute substantially to the exchange of air between the ABL and FT [6]. In the case of MCSs, the exchanges are brought about by individual convective updrafts but also via coherent mesoscale flow structures associated with these systems (e.g., [14,15]). Boundary-layer venting from deep convection can also accompany synoptic systems, as in the case of embedded convective elements along a cold front [16]. Penetrative downdrafts would presumably serve as a means of injecting FT air into the ABL, but this mechanism has not been emphasized in these previous tracer and budget studies. A recent study examining total column CO\({}_{2}\) finds that during a frontal system passing over the Park Falls, WI tall tower, CO\({}_{2}\) concentration above 5 km increased around 5 ppm while drawdown of boundary layer CO\({}_{2}\) decreased [5]. These observations confirm that horizontal advection and gradients play a role in total CO\({}_{2}\) column variation on a subdaily time scale. Advection also influences total CO\({}_{2}\) column up to seasonal time scales, especially at the onset of the growing season. [PERSON] _et al._[5,17] discuss a north-south gradient, which constitutes about a 4 ppm variation between 30\({}^{\circ}\)N and 60\({}^{\circ}\)N during the growing season, correlated with variations in FT potential temperature.