Physical atmospheric structure and tropospheric mixing information in vertical profiles of atmospheric CO₂ mixing ratios

Abstract

[1] Vertical distribution of atmospheric CO 2 mixing ratios, as well as CO 2 vertical variance and gradient are related to the vertical stability at the time of measurement, to the transport of coherent upstream plumes studied through changes in the upstream surface influence or to the historic mixing processes and dispersive behavior. Three vertical profiles of CO 2 mixing ratios measured from 900 to 4200 m above sea level (masl) in 2006 at La Muela, Spain (LMU, 41.60°N 1.10°W, 570 masl) are examined. Changes in CO 2 mixing ratio are associated with changes of the atmospheric physical parameters on the day of the survey; and with the transport of coherent air masses. Its consistency is examined through changes of the historical horizontal dispersion and chaotic mixing dynamics of air masses during the four days prior to measurements. A climatology of Lagrangian backward simulations run once a week at four altitudes (600, 1200, 2500 and 4000 masl) at LMU for 2006 shows that dispersion in these altitudes is superdiffusive (exponent coefficient g > 1/2) and mixing follows a chaotic dynamics (power law exponent l > 0) at all altitudes and in all seasons. Furthermore, a Horizontal Mixing Discontinuity (HMD) at ∼2500 masl separates two layers with different constraints on vertical mixing. Above the HMD, more coherent air masses and laminar transport characterizes the dynamics of atmospheric horizontal mixing whereas below it, filamentation and chaotic mixing dominate horizontal mixing. In the lower part of the vertical profile, within the ABL, mixing takes place by convection. Chaotic mixing below the HMD induces the boundary layer entrainment. Results highlight that there are two main discontinuities in the air column which separates different atmospheric dynamics. The ABL is driven by local meteorological conditions of the site at the sampling time; the HMD is driven by the synoptic-scale historical mixing conditions of air masses. The effect of horizontal transport in the free troposphere should be considered equally as important as the local vertical mixing processes in the atmospheric boundary layer when interpreting CO 2 vertical gradients. The dispersive exponents can be used to identify the transport of coherent plumes from anthropogenic emissions with different carbon composition that the one-single backtrajectories models do not detect.Citation: Font, A., J.-A. Morguí, and X. Rodó (2010), Physical atmospheric structure and tropospheric mixing information in vertical profiles of atmospheric CO 2 mixing ratios,

Carbon Dioxide in the Free Troposphere and Boundary Layer at the Mt. Bachelor Observatory

“…The peak in CO 2 usually coincides with low water vapor mixing ratios and, therefore, (based on our water vapor criterion) more hours in the FT. This indicates a higher mixing ratio of CO 2 in the FT, consistent with Font et al (2010), Gurk et al (2008), and Haszpra et al (2012). Highest FT CO 2 mixing ratios occur during winter and spring.…”

“…According to Font et al (2010) and Stohl et al (2004), back-trajectories can suffer from artificial mixing (due to improper meteorological inputs) and, after 4-5 days back, the structure of a coherent plume can be lost. Without the simultaneous analysis of trace gases, back-trajectories by themselves cannot accurately describe FT/BL mixing.…”

“…Because CO 2 has a sufficiently long atmospheric lifetime (not readily removed) and is produced and removed near the surface, it can be used as a tracer of long-range pollution transport (Sidorov et al, 2002). Measurements of CO 2 in the free troposphere are important in understanding the carbon cycle and provide insight into vertical distribution (Tans et al, 1990;Wang et al, 2007;Gurk et al, 2008;Font et al, 2010). This type of data can be used for inverse modelling of CO 2 sources and sinks along with model validation (Bakwin et al, 2004;Yang et al, 2007;Engelen et al, 2009;Pickett-Heaps et al, 2011).…”

“…Even though there are numerous methodologies for the measurement of CO 2 and data on atmospheric CO 2 concentrations have been available since the late 1950s, atmospheric chemistry models still have difficulty estimating CO 2 concentrations in conditions other than in a well-mixed planetary boundary layer (Haszpra et al, 2012). Because FT/BL exchange varies by season and by day, long-term, high-altitude, observations of CO 2 are important in understanding the atmospheric CO 2 cycle (Gurk et al, 2008;Font et al, 2010;Haszpra et al, 2012 (Jaffe et al, 2005;Weiss-Penzias et al, 2006;Weiss-Penzias et al, 2007;Fischer et al, 2009), mercury , O 3 (Ambrose et al, 2011), and CO (Gratz et al, 2015). In all of these studies, the FT/BL exchange was considered, especially in the studies performed at MBO by Reidmiller et al (2010) and Weiss-Penzias et al (2006).…”