Oxygen isotopic composition of carbon dioxide in the middle atmosphere

The isotopic composition of long-lived trace molecules provides a window into atmospheric transport and chemistry. Carbon dioxide is a particularly powerful tracer, because its abundance remains >100 parts per million by volume (ppmv) in the mesosphere. Here, we successfully reproduce the isotopic composition of CO2 in the middle atmosphere, which has not been previously reported. The mass-independent fractionation of oxygen in CO2 can be satisfactorily explained by the exchange reaction with O(1D). In the stratosphere, the major source of O(1D) is O3 photolysis. Higher in the mesosphere, we discover that the photolysis of 16O17O and 16O18O by solar Lyman-{alpha} radiation yields O(1D) 10–100 times more enriched in 17O and 18O than that from ozone photodissociation at lower altitudes. This latter source of heavy O(1D) has not been considered in atmospheric simulations, yet it may potentially affect the "anomalous" oxygen signature in tropospheric CO2 that should reflect the gross carbon fluxes between the atmosphere and terrestrial biosphere. Additional laboratory and atmospheric measurements are therefore proposed to test our model and validate the use of CO2 isotopic fractionation as a tracer of atmospheric chemical and dynamical processes

A case study of boundary layer ventilation by convection and coastal processes

It is often assumed that ventilation of the atmospheric boundary layer is weak in the absence of fronts, but is this always true? In this paper we investigate the processes responsible for ventilation of the atmospheric boundary layer during a nonfrontal day that occurred on 9 May 2005 using the UK Met Office Unified Model. Pollution sources are represented by the constant emission of a passive tracer everywhere over land. The ventilation processes observed include shallow convection, turbulent mixing followed by large-scale ascent, a sea breeze circulation and coastal outflow. Vertical distributions of tracer are validated qualitatively with AMPEP (Aircraft Measurement of chemical Processing Export fluxes of Pollutants over the UK) CO aircraft measurements and are shown to agree impressively well. Budget calculations of tracers are performed in order to determine the relative importance of these ventilation processes. Coastal outflow and the sea breeze circulation were found to ventilate 26% of the boundary layer tracer by sunset of which 2% was above 2 km. A combination of coastal outflow, the sea breeze circulation, turbulent mixing and large-scale ascent ventilated 46% of the boundary layer tracer, of which 10% was above 2 km. Finally, coastal outflow, the sea breeze circulation, turbulent mixing, large-scale ascent and shallow convection together ventilated 52% of the tracer into the free troposphere, of which 26% was above 2 km. Hence this study shows that significant ventilation of the boundary layer can occur in the absence of fronts (and thus during high-pressure events). Turbulent mixing and convection processes can double the amount of pollution ventilated from the boundary layer

Variations of PM10 and its relationship with 7Be and 210Pb measurements at Malaga (Southeastern coast of Spain)

INTRODUCTION Levels of particulate matter fraction PM10 were monitored between 2009 and 2011 in Malaga (Spain) in one of the Atmospheric Pollution Monitoring network managed by the Environmental Health Service of the Andalusian Government. Long-term measurements of cosmogenic radionuclides such as 7Be provide important data in studying global atmospheric processes and comparing environmental impact of radioactivity from man-made sources to natural ones. 7Be is a natural radionuclide tracer of aerosols originated over a range of high altitudes in the atmosphere. On the other hand, 210Pb is produced by radioactive decay from its progenitor, 222Rn, which emanates primarily from land surface. Therefore, 210Pb in the air is an effective tracer of the continental surface air mass. The variation of the data with time was studied by time series analyses and seasonal patterns were identified. The study of air back-trajectories were computed by means of the Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) trajectory model (Draxler, 1994) using meteorological data supplied by the US National Climatic Data Centr

ATLAS: Airborne Tunable Laser Absorption Spectrometer for stratospheric trace gas measurements

The ATLAS instrument is an advanced technology diode laser based absorption spectrometer designed specifically for stratospheric tracer studies. This technique was used in the acquisition of N2O tracer data sets on the Airborne Antarctic Ozone Experiment and the Airborne Arctic Stratospheric Expedition. These data sets have proved valuable for comparison with atmospheric models, as well as in assisting in the interpretation of the entire ensemble of chemical and meteorological data acquired on these two field studies. The N2O dynamical tracer data set analysis revealed several ramifications concerning the polar atmosphere: the N2O/NO(y) correlation, which is used as a tool to study denitrification in the polar vertex; the N2O Southern Hemisphere morphology, showing subsidence in the winter polar vortex; and the value of the N2O measurements in the interpretation of ClO, O3, and NO(y) measurements and of the derived dynamical tracer, potential vorticity. Field studies also led to improved characterization of the instrument and to improved accuracy

Global-mean Vertical Tracer Mixing in Planetary Atmospheres II: Tidally Locked Planets

In Zhang $\&$ Showman (2018, hereafter Paper I), we developed an analytical theory of 1D eddy diffusivity $K_{zz}$ for global-mean vertical tracer transport in a 3D atmosphere. We also presented 2D numerical simulations on fast-rotating planets to validate our theory. On a slowly rotating planet such as Venus or a tidally locked planet (not necessarily a slow-rotator) such as a hot Jupiter, the tracer distribution could exhibit significant longitudinal inhomogeneity and tracer transport is intrinsically 3D. Here we study the global-mean vertical tracer transport on tidally locked planets using 3D tracer-transport simulations. We find that our analytical $K_{zz}$ theory in Paper I is validated on tidally locked planets over a wide parameter space. $K_{zz}$ strongly depends on the large-scale circulation strength, horizontal mixing due to eddies and waves and local tracer sources and sinks due to chemistry and microphysics. As our analytical theory predicted, $K_{zz}$ on tidally locked planets also exhibit three regimes In Regime I where the chemical and microphysical processes are uniformly distributed across the globe, different chemical species should be transported via different eddy diffusivity. In Regime II where the chemical and microphysical processes are non-uniform---for example, photochemistry or cloud formation that exhibits strong day-night contrast---the global-mean vertical tracer mixing does not always behave diffusively. In the third regime where the tracer is long-lived, non-diffusive effects are significant. Using species-dependent eddy diffusivity, we provide a new analytical theory of the dynamical quench points for disequilibrium tracers on tidally locked planets from first principles.Comment: Accepted at ApJ, 16 pages, 12 figures. This is the part II. Part I is "Global-mean Vertical Tracer Mixing in Planetary Atmospheres I: Theory and Fast-rotating Planets

Can seasonal and interannual variation in landscape CO2 fluxes be detected by atmospheric observations of CO2 concentrations made at a tall tower?

The coupled numerical weather model WRF-SPA (Weather Research and Forecasting model and Soil-Plant-Atmosphere model) has been used to investigate a 3 yr time series of observed atmospheric CO₂ concentrations from a tall tower in Scotland, UK. Ecosystem-specific tracers of net CO₂ uptake and net CO₂ release were used to investigate the contributions to the tower signal of key land covers within its footprint, and how contributions varied at seasonal and interannual timescales. In addition, WRF-SPA simulated atmospheric CO₂ concentrations were compared with two coarse global inversion models, CarbonTrackerEurope and the National Oceanic and Atmospheric Administration's CarbonTracker (CTE-CT). WRF-SPA realistically modelled both seasonal (except post harvest) and daily cycles seen in observed atmospheric CO₂ at the tall tower (<i>R</i>² = 0.67, rmse = 3.5 ppm, bias = 0.58 ppm). Atmospheric CO₂ concentrations from the tall tower were well simulated by CTE-CT, but the inverse model showed a poorer representation of diurnal variation and simulated a larger bias from observations (up to 1.9 ppm) at seasonal timescales, compared to the forward modelling of WRF-SPA. However, we have highlighted a consistent post-harvest increase in the seasonal bias between WRF-SPA and observations. Ecosystem-specific tracers of CO₂ exchange indicate that the increased bias is potentially due to the representation of agricultural processes within SPA and/or biases in land cover maps. The ecosystem-specific tracers also indicate that the majority of seasonal variation in CO₂ uptake for Scotland's dominant ecosystems (forests, cropland and managed grassland) is detectable in observations within the footprint of the tall tower; however, the amount of variation explained varies between years. The between years variation in detectability of Scotland's ecosystems is potentially due to seasonal and interannual variation in the simulated prevailing wind direction. This result highlights the importance of accurately representing atmospheric transport used within atmospheric inversion models used to estimate terrestrial source/sink distribution and magnitude

3D mixing in hot Jupiter atmospheres. I. application to the day/night cold trap in HD 209458b

Hot Jupiters exhibit atmospheric temperatures ranging from hundreds to thousands of Kelvin. Because of their large day-night temperature differences, condensable species that are stable in the gas phase on the dayside, such as TiO and silicates, may condense and gravitationally settle on the nightside. Atmospheric circulation may counterbalance this tendency to gravitationally settle. This three dimensional (3D) mixing of chemical species has not previously been studied for hot Jupiters, yet it is crucial to assess the existence and distribution of TiO and silicates in the atmospheres of these planets. We perform 3D global circulation models of HD209458b including passive tracers that advect with the 3D flow, including a source/sink on the nightside to represent condensation and gravitational settling of haze particles. We show that global advection patterns produce strong vertical mixing that can keep condensable species lofted as long as they are trapped in particles of sizes of a few microns or less on the night side. We show that vertical mixing results not from small-scale convection but from the large-scale circulation driven by the day-night heating contrast. Although this vertical mixing is not diffusive in any rigorous sense, a comparison of our results with idealized diffusion models allows a rough estimate of the vertical diffusion coefficient. Kzz=5x10**4/Sqrt(Pbar) m2/s can be used in 1D models of HD 209458b. Moreover, our models exhibit strong spatial and temporal variability in the tracer concentration that could result in observable variations during transit or secondary eclipse measurements. Finally, we apply our model to the case of TiO in HD209458b and show that the day-night cold trap would deplete TiO if it condenses into particles bigger than a few microns on the planet's night side, making it unable to create the observed stratosphere of the planet.Comment: Accepted in A&A in August 2013 http://dx.doi.org/10.1051/0004-6361/20132113

Be-10/Be-7 tracer of atmospheric transport and stratosphere-troposphere exchange

The 10Be/7Be ratio is a sensitive tracer of atmospheric transport and stratosphere-troposphere exchange (STE). Data from five NASA aircraft field missions (PEM: West A and B, Tropics A; SONEX; and SUCCESS) have been assembled to produce the largest data set of 10Be,7Be, and their ratio collected to date (\u3e300 samples). Ratios near 0.60 are indicative of tropospheric air with little stratospheric influence, while higher ratios are found in stratospheric air. Samples from the lower stratosphere were all collected within 2.5 km of the tropopause and had ratios \u3e1.27. Of these lower stratosphere samples only 16% had ratios in excess of 3.0, suggesting that higher ratio air resides away from the tropopause. Seasonality observed in the10Be/7Be ratios results from the downwelling of air with elevated ratios from higher in the stratosphere in the spring and summer (midlatitudes) and from the decay of 7Be during descent in the winter polar vortex (high latitudes). Our results illustrate the complexity of STE and some of the mechanisms through which it occurs, including tropopause folding, mixing associated with subtropical jets, and the effect of synoptic systems such as hurricanes and northeasters. The10Be/7Be ratio provides important information beyond that which can be derived from studies that rely on chemical mixing ratios alone