On the origin of elevated surface ozone concentrations at Izana Observatory, Tenerife during late March 1996

The origin of relatively high surface ozone concentrations measured at Izana Observatory (Canary Islands) during the end of March 1996 is studied using a coupled chemistry-GCM (ECHAM4) at T63 resolution (1.875° × 1.875°). Meteorological fields (geopotential height, potential vorticity, specific humidity), and a model-simulated stratospheric ozone tracer as well as 3-D back trajectories, show the stratospheric origin of these relatively high surface ozone values caused by cross-tropopause exchange at the western flank of an upper level trough/cut-off low (COL) over the extratropical North-Atlantic Ocean. The good agreement between observations and model results (within 10–15%) indicates that the high resolution chemistry-GCM is a useful tool towards the understanding of natural sources controlling background surface ozone variability. The results underscore the importance of stratosphere-troposphere exchange (STE) during late winter/early spring for lower free tropospheric ozone at subtropical latitudes

A model perspective on total tropospheric O-3 column variability and implications for satellite observations

In recent years several methods have been developed that derive total tropospheric 03 columns from satellite measurements. However, one issue that has not been paid much attention to is the interpretation of (extratropical) total tropospheric O3 columns. Different processes contribute to the total tropospheric 03 column: stratosphere-troposphere exchange, tropospheric O 3 production and loss, transport and the height of the tropopause. Each process contributes differently to the total tropospheric O3 column variability depending on season, geographical location, and altitude. This paper investigates the contribution of these different processes on total tropospheric O3 column variability using a chemistry-climate model simulation of tropospheric 03, and reflects on the implications for total tropospheric 03 column measurements. On the basis of tropospheric 03 column (satellite) measurements and without other sources of information (e.g., model simulations, observations of other trace species) it is not possible to determine the separate contributions by the aforementioned processes to the extratropical total tropospheric 03 column variability. Furthermore, typical extratropical synoptic-scale (daily) total tropospheric 03 column variability is of the order of 10 DU (1-σ value), implying the errors in (satellite) measurements should be of the order of magnitude at maximum (~10 DU) for daily measurements. For tropical total tropospheric O3 column (satellite) measurements the requirements are less stringent because the most important variability occurs on seasonal timescales. Errors in tropical total tropospheric 03 column (TTOC) measurements should be of the order of 5 DU for monthly means. Copyright 2005 by the American Geophysical Union

Global tropospheric ozone modelling:quantifying errors due to grid resolution.

Ozone production in global chemical models is dependent on model resolution because ozone chemistry is inherently nonlinear, the timescales for chemical production are short, and precursors are artificially distributed over the spatial scale of the model grid. In this study we examine the sensitivity of ozone, its precursors, and its production to resolution by running a global chemical transport model at four different resolutions between T21 (5.6° × 5.6°) and T106 (1.1° × 1.1°) and by quantifying the errors in regional and global budgets. The sensitivity to vertical mixing through the parameterization of boundary layer turbulence is also examined. We find less ozone production in the boundary layer at higher resolution, consistent with slower chemical production in polluted emission regions and greater export of precursors. Agreement with ozonesonde and aircraft measurements made during the NASA TRACE-P campaign over the western Pacific in spring 2001 is consistently better at higher resolution. We demonstrate that the numerical errors in transport processes on a given resolution converge geometrically for a tracer at successively higher resolutions. The convergence in ozone production on progressing from T21 to T42, T63, and T106 resolution is likewise monotonic but indicates that there are still large errors at 120 km scales, suggesting that T106 resolution is too coarse to resolve regional ozone production. Diagnosing the ozone production and precursor transport that follow a short pulse of emissions over east Asia in springtime allows us to quantify the impacts of resolution on both regional and global ozone. Production close to continental emission regions is overestimated by 27% at T21 resolution, by 13% at T42 resolution, and by 5% at T106 resolution. However, subsequent ozone production in the free troposphere is not greatly affected. We find that the export of short-lived precursors such as NO x by convection is overestimated at coarse resolution

Effects of stratosphere-troposphere chemistry coupling on tropospheric ozone

A new, computationally efficient coupled stratosphere-troposphere chemistry-climate model (S/T-CCM) has been developed based on three well-documented components: a 64-level general circulation model from the UK Met Office Unified Model, the tropospheric chemistry transport model (STOCHEM), and the UMSLIMCAT stratospheric chemistry module. This newly developed S/T-CCM has been evaluated with various observations, and it shows good performance in simulating important chemical species and their interdependence in both the troposphere and stratosphere. The modeled total column ozone agrees well with Total Ozone Mapping Spectrometer observations. Modeled ozone profiles in the upper troposphere and lower stratosphere are significantly improved compared to runs with the stratospheric chemistry and tropospheric chemistry models alone, and they are in good agreement with Michelson Interferometer for Passive Atmospheric Sounding satellite ozone profiles. The observed CO tape recorder is also successfully captured by the new CCM, and ozone-CO correlations are in accordance with Atmospheric Chemistry Experiment observations. However, because of limitations in vertical resolution, intrusion of CO-rich air in the stratosphere from the mesosphere could not be simulated in the current version of S/T-CCM. Additionally, the simulated stratosphere-to-troposphere ozone flux, which controls upper tropospheric OH and O3 concentrations, is found to be more realistic in the new coupled model compared to STOCHEM. © 2010 by the American Geophysical Union

Flux Distributions as Robust Diagnostics of Stratosphere-Troposphere Exchange

We perform the first analysis of stratosphere-troposphere exchange in terms of distributions that partition the one-way flux across the thermal tropopause according to stratospheric residence time τ and the regions where air enters and exits the stratosphere. These distributions robustly quantify one-way flux without being rendered ill defined by the short-τ eddy-diffusive singularity. Diagnostics are computed with an idealized circulation model with topography only in the Northern Hemisphere (NH) run under perpetual NH winter conditions. Suitable integrations of the flux distribution are used to determine the stratospheric mean residence time inline image and the mass fraction of the stratosphere in any given residence time interval. We find that the largest mass fraction is destined for isentropic cross-tropopause transport, with one-way fluxes that are sustained over a broad range of residence times. Air exiting the stratosphere in the winter hemisphere has significantly longer mean residence times than air exiting in the summer hemisphere because the winter hemisphere has a deeper circulation and stronger eddy diffusion. We also explore the sensitivity of the stratosphere-troposphere exchange to changes in the circulation by increasing the amplitude of the topography. The resulting more vigorous residual mean circulation dominates over increased eddy diffusion, leading to decreased inline image except for air exiting at high NH latitudes, for which inline image increases. These findings underline that the flux distributions diagnose the integrated advective-diffusive tropopause-to-tropopause transport and not merely advection by the residual mean circulation

CO2: An operational anthropogenic CO2 emissions monitoring & verification support capacity

This is the third report form the CO2 Monitoring Task Force on the multiple input streams of in-situ observations that are requirement for the Copernicus CO2 Monitoring and Verification Support capacity to: (i) calibrated and validate the space component, (ii) assimilate data in the models and integrate information in the core of the system, and (iii) evaluate the output generated by the system for its end users. The availability of sustained in situ networks is currently a significant factor of risk that needs to be mitigated to establish a European CO 2 support capacity which is fit-for-purpose. The current status of existing networks may be the source of large uncertainties in anthropogenic CO2 emission estimates as well as limited capability in meeting the requirements for country, large city and point source scale assessments. This conclusion results from a risk analysis formulated for four scenarios: 1) maintaining the status quo, 2) assuring sustained funding for the status quo, 3) enhancing network capabilities at European scale with sustained funding and 4) with a significantly improved in situ infrastructure in Europe and beyond. This report substantiates the multifaceted needs and requirements of the European CO2 support capacity with respect to in situ observations. The analysis concerns all core elements of the envisaged integrated system with a particular attention on the impact of such observations in achieving the proposed objectives. The specific needs for the validation of products delivered by the space component that is, the Copernicus Sentinels CO2 monitoring constellation, are addressed as another prerequisite for the success of the CO2 support capacity. This European asset will represent a significant contribution to the virtual constellation proposed by the Committee on Earth Observation Satellites (CEOS) and, accordingly, complementary requirements are elaborated in that international frame. The report highlights that although high measurement standards are present within existing networks such as ICOS, in the context of the needs for targeted in situ data for the realization of the operational system, these data are not fully fit-for-purpose. A fundamental prerequisite is to have a good geographical coverage over Europe for evaluating the data assimilation and modeling system over a large variety of environmental conditions such as, for instance, urban areas, agricultural regions, forested zones and industrial complexes. The in situ observations need to be extended under a coordinated European lead with sustained infrastructure and targeted additional and maintained long-term funding. It has been clearly understood from the onset that the international dimension of the European CO2 support capacity would be critical and that these aspects should be developed in parallel to, and in synergy with the definition and implementation of a European contributing system. It was also understood that this international dimension had both strategic, policy relevant and technical dimensions and the Commission and the relevant European institutional partners have started since several years to engage both bilaterally and multilaterally with the relevant stakeholders and counterparts to develop these relations. Specifically, CEOS will undertake, over the next few years, dedicated preparatory work in a coordinated international context, to provide cumulative added value to the specific programmatic activities of their member agencies. Concerted efforts have already begun in the context of the European Commission's Chairmanship of CEOS in 2018. It is recognized in the context of the European efforts, and increasingly by our international counterparts that a broad and holistic system approach is required to address the requirements which are represented by the climate policy, of which the satellite component, whilst important, cannot effectively be developed in isolation. This system indeed includes the satellite observing capability but in addition, the required modelling component and data integration elements, prior information, ancillary data and in situ observations delivered by essential networks. Acknowledging the need for an efficient coordination at international level for instance via the Global Atmosphere Watch programme of the World Meteorological Organisation is a key towards a successful implementation of appropriate actions to ensure the sustainability of essential networks, to enhance current network capabilities with new observations and to propose adequate governance schemes. Such actions to mitigate current network limitations are deemed critical to implementing the Copernicus CO 2 Monitoring & Verification Support capacity in its full strength.JRC.D.6-Knowledge for Sustainable Development and Food Securit

A new perspective of the climatological features of upper-level cut-off lows in the Southern Hemisphere

This study presents a detailed view of the seasonal variability of upper-level cut-off lows (COLs) in the Southern Hemisphere. The COLs are identified and tracked using data from a 36-year period of the European Centre for Medium Range Weather Forecast reanalysis (ERA-Interim). The objective identification of the COLs uses a new approach, which is based on 300 hPa relative vorticity minima, and three restrictive criteria of the presence of a cold-core, stratospheric potential vorticity intrusion, and cut-off cyclonic circulation. The highest COL activity is in agreement with previous studies, located near three main continental areas (Australia, South America, and Africa), with maximum frequencies usually observed in the austral autumn. The COL mean intensity values show a marked seasonal and spatial variation, with maximum (minimum) values during the austral winter (summer), a unique feature that has not been observed previously in studies based on the geopotential. The link between intensity and lysis is examined, and finds that weaker systems are more susceptible to lysis in the vicinity of the Andes Cordillera, associated with the topographic Rossby wave. Lysis and genesis regions are close to each other, confirming that COLs are quasi-stationary systems. Also, COLs tend to move eastward and are faster over the higher latitudes. The mean growth/decay rates coincide with the major genesis and lysis density regions, such as the significant decay values across the Andes all year. As a consequence of using vorticity for the tracking method a longer lifetime of COLs is detected than in other studies, but this does not affect the total frequency of occurrence. Comparisons with other studies suggest that the differences in seasonality are due to uncertainties in the reanalyses and the methods used to identify COLs