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

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

Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic

Intercomparison of tropospheric ozone models: Ozone transport in a complex tropopause folding event

International audienceThe present generation of tropospheric chemistry models applies horizontal and vertical model resolutions that are sufficiently fine to represent synoptic-scale processes. In this study we compare simulations of a tropopause folding event on 20-21 June 2001 from six tropospheric ozone models with tropospheric ozone profiles observed at Garmisch-Partenkirchen (Germany). The event involves air masses of stratospheric origin and of North Atlantic and North American tropospheric origin. Two coupled chemistryclimate models, three chemistry-transport models, and one chemistry-trajectory model participate in the intercomparison. The models do not explicitly include stratospheric chemistry, and stratospheric ozone is parameterized instead. The horizontal resolution of the Eulerian models, T42 (2.8°Â 2.8°) or finer, appears adequate to represent two prominent features, namely, the stratospheric intrusion descending from the upper troposphere to about 4 km altitude on the first day and an ozone-poor air mass of marine origin in the lower troposphere on the second day. The ozone distribution from the Lagrangian model is less representative because of an insufficient air parcel density. Major discrepancies between model results and observations are the underestimation of ozone levels in the intrusion, too strong downward transport of ozone between the lower stratosphere and the upper troposphere on the first day, and too fast and deep descent of the intrusion. Accurate representation of ozone levels in the intrusion depends directly on the accuracy of the simulated ozone in the lower stratosphere. Additionally, for Eulerian models a relatively coarse vertical resolution in the tropopause region may add to inaccuracies in the simulated ozone distributions

Stratosphere-troposphere exchange : a model and method intercomparison

This paper presents one of the first extensive intercomparisons of models and methods used for estimating stratosphere-troposphere exchange (STE). The study is part of the European Union project Influence of Stratosphere Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO). Nine different models and methods, including three trajectory methods, one Eulerian method, two Lagrangian and one Eulerian transport model, and two general circulation models applied the same initialization. Stratospheric and tropospheric tracers have been simulated, and the tracer mass fluxes have been calculated through the tropopause and the 700 hPa surface. For a 12-day case study over Europe and the northeast Atlantic the simulated tracer mass fluxes have been intercompared. For this case the STE simulations show the same temporal evolution and the same geographical pattern of STE for most models and methods, but with generally different amplitudes (up to a factor of 4). On the other hand, for some simulations also the amplitudes are very similar