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

Controls on boundary layer ventilation: Boundary layer processes and large-scale dynamics

Midlatitude cyclones are important contributors to boundary layer ventilation. However, it is uncertain how efficient such systems are at transporting pollutants out of the boundary layer, and variations between cyclones are unexplained. In this study 15 idealized baroclinic life cycles, with a passive tracer included, are simulated to identify the relative importance of two transport processes: horizontal divergence and convergence within the boundary layer and large-scale advection by the warm conveyor belt. Results show that the amount of ventilation is insensitive to surface drag over a realistic range of values. This indicates that although boundary layer processes are necessary for ventilation they do not control the magnitude of ventilation. A diagnostic for the mass flux out of the boundary layer has been developed to identify the synoptic-scale variables controlling the strength of ascent in the warm conveyor belt. A very high level of correlation (R-2 values exceeding 0.98) is found between the diagnostic and the actual mass flux computed from the simulations. This demonstrates that the large-scale dynamics control the amount of ventilation, and the efficiency of midlatitude cyclones to ventilate the boundary layer can be estimated using the new mass flux diagnostic. We conclude that meteorological analyses, such as ERA-40, are sufficient to quantify boundary layer ventilation by the large-scale dynamics

Mesoscale analysis of transport across the subtropical tropopause

International audienceAn airborne ozone lidar has been operated on March 26 and 27, 1999 in order to document the ozone distribution near the subtropical jet (STJ) in the 5°W–15°W longitude band which corresponds to an area where the STJ accelerates and interacts strongly with mid-latitude cyclones. The two main features observed are a tropopause fold in the region where the STJ accelerates and an intrusion of subtropical tropospheric air into the mid-latitude lower stratosphere. A mesoscale meteorological model is applied with high vertical resolution in order to study the strong layering in the upper troposphere and lower stratosphere

Tracer analysis of transport from the boundary layer to the free troposphere

International audienceA mesoscale meteorological model with passive tracers is applied in order to analyze transport from the atmospheric boundary layer to the free troposphere. The validation of the model against aircraft measurements indicates that the model adequately simulates the tracer distributions in the free troposphere as well as in the boundary layer. Budget calculations of passive tracers are performed in order to estimate the amount of transport in the area of a frontal system. The results show a very effective uplift associated in particular with a WCB transporting up to ∼70% of a passive tracer initialized in the boundary layer to the free troposphere within 3 days

EPOS - Episodenrechnungen und Prozessstudien zum Ozonhaushalt in der Stratosphaere und MESSTRO - Mesoskalige Simulation von Dynamik, Transport und Chemie in der unteren Stratosphaere und oberen Troposphaere Abschlussbericht

EPOS: Das dreidimensionale globale COMMA-Modell wurde weiterentwickelt und zur Simulation des Ozonhaushalts der arktischen Winterstratosphaere eingesetzt. Mit Hilfe von Datenassimilation sowie mit einer Chemie-Transport-Version des Modells gelang es, reale Episoden zu simulieren. COMMA wurde im Vergleich mit anderen Modellen getestet und mit Realdaten evaluiert. Es wurde u.a. gezeigt, dass Ozonverluste durch PSC-Chemie auch ueber Europa auftreten koennen, dass der beobachtete chemische Ozonverlust in der Stratosphaere weitgehend durch anthropogene Einfluesse erklaert werden kann und dass ein weiterer Anstieg des atmosphaerischen Halogengehalts zu staerkerem Ozonabbau in der Winterstratosphaehre fuehren wird. MESSTRO: Das mesoskalige EURAD-Modellsystem wurde fuer die Behandlung von Dynamik, Chemie und Transport in der Tropopausenregion eingerichtet. Es wurden neue Analyseverfahren entwickelt und implementiert. Mit ihnen ist eine quantitative Bewertung der Luftmassen und Spurenstofftransport durch die Tropopause aussertropischer Breiten moeglich. Entsprechende Flussberechnungen wurden fuer unterschiedliche Episoden, gepraegt durch Tropopausenfalten, Kaltlufttropfen und Streamer, durchgefuehrt. Es wurde gezeigt, dass die Intensitaet des stratosphaerisch-troposphaerischen Austausches in Abhaengigkeit von der Art der Austauschereignisse und der Jahreszeit erheblich schwankt. (orig.)EPOS: The 3-dim. global model COMMA was further improved and used to simulate ozone in the arctic winter stratosphere. Realistic episodes were treated employing meteorological data assimilation and using a chemical transport version of the model. COMMA was tested by means of model comparisons. Evaluation studies have been carried out using available observations. It could be shown by numerical simulations that ozone losses due to PSC impacts can also occur over Europe. The decrease of stratospheric ozone content due to anthropogenic effects could be modelled. Furthermore, the role of increasing halogen compounds for the acceleration of ozone destruction in the winter stratosphere could be analyzed. MESSTRO: The mesoscale model system EURAD was adapted to the treatment of dynamics, chemistry and transport in the upper troposphere and lowermost stratosphere. New methods for analyzing and evaluating the flux of air mass and trace substances across the tropopause at extratropical latitudes were implemented. Air mass fluxes were calculated for episodes with tropopause folds, cut-off lows and streamers. Considerable variability of flux intensity was found. (orig.)SIGLEAvailable from TIB Hannover: F02B706 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Thesenpapier Nationale Forschungsdateninfrastruktur für die Chemie (NFDI4Chem)

“Der stufenweise Aufbau einer Nationalen Forschungsdateninfrastruktur in Netzwerkform hat das Ziel, ein verlässliches und nachhaltiges Dienste-Portfolio zu schaffen, welches generische und fachspezifische Bedarfe des Forschungsdatenmanagements in Deutschland abdeckt.” Für das Fachgebiet Chemie ermöglicht eine solche nationale Forschungsdateninfrastruktur, öffentlich-finanzierte Forschungsdaten effizient zu erheben, standardisiert zu beschreiben, dauerhaft zu speichern und durch Persistent Identifier (PID) eindeutig referenzierbar und auffindbar zu machen. Sie unterstützt gemäß den Vorgaben des RfII die Reproduzierbarkeit und Nachnutzbarkeit der Daten zum Zwecke einer perpetuierten Wissensgenerierung. Mit der Reproduzierbarkeit von Forschungsergebnissen unterstützt eine solche Forschungsdateninfrastruktur den Peer Reviewing Prozess zur Förderung der wissenschaftlichen Selbstkontrolle und erhöht die Datenqualität, insbesondere in wissenschaftlichen Publikationen. Die NFDI4Chem ist ein gemeinschaftlicher Ansatz von Wissenschaftlern aus der Chemie, der Fachgesellschaft Gesellschaft Deutscher Chemiker und deren Fachgruppen, Einrichtungen aus der Forschungsförderung und Infrastruktureinrichtungen (Technische Informationsbibliothek). Eine Gruppe von Vertretern dieser Stakeholder hat sich Ende April 2018 zu einem Auftakttreffen “Fachgespräch NFDI4Chem” in Hannover getroffen. Dieses Papier fasst die Erkenntnisse des Fachgespräches zusammen. Weitere Stakeholder wie Verlage oder Datenbankanbieter sind im folgenden Diskurs willkommen

Mechanisms of midlatitude cross-tropopause transport using a potential vorticity budget approach

[ 1] A potential vorticity (PV) budget method has been used to attribute vertical transport across the near-tropopause ( 1 PVU surface) in extratropical weather systems to radiative, latent heating and cooling, and mixing processes. Sources and sinks of PV due to nonconservative processes are calculated online and advected as passive tracers. There is reasonable agreement between the spatial distribution of transport determined from the PV budget method and the transport across the 1 - 2 PVU zone from a passive tracer and trajectories, but different aspects of exchange can be diagnosed with each method. Stratosphere-to-troposphere transport occurred in the broad upper level PV anomalies and was attributed mainly to latent heating and cooling processes; troposphere-to-stratosphere transport occurred toward the tail of a PV filament and in a ridge region and was attributed mainly to radiative processes. The contribution of mixing processes to transport was comparatively small. Using the PV budget method, the domain integrated exchange across the 1 PVU surface was from stratosphere to troposphere, and the magnitude of 1 x 10(15) kg over a 2 day winter integration in a large North Atlantic domain is consistent with stratosphere-troposphere exchange calculations from other studies. This exchange arises from an approximate balance between the dominant stratosphere-to-troposphere transport due to latent heating and cooling processes and troposphere-to-stratosphere transport due to radiative processes. The direction of transport across the tropopause in a fold was found to be critically dependent on the PV surface considered to represent the tropopause