Midlatitude stratosphere - troposphere exchange as diagnosed by MLS O3 and MOPITT CO assimilated fields

International audienceThis paper presents a comprehensive characterization of a very deep stratospheric intrusion which occurred over the British Isles on 15 August 2007. The signature of this event is diagnosed using ozonesonde measurements over Lerwick, UK (60.14 N, 1.19 W) and is also well characterized using meteorological analyses from the global operational weather prediction model of Météo-France, ARPEGE. Modelled as well as assimilated fields of both ozone (O3) and carbon monoxide (CO) have been used in order to better document this event. O3 and CO from Aura/MLS and Terra/MOPITT instruments, respectively, are assimilated into the three-dimensional chemical transport model MOCAGE of Météo-France using a variational 3-DFGAT (First Guess at Appropriate Time) method. The validation of O3 and CO assimilated fields is done using selfconsistency diagnostics and by comparison with independent observations such as MOZAIC (O3 and CO), AIRS (CO) and OMI (O3). It particularly shows in the upper troposphere and lower stratosphere region that the assimilated fields are closer to MOZAIC than the free model run. The O3 bias between MOZAIC and the analyses is −11.5 ppbv with a RMS of 22.4 ppbv and a correlation coefficient of 0.93, whereas between MOZAIC and the free model run, the corresponding values are 33 ppbv, 38.5 ppbv and 0.83, respectively. In the same way, for CO, the bias, RMS and correlation coefficient between MOZAIC and the analyses are −3.16 ppbv, 13 ppbv and 0.79, respectively, whereas between MOZAIC and the free model run, the corresponding values are 33 ppbv, 38.5 ppbv and 0.83, respectively. In the same way, for CO, the bias, RMS and correlation coefficient between MOZAIC and the analyses are −3.16 ppbv, 13 ppbv and 0.79, respectively, whereas between MOZAIC and the free model they are 6.3 ppbv, 16.6 ppbv and 0.71, respectively. The paper also presents a demonstration of the capability of O3 and CO assimilated fields to better describe a stratosphere-troposphere exchange (STE) event in comparison with the free run modelled O3 and CO fields. Although the assimilation of MLS data improves the distribution of O3 above the tropopause compared to the free model run, it is not sufficient to reproduce the STE event well. Assimilated MOPITT CO allows a better qualitative description of the stratospheric intrusion event. The MOPITT CO analyses appear more promising than the MLS O3 analyses in terms of their ability to capture a deep STE event. Therefore, the results of this study open the perspectives for using MOPITT CO in the STE studies

Le réseau de radar Stratophérique-Troposphérique au cours de la campagne MAP: aspects observationnels et scientifiques

International audienceEine internationale Kampagne des Mesoscale Alpine Program (MAP) fand vom 7. September bis 15. November 1999 in den Alpen statt. Sie widmete sich der Untersuchung von Wechselwirkungen zwischen großräumigen Prozessen und der mesoskaligen Strömung über komplexem, gebirgigem Untergrund. Zahlreiche Instrumentensysteme in der Luft und am Boden, mesoskalige numerische Modelle, sowie Radiosonden und Satellitenmessungen kamen bei der Kampagne zum Einsatz. Während MAP bestand das französische ST (Strato-troposphärische) Forschungsradarnetz aus fünf VHF (Very High Frequency) und drei UHF (Ultra High Frequency) Profilern. Vier VHFs und zwei UHFs waren in Südfrankreich stationiert und ein VHF sowie ein UHF befanden sich in Italien, im Gebiet des Lago Maggiore. Die VHFs lieferten in 15-minütiger Zeitauflösung Vertikalprofile des Windes und die vertikale SNR (Signal-to-Noise Ratio) von der unteren Troposphäre bis zu oberen Troposphären- und unteren Stratosphärenschichten, je nach Instrument und/oder Atmosphärenbedingungen. Die gleiche Art Daten wurde von den UHFs erzeugt, jedoch aus Höhen von einigen 100 m bis zu etwa 3 km. Alle Instrumente gestatteten es, in ihrem jeweiligen Höhenbereich die zeitliche Entwicklung und die Vertikalstruktur der mesoskaligen dynamischen Prozesse aufzuzeichnen. Es werden hier VHF-Beobachtungen vorgestellt, die während des Durchgangs von Anomalien der PV (Potentielle Vorticity) - sogenannte PV-streamer - über Südfrankreich und der Gegend des Lago Maggiore entstanden. Dies beinhaltet Durchgänge des Strahlstroms und Tropopausen-Variationen. Außerdem werden UHF-Beobachtungen des Winds in der unteren Troposphäre am Ausgang des Rhônetals, als Mistral bekannt, vorgestellt. Vorläufige Analysen zeigen, dass unsere Beobachtungen sowohl untereinander als auch mit Modell-Analysen im synoptischen Scale des ECMWF (European Centre for Medium-Range Weather Forecasts) konsistent sind. Darüber hinaus werden Quervergleiche mit Mesoskalen-Modellen durchgeführt, mit deren Hilfe es möglich ist, einige mesoskalige Aspekte der atmosphärischen Dynamik zu untersuchen.The Mesoscale Alpine Program (MAP) international cooperative campaign took place over and around the Alps between 99/09/07 and 99/11/15 and was devoted to the study of the interactions between large-scale processes and the meso-scale flow over a complex mountainous terrain. Numerous airborne and ground based instrumental systems and meso-scale numerical models were involved in the campaign, as well as radiosoundings and satellite observations. During MAP the French ST (Strato-Tropospheric) radar research-network consisted of five VHF (Very High Frequency) and three UHF (Ultra High Frequency) profilers. Four VHF's and two UHF's were installed in southern France and one VHF and one UHF were in Italy, in the Lago Maggiore target area. The VHF's provided 15-min time-resolution vertical profiles of wind and vertical SNR (Signal-to-Noise Ratio) from the low troposphere up to high tropospheric or low stratospheric levels, depending on the instrument and/or the atmospheric conditions. The same kind of data were obtained by the UHF's, but from a few hundreds of meters up to about 3 km. In their respective altitude ranges, all these instruments allowed the time evolution and the vertical structure of meso-scale dynamic processes to be documented. VHF observations made during upper-level PV-anomaly passages (PV streamers) above southern France and Lago Maggiore area, including jet-stream passages and tropopause variations, are presented here. UHF observations of the low-tropospheric wind at the exit of the Rhône-valley, locally called Mistral, are also presented. Preliminary analyses show that our observations are consistent both between themselves and with synoptic-scale ECMWF (European Centre for Medium-Range Weather Forecasts)-model analyses. In addition, cross-comparisons with meso-scale model simulations are made allowing some meso-scale aspects of the atmospheric dynamics to be investigated