Episodes of cross-polar transport in the Arctic troposphere during July 2008 as seen from models, satellite, and aircraft observations
1Norwegian Institute for Air Research (NILU), Kjeller, Norway
2UPMC Univ. Paris 06, Université Versailles St-Quentin, CNRS/INSU, LATMOS-IPSL, Paris, France
3Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, UK
4Atmospheric Sciences, NASA Langley Research Center, Hampton, Virginia, USA
5Spectroscopie de l'Atmosphère, Chimie Quantique et Photophysique, Université Libre de Bruxelles, Brussels, Belgium
6Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
7Oslo University, Norway
Abstract. During the POLARCAT summer campaign in 2008, two episodes (2–5 July and 7–10 July 2008) occurred where low-pressure systems traveled from Siberia across the Arctic Ocean towards the North Pole. The two cyclones had extensive smoke plumes embedded in their associated air masses, creating an excellent opportunity to use satellite and aircraft observations to validate the performance of atmospheric transport models in the Arctic, which is a challenging model domain due to numerical and other complications.
Here we compare transport simulations of carbon monoxide (CO) from the Lagrangian transport model FLEXPART, the Eulerian chemical transport model TOMCAT, and for numerical aspects the limited-area chemical transport model WRF-Chem. Retrievals of total column CO from the IASI passive infrared sensor onboard the MetOp-A satellite are used as a total column CO reference for the two simulations. Main aspect of the comparison is how realistic horizontal and vertical structures are represented in the model simulations. Analysis of CALIPSO lidar curtains and in situ aircraft measurements provide further independent reference points to assess how reliable the model simulations are and what the main limitations are.
The horizontal structure of mid-latitude pollution plumes agrees well between the IASI total column CO and the model simulations. However, finer-scale structures are too quickly diffused in the Eulerian models. Aircraft data suggest that the satellite data are biased high, while TOMCAT and WRF-Chem are biased low. FLEXPART fits the aircraft data rather well, but due to added background concentrations the simulation is not independent from observations. The multi-data, multi-model approach allows separating the influences of meteorological fields, model realisation, and grid type on the plume structure. In addition to the very good agreement between simulated and observed total column CO fields, the results also highlight the difficulty to identify a data set that most realistically represents the actual state of the atmosphere.