A continental outbreak of air during the Second Aerosol Characterization Experiment (ACE 2): A Lagrangian experiment

Abstract

A mesoscale meteorological model is used to simulate the continental outbreak of air that occured over North Atlantic Ocean during the Second Aerosol Characterization Experiment (ACE 2). Comparison with Meteosat 6 visible images shows that the model is able to reproduce most of the observed cloud features in the entire modeling domain, including a frontal system, orographic clouds over the Pyrenees and the Iberian Peninsula, boundary layer clouds in the ACE 2 region, and cloud-free areas in the dry air outflow off the Portuguese coast. The model reproduces correctly the temperature, humidity, wind speed and direction, cloud water content, and light precipitation events observed by the aircraft during the Lagrangian experiment, while following a tagged boundary layer air parcel over a 28-hour long period. A passive tracer, introduced in the model at the time corresponding to the balloon launch, followed the balloon track with an error in position that is smaller than 1° after 24-hours with about 20% higher speed. An estimate of the boundary layer entrainment velocity is obtained, based on observed boundary layer growth rates and modeled vertical wind speed. The average entrainment velocity of 1.28 cm/s for the 28-hour Lagrangian period agrees with experimentally derived entrainment velocities. Copyright 2000 by the American Geophysical Union.