A three-dimensional Lagrangian model (TRACOMX) has been developed to simulate large-scale atmospheric transport over complex terrain. Trajectories are integrated in time steps, assuming constant velocity during the time interval, non-interaction with the environment and non-diffusive processes. The vertical velocity is computed, at high levels, by three-dimensional relaxation from the Q-vector formulation of the omega equation. At low levels, the vertical velocity is computed by means of a 'specific treatment' of the orography consisting of the application of the kinematic boundary condition to the cells intersected by the orography, and taking into account the kinetic energy of the flow, the atmospheric stability and the presence of horizontal thermal gradients. These effects are parameterized by means of a multiplicative factor obtained from the Froude number value. The trajectory computation is achieved by successive approximations, using an iterative method, to the final position for each trajectory vector. The model has been applied to a case study of strong convection over NE Spain and the results have been compared with those obtained from an isentropic method. © 2001 Elsevier Science Ltd. All rights reserved.

Part of this work was supported by DGICYT Grant PB94-1169-CO2-2. Meteorological data were provided by the Spanish Instituto Nacional de Meteorologı́a (INM).

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