Modelling vertical motion and surface exchange of heat and water vapour in a trajectory model

The paper concerns features of a trajectory model under development by the Royal Netherlands Meteorological Institute, in particular the incorporation of (a) vertical motion and (b) a boundary layer sub-model. Air-mass trajectories are calculated from wind fields that are either analysed or forecast by an operational four-level vorticity model. An example is given in which the model is applied real-time to predict the trajectory of a hypothetical (radioactive) puff. Because the vertical motions of air-masses of interest are described, it is possible to evaluate the probability of precipitation along the trajectory. This can be applied to the estimation of wet deposition of radioactive materials. The boundary layer sub-model describes the exchange of sensible heat and water vapour near the ground. It yields the variation of stability and mixing height of the lowest air-masses during the motion along the trajectory. Preliminary results of computed boundary layer parameters are given