init_particle Subroutine

public subroutine init_particle(itime, ipart, ithread)

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Calculation of trajectories utilizing a zero-acceleration scheme. The time* step is determined by the Courant-Friedrichs-Lewy (CFL) criterion. This * means that the time step must be so small that the displacement within * this time step is smaller than 1 grid distance. Additionally, a temporal * CFL criterion is introduced: the time step must be smaller than the time * interval of the wind fields used for interpolation. * For random walk simulations, these are the only time step criteria. * For the other options, the time step is also limited by the Lagrangian * time scale. * * Author: A. Stohl * * 16 December 1997 * * Literature: * *

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Variables: * h [m] Mixing height * lwindinterv [s] time interval between two wind fields * itime [s] current temporal position * ldt [s] Suggested time step for next integration * ladvance [s] Total integration time period * rannumb(maxrand) normally distributed random variables * usig,vsig,wsig uncertainties of wind velocities due to interpolation * xt,yt,zt Next time step's spatial position of trajectory * * * Constants: * cfl factor, by which the time step has to be smaller than * the spatial CFL-criterion * cflt factor, by which the time step has to be smaller than * the temporal CFL-criterion * *

1. Interpolate necessary data

If particle is in the PBL, interpolate once and then make a time loop until end of interval is reached

For all particles that are outside the PBL, make a single time step. Only horizontal turbulent disturbances are calculated. Vertical disturbances are reset.

Add mesoscale random disturbances This is done only once for the whole lsynctime interval to save computation time

Arguments