The Runge-Kutta technique uses an adaptive time step, with a first guess of ten minutes. In summary, the wind arrows circulate with the surface wind, and the length of the vectors can be used to estimate the wind speed. Arrow color Horizontal divergence for surface air is calculated at the grid points as a second order finite difference. The divergence field is bi-linearly interpolated to the central position of each moving vector. Divergence are shown by the color of the wind vector.
Blue vectors indicate convergent flow, and red vectors indicate divergent flow.
This coloring scheme helps highlight convergence zones, fronts, and structure within strong cyclones . The relative vorticity field is also calculated as a second order finite difference. In the northern hemisphere, weather systems with high surface pressure have anticyclonic rotation, and low pressure systems have cyclonic rotation.