ZAMG, the Austrian national weather service has produced two animated GIF maps simulating the possible spread of a radioactive cloud from the Japanese nuclear power station damaged by the recent earthquake and tsunami. One showing South East Asia, the other a world map.
The computer model uses weather forecasts to model and predict the plume’s diffusion from Japan, eastwards across the Pacific over the course of a week.
As I understand it, this computer simulation is based on the assumption a cloud has been released constantly from the power plant since March 12th – not necessarily a reflection of true events.
The article is in German, but Google Translate is good.