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Trajectories from Japan

The figures below show forecast trajectories of air parcels emitted from the location of Fukushima, Japan. The best way to picture a trajectory is to imagine a party balloon released over Fukushima and allowed to drift with the winds. Using forecast winds from weather forecast models, we can predict the path of the balloon - and thus create what we call a trajectory .

For the figure below, we pretend a balloon is released over Fukushima every 12 hours, and create a new trajectory every 12 hours. The different trajectories are shown in different colors. The top figure shows the horizontal drift of the balloons - generally eastward and southward. The lower figure shows the vertical motions of the parcels. So for example, a blue line on the lower plot shows the vertical motion of the parcel over the next few days, and the blue line on the upper figure shows the horizontal motion over that same time period.

{ More technical stuff : On the lower figure, time runs from left to right, and the height to which the balloon would rise is shown on the right axis (e.g., 4000 m = 4 km). Pick a color, and follow that trajectory over a few days as it rises/sinks. On the upper figure, along each trajectory, each dot represents the location of the balloon every 12 hours.}

These trajectories were created using the HYSPLIT model running online at For the figures below, we used winds forcast by the GFS model over a 10-day period. The balloons are assumed to be released at an altitude of 500 m above the ground.

Monday March 21 synopsis: at the moment, high pressure continues to dominate the weather over northern Japan. Trajectories show that balloons released now will stay at low levels, and will remain close to the Japanese mainland. Storms predicted to pass on 3/23 and 3/26 will provide more lift, shooting the balloons higher into the atmosphere (up to 5000 m - roughly 3 miles - according to the lower figure). These balloons would also move further eastward over the Pacific (towards the Aleutians, according to the upper figure). However, even these will not make it east of the dateline!

The upper panel shows the evolution of each trajectory, while the lower panel also shows the height to which each trajectory would rise.

A Pacific-wide view of the forecast trajectories is shown here (shockwave plugin required).