Onshore winds push radioactivity towards Tokyo

Radioactive plumes emitted from Japan's troubled Fukushima nuclear power plant are headed to the southwest towards Tokyo today, carried by onshore northeasterly winds. An elongated area of low pressure is located off the southeast coast of Japan, and the counter-clockwise flow of air around this low may bring several periods of onshore northeasterly winds through Tuesday to northern Japan. According to the latest trajectory plots from NOAA's HYSPLIT model, air moving towards Tokyo today will be lifted by the ascending air associated with the low pressure system, and the radioactive particles may not make it all the way to Tokyo before getting lifted high enough that they get caught in a strong upper-level flow of air from the southwest and carried out to sea. Latest radar loops from the Japan Meteorological Agency show a wide region of light rain affecting Tokyo and surrounding regions, and this rain will tend to remove the great majority of the radioactive particles from the air in a few hours, so it is uncertain how much radioactivity might make it to Tokyo. High pressure will begin building in on Tuesday over Japan, and wind will gradually shift to blow out the north, which would carry radioactivity offshore just to the east of Tokyo. Offshore winds are expected on Wednesday, but onshore winds could re-develop late in the week as a new weak low pressure system affects the region. Radiation at the levels being reported coming from the troubled plant are not high enough to be of concern to human heath outside of Japan, so I will not be posting further plots showing the long-range path of the radioactivity unless there is a major explosion resulting in a significant release of radioactive emissions.


Figure 1. One-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 100 meters (blue line) at 18 UTC (2pm EDT) Monday, March 21, 2011 from the Fukushima Daiichi nuclear plant. The plumes get blown by northeasterly winds close to Tokyo, before getting lifted high enough to get caught in a strong flow of air from the southwest that carries the radioactive air out to sea. Image created using NOAA's HYSPLIT trajectory model.


Figure 2. One-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 100 meters (blue line) at 18 UTC (2pm EDT) Tuesday, March 22, 2011 from the Fukushima Daiichi nuclear plant. Northerly winds are predicted to carry radioactivity just to the east of Tokyo. A modest wind shift could bring the radioactivity to the city. Image created using NOAA's HYSPLIT trajectory model.

Resources
Seven-day weather forecast for Sendai near the Fukushima nuclear plant

The Austrian Weather Service is running trajectory models for Japan.

Current radar loops from the Japan Meteorological Agency

Jeff Masters