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Long-distance Transport of Radioactive Plume by Nocturnal Local Winds


Long-distance Transport of Radioactive Plume by Nocturnal Local Winds

Takao Yoshikane et al. Sci Rep.


Radioactive plumes can spread far and wide depending on wind conditions. The plumes often frequently reached the Tokyo metropolitan area, which is approximately 200 km away from the Fukushima Daiichi nuclear power plant, under spatially heterogeneous wind fields in March 2011. To reduce exposure to radioactive plumes, the behaviour of the plumes must be known. However, the transport mechanism of radioactive plumes is not fully understood. Using a regional climate model, we show that multiple diurnal cycle processes play a key role in the frequent transport of radioactive plumes to the Tokyo metropolitan area. The observed data and hindcast results indicate that the radioactive plume moves along the local winds, which comprise the northeasterly local wind (NELW) associated with the meso-scale low-pressure system (meso-low) and the northerly sea wind (NSW) during the night. The long-term analysis and sensitivity simulations also show the nocturnal processes that the NELW caused by the meso-low and the NSW are formed east of the Tokyo metropolitan area and from Fukushima offshore east of the Tokyo metropolitan area, respectively, when neither winter monsoons nor extra-tropical cyclones are predominant. These findings indicate that the radioactive plumes could reach faraway places frequently via nocturnal local processes.

Conflict of interest statement

The authors declare no competing financial interests.


Figure 1
Figure 1. A common feature of the atmospheric fields when a high air dose was observed in the Tokyo metropolitan area.
(a) The locations of Fukushima, Tokai-mura, and the Tokyo metropolitan area. (b) Time variations of the observed air doses at the observation sites in Tokai-mura. Cases 1, 2, 3, and 4 correspond to the spikes in the air dose. (c) The wind field and geo-potential height of MSM-GPV (975 hPa) at midnight before each of the four cases. Dark areas indicate low pressure. The maps were created by using GrADS 2.0.1 ( (a,c) and Microsoft Excel for Mac 2011 (b).
Figure 2
Figure 2. Diurnal variation of the wind fields under calm conditions.
Diurnal variation of the composite data of wind fields, geo-potential height, and temperature at 975 hPa and 850 hPa on calm days from 2008 to 2014 according to the MSM-GPV data. The dark areas indicate areas of low geo-potential height (low pressure). The maps were created by using GrADS 2.0.1 (
Figure 3
Figure 3. Sensitivity test.
The wind fields, geo-potential heights, and temperatures at 975 hPa in the morning (6 JST) of Ex. 1 and Ex. 2. The atmospheric fields of the global zonal mean and area-averaged values in March 2011 were applied as the lateral boundary conditions of Ex. 1 and Ex. 2, respectively. The maps were created by using GrADS 2.0.1 (
Figure 4
Figure 4. Long-distance transport of the radioactive plume via multiple diurnal processes.
The 3D image of the mixing ratio of 131I in Case 1. The maps were created by using Volume Data Visualizer for Google Earth (VDVGE) 1.1.7 ESC JAMSTEC ( and Adobe Illustrator CS5 (

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