Nuclear Meteorology – A Primer

GeekMom Science
Fukushima Daiichi Nuclear Plant on 15 March 2011, before Reactor #2 exploded. Photo by Flickr user daveeza.

Wow — how did the GeekMoms get their hands on a trained nuclear meteorologist?

I don’t really talk much about it because ordinarily peoples’ eyes tend to glaze over.  I mean, who wants to hear about such stuff?

Right now, everyone wants to hear about it!  With the recent events in Japan, everyone is tuning in to the experts to hear their forecasts on where the radiation is going to go!   The Japanese are particularly interested, as are those in Alaska and the west coast of North America!

Note: I am NOT issuing my own forecast on this blog.  While I have had the training, I am NOT currently in the work force and therefore do not have the resources to make my own forecast.  What I will do here is discuss the fundamentals of nuclear meteorology and the tools the authorities in the U.S. and Japan are using to make the forecasts.  I will be happy to point you to some of the sources that the media is pointing to, and you other geeky Moms are smart folks: you will enjoy knowing where CNN and Fox News are getting their radioactivity forecasts!

First of all, if you’d like some introduction to how a nuclear power plant works, you can check here and here.  If you’d like to learn more about why the earthquake and tsunami caused so many problems for this plant, you can read about it here.

Perhaps you’re seeing the media speculating on all these wind forecasts.  This is an example of what we’re seeing…

A HYSPLIT transport and dispersion model output graphic. You’re looking at forecast locations and elevations of hypothetical “parcels” of air originating at Fukushima on 19 March 2011 at 1800 UTC. The red line is a parcel originating at 10m height, the blue line is originating at 300m height. The map shows the latitudes/longitudes of the parcels as they travels across the Pacific, the bottom graph shows the elevation of the parcel over time. Please understand that authorites do NOT know how much pollutant is emerging from Fukushima right now, so these estimates are for planning purposes only. Picture from NOAA/ARL.

Yes, you’re seeing a plume end up on the west coast of California.  It’s quite possible for this to happen.  But before we head for the door with our “go bags”, let’s discuss the variables in an atmospheric transport and dispersion forecast.

  • The source term.  This is the “stuff” being emitted that we’re concerned with in our atmosphere.  A pollutant…or in Fukushima’s case, the assorted pieces of the nuclear plant, from pieces of the fuel rods to pieces of the buildings that were involved in the explosion, but even pieces of the buildings will be irradiated.  Different “sources” will behave in different ways — heavier materials (such as Uranium-235) will behave differently than lighter materials (such as Iodine-131).
  • The temperature of the source term.  Depending on the amounts of the material launched into the atmosphere, sometimes the material is so hot, it causes its own “microclimate”.  This blogger shows a picture of a nuclear test mushroom cloud producing its own tornado!
  • Source location and height. Is the pollutant coming from a smokestack?  A small chimney?  A reactor explosion?  That will impact the starting height of the pollutant release, as well as the size of the release: from a pinpoint origin, or from a more broad origin.
  • The surrounding terrain near the release site.  A nuclear power plant in the mountains will launch pollutants differently than one on the coastline.
  • Obstructions to the release in the vicinity. This type of issue was important when military members were attempting to document where the pollutants would flow after the Twin Towers fell in 2001.  The other skyscrapers in the area had a significant impact on the accuracy of the forecast.

These variables all impact the accuracy of the forecast.  Throw in the meteorological variables and the general accuracy of the weather model, and you can now understand why all the different media outlets currently have different answers about much of this.  There’s a LOT to take into account.

And one more thing, so far there’s been NO absolute data on how much radiation is coming from Fukushima.

There are many “transport and dispersion” models out there that the authorities are tapping into:

  • NARAC: Lawrence Livermore Lab’s National Atmospheric Release Advisory Center has its own in-house model.  The agency has been activated to assist the Nuclear Regulatory Commission with possible radiation coming into the United States.
  • HYSPLIT: National Oceanic and Atmospheric Administration’s Hybrid Single Particle Lagrangian Integrated Trajectory Model.  Anyone in the atmospheric sciences fields can run this model straight from the web (so long as you register)!
  • HPAC: Hazard Prediction and Assessment Capability.  This is the Department of Defense’s transport and dispersion model of choice.

It’s also important to point out that some radioactive material loses its radioactive traits over time.  You might remember the term “half life” from high school chemistry?  For example, Iodine-131, one of the radioactive materials suspected to be coming from Fukushima (and causes damage to the thyroid), has a half life of 8 days.  This means, 1/2 of the atoms in a set release period are expected to be GONE in 8 days.  Returning to the map above, if there is Iodine-131 in the material traveling across the Pacific Ocean, and it’s expected to reach the west coast of the U.S. in 5 days, you can expect about 30% of the material to have decayed.

Earlier this week the NY Times published a primer on the half-lifes of some of the materials that could come from the Fukushima accident.

Remember, a forecast is only as accurate as the initial conditions that go into it.  As they used to say in my first computer programming classes in college: GIGO.  Garbage in, Garbage out.

I wish this could be a happier post, all I can offer is to keep aware and listen to your local authorities.  They’re working with some of the brightest out there to take care of us!

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3 thoughts on “Nuclear Meteorology – A Primer

  1. Fascinating! This will help interpret what’s coming out of NHK. We are watching the weather very closely here in Yokohama.

  2. I found useful easy to read information here from Massachussets Institute of Technology Nuclear Science & Engineering about Radiation and laymans definition of terms and processes related to Nuclear Power and specific information about the Fukushima plant problems.
    MIT NSE Nuclear Information Hub (

    Reading these webpages Increased me knowledge and understanding of what is going on in Japan. I live near Portland Oregon USA so the predicted radiation fallout pattern is interesting to me.

    Wishing the Japanese people courage to continue on through this earthquake and Tsunami, and radialogical disaster. Life is hard sometimes. God be with you.

    1. This is the exact link I meant to convey in the above post. Easy reading for a regular layperson. Fred

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