If the ionosphere has D, E, and F layers, what happened to the A, B, and C layers?

On Google+, Bob, K0NR posted,

Interesting question from a 10-year-old student in the ham radio class today: Why do we always talk about the D, E and F layers of the ionosphere…are there A, B or C layers? I don’t know the answer to that one.

Now, I’d always heard that the reason the lowest layer is the D layer is because when scientists first started studying the ionosphere, they found these three layers and postulated that they would find three layers below them, i.e. the A, B, and C layers. They did not find them, but never went back and relabeled ones that they did find.

I posted this as a reply, and Bob asked if I had a reference. Well, I Googled all over for one, but came up empty. Do any of you know if this explanation is true, or if this is a ham radio urban legend?

Comments

  1. Ethan, KG8U, emailed me the following:

    I have devoted much of the past six years of my professional life to ionospheric physics and so know the answer and source to your question about naming the ionospheric layers. The answer can be found in Kivelson and Russell’s book Introduction to Space Physics in the chapter “A Brief History of Solar-Terrestrial Physics.” It says:

    In drawing diagrams of the electromagnetic waves reflected by the ionosphere, Appleton used the letter E for the electric vector of the downcoming wave. When he found reflections from a higher layer, he used the letter F for the electric vector of those reflected waves, and when he occasionally got reflections from a lower layer, he naturally chose the letter D. When it came time to name these layers, he chose the same letters, leaving the letters A, B, and C for possible later discoveries that never came.”

    So, yes, you were told correctly, although I find the additional backstory at the beginning amusing. This book is in Google Books and you can read the brief section on page 10 of the 1995 edition.

    73,

    –Ethan, K8GU/3.

  2. Dan and Ethan,
    Thanks for the information!

    Bob

  3. Curt/KF5KGN says:

    Yes, thank you!

  4. Appleton recalled [1], “The story of how I came to give the names D, E and F is really a simple one. In the early work with broadcasting wavelength, I obtained reflections from the Kennelly-Heaviside layer and I used on my diagrams the letter E for the electric vector of the down coming wave. When I found in winter 1925 that I could get reflections from a higher and completely different layer, I used the letter F for the electric vector of the down coming wave. Then about the same time I got occasionally reflections from a very low height and so naturally used the letter D for the electric vector of the returning waves. Then I suddenly realized that I must name these discrete layers and being rather fearful of assuming any finality about measurements, I felt I ought not to call these layers A, B, and C, since there might be undiscovered layers, both below and above them. I therefore felt that the original designations for the electric field vector D, E and F might be used for the layers themselves”

    [1] R. Silberstein, “The Origin of the Current Nomenclature for the Ionospheric Layers”, J. Atmos. Terr. Physics. (JATP 0259), p.382

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