Model modulation to add smaller scale structures to large scale electron density models

Abstract. Usually regional and global electron density models provide large scale spatial structures only and smooth out the smaller scale features of the electron density distribution. We present a method to modulate existing electron density models by multiplication: M(h, φ, λ, t) = L(h, φ, λ, t) × S₁(h, φ, λ, t) × S₂(h, φ, λ, t) × ... S_n(h, φ, λ, t)
M: resulting electron density distribution, L: large scale model, S₁...S_n: modulating models for n the smaller scale structures; h: height; φ, λ: geographic coordinates, t: Universal Time. There are no restrictions to the nature of the large scale model provided it takes height and horizontal coordinates as input. Examples are models of the "profiler" type which use large scale "maps" for profile anchor points (e.g., E, F1, F2 peak properties) like the International Reference Ionosphere (IRI). Typical examples for smaller scale structures are ridges, troughs and wavelike disturbances. The advantage of modulation by multiplication is that there is no danger to get zero or negative values of electron density as long as the background and modulations are >0 everywhere. For each modulation model, unity means "undisturbed".