Abstract
Various modern applications of empirical electron density models need realistic structures of the electron density distribution with smaller scales than the model background. Travelling Ionospheric Disturbances (TIDs) produce three dimensional and time dependent disturbances of the background ionization. We present a TID model suitable to «modulate» large scale electron density distributions by multiplication. A model TID takes into account the forward tilt of the disturbance wave front, a distinct vertical structure, a fan type horizontal radiation characteristic, geometric dilution and attenuation. More complicated radiation patterns can be constructed by means of superposition. The model TIDs originate from source regions which can be chosen arbitrarily. We show examples for TID modulations of the background model family developed at Trieste and Graz (NeQuick, COSTprof and NeUoG-plas).
Highlights
IntroductionTravelling Ionospheric Disturbances (TIDs) are the plasma signatures of Atmospheric (acoustic) Gravity Waves (AGWs)
Travelling Ionospheric Disturbances (TIDs) are the plasma signatures of Atmospheric Gravity Waves (AGWs)
The data for the closely spaced receiving stations show strong differences in TID amplitudes which indicates that the AGWs behind the Travelling Ionospheric Disturbances are not radiated from an isotropic source but have a distinct «radiation pattern»
Summary
Travelling Ionospheric Disturbances (TIDs) are the plasma signatures of Atmospheric (acoustic) Gravity Waves (AGWs). The theoretical understanding of these wavelike disturbances was first given by Hines (1960) According to their horizontal wavelengths we distinguish between three classes of TIDs (table I; see e.g., Van Velthoven, 1990). Cs= c ^p0 t0h is the velocity of sound, γ = cp/cv is the ratio of specific heats at constant pressure and at constant volume, p0 and ρ0 are pressure and mass density at the starting level for the displacement This equation (Newton’s second law) can be considered as a differential equation for an oscillation with the general solution (for small amplitudes A) ∆z=Aexp(jωBt); j = - 1, ωB2= = ωb2+ (g/cs2) (d(cs2)/dz) is the square of the (general) Brunt-Väisälä or buoyancy angular frequency, ω.
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