Response of the unstable near-equatorial F region of the ionosphere to the atmospheric gravity waves excited by the sources of seismic origin

Rapoport Yu. G.(1), Hayakawa M.(2), Gotynyan O. E.(3), Ivchenko, V. N.(1,3), Fedorenko A. K.(3)
(1)Kiev National Taras Shevchenko University, Kiev, Ukraine
(2)University of Electro-Communications, Tokyo, Japan
(3)Institute for Space researches, NAS and NSA of Ukraine, Kiev, Ukraine
Ionospheric response (IR) to the spatial packet of atmospheric gravity waves (AGW), radiated
by the lithospheric source, is searched numerically and compared with the results of satellite
observations after strong earthquakes. Given bell-shaped spatial distribution of the vertical
velocity of the AGW on the ground level is used. Spectrum of AGW (horizontal) velocity in the
F region includes two groups of modes which could cause development of the Rayleigh-Tailor
instability (RTI) in the ionosphere: (a) modes with largest amplitudes in the very close vicinity to
the spectral boundary between vertically propagating and non-propagating (reactive) modes with
wavelength of order of 800 km for AGW period 40 min; (b) and much wider spectrum of modes
with much shorter horizontal wavelength, lower amplitudes and possibility of larger increment of
RTI. Different possible dynamical regimes of the development of IR with and without RTI and
with different development of two above mentioned gropes of modes are revealed and studied.
An influence on the IR of the following factors are searched in the frame of 2D model: (1) of
horizontal and vertical ion velocity in the absence of wind; (2) of horizontal wind together with
ion motion; (3) of presence or absence of the RTI for the ionospheric modes drawn by the AGW
closed to the boundary between reactive and vertically propagating modes; (4) contribution into
IR of the ionospheric modes excited by AGW propagating under oblique angle to the
geomagnetic field is under consideration (Fig. 1a, b). Solution of this problem is the part of the
development of 3D model of IR.
The model is valid, what is proven by qualitative coincidence between spatial scales, location,
shapes and relative values of IR and neutral perturbations, observed after strong earthquakes [1]
and corresponding characteristics obtained by means of the numerical modelling.

Fig. 1a. Dependence of relative change of electron concentration on the time counted since the
moment of “switching on” an influence of AGW on ionospheric plasma. The angle between the
direction of propagation of AGW and (horizontal) geomagnetic field is equal to 45o .

Fig. 1b. Spatial distribution of the absolute value of relative change of electron concentration at
the time equal to 250 min. since the moment of “switching on” an influence of AGW on
ionospheric plasma. The angle between the direction of propagation of AGW and (horizontal)
geomagnetic field is equal to 45o .
[1] Fedorenko А. К., Lizunov G. V., Rotkel Х. Satellite measurements of quasiwave
perturbations of the atmosphere on the altitudes of F region caused by powerful earthquakes //
Geomagnetism and aeronomy.- 2005.- V. 45, № 3.-P. 403-410.

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