The generation of small‐scale field‐aligned irregularities in ionospheric heating experiments is explained in terms of a purely growing parametric instability with thermal coupling based on the scattering of the pump field by the irregularities into plasma oscillations. The standing wave nature of the pump field is a necessary aspect of the present instability which does not require the previous presence of nonthermal irregularities.
Using the Total Electron Content (TEC) data recorded by the GPS receiver network, installed under the GPS and Geo Augmented Navigation (GAGAN) program, ionospheric electron content on the day of the great Sumatra-Andaman earthquake of December 26, 2004 was examined. A significant perturbation of 1.5 to 2 TEC units over a smooth variation of TEC in the morning hours was observed within 45 minutes of the quake at stations situated near the east coast of the Indian subcontinent. The disturbance was found to propagate northwestward with its origin situated about 2• northeast of the quake epicenter. Possible coupling mechanism of the crustal movement and the ionosphere are discussed.
A mechanism for generating the small-scale field-aligned irregularities observed in ionospheric heating experiments is proposed. The Langmuir waves that result from the scattering of the electromagnetic pump wave of ordinary polarization by the irregularities, interact with the irregularities by secondary scattering processes. The differential dissipation of the resulting Langmuir waves causes the growth of the irregularities and of the Langmuir waves resulting from the secondary scattering. The instability is explosive in nature and initial irregularities whose fractional density perturbations exceed about 10 -4, are needed for its occurrence. It is shown for a periodically varying field-aligned density perturbation that although successive scattering of the Langmuir waves eventually becomes very intense and approaches an equipartition of the energy among the waves, it does not saturate the instability. It seems that the proposed mechanism is able to generate small-scale field-aligned irregularities that can reach the amplitudes observed in ionospheric heating experiments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.