J. R. Abalde

Observations of equatorialFregion plasma bubbles using simultaneous OI 777.4 nm and OI 630.0 nm imaging: New results

Simultaneous observations of the OI 630.0 nm and OI 777.4 nm nightglow emissions using all-sky imaging systems and ionospheric radio sounding using a Canadian Advanced Digital Ionosonde (CADI) digisonde have been recently carried out at Sao Jose dos Campos (23.21°S, 45.86°W), Brazil. The all-sky imaging systems use novel CCD devices, with high quantum efficiency and which provide an exceptional capacity for quantitative measurement of faint- and low-contrast emissions. On October 23–24, 2000 (high solar activity), the presence of large-scale F region plasma irregularities (plasma bubbles) was observed using both techniques (i.e., optical and radio). The high-resolution images, recorded using the OI 777.4 nm nightglow emission, show a new striated or ray-like pattern, which has not been detected before. These OI 777.4 nm optical observations show for the first time, in great detail, the field-aligned ionospheric plasma bubble structures, in contrast with the OI 630.0 nm images, which show a diffuse image of the bubbles. The optical signatures of the OI 777.4 nm emission are more closely related to the actual ionospheric bubble structure, owing to its prompt emission and dependence only on the electron density, with no F layer height dependence. On the other hand, the OI 630.0 nm emission comes from the bottomside of the F layer with a strong F layer height dependence and shows blurred images due to its 110-s lifetime. An additional advantage of using the OI 777.4 nm emission for ionospheric irregularity studies is that the plasma bubbles can be observed earlier on the OI 777.4 nm images than on the OI 630.0 nm images (by ∼ 15 min).

Chaotic dynamics of nonthermal planetary radio emissions

Abstract A dynamical theory of nonlinear three-wave interactions involving Langmuir, whistler and Alfven waves in the planetary magnetospheres is developed. By assuming linear growth for the Langmuir wave and linear damping for both whistler and Alfven waves, the wave triplet is shown to evolve temporarily from order to chaos via either the period doubling route or the type-I Pomeau–Manneville intermittency route. Numerical solutions of this dynamical system are presented, showing the time series of the wave amplitude and the corresponding power spectra. The characterization of orderly and chaotic states is performed by plotting the Poincare maps and calculating the largest Lyapunov exponent. The relevance of this theory for observation of chaos in the time series of nonthermal planetary radio emissions is discussed.

Fundamental plasma radiation generated by a travelling Langmuir wave : hybrid stimulated modulational instability

A new generation mechanism for electromagnetic waves near the fundamental plasma frequency is discussed. It is shown that a travelling Langmuir pump wave can nonlinearly convert into electromagnetic, Langmuir and ion-acoustic daughter waves via a hybrid stimulated modulational instability. The linear and nonlinear temporal dynamics of this modulational process involving coupling to a resonant ion-acoustic wave are studied. The wave energy conservation relations are derived. The roles of frequency mismatch, dissipation and wave dispersion in the temporal evolution of nonlinear coupling of two wave triplets are analysed.

A theory of the fundamental plasma emission of type-III solar radio bursts

Results from plasma wave experiments in spacecraft give support to nonlinear interactions involving Langmuir waves, electromagnetic waves and ion-acoustic waves in association with type III solar radio bursts. In this paper we present a theory of the fundamental plasma emission of type-III solar radio bursts. Starting from the generalized Zakharov equations, considering the pump wave as a pair of oppositely propagating Langmuir waves with different amplitudes, and the excitation of electromagnetic and induced Langmuir waves, we obtain a general dispersion relation for the coupled waves. We numerically solve the general dispersion relation using the pump wave amplitude and plasma parameters as observed in the interplanetary medium. We compare our results with previous models. We find that the stability properties depend on the pump wave numbers and on the ratio of wave amplitude between the forward and backward pump wave. The inclusion of a second pump wave allows the simultaneous generation of up and down converted electromagnetic waves. The presence of a second pump with different amplitude from the first one brings a region of convective instability not present when amplitudes are the same.

Nonlinear Dynamics and Chaos in Space Plasmas

The theory and observation of nonlinear wave coupling phenomena in solar-system plasmas are reviewed. Rocket and satellite observations have provided evidence of nonlinear wave interactions in space plasmas, in particular, in relation to the generation and propagation of radio waves in solar corona, interplanetary medium and Earth’s magnetosphere. These radio waves represent the electromagnetic signature of solar-terrestrial coupling and are useful for forecasting and monitoring of space weather. Nonlinear wave-wave coupling in plasmas can be modeled as a dynamical system of coupled oscillators involving one, two or higher-order wave triplets. For a three-wave dissipative system, the temporal transition from order to chaos may evolve via period doubling or intermittence. For a four-wave Hamiltonian system involving two coupled wave triplets, the spatiotemporal transition from order to chaos is analyzed using the concepts of stable and unstable homogeneous manifolds. Plasma dynamics is governed by a variety of wave motions resulting from the collective electrodynamic interactions involving plasma fields and plasma particles. Nonlinear wave-wave coupling in plasmas can occur due to the growth of parametric instabilities. In this paper, we present an overview of theoryand observation of nonlinear mode coupling in space plasmas. In §2 we discuss the theoryof nonlinear interaction involving a single wave triplet in the presence of source and dissipation. We consider the transition from order to low-dimensional temporal chaos. In § 3w e discuss the theoryof nonlinear interaction involving two wave triplets in the absence of source and dissipation. We treat the transition from order to high-dimensional spatiotemporal chaos. Before discussing the theorylet us first summarize some recent observational evidence of nonlinear wave-wave interactions in the solar system. Comprehensive reviews of this topic are given in Refs. 1) and 2). Radio waves provide the electromagnetic signature of solar-terrestrial relation and serve as a tool to forecast and monitor the space weather. The radio emis

Generation of circularly polarized radio waves within magnetic holes of the solar wind

The possibility of nonlinear interaction between Langmuir waves and ion–acoustic waves in the solar wind has received considerable interest in the last years. However, little attention has been paid to the possibility of nonlinear coupling between Langmuir waves and whistler waves in the interplanetary medium. Close temporal correlation between high-frequency Langmuir waves and low-frequency electromagnetic whistler waves has been observed recently within magnetic holes of the solar wind. In order to account for these observations within magnetic holes of the solar wind, we develop a nonlinear three-wave theory describing the parametric interaction of Langmuir waves, electromagnetic whistler waves with either right- or left-hand circularly polarized electromagnetic waves. We suggest that the nonlinear coupling of Langmuir waves and whistler waves may lead to the formation of modulated Langmuir wave packets as well as the generation of circularly polarized radio waves at the plasma frequency in the solar wind.

Multi-spectral optical imaging of the spatiotemporal dynamics of ionospheric intermittent turbulence.

Equatorial plasma depletions have significant impact on radio wave propagation in the upper atmosphere, causing rapid fluctuations in the power of radio signals used in telecommunication and GPS navigation, thus playing a crucial role in space weather impacts. Complex structuring and self-organization of equatorial plasma depletions involving bifurcation, connection, disconnection and reconnection are the signatures of nonlinear evolution of interchange instability and secondary instabilities, responsible for the generation of coherent structures and turbulence in the ionosphere. The aims of this paper are three-fold: (1) to report the first optical imaging of reconnection of equatorial plasma depletions in the South Atlantic Magnetic Anomaly, (2) to investigate the optical imaging of equatorial ionospheric intermittent turbulence, and (3) to compare nonlinear characteristics of optical imaging of equatorial plasma depletions for two different altitudes at same times. We show that the degree of spatiotemporal complexity of ionospheric intermittent turbulence can be quantified by nonlinear studies of optical images, confirming the duality of amplitude-phase synchronization in multiscale interactions. By decomposing the analyses into North-South and East-West directions we show that the degree of non-Gaussianity, intermittency and multifractality is stronger in the North-South direction, confirming the anisotropic nature of the interchange instability. In particular, by using simultaneous observation of multi-spectral all-sky emissions from two different heights we show that the degree of non-Gaussianity and intermittency in the bottomside F-region ionosphere is stronger than the peak F-region ionosphere. Our results are confirmed by two sets of observations on the nights of 28 September 2002 and 9 November 2002.

Physics of plasma radiation

We present a theory of the fundamental plasma emission of type-III solar radio bursts. Starting from the generalized Zakharov equations, considering the pump wave as a pair of oppositely propagating Langmuir waves with different amplitudes, and the excitation of electromagnetic and induced Langmuir waves, we obtain a general dispersion relation for the coupled waves. We numerically solve the general dispersion relation using the pump wave amplitude and plasma parameters observed in the interplanetary medium.

PLASMA EMISSION MECHANISM FOR RADIO SPIKES FROM SOLAR FLARES

Abstract Narrowband spiky radio bursts, at decimetric and decametric wavelengths, with high degree of circular polarization are observed in solar flares. We discuss a new plasma emission mechanism for solar radio spikes. It is shown that narrowband radio bursts of right- and left-hand circular polarizations can be produced via nonlinear conversion of Langmuir waves into high-frequency electromagnetic electron cyclotron waves near the plasma frequency by coupling to low-frequency electromagnetic cyclotron waves such as Alfven-ion cyclotron or magnetosonic-whistler waves.