Observations suggest that at altitudes of 1000 − 2000 km the interaction between the solar wind and Venus’ ionospheric plasma leads to ion-acoustic waves (IAWs) formation. For studying this hypothesis, a suitable hydrodynamic model relying on the observational data from Pioneer Venus Orbiter (PVO) and Venus Express (VEX) is developed. It consists of two ionospheric fluids of positive ions, hydrogen (H+) and oxygen (O+), and isothermal ionospheric electrons interacting with streaming solar wind protons and isothermal solar wind electrons. The favourable conditions and propagation characteristics of the fully nonlinear IAWs along with their dependence on solar wind parameters are examined and compared with the available space observations. It is found that the pulse amplitude is decreased by increasing the temperature of either the solar wind protons or electrons. In contrast, a higher relative density or velocity of the solar wind protons amplifies the amplitude of the solitary structures. Moreover, only velocity variations within a certain range called the plasma velocity scale can affect the basic features of the solitary pulses. Beyond this scale, solitary waves are not affected by the solar wind protons’ velocity anymore. This theoretical model predicts the propagation of electrostatic solitary waves with a maximum electric field of 7.5 mV/m and a pulse time duration of 3 ms. The output of the fast Fourier transformation (FFT) power spectra of the electric field pulse is a broadband electrostatic noise in a frequency range of ∼0.1 − 4 kHz. These FFT calculations are in good agreement with PVO’s observations.

Propagation properties of weakly nonlinear ion acoustic waves are investigated in a plasma at the Venusian ionosphere. The plasma model consists of two positive cold ions (oxygen O + and hydrogen H +), as well as isothermal electrons. The basic set of fluid equations is reduced to Zakharov-Kuznetsov (ZK) equation and linear inhomogeneous ZK-type equation (LIZKT) equation. The renormalization method is adopted to obtain solitary solutions of both equations. The effects of plasma parameters and higher-order correction on the nature of the solitary waves are investigated. It is found that the wave phase velocity is supersonic, which is in agreement with the observations. Furthermore, the higher-order correction enlarges the soliton amplitude, which is suitable for describing the solitary waves when the wave amplitude grows.

The influence of gradients of number density, magnetic field, and flow velocity in a plasma on the propagation of low-frequency electrostatic waves is investigated in plasma conditions relevant for the Venusian ionosphere (vicinity of Venus terminator). For this purpose, we assume a collisionless inhomogeneous plasma model consisting of two positive ion species, hydrogen H+ and oxygen O+, as well as neutralizing electrons. Linear dispersion relations predict two types of plasma modes, namely, ion-acoustic mode and drift mode. It is found that these modes have relatively long wavelengths, extending to 10 km and frequencies on the order of ∼10−3−10−2 Hz. The characteristics of these modes show a strong dependence on the gradients of plasma parameters, and numerical analysis reveals that the coupling of these modes may lead to nonlinear instabilities. However, unstable modes occur only when the field-aligned shear flows are introduced. These results help explain the presence of low-frequency electrostatic modes and their basic features in the Venusian ionosphere, and will allow future studies to extend modeling to other planetary or even cometary conditions.

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Space observations show that Venus suffers significant atmospheric erosion caused by the solar wind forcing. Plasma acceleration is found to be one of the main mechanisms contributing to the global atmospheric loss at Venus through its magnetotail. Motivated by these observations, we propose that kinetic Alfvén waves (KAW) may be a possible candidate for charged particle energization at the upper atmosphere of Venus. To test this hypothesis, we explored the basic features of both linear and nonlinear KAW structures at Venus. We considered a low-but-finite β plasma consisting of ionospheric populations (consisting of hydrogen H+, oxygen O−, and isothermal ionospheric electrons) and solar wind populations (protons and isothermal electrons). In the linear regime, we obtain a linear dispersion relation that exhibits a dependence on the intrinsic plasma configuration at Venus. The linear analysis predicts wave structures with wavelengths of ~10–102 km and frequencies of up to ~5 Hz. In the nonlinear regime, small-but-finite-amplitude solitary excitations with their corresponding bipolar electric field are obtained through the reductive perturbation technique. We discuss the influence of the intrinsic plasma parameters (the ionic concentration, solar wind electron temperature, magnetic field strength, and obliqueness) on the nature of the structures of the solitary KAWs and their corresponding electric field. We find that the ambipolar field is amplified with increasing propagation angle, magnetic field strength, and relative temperature of electrons. Our theoretical analysis predicts the propagation of elliptically polarized ultra-low-frequency (ULF) solitary structures with a maximum magnitude of ~0.01–0.034 mV m−1 and a time duration of 20–30 s. The result of the fast Fourier transform (FFT) power spectra of the ambipolar parallel electric field is broadband electromagnetic noise in the frequency range of ~0.5–2 Hz.