Self-similar plasma expansion approach is used to solve a plasma model based on the losing phenomenon of Titan atmospheric composition. To this purpose, a set of hydrodynamic fluid equations describing a plasma consisting of two positive ions with different masses and isothermal electrons is used. With the aid of self-similar transformation, numerical solution of the fluid equations has been performed to examine the density, velocity, and potential profiles. The effects of different plasma parameters, i.e., density and temperature ratios, are studied on the expanding plasma profiles. The present investigation could be useful to recognize the ionized particles escaping from Titan atmosphere.
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.
The nature of ionospheric losses from Venus is of essential importance for understanding the ionosphere dynamics of this unmagnetized planet. A plausible mechanism that can explain the escape of charged particles involves the solar wind interaction with the upper atmospheric layers of Venus. The hydrodynamic approach proposed for plasma expansion in the present study comprises two populations of positive ions and the neutralizing electrons, which interact with the solar wind electrons and protons. The fluid equations describing the plasma are solved numerically using a self-similar approach. The behavior of plasma density, velocity, and electric potential, as well as their reliance upon solar wind parameters have been examined. It is found that for noon midnight sites, the oxygen ion-to-electron relative density may be the main factor to enhance the ionic loss. However, the other parameters, like hydrogen density and solar wind density and velocity seem to do not stimulate the runaway ions. For lower dawn-dusk region, the plasma are composed of hydrogen and oxygen ions as well as electrons, but for higher altitudes only hydrogen ions and electrons are encountered. All ionic densities play an important role either to reduce or boost the ionic loss. The streaming solar wind velocity has no effect on the plasma escaping for lower altitudes, but it reduces the expansion at higher altitudes.
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