Plasma environment of Venus: Comparison of Venus Express ASPERA‐4 measurements with 3‐D hybrid simulations

Abstract

[ 1 ] We use data of the ASPERA-4 ion and electron spectrometers onboard Ve nus Express to determine the locations and shapes of the plasma boundaries (bow shock, ion composition boundary,a nd mantle) at Ve nus. We also investigate the variation of the terminator bow shock position as afunction of the solar wind dynamic pressure and solar EUV flux. We compare the results with a3 -D hybrid simulation. In the hybrid model, ions are treated as individual particles moving in self-consistently generated electromagnetic fields and electrons are modeled as am assless charge neutralizing fluid. The planetary heavy ion plasma is generated by an oxygen ionosphere and exosphere adapted to ap rofile, which depends on the solar zenith angle (Chapman layer). A comparison between observations and simulations indicates that the hybrid model is able to produce an adequate picture of the global plasma environment at Ve nus. The positions of the plasma boundaries are well reproduced by the model but asignificant disagreement appears in the absolute values of the considered parameters.

Low-frequency magnetic field fluctuations in Venus' solar wind interaction region: Venus Express observations

“…They also pointed out that the model streamlines are in good agreement with that of the gasdynamic model of Spreiter and Stahara (1980) for the solar wind interaction with Venus. We note here that the nightside mantle boundaries of Martinecz et al (2009) transition is lacking at the terminator which cannot be reproduced by the analytical streamline model. As our focus lies on the dayside magnetosheath and the intensity on the nightside is generally much lower, no major deviations are expected by considering a straight streamline parallel to the x -axis.…”

“…1 the data are presented in the range 2 R V ≤ x cyl ≤ −4 R V and y cyl ≤ 4 R V and each colour-coded bin has a size of 0.05 R V × 0.05 R V (R V : Venus radius). The locations of the bow shock (BS), the upper mantle boundary (UMB), and the ion composition boundary (ICB) determined by the models of Martinecz et al (2009) are plotted for orientation and distinction of the different solar wind interaction regions, too. The magnetic field strength becomes enhanced downstream of the bow shock.…”

Interplanetary magnetic field orientation and the magnetospheres of close-in exoplanets

“…Having this range of simulations also has the additional advantage that one can more easily compare with simulations in the literature, e.g. Venus studies such as Martinecz et al (2009) and Kallio et al (2006). Thus, we chose to perform three simulation runs, all of them identical with the exception of the angle α sw,0 between the undisturbed stellar wind velocity and the IMF.…”

Oxygen ion escape from Venus in a global hybrid simulation: role of the ionospheric O<sup>+</sup> ions

“…23 in Brace and Kliore, 1991). Estimates of the total solar wind induced oxygen ion escape from Venus range from the order of 10 24 s −1 to 10 26 s −1 including observational and simulation studies (e.g., Brace et al, 1987;Moore and McComas, 1992;Terada et al, 2004;Lammer et al, 2006;Kallio et al, 2006b;Barabash et al, 2007a;Martinecz et al, 2009). We select to call the value 10 25 s −1 as the nominal O + escape rate.…”

“…Terada et al (2004) considered in their hybrid code different Venusian ion escape processes. Martinecz et al (2009) compared their hybrid simulation to the VEX/ASPERA-4 and VEX/MAG observations in an orbit case study concentrating on the boundaries.…”