Plasma in the near Venus tail: Venus Express observations

Abstract

[1] Although Venus has no global intrinsic magnetic fields, it possesses a long magnetotail of induced origin. The topology of the tail is determined by the interplanetary magnetic field orientation. We present recent plasma and magnetic field observations in the near Venus tail (X -3R V ) made by the Venus Express spacecraft. We show that ion acceleration in the Venus plasma sheet is produced by the slingshot effect of the draping magnetic field lines, though some features as differential streaming of different ion species point to the existence of other forces. We explain a bell shape of ion spectrograms while the spacecraft crosses the current sheet. The absence of a balance between the lobe magnetic pressure and thermal pressure of plasma in the plasma sheet indicates a dynamic rather than a static equilibrium in the Venus magnetotail. A strong asymmetry of the plasma sheet is controlled by the direction of the motional electric field in the upstream solar wind. In the hemisphere pointed in the direction of the motional electric field, the j B force accelerates plasma tailward supplying the plasma sheet, while in the opposite hemisphere, the flow pattern occurs less regularly with smaller speeds but higher number densities.

Solar Wind Interaction and Impact on the Venus Atmosphere

“…Here the draped field pushes the plasma into the tail by means of the j × B-force. In the −E-hemisphere the flow pattern is more irregular and a planetward motion is more often observed (Dubinin et al 2013b). As discussed above the magnetic field is more tightly wrapped around the planet in this hemisphere and the average field pattern does not show a distinct current sheet but is more irregular Rong et al 2014).…”

“…This is motivated mainly by the observations on VEX which show evidence for solar wind convection electric field-related asymmetries in the solar wind interaction (e.g. Dubinin et al 2013bDubinin et al , 2014Zhang et al , 2015. Most recently, explain an observed interplanetary field orientation bias in the north polar region magnetic field strength found by VEX using a multifluid version of the Ma et al (2013) model.…”

Asymmetries in the Magnetosheath Field Draping on Venus' Nightside

“…From magnetometer and plasma data from Venus Express, already known asymmetry effects have been confirmed and new ones discovered: Zhang et al () confirmed the bilobed nature of the tail and found also an asymmetry in closer wrapping of the IMF around the planet in the hemisphere where E points toward the planet. Dubinin et al () reported about plasma sheet asymmetries controlled by the direction of the motional electric field, with higher acceleration and lower plasma density in the hemisphere where E is pointing away from the planet (positive E hemisphere). A stronger magnetosheath magnetic field in the positive E hemisphere was found by Du et al (); these authors also confirmed the closer wrapping around the planet in the negative E hemisphere.…”

Is the flow‐aligned component of IMF really able to impact the magnetic field structure of Venusian magnetotail?

“…At 02:17:50, as marked by the vertical red line, when VEX is located at [−1.47, −0.76, 0.29] R V , the sign of B x component changes; i.e., the field orientation changes from tailward to the Venusward. The reversal is accompanied by an enhancement of the energetic electron flux (>10 eV) and ion flux (>300 eV), which suggests that VEX is indeed crossing the magnetotail CS [ Dubinin et al ., ].…”

“…Magnetic field data with a time resolution of 4 s recorded from April 2006 to December 2014 is scanned to select cases. The selected cases fulfill the following criteria: VEX should be located in the nominal magnetotail region (−3 < X < −0.5 R V , ( Y 2 + Z 2 ) 1/2 < 1.3 R V ). The CS crossing can be identified by the reversal of the B x component as well as the enhancement of energetic plasma flux [e.g., Dubinin et al ., , ]. The CS should not show evident flapping [ Rong et al ., , ], and the CS crossing should occur only one time during the passage through the tail.…”