No abstract

The magnetotail current sheet is active and often flaps back and forth. Knowledge about the flapping motion of current sheet is essential to explore the related magnetotail dynamic processes, e.g., plasma instabilities. Due to the inability of single-point measurements to separate the spatial-temporal variation of magnetic field, the moving velocity of flapping current sheets cannot be revealed generally until the multipoint measurements are available, e.g., the Cluster mission. Therefore, currently, the flapping behaviors are hard to be resolved only relying on single-point magnetic field analysis. In this study, with minimum variance analysis, we develop a technique based on single-point magnetic field measurement to qualitatively diagnose the flapping properties including the flapping type and the traveling direction of kink-like flapping. The comparison with Cluster multipoint analysis via several case studies demonstrates that this technique is applicable; it should, however, be used with caution especially when the local sheet surface is either quasi-horizontal, or quasi-vertical. This technique will be useful for the planetary magnetotail exploration where no multipoint observations are available.

Abstract. We present a statistical study of the low (<1 Hz) frequency electric and magnetic field spectral densities observed by Cluster spacecraft in the high altitude cusp and mantle region. At the O + gyrofrequency (0.02-0.5 Hz) for this region the electric field spectral density is on average 0.2-2.2 (mV m −1 ) 2 Hz −1 , implying that resonant heating at the gyrofrequency can be intense enough to explain the observed O + energies of 20-1400 eV. The relation between the electric and magnetic field spectral densities results in a large span of phase velocities, from a few hundred km s −1 up to a few thousand km s −1 . In spite of the large span of phase velocity, the ratio between the calculated local Alfvén velocity and the estimated phase velocity is close to unity. We provide average values of a coefficient describing diffusion in ion velocity space at different altitudes, which can be used in studies of ion energization and outflow. The observed average waves can explain the average O + energies measured in the high altitude (8-15 R E ) cusp/mantle region of the terrestrial magnetosphere according to our test particle calculations.

With a newly developed technique and magnetic field measurements obtained by the magnetometer on Venus Express, we study the flapping motion of the Venusian magnetotail. We find that the flapping motion generally comprises contributions both from a nonpropagating steady flapping and a propagating kink‐like flapping. The flapping motion tilts the current sheet normal significantly in the plane perpendicular to the Venus‐Sun line. The kink‐like flapping waves traveling along solar wind electric field or its antidirection can be found in either magnetotail hemisphere where solar wind electric field pointing toward/away. The traveling behaviors suggest that the locations of the triggers for kink‐like flappings are near the boundaries between magnetotail current sheet and magnetosheath, not near the central region of magnetotail as is for the Earth's magnetotail.

Knowledge of the magnetic field morphology in the near-Venus wake is essential to the studies of magnetotail dynamics and the planetary plasma escape. In this study we use the magnetic field measurements made by Venus Express during the period of April 2006 to December 2012 to investigate the global magnetic field morphology in the near-Venus magnetotail (0-3 Venusian radii, R V , down tail) in the frame of solar wind electric field coordinates. The hemisphere with electric field pointing toward/away is indicated as ±E hemisphere. It has been reported that the cross-tail field component has a hemispheric asymmetry in the Venusian magnetotail. We report here that this asymmetry should have been formed at the terminator and would transport tailward. In addition, we find that the draped magnetic field lines near both hemispheric flanks are directed equatorward in the region 0-1.5 R V down tail as it looks like "sinking" into Venus umbra. We estimate the thickness of the magnetotail current sheet and the current density at the sheet center. We find that the average half thickness of central current sheet near +E hemispheric flank (~460 km) is almost twice as thick as that near magnetic equatorial plane (~200 km), but the corresponding current densities at the sheet center are comparable (~6.0 nA/m 2 ). As a result, the larger cross-tail field component found near the +E hemispheric flank suggests a stronger tailward j × B force, i.e., the more efficient tailward acceleration of plasma in this region, showing the agreement with previous observations of heavy ion outflow from Venus. In contrast, the average magnetic field structure near ÀE hemispheric flank is irregular, which suggests that dynamic activities, such as magnetic reconnection and magnetic field turbulence, preferentially appear there.

[1] We have applied the Direct Simulation Monte Carlo method to solve the kinetic equation for the H/H + transport in the upper Martian atmosphere. We calculate the upward H and H + fluxes, values that can be measured, and the altitude profile of the energy deposition to be used to understand the energy balance in the Martian atmosphere. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. We use an energy spectrum of the down moving protons in the altitude range 355-437 km adopted from the Mars Express Analyzer of Space Plasma and Energetic Atoms measurements in the range 700 eV-20 keV. The particle and energy fluxes of the downward moving protons were equal to 3.0 × 10 6 cm −2 s −1 and 1.4 × 10 −2 erg cm −2 s −1 . It was found that 22% of particle flux and 12% of the energy flux of the precipitating protons is backscattered by the Martian upper atmosphere, if no induced magnetic field is taken into account in the simulations. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85-500 km, we find that up to 40%-50% of the energy flux of the precipitating protons is backscattered depending on the velocity distribution of the precipitating protons. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind.

[1] We study atmospheric escape from Venus during solar minimum conditions when 147 corotating interaction regions (CIRs) and interplanetary coronal mass ejections (ICMEs) combined impact on the planet. This is the largest study to date of the effects of stormy space weather on Venus and we show for the first time statistically that the atmosphere of Venus is significantly affected by CIRs and ICMEs. When such events impact on Venus, as observed by the ACE and Venus Express satellites, the escape rate of Venus's ionosphere is measured to increase by a factor of 1.9, on average, compared to quiet solar wind times. However, the increase in escape flux during impacts can occasionally be significantly larger by orders of magnitude. Taking into account the occurrence rate of such events we find that roughly half (51%) of the outflow occurs during stormy space weather. Furthermore, we particularly discuss the importance of the increased solar wind dynamic pressure as well as the polarity change of the interplanetary magnetic field (IMF) in terms of causing the increase escape rate. The IMF polarity change across a CIR/ICME could cause dayside magnetic reconnection processes to occur in the induced magnetosphere of Venus, which would add to the erosion through associated particle acceleration.

More than three years of data from the ASPERA-3 instrument on-board Mars Express has been used to compile average distribution functions of ions in and around the Mars induced magnetosphere. We present samples of average distribution functions, as well as average flux patterns based on the average distribution functions, all suitable for detailed comparison with models of the near-Mars space environment. The average heavy ion distributions close to the planet form thermal populations with a temperature of 3 to 10 eV. The distribution functions in the tail consist of two populations, one cold which is an extension of the low altitude population, and one accelerated population of ionospheric origin ions. All significant fluxes of heavy ions in the tail are tailward. The heavy ions in the magnetosheath form a plume with the flow aligned with the bow shock, and a more radial flow direction than the solar wind origin flow. Summarizing the escape processes, ionospheric ions are heated close to the planet, presumably through wave-particle interaction. These heated populations are accelerated in the tailward direction in a restricted region. Another significant escape path is through the magnetosheath. A part of the ionospheric population is likely accelerated in the radial direction, out into the magnetosheath, although pick up of an oxygen exosphere may also be a viable source for this escape. Increased energy input from the solar wind during CIR events appear to mainly increase the number flux of escaping particles, the average energy of the escaping particles is not strongly affected. Heavy ions on the dayside may precipitate and cause sputtering of the atmosphere, though fluxes are likely lower than 0.4 × 10 23 s −1 .