More than 7 years of ion flux measurements in the energy range 10 eV-15 keV have allowed the ASPERA-3/IMA (Analyzer of Space Plasmas and Energetic Ions/Ion Mass Analyzer) instrument on Mars Express to collect a large database of ion measurements in the Mars environment, over a wide range of upstream solar wind (density and velocity) and radiation (solar EUV intensity) conditions. We investigate the influence of these parameters on the Martian atmospheric ion escape rate by integrating IMA heavy ion flux measurements taken in the Martian tail at similar (binned) solar wind density (n sw ), velocity (v sw ), and solar EUV intensity (I EUV ) conditions. For the same solar wind velocity and EUV intensity ranges (v sw and I s constrained), we find a statistically significant decrease of up to a factor of 3 in the atmospheric ion escape rate with increased average solar wind density (5.6 × 10 24 s −1 to 1.9 × 10 24 s −1 for 0.4 cm −3 and 1.4 cm −3 , respectively). For low solar wind density (0.1-0.5 cm −3 ) and low EUV intensity, the escape rate increases with increasing solar wind velocity from 2.4 × 10 24 s −1 to 5.6 × 10 24 s −1 . During high solar EUV intensities the escape fluxes are highly variable, leading to large uncertainties in the estimated escape rates; however, a statistically significant increase in the escape rate is found between low/high EUV for similar solar wind conditions. Empirical-analytical models for atmospheric escape are developed by fitting calculated escape rates to all sufficiently sampled upstream conditions.
[1] The variability of planetary ion escape from Mars is studied using data from the Ion Mass Analyzer, IMA, on Mars Express (MEX). 42 orbits were selected during 17 months for different solar wind conditions, focusing on the low energy (%30 -800 eV) heavy ion (e.g. O + , O 2 + and CO 2 + ) outflow. A strong correlation is found between solar wind forcing of the obstacle, the cross-sectional area enclosing the ion outflow from Mars and the total heavy ion escape flux. The at least one order of magnitude changes of the ion outflow on the short term (hours, days), is directly connected with the variability of solar wind, solar soft x-ray and solar EUV (XEUV). The latter was first inferred from an analysis of how the obstacle size changes with changing solar wind and solar XEUV forcing. The 17-month trend of decreasing ion outflow with EUV during a declining phase of solar cycle 23, the EUV determined from the Neutral Particle Imager (NPI) on MEX, illustrates the influence of solar EUV forcing. On the basis of this we conclude that changes in solar wind-and solar XEUV forcing governs the variable ion escape from Mars. Both forcing terms appear to be equally important for the escape rate. Considering the difference in travel time for XEUV and the solar wind to Mars, the XEUV effect will precede the solar wind effect by several (3 -9) days. Citation: Lundin, R
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.
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