MAVEN observations on a hemispheric asymmetry of precipitating ions toward the Martian upper atmosphere according to the upstream solar wind electric field

Abstract

The Mars Atmosphere and Volatile Evolution (MAVEN) observations show that the global spatial distribution of ions precipitating toward the Martian upper atmosphere has a highly asymmetric pattern relative to the upstream solar wind electric field. MAVEN observations indicate that precipitating planetary heavy ion fluxes measured in the downward solar wind electric field (−E) hemisphere are generally larger than those measured in the upward electric field (+E) hemisphere, as expected from modeling. The −E (+E) hemispheres are defined by the direction of solar wind electric field pointing toward (or away from) the planet. On the other hand, such an asymmetric precipitating pattern relative to the solar wind electric field is less clear around the terminator. Strong precipitating fluxes are sometimes found even in the +E field hemisphere under either strong upstream solar wind dynamic pressure or strong interplanetary magnetic field periods. The results imply that those intense precipitating ion fluxes are observed when the gyroradii of pickup ions are estimated to be relatively small compared with the planetary scale. Therefore, the upstream solar wind parameters are important factors in controlling the global spatial pattern and flux of ions precipitating into the Martian upper atmosphere.

Variability of Precipitating Ion Fluxes During the September 2017 Event at Mars

“…According to Leblanc et al (), the precipitating ion flux is highly dependent on the solar zenith angle, on the position of the most intense crustal magnetic field structures, and on the orientation of the convective electric field. Indeed, Hara, Luhmann, Leblanc, Curry, Seki, et al () showed that the intensity of the precipitating ion flux peaked on the hemisphere toward which the E SW field pointed (the −E SW hemisphere). In order to restrict the range of solar zenith angle covered by our sampling, we therefore chose to show only reconstructed precipitating ion flux obtained close to the MSO equator, between −10° and 15° in latitude, that is, corresponding to time intervals when MAVEN is located between 200 and 350 km in altitude during the inbound part of its orbit.…”

“…The MSE angle corresponds to the counterclockwise angle between the vector formed by the latitude and the longitude in MSE of MAVEN during its measurements of the precipitating ion flux and the East MSE direction (MSE longitude equal to +180° and latitude equal to 0°). According to Hara, Luhmann, Leblanc, Curry, Seki, et al (), the precipitating ion flux should reach a maximum around a MSE angle of 270° (ax –E). Indeed, planetary picked up ions should precipitate toward the southern hemisphere (−E) because of the acceleration of the electric field of convection toward this hemisphere.…”

“…The first evidence of heavy ion precipitation during quiet solar wind conditions has been reported by Leblanc et al (), suggesting that atmospheric sputtering must occur almost continuously at Mars. In addition, Hara, Luhmann, Leblanc, Curry, Seki, et al () showed that the precipitating flux can be organized with respect to the orientation of the solar wind convective electric field. Lillis et al () and Edberg et al () also suggested that the precipitating flux should be dependent on other upstream solar wind conditions, such as the solar UV/EUV and the Solar Energetic Particle (SEP) flux, and the dynamic pressure.…”

On Mars's Atmospheric Sputtering After MAVEN's First Martian Year of Measurements

“…As an example, Hara et al (2018) and Hara et al (2017) have shown that large variation of the precipitating flux can be expected in correlation with the solar wind pressure, the orientation of the electric field of convection, and with the presence of crustal magnetic fields. As an example, Hara et al (2018) and Hara et al (2017) have shown that large variation of the precipitating flux can be expected in correlation with the solar wind pressure, the orientation of the electric field of convection, and with the presence of crustal magnetic fields.…”

“…Among these channels, sputtering of the Martian atmosphere by precipitating heavy ions has been identified as one of these potential channels (Luhmann & Kozyra, 1991). Hara et al (2017), analyzing the first 1.5 years of MAVEN measurements, showed that this precipitation is organized with respect to the orientation of the solar wind convection electric field and is dependent on the upstream solar wind conditions. Hara et al (2017), analyzing the first 1.5 years of MAVEN measurements, showed that this precipitation is organized with respect to the orientation of the solar wind convection electric field and is dependent on the upstream solar wind conditions.…”