Analysis of high altitude ionopause like boundaries observed from LPW on board MAVEN
Abstract
Since late 2014 MAVEN is orbiting at 75$ ^{o}$ inclination elliptical orbit of 4.6 h with periapsis altitude of ~150 km and apoapsis altitude of ~6200 km. It carried a suite of plasma and field instruments namely magnetometer (MAG), Neutral Gas Ion Mass Spectrometer (NGMIS), Langmuir Probe and Waves (LPW) and Solar Wind and Ion Analyser (SWIA). Our main objective is to study the characteristics of ionopause like density gradient within the magnetic pile-up boundary due to solar wind interaction on Mars. We have analysed plasma and magnetic field data of MAG, NGIMS, LPW, and SWIA instruments obtained from nearly 500 orbits of MAVEN passing through the upper ionosphere of Mars between 2017 and 2018. In most of these orbits MAG instrument has observed the bow shock crossings, magnetic pile-up region and cavity boundary. The NGIMS and LPW instruments have observed the ion and electron densities respectively in the both inbound and outbound orbits of the MAVEN within the magnetic pile-up boundary. The solar wind velocity is observed from SWIA instrument. The inbound orbit is from geometric apoapsis to next geometric periapsis in time and outbound orbit is the reverse. In the present paper we have reported that Mars should have mainly three steep ionopause like boundaries: (1) low, (2) mid, and (3) high ionopauses at altitude range 300-400 km, 600-700 km and 1000-1500 km respectively. These measurements demand a source mechanism to understand the physical, chemical and dynamical processes in the upper ionosphere of Mars. It is found that the magnetic pile-up boundary is dominated by the horizontal magnetic field. MAVEN has observed two broad peaks and a drop in this magnetic field region. A steep ionopause like boundary is observed in the dayside ionosphere during the inbound orbit of MAVEN in presence of horizontal magnetic field of high strength, while the nightside ionosphere is observed during the outbound orbit which does not show such a boundary in presence of horizontal magnetic field of low strength. The topside of the dayside ionosphere is magnetically controlled inside the magnetic pile-up boundary. We propose that a precise intensity of horizontal magnetic field can form the ionopause like structure in the upper ionosphere during the daytime if time and location of this magnetic anomaly coincide with the ion and electron density measurements. The nighttime ionosphere is thought to be produced within the magnetic pile-up boundary due to transportation of plasma from dayside to nightside across the terminator by a horizontal plasma flow velocity as has been predicted by the previous studies.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.763H