INVESTIGATION OF THE MARTIAN ATMOSPHERE USING REMOTE SENSING AND IN-SITU MEASUREMENTS

Abstract

This thesis comprises the investigation on the impact of different space weather events on the Martian atmosphere/ionosphere using the datasets from the diverse suite of in-situ and remote-sensing instruments aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Along with MAVEN datasets, the various catalogs, MAVEN science data center, and the NASA space weather database of notifications, knowledge, information (DONKI) have been utilized to select the interplanetary coronal mass ejections (ICMEs), corotating interaction regions (CIRs), and solar flares events at Mars. Primarily, the impact of these different space weather events on the Martian thermospheric-ionospheric system have been examined. These intense solar events inject particle fluxes, and electromagnetic energy in the Martian upper atmosphere, causing a variation in the ionospheric vertical structure, induce energization and alter the dynamics of the ionosphere and induce magnetosphere. In order to address the impact of ICMEs and CIRs, a comprehensive scenario of the Martian dayside and nightside topside ionosphere (above 150 km) has been presented during the passage of ICMEs and CIRs. An attempt has been made to assess whether the ICMEs and CIRs impact the ionosphere with same magnitude or are their impact different. During the declining phase of the solar cycle 24 (2015-2020), 15 ICMEs and 15 CIRs events have been chosen. An extensive analyses have been carried out on the both dayside and nightside profiles of ionospheric species during each of the ICME and CIR events. By analyzing the Martian ionosphere during each ICME and CIR events, those electrons and ions (O+,O+2 ,CO+2 ,NO+,C+,N+, and OH+) profiles have been selected which showed significant differences from the average quiet time periods and lie beyond the standard deviation. Finally, a comparative average analysis has been performed on the both dayside and nightside ionospheric species. A significant difference can be observed in the profiles of the Martian dayside and nightside ionospheric species (O+,O+2 ,CO+2 ,NO+,C+,N+, and OH+) during passage of ICMEs and CIRs in comparison to mean quiet-time profile. The difference is more prominent on the nightside compared to the dayside ionosphere. During CIRs, the nightside ion density is nearly one order of magnitude less (above 250 km) in comparison to ICMEs. The mean peak altitude and density of the lighter ions (O+,C+,N+, and OH+) were at lower altitudes during the CIRs compared to ICMEs. These results suggest that during the declining phase of solar cycle 24, the impact of CIRs on the Martian topside ionosphere is more prominent compared to ICMEs. The depletion observed in the topside ionosphere is attributed to the higher dynamic pressure and IMF during ICMEs and CIRs. During many CIRs, the magnetic lines drape around the planet in the pileup region of Mars and change the orientation such that the oppositely directed magnetic field lines can verge upon with each other. This leads to a reconnection related escape mechanism, eventually reduce the plasma density. The collective role of reconnection related mechanism, convective electric field (-u × B), and J × B force can accelerate and energize topside ionospheric plasma, and eventually, cause a depletion.