Doktorski seminar - Akshay Kumar Remeshan

O B A V I J E S T

AKSHAY KUMAR REMESHAN

održat će znanstveni kolokvij (doktorski seminar) iz Astrofizike pod naslovom:

Interaction of High-Speed Solar Wind Flows and Interplanetary Coronal Mass Ejections

A Coronal Mass Ejection (CME) is a violent eruption of magnetoplasma from the Sun. As it propagates through the Heliosphere it can interact with high-speed solar wind streams (HSS), potentially altering its magnetic and plasma properties. Where the interaction occurs in the heliosphere might affect how much the CME properties are altered. To study this, we develop a fast, analytical, two-step Drag-Based Model (DBM) using a case study to identify where along the Sun-Earth line the interaction occurs. We next establish a sample of 28 CME-HSS interaction events and characterise the interaction signatures at 1 au through a statistical analysis. We examine two classes of interactions at 1 au: CMEs seen in front of the HSS and CMEs seen behind the HSS. We find that HSS catching up to ICMEs tends to accelerate them from behind. In contrast, HSS in front of ICMEs does not significantly alter the typical speed-expansion profiles but tends to inhibit sheath formation. Regions of the CME partially engulfed by the HSS seem to be kinematically affected the most. Next, we apply the 2-Step DBM to the compiled sample to derive the interaction point in the Heliosphere. Furthermore, we analyse two benchmark events from each interaction class using Heliospheric magnetohydrodynamical model EUHFORIA (European Heliospheric Forecasting Information Asset) coupled with the CME Cone model to probe the global nature of the interaction in 3D space. While we generally do not find a significant relation between where in the Heliosphere the interaction takes place and specific in situ signatures of the interaction, finding such relation seems to be heavily hampered by the observational uncertainties. We conduct a sensitivity analysis of the 2-step DBM to assess the method's feasibility. In general, we find that ICMEs interacting with HSS show distinct speed profiles depending on whether HSS is in front of or behind. The two-step method is found to be feasible for identifying interaction regions when a slow CME interacts with a fast HSS and most of such interactions happens close to Earth. In addition, we find that because the CME Cone model lacks embedded magnetic structure, it does not model interaction scenarios where the CME is in front of the HSSs realistically. In general, we identify distinct signatures for CMEs observed ahead of and behind the HSS at 1 au. However, the two-step DBM is applicable only to interactions between fast HSSs and slow CMEs and cannot be applied to other interaction scenarios. This limitation prevents us from drawing broader statistical conclusions about the relationship between the location of the interaction and the observed signatures at 1 au in the general case.

Seminar će se održati u četvrtak, 22. listopada 2026. godine u 10:00 sati u predavaonici F-201 Fizičkog odsjeka Prirodoslovno-matematičkog fakulteta Sveučilišta u Zagrebu.
Pozivaju se studenti doktorskog studija Fizike, smjer Astrofizika, da prisustvuju seminaru, ako nisu spriječeni.

Voditelj smjera:

Prof. dr. sc. Vernesa Smolčić, v.r.