4 research outputs found
Distinct polytropic behavior of plasma during ICME-HSS Interaction
Interplanetary Coronal Mass Ejections (ICMEs) and High Speed Streams (HSSs)
are noteworthy drivers of disturbance of interplanetary space. Interaction
between them can cause several phenomena, such as; generation of waves,
enhanced geo-effectiveness, particle acceleration, etc. However, how does
thermodynamic properties vary during the ICME-HSS interaction remain an open
problem. In this study, we investigated the polytropic behavior of plasma
during an ICME-HSS interaction observed by STEREO and Wind spacecraft. We find
that the ICME observed by the STEREO-A has polytropic index ,
i.e., exhibiting isothermal process. Moreover, Wind spacecraft observed the HSS
region, non-interacting ICME, and ICME-HSS interaction region. During each
regions we found =1.8, =0.7, and =2.5, respectively. It
implies that the HSS region exhibits a nearly adiabatic behaviour, ICME region
is closely isothermal, and the ICME-HSS interaction region exhibits
super-adiabatic behaviour. The insufficient expansion of the ICME due to the
interaction with HSS triggers the system for heating and cooling mechanisms
which dependent on the degrees of freedom of plasma components
Observation of Alfven wave in ICME-HSS interaction region
The Alfv\'en wave (AW) is the most common fluctuation present within the
emitted solar wind from the Sun. Moreover, the interaction between
interplanetary coronal mass ejection (ICME) and high-speed stream (HSS) has
been observed on several occasions. However, can such interaction generate an
AW? What will be the nature of AW in such a scenario remains an open question.
To answer it, we have investigated an ICME-HSS interaction event observed on
21st October 1999 at 1 AU by Wind spacecraft. We have used the Wal\'en test to
identify AW and estimated Elsasser variables to find the characteristics of the
AWs. We explicitly find that ICME were dominant with Sunward AWs, whereas the
trailing HSS has strong anti-Sunward AW. We suggest that the ICME-HSS
interaction deforms the MC of the ICME, resulting in the AWs inside the MC. In
addition, the existence of reconnection within the ICME early stage can also be
the leading cause of the origin of AW within it
First analysis of in-situ observation of surface Alfv\'en waves in ICME flux rope
Alfv\'en waves (AWs) are inevitable in space and astrophysical plasma. Their
crucial role in various physical processes, occurring in plasma, has triggered
intense research in solar-terrestrial physics. Simulation studies have proposed
the generation of AWs along the surface of a cylindrical flux rope, referred to
as Surface AWs (SAWs); however the observational verification of this distinct
wave has been elusive to date. We report the first \textit{in-situ} observation
of SAWs in an interplanetary coronal mass ejection flux rope. We apply the
Wal\'en test to identify them. The Elsa\"sser variables are used to estimate
the characterization of these SAWs. They may be excited by the movement of the
flux rope's foot points or by instabilities along the plasma magnetic cloud's
boundaries. Here, the change in plasma density or field strength in the
surface-aligned magnetic field may trigger SAWs
Statistical Study of Geo-Effectiveness of Planar Magnetic Structures Evolved within ICME’s
Interplanetary coronal mass ejections (ICME) are large-scale eruptions from the Sun and prominent drivers of space weather disturbances, especially intense/extreme geomagnetic storms. Recent studies by our group showed that ICME sheaths and/or magnetic clouds (MC) could be transformed into a planar magnetic structure (PMS) and speculate that these structures might be more geo-effective. Thus, we statistically investigated the geo-effectiveness of planar and non-planar ICME sheaths and MC regions. We analyzed 420 ICME events observed from 1998 to 2017, and we found that the number of intense (−100 to −200 nT) and extreme (−200 nT) geomagnetic storms are large during planar ICMEs (almost double) compared to non-planar ICMEs. In fact, almost all the extreme storm events occur during PMS molded ICME crossover. The observations suggest that planar structures are more geo-effective than non-planar structures. Thus, the current study helps us to understand the energy transfer mechanism from the ICME/solar wind into the magnetosphere, and space-weather events