Zubair Shaikh | Indian Institute of Geomagnetism (original) (raw)

articles by Zubair Shaikh

$Research paper thumbnail of Co-existence of Planar Magnetic Structure and Alfv{\'e}n wave in ICME shock-sheath \& associated Geomagnetic storm$

$Research paper thumbnail of Concurrent effect of Alfv{\'e}n waves and planar magnetic structure on geomagnetic storms$

$Research paper thumbnail of Coexistence of a planar magnetic structure and an Alfv{\'e}n wave in the shock-sheath of an interplanetary coronal mass ejection$

Papers by Zubair Shaikh

arXiv: High Energy Astrophysical Phenomena, Aug 12, 2016

The sudden short duration decrease in cosmic ray flux is known as Forbush decrease which is mainl... more The sudden short duration decrease in cosmic ray flux is known as Forbush decrease which is mainly caused by interplanetary disturbances. A generally accepted view is that the first step of Forbush decrease is due to shock sheath and second step is due to magnetic cloud (MC) of interplanetary coronal mass ejection (ICME). This simplistic picture does not consider several physical aspects, such as, whether the complete shock-sheath or MC (or only part of these) are contributing to the decrease, what effect does the internal structure within the shock-sheath region / MC have on the decrease, etc. We present a summary of the analysis of a total of 18 large (≥ 8%) Forbush decrease events and the associated ICMEs, a majority of which show multiple steps in the Forbush decrease profile. We propose a re-classification of Forbush decrease events depending upon the number of steps observed in their respective profile, and the physical origin of these steps. Our analysis clearly indicates that not only broad regions (shock-sheath and MC), but also localized structures within the shock-sheath and MC, have a very significant role in influencing the Forbush decrease profile. The detailed analysis in the present work is expected to contribute toward understanding the relationship between FD and ICME parameters in better way.

The Forbush decrease (FD) and Geomagnetic storm (GS) are the two distinct space weather events ha... more The Forbush decrease (FD) and Geomagnetic storm (GS) are the two distinct space weather events having common causing agents like interplanetary coronal mass ejection (ICME) or corotating interacting region (CIR). Generally, an ICME causes high amplitude FDs and extreme GSs. However, the interlinks between extreme GS and strong FDs are poorly studied. Here, we demonstrate five ICME induced extreme storms and their effects on respective FD profiles. We observed the sudden storm commencement of the GS coincides with the FD onset. Interestingly, we also noted a gradual increase in neutron counts during the main and recovery phases of GS. The maximum enhancement in neutron counts coincides with the minimum value of the Sym-H index. The enhancement is visible primarily in all the neutron monitors but significantly pronounced in high-energy neutrons compared to low-energy neutrons. The weakening of Earth’s magnetic shield due to ICME-Magnetosphere interaction allows more cosmic rays to rea...

The dynamic processes of magnetic reconnection and turbulence cause magnetic islands/flux-ropes g... more The dynamic processes of magnetic reconnection and turbulence cause magnetic islands/flux-ropes generation. The in-situ observations suggest that the coalescence or/and contraction of magnetic islands are responsible to the charged particle acceleration (keV to MeV energy range). Numerical simulations also support this acceleration mechanism. However, the most fundamental question raise here is, does this mechanism contribute to the cosmic rays acceleration? To answer this, we report, in-situ evidence of flux-ropes formation, their magnetic re-connection and its manifestation as cosmic ray (GeV charged particle) acceleration in interplanetary counterpart of coronal mass ejection(ICME). Further, we propose that cosmic ray (high and/or ultra-high energy) acceleration by Fermi mechanism is valid not only through stochastic reflections of particles from the shock boundaries but also through the boundaries of contracting magnetic islands or/and their merging via magnetic re-connection. T...

The dynamic evolution of coronal mass ejection (CME) in interplanetary space generates highly tur... more The dynamic evolution of coronal mass ejection (CME) in interplanetary space generates highly turbulent, compressed and heated shock-sheath. This region furnishes a unique environment to study the turbulent fluctuations at the small scales and serve an opportunity for unfolding the physical mechanisms by which the turbulence is dissipated and plasma is heated. How does the turbulence in the magnetized plasma control the energy transport process in space and astrophysical plasmas is an attractive and challenging open problem of the 21st century. The literature discusses three types of incompressible magnetohydrodynamics (MHD) shocks as the magnetosonic (fast), Alfvenic (intermediate), and sonic (slow). The magnetosonic shock is most common in the interplanetary medium. However, Alfvenic shocks have not been identified till date in interplanetary space. In fact, the questions were raised on their existence based on the theoretical ground. Here, we demonstrate the first observable in-s...

arXiv: High Energy Astrophysical Phenomena, Aug 12, 2016

The Astrophysical Journal, 2018

A Forbush decrease is a sudden decrease in cosmic-ray intensity caused by transient interplanetar... more A Forbush decrease is a sudden decrease in cosmic-ray intensity caused by transient interplanetary disturbances. The substructure of an interplanetary counterpart of a coronal mass ejection (ICME) such as a shock sheath and/ or a magnetic cloud independently contributes to cosmic-ray decrease, which is evident as a two-step decrease. Our earlier work has shown multistep decrease and recovery within the ICME-driven shock-sheath region. Further, we have suggested that the presence of a small-scale flux rope within the shock-sheath region causes a steady/gradual recovery in cosmic-ray intensity. Here, we demonstrate the presence of a planar magnetic structure (PMS) and small-scale flux rope within a single shock sheath of an ICME. The plot of the elevation (θ) versus azimuthal (f) angle of the interplanetary magnetic field (IMF) is used for the identification of the PMS. The planarity, efficiency, and a plane-normal vector are estimated by employing a minimum variance analysis (MVA) technique, which confirmed the presence of the PMS. In addition, a 2D-hodogram method in conjunction with the MVA technique is utilized to identify the flux-rope structure and turbulent conditions in the corresponding ICME region. The observation in the visible suggests that the PMS region within the ICME shock sheath caused the decrease in the cosmic-ray flux observed at Earth. It has also been observed that the sharp variations in the IMF (i.e., turbulence) cause a decrease, whereas the flux-rope structure is responsible for the recovery of the CR flux. Further studies are needed to investigate their origins and to confirm their effects on space weather.

Solar Physics, 2017

Physical Review D, 2020

The interplanetary counterpart of coronal mass ejections (ICMEs) and the interaction regions of s... more The interplanetary counterpart of coronal mass ejections (ICMEs) and the interaction regions of slowfast solar wind (CIRs) have both been known as potential drivers of Forbush decrease (FD). However, reported studies often take an independent approach for investigating FD caused by ICMEs and CIRs, since both the structures show different signature in in-situ observations. In this paper, we explore the common origin of the FD profile caused by these two large scale structures, within the framework of a diffusionconvection model. As a case study, we present one event of each type, in both of which, the solar wind is the most prominent driver. Possible extensions of this model could incorporate other parameters such as magnetic field strength, turbulence, etc which influence the observed FD features. This attempt could help to resolve the complex problem of the diversity in observed FD profiles.

The Astrophysical Journal, 2017

The transient interplanetary disturbances evoke short time cosmic ray flux decrease which is know... more The transient interplanetary disturbances evoke short time cosmic ray flux decrease which is known as Forbush decrease. The traditional model and understanding of Forbush decrease suggest that the substructure of interplanetary counterpart of coronal mass ejection (ICME) independently contributes in cosmic ray flux decrease. These substructures, shock-sheath and magnetic cloud (MC) manifest as classical two-step Forbush decrease. The recent work by Raghav et al (2016a) has shown multi-step decreases and recoveries within shock-sheath. However, this can not be explained by ideal shock-sheath barrier model. Further, they suggested that the local structures within the ICME's sub-structure (MC and shock sheath) could explain this deviation of FD profile from the classical FD. Therefore, present study attempts to investigate the cause of multi-step cosmic ray flux decrease and their respective recovery within shock-sheath in detail. 3D-hodogram method has been utilized to get more details of the local structures within the shock-sheath. A 3D-hodogram method unambiguously suggests the formation of small scale local structures within the ICME (shock-sheath and even in MC). Moreover, the method could differentiate the turbulent and ordered Interplanetary Magnetic Field (IMF) regions within the substructures of ICME. The study explicitly suggests that the turbulent and ordered IMF regions within shock-sheath do influence cosmic-ray variations uniquely.

The Astrophysical Journal