This work aims to investigate the phenomenon of unusual variations in cosmic ray intensity in the period 1981-1994, particularly in the context of interplanetary magnetic clouds and low-amplitude anisotropic wave trains.
The text provides a detailed analysis of the relationship between low-amplitude anisotropic wave trains and interplanetary perturbations, particularly with respect to changes in cosmic ray intensity. By analysing data from the Deep River Neutron Monitor, the interaction between high solar wind velocities, the orientation of the interplanetary magnetic field and the proton density is highlighted.
Table of Contents
Introduction
Data Analysis
Results and Discussion
Conclusions
Acknowledgements
References
Research Objectives and Topics
The study investigates the variations in cosmic ray intensity during low-amplitude anisotropic wave train events (LAEs) to understand the physical relationship between interplanetary magnetic clouds and cosmic ray flux. It seeks to determine how parameters like solar wind velocity, interplanetary magnetic field (IMF) components, and geomagnetic activity indices correlate with cosmic ray intensity fluctuations before, during, and after the arrival of magnetic clouds.
- The causal role of interplanetary magnetic clouds in cosmic ray intensity variations.
- Analysis of correlations between cosmic ray intensity and solar/interplanetary parameters (Dst, Ap, Bz, IMF B).
- Examination of solar wind velocity and proton density during high-speed stream events.
- Application of the Chree analysis of superposed epoch to quantify the time profile of intensity changes.
- Evaluation of the physical mechanisms, such as turbulent sheaths and field-line configurations, that modulate galactic cosmic rays.
Excerpt from the Book
Introduction
Previously a lot of low amplitude anisotropic wave train events have been observed with a significant shift in the diurnal time of maximum to co-rotational direction or later hours [1 and references therein]. Agrawal and Bercovitch [2] have shown that the direction of the 22-year component is perpendicular to the diurnal anisotropy vector and is along the line 162° east of the Sun-Earh line; they have attributed the 11-year component to the variation of cut-off rigidity. A significant increase is observed in the amplitude of first three harmonics (diurnal/semi-diurnal/tri-diurnal) during the passage of high speed solar wind stream, whereas the direction of the anisotropy have no time variation characteristics associated with solar wind velocity and north south component of interplanetary magnetic field for three neutron monitoring stations located at different geomagnetic cutoff rigidities and altitudes [3].
Interplanetary magnetic clouds belong to one of the several classes of transient flows in the solar wind. Magnetic clouds as ideal force free objects (cylinders or spheres) are ejected near the Sun and followed beyond the Earths orbit. It is found that the decrease in cosmic ray intensity, which are associated with magnetic cloud preceded by a shock, are very high and these decrease starts few days earlier than the arrival of cloud at Earth.
Summary of Chapters
Introduction: This section provides a historical overview of low-amplitude anisotropic wave train events and defines the role of interplanetary magnetic clouds as transient solar wind features that modulate cosmic rays.
Data Analysis: This chapter details the selection criteria for 28 LAEs between 1981 and 1994 and the methodology for processing Deep River Neutron Monitor data using Fourier analysis and the Chree superposed-epoch technique.
Results and Discussion: This section presents the correlation analysis between cosmic ray intensity and solar/interplanetary parameters, demonstrating the relationship between magnetic field orientation, solar wind speed, and intensity dips.
Conclusions: This chapter summarizes the empirical findings, confirming the significant impact of magnetic clouds on cosmic ray intensity and the strong correlations observed between Bz, Dst, and geomagnetic activity.
Keywords
cosmic ray, solar wind, interplanetary magnetic field, magnetic cloud, geomagnetic activity, anisotropic wave train, modulation, Dst index, Ap index, Forbush decrease, neutron monitor, solar wind velocity.
Frequently Asked Questions
What is the primary subject of this research paper?
The work examines the variation of cosmic ray intensity during low-amplitude anisotropic wave train events (LAE) caused by interplanetary magnetic clouds.
What are the central themes discussed in this study?
The central themes include interplanetary disturbances, solar wind plasma parameters, and the modulation mechanisms of galactic cosmic rays.
What is the primary research objective?
The research aims to investigate the physical processes and parameters responsible for unique cosmic ray intensity fluctuations observed during the period 1981–1994.
Which scientific methodology is employed?
The authors utilize Fourier analysis for detrending data and the Chree analysis of superposed epoch to study the impact of interplanetary magnetic clouds on cosmic ray intensity.
What topics are covered in the main section of the paper?
The main section covers data selection criteria, correlation analysis between solar parameters and cosmic ray flux, and the interpretation of magnetic field geometry in relation to intensity decreases.
Which keywords best describe the scientific focus?
Key terms include cosmic ray intensity, magnetic cloud, interplanetary magnetic field, solar wind, and geomagnetic activity.
What role does the Bz component of the IMF play in these events?
The study finds that the north-south component (Bz) often turns southward before the cloud's arrival and stays in that direction, showing a significant correlation with geomagnetic indices.
How is the onset time of cosmic ray intensity decrease related to magnetic clouds?
The authors observe that the decrease does not start exactly at the onset of the cloud but is often triggered by the associated shock front or occurs a few days later.
What is the significance of the 90-hour peak?
Cosmic ray intensity values show a significant enhancement or deviation before and after 90 hours relative to the passage of the magnetic cloud.
Does the solar activity (sunspot number) change significantly during these events?
The study reports that the solar activity, as represented by sunspot numbers, remains relatively constant before and after the onset of the interplanetary magnetic cloud.
- Quote paper
- Rajesh Kumar Mishra (Author), Rekha Agarwal Mishra (Author), 2023, Anisotropic wave train events and interplanetary disturbances, Munich, GRIN Verlag, https://www.grin.com/document/1434252
