A lot of efforts have been made to find out the possible origin of the ‘high amplitude anisotropic wave trains’ of enhanced diurnal variation of cosmic rays and to develop a suitable realistic theoretical model, which can explain the different harmonics in individual days. The main objective of this work is to study the first three harmonics of high amplitude wave trains of cosmic ray intensity over the period 1981-1994 for Deep River neutron monitoring station and their association with different solar and interplanetary transients. The amplitude of all the three harmonics (diurnal/semi-diurnal/tri-diurnal) of HAE events significantly remains quite high and statistically constant as compared to the annual average amplitude for majority of the events, whereas the time of maximum significantly shifts towards earlier hours for first harmonic and towards later hours for second and third harmonic as compared to the co-rotational direction for majority of the events. The occurrence of HAE events is dominant, when the value of interplanetary magnetic field (B) remains in the range (4 -10 nT); the product Ap x Dst remains negative only the ion density remains 20. It is noteworthy that the occurrence of high amplitude day is dominant during solar activity minimum years (1986-87) and solar activity maximum years (1991-92). The amplitude as well as time of maximum of the cosmic ray diurnal anisotropy is positively correlated to the sunspot numbers during HAEs.
Table of Contents
1. INTRODUCTION
2. Analysis of Data:
2.1 Harmonic Analysis:
2.2 Trend Correction:
2.3 Mode of Analysis:
2.4 Criteria for selection of events
3 RESULTS AND DISCUSSION
4 CONCLUSIONS:
Objectives and Research Focus
The primary objective of this study is to analyze the first three harmonics of high amplitude cosmic ray intensity wave trains (HAE) recorded at the Deep River neutron monitoring station between 1981 and 1994 and to investigate their association with solar and interplanetary transients.
- Investigation of diurnal, semi-diurnal, and tri-diurnal harmonics of cosmic ray intensity.
- Evaluation of high amplitude anisotropic wave train (HAE) events in relation to solar cycle activity.
- Statistical correlation between cosmic ray modulation and interplanetary magnetic field (B) variables.
- Analysis of the relationship between cosmic ray diurnal anisotropy phase shifts and geomagnetic (Ap x Dst) indices.
Excerpt from the Book
2.4 Criteria for selection of events
Using the long-term plots of the cosmic ray intensity data as well as the amplitude observed from the cosmic ray pressure corrected hourly neutron monitor data using harmonic analysis the High amplitude wave train events (HAE) have been selected on the basis of following criteria:
• High amplitude wave train events of continuous days have been selected when the amplitude of diurnal anisotropy remains higher than 0.4% on each day of the event for at least five or more days.
• In the selection of these types of events, special care has been taken, i.e. if there occurred and pre-Forbush decreases or post-Forbush decrease before or after the event or the event is in recovery phase or declining phase are not considered.
On the basis of above selection criteria we have selected 38 high amplitude wave train events during the period 1981-94. The hourly cosmic ray intensity data for Deep River neutron monitoring station [Geog. Lat. 46.10 (Deg.), Geog. Long. 282.50 (Deg.), Vertical cut off rigidity 1.02 (GV)] has been investigated in the present study.
Annual average values have been taken as a reference line for all the respective HAE events.
Summary of Chapters
1. INTRODUCTION: Provides a background on cosmic ray intensity variations, the co-rotational concept, and the limitations of previous studies in explaining abnormally large amplitude events.
2. Analysis of Data: Details the Fourier analysis process used to derive amplitudes and phases, the mathematical trend correction methods, and the strict selection criteria for identifying 38 distinct HAE event periods.
3 RESULTS AND DISCUSSION: Examines the statistical trends of the first three harmonics, comparing HAE event data against annual averages and correlating results with interplanetary magnetic fields and sunspot activity.
4 CONCLUSIONS: Summarizes the key findings, including the constant high amplitude of HAE events and the specific correlations found between cosmic ray anisotropy and interplanetary/solar parameters.
Keywords
cosmic ray, diurnal anisotropy, semi-diurnal anisotropy, tri-diurnal anisotropy, solar wind, interplanetary magnetic field, HAE events, geomagnetic activity, Deep River neutron monitor, Fourier analysis, solar cycle, sunspot numbers, modulation, Ap index, Dst index
Frequently Asked Questions
What is the core subject of this research document?
The work focuses on the modulation of cosmic ray intensity and the phenomenon of High Amplitude Anisotropic Wave Train (HAE) events, specifically analyzing how these events fluctuate over time in relation to solar activity.
What are the central thematic areas?
The document covers the analysis of cosmic ray harmonics, the influence of the interplanetary magnetic field (IMF), solar cycle dynamics, and the impact of geomagnetic indices on high-amplitude cosmic ray occurrences.
What is the primary objective of this research?
The primary goal is to study the first three harmonics of HAE events (1981-1994) to understand their origin, their statistical behavior compared to annual averages, and their association with solar-interplanetary transients.
Which scientific method is utilized?
The researchers employ Fourier analysis to determine the amplitude and phase of diurnal, semi-diurnal, and tri-diurnal variations, alongside statistical correlation analysis to check relationships with environmental parameters.
What topics are covered in the main body?
The main body details the data preparation including trend corrections, the specific criteria for selecting 38 representative HAE events, and a thorough discussion of the results linking phase shifts to solar and geomagnetic variables.
Which keywords define this work?
Key terms include cosmic ray, diurnal anisotropy, interplanetary magnetic field, HAE events, solar wind, and geomagnetic indices like Ap and Dst.
How is the interplanetary magnetic field correlated with these events?
The study finds that the amplitude of second and third harmonics increases with the interplanetary magnetic field (B), and that HAE event occurrence is dominant when the value of B is in the 4-10 nT range.
What is the significance of the (Ap x Dst) index in this study?
The researchers observed that the (Ap x Dst) index remains consistently negative for the majority of HAE cases, concluding that this negativity is a significant indicator that had not been previously reported.
How does the solar cycle impact the occurrence of high-amplitude days?
The document illustrates that high-amplitude days are most prevalent during solar activity minimum years (1986-87) and solar activity maximum years (1991-92).
- Citation du texte
- Rajesh Kumar Mishra (Auteur), Dr. Rekha Agarwal (Auteur), 2023, Cosmic ray modulation and interplanetary turbulences, Munich, GRIN Verlag, https://www.grin.com/document/1430666
