Galactic Cosmic Ray Variability in the High and Mid Latitudes During Solar Cycles 22 and 23

ABSTRACT Galactic cosmic rays are modulated in the heliosphere primarily due to the global merged interaction regions with intense magnetic field which leads to a decrease in the galactic cosmic rays throughout the heliosphere. Using long term averages of solar wind (SW) component parameters in addition to cosmic ray count rates of two high latitude Neutron monitor stations (Apatity and Thule) and two mid latitude stations (Newark and Tbilisi) with different rigidity cut-offs, we analyzed the effect of these SW components on the counts rates under different interplanetary magnetic field (IMF) disturbance levels. From first order partial correlation, we found that the total interplanetary magnetic field (Total B) was the most dominant modulating parameter especially during quiet conditions and the solar wind dynamic pressure (SWDP) was more effective during disturbed conditions. The influence of the more subtle parameters like solar wind speed (SWS), Z component of IMF (Bz) and solar wind density were masked by these dominant parameters vis IMF (Total B) and SWDP. Also, cosmic ray count rates on these stations studied showed similar annual variation trend, with station of lowest cut-off rigidity having highest amplitude and vice versa, confirming cut-off rigidity as another important modulating factor.

TABLE OF CONTENT

Title Page --------------------------------------------------------------- i

Certification --------------------------------------------------------------- ii

Approval page --------------------------------------------------------------- iii

Dedication --------------------------------------------------------------- iv

Acknowledgement --------------------------------------------------------------- v

List of Tables --------------------------------------------------------------- vi

List of Figures --------------------------------------------------------------- vii

Table of Content --------------------------------------------------------------------- viii

Abstract --------------------------------------------------------------- x

CHAPTER ONE: INTRODUCTION

1.1 Cosmic rays ------------------------------------------------------------- 1

1.2 Types of cosmic rays ------------------------------------------------ 1

1.2.1 Galactic Cosmic ---------------------------------------------------------- 4

1.2.2 Solar Cosmic Rays (SCRs) ------------------------------------------- 5

1.2.3 Anomalous Cosmic Rays (ACRs) -------------------------------------- 5

1:3 Variability of galactic cosmic rays ------------------------------------- 6

1.4 Cosmic ray modulation ------------------------------------------------- 7

1.4.2 Geomagnetic field modulation ----------------------------------------- 9

1.4.3 Solar modulation ------------------------------------------------------- 9

 1:5 Current missions to understand cosmic ray sources and transport ----- 11

 1.5.1 Equations (S) For Cosmic Ray Transport ------------------------------- 11

1.7 Solar activity and the cycles 22 and 23 ----------------------------- 13

1.8 Purpose of study ------------------------------------------------------ 14

CHAPTER TWO: LITERATURE REVIEW

2.1 Recent review literature on day – to – day variability --------------- 15

2.2 Review literature on cosmic ray variability ---------------------------- 16

2.3 Factors affecting cosmic ray production and/or transport ------------- 19

2.4 Solar cycle 22 and 23 ---------------------------------------------------- 21

CHAPTER THREE: SOURCES OF DATA

3.1 Cosmic ray data ----------------------------------------------------------- 23

3.2 Data on solar wind parameters ------------------------------------------ 23

CHAPTER FOUR: METHODS OF DATA ANALYSIS

4.1 Calculation of yearly average ----------------------------------------- 24

4.2 Calculation of percentage variation of yearly average data --------- 25

4.3 Method of analysis for yearly average data ------------------------- 25

CHAPTER FIVE: RESULTS AND DISCUSSION

5.1 Result ----------------------------------------------------------------------- 32

CHAPTER SIX: CONCLUSION

6.1 Conclusions -------------------------------------------------------------- 35

APPENDICES

Appendix i Yearly average for quietest conditions ---------------------------- 36