Abstract rays, characterized by a slow decrease and

Abstract

For this
investigation consider symmetric cosmic ray intensity decreases

4%,
observed at Oulu super neutron monitor
and we have observed 47 short term symmetric cosmic ray intensity decreases for
the period of 1997-2013, Out
of these 47 events 29 (61.7%) symmetric cosmic rays intensity decreases have
been found to be associated with geomagnetic storms. Further we have found 44 (93.63%) events are associated
with jump in solar wind plasma temperature (JSWT) and 41 (87.23%) events are
associated with jump in solar wind plasma density (JSWD). From the analysis we have
found that the magnitude of symmetric cosmic ray intensity decreases has
positive correlation with the magnitude of geomagnetic storms with correlation
coefficient of 0.09. Further we have found the positive correlation with
correlation coefficients of 0.14 between the magnitude of symmetric cosmic ray intensity
decreases and magnitude of jump in solar wind plasma temperature. Further we
have found the negative correlation with correlation coefficients of -0.15
between the magnitude of symmetric cosmic ray intensity decreases and magnitude
of jump in solar wind plasma density.

Keywords: – cosmic
ray intensity decreases, solar wind plasma disturbances, geomagnetic storms.

Introduction

The
galactic cosmic ray intensity remains constant in time and space outside the
heliosphere, within the heliosphere, due to various dynamical processes
occurring on the sun and extending into interplanetary space, the long term and
short term variation in cosmic ray intensity takes place. There are mainly two
specific types of cosmic ray intensity depressions, namely corotating and symmetric
short term (Fds) decreases, forbush decreases, characterized by a fast decrease
within ~1 day followed by a more gradual nearly exponential recovery over a few
days, have been observed continuously with neutron monitors since the 1950’s.
Recurrent modulations of galactic cosmic rays, characterized by a slow decrease
and a gradual recovery within a period of ~27 days, comparatively, are less
impressive changes in cosmic ray intensity. Since their discovery through
world-wide distribution of ion-chambers, these decreases have been extensively
studied to search for their solar source 5,10, interplanetary structure
responsible 3,4,6,9,12,14,16 and the mechanism(s) playing major role in this
phenomenon 1, 7,19,.The recurrent or corotating decreases in cosmic ray
intensity have been analyzed by several scientists 13,19 it has been found
that these decreases are closely related to coronal holes, corotating
interaction regions. Some other scientists have also studied these variations
with several interplanetary parameters Richardson et al. 15, 17, 18 22 to
identify potential sources and relative role of corotating interaction regions,
high speed streams and heliospheric current sheet in corotating modulation.

Experimental
Data

In
this work monthly and hourly data of oulu super neutron monitor have been used
to determine symmetric cosmic ray decreases. To determine disturbances in solar
wind plasma parameters, hourly data of solar wind plasma temperature and density
has been used, these data has also been taken from omni web data.

Table: –
Symmetric cosmic ray intensity decreases associated with geomagnetic storms and
solar wind parameters.

 

 
 
 
 
 
S. No.

 
 
 
 
 
Date

Symmetric
cosmic ray intensity decreases
 

Geomagnetic
Storms

Jump in solar
wind temperature

Jump in solar
wind density

Onset set time dd 
(hh)

Magnitude%

Onset time dd (hh)

Magnitude in nT

Start time dd (hh)

Maximum Jump time dd (hh)

Magnitude of Jump in Deg. k

Sart time dd (hh)

Maximum Jump time dd (hh)

Magnitude of Jump n/cc

1

06.10.97

06(08)

3

na

na

09(21)

10(02)

20841

10(05)

10(16)

4.8

2

17.11.97

17(12)

6

16(21)

-35

16(17)

16(21)

66089

16(04)

16(09)

8

3

09.12.97

9(12)

3

10(10)

-61

na

na

na

na

na

na

4

06.01.98

6(00)

3

6(15)

-83

06(02)

06(15)

126983

06(13)

06(21)

19.1

5

05.06.98

05(18)

5

06(16)

-49

05(12)

06(01)

89988

04(22)

05(09)

13.4

6

23.10.98

23(12)

4

na

na

23(08)

23(17)

849786

23(01)

23(14)

7.5

7

11.12.98

11(12)

4

na

na

10(14)

10(16)

24850

10(15)

11(06)

18.1

8

05.05.99

5(12)

4

na

na

05(11)

05(19)

109721

15(02)

15(17)

16.6

9

22.05.99

22(18)

4

na

na

22(09)

22(14)

29329

na

na

na

10

12.09.99

12(02)

3

12(09)

-78

12(01)

12(17)

363153

12(03)

12(08)

31.4

11

22.03.00

22(06)

3

na

na

21(23)

22(03)

69823

22(01)

22(11)

52.8

12

12.10.00

12(04)

4

13(00)

-73

11(10)

12(16)

148024

11(05)

11(06)

1.7

13

23.01.01

23(06)

3

23(18)

-53

23(02)

23(11)

230408

23(05)

23(23)

13.8

14

22.07.01

22(18)

3

na

na

22(04)

22(11)

178323

21(23)

22(05)

2.5

15

03.12.01

03(20)

3.5

03(18)

-30

03(06)

03(14)

96635

03(05)

03(06)

3.4

16

27.01.02

27(18)

4

na

na

na

na

na

na

na

na

17

09.04.02

9(12)

4

na

na

08(23)

09(03)

18921

09(08)

10(18)

20.1

18

01.11.02

01(18)

4

na

na

01(14)

01(18)

39058

01(09)

01(15)

7.3

19

09.01.03

9(18)

3

na

na

09(08)

09(14)

27092

09(12)

09(16)

13.1

20

07.04.03

07(12)

4

na

na

07(07)

07(18)

41554

07(04)

08(01)

33.2

21

02.04.04

2(18)

3

3(14)

-113

02(14)

02(18)

55823

na

na

na

22

05.08.05

5(12)

3

6(110

-35

na

na

na

na

na

na

23

09.07.06

9(18)

3

na

na

09(15)

10(01)

95996

09(15)

10(03)

13.8

24

09.11.06

9(12)

3

9(21)

-53

09(11)

10(03)

389111

09(07)

09(18)

31.3

25

17.05.07

17(12)

3

17(12)

-25

17(16)

18(13)

496948

17(15)

18(08)

24

26

05.01.08

5(00)

4

na

na

04(18)

05(17)

433545

04(06)

04(23)

33.5

27

08.02.08

8(12)

3

na

na

08(18)

10(12)

444007

08(22)

10(05)

18.8

28

14.06.08

14(18)

4

14(20)

-31

14(15)

14(22)

722202

14(03)

14(13)

33.7

29

06.11.08

6(21)

3

07(20)

-30

06(21)

07(00)

339848

06(08)

07(00)

21.3

30

22.12.08

22(12)

3

na

na

22(05)

23(15)

268595

21(06)

22(16)

21.3

31

20.01.10

20(06)

3

20(16)

-38

20(08)

20(19)

435945

20(11)

20(16)

27.1

32

14.09.10

14(18)

3

14(15)

-28

14(01)

14(18)

140551

14(03)

14(11)

6.2

33

12.12.10

12(18)

5

13(21)

-22

12(10)

13(06)

196020

11(20)

12(16)

15.7

34

11.04.11

11(6)

3

12(09)

-55

11(05)

11(23)

387351

10(13)

11(16)

49.9

35

10.06.11

10(06)

3

11(02)

-24

11(05)

11(13)

184111

10(06)

10(21)

12.8

36

16.06.11

16(12)

5

na

na

16(07)

17(03)

232993

16(14)

17(13)

5.1

37

23.06.11

23(00)

4

23(04)

-28

22(03)

23(04)

446492

22(03)

22(17)

4.7

38

05.08.11

5(06)

6

05(20)

-111

05(08)

06(16)

999127

05(16)

05(20)

25.9

39

16.09.11

16(12)

3

17(09)

-65

16(23)

17(06)

177546

16(19)

17(03)

28.4

40

21.11.11

21(00)

3

22(01)

-27

10(21)

13(06)

184778

10(19)

11(23)

21.8

41

22.01.12

22(18)

4

22(11)

-71

22(00)

22(08)

256982

22(22)

22(12)

39.1

42

13.02.12

13(12)

4

13(14)

-62

13(05)

13(11)

110272

12(14)

12(18)

22.3

43

18.01.13

18(00)

4

17(15)

-53

18(04)

18(17)

57928

18(00)

18(13)

30.2

44

16.02.13

16(18)

3

17(07)

-35

16(03)

16(19)

150421

16(00)

16(15)

9.8

45

24.04.13

24(18)

3

24(10)

-74

24(07)

24(21)

265436

23(23)

24(06)

30.5

46

24.05.13

24(06)

3

24(18)

-55

24(15)

25(00)

499123

24(12)

24(19)

11.6

47

25.06.13

25(00)

3

na

na

24(08)

25(12)

290257

na

na

na

 

Data Analysis
and Results

The data of
symmetric cosmic ray intensity decreases and associated geomagnetic storms are
listed in table. From the data analysis given in table, we have found 47 total
number of symmetric cosmic ray intensity decreases during the period1997-2013. Out
of these 47 events 29 (61.7%) symmetric cosmic rays intensity decreases have
been found to be associated with geomagnetic storms.

To know the
possible correlation between magnitude of symmetric cosmic ray intensity
decreases and magnitude of associated geomagnetic storms. A scatter plot has
been plotted between magnitude of symmetric cosmic ray intensity decreases and
magnitude of associated geomagnetic storms (Fig.1). The trend line of the
scatter plot shows positive correlation between magnitude of symmetric cosmic
ray intensity decreases and magnitude of associated geomagnetic storms with correlation
coefficient 0.09.

 

Figure1- Shows magnitude symmetric cosmic ray
intensity decreases and magnitude of associated geomagnetic storms for the
period of 1997-2013 showing positive correlation with correlation coefficient
0.09.

Further from the data analysis given in table. It is
observed that we have 47 symmetric cosmic ray decreases out which 44 (93.63%)
symmetric cosmic ray decreases have been found to be associated with jump in
solar wind plasma temperature (JSWT) events.

To know the statistical behavior of symmetric cosmic ray intensity
decreases with jump in solar wind plasma temperature (JSWT) events we have
plotted a scatter diagram between magnitude of symmetric cosmic ray intensity
decreases and magnitude of jump in solar wind plasma temperature (Fig.2). From
the figure it is inferred that, most of the symmetric cosmic ray intensity
decreases of higher magnitudes are associated with such JSWT events having
higher peak value but these two events do not have any fixed proportion, We
have found some symmetric cosmic ray intensity decreases which have higher
magnitude value but they are associated with such JSWT events which have relatively
low magnitude and vice versa.  From the
trend line of the scatter plot, it may be inferred that there is positive correlation
between magnitude of symmetric cosmic ray intensity decreases and peak value of
JSWT events. Statistically calculated co-relation co-efficient is 0.14 between
these two events.

 

Figure2- Shows
scatter plot between magnitude of symmetric cosmic ray intensity decreases and
magnitude of jump in solar wind plasma temperature for the period 1997-2013
showing positive correlation with correlation coefficient 0.14.

 

From the data analysis given in table, it is observed that
out of 47, 41(87.23%) symmetric cosmic ray intensity decreases have been found
to be associated with jump in solar wind plasma density (JSWD) events.

To know the statistical behavior of symmetric cosmic ray
decreases with jump in solar wind plasma density (JSWD) events we have plotted
a scatter diagram between magnitude of symmetric cosmic ray intensity decreases
and magnitude of jump in solar wind plasma density (Fig.3). From scatter plot
it is inferred that, most of the symmetric cosmic ray intensity decreases of
higher magnitudes are associated with such JSWD events having relatively low
magnitude and symmetric cosmic ray intensity decreases which have small
magnitude are associated with such JSWD events which have higher  magnitude but these two events do not have any
fixed proportion. From the trend line of the scatter plot, it may be inferred
that there is negative correlation between magnitude of symmetric cosmic ray
intensity decreases and magnitude of jump in solar wind plasma density.
Statistically calculated co-relation co-efficient is- 0.15 between these two
events.

Figure3- Shows
scatter plot between magnitude of symmetric cosmic ray intensity decreases and
magnitude of jump in solar wind plasma density for the period 1997-2013 showing
negative correlation with correlation coefficient -0.15

Conclusion

From
this investigation in which we consider symmetric cosmic ray intensity
decreases of magnitude

4%,
we found that the some events are associated with geomagnetic storms and most
of events are associated with solar wind plasma parameters which are taken in
to consideration. By the statistical relation between all parameters with
intensity decreases we found the positive correlation excepting solar wind
plasma density parameter. Cosmic rays are responsible for the geomagnetic
storms and other parameters.

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