Two Types of Coronal Bright Points in the 24-th Cycle of Solar Activity

Two Types of Coronal Bright Points

in the 24-th Cycle of Solar Activity

Chori T. Sherdanov, Ekaterina P. Minenko, A.M. Tillaboev, Isroil Sattarov.

Abstract We applied an automatic program for identification of coronal bright 5

points (CBPs) to the data obtained by SOHO/EIT observations taken at the 6

wavelength 195 °A, in the time interval from the end of the 23rd to the early 24th 7

solar cycle.We studied the total number of CBPs and its variations at the beginning 8

of the given cycle of solar activity, so that the development of the solar activity 9

could be predicted with the use of CBPs. For a primary reference point for the 24th 10

solar cycle, we took the emergence of a high-latitude sunspot with the reversed 11

polarity, which appeared in January, 2008. We show that the observed number of 12

CBPs reaches the highest point around the minimum of the solar activity, which in 13

turn may result from the effect of visibility. The minimum solar activity at this time 14

provides the opportunity to register the number of CBPs with the highest accuracy, 15

with its uniform latitudinal distribution. We also study the properties of CBPs in a 16

new 24th cycle of solar activity. It is shown that variations in the cyclic curve of 17

the number of coronal bright points associated with variations in the solar activity, 18

for the latitudes of the quiet Sun to be anticorrelation characteristic changes in the 19

number CBPs to the solar activity, and the observational data are for the regions of 20

active formations on the Sun almost identical on character on the equatorial latitude, 21

but this have lightly expressed character in high-latitude zone. To explain the cyclic 22

curves of variation in the number of coronal bright points in connection with the 23

AQ1 C.T. Sherdanov (_) _ I. Sattarov

Astronomical Institute AS of Uzbekistan, 33 Astronomical str., Tashkent 100052, Uzbekistan

Tashkent State Pedagogical University, 103 Yusuf Khos Khojib Street, Tashkent 100100,

Uzbekistan

E.P. Minenko

Astronomical Institute AS of Uzbekistan, 33 Astronomical str., Tashkent 100052, Uzbekistan

V.N. Obridko et al. (eds.), The Sun: New Challenges, Astrophysics and Space

Science Proceedings 30, DOI 10.1007/978-3-642-29417-4 18,

© Springer-Verlag Berlin Heidelberg 2012

C.T. Sherdanov et al.

solar cycle in different latitudinal zones, we suggest a hypothesis of the existence of 24

two types of coronal bright points: those associated with the quiet corona and those 25

related to active formations. 26

1 Introduction 27

Bright X-ray points (XRTs, or coronal bright points, CBPs)—see their identification 28

AQ2 29

temperature about 2–4 millionK and the average lifetime between 8 h and 2 days 30

31

small (less than 60 arcsec in diameter) to have been discovered with the previous 32

generation of X-ray telescopes. Later, the coronal bright points were also identified 33

with the extreme ultraviolet telescope (EIT/SOHO) and called EIT bright points or 34

EUV bright spots, according to the wavelength at which they were observed. Bright 35

points are recorded in the photosphere, in the corona, and in the transition zone 36

37

Bright points have central cores of approximately 10,000km in diameter and 38

generally occur over the areas of opposite magnetic polarity in the photosphere, 39

when the regions of opposite polarity meet and destroy each other, releasing energy 40

41

formations can also occur when a newly emerging magnetic field interacts with the 42

existing magnetic field in the corona, again with the release of magnetic energy, 43

which heats the gas. Being short-lived, transient objects, they are distributed almost 44

evenly over all latitudes [2], and are observed in the equator, in active and quiet 45

regions, and in coronal holes. 46

Despite the fact that the bright points have been studied both theoretically and 47

observationally, numerous questions related to the formation of these bright spots 48

in the lower corona (or rather in the transition zone between the chromosphere and 49

corona) still remain unanswered. For example, it is still unclear how these structures 50

emit energy and what is their role in the formation of the solar activity and solar 51

radiation, whether they have a pronounced magnetic field, whether the effect of 52

visibility is the only mechanism responsible for the anticorrelation of CBPs figures 53

and sunspots, how the transients evolve, what is their connection with the corona 54

heating and solar wind, etc. 55

The Sun, as a magneto-active star, has a strong magnetic field which, on average 56

and on a large scale, is described as a magnetic dipole. The axis of this dipole 57

changes its direction to opposite approximately every 11 years, which corresponds 58

to the 11-year cycle of the solar activity; in turn, it is reflected in the sunspot cycle 59

measured by the Wolf numbers. 60

Based on the data from SOHO, we constructed a curve of solar activity for 61

the time interval from 1996 to 2011 (see Fig. 1). In the course of observations in 62

Tashkent, the first appearance of a high-latitude spot was recorded on November 3, 63

2008 in the northern hemisphere, which indicates the beginning of the 24th solar 64

Two Types of Coronal Bright Points in the 24-th Cycle of Solar Activity

Fig. 1 Solar activity from

1996 to early 2011

cycle. The diagram (Fig. 1) shows that the second observed minimum of the 23rd 65

solar cycle occurred at the end of 2008–2009, which yields the length of the cycle 66

of about 13 years. The dynamics of the observed variations in the cycle and the 67

comparison with the cyclic changes in the curves of CBPs for different latitudes can 68

indicate not only the degree of the dependence of the CBPs phase on the phase of 69

the solar activity cycle, but also will make it possible to hypothetically forecast the 70

subsequent likelihood in the development of the further cycle. 71

2 Observations and Data Analysis 72

In this study, we use a series of data (an average of four images per day) obtained 73

from the extreme ultraviolet telescope EIT installed on board of SOHO mission. The 74

data were taken at the wavelength 195 °A from the 23rd to the beginning of the 24th 75

solar cycle. The data were obtained using an automatic program for identification of 76

coronal bright points (CBPs); the cyclic curves for different latitudes are constructed 77

on the basis of these data.We studied the distribution of coronal bright points on the 78

solar disk for different latitudes, for the quiet Sun and for active regions on the Sun, 79

in order to identify patterns of variations in the 23rd—the beginning of 24th cycles 80

of solar activity and to predict the nature of the cycle development. 81

We plotted the curves of the cyclic changes in the number of CBPs for the quiet 82

Sun (QS) and for active regions of the Sun (AS) at different latitudes, to detect a 83

connection with the cycle of solar activity (SA), processing the data derived from 84

the images at the wavelength of 19.5 nm (EIT/SOHO) within the time interval 1996– 85

2010. The hypothesis of the existence of two types of CBPs is discussed in more 86

detail in the studies of Golub et al. AQ3 [1] and Sattarov et al. (2010) [8]. 87

The diagrams in Fig. 2 show the cyclic curves of the variation in the number of 88

CBPs: a curve of the total number of CBPs and of the numbers in three latitude 89

C.T. Sherdanov et al.

zones, at the equator between C5ı and _5ı, in the zone of active formations (˙ j 90

25ı _ 35ı j), and at high latitudes (˙ j 45ı _ 55ı j). For the sake of clarity, the 91

curves are compared with the total variation in the CBPs number, for the quiet and 92

active Sun, respectively. It is clearly seen that the variation in the number of CBPs at 93

different latitudes has a different character depending on the variation in the phase 94

of the solar activity. Thus, in the zone of active regions and at the equator, variations 95

in the total number of CBPs (Fig. 2, column GN) do not show a significant link with 96

the solar activity cycle, whereas at the high latitude zone the anticorrelation between 97

the number of CBPs and the phase of solar activity is clearly seen. This result will 98

be discussed below.When the data for the total width of the Quiet Sun (QS) and for 99

active regions in the Sun (AS) are separated, another pattern is seen: in this case, 100

correlation is observed only at high latitudes. 101

The analysis of the cyclic curves showed the decline in the total cyclic curve for 102

the CBPs (Fig. 2 GN-a–d) in 1998 and 1999. This decline is noted at the equator and 103

visible for the active regions. The solar activity grew steadily to its maximum in the 104

early 2000–2001, without sharp peaks. There was a sharp drop in the solar activity 105

in the 23rd cycle in 2001 followed by an increase in 2002 (the difference was about 106

2 years).

Two Types of Coronal Bright Points in the 24-th Cycle of Solar Activity

For the cyclic curve of the total number of CBPs in high-latitude areas (Fig. 2 108

GN, d) a reverse relationship with the cycle of solar activity is observed; the number 109

of CBPs was in anticorrelation with variations in the solar activity. 110

It should be noted that the number of CBPs varies with the solar activity, and 111

the cyclic curve of CBPs not only displays a distinct two-humped pattern, but also 112

shows anticorrelation between the number of CBPs and the cycle of solar activity at 113

all latitudes of the quiet Sun. The tendency of the cyclic curve of CBPs on the quiet 114

Sun to form the double-hump shape is seen for the equator, in active regions, and at 115

high latitudes. For high-latitude zones of solar activity, this trend is not typical. Also 116

the AS and QS’s cyclic curves more clearly display the solar activity minimum 117

in 2009, while on the curve of solar activity (Fig. 1) the minimum value can be 118

traced from the end of 2008 to the middle 2009. Also can be more clearly observe 119

of the solar activity minimum in 2009 on the AS and QS’s cyclic curves of the 120

number CBPs, while on the curve of solar activity (Fig. 1) the period of solar activity 121

minimum can be traced with the end of 2008 to the middle 2009. 122

The cyclic curve of the CBPs on the active Sun is more or less consistent with 123

the solar activity phases (see Fig. 2 GN, a), with the only difference in the graph 124

of the total number CBPs in the cyclic curve AS (Fig. 2, AS, a), which shows a 125

small but rather sharp jump in the number of CBPs from mid-1997 to early 1998; 126

the SA curve during this period displays a more uniform growth. At the equator, the 127

maximum number of CBPs is seen only in 2001–2002, and an increase in the CBPs 128

number begins only in 2000, while the growth of the 23rd solar activity cycle starts 129

at the beginning of 1998 and reaches its peak in 2000 (with the delay of about 2 130

years). The equator is characterized by a broad profile of the cyclic curve of CBPs 131

for both the active and quiet Sun. 132

133

The following conclusions can be made from the study: 134

• Variations in the number of CBPs during a solar cycle cannot be explained only 135

by the effect of visibility for the equatorial and high latitudes. 136

• The number of CBPs at different latitudes varies differently, depending on the 137

phase of solar activity. 138

• To explain the cyclic curve of variations in the number of coronal bright points 139

in connection with the solar cycle in different latitude zones, we suggest the 140

hypothesis of the existence of two types of coronal bright points: those connected 141

to the quiet corona and to active formations. 142

• The difference between the numbers of coronal bright points in the years of the 143

minimum and maximum of the solar activity for the same latitude is different 144

for the quiet and active Sun, and one can trace the following relationship: the 145

Quiet Sun displays an inverse relationship, with the double-humped shape of 146

the distribution, and with the number of CBPs in anticorrelation with the cycle 147

C.T. Sherdanov et al.

of the solar activity; in the Active Sun’s regions, the variations of the number of 148

CBPs almost correspond to those of the solar activity cycle. 149

• Regarding the SA curve, we can forecast the development of the next peak in the 150

late 2012–early 2013. A more detailed analysis and conclusions, with more data 151

obtained for 2 years to provide further CBP analysis will confirm our hypothesis. 152

• Our suggested determination of the solar activity using cyclic curves and two 153

types of CBPs (AS and QS) describes more clearly the phase of the cycle in the 154

corona. 155

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