Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.iki.rssi.ru/people/cosr21.pdf Äàòà èçìåíåíèÿ: Tue Feb 1 16:03:29 2011 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 00:28:49 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ï ï ï ï ï ï ï ï ï ï ï ï ï ï

ISSN 0010 9525, Cosmic Research, 2011, Vol. 49, No. 1, pp. 21­34. © Pleiades Publishing, Ltd., 2011. Original Russian Text © Yu.I. Yermolaev, I.G. Lodkina, N.S. Nikolaeva, M.Yu. Yermolaev, 2011, published in Kosmicheskie Issledovaniya, 2011, Vol. 49, No.1, pp. 24­37.

Statistical Study of Interplanetary Condition Effect on Geomagnetic Storms: 2. Variations of Parameters
Yu. I. Yermolaev, I. G. Lodkina, N. S. Nikolaeva, and M. Yu. Yermolaev
Space Research Institute, Russian Academy of Sciences, Profsoyuznaya st. 84/32, Moscow 117997, Russia E mail: yermol@iki.rssi.ru
Received January 27, 2010

Abstract--We investigate the behavior of mean values of the solar wind's and interplanetary magnetic field's (IMF) parameters and their absolute and relative variations during the magnetic storms generated by various types of the solar wind. In this paper, which is a continuation of paper [1], we, on the basis of the OMNI data archive for the period of 1976­2000, have analyzed 798 geomagnetic storms with Dst ­50 nT and their interplanetary sources: corotating interaction regions CIR, compression regions Sheath before the interplan etary CMEs; magnetic clouds MC; "Pistons" Ejecta, and an uncertain type of a source. For the analysis the double superposed epoch analysis method was used, in which the instants of the magnetic storm onset and the minimum of the Dst index were taken as reference times. It is shown that the set of interplanetary sources of magnetic storms can be sub divided into two basic groups according to their slowly and fast varying char acteristics: (1) ICME (MC and Ejecta) and (2) CIR and Sheath. The mean values, the absolute and relative variations in MC and Ejecta for all parameters appeared to be either mean or lower than the mean value (the mean values of the electric field Ey and of the Bz component of IMF are higher in absolute value), while in CIR and Sheath they are higher than the mean value. High values of the relative density variation sN/N are observed in MC. At the same time, the high values for relative variations of the velocity, Bz component, and IMF magnitude are observed in Sheath and CIR. No noticeable distinctions in the relationships between considered parameters for moderate and strong magnetic storms were observed. DOI: 10.1134/S0010952511010035

1. INTRODUCTION The present work is devoted to continuation of studying the mechanisms of energy transfer from the solar wind into the magnetosphere and of geomagnetic storms excitation. In our previous work [1] we have analyzed, based on our "Catalog of large scale types of solar wind in 1976­2000" [2], the interplanetary sources of 798 magnetic storms with Dst ­50 nT on the basis of the OMNI data archive for the period of 1976­2000. The following large scale types of solar wind were considered as storm sources: 145 magnetic storms were caused by the CIR events, 96 magnetic storms--by Sheath (12 magnetic storms were gener ated by the Sheath before MC, ShMC, and 84 mag netic storms by the Sheath before Ejecta, ShE); 62 magnetic storms were associated with magnetic clouds MC (50 storms being caused by MC with Sheath and 12 by MC without Sheath); 161 magnetic storms were associated with the Ejecta events (115 storms being caused by Ejecta with Sheath, and 46 by Ejecta with out Sheath). The source of remaining 334 magnetic storms (i.e., 42 % of 798 storms) occurred to be unde termined, mainly because of the absence of a complete set of measurements for separate time intervals in the OMNI database. Unlike our previous studies [3­5], in which we have used the superposed epoch analysis
21

(SEA) method with the reference time (the epoch time) at the storm onset or at the Dst index minimum, in the above mentioned work [1] the double super posed epoch analysis method was used for the analysis. In this technique both time instants were simulta neously taken as reference times, namely, the instants of magnetic storm onset and Dst index minimum, and the durations of main phases of all magnetic storms were changed in such a manner, that they should become equal. This allowed us to investigate the dynamics of parameters for storms with various dura tions of the main phase. Using this technique, we have analyzed the time behavior of some parameters of the solar wind, interplanetary magnetic field (IMF), and magnetospheric indices during the magnetic storm's main phase, this being done separately for various large scale types of the solar wind. It was noted in many works, that the solar wind had essentially turbulent character (see, e.g., the materials of the Solar Wind 12 International Conference held in 2009 [6]), and, therefore, its turbulence influences the magnetospheric disturbance generation processes (see, e.g., reviews and recent papers [7­14], and refer ences therein). For example, Borovsky and Funsten have shown in their paper [10] that the magnetosphere disturbance level, described by various magneto


22

YERMOLAEV et al.

spheric indices, increases with increasing level of fluc tuations of the IMF magnitude and components in the presence of both southward and northward IMF com ponents. In a number of papers (see, e.g., recent papers [11, 13­17] and references therein) it was shown that the magnetic storm development can be influenced, along with the value (or slow changes) of various parameters also by fast variations of these parameters. However, these studies had some drawbacks. First, the variations of IMF magnitude and components have mainly been studied without analyzing the effect of variations of other parameters. Second, the features of various solar wind types were not taken into account, since the analysis was carried out without selecting the data according to such types. We tried to overcome some of these drawbacks in our previous work [4], where we have studied, by the SEA method (with the epoch beginning at the mag netic storm onset), the variations (1 h standard devia tions) of the velocity, temperature, density, and magni tude of IMF for the magnetic storms generated by CIR, Sheath, and ICME. Unlike the previous work [4], in the present paper: 1) we use a more advanced classification of solar wind types including 2 ICME subtypes, namely, MC and Ejecta; 2) we analyze the data according to the double superposed epoch analysis method, as in the previous paper [1]; 3) we study the variations of 12 parameters of the solar wind and IMF; 4) we analyze the conditions for moderate and strong storms separately; 5) we analyze not only the absolute values of varia tions, but relative (i.e., related to the mean values of a corresponding parameter) as well. The time behavior of hourly mean standard devia tions taken from the OMNI database for 1976­2000 [18], is used as initial data in the present paper. 2. METHOD The technique of identification of large scale types of the solar wind was described in detail in our work [2], and it consists in the comparison of each point of the OMNI database with the set of threshold criteria in key parameters of the solar wind and IMF. A solar wind event is supposed to result in a magnetic storm, if the Dst minimum falls inside the event interval or fol lows it within the interval no longer than 2 h. The data for intervals, selected according to solar wind types, have been processed by the superposed epoch analysis method with two checking times (see paper [1] for more details): the time of the magnetic storm onset (time "0") and the time of the Dst index

minimum (time "6"). The time interval from "0" to "6" contains artificially changed durations of events; therefore, in order to distinguish these times from a really measured time, we give them in quotation marks. The first 1 h point of sharp decrease of the Dst index was taken as the magnetic storm "beginning" [3­5]. For all events (intervals) the time scale between these times was divided into 5 subintervals with equal relative duration, and the data in one subinterval were averaged according to the number of points which had fallen into the given subinterval (their number can be different in different subintervals). This procedure implies that, for real data, the time scale in the range between points "0" and "6" changed linearly, but this change was small (for 2/3 of events the duration has changed no more than by 1/3), since the duration of the main phase of a storm equaled 7 ± 4 h, on the aver age [2­5]. The time scale before time "0" and after time "6" remained unchanged, and in these intervals the time is indicated without quotation marks. The advantage of this method is the possibility of compar ison of the dynamics of interplanetary and magneto spheric parameters during the main phase of magnetic storms having different durations. In accordance with the SEA method, the data were processed within the intervals from ­12 to "0" and from "6" to +24, the duration of each interval of the given solar wind type being taken into account. According to our results, the durations of various solar wind types for the 1976­2000 interval were equal to: 20.6 ± 12.2 hours for CIR, 29.8 ± 20.5 for the Ejecta, 28.2 ± 13.4 for MC, and 15.7 ± 10.1 for Sheath [2], and they were close to average durations of these solar wind types, which resulted in magnetic storms [3­5,19]. Therefore, the number of points in the intervals of averaging noticeably decreases (accordingly, the error becomes larger) to the edges of the chosen interval from ­12 to +24, especially for Sheath. The only principal distinction of the present paper from previous one [1] is the fact, that in this paper the variations of plasma and IMF parameters (hourly standard deviations) were analyzed, rather than the parameters themselves. These standard deviations taken from the OMNI database are designated here with symbol s, i.e., sV for velocity, sT for temperature, sN for density, etc. Since the standard deviations for some parameters is not included into the OMNI data base, for them we were compelled, for each hour i, to calculate variations proceeding from the variations of parameters, which appeared in their calculation for mulas and contained in the OMNI database: [s(T/Texp)]i = (T/Texp)i{[(sT)i/Ti)]2 + [2(sV)i/Vi)]2}1/2 for the ratio of the measured proton temperature to the temperature estimated from velocity magnitude, (sPd)i = (Pd)i{[(sN)i/Ni]2 + [2(sV)i/Vi)]2}1/2 for kinetic pressure,
COSMIC RESEARCH Vol. 49 No. 1 2011


STATISTICAL STUDY OF INTERPLANETARY CONDITION EFFECT 2. VARIATIONS

23

(sPt)i = (Pt)i{[(sN)i/Ni]2 + [(sT)i/Ti]2}1/2 for thermal pressure, (s)i = i{[(sN)i/Ni]2 + [(sT)i/Ti]2 + [2(sB)i/Bi]2}1/2 for the ratio of thermal and magnetic pressures and (sEy)i = (Ey)i{[(sV)i/Vi]2 + [(sBz)i/(Bz)i]2}1/2 for the electric field component. Further, the variations of parameters from the OMNI database and these calcu lated variations were processed uisng the double SEA method. The obtained results were presented in two forms: as variations of parameters (standard devia tions) and as relative variations (variations divided by the mean values of parameters for given solar wind types). 3. RESULTS Figure 1 shows, in the compressed form, the results, which have been discussed in more detail in our previous paper [1], and presents the average values of some solar wind and IMF parameters (the left col umn: V is velocity, T and T/Texp are the measured pro ton temperature and the temperature related to the temperature calculated from the average temperature velocity dependence [20], Ey is the electric field com ponent, Bz is the magnetic field component, is the ratio of thermal and magnetic pressures; the right col umn: N is density, Pd and Pt are the dynamic and ther mal pressures of the solar wind, Bx, By, and B are the components and magnitude of the IMF), and mag netospheric Dst and Kp indices. Different lines in fig ures designate different types of the solar wind: (MC+Ejecta), MC and Ejecta, Sheath, CIR and IND (indeterminate type). Designations of solar wind types are given at the bottom of figure together with the indi cation of statistics (this statistics corresponds to the number of events; the number of points in separate intervals can differ from this number). The data presented in Fig. 1 show, that: (1) irre spective of the solar wind type any magnetic storm begins in 1­2 h after IMF turn southward and is ter minated in 1­2 h after sharp decrease of the southward IMF component; (2) the magnetic storms for Sheath and CIR develop, as a rule, at higher velocity, temper ature, IMF magnitude, dynamic and thermal pres sure, and parameter; (3) Sheath turns out to be the most effective interplanetary cause of the storms from all types. Figure 2 shows variations of the same solar wind and IMF parameters, as in Fig. 1. The time behavior of mean values of magnetospheric indices Dst and Kp was taken without changes from Fig. 1. Variations are higher in Sheath and CIR for the same parameters, for which the mean values are higher, except for the parameter. In these solar wind types the variations of all IMF components, including Bz, are higher as well. Figure 3 shows the relative (i.e., normalized with respect to the mean values in a given interval of aver
COSMIC RESEARCH Vol. 49 No. 1 2011

aging for the same solar wind type) variations of the same parameters as in Fig. 2. One should note that some relative variations exceed 1000 %, since the mean values are close to zero, and such parameters ( parameter, IMF components, thermal pressure) should be analyzed with care. Figure 3 shows that the relative variations for all types of streams are very close between each other, and only relative variations of the IMF magnitude and the value of velocity sV/V are 1.5 times higher in Sheath and CIR. It should be noted that variations of the most geoeffective interplanetary parameters sBz and sEy turn out to have minimum on the main phase of a storm for all solar wind types. The mean values of parameters discussed above, their absolute and relative variations separately for mod erate (­100 < Dst ­50 nT) and strong (Dst ­100 nT) magnetic storms are shown, respectively, in Figs. 4 and 7, 5 and 8, 6 and 9. As in Figs. 1­3, in these figures the statistics (the number of events) is indicated below in brackets, near the lines for a corresponding solar wind type. A higher degree of scatter of parameters in Figs. 7­9 (for strong magnetic storms with Dst ­100 nT) is mainly associated with lower statistics than in previ ous figures (Figs.1­6). Except for different values of the southward component of the IMF and electric field Ey, all parameters and their variations for moder ate and strong magnetic storms behave in a similar manner both qualitatively and quantitatively. The comparison will be made in more detail in the next Section of the paper. 4. DISCUSSION AND CONCLUSIONS Thus, the behavior of mean values of parameters (and their absolute and relative variations) at the main phase of magnetic storms, generated by various large scale solar wind types, has been analyzed in the present work by the double superposed epoch analysis method similar to that used in paper [1]. This behavior is shown in Figs. 1­3, 4­6 and 7­9, for "all" (Dst ­50 nT), moderate (­100 < Dst ­50 nT) and strong (Dst ­100 nT) magnetic storms, respectively. The data presented for the main phase (time "0"­"6") of these figures are summarized in Table. This table qualitatively presents, for various solar wind types (horizontally) and various parameters (vertically) the behavior (level designated by letters "l," "m," and "h") of the corresponding parameter with respect to the behavior of other solar wind types, i.e., the low (lower than the mean), mean (about the mean position), and high (higher than the mean) value, respectively. The mean values, the abso lute and relative variations are presented for each solar wind type (the corresponding columns are marked by labels , s, and s/ ), where all data on the mean variations and relative variations are subdivided into "all", moderate, and strong storms, which are pre sented in 3 neighboring columns, respectively. Since Figs. 1, 4, and 7 represent the information of paper [1]


24

YERMOLAEV et al. All storms 550 V, km/s N, m3 Pt, nPa Pd, nP By, n Bx, n B, n 10­1 0 Dst, n ­40 ­80 ­120 ­12 ­6 0 6 12 18 24 Kp 10 30 ­12 ­6 0 6 12 18 24 Epoch time, h MC + EJECTA (196) MC (56) EJECTA (139) SHEATH (93) CIR (120) IND (335) 60 500 450 400 10 T, 105 10

10

1

­1

­2

10

1

T/Texp Ey, mV/m

1

4 0 ­4 8

4 0 ­4 2 0 ­2

Bz, n

0 ­8 1

10

1

Fig. 1. Time dependence of mean values of 12 solar wind and IMF parameters and 2 magnetospheric indices obtained by the dou ble superposed epoch analysis method for all storms with Dst ­50 nT.

in a more compressed form than in the original, Table also summarizes the results of the mentioned paper in columns marked by the label . Before starting the discussion about the obtained results, one should remind the following points. 1. The hourly average standard deviations of OMNI database parameters used by us as variations

were obtained by various instruments and may contain some peculiarities of method (see "Discussion" in paper [4]) for more details). 2. For some composite parameters (see the "Method" Section) there are no direct measurements of variations in the OMNI database, and we have esti mated these parameters on the basis of variations of
COSMIC RESEARCH Vol. 49 No. 1 2011


STATISTICAL STUDY OF INTERPLANETARY CONDITION EFFECT 2. VARIATIONS All storms sV, km/s
1

25

10

sN, m3 1 sPt, nP sPd, nP sBy, n 1 sBx, n 1 sB, n Kp 10 30 ­6 0 6 12 18 24 ­12 ­6 0 6 12 18 24 Epoch time, h MC + EJECTA (196) MC (56) EJECTA (139) SHEATH (93) CIR (120) IND (335)
Vol. 49 No. 1 2011

105 sT,

1 10 10­2 10­3
­1

104 10
1

sT/Texp

1 10
­1

1

sEy, mV/m sBz, n s

10 1 0.1

1 10
1

1 10
­1

1

10­2 0 Dst, n ­40 ­80 60

­120 ­12

Fig. 2. Time dependence of averaged values of standard deviations for the same 12 parameters, as in Fig. 1, obtained by the double superposed epoch analysis method for all storms generated by various interplanetary types of streams.

parameters included in these composite parameters, which are included in the OMNI database. 3. The negative values of electric field and Bz components of the interplanetary magnetic field were supposed to be geoeffective, and, consequently, the lower mean values of these parameters for any solar wind type imply the higher values of the quantity
COSMIC RESEARCH

(magnitude), i.e., more "energetic" values of disturb ing interplanetary factors. The results on behavior of 10 interplanetary parameters in various solar wind types during the main phase of magnetic storms, presented in figures and in Table, can be formulated as follows.


26

YERMOLAEV et al. All storms sV, %

N, % 1 102 10 Pt, % 101 103 102 sPd, % sBy, % sBx, % sB, % Kp 10 30 ­6 0 6 12 18 24 ­12 ­6 0 6 12 18 24 Epoch time, h MC + EJECTA (196) MC (56) EJECTA (139) SHEATH (93) CIR (120) IND (335) 104 103 102 104 103 102 101 104 103 102 0 ­40 ­80 ­120 ­12
1

sT, %

103 102 102

sT/Texp, %

10

1

sEy, %

104 103 102 104 103 102

s, %

sBz, %

10

1

Fig. 3. Time dependence of relative variations (divided by the mean value and multiplied by 100) for the same parameters as shown in Fig. 2.

According to their characteristics, including both the mean values and the absolute and relative varia tions, all solar wind types resulting in magnetic storms obviously have a bent for two groups: (1) MC and Ejecta and (2) Sheath and CIR. Below we consider these two groups.

Dst, n

60

1. MC and Ejecta Types of Streams The mean values, absolute and relative variations for all parameters turn out to be either mean, or lower than the mean values (this also relates to the mean val ues of the electric field and to Bz component of the interplanetary magnetic field).
COSMIC RESEARCH Vol. 49 No. 1 2011


STATISTICAL STUDY OF INTERPLANETARY CONDITION EFFECT 2. VARIATIONS 600 V, km/s 500 400 ­100 < Dst ­50 n N, m3

27

101 10­1

T,

10

5

Pt, nP Pd, nP By, n Bx, n B, n Kp 10

10

­2

T/Texp

101

1

4 Ey, mV/m 0 ­4 4 Bz, n 0 ­4 ­8 1 10­1 0 Dst, n ­40 ­80 ­12

8 4 0 ­4 4 0 ­4 101

60

30 ­12 ­6 0 6 12 18 24 Epoch time, h

­6

0

6

12

18

24

MC + EJECTA (123) MC (29) EJECTA (94)

SHEATH (56) CIR (96) IND (256)

Fig. 4. Time dependence of averaged parameters, as in Fig. 1. Unlike Fig. 1, this figure presents only the data for moderate storms with ­100 nT < Dst ­50 nT.

High values of the relative variation of density sN/N (and, probably, of derivative parameters--the dynamic and thermal pressure) and the mean value of the magnetic field magnitude B in MC turn out to be an exception.

Unlike the MC events, the components and the value (magnitude) of the magnetic field and the elec tric field intensity in Ejecta are lower and close to the mean values for all solar wind types.

COSMIC RESEARCH

Vol. 49

No. 1

2011


28

YERMOLAEV et al. ­100 < Dst ­50 n sV, km/s 10 sN, 3 1 10 sT,
5 1

sPt, nP sPd, nP sBy, n sBx, n sB, n Kp 10 ­6 6 12 18 24

1 10 10­2 10­3
­1

104 sT/Texp 10
1

1 0.1

1

sEy, mV/m

10

­1

1 0.1

1

sBz, n

1 10 s
1

1

1 10
­1

1 60

10­2 0 Dst, n ­40 ­80 ­12

30

0

­12

­6

0

6

12 18 24 Epoch time, h

MC + EJECTA (123) MC (29) EJECTA (949)

SHEATH (56) CIR (96) IND (256)

Fig. 5. Time dependence of variations of parameters, as in Fig. 2. Unlike Fig. 2, this figure presents only the data for moderate storms with ­100 nT < Dst ­50 nT.

No noticeable distinctions of considered parameters are observed for "all", moderate, and strong storms. 2. Sheath and CIR Types of Streams The values and behavior of parameters and their variations in Sheath and CIR are close to each other,

and in most cases not only qualitatively, but also quan titatively. They demonstrate high mean values and absolute variations virtually for all parameters. High values are observed for the relative variations of velocity, Bz component, and IMF magnitude.
COSMIC RESEARCH Vol. 49 No. 1 2011


STATISTICAL STUDY OF INTERPLANETARY CONDITION EFFECT 2. VARIATIONS ­100 < Dst ­50 n sN, % sV, %

29

1 102 sT, % Pt, % 101 103 102 sPd, % sBy, % sBx, % sB, % Kp 10 0 105 104 103 102 104 103 102 101 103 102 0 Dst, n ­40 ­80 ­12

101 104 103 102 101 102

sT/Texp, %

101 104 103 102 104 103 102 101 101

s, %

sBz, %

sEy, %

60

30 ­6 6 12 18 24 ­12 ­6 0 6 12 18 24 Epoch time, h

MC + EJECTA (123) MC (29) EJECTA (94)

SHEATH (56) CIR (96) IND (256)

Fig. 6. Time dependence of relative variations of parameters, as in Fig. 3. Unlike Fig. 3, this figure presents only the data for mod erate storms with ­100 nT < Dst ­50 nT.

It is interesting to note that for strong magnetic storms the high relative variations of density were observed, unlike the other parameters, in MC and Ejecta, and they are low in Sheath. The mean values of parameters are determined, in many respects, by the type of solar wind stream (and by the used classification criteria of solar
COSMIC RESEARCH Vol. 49 No. 1 2011

wind types) and have already been discussed in paper [1]. As it was noted in the Introduction, the va riations of some parameters have been rather poorly investigated, and, in general, the presented results satisfactorily agree with earlier published ones [7­17]. Howeve r, our results have some adva ntages:


30

YERMOLAEV et al. Dst ­100 n 10 V, km/s
3

N, m3 10
5

101

Pt, nPa Pd, nPa By, n Bx, n B, n Kp 10 0

10­1 10 10
­2 ­3

T,

10 T/Texp

4

101

1 10
­1

Ey, mV/m

8 0 ­8 16 8 0 ­8 ­16 1

1 8 0 ­8 ­16 8 0 ­8 24 16 8 60 30 ­6 6 12 18 24 ­12 ­6 0 6 12 18 24 Epoch time, h

Bz, n Dst, n

10

­1

10­2 0 ­40 ­80 ­120 ­160 ­12

MC + EJECTA (73) MC (28) EJECTA (45)

SHEATH (37) CIR (24) IND (79)

Fig. 7. Time dependence of averaged parameters, as in Fig. 1. Unlike Fig. 1, this figure presents only the data for strong storms with Dst ­100 nT.

1. they use a rather complete (at the modern sci ence development stage) classification of solar wind types, in particular, the separate analysis of two ICME subtypes: MC and Ejecta; 2. they represent the analysis of a rather complete set of solar wind and IMF parameters; 3. the solar wind and IMF parameters were ana lyzed not only at the magnetic storm maximum, but in

the dynamics, during the entire main phase of the magnetic storm (by the double superposed epoch analysis method); 4. not only absolute (or only relative) variations of parameters were compared, but the full set of charac teristics (dynamics, mean values, absolute and relative variations) of parameters; and
COSMIC RESEARCH Vol. 49 No. 1 2011


STATISTICAL STUDY OF INTERPLANETARY CONDITION EFFECT 2. VARIATIONS Dst ­100 n 101 sV, km/s 101 sN, m3 1 101 1 ­1 10 10­2 10­3 101 1 10 sBy, n
­1

31

104

sT/Texp

1 10­1 10 1 101

sPd, nP sBx, n sB, n Kp 10 0

101

sPt, nP

105 sT,

sEy, mV/m

101

1

sBz, n

1 101 s 10­1 10­3 0 ­40 ­80 ­120 ­160 ­12

1

1

Dst, n

60 30

­6

6

12

18

24

­12

­6

0

6

12 18 24 Epoch time, h

MC + EJECTA (73) MC (28) EJECTA (45)

SHEATH (37) CIR (24) IND (79)

Fig. 8. Time dependence of variations of parameters, as in Fig. 2. Unlike Fig. 2, this figure presents only the data for strong storms with Dst ­100 nT.

5. the conditions for moderate and strong magnetic storms were studied separately. It is well known that two physical mechanisms are most frequently used in the description of solar wind effect on the magnetosphere: (1) the reconnection of magnetic fields of interplanetary and magnetospheric origin on the magnetopause [21], and (2) viscous
COSMIC RESEARCH Vol. 49 No. 1 2011

interaction of plasma streams of interplanetary and magnetospheric origin on the magnetopause [22]. The dependence of the storm intensity on the IMF south ward component (or electric field Ey) value testifies to the effect of reconnection. However, the efficiency of both these mechanisms essentially grows with increas ing turbulence level in the interacting streams. The


32

YERMOLAEV et al. Dst ­100 n sN, % sPt, % sPd, % sBy, % sBx, % sB, % Kp 10 sV, %

1 103

101

sT, %

102 10
1

10 10

3 2

101 10
2

sT/Texp, %

103 102 10
1

101 10 10 10 10 10 10
4 3 2

sEy, %

104 103 102 104 103 102 101 103 102 101 0 ­40 ­80 ­120 ­160 ­12

101
4 3 2

s, %

sBz, %

101 1 60 30

Dst, n

­6

0

6

12

18

24

­12

­6

0

6

12 18 24 Epoch time, h

MC + EJECTA (73) MC (28) EJECTA (45)

SHEATH (37) CIR (24) IND (79)

Fig. 9. Time dependence of relative variations of parameters, as in Fig. 3. Unlike Fig. 3, this figure presents only the data for strong storms with Dst ­100 nT.

obtained evidences of the fact that those solar wind stream types, which contain a higher level of variations (Sheath and CIR), more effectively excite magnetic storms than the types with a low level of variations (MC), indicate to possible additional effect of both mechanisms with increasing turbulence level in the

incident solar wind stream. A higher level of fluctua tions (along with distinctions of mean values for some parameters) in Sheath and CIR as compared to MC can be responsible for different reaction of the mag netosphere on various solar wind types [23­27]. More detailed information on this subject can be obtained by
COSMIC RESEARCH Vol. 49 No. 1 2011


STATISTICAL STUDY OF INTERPLANETARY CONDITION EFFECT 2. VARIATIONS Character of variation of solar wind parameters in various types of streams reduced to magnetic storms with Dst ­50 nT Param. V T T/Texp N Pt Pd Ey Bz Bx By B MC + Ejecta s lll lll lll lll lll lll mmm mmm mmm mmm mmm lll lll lll mlm lm m mlm lml mmm lll lll lll lll mmm s/ lll lll mmm lll mmm lll m h m lll m h m lll mmm lll mmm lll lll lll mlm llm mlm mmm lll h h m h m h lll MC s lll lll mlm llm llm lll mll lll lll lll lml mlm s/ lll mmm mmm h hm mlm mmm lml lll llm mlm lll mmm lm m lll lll lll lll lll mmm mmm mmm mmm lll lll Ejecta s lll lll mmm lm m mmm lm m mmm lll lll lll lll mmm s/ llm mmm mmm m hm mmm mmm mmm lll mmm mlm lll mmm hhh hhh hhh hm h hhh hhh mmm mmm h hm mmm hhh hhh Sheath s hhh hhh m hm hmh h hm hhh mmm hhh hhh hhh hhh mmm s/ h hm mm h mmm mlm m hm mmm mmm hhh mmm mm h hm h lml lm m hhh hhh hhh hhh m hm mmm mmm m hm mmm h hm hhh CIR s hhh hhh m hm h hm mmm mmm mmm hhh h hm h hm hhh mmm s/ h hm mmm mmm lm m mlm mmm mmm hhh mmm mhm hhh mmm m hm hhh hmh llm mmm lml mmm mmm mmm mmm lm m h hm IND s hhh hhh mmm lm m mmm mmm mmm mm h mmm llm lm m mmm s/

33

h hm mmm mmm mlm mmm mmm mmm hhh mmm mmm hm h mmm

Designations l, m and h indicate the quantities, which are lower than the mean, close to the mean, and higher than the mean value, respec tively.

studying the budget of the energy coming from the solar wind and spent for magnetospheric disturbances [28, 29]. One can often find in literature the statements about the relationship between the magnetospheric activity and high velocity solar wind streams (see, e.g., paper [30] and references therein). The data pre sented above do not confirm such statements for mag netic storms: on the average, at the main phase of a storm the velocity magnitudes only slightly differ from the mean values of solar wind velocity and change, depending on the solar wind type, within a rather nar row range of values: 450­550 km/s. More important than mean values of velocity for the magnetic storm generation are velocity fluctuations at the main phase of a storm, since the distinctions in the mean velocity between the types of streams are about 10­20%, while the distinctions in the absolute velocity variations are about 100%, but these fluctuations are mainly associ ated with the solar wind type (they are observed in the CIR and Sheath compression regions) rather than with its velocity. Since the compression regions are observed before the fast solar wind types (CIR before the fast streams from coronal holes and Sheath before the fast ICMEs), then, though the necessary condi tions for storm generation arise in the CIR and Sheath compression regions, the high velocity solar wind streams are erroneously considered to be the sources of storms. The data we have obtained give evidence in favor of the hypotheses of considerable effect of den sity and its variations (and derivatives of the density,
1

the dynamic and thermal pressures, first of all) and IMF variations on the magnetospheric activity (see, e.g., papers [31­33] and references therein), and the studies in this direction seem to be rather promising. ACKNOWLEDGMENTS The authors are grateful for the possibility of using the OMNI database. The OMNI data were obtained from the GSFC/SPDF OMNIWeb on the site http:// omniweb.gsfc.nasa.gov. This work was supported by the Russian Foundation for Basic Research, projects nos. 07 02 00042 and 10 02 00277a, and by the Pro gram 16 of OFN RAS. REFERENCES
1. Yermolaev, Yu.I., Lodkina, I.G., Nikolaeva, N.S., and Yermolaev, M.Yu., Statistical Study of Interplanetary Condition Effect on Geomagnetic Storms, Kosm. Issled., 2010, vol. 48, no. 6, pp. 499­515. [Cosmic Research, pp. 485­501]. 2. Yermolaev, Yu.I., Nikolaeva, N.S., Lodkina, I.G., and Yermolaev, M.Yu., Catalog of Large Scale Solar Wind Phenomena during 1976­2000, Kosm. Issled., 2009, vol. 47, no. 2, pp. 99­113. [Cosmic Research, pp. 81­94]. 3. Yermolaev, Yu.I., Yermolaev, M.Yu., Lodkina, I.G., and Nikolaeva, N.S., Statistical Investigation of Helio spheric Conditions Resulting in Magnetic Storms, Kosm. Issled., 2007, vol. 45, no. 1, pp. 3­11. [Cosmic Research, pp. 1­8]. 4. Yermolaev, Yu.I., Yermolaev, M. Yu., Lodkina, I.G., and Nikolaeva, N.S., Statistical Investigation of Helio spheric Conditions Resulting in Magnetic Storms, 2, Kosm. Issled., 2007, vol. 45, no. 6, pp. 489­498. [Cos mic Research, pp. 461­470].

1

Probably, in some papers the used terminology follows from established traditions. However, in our opinion, this terminology does not reflect real physical processes and misleads a reader. COSMIC RESEARCH Vol. 49 No. 1 2011


34

YERMOLAEV et al. Kosm. Issled., 2010, vol. 48, no. 1, pp. 3­32. [Cosmic Research, pp. 1­30]. 20. Lopez, R.E. and Freeman, J.W., Solar Wind Proton Temperature­Velocity Relationship, J. Geophys. Res., 1986, vol. 91, p. 1701. 21. Dungey, J.W., Interplanetary Magnetic Field and the Auroral Zones, Phys. Rev. Lett., 1961, no. 6, p. 47. 22. Axford, W.I. and Hines, C.O., A Unifying Theory of High Latitude Geophysical Phenomena and Geomag netic Storms, Can. J. Phys., 1961, no. 39, p. 1433. 23. Borovsky, J.E. and Denton, M.H., Differences between CME Driven Storms and CIR Driven Storms, J. Geophys. Res., 2006, vol. 111, A07S08. doi: 10.1029/2005JA011447. 24. Denton, M.H., Borovsky, J.E., et al., Geomagnetic Storms Driven by ICME and CIR Dominated Solar Wind, J. Geophys. Res., 2006, vol. 111, A07S07. doi: 10.1029/2005AJ011436. 25. Despirak, I.V., Lubchich, A.A., Yahnin, A.G., et al., Development of Substorm Bulges during Different Solar Wind Structures, Ann. Geophys., 2009, vol. 27, no. 5, p. 1951. 26. Huttunen, K.E.J., Koskinen, H.E.J., Karinen, A., and Mursula, K., Asymmetric Development of Magneto spheric Storms during Magnetic Clouds and Sheath Regions, Geophys. Res. Lett., 2006, vol. 33, L06107. doi: 10.1029/2005GL024894. 27. Pulkkinen, T.I. Partamies, N., et al., Differences in Geomagnetic Storms Driven by Magnetic Clouds and ICME Sheath Regions, Geophys. Res. Lett., 2007, vol. 34, L02105. doi: 10.1029/2006GL027775. 28. Yermolaev, Yu.I., Nikolaeva, N.S., Lodkina, L.G., and Yermolaev, M.Yu., Specific Interplanetary Conditions for CIR , Sheath , ICME induced Geomagnetic Storms Obtained by Double Superposed Epoch Analy sis, Preprint http://arxiv.org/abs/0911.3315, 2009. 29. Turner, N.E., Cramer, W.D., Earles, S.K., and Emery, B.A., Geoefficiency and Energy Partitioning in CIR Driven and CME Driven Storms, J. Atmospheric and Solar Terrestrial Physics, 2009, vol. 71, no. 10­11, pp. 1023­1031. 30. Borovsky, J.E. and Denton, M.H. Magnetic field at geosynchronous orbit during high speed stream driven storms: Connections to the solar wind, the plasma sheet, and the outer electron radiation belt, J. Geophys. Res., 2010, no. l15, A08217. doi: 10.1029/2009 JA015116. 31. Khabarova, O.V. and Yermolaev, Yu.I. Solar wind pa rameters behavior before and after magnetic storms, J. Atmospheric and Solar Terrestrial Physics, 2008, vol. 70, pp. 384­390. doi: 10.1016/j.jastp.2007.08.024. 32. Weigel, R.S. Solar wind density influence on geomag netic storm intensity, J. Geophys. Res., 2010. doi: 10.1029/2009JA015062. 33. Simms, L.E., Pilipenko, V. and Engebretson, M.J. Determining the Key Drivers of Magnetospheric Pc5 Wave Power, J. Geophys. Res., 2010. doi: 10.1029/2009JA015025.
COSMIC RESEARCH Vol. 49 No. 1 2011

5. Yermolaev, Yu.I., Yermolaev, M.Yu., Nikolaeva, N.S., and Lodkina, L.G., Interplanetary Conditions for CIR Induced and MC Induced Geomagnetic Storms, Bulg. J. Phys., 2007, vol. 34, pp. 128­135. 6. Twelfth International Solar Wind Conference, Saint Malo, France, 21­26 June 2009, vol. 1216 of AIP Confer ence Proceedings, Maksimovic, M., Meyer Vernet, N., Moncuquet, M., and Pantellini, F., Eds., 2010. 7. Feldstein, Y.I., Modelling of the Magnetic Field of Magnetospheric Ring Current as a Function of Inter planetary Medium Parameters, Space Sci. Rev., 1992, vol. 59, pp. 83­165. 8. Tsurutani, B.T., Gonzalez, W.D., Gonzalez, A.L.C., et al., Interplanetary Origin of Geomagnetic Activity in the Declining Phase of the Solar Cycle, J. Geophys. Res., 1995, vol. 100, no. A11, pp. 21717­21733. 9. Goncharova, M.Yu. and Maltsev, Yu.P., Correlation of the Kp Index with the Solar Wind Parameter, Geomagn. Aeron., 2001, vol. 41, no. 3, pp. 305­309. 10. Borovsky, J.E. and Funsten, H.O., Role of Solar Wind Turbulence in the Coupling of the Solar Wind to the Earth's Magnetosphere, J. Geophys. Res., 2003, vol. 108, no. A6, p. 1246. 11. D'Amicis, R., Bruno, R., and Bavassano, B., Is Geo magnetic Activity Driven by Solar Wind Turbulence?, Geophys. Res. Lett., 2007, vol. 34, p. L05108. doi: 1029/2006GL028896. 12. Romanova, N., Pilipenko, V., Crosby, N., and Kha barova, O., ULF Wave Index and Its Possible Applica tions in Space Physics, Bulg. J. Phys., 2007, vol. 34, pp. 136­148. 13. Jankovicova, D., Voros, Z., and Simkanin, J., The Influence of Solar Wind Turbulence on Geomagnetic Activity, Nonlin. Processes Geophys., 2008, vol. 15, pp. 53­59. 14. Badruddin, V.G., Interplanetary Structures and Solar Wind Behaviour during Major Geomagnetic Perturba tions, J. Atmos. Terr. Phys., 2009, vol. 71, pp. 885­896. 15. Yokoyama, N. and Kamide, Y., Statistical Nature of Geomagnetic Storms, J. Geophys. Res., 1997, vol. 102, no. A7, p. 14215. 16. Kershengolts, S.Z., Barkova, E.S., and Plotnikov, I.Ya., Dependence of Geomagnetic Disturbances on Extreme Values of the Solar Wind Ey Component, Geomagn. Aeron., 2007, vol. 46, no. 2, pp. 1­9. 17. Plotnikov, I.Ya. and Barkova, E.S., Advances in Space Research Nonlinear Dependence of Dst and AE Indices on the Electric Field of Magnetic Clouds, Adv. Space Res., 2007, vol. 40, pp. 1858­1862. 18. King, J.H. and Papitashvili, N.E., Solar Wind Spatial Scales in and Comparisons of Hourly Wind and ACE Plasma and Magnetic Field Data, J. Geophys. Res., 2004, vol. 110, no. A2, A02209. doi: 10.1029/2004JA010804. 19. Yermolaev, Yu.I., Nikolaeva, N.S., Lodkina, I.G., and Yermolaev, M.Yu., Relative Occurrence Rate and Geo effectiveness of Large Scale Types of the Solar Wind,