M. Y. Yermolaev

Geoeffectiveness and efficiency of CIR, sheath, and ICME in generation of magnetic storms

We investigate relative role of various types of solar wind streams in generation of magnetic storms. On the basis of the OMNI data of interplanetary measurements for the period of 1976-2000 we analyze 798 geomagnetic storms with Dst < -50 nT and their interplanetary sources: corotating interaction regions (CIR), interplanetary CME (ICME) including magnetic clouds (MC) and Ejecta and compression regions Sheath before both types of ICME. For various types of solar wind we study following relative characteristics: occurrence rate; mass, momentum, energy and magnetic fluxes; probability of generation of magnetic storm (geoeffectiveness) and efficiency of process of this generation. Obtained results show that despite magnetic clouds have lower occurrence rate and lower efficiency than CIR and Sheath they play an essential role in generation of magnetic storms due to higher geoeffectiveness of storm generation (i.e higher probability to contain large and long-term southward IMF Bz component).

Comment on ''Interplanetary origin of intense geomagnetic storms (Dst < 100 nT) during solar cycle 23'' by W. D. Gonzalez et al.

[1] Gonzalez et al. [2007] studied the interplanetary causes of 87 intense geomagnetic storms (Dst < 100 nT) that occurred during solar cycle 23 (1997–2005). Their classification of interplanetary causes of storms includes CIR (corotating interaction region associated with a high speed stream), MC (magnetic cloud), ‘‘Sh’’ (sheath field with southward component of interplanetary magnetic field), ‘‘Sh + MC’’ (sheath field followed by a magnetic cloud), SBC (a sector boundary crossing), ‘‘S + MC’’ (magnetic cloud compressed by a shock), and ‘‘Complex’’ (for a case in which none of the other cases were identified). The category of ‘‘ICMEs’’ (interplanetary coronal mass ejections) corresponds to several types of structures that are not magnetic clouds, namely that they have not the typical signatures for magnetic clouds [Burlaga et al., 1987]. They found that the most common interplanetary structures leading to the development of an intense storm were magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud and corotating interaction regions leading high speed streams and presented the relative importance of each of those driving structures in three phases of solar cycle: rising, maximum and declining phases. [2] However, the interaction between two CMEs close to the Sun [Gopalswamy et al., 2001, 2002] and between magnetic clouds near the Earth [see, e.g., Burlaga et al., 2001; Berdichevsky et al., 2003; Gonzalez-Esparza et al., 2004; Farrugia et al., 2006a; and references therein] has been reported. A number of papers showed that several strong magnetic storms (see, for instance, events on 31 March, 2001, minimum Dst value of 387 nT, 11–13 April, 2001, Dstmin = 271 nT [Wang et al., 2003]; 28– 30 October, 2003, Dstmin = 363 nT [Veselovsky et al., 2004; Skoug et al., 2004]; 20 November, 2003, Dstmin = 472 nT [Ermolaev et al., 2005]; 8–10 November, 2004, Dstmin = 373 nT [Yermolaev et al., 2005]) have been generating by multiple interacting magnetic clouds. Recently Farrugia et al. [2006b] studied interplanetary conditions for magnetic storms during 1995–2003 and found ‘‘that a significant number of our large events (6 out of 16) consisted of ICMEs/magnetic clouds interacting with each other forming complex ejecta.’’ Xie et al. [2006] studied 37 long-lived geomagnetic storms (LLGMS events) with Dst < 100 nT and the associated CMEs which occurred during 1998–2002 and found that 24 of 37 events were caused by successive CMEs and number of interacting magnetic clouds was observed from 2 up to 4. [3] Thus, classification of interplanetary sources of strong magnetic storms used by Gonzalez et al. [2007] is not complete and does not contain the important category of sources (interacting magnetic clouds) widely discussed in the literature. Therefore, though the obtained results are of limited interest, the used classification excludes from consideration the important mechanism on the solar-terrestrial physics resulting in strong Space Weather events.

Recovery phase of magnetic storms induced by different interplanetary drivers

Statistical analysis of Dst behaviour during recovery phase of magnetic storms induced by different types of interplanetary drivers is made on the basis of OMNI data in period 1976-2000. We study storms induced by ICMEs (including magnetic clouds (MC) and Ejecta) and both types of compressed regions: corotating interaction regions (CIR) and Sheaths. The shortest, moderate and longest durations of recovery phase are observed in ICME-, CIR-, and Sheath-induced storms, respectively. Recovery phases of strong (

A year later: Solar, heliospheric, and magnetospheric disturbances in November 2004

Dst_{min} < -100

Occurrence rate of extreme magnetic storms

nT) magnetic storms are well approximated by hyperbolic functions

Dynamics of Large-Scale Solar-Wind Streams Obtained by the Double Superposed Epoch Analysis: 2. Comparisons of CIRs vs. Sheaths and MCs vs. Ejecta

Dst(t)= a/(1+t/\tau_h)

Some problems of identifying types of large-scale solar wind and their role in the physics of the magnetosphere

with constant

The “Floor” in the Interplanetary Magnetic Field: Estimation on the Basis of Relative Duration of ICME Observations in Solar Wind During 1976 – 2000

\tau_h

Dynamics of Large-Scale Solar-Wind Streams Obtained by the Double Superposed Epoch Analysis: 3. Deflection of the Velocity Vector

times for all types of drivers while for moderate (

Recovery phase of magnetic storms induced by different interplanetary drivers: RECOVERY PHASE

-100 < Dst_{min} < -50