GEOEFFECTIVE INTERPLANETARY STRUCTURES: 1997 – 2001 A. N. Zhukov 1,2, V. Bothmer 3, A. V. Dmitriev 2, I. S. Veselovsky 2 1 Royal Observatory of Belgium 2 Institute of Nuclear Physics, Moscow State University, Russia 3 Max–Planck–Institut für Sonnensystemforschung, Germany SOLI INVICTO

General outline  An event: a day with Ap index more than 20 (one standard deviation interval during 1997 – 2000).  In total: 255 events in 1997 – 2000: in 1997 – 23; in 1998 – 41; in 1999 – 68; in 2000 – 74, in 2001 – 49.  Events are compiled into a database:  ACE and WIND spacecraft are used for the solar wind data.  I won’t talk about composition signatures, BDEs, etc.  This is an informal presentation of preliminary results. The investigations are not finished yet (to be published when the cycle ends).

Coordinate system

IMF polarity for 400 km/s ~135°

IMF polarity for 400 km/s ~315°

Geoeffective interplanetary structures ICME = Interplanetary Coronal Mass Ejection MICME = Multiple ICME CH/CIR = Corotating Interaction Region/Croronal Hole ICME/CIR Slow wind

Fast solar wind High speed: 400 – 800 km/s Low density: ~ 3 cm -3 High temperature: ~ 10 5 K ~ 10 eV Stationary for long times Strong Alfvenic fluctuations By the way: 1 eV = K

Slow solar wind Low speed: 250 – 400 km/s High density: ~ 10 cm -3 Low temperature: ~ 10 4 K ~ 1 eV Very variable By the way: 1 eV = K

Scheme of a CIR

Event 26: CIR/CH

IP shocks

A typical CIR: with a forward/reverse shock pair (Lazarus et al. 1999) CIR shocks

CME-driven interplanetary shocks (Courtesy R. Schwenn) Gold was right: interplanetary shocks (except CIR shocks) are CME-driven!

CME-driven shocks have larger angular extent than CMEs themselves

ICME Shock (if the ICME is fast enough) …followed by shocked sheath plasma (compressed and heated, with oscillating B) …followed often by the driver gas (ICME itself): Strong magnetic field Temperature depression: typically < ~ 10 5 K ~ 10 eV Low variance of the magnetic field Large-scale smooth field rotation (magnetic cloud): in about 30% of cases Low Usually only a subset of these signatures is observed.

ICME

ICME/CIR

MICME

Slow wind

1997 – 2001

During the whole studied period storms associated with ICMEs dominate (44%). However, in 1998 the fraction of storms produced by CIR/CH (41%) is comparable with the one of ICMEs (31%), and in 1999 it even becomes dominant (51%).

1997 – 2001 Although the fraction of storms produced by ICMEs has its minimum in 1999 (22%), the number of geoeffective ICMEs remains more or less the same in 1997 (9 separate ICMEs, 13 in total), 1998 (11 separate ICMEs, 19 in total) and 1999 (10 separate ICMEs, 19 in total). Therefore, the activity in 1999 is only very slightly anomalous.

1997 – 2001 The number of geoeffective ICMEs increased essentially during high activity years (2000 – 2001), as expected. The number of fast flows (CIR/CH) has its maximum during the rising phase of the cycle (1999). The number of storms caused by slow solar wind flows remains rather constant during the cycle.

Geoeffective ICMEs 1.Almost half of geoeffective IMCEs are magnetic clouds (MC). 2.MCs of left-handed chirality slightly dominate.

Geoeffective ICMEs In 1997 right-handed clouds are strongly predominant, in 1998 – 2000 the number of left-handed and right-handed clouds is almost the same and in 2001 (after the activity maximum and the reversal of the solar magnetic field!) left-handed MCs became strongly predominant. The relative fraction of MCs in respect to all ICMEs drops with the increase of solar activity.

Geoeffective MCs MCs with both high and low inclination to the ecliptic are present.

Ap index

Storms produced by MICME and ICME/CIR have larger average Ap index. This could be due to two reasons: larger peak a p (interaction provides favorable conditions for producing stronger storms?) and/or longer duration of a p increase (natural if there are two or more structures). Ap index

Peak a p (Kp) index