Response of geomagnetic activity indices Response of geomagnetic activity indices to the solar wind parametersto the solar wind parameters

Byung-Ho AhnKyungpook National University

Daegu, Korea

2009 UN BSS & IHY Workshop Daejeon, Korea

September 21-25, 2009

The response of Dst index to the variation of The response of Dst index to the variation of the interplanetary magnetic field (IMF), the interplanetary magnetic field (IMF), more specifically, interplanetary electric field,more specifically, interplanetary electric field, Ey(VBs). Ey(VBs).

The relationship between AL and Dst duringThe relationship between AL and Dst during geomagnetic storm.geomagnetic storm.

Storm – substorm relationshipStorm – substorm relationship

• The goal of this studyThe goal of this study

• DataData

Dst indexDst index : 1998 - 2006 : 1998 - 2006

((dynamic pressure of the solar wind has been dynamic pressure of the solar wind has been removed.)removed.)

IMF parametersIMF parameters : 1998 - 2006 (from Ace : 1998 - 2006 (from Ace Satellite)Satellite)

AL index AL index : 1998 - 2006 : 1998 - 2006

(Quick Look Preliminary hourly-mean indices)(Quick Look Preliminary hourly-mean indices)

Dst – Ey relationshipDst – Ey relationship

For a given VBs, there seems to be an upperFor a given VBs, there seems to be an upper

limit of the Dst index.limit of the Dst index.

Dst (nT) Dst (nT) ≈≈ -15 VBs (mV/m) + 50 -15 VBs (mV/m) + 50

For example, whenever the VBs reaches For example, whenever the VBs reaches

10 mV/m, the Dst becomes less than -100 nT.10 mV/m, the Dst becomes less than -100 nT.

Dst-Ey relation (main phase)Dst-Ey relation (main phase)

Dst –Ey relation (recovery phase)Dst –Ey relation (recovery phase)

Scatter of Dst for a given EyScatter of Dst for a given Ey

The significant scatter of the Dst index The significant scatter of the Dst index

during a given level of the VBs suggests during a given level of the VBs suggests

that there is another factor(s) contributing that there is another factor(s) contributing

to development of magnetic storms other to development of magnetic storms other

than magnetospheric convection.than magnetospheric convection.

Are we successful in predicting Dst Are we successful in predicting Dst based on IMF parameters? based on IMF parameters?

Burton et al.(1975) Burton et al.(1975)

Q(t) : injection termQ(t) : injection term τ : decay time : decay time

dDst*

dt== Q(t) --

Dst*

τ

Improvement of Burton et al. (1975)Improvement of Burton et al. (1975)' ' ss algorithm has been proposed. algorithm has been proposed.

Fenrich and Luhmann(1998)Fenrich and Luhmann(1998)

O’Brein and McPherron(2000)O’Brein and McPherron(2000)

Wang et al.(2003) Wang et al.(2003)

Park and Ahn(2009)Park and Ahn(2009)

etc.etc.

Q(t) and Q(t) and τ of several models of several models

Injection Term by Park and Ahn(2009)Injection Term by Park and Ahn(2009)

Q(t) = Q(t) = ΔΔDst*Dst*

= function of Ey= function of Ey

Main phaseMain phase : Q(t) = -3.16 VBs – 4.00 : Q(t) = -3.16 VBs – 4.00 Recovery phaseRecovery phase : Q(t) = 0 : Q(t) = 0

ΔΔDst – Ey relationship (main phase)Dst – Ey relationship (main phase)

ΔΔDst – Ey relationship (recovery phase)Dst – Ey relationship (recovery phase)

Dst predictions by IMF parameters Dst predictions by IMF parameters

Burton et al. (1975)Burton et al. (1975) and and

O’Brein and McPherron(2000) O’Brein and McPherron(2000)

c.c = 0.85 c.c = 0.85

Park and Ahn(2009)Park and Ahn(2009)

c.c = 0.84

Most important Interplanetary structures Most important Interplanetary structures that caused intense geomagnetic storms that caused intense geomagnetic storms (Dst≤-100nT) during solar cycle 23(Dst≤-100nT) during solar cycle 23

Sheath field(SH) : 24%Sheath field(SH) : 24% Magnetic cloud proceeded by a fast Magnetic cloud proceeded by a fast

shock(sMC) : 24%shock(sMC) : 24% Sheath field followed by a magnetic Sheath field followed by a magnetic

cloud(SH+MC) : 16%cloud(SH+MC) : 16% Corotating interaction region(CIR) : 13%Corotating interaction region(CIR) : 13%

Echer et al., 2008Echer et al., 2008

Sheath field(SH)Sheath field(SH)

Magnetic cloud proceeded by a fast shock(sMC)Magnetic cloud proceeded by a fast shock(sMC)

Sheath field followed by a magnetic cloud(SH+MC)Sheath field followed by a magnetic cloud(SH+MC)

Corotating interaction region(CIR)Corotating interaction region(CIR)

All types of IMF structuresAll types of IMF structures

No clear signature reflecting the type of No clear signature reflecting the type of interplanetary structure in the Dst-Ey interplanetary structure in the Dst-Ey relationship is noted.relationship is noted.

Dst depends primarily upon Bs/Ey.Dst depends primarily upon Bs/Ey.

Gonzalez and Tsurutani(1987)Gonzalez and Tsurutani(1987) Ey>5 mV/m with T(duration)>3 hours Ey>5 mV/m with T(duration)>3 hours lead to intense (Dst < -100nT) magneticlead to intense (Dst < -100nT) magnetic storms.storms.

Kamide et al.(1998)Kamide et al.(1998) Dst variance during magnetic storm can Dst variance during magnetic storm can be solely reproduced by Ey.be solely reproduced by Ey.

Needed to identify the role of substorm Needed to identify the role of substorm during magnetic storm.during magnetic storm.

Substorm contributionSubstorm contribution

Daglis(1997)Daglis(1997) : enhanced O : enhanced O++ (ionospheric) (ionospheric) contribution to the ring current during contribution to the ring current during intense stormsintense storms

Lui et al.(2001)Lui et al.(2001) : Both substorms and : Both substorms and enhanced convection contribute to the enhanced convection contribute to the buildup of the storm-time ring current.buildup of the storm-time ring current.

Dst-Ey relation (main phase)Dst-Ey relation (main phase)

Dst –Ey relation (recovery phase)Dst –Ey relation (recovery phase)

ΔΔDst – Ey relationship (main phase)Dst – Ey relationship (main phase)

ΔΔDst – Ey relationship (recovery phase)Dst – Ey relationship (recovery phase)

November. 20 – 21, 2003November. 20 – 21, 2003

August 30 – 31, 2004August 30 – 31, 2004

Summary

1. For a given level of VBs, there seems to be an lower limit of the Dst index, indicating that Ey determines at least the minimum size of magnetic storms.

2. No clear signature reflecting the type of 2. No clear signature reflecting the type of interplanetary structures in the Dst-Ey interplanetary structures in the Dst-Ey relationship is noted. Dst depends relationship is noted. Dst depends

primarily upon Bs/Ey.primarily upon Bs/Ey.

3. The significant scatter of the Dst index during a given level of the VBs suggests that there is another factor contributing to the development of magnetic storms other than the magnetospheric convection, possibly substorms.

4. Substorms seem to contribute more 4. Substorms seem to contribute more significantly to the ring current significantly to the ring current intensification during intense storms than intensification during intense storms than moderate ones. moderate ones.

Thank YouThank You