geosynchronous orbit and subauroral latitude during sudden - - PowerPoint PPT Presentation

Pc1/EMIC waves observed at geosynchronous orbit and subauroral latitude during sudden magnetospheric compressions

Khan-Hyuk Kim1, K. Shiokawa2, D.-H. Lee1, H.-J. Kwon1, E. Lee1, and M. Connors3

• 1Dept. of Astronomy and Space Science, Kyung-Hee University, Korea.

2Solar-Terrestrial Environment Laboratory, Nagoya University, Japan. 3Centre for Science, Athabasca University, Canada.

Outline

• Introduction
• Previous studies: Sudden commencement (SC)-

associated EMIC/Pc1 waves

• SC-associated EMIC/Pc1 waves :
• Case study: GOES observations in space and ground
• bservation at Athabasca station, Canada (ATH:

54.7N, 246.7E, MLAT ~ 62N, L ~ 4.6)

• Statistical results: SC-associated EMIC/Pc1 waves at

ATH station

• Summary

Magnetospheric compressions and EMIC waves

Anderson and Hamilton [1993]

MLT ~ 13.8-14.3 (7.5-8.7 RE)

• The compression events not only increase

the magnetospheric field but also convect plasma earthward.

• Thus the compression-Pc1 correlation

can be caused by

• inward motion of plasma previously

unstable to EMIC waves (i.e., spatial convection of EMIC waves) or

• temporal onset of EMIC waves

B = Obs./T87-1 Integrated power: from fHe+ to fH+

B

Data

• Case study: Sudden Commencement (SC) event on 19

November 2007 * In space: Fluxgate magnetometer data (~0.6s) from GOES 10, 11, and 12. * On the Ground: Induction magnetometer (~0.02s) at Athabasca, Canada (ATH: 54.7N, 246.7E, MLAT ~ 62N, L ~ 4.6) station and SYM-H to determine SC

• nset.
• Statistical study: SC-associated PC1 waves

* Only used ATH ground data: Sept. 2005 ~ Aug. 2011 * 47 SC events were identified.

~400 km/s N < 10 /cc ~500-800 km/s N > 10 /cc Averaged MP Compressed MP Geosynchronous

• rbit

Dawn-Dusk E field ExB flows RC 5 10 15 5 10 15

CME Solar wind (V, N)/IMF (B) variations Interplanetary (IP) space:

IP shock+ Magnetic cloud

Time

~ several minutes the order of 10 nT Sudden increase in H- component at low latitude Sudden Commencement (SC): Ground observation

Magnetospheric response to Interplanetary (IP) shock

Case study: SC event on 19 Nov 2007

Solar wind obs. at ACE Magnetospheric responses

Vsw Pdyn BT Bz

On the ground SC onset at 18:10 UT Geosynchronous orbit

18:10 UT 17:15 UT

BT SYM-H

Magnetopause

Geosynchronous

• rbit

06 00 12 18 Compressed magnetopause

Comparison of BT at geosynchronous orbit

BT

IP shock front direction

MLT vs UT

G10 G12 G11 G11 G12 G10

Sudden decrease in BT at GOES 10 & 12

GOES 10 BT AL index

SC-associated EMIC/Pc1 waves at GOES S/C

He+ O+ He+ O+

GOES 11 in MFA coordinates (MLT = 9.3 at SC onset)

By (B) Bz (B||)

Log PSD [(nT/0.6s)2/Hz]

GOES 10 in MFA coordinates (MLT = 14.4 at SC onset)

Bx (B) Bx (B) By (B) Bz (B||)

SC-associated EMIC/Pc1 waves at GOES S/C

He+ O+

Log PSD [(nT/0.6s)2/Hz]

GOES 10 in MFA coordinates (MLT = 14.4 at SC onset) GOES 12 in MFA coordinates (MLT = 13.3 at SC onset)

He+ O+ Bx (B) Bx (B) By (B) By (B) Bz (B||) Bz (B||)

Coherence analysis of EMIC/Pc1 waves

Transverse components at GOES 11 (MLT = 9.3 at SC onset)  > 0.7 Sample time series plots near SC onset time Bx (B) By (B) GOES 11 B

Why low coherence between Bx and By?

 > 0.7

Coherence Cross phase

The cross correlation function:



 

  T T

dt t t T R ) ( ) ( 1 lim ) (    



) ( ) ( ) ( f iQ f C f G

  

 

The cross-spectral function G(f): the Fourier transformation of R()

) ( ) ( ) ( ) (

2

f G f G f G f

   

  ) ( ) ( tan ) (

1

f C f Q f

  







: Cross phase : Coherence

In order for  and  signals to produce high coherence both the phase delay and amplitude ratio need to remain constant.

B

GOES 10 (MLT = 14.4 at SC onset) GOES 12 (MLT = 13.3 at SC onset) Bx Bx By By  > 0.7  > 0.7

Coherence analysis of EMIC/Pc1 waves

GOES 11 (MLT = 9.3 at SC onset)  > 0.7 Bx By He+ O+ ATH (LT = UT  7.6) (MLT = 10.6 at SC onset) Sym-H dH/dt dD/dt SC-associated PC1/EMIC waves: Low coherence between Bx and By and between dH/dt and dD/dt

SC-associated Pc1 at ATH (L ~ 4.6, MLAT ~ 62)

SYM-H = 14 nT

Pc1 observations at ATH (L ~ 4.6, MLAT ~ 62)

2005 Day 252 Sep 9 (ATH: 6.4 MLT) dH/dt dD/dt Coherence Cross phase SYM-H He+

SYM-H = 39 nT

Comparison of Pc1 pulsations before SC and associated with SC Very complex SC-associated Pc1 waves could originate from sources on several different field lines.

SYM-H 2005 Day 252 Sep 15 (ATH: 1.4 MLT)

Pc1 observations at ATH (L ~ 4.6, MLAT ~ 62)

dH/dt dD/dt Coherence Cross phase

Universal time

Sep 9, 2005 event: Low coherence

• ATH was in the early morning (MLT ~

6.4) when SC occurred.

• SC-associated Pc1 waves in dH/dt and

dD/dt with relatively broadband spectrum.

• Low coherence between dH/dt and

dD/dt. Sep 15, 2005 event: High coherence

• ATH was near the midnight (MLT ~

1.4) when SC occurred.

• SC-associated Pc1 waves in dH/dt and

dD/dt with broadband spectrum.

• High coherence between dH/dt and

dD/dt.

SC-associated EMIC/Pc1 waves

Statistical results of SC-associated PC1 waves

• 47 SC events for the time interval from September 2005 to August 2011.
• Out of 47 SC events, 24 SC-associated PC1 waves were observed at ATH

station.

• Out of 24 SC-associated Pc1 events, only four events show high coherence

between dH/dt and dD/dt.

Local time distribution Local time distribution

:47 :24

Min et al. [2012]

THEMIS Observations SC-associated Pc1 waves at ATH (L ~ 4.6)

Comparison of EMIC/Pc1 and SC-associated EMIC/Pc1 wave occurrence probabilities

:24 :47

MLT dependence of PC1 wave power

2 / 1 2

) ( _ Power          



Hz f H

O

df f P PSD

2005 Day 252 Sep 9 (ATH: 6.4 MLT)

fO+

SYM-H

24 SC-associated Pc1 events

MLT of ATH

No clear MLT dependence

• f Pc1 wave power

SC-associated PC1 wave power depending on solar wind dynamic pressure variation (Pdyn

1/2)

Pc1 power vs. Pdyn

1/2

Pc1 power vs. SYM-H

Magnetospheric compressions enhance EMIC/Pc1 wave activity: Q) By increasing the energetic proton temperature, anisotropy, and hot particle density?

Pc1 power vs. Pdyn

1/2

Bortnik et al. [2011]

NHot = 3% (solid line) NHot = 6% (dash-dot line) NHot = 12% (dashed line)

Hybrid code simulation

Magnetospheric compressions enhance EMIC/Pc1 wave activity: Q) By enhanced compressional power?

Pc1 power vs. Pdyn

1/2

Time Pdyn Pdyn Frequency

Source

It is well known that intensifications in ground ULF wave power are related to increases in the solar wind dynamic pressure.

SC-associated EMIC/Pc1 waves at GOES S/C

He+ O+ He+ O+

GOES 11 in MFA coordinates (MLT = 9.3 at SC onset)

By (B) Bz (B||)

Log PSD [(nT/0.6s)2/Hz]

GOES 10 in MFA coordinates (MLT = 14.4 at SC onset)

Bx (B) Bx (B) By (B) Bz (B||)

Pc1 observations at ATH (L ~ 4.6, MLAT ~ 62)

2005 Day 252 Sep 9 (ATH: 6.4 MLT) dH/dt dD/dt Coherence Cross phase SYM-H He+

SYM-H = 39 nT

Comparison of Pc1 pulsations before SC and associated with SC Very complex SC-associated Pc1 waves could originate from sources on several different field lines.

Summary

SC-associated EMIC/Pc1 waves:

• Low coherence between transverse components (i.e., Bx

and By) at geosynchronous orbit and between dH/dt and dD/dt at ATH ground station (L ~ 4.6).

• Low coherence is due to the fact that the phase delay

between Bx and By (dH/dt and dD/dt) is not constant during the interval of SC-associated EMIC/Pc1 wave enhancement (i.e., the very complex waves originated from sources on several field lines).

• Positive correlation between EMIC/Pc1 wave power and

solar wind dynamic pressure variation (Pdyn).