Pc1/EMIC waves observed at geosynchronous orbit and subauroral latitude during sudden magnetospheric compressions Khan-Hyuk Kim 1 , K. Shiokawa 2 , D.-H. Lee 1 , H.-J. Kwon 1 , E. Lee 1 , and M. Connors 3 1 Dept. of Astronomy and Space Science, Kyung-Hee University, Korea. 2 Solar-Terrestrial Environment Laboratory, Nagoya University, Japan. 3 Centre 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 observation 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] B • The compression events not only increase the magnetospheric field but also convect MLT ~ 13.8-14.3 (7.5-8.7 R E ) plasma earthward. • Thus the compression-Pc1 correlation can be caused by - inward motion of plasma previously B = Obs./T87-1 unstable to EMIC waves (i.e., spatial convection of EMIC waves) or - temporal onset of EMIC waves Integrated power: from f He+ to f H+
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 onset. • Statistical study: SC-associated PC1 waves * Only used ATH ground data: Sept. 2005 ~ Aug. 2011 * 47 SC events were identified.
Magnetospheric response to Averaged MP Interplanetary (IP) shock Compressed MP Interplanetary (IP) space: ~500-800 km/s N > 10 /cc Solar wind (V, N)/IMF (B) RC variations ExB flows ~400 km/s N < 10 /cc IP shock+ 15 10 5 Magnetic 5 cloud Dawn-Dusk Geosynchronous E field CME Time orbit 10 15 Sudden Commencement (SC): Ground observation Sudden increase in H- component at low latitude the order of 10 nT ~ several minutes
Case study: SC event on 19 Nov 2007 Solar wind obs. at ACE Magnetospheric responses SYM-H B T 18:10 UT SC onset at 18:10 UT B z 17:15 UT On the ground Geosynchronous orbit B T Vsw Pdyn
Comparison of B T at geosynchronous orbit IP shock front direction MLT vs UT G10 12 Magnetopause G12 G11 18 06 B T G11 Geosynchronous G12 orbit 00 G10 Compressed magnetopause
Sudden decrease in B T at GOES 10 & 12 AL index GOES 10 B T
SC-associated EMIC/Pc1 waves at GOES S/C GOES 11 in MFA coordinates GOES 10 in MFA coordinates Log PSD (MLT = 9.3 at SC onset) (MLT = 14.4 at SC onset) [(nT/0.6s) 2 /Hz] Bx (B ) Bx (B ) He+ He+ O+ O+ By (B ) By (B ) Bz (B || ) Bz (B || )
SC-associated EMIC/Pc1 waves at GOES S/C GOES 12 in MFA coordinates GOES 10 in MFA coordinates Log PSD (MLT = 13.3 at SC onset) (MLT = 14.4 at SC onset) [(nT/0.6s) 2 /Hz] Bx (B ) Bx (B ) He+ He+ O+ O+ By (B ) By (B ) Bz (B || ) Bz (B || )
Coherence analysis of EMIC/Pc1 waves Transverse components at GOES 11 Sample time series plots (MLT = 9.3 at SC onset) near SC onset time Bx (B ) GOES 11 By (B ) B > 0.7
Why low coherence between Bx and By? The cross correlation function: T 1 R ( ) lim ( t ) ( t ) dt T T 0 The cross-spectral function G ( f ): the Fourier transformation of R ( ) ( ) ( ) ( ) G f C f iQ f B 2 G ( f ) ( f ) : Coherence G ( f ) G ( f ) Coherence Q ( f ) 1 ( f ) tan : Cross phase C ( f ) > 0.7 In order for and signals to produce Cross phase high coherence both the phase delay and amplitude ratio need to remain constant.
Coherence analysis of EMIC/Pc1 waves GOES 10 GOES 12 (MLT = 14.4 at SC onset) (MLT = 13.3 at SC onset) Bx Bx By By > 0.7 > 0.7
SC-associated Pc1 at ATH (L ~ 4.6, MLAT ~ 62 ) ATH (LT = UT 7.6) GOES 11 (MLT = 9.3 at SC onset) (MLT = 10.6 at SC onset) Bx Sym-H dH/dt He+ O+ By dD/dt SYM-H = 14 nT > 0.7 SC-associated PC1/EMIC waves: Low coherence between Bx and By and between dH/dt and dD/dt
Pc1 observations at ATH (L ~ 4.6, MLAT ~ 62 ) 2005 Day 252 Sep 9 (ATH: 6.4 MLT) Comparison of Pc1 pulsations before SC and associated with SC SYM-H SYM-H = 39 nT dH/dt He+ dD/dt Coherence Cross phase Very complex SC-associated Pc1 waves could originate from sources on several different field lines.
Pc1 observations at ATH (L ~ 4.6, MLAT ~ 62 ) 2005 Day 252 Sep 15 (ATH: 1.4 MLT) SYM-H SC-associated EMIC/Pc1 waves Sep 9, 2005 event: Low coherence • ATH was in the early morning (MLT ~ dH/dt 6.4) when SC occurred. • SC-associated Pc1 waves in dH/dt and dD/dt with relatively broadband spectrum. dD/dt • Low coherence between dH/dt and dD/dt. Sep 15, 2005 event: High coherence 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. Cross phase • High coherence between dH/dt and dD/dt. Universal time
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
Comparison of EMIC/Pc1 and SC-associated EMIC/Pc1 wave occurrence probabilities SC-associated Pc1 waves THEMIS Observations at ATH (L ~ 4.6) :47 :24 Min et al. [2012]
MLT dependence of PC1 wave power 2005 Day 252 Sep 9 (ATH: 6.4 MLT) 24 SC-associated Pc1 events SYM-H f O+ MLT of ATH 1 / 2 2 Hz Power PSD _ P ( f ) df H No clear MLT dependence f O of Pc1 wave power
SC-associated PC1 wave power depending on solar wind dynamic pressure variation ( P dyn 1/2 ) Pc1 power vs. P dyn Pc1 power vs. SYM-H 1/2
Magnetospheric compressions enhance EMIC/Pc1 wave activity: Q) By increasing the energetic proton temperature, anisotropy, and hot particle density? Pc1 power vs. P dyn 1/2 Hybrid code simulation N Hot = 3% (solid line) N Hot = 6% (dash-dot line) N Hot = 12% (dashed line) Bortnik et al. [2011]
Magnetospheric compressions enhance EMIC/Pc1 wave activity: Q) By enhanced compressional power? Source Pc1 power vs. P dyn 1/2 P dyn P dyn Time It is well known that intensifications in ground ULF wave power are related to Frequency increases in the solar wind dynamic pressure.
SC-associated EMIC/Pc1 waves at GOES S/C GOES 11 in MFA coordinates GOES 10 in MFA coordinates Log PSD (MLT = 9.3 at SC onset) (MLT = 14.4 at SC onset) [(nT/0.6s) 2 /Hz] Bx (B ) Bx (B ) He+ He+ O+ O+ By (B ) By (B ) Bz (B || ) Bz (B || )
Pc1 observations at ATH (L ~ 4.6, MLAT ~ 62 ) 2005 Day 252 Sep 9 (ATH: 6.4 MLT) Comparison of Pc1 pulsations before SC and associated with SC SYM-H SYM-H = 39 nT dH/dt He+ dD/dt Coherence Cross phase 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 ( P dyn ).
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