Application of a global magnetospheric-ionospheric current model for dayside and terminator Pi2 pulsations S. Imajo1), A. Yoshikawa2),3), T. Uozumi3), Shin. Ohtani4), A. Nakamizo5), P. J. Chi6) 1) WDC for geomagnetism, Kyoto, Kyoto University, Japan 2) Department of Earth and Planetary Science, Kyushu University, Japan. 3) International Center for Space Weather Science and Education, Kyushu University, Japan. 4) Johns Hopkins University Applied Physics Laboratory, USA. 5) National Institute of Information and Communications Technology, Japan. 6) Institute of Geophysics and Planetary Physics, University of California, USA The results are included in the published paper: Imajo, S., A. Yoshikawa, T. Uozumi, S. Ohtani, A. Nakamizo, and P. J. Chi (2017), Application of a global magnetospheric-ionospheric current model for dayside and terminator Pi2 pulsations, J. Geophys. Res. Space Physics, 122, 8589‒8603, doi: 10.1002/2017JA024246. Key points • The magnetic fields derived by a numerical M-I current model reproduce observed spatial characteristics of dayside and terminator Pi2s. • The oscillating global ionospheric current driven by localized nightside FACs can be a main source of dayside Pi2s. • The terminator effects on Pi2s can be explained by a change in the main contributing currents between FACs and ionospheric currents. Chapter 3. Solar Terminator Effects on Pi2 Pulsations 29 (a) 2011/11/26 AL index (b) 2012/03/06 AL index (c) 2012/03/26 AL index 0 0 0 AEI AL AEI AL AEI AL −500 −500 −500 [nT] [nT] [nT] −1000 −1000 −1000 2100 2130 2200 2230 2030 2100 2130 2200 2030 2100 2130 2200 UT[hhmm] UT[hhmm] UT[hhmm] 2011/11/26 filt 040−150 data 2012/03/06 filt 040−150 data 2012/03/26 filt 040−150 data HVD H −0.5 −1 HVD H (ΔTsr=−1.8 h) −1 Δ HVD H θ =42.0, θ =8.1, ( Tsr=−2.3 h) −1 Δ −1.5 H H θ =8.8, ( Tsr=−2.5 h) C =0.99 −1.5 C =1.00 −1.5 H H ASB H H ASB H C =0.99 −2 −2 H ASB H (ΔTsr=1.4 h) (ΔTsr=1.3 h) −2 (ΔTsr=0.9 h) −2.5 −2.5 −2.5 HVD D [nT] HVD D [nT] HVD D [nT] −3 −3 −3 (ΔTsr=−1.8 h) θ (ΔTsr=−2.3 h) (ΔTsr=−2.5 h) θ =195.5, =183.2, θ =156.1, −3.5 D −3.5 D −3.5 D C =1.00 C =1.00 C =0.98 D D ASB D D ASB D ASB D −4 −4 −4 Δ (ΔTsr=1.3 h) (ΔTsr=0.9 h) ( Tsr=1.4 h) 2150 2155 2200 2205 2055 2100 2105 2110 2055 2100 2105 2110 UT[hhmm] UT[hhmm] UT[hhmm] (d) 2012/04/04 AL index (e) 2012/04/06 AL index (f) 2012/07/06 AL index 0 0 0 AEI AL AEI AL −500 −500 −500 AEI AL [nT] [nT] [nT] −1000 −1000 −1000 2130 2200 2230 2300 2130 2200 2230 2300 1830 1900 1930 2000 UT[hhmm] UT[hhmm] UT[hhmm] 2012/04/04 filt 040−150 data 2012/04/06 filt 040−150 data 2012/07/06 filt 040−150 data HVD H 0 HVD H −1 −1 Δ (ΔTsr=−0.2 h) θ =236.7, ( Tsr=−0.3 h) θ =−42.8, −1.5 H −1.5 H HVD H C =0.82 C =0.97 −1 Δ H ASB H H ASB H θ =18.1, ( Tsr=−1.7 h) −2 −2 H (ΔTsr=2.9 h) (ΔTsr=3.0 h) C =0.97 ASB H −2 H −2.5 −2.5 (ΔTsr=1.2 h) HVD D [nT] −3 [nT] HVD D [nT] HVD D (ΔTsr=−0.3 h) −3 θ =168.2, (ΔTsr=−0.2 h) −3 θ Δ D θ =157.6, =158.1, ( Tsr=−1.7 h) −3.5 C =0.95 −3.5 D D D ASB D C =0.96 C =1.00 ASB D −4 D ASB D −4 D (ΔTsr=2.9 h) −4 (ΔTsr=1.2 h) (ΔTsr=3.0 h) −4.5 2205 2210 2215 2220 2205 2210 2215 2220 1855 1900 1905 1910 UT[hhmm] UT[hhmm] UT[hhmm] (g)2012/08/10 AL index (h) 2012/08/17 AL index (i) 2012/08/19 AL index 0 AEI AL 0 0 AEI AL AEI AL −500 −500 −500 [nT] [nT] [nT] −1000 −1000 −1000 1900 1930 2000 2030 2000 2030 2100 2130 2100 2130 2200 2230 UT[hhmm] UT[hhmm] UT[hhmm] 2012/08/10 filt 040−150 data 2012/08/17 filt 040−150 data 2012/08/19 filt 040−150 data HVD H HVD H −1 Δ −1 HVD H Daysideθ and (terminatorTsr=−1.7 h) Pi2 pulsations(ΔTsr=−0.9 h) −1 =7.2, θ =70.2, θ =−75.4, (ΔTsr=−0.3 h) −1.5 H −1.5 H H C =0.97 C =0.99 H ASB H H ASB H C =0.94 ASB H Dayside−2 Pi2 pulsations are not a simple−2 extension of nightside Pi2s. −2 H (ΔTsr=1.4 h) (ΔTsr=2.2 h) (ΔTsr=2.8 h) SHINOHARA ET AL- GEOMAGNETIC PULSATIONS ACROSS THE DIP EQUATOR 11,749 −2.5 −2.5 HVD D −3 HVD D Jun. 20,1992HVD 13:14-13:22UTD We concludeθ =223.7,that the phase lag of Pi2 pulsationsis (ΔTsr=−0.3 h) Dayside[nT] −3 Pi2 [nT] −3 Δ equator most[nT] lagged D at the dip equator.With increasingof the Δ . θ ( Tsr=−1.7 h) θ =203.6, ( Tsr=−0.9 h) dip latitude,C =0.98 the phaselag is graduallydecreasing. ASB D • =204.0, D D EquatorialD enhancement [Yanagihara and Shimizu,−3.5 1969] SLZ −4 Δ −3.5 C =0.99 C =0.97 3.2. Equatorial Enhancement of Pi2 ( Tsr=2.8 h) ChapterD 3. Solar TerminatorASB D EffectsD on Pi2 PulsationsASB D Amplitudes 30 • Small phase delay at the equator [Shinohara −et4 al., 1997] TER −4 Δ (ΔTsr=2.2 h) −Sastry5 et al. [1983]and Sarma and Sastry [1995] ex- ( Tsr=1.4 h) amined the local time dependenceof amplitude en- −4.5 hancementof the pulsationsignal at the dip equator. In • Near zero m-number (H comp) [Kitamura et al., 1988] EUS 1950 1955 2000 2005 2045 2050 2055 2100 order to discuss2125the relationship2130between 2135amplitude en-2140 UT[hhmm] UT[hhmm] hancementand phaselag UT[hhmm] in the equatorialregion, the CPA amplituderatios between the dip stationand off-dip sta- tionswere plotted as a functionof localtime in Figure 7. Terminator(a)(j) 2012/08/242012/01/17 Pi2 (Pi2 ALAL nearindexindex the dawn/dusk(b) terminator)2012/08/242012/03/03 ALAL indexindex (m)(c) Figure7a shows2012/09/052012/03/23the ratio of Pi2 amplitudesAL AL index indexobserved (k) SMA 00 AEI AL 00 at the0 0Brazilian east coastarray at $LZ (dip latitude • Large D amplitude on the sunlitAEI morningAL [Saka et al., 1982] AEI AL is 0.3ø) to thoseobserved at TER (-2.5ø). The ampli- AEIAEI AL AL AEI ALoff equator tude ratio was distributedat ,.- I during the entire day. −−500500 −−500500 1315UT 1320 −Figure500−500 7b showsthe ratio of Pi2 amplitudesat SLZ to [nT] • [nT] [nT] [nT] D component phase reversals [Imajo et al., [nT] 2015] [nT] thoseat EUS (-3.8ø). The amplituderatio becomes Figure 5. Exp•ndedDayside amplitude-time recordsPi2 from the −1000 −1000 Brazilian east coast arrw SLZ, TER, EUS, CPA, and −1000,.- I duringlocal nighttime, whereas the averagedra- −•1000 −1000 SMA for the period from 1314 to 1322 UT. −1000tio reaches1.5 duringlocal d•ytime. Figure7c shows Dawn-dusk19300700 20000730 asymmetry20300800 2100of0830 terminator effects [Imajo et0800 2130al., 2016]08302200 09002230[Shinohara09302300 et al., 1998] the ratio2130 of Pi20830 amplitudes22000900at SLZ2230 and SMA0930 (-19.8ø).23001000 UT[hhmm]UT[hhmm] UT[hhmm]UT[hhmm] UT[hhmm]UT[hhmm] 120 2012/08/242012/01/17 filtfiltDawn 040040−−150150 side datadata 2012/08/242012/03/03 filtfiltDusk 0403.1.040 Phase−−150 150side Relation datadata of Pi2 at the Dip Equator 2012/09/052012/03/23 filt filt 040 040−150−150 data data −0.5 −0.5 In order to clarify the dependenceof phaselag of an HVD H equatorial Pi2 on localHVD HVDtime andH H dip latitude, we sta- −1 HVD H −0.5 HVD H −1 −1 (∆Tss=−3.9 h) −1 HVD H −1 tistically analyzed 107( Pi2Δ∆Tsr=0.1 events observed h)from June θ =28.2, (ΔTsr=−0.0 h) −1 (∆Tss=−3.7 h) θθ==6.0,−47.1, 1, 1992,to July 5, 1992,( atTss= the Brazilian−4.0east h) coast θ =39.9,H θθ =20.0,=21.6, (ΔTsr=−1.8 h) −−1.51.5 HH −1.5−1.5H −1.5 HH CC=0.99=1.00 array. The diurnal changesin the phase differencebe- CC=0.98=0.99 −1.5 C =0.99 HH tweena pair of stationsASB(TER (dipH latitude = -2.50) - H ASB H C H=0.99 ASB H −2 H ASB H H ASBASB HH −−22 SLZ (0.3ø), EUS (-3.8ø)-SLZ, and SMA (-19.8ø) - −2 (∆Tss=−0.5 h) −−22 SLZ) were obtainedby ( using(Δ∆Tsr=3.2Tss=the cross-correlation−0.6 h) h)func- TER- SLZ (ΔTsr=3.2 h) ((Δ∆Tsr=1.4Tss=−0.5 h) h) i i I i i −2.5 tion. 6 12 −2.5 −2.5 −2.5−2.5-120•) 18 LT 24 −2.5 The phaselags of Pi2 HVDpulsations D between TER-SLZ, 120 - [nT] [nT] [nT] [nT] HVD D [nT] [nT] HVD D HVD D −3 EUS-SLZ, and SMA-SLZHVD are D shown as a function of HVD D −3 Δ −3 θ =146.7, local time in Figure 6.