Day-to-day Variations in the Solar Quiet (Sq) Current System

Transcription

1 14th International Symposium on Equatorial Aeronomy (ISEA) Bahir Dar, Ethiopia, 19 October 2015 Day-to-day Variations in the Solar Quiet (Sq) Current System Yosuke Yamazaki (YY) Department of Physics, Lancaster University, Lancaster, UK

2 [Richmond et al., 1976] J = "(E + U # B) Neutral wind in the dynamo region ( km) Geomagnetic Sq variations [Campbell et al., 1993] Ionospheric Sq current system

3 Data-model comparison J = "(E + U # B) Global models (First-principles models) Validation Physical insight Global observations of Sq variations [Campbell et al., 1993] Ionospheric Sq current system

4 2009 solar minimum Kp<3 for 39 continuous days! From 15-May-2009 through 22-June-2009

5 Total 144 stations below 60 magnetic latitudes

6 (1) 105 stations from WDC for Geomagnetism (Edinburgh) (2) 11 stations MAGDAS/CPMN, Kyushu University (3) 13 stations from Geographical Survey Institute (GSI) of Japan (4) 3 stations from Ocean Hemisphere network Project (OHP), Tokyo University (5) 2 stations from Ionospheric Prediction Service (IPS), Australia (6) 10 stations from SuperMAG [

7 Data Procedures Magnetic apex coordinates Examples of spherical harmonic functions m=1, n=1 m=1, n=2 m=2, n=2 m=1, n=3 [Richmond, 1995] (1) Spherical harmonic analysis similar to Takeda [2002] (2) Perform S.H.A. in Magnetic apex coordinates (3) Calculate equivalent Sq current system at 0200UT (4) Map into geographic coordinates

8 TIME-GCM: Thermospher Ionosphere Mesosphere Electrodynamics General Circulation Model (NCAR) [Roble and Ridley, 1994] (1) Global, 3-D, and time dependent (2) Height range: km (3) Electric fields & currents in IGRF (4) Weather effects [H.-L. Liu et al., 2013] Zonal mean zonal wind WACCM-X nudging Latitude [Roble and Ridley, 1994] 90 Height (km) m NmF2 (51S, 58W) LT [H.-L. Liu et al., 2013] Day-to-day variability of the ionosphere

9 Alt. (km) Alt. (km) Day-to-day variability in the quiet-time EEJ Kp=1 (constant) F10.7=70 (constant) [Yamazaki et al., 2014] Mag. Field (nt) Latitude Mag. Latitude Time (date) Daytime cross section of zonal wind in the HUA longitude Equatorial electrojet over HUA Geomagnetic Sq variations at HUA Local time (hrs)

10 Observations TIMEGCM/WACCM-X Kp=1 (constant) F10.7=70 (constant)

11 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current Discrepancies: (1) High-latitude currents (2) Cross equatorial currents (3) N-S asymmetry Model (4) Longitudinal displacement

12 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current Discrepancies: (1) High-latitude currents (2) Cross equatorial currents (3) N-S asymmetry Model (4) Longitudinal displacement

13 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current Discrepancies: (1) High-latitude currents (2) Cross equatorial currents (3) N-S asymmetry Model (4) Longitudinal displacement

14 Data 151 ka 65 ka Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka (3) Little nocturnal current Model 105 ka 90 ka Discrepancies: (1) High-latitude currents (2) Cross equatorial currents (3) N-S asymmetry (4) Longitudinal displacement

15 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current Discrepancies: (1) High-latitude currents (2) Cross equatorial currents (3) N-S asymmetry Model (4) Longitudinal displacement

16 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current Data-model discrepancies: The model does not reproduce N-S asymmetry which Discrepancies: observations strongly suggest. (1) High-latitude currents (2) Cross equatorial currents (3) N-S asymmetry Model (4) Longitudinal displacement

17 TIE-GCM: Thermospher Ionosphere Electrodynamics General Circulation Model (NCAR) [Richmond et al., 1992] (1) Global, 3-D, and time dependent (2) Height range: km (3) Electric fields & currents in IGRF (4) Lower boundary tides [Wu et al., 2012] Zonal mean zonal wind Advantage: More accurate tidal winds (constrained by satellite data at 96 km) Tides from TIMED sat. (1) TIDI winds (2) SABER temp Latitude [Roble and Ridley, 1994] 90 Height (km) Disadvantage: No day-to-day variability

18 Observations Data TIEGCM/TIMED Model

19 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current (4) Cross equatorial currents (5) N-S asymmetry (6) Longitudinal displacement Discrepancies: (1) High-latitude currents Model

20 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current (4) Cross equatorial currents (5) N-S asymmetry (6) Longitudinal displacement Discrepancies: (1) High-latitude currents Model

21 151 ka Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data Model 65 ka 103 ka 67 ka (3) Little nocturnal current (4) Cross equatorial currents (5) N-S asymmetry (6) Longitudinal displacement Discrepancies: (1) High-latitude currents

22 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current (4) Cross equatorial currents (5) N-S asymmetry (6) Longitudinal displacement Discrepancies: (1) High-latitude currents Model

23 Similarities: (1) Northern c.c.w. vortex southern c.w. vortex (2) Current intensity ~100 ka Data (3) Little nocturnal current Data-model agreement improved: (4) Cross equatorial currents The model #2 was able to reproduce N-S (5) N-S asymmetry asymmetry in the Sq current system (6) Longitudinal displacement Discrepancies: (1) High-latitude currents Model

24 Model #1 TIMEGCM/WACCM-X (1) Semidiurnal tides are dominant. (2) Tidal amplitudes are comparable. Model #2 TIEGCM/TIMED

25 Model #1 TIMEGCM/WACCM-X Semidiurnal tide symmetric mode Model #2 TIEGCM/TIMED Semidiurnal tide anti-symmetric mode

26 Equivalent Sq current systems, derived using groundmagnetometer data from 144 mid-low latitude stations, are compared with global models. TIMEGCM/WACCM-X (Model #1) Forcing from the lower atmosphere can be a significant source of the day-to-day variability in Sq currents TIEGCM/TIMED (Model #2) Anti-symmetric mode semidiurnal tide plays an important role to produce the N-S asymmetry of Sq currents

27 Model Use of accurate neutral winds at E-region heights Realistic features of Sq current system Ground magnetometers Observation

28 Model Accurate neutral winds at E-region heights Accurate global Sq current system Day-to-day variations Historical reconstruction Ground magnetometers Satellite magnetometers Observation

29 Thank you for your attention!