Geosynchronous Magnetic Field Response to Solar Wind Dynamic Pressure

  • Park, Jong-Sun ;
  • Kim, Khan-Hyuk ;
  • Lee, Dong-Hun ;
  • Lee, En-Sang ;
  • Jin, Ho
  • Received : 2010.12.06
  • Accepted : 2011.01.09
  • Published : 2011.03.15


The present study examines the morning-afternoon asymmetry of the geosynchronous magnetic field strength on the dayside (magnetic local time [MLT] = 06:00~18:00) using observations by the Geostationary Operational Environmental Satellites (GOES) over a period of 9 years from February 1998 to January 2007. During geomagnetically quiet time (Kp < 3), we observed that a peak of the magnetic field strength is skewed toward the earlier local times (11:07~11:37 MLT) with respect to local noon and that the geosynchronous field strength is larger in the morning sector than in the afternoon sector. That is, there is the morning-afternoon asymmetry of the geosynchronous magnetic field strength. Using solar wind data, it is confirmed that the morning-afternoon asymmetry is not associated with the aberration effect due to the orbital motion of the Earth about the Sun. We found that the peak location of the magnetic field strength is shifted toward the earlier local times as the ratio of the magnetic field strength at MLT = 18 (B-dusk) to the magnetic field strength at MLT = 06 (B-dawn) is decreasing. It is also found that the dawn-dusk magnetic field median ratio, B-dusk/B-dawn, is decreasing as the solar wind dynamic pressure is increasing. The morning-afternoon asymmetry of the magnetic field strength appears in Tsyganenko geomagnetic field model (TS-04 model) when the partial ring current is included in TS-04 model. Unlike our observations, however, TS-04 model shows that the peak location of the magnetic field strength is shifted toward local noon as the solar wind dynamic pressure grows in magnitude. This may be due to that the symmetric magnetic field associated with the magnetopause current, strongly affected by the solar wind dynamic pressure, increases. However, the partial ring current is not affected as much as the magnetopause current by the solar wind dynamic pressure in TS-04 model. Thus, our observations suggest that the contribution of the partial ring current at geosynchronous orbit is much larger than that expected from TS-04 model as the solar wind dynamic pressure increases.


geosynchronous magnetic field;solar wind dynamic pressure;partial ring current


  1. Bakhmina KY, Kalegaev VV, Modeling the partial ring current effect in a disturbed magnetosphere, Ge&Ae, 48, 737-746 (2008). doi: 10.1134/S0016793208060066
  2. Borovsky JE, Denton MH, Magnetic field at geosynchronous orbit during high-speed stream-driven storms: Connections to the solar wind, the plasma sheet, and the outer electron radiation belt, JGR, 115, A08217 (2010). doi: 10.1029/2009JA015116
  3. Bostrom R, Physics of the hot plasma in the magnetosphere (Plenum Press, New York, 1975), 341.
  4. Cummings WD, Asymmetric ring currents and the low-latitude disturbance daily variation, JGR, 71, 4495-4503 (1966). doi: 10.1029/JZ071i019p04495
  5. Dmitriev AV, Suvorova AV, Chao JK, Yang YH, Dawn-dusk asymmetry of geosynchronous magnetopause crossings, JGR, 109, A05203 (2004). doi: 10.1029/2003JA010171
  6. Kim K, Hwang J, Sung S, Geosynchronous magnetic field variations associated with the passage of interplanetary shocks or solar wind discontinuities, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract SM41B-01 (2007).
  7. Kokubun S, Characteristics of storm sudden commencement at geostationary orbit, JGR, 88, 10025-10033 (1983). doi: 10.1029/JA088iA12p10025
  8. Le G, Russell CT, Takahashi K, Morphology of the ring current derived from magnetic field observations, AnGeo, 22, 1267-1295 (2004). doi: 10.5194/angeo-22-1267-2004
  9. Lui ATY, Inner magnetospheric plasma pressure distribution and its local time asymmetry, GeoRL, 30, 1846-1849 (2003) doi: 10.1029/2003GL017596
  10. McComas DJ, Bame SJ, Barraclough BL, Donart JR, Elphic RC, et al., Magnetospheric plasma analyzer: initial three-spacecraft observations from geosynchronous orbit, JGR, 98, 13453-13465 (1993). doi: 10.1029/93JA00726
  11. Nakano S, Ueno G, Ohtani S, Higuchi T, Impact of the solar wind dynamic pressure on the Region 2 field-aligned currents, JGR, 114, A02221 (2009). doi: 10.1029/2008JA013674
  12. Rufenach CL, McPherron RL, Schaper J, The quiet geomagnetic field at geosynchronous orbit and its dependence on solar wind dynamic pressure, JGR, 97, 25-42 (1992). doi: 10.1029/91JA02135
  13. Shue JH, Song P, Russell CT, Steinberg JT, Chao JK, et al., Magnetopause location under extreme solar wind conditions, JGR, 103, 17691-17700 (1998). doi: 10.1029/98JA01103
  14. Tsyganenko NA, Sitnov MI, Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms, JGR, 110, A03208 (2005). doi: 10.1029/2004JA010798
  15. Wolf RA, Spiro RW, Sazykin S, Toffoletto FR, How the Earth’s inner magnetosphere works: An evolving picture, JASTP, 69, 288-302 (2007). doi: 10.1016/j.jastp.2006.07.026


Supported by : National Research Foundation of Korea