World Library  

Add to Book Shelf
Flag as Inappropriate
Email this Book

Physical Meaning of the Equinoctial Effect for Semi-annual Variation in Geomagnetic Activity : Volume 27, Issue 5 (04/05/2009)

By Yoshida, A.

Click here to view

Book Id: WPLBN0004001996
Format Type: PDF Article :
File Size: Pages 6
Reproduction Date: 2015

Title: Physical Meaning of the Equinoctial Effect for Semi-annual Variation in Geomagnetic Activity : Volume 27, Issue 5 (04/05/2009)  
Author: Yoshida, A.
Volume: Vol. 27, Issue 5
Language: English
Subject: Science, Annales, Geophysicae
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


APA MLA Chicago

Yoshida, A. (2009). Physical Meaning of the Equinoctial Effect for Semi-annual Variation in Geomagnetic Activity : Volume 27, Issue 5 (04/05/2009). Retrieved from

Description: National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo, 173-8515, Japan. Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity is investigated based on the three-hourly am index and solar wind parameters. When the z component of the interplanetary magnetic field (IMF) in geocentric solar magnetospheric (GSM) coordinates is southward, am indices are well correlated with BsVx2, where Bs is the southward component of the IMF and Vx is the solar wind velocity in the sun-earth direction. The am-BsVx2 relationship, however, depends on the range of Vx2: the am in higher ranges of Vx2 tends to be larger than am in lower ranges of Vx2 for the same value of BsVx2 for both equinoctial and solstitial epochs. Using the data sets of the same Vx2 range, it is shown that distribution of points in the am-BsVx2 diagram at the solstitial epochs overlaps with that at the equinoctial epochs and the average am values in each BsVx2 bin in solstitial epochs are closely consistent with those in equinoctial epochs, if Vx2 for each point at solstices are reduced to Vx2sin2 (Ψ) where Ψ is the geomagnetic colatitude of the sub-solar point. Further, it is shown that monthly averages of the am index in the long period is well correlated with the values of sin2(ψ) for the middle day of each month. These findings indicate that the factor that contributes to the generation of geomagnetic disturbance is not the velocity of the solar wind, but the component of the solar wind velocity perpendicular to the dipole axis of the geomagnetic field. The magnitude of the perpendicular velocity component varies semi-annually even if the solar wind velocity remains constant, which is considered to be the long-missed key factor causing the equinoctial effect.

Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity

Bartels, J.: Terrestrial-magnetic activity and its relation to solar phenomena, Terr. Mag. Atmos. Electr., 37, 1–52, 1932.; Berthelier, A.: Influence of the polarity of the interplanetary magnetic field on the annual and diurnal variations of magnetic activity, J. Geophys. Res., 81, 4546–4551, 1976.; Berthelier, A.: Comments on The universal time variation of magnetic activity, Geophys. Res. Lett., 17, 307–308, 1990.; Boller, B. R. and Stolov, H.: Kelvin-Helmholtz instability and the semiannual variation of geomagnetic activity, J. Geophys. Res., 75, 6073–6084, 1975.; Cliver, E. W., Kamide, Y., and Ling, A. G.: Mountains versus valleys: Semiannual variation of geomagnetic activity, J. Geophy. Res., 105, 2413–2424, 2000.; Cliver, E. W., Svalgaard, L., and Ling, A. G.: Origins of the semiannual variation of geomagnetic activity in 1954 and 1996, Ann. Geophys., 22, 93–100, 2004.; Cliver, E. W., Kamide, Y., and Ling, A. G.: The semiannual variation of geomagnetic activity: phases and profiles for 130 years of \textitaa data, J. Atmos. Solar-Terr. Phys., 64, 47–53, 2002.; Cliver, E. W., Kamide, Y., Ling, A. G., and Yokoyama, N.: Semiannual variation of the geomagnetic $D_st$ index: Evidence for a dominant nonstorm component, J. Geophy. Res., 106, 21297–21304, 2001.; Cortie, A. L.: Sunspots and terrestrial magnetic phenomena, 1898–1911, Mon. Notic. R. Astron. Soc., 73, 52–60, 1912.; Crooker, N. U. and Siscoe, G. L.: On the limits of energy transfer through dayside merging, J. Geophys. Res., 91, 13393–13397, 1986.; de La Sayette, P. and Berthelier, A.: The \textitam annual-diurnal variations 1959–1988: A 30-year evaluation, J. Geophys. Res., 10653–10663, 1996.; Feynman, J.: Implications of solar cycles 19 and 20, Geophys. Res. Lett., 7, 971–973, 1980.; Hill, T. W.: Rates of mass, momentum, and energy transfer at the magnetopause, Magnetospheric Boundary Layers, edited by Battrick, B, Eur. Space Agency Spec. Publ., ESA SP-148, 325–332, 1979.; Maezawa, K. and Murayama, T.: Solar wind velocity effects on the auroral zone magnetic disturbances, in: Solar Wind-Magnetosphere Coupling, edited by: Kamide Y. and Slavin, J. A., pp. 59–83, Terra Scientific, Tokyo, 1986.; Mayaud, P. N.: The annual and daily variations of the \textitDst index, Geophys. J. R. Astron. Soc., 55, 193–201, 1978.; McIntosh, D. H.: On the annual variation of magnetic disturbance, Phil. Trans. Roy. Soc. London, Ser. A, 251, 525–552, 1959.; Menvielle, M. and Berthelier, A.: The K-derived planetary indices: Description and availability, Rev. Geophys., 29, 415–432, 1991.; Murayama, T.: Origin of the semiannual variation of geomagnetic \textitKp indices, J. Geophys. Res., 79, 297–300, 1974.; O'Brien, T. P. and McPherron, R. L.: Semiannual and diurnal variation of \textitDst dynamics, J. Geophys. Res., 107(A11), 1341, doi:10.1029/2002JA009435, 2002.; Russell, C. T. and McPherron, R. L.: Semiannual variation of geomagnetic activity, J. Geophys. Res., 78, 92–108, 1973.; Sabine, E.: On periodical laws discoverable in the mean effects of the larger magnetic disturbances, II, Philos. Trans. R. Soc. London, 142, 103–124, 1852.; Schreiber, H.: Correlation of geomagnetic activity indices Ap with the solar wind speed and southward interplanetary magnetic field, J. Geophys., 49, 169–175, 1981.; Svalgaard, L.: The semiannual variation of great geomagnetic storms, Geophys. Res. Lett., 29(16), 12, doi:10.1029/2001GL014145, 2002.; Svalgaard, L.: Geomagnetic activity: Dependence on solar wind parameters, in: Coronal Holes and High Speed Wind Streams, edited by: Zirker, J. B., pp. 371–441, Colo. Assoc. Univ. press, Boulder, Colo., 1977.; Yoshida, A.: Why was the geomagnetic activity in 2003 extraordinarily high?, J. Atmos. Solar-Terr. Phys., in review, 2009a.; Yoshida, A.: Semi-annual variations in the \textitAE and \textitam indices, Japan Geoscience Union Meeting 2009, E118, 2009b.


Click To View

Additional Books

  • Observations and Modeling of Post-midnig... (by )
  • Letter to the EditiorTesting the Hypothe... (by )
  • The Emission of Oxygen Green Line and De... (by )
  • Sensitivity of the Simulated Precipitati... (by )
  • Conjugate Observation of Sharp Dynamical... (by )
  • Origin of Some Anisotropic Tailward Flow... (by )
  • Electronic Kinetics of Molecular Nitroge... (by )
  • Surface Heat Fluxes and Ecosystem Functi... (by )
  • Distortions of the Magnetic Field by Sto... (by )
  • Coastal Upwelling Along the Southwest Co... (by )
  • Interpolation of Externally-caused Magne... (by )
Scroll Left
Scroll Right


Copyright © World Library Foundation. All rights reserved. eBooks from National Public Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.