The semiannual variation of geomagnetic activity: phases and profiles for 130 years of aa data

Cliver, E. W.; Kamide, Y.; Ling, A. G.

doi:10.1016/s1364-6826(01)00093-1

Cited by 68 publications

(76 citation statements)

References 17 publications

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“…However, the most significant effect on the average auroral arc altitude (and by inference the electron energy , geomagnetic effects (Lyatsky et al, 2001), and auroral brightness (Shue et al, 2001)) appears to be the initial ionospheric conductance. It has been found adequate for and consistent with the equinoctial preference for auroral activity as well Cliver et al, 2002;Liou et al, 2001;Lyatsky et al, 2001) The purpose of this exercise has been to show that whatever the magnetospheric auroral electron acceleration mechanism is, it appears to be affected by the state of the ionosphere, in particular the Pedersen conductance. If this is true, some limitations are imposed on the possible acceleration mechanism.…”

Section: Altitude With Ionospheric Conductancementioning

confidence: 85%

Influence of the ionosphere on the altitude of discrete auroral arcs

et al. 2005

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Abstract. The altitude of the maximum luminosity of single, discrete auroral arcs was measured by photometric triangulation from two stations (College and Fort Yukon, Alaska) located 226 km apart on nearly the same magnetic meridian. The average height of the evening aurora decreases smoothly with increasing solar depression angle (sda) from 160 km near 12 • sda to 100 km after 18 • sda. The average height remains constant until around 12 • sda in the morning. This diurnal variation is similar to that of the electron density in the F region of the ionosphere. Thus, the behavior is consistent with the concept that the mean auroral electron energy increases as the ionospheric conductivity decreases due to ionospheric recombination in the evening twilight. However, the mean electron energy decreases in magnitude at dawn when the solar ionizing radiation returns and the electron density in the F region increases. The magnetospheric acceleration mechanism associated with discrete auroral arcs thus appears to be inversely proportional to the ionospheric conductivity, because the time variation of the acceleration mechanism coincides with the local F region electron density and not with any obvious magnetospheric process. Previous auroral altitude observations, using similar triangulation methods, showed that the altitude of discrete auroral arcs increases as a function of latitude. When these data are corrected for the twilight effect, the dependence of altitude on latitude disappears. Thus, the average altitude of discrete auroral arcs and, by inference the magnetospheric auroral electron acceleration mechanism, is significantly influenced by the initial ionospheric conductance.

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Section: Altitude With Ionospheric Conductancementioning

confidence: 85%

Influence of the ionosphere on the altitude of discrete auroral arcs

et al. 2005

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“…It is evident that there is no strong systematic trend in the times of the peak position (within 1 to 2 sigma) as a function of L. Only for the vernal equinox during ascending phase, there appears to be a weak dependence of the peak times on L. This suggests that radial diffusion may not play a substantial role in determining the peak times for electrons in this energy range. Cliver et al (2002) 4 Summary and conclusions Cliver et al (2002) have suggested that the seasonal modulation of geomagnetic activity, as measured by the aa index support the equinoctial hypothesis. In separate studies Cliver et al (2001) and Cliver et al (2000), examined the seasonal variation observed in other geomagnetic indices such as the Dst and am.…”

Section: Observationsmentioning

confidence: 89%

On the seasonal dependence of relativistic electron fluxes

2010

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Abstract. The nature of the seasonal dependence of relativistic electron fluxes in the Earth's outer zone is investigated using 11 years of data from sensors onboard the SAMPEX spacecraft. It is found that, the relativistic electron fluxes show a strong semiannual modulation. However, the highest electron fluxes occur at times well away from the nominal equinoxes, lagging them by about 30 days. The time lag also shows a solar cycle phase dependence for the peak fluxes. The electron peak fluxes lag the vernal equinox by almost 60 days during the ascending phase of the solar cycle while the time lag near the autumnal equinox remains unchanged. The observed times of the peak electron fluxes during the descending phase of the solar cycle agrees most closely with the Russel-Mcpherron effect and less so with the equinoctial effect even after including propagation effects for finite solar wind speed. The observed times of the electron peaks are in disagreement with the axial effect. The asymmetrical response of the relativistic electrons during the ascending part of the solar cycle remains a puzzle.

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“…This will be done not only by means of pixel diagrams but also by the use of Cliver et al (2002) results.…”

Section: Methodsmentioning

confidence: 99%

“…This mechanism is also explained by seasonal variation of solar wind speed (Murayama, 1974); (2) equinoctial mechanism (Svalgaard, 1977) where the peak occurrence times are those of the minima of the solar declination and (3) Russell-McPherron mechanism (Russell and McPherron, 1973) where the peak occurrences are due to those of the maximum of solar P angle. The solar B 0 angle corresponds to Earth's heliographic latitude; and the solar P angle is the position angle of the northern extremity of the Sun's rotation axis, measured eastward from the north point of the disk (Cliver et al, 2002).…”

Section: Introductionmentioning

confidence: 99%