Solar illumination as cause of the equinoctial preference for geomagnetic activity

Lyatsky, W.; Newell, P. T.; Hamza, A. M.

doi:10.1029/2000gl012803

Cited by 98 publications

(158 citation statements)

References 16 publications

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“…For example, we must account for the observation of low altitude discrete arcs in twilight by admitting that the magnetosphere/ionosphere is a coupled system and that there are times when the magnetospheric electron acceleration mechanism is able to function at full power, even into a sunlit, conducting atmosphere. 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.…”

Section: Altitude With Ionospheric Conductancementioning

confidence: 99%

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: 99%

Influence of the ionosphere on the altitude of discrete auroral arcs

et al. 2005

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“…Figure 10b shows the annual variation of the number of auroral nights and reveals the semi-annual variation (Sabine 1852) (equinoctial peaks in auroral occurrence were noted by de Mairan 1733). A corresponding semi-annual variation in geomagnetic activity (Sabine 1852;Cortie 1912) is mainly caused by the effect of solar illumination of the nightside auroral current electrojets (Cliver et al 2000;Lyatsky et al 2001;Newell et al 2002), leading to equinoctial maxima in geomagnetic activity.…”

Section: Surveys Of Historic Auroraementioning

confidence: 99%

The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets

Usoskin

Arlt

Asvestari

et al. 2015

A&A

193

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Aims. Although the time of the Maunder minimum (1645-1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle #24. We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum. Methods. We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum.Results. The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets. Conclusions. We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level.

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“…Besides these explanations dominated by the solar wind interaction efficiency there are also some other attempts to explain the annual variation of magnetic activity, for example, the changing illumination of the polar ionosphere (e.g. Lyatsky et al, 2001;Nagatsuma, 2006). Recently, it was shown that the solar illumination could control the saturation of the polar cap potential (Nagatsuma, 2004) and the latitudinal position of the dayside field-aligned currents (Wang et al, 2005a).…”

Section: Introductionmentioning

confidence: 99%

Interhemispheric comparison of average substorm onset locations: evidence for deviation from conjugacy

Wang

Lühr

et al. 2007

Ann. Geophys.

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Abstract. Based on 2760 well-defined substorm onsets in the Northern Hemisphere and 1432 in the Southern Hemisphere observed by the FUV Imager on board the IMAGE spacecraft, a detailed statistical study is performed including both auroral regions. This study focuses on the hemispheric comparisons. Southward pointing interplanetary magnetic field (IMF) is favorable for substorm to occur, but still 30% of the events are preceded by northward IMF. The magnetic latitude (MLat) of substorm onset depends mainly on the merging electric field (E m ) with a relationship of |dMLat|=−5.2 E 0.5 m , where dMLat is the deviation from onset MLat. In addition, seasonal effects on onset MLat are also detected, with about 2 degrees higher latitudes during solstices than equinoxes. Both IMF B y and solar illumination have a significant influence on the magnetic local time (MLT) of onsets. An average relation, dMLT=0.25 B y between IMF B y and the deviation from onset MLT, was found. The B y dependence varies slightly with the onset latitude. At lower latitudes (higher activity) it is reduced. After removal of the relationship with IMF B y a linear relationships remains between the solar zenith angle and onset MLT with dMLT=1 min/deg. Therefore, both solar illumination and IMF B y can contribute to hemispheric longitudinal displacements of substorm onset locations from conjugacy. No indications for systematic latitudinal displacements between the hemispheres have been found.

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Solar illumination as cause of the equinoctial preference for geomagnetic activity

Cited by 98 publications

References 16 publications

Influence of the ionosphere on the altitude of discrete auroral arcs

Influence of the ionosphere on the altitude of discrete auroral arcs

The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets

Interhemispheric comparison of average substorm onset locations: evidence for deviation from conjugacy

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