Abnormal quiet days and the effect of the interplanetary magnetic field on the apparent position of the Sq focus

Butcher, E. C.; Brown, Geoffrey

doi:10.1111/j.1365-246x.1980.tb02652.x

Cited by 17 publications

(26 citation statements)

References 8 publications

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“…On the other hand, the reverse is the case in summer (see Butcher & Brown 1980). A similar seasonal variation in the amplitude of the imposed northward field is evident in the latitude variations reported by Butcher (1982), particularly for days when the IMF is directed away from the Sun (when most AQDs occur anyway).…”

Section: The Imposed Meridional Fieldsupporting

confidence: 58%

“…It was shown by Butcher & Brown (1980) that this phenomenon, which can also be expressed in terms of a poleward movement of the position of the apparent S , focus on AQDs, is related to the direction of the azimuthal ( B y ) component of the IMF. It appears llkely that the terrestrial phenomenon is caused by an ionospheric current, the magnitude of which is controlled by the diurnal variation in conductivity.…”

Section: Introductionmentioning

confidence: 97%

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The change in Sq(H) amplitude on Abnormal Quiet Days

Brown

1986

Geophysical Journal International

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Analysis of geomagnetic data has shown that the superposed northward magnetic field, which reduces the S,(H) amplitude at northern mid-latitude stations on Abnormal Quiet Days, and increases the amplitude at stations on the equatorward side of the S, focus, builds up in amplitude over four to five days before the AQD occurs, and subsides over a similar period after the AQD. It is inferred indirectly that the azimuthal component By of the interplanetary magnetic field varies similarly. Data for the opposite meridian show that the imposed field reverses to a southward direction at lower latitudes. The inferred currents to account for these fields are believed to flow in the ionosphere, but to arise from magnetospheric electric fields induced by the solar wind-transported IMF.

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Section: The Imposed Meridional Fieldsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 97%

The change in Sq(H) amplitude on Abnormal Quiet Days

Brown

1986

Geophysical Journal International

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“…Such an additional field therefore has the effect of shifting the apparent position of the focus (determined from the latitude at which the amplitude of S 4 ( H ) changes sign) poleward. The magnitude of this poleward movement in focus latitude was found to be significantly larger in winter than summer and was found to be dependent on the IMF polarity (Butcher & Brown 1980), it being greater on A-days (IMF away from the Sun) than on T-days (IMF towards the Sun).…”

Section: Introductionmentioning

confidence: 91%

On the latitude of the Sq(H) focus at sunspot minimum

Butcher¹

1982

Geophysical Journal International

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The latitude of the S 4 ( H ) focus along the 0" longitude meridian in the northern hemisphere has been determined for all the quiet days, as determined from the aa indices, for the sunspot minimum years 1963-64-65. It is shown that: (a) most of the large variability of the focus latitude is due to the effect of a superposed northward magnetic field that is present on AQDs and which tends to move the apparent focus latitude poleward in the northern hemisphere, and (b) a smaller equatorward motion is caused by the negative AQD events that occur in the 0830-1330 LT range. When these two classes of days are removed from the data set, the focus latitude is found to be completely contained within the range 36"-48" for the months MarchOctober with an average value of 41.5T2.3, whilst in winter the range is larger with an average value of 36.7k3.4. However, since the magnitude of the superposed northward field is longitude-dependent, it may be present even on days not classed as AQDs. It is shown that much of the variability in the focus latitude of the normal days along the 0" longitude meridian is caused by variations in the amplitude of the superposed northward field.

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“…Comparison of the data with IMF parameters shows that the AQD events on 9 July 2004 and 6 and 9 January 2005 (Fig. 10a-c) are due to extra-terrestrial or magnetospheric origin (Butcher and Brown, 1980), whereas the source of the 11 December 2009 AQD (Fig. 9) event is due to an ionospheric origin.…”

Section: Discussionmentioning

confidence: 99%

“…However, on the basis of minimum in H occurred near midnight at the same UT at all the five stations almost in the same latitude range but spread over a longitude range of~115°, Mizzi and Schlapp (1971) suggests that the probable cause of these AQDs event might be extra-terrestrial in origin. Butcher and Brown (1980) also found the connection between the occurrences of AQDs and the interplanetary magnetic field and suggested that the most likely source of the AQDs event would be an extra-terrestrial or magnetospheric origin. Analysis of H-data in both hemispheres along the same longitude meridian, Butcher (1987) proposes that the magnetic effects on AQDs were caused by single current vortex (SCV) that flows clockwise and extended over both hemispheres.…”

Section: Introductionmentioning

confidence: 99%

Abnormal quiet day variations in Indian region along 75° E meridian

2015

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The present study mainly focuses on the anomalous characteristics observed in some abnormal quiet day (AQD) variations of the north-south (H) and east-west (D) components of geomagnetic field at 11 Indian stations for the years 2004, 2005, and 2009 during low solar activity period for summer and winter months. In this study, during some quiet days, horizontal component (H) at stations situated near equator to the Sq focus latitudes has shown double peak structure, exhibiting maximum in the forenoon and afternoon hours. Correspondingly, declination component (D) over the low latitudes has shown features outside the normal trend, i.e., westward-directed field in the morning hours and eastward-directed field in the afternoon hours and shows negative bay-type of variations. The technique of principal component analysis (PCA) has been applied to the data sets for presenting a quantitative estimate of the influence of day-to-day variability in the Sq current system on normal (NQD) and abnormal quiet (AQD) days. AQDs observed at the Indian stations are reflected in the second principal component PC-2. Anomalous changes in day-to-day variations (H and D) are interpreted as an influence of high latitude magnetospheric current systems as well as due to single current vortex (SCV) located in the ionosphere whose focus lie between 10°and 15°N geomagnetic latitude for the northern hemisphere winter AQDs.

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Abnormal quiet days and the effect of the interplanetary magnetic field on the apparent position of the Sq focus

Cited by 17 publications

References 8 publications

The change in Sq(H) amplitude on Abnormal Quiet Days

The change in Sq(H) amplitude on Abnormal Quiet Days

On the latitude of the Sq(H) focus at sunspot minimum

Abnormal quiet day variations in Indian region along 75° E meridian

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