Average high latitude magnetic field: Variation with interplanetary sector and with season—II

Langel, R. A.; Brown, Nathan

doi:10.1016/0032-0633(74)90105-6

Cited by 12 publications

(5 citation statements)

References 14 publications

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“…thesis of Friis-Christensen [1971] was the earliest comprehensive presentation of the unique polar station geomagnetic sector effects. Langel [1973Langel [ , 1974, Langel and Svalgaard [1974], Langel and Brown [1974], and Mozer et al In contrast to my results he found that employing the daily mean values of the Z component at Thule was a usable method but not the best one for determining sector structure.…”

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confidence: 97%

Polar cap geomagnetic field responses to solar sector changes

Campbell¹

1976

J. Geophys. Res.

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I made a computerized analysis of digitized magnetograms from Alert, Thule, Resolute Bay, Mould Bay, and Godhavn for 1965 and from Thule and Vostok for 1967 to determine the characteristic features of the day‐to‐day geomagnetic field variations related to the interplanetary solar sector field direction. Higher invariant latitude stations showed the sector effects most clearly. A sector‐related phase shift in the characteristic diurnal variation of the field occurred principally for the dayside vertical geomagnetic component. The amplitude of this diurnal variation was related to Ap and could not be used to identify the sector direction. The quiet nighttime level of field Z component rose and fell on days when the interplanetary magnetic field was directed toward or away from the sun, respectively. When a station's base level field was determined from quiet magnetospheric conditions by using days with low values of Dst and AE indices, the mean field level of the Z component for the whole day increased or decreased (often over 100 γ) from this level as the solar sector direction was toward or away, respectively. With respect to the earth's main field direction the southern polar station field level changes were opposite those at the northern stations. This level shift corresponded with the two solar field directions during the summer months at polar stations for about 70% of the days in 1965 and 88% of the days in 1967. In 1967 the standoff locations of the magnetopause and magnetoshock boundaries were about 1 RE more distant from the earth for the average toward sector days than for the away sector days.

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confidence: 97%

Polar cap geomagnetic field responses to solar sector changes

Campbell¹

1976

J. Geophys. Res.

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“…First, Svalgaard's conclusion was based on data from only five stations, all of which are clustered in one local time sector; this makes it impossible to separate UT effects definitely from MLT effects [Langel and Svalgaard, 1974]. Second, the peak does not occur at 1800 UT for all stations [Langel and Brown, 1974], including those studied by Svalgaard [1973], or for the same station in different seasons [Svalgaard, 1973;Langel and Svalgaard, 1974]. Finally, examination of Pogo data at 1800 UT from other time periods (when electric field data are unavailable) does not show large deviations from the AB patterns discussed in the present paper.…”

Section: Data Selectionmentioning

confidence: 98%

“…The strong correlation observed between the electric field zero crossing (feature 4) and the peak negative AB (feature IV) strongly supports this second interpretation. Langel [1973] and Langel and Brown [1974] noted two distinct negative peaks in the averaged high-latitude AZ at the earth's surface during away sectors for summer. Since fib -' AZ at these latitudes, it is appropriate to look for this feature in the satellite AB.…”

Section: In Most Cases the Electric Field Crossing (Feature 3) Is Notmentioning

confidence: 99%

A comparison of electric and magnetic field data from the Ogo 6 spacecraft

Langel

1975

J. Geophys. Res.

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Previous studies a ABSTRACT ~f the OGO-6 electric field data by Heppner and of magnetic field magnitude observations by Langel have indicated a distinct dependence of disturbance characteristics on interplanetary sector polarity. Examination of simultaneous patterns of disturbance below 600 km over the summer polar cap shows that pattern changes in electric field and in the disturbance in magnetic field magnitude sre highly correlated. This correlation extends to pattern shapes, boundary locations, and to the amplitudes of the cori.elated quantities. In the winter hemisphere, at altitudes above 800 km, correlations between boundaries exist, pattern correlations are present but are not as strong as at low altitudes in summer, and amplitude correlations are essentially absent. These studies verify that below 600 km the region of positive AB, from 2200 to 1000 MLT, has a significant contribution from both ionospheric and non-ionospheric sources.Above 800 km the non-ionospheric sources dominate. These data also are consistent with the existence of a latitudinally broad current system at sunlit MLT as the source of the negative AB region between 1000 and 2200 MLT. In this region broad structures in electric field patterns and in LIB patterns are highly correlated. Multiple peaks in the negative bB, presumably to be identified with the multiple peaks in negative A Z found by Langel (1973) in average surface data, occur when the electric field paUern has multiple reversals near dusk. Pattern variability is large enough so that it is probably not meaningful to draw equivalent current system. iii CONTENTS

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“…Langel and Svalgaard (1974) found that those magnetic variations in the polar cap that change characteristics between interplanetary magnetic sectors were best represented in solar local time rather than magnetic local time. Langel and Brown (1974) as well as Friis-Christensen and Wilhjelm (1975) plotted the high-latitude horizontal disturbance field vectors separated for sector direction and for activity level. Matsushita and Xu (1982) profiled the equivalent ionospheric current systems representing the IMF sector effects in the polar region.…”

Section: Introductionmentioning

confidence: 99%

Polar Cap Field Response to IMF By Sector Changes on Quiet Days at a Longitude Line of Observatories.

Campbell

Arora

Schiffmacher³

1994

J. geomagn. geoelec

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The fields for quiet days of 1976 and 1977 are studied for a line of observatories established near 76°E longitude in the Northern Hemisphere. Using a special spherical harmonic analysis (SHA) technique to separate the external and internal parts of the observed field changes when the geomagnetic activity index Kp had low values, we demonstrate that a selection of SHA polynomials with (n -m) > 1 serves to isolate the polar region field contributions. The equivalent external current representation of the polar fields (sometimes called SqP) show two vortices separated by the day-night hemisphere boundary. When plotted in local time, the nighttime current patterns are usually observed to change positions to earlier locations when the IMF sector structure varied from the Toward (IMF By negative) to the Away (IMF By positive) direction (with respect to the Sun) of the arriving solar wind field at the magnetospheric boundary. The addition of these changing polar current patterns with the more stable lower-latitude Sq (solar quiet-time) dynamo currents probably accounts for the previously reported sector effects in the Sq. The technique of selective separation of polynomials shows that the Sq could be adequately described by the SHA polynomial terms having (n -m) < 2 and that there persisted a small mid-latitude vortex of SHA polynomial (n -m) = 1 currents in winter. The polar region activity and the Southern Hemisphere Sq vortex extension into the Northern Hemisphere had overshadowed the wintertime expression of the low amplitude Sq vortex in the full-field daily variation records.

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Average high latitude magnetic field: Variation with interplanetary sector and with season—II

Cited by 12 publications

References 14 publications

Polar cap geomagnetic field responses to solar sector changes

Polar cap geomagnetic field responses to solar sector changes

A comparison of electric and magnetic field data from the Ogo 6 spacecraft

Polar Cap Field Response to IMF By Sector Changes on Quiet Days at a Longitude Line of Observatories.

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