Long-lived coronal structures and recurrent geomagnetic patterns in 1974

Hansen, R. T.; Hansen, Shirley F.; Sawyer, C.

doi:10.1016/0032-0633(76)90051-9

Cited by 73 publications

(26 citation statements)

References 19 publications

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“…The quantity pB is basically a measure of the integral of coronal electron density along the line of sight; one might expect coronal holes to appear as regions of low pB on these maps. This expectation is confirmed by direct comparison with other identifications of holes (11,24,25), and the K-coronameter data has been used in numerous studies of these features. The polar holes are usually well defined on the K-coronal maps as regions of low pB sharply bounded by steep brightness gradients.…”

supporting

confidence: 67%

Polar Coronal Holes and Cosmic-Ray Modulation

Hundhausen

Sime

Hansen

et al. 1980

Science

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supporting

confidence: 67%

Polar Coronal Holes and Cosmic-Ray Modulation

Hundhausen

Sime

Hansen

et al. 1980

Science

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“…Although the speed gradient at some latitudes is very much larger than ever reported, it now appears that the gradient is large only over a narrow range in latitude corresponding to the latitudinal boundaries of individual coronal holes. Hansen et al [1976] have shown that most of the time during the declining part of the present solar activity cycle the extensions of the polar coronal holes reach right into the equatorial region of the sun (see Figure 3a). This could explain the relatively high latitude gradient values obtained from studies based on in situ measurements within the equatorial band.…”

Section: Dec • Nov T Oct I Sep • Aug I Duly • Dune • Maymentioning

confidence: 98%

Direct observation of the latitudinal extent of a high‐speed stream in the solar wind

Schwenn¹,

Montgomery²,

Rosenbauer³

et al. 1978

J. Geophys. Res.

108

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Solar wind speeds measured from the Helios 1 solar probe between 0.31 and 1 AU and the earth‐orbiting Imp 7/8 satellites have been correlated with coronal holes as determined from K coronal brightness measurements. In March 1975 during perihelion passage, Helios 1 traversed the range of heliographic latitudes from −6° to +6° in a period of only 20 days. During that time the space probe crossed the northern boundary of the high‐speed stream associated with an equatorward extension of the south polar coronal hole. While this same stream continued to be observed by Imp satellites at −5° latitude, it was no longer observable from Helios 1 at +5° latitude. The conclusion is that sharp boundaries separate high‐speed flows from the surrounding solar wind. The thickness of the boundary in latitude appears to be narrower than about 10°. The local latitudinal gradient in flow speed is at least 30 km s−1 deg−1. With less confidence it can be deduced from the Helios 1 data that the actual gradients at 0.31 AU might even exceed 100 km s−1 deg−1.

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“…liospheric current sheet structure (Neupert and Pizzo, 1974;Hansen et al, 1976;Sheeley et al, 1976;Burlaga and Lepping, 1977). And recently it is refined by emphasizing the importance of stream-stream interaction and coronal mass ejection (Crooker and Cliver, 1994).…”

Section: Introductionmentioning

confidence: 99%

Prediction of recurrent geomagnetic disturbances by using adaptive filtering

Zhou

Wei

2014

Earth Planet Sp

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Recurrent geomagnetic disturbances are an important part of geomagnetic activities, which are associated with the neutral sheet structure in the heliosphere and the activities of long lived solar coronal holes. Another significant character is the periodic activities recorded by geomagnetic indices. In this paper an algorithm-Adaptive Filtering (AF), is introduced to forecast recurrent geomagnetic events based on the geomagnetic K index. Adaptive filtering can deal with nonstationary data and can adapt to changes in the data pattern. Therefore it is a very helpful method for forecasting the geomagnetic disturbances and the disturbances in the interplanetary space. By using AF technique a prediction for whole Bartels rotation can be obtained when output length is taken as 27-point. For recurrent periods the prediction efficiency is about 30%, the correlation coefficient is 0.55. For nonrecurrent periods the prediction efficiency and correlation coefficient decrease obviously, but the standard variance does not change very much.

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Long-lived coronal structures and recurrent geomagnetic patterns in 1974

Cited by 73 publications

References 19 publications

Polar Coronal Holes and Cosmic-Ray Modulation

Polar Coronal Holes and Cosmic-Ray Modulation

Direct observation of the latitudinal extent of a high‐speed stream in the solar wind

Prediction of recurrent geomagnetic disturbances by using adaptive filtering

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