Coronal holes and the solar polar field reversal

Bilenko, I. A.

doi:10.1051/0004-6361:20021412

Cited by 44 publications

(37 citation statements)

References 28 publications

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“…This coincides with disappearance of polar holes; instead, small coronal holes were observed distributed over the whole solar surface (Bilenko 2002). It seems, however, that in 2001 a north coronal hole opened again and some traces of the southern hole appeared as well.…”

Section: Latitudinal Structure Of the Ionization Fieldmentioning

confidence: 60%

“…More detailed analysis of the profiles is beyond the scope of ths paper, since it requires a much more sophisticated modelling. But evidence that our hypothesis is justified is given by Bilenko (2002), who studied the distribution of coronal holes versus heliographic latitude during the past solar cycle-there exist distinct maxima of coronal holes densities at midlatitudies during the solar minimum and transition phases.…”

Section: Comparison Of Observed Profiles With Modelmentioning

confidence: 79%

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Latitudinal structure and north-south asymmetry of the solar wind from Lyman-αremote sensing by SWAN

Bzowski

Mäkinen

Kyrölä

et al. 2003

A&A

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Abstract. Based on SWAN/SOHO observations carried out during 1996-2002, we analyze latitudinal profiles of the heliospheric backscatter Lyman-α radiation. We use these results to investigate the ionization field of neutral hydrogen in the inner heliosphere and the latitudinal distribution of the solar wind mass flux. The the depth and latitudinal range of the equatorial depression in the Lyman-α backscatter glow (the so-called "groove") are correlated with the corresponding parameters of the ionization field. We show that the groove is entirely due to latitudinal anisotropy of the solar wind, since, as we are able to demonstrate, the photoionization rate remains spherically symmetric throughout the solar cycle. During the last solar minimum the groove was well developed and stable. During the ascending phase of solar activity, it expanded in latitude (first south, then north), and disappeared altogether during the solar maximum. Shortly after the maximum it reappeared, but its structure was more complex than during the ascending phase. The groove feature is correlated with the equatorial band occupied by the slow solar wind, while the polar maxima of the Lyman-α intensity correspond to the fast solar wind from the polar holes. The groove observations (supported by appropriate modeling) show that during the last solar minimum the mass flux of the fast solar wind from the north and south polar holes were different from each other: a true north-south asymmetry between the polar regions was detected. During the solar minimum, the area occupied by the slow solar wind was quite stable and offset slightly to the south with respect to the solar equator: it extended to about 30 • N and 35 • S from the beginning of observations in May 1996 till 1998. Then it expanded by about 10 • north and south, and subsequently migrated towards southern latitudes, so that it engulfed the south pole in May/June 2000. The north region of the fast wind survived longer and disappeared as late as November/December 2001. To check for the persistence of the north-south asymmetry, we analyze as a proxy the net sunspot area in the north and south hemispheres of the Sun during the 12 past solar cycles. Small north-south asymmetries are found to be commonplace during the past cycles, but the polarity of the asymmetries changes, leaving no statistically significant remnant asymmetry. This suggests that the solar dynamo is solely responsible for the asymmetry, with no remnant magnetic field from the protosolar nebula.

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Section: Latitudinal Structure Of the Ionization Fieldmentioning

confidence: 60%

Section: Comparison Of Observed Profiles With Modelmentioning

confidence: 79%

Latitudinal structure and north-south asymmetry of the solar wind from Lyman-αremote sensing by SWAN

Bzowski

Mäkinen

Kyrölä

et al. 2003

A&A

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show abstract

“…The holes isolated from the poles show an occurrence rate that tends to follow the Schwabe cycle (Insley et al 1995;Luo et al 1997;Hofer and Storini 2003) and they are generally located at the so-called active region latitudes. The majority, but not all, of the ICHs follow the hemispheric polarity rule (they match the polarity of the hemispheric polar field, Bohlin and Sheeley 1978;Harvey and Sheeley 1979;Hofer and Storini 2002;Bilenko 2002). Moreover, some I-CHs show a close connection with active regions during their time evolution (McIntosh 1992;Wang et al 1996;Bravo et al 1998a;Storini and Hofer 1999;Hofer and Storini 2003).…”

Section: Isolated Coronal Holesmentioning

confidence: 99%

“…10). Recently, Bilenko (2002Bilenko ( , 2004 extended the work to 2002 (but the catalogue is not yet available). The extensive use of the catalogues, together with the study of individual holes, led to relevant information for the development of climatological models in the next future, which should be tested with "in situ" observations.…”

Section: Coronal Holesmentioning

confidence: 99%

Solar Weather Event Modelling and Prediction

et al. 2009

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Key drivers of solar weather and mid-term solar weather are reviewed by considering a selection of relevant physics-and statistics-based scientific models as well as a selection of related prediction models, in order to provide an updated operational scenario for space weather applications. The characteristics and outcomes of the considered scientific and prediction models indicate that they only partially cope with the complex nature of solar activity for the lack of a detailed knowledge of the underlying physics. This is indicated by the fact that, on one hand, scientific models based on chaos theory and non-linear dynamics reproduce better the observed features, and, on the other hand, that prediction models based on statistics and artificial neural networks perform better. To date, the solar weather prediction success at most time and spatial scales is far from being satisfactory, but the forthcoming ground-and space-based high-resolution observations can add fundamental tiles to the modelling and predicting frameworks as well as the application of advanced mathematical approaches in the analysis of diachronic solar observations, that are a must to provide comprehensive and homogeneous data sets.

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“…Several studies have investigated how the long-term CHs evolution is related to the changes in the global solar magnetic field over solar cycle (e.g. Bilenko 2002;Sanderson et al 2003;Wang 2009;Obridko & Shelting 2011). CHs originate in sufficiently large unipolar regions with predominantly open configuration of the magnetic field lines.…”

Section: Introductionmentioning

confidence: 99%

Magnetic field sector structure and origins of solar wind streams in 2012

Shugay

Slemzin

Veselovsky

2014

J. Space Weather Space Clim.

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The origins of the solar wind and the interplanetary magnetic field sector structure in the beginning of the magnetic polarity reversal of 24th solar cycle were investigated using the Wilcox Solar Observatory magnetic field measurements and their products as well as the solar wind data from ACE and the SDO/AIA EUV images. The dominance of the quadrupole harmonics in the solar magnetic field in this period resulted in a four-sector structure of the interplanetary magnetic field. The dominating source of recurrent high-speed solar wind stream was a large trans-equatorial coronal hole of negative polarity evolving in the course of the polarity reversal process. The contribution of ICMEs to the high-speed solar wind did not exceed 17% of the total flux. The solar wind density flux averaged over the year amounted to 1 · 10 8 cm À2 s À1 which is considerably lower than the typical long-term value (2-4 · 10 8 cm À2 s À1 ). The slow-speed component of solar wind density flux constituted in average more than 68% of the total flux, the high-speed component was about 10%, reaching the maximum of 32% in some Carrington rotations.

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Coronal holes and the solar polar field reversal

Cited by 44 publications

References 28 publications

Latitudinal structure and north-south asymmetry of the solar wind from Lyman-αremote sensing by SWAN

Latitudinal structure and north-south asymmetry of the solar wind from Lyman-αremote sensing by SWAN

Solar Weather Event Modelling and Prediction

Magnetic field sector structure and origins of solar wind streams in 2012

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