The three‐dimensional solar wind around solar maximum

McComas, D. J.; Elliott, H. A.; Schwadron, N. A.; Gosling, J. T.; Skoug, R. M.; Goldstein, B. E.

doi:10.1029/2003gl017136

Cited by 279 publications

(226 citation statements)

References 16 publications

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“…Ulysses measurements showed that the polar solar wind observed at the southern pole differed slightly but distinctly from the polar wind in the northern hemisphere (McComas et al 2003). First evidence of such asymmetry was pointed out by Bertaux et al (1996a) based on Lyman-α observations from Prognoz.…”

Section: Introductionmentioning

confidence: 91%

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: Introductionmentioning

confidence: 91%

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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“…At solar minimum, slow, hot solar wind forms a relatively narrow band around the heliographic equator, while the fast, cool wind fills the midlatitude and polar heliosphere, whereas at solar maximum, the slow wind extends to much higher latitudes [McComas et al, 2003]. In this view the slow solar wind is collocated with the dipolar streamer belt, the region where open solar magnetic field lines from opposite polarity polar coronal holes converge to form the heliospheric current sheet.…”

Section: Introductionmentioning

confidence: 92%

Solar cycle evolution of dipolar and pseudostreamer belts and their relation to the slow solar wind

Owens

Crooker

Lockwood

2014

J. Geophys. Res. Space Physics

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“…Figure 1 shows that A He is clearly correlated to wind speed at solar minimum, and more loosely so throughout the solar cycle. The correlation between wind speed and heliographic latitude during solar minimum has been demonstrated using the first Ulysses fast latitude scan in 1994(McComas et al 2003 and references therein). The key observation here, however, stems from the fact that the wind speed is not perfectly determined by heliographic latitude.…”

Section: Effect Of the Solar Wind Expansion Profile On A Hementioning

confidence: 99%

Solar Wind Helium Abundance as a Function of Speed and Heliographic Latitude: Variation through a Solar Cycle

Kasper

Stevens

Lazarus

et al. 2007

ApJ

179

223

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We present a study of the variation of the relative abundance of helium to hydrogen in the solar wind as a function of solar wind speed and heliographic latitude over the previous solar cycle. The average values of A He , the ratio of helium to hydrogen number densities, are calculated in 25 speed intervals over ($27 day) Carrington rotations using Faraday cup observations from the Wind spacecraft between 1995 and 2005. We find that for solar wind speeds between 350 and 415 km s À1 , A He varies with a clear 6 month periodicity, with a minimum value at the heliographic equatorial plane and a typical gradient of 1% per degree in latitude. Once the gradient is subtracted, we find that A He is a remarkably linear function of solar wind speed. We identify the implied speed at which A He is zero as 259 AE 12 km s À1 and note that this speed corresponds to the minimum solar wind speed observed at 1 AU. The vanishing speed may be related to previous theoretical work in which enhancements of coronal helium lead to stagnation of the escaping proton flux. During solar maximum the A He dependences on speed and latitude disappear, and we interpret this as evidence of two source regions for slow solar wind in the ecliptic plane, one being the solar minimum streamer belt and the other likely being active regions.

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The three‐dimensional solar wind around solar maximum

Cited by 279 publications

References 16 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 cycle evolution of dipolar and pseudostreamer belts and their relation to the slow solar wind

Solar Wind Helium Abundance as a Function of Speed and Heliographic Latitude: Variation through a Solar Cycle

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