Latitudinal velocity structures up to the solar poles estimated from interplanetary scintillation tomography analysis

Kojima, M.; Fujiki, K.; Ohmi, Tetsuo; Tokumaru, M.; Yokobe, A.; Hakamada, K.

doi:10.1029/2001ja900037

Cited by 24 publications

(26 citation statements)

References 13 publications

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“…We must emphasise, however, that it is not possible to distinguish between effects of the ionization by charge exchange and by EUV radiation based solely on observations of the Lyman-α backscatter glow (Bertaux et al 1996a). The picture of evolution of the latitudinal structure of solar wind resulting from our analysis is in qualitative agreement with the results from Ulysses (McComas et al 2000a) and from radio scintillation observations (Kojima et al 2001).…”

Section: Discussionsupporting

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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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: Discussionsupporting

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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“…At solar minimum the bimodal velocity structure is reproduced well, and IPS CAT results agree well with Ulysses' first fast latitude scan observations (e.g. Kojima et al, 1998Kojima et al, , 2001. The tomographic analysis requires a stable solar wind velocity structure over one solar rotation, because all of the IPS data in a given Carrington rotation are used to produce a velocity map (V-map).…”

Section: Introductionsupporting

confidence: 64%

How did the solar wind structure change around the solar maximum? From interplanetary scintillation observation

et al. 2003

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Abstract.Observations from the second Ulysses fast latitude scan show that the global structure of solar wind near solar maximum is much more complex than at solar minimum. Soon after solar maximum, Ulysses observed a polar coronal hole (high speed) plasma with magnetic polarity of the new solar cycle in the Northern Hemisphere. We analyze the solar wind structure at and near solar maximum using interplanetary scintillation (IPS) measurements. To do this, we have developed a new tomographic technique, which improves our ability to examine the complex structure of the solar wind at solar maximum. Our IPS results show that in 1999 and 2000 the total area with speed greater than 700 km s −1 is significantly reduced first in the Northern Hemisphere and then in the Southern Hemisphere. For year 2001, we find that the formation of large areas of fast solar wind around the north pole precedes the formation of large polar coronal holes around the southern pole by several months. The IPS observations show a high level agreement to the Ulysses observation, particularly in coronal holes.

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“…This data set enables detailed studies of the evolution of the SW speed profile with changes in solar activity (Kojima and Kakinuma, 1987;Kojima et al, 1999Kojima et al, , 2001Kojima et al, , 2007Fujiki et al, 2003aFujiki et al, , 2003bFujiki et al, , 2003cTokumaru et al, 2009, Tokumaru, Kojima, andFujiki, 2010).…”

Section: Remote-sensing Observations Of Interplanetary Scintillationsmentioning

confidence: 99%

Heliolatitude and Time Variations of Solar Wind Structure from in situ Measurements and Interplanetary Scintillation Observations

et al. 2012

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The 3D structure of the solar wind and its evolution in time are needed for heliospheric modeling and interpretation of energetic neutral atoms observations. We present a model to retrieve the solar wind structure in heliolatitude and time using all available and complementary data sources. We determine the heliolatitude structure of solar wind speed on a yearly time grid over the past 1.5 solar cycles based on remote-sensing observations of interplanetary scintillations, in situ out-of-ecliptic measurements from Ulysses, and in situ in-ecliptic measurements from the OMNI 2 database. Since in situ out-of-ecliptic information on the solar wind density structure is not available apart from the Ulysses data, we derive correlation formulae between the solar wind speed and density and use the information on the solar wind speed from interplanetary scintillation observations to retrieve the 3D structure of the solar wind density. With the variations of solar wind density and speed in time and heliolatitude available, we calculate variations in solar wind flux, dynamic pressure, and charge-exchange rate in the approximation of stationary H atoms.

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Latitudinal velocity structures up to the solar poles estimated from interplanetary scintillation tomography analysis

Cited by 24 publications

References 13 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

How did the solar wind structure change around the solar maximum? From interplanetary scintillation observation

Heliolatitude and Time Variations of Solar Wind Structure from in situ Measurements and Interplanetary Scintillation Observations

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