Solar wind proton flux latitudinal variations: Comparison between Ulysses in situ data and indirect measurements from interstellar Lyman α mapping

Summanen, T.; Lallement, R.; Quémerais, Éric

doi:10.1029/96ja02091

Cited by 20 publications

(9 citation statements)

References 14 publications

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“…Charge exchange (and to a lesser extent, photoionization) creates a cavity of reduced interstellar hydrogen density within the inner heliosphere. Recent analyses [Bertaux et al, 1997;Summanen et al, 1997;Pryor et al, 1998] have included an enhanced low latitude proton flux, as observed by Ulysses [Phillips et al, 1996]; this aided the interpretation of an observed reduction or "groove" in these observations at low heliolatitudes. The details of the solar wind flux are clearly critical for the modeling and inversion of these Lyman-ct images.…”

Section: Introductionmentioning

confidence: 99%

Ulysses measurements of variations in the solar wind‐interstellar hydrogen charge exchange rate

McComas¹,

Funsten²,

Gosling³

et al. 1999

Geophysical Research Letters

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Abstract. Charge exchange with solar wind protons is the primary ionization process for interstellar hydrogen traveling through the hellosphere. In this study we use Ulysses solar wind observations to examine and quantify variations in charge exchange. We find that these variations are largest within stream interaction regions where the charge exchange rate is tens of times larger in compressional, corotating interaction regions (CIRs) than in rarefactions. Similarly, we find enhanced charge exchange in compression regions ahead of fast CMEs. As a consequence, much of the interstellar hydrogen at low latitudes is picked up in pulses as CIRs and fast CMEs sweep past. Observations over Ulysses' first full polar orbit indicate that the charge exchange rate is higher at low than at high latitudes, and that this rate drops off more slowly than the inverse square of heliocentric distance. We believe that this is due to the growth of CIRs as they propagate out through the inner hellosphere. The variability of hydrogen charge exchange has implications for the analysis of scattered Lyman-{x observations and produces variations in the pickup rates of newly ionized interstellar hydrogen, which is a seed population for anomalous cosmic rays.

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Section: Introductionmentioning

confidence: 99%

Ulysses measurements of variations in the solar wind‐interstellar hydrogen charge exchange rate

McComas¹,

Funsten²,

Gosling³

et al. 1999

Geophysical Research Letters

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“…The other factor is the geometry of observations: they were performed in the planes offset by 1 AU to the upwind and downwind side from the solar crosswind plane, and in consequence the imprints from solar ionization are more pronounced in the downwind plane than in the upwind plane. Following Bertaux et al (1996b, Kyrölä et al (1998), Summanen et al (1997Summanen et al ( , 2001Summanen et al ( , 2002, we interpret the existence of the groove as due to an enhancement of the hydrogen ionization rate at equatorial latitudes ("the ionization bulge"). Based on Ulysses observations (Smith & Marsden 1995;Phillips et al 1995a;Marsden & Smith 1997;McComas et al 1999), the ionization bulge is related to the slow solar wind, while the area of low ionization rate beyond the bulge is related to polar coronal holes, from which the fast solar wind is emitted.…”

Section: Observations Of Heliospheric Backscatter Groovementioning

confidence: 99%

“…To observe the anisotropies of the heliospheric glow on a more regular and systematic basis, the SWAN experiment was proposed in 1987 (Bertaux et al 1995) and launched aboard the SOHO spacecraft in 1995. It has been successfully operated for more than 7 years now, bringing heliospheric backscatter glow data covering the time since the solar minimum in 1996 (Bertaux et al 1996b(Bertaux et al , 1997a(Bertaux et al ,b, 1999Kyrölä et al 1998;Summanen 1996Summanen , 2000Summanen et al 1997Summanen et al , 2001Summanen et al , 2002.…”

Section: Introductionmentioning

confidence: 99%

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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“…This also creates two local maxima in the Lyman intensity pattern, one north of the ecliptic plane and one in the south [Bertaux et al, 1997]. Early analyses of the SWAN maps were published by Summanen et al [1997] and Bzowski et al [2003].…”

Section: Introductionmentioning

confidence: 99%

Interplanetary hydrogen absolute ionization rates: Retrieving the solar wind mass flux latitude and cycle dependence with SWAN/SOHO maps

Quémerais¹,

Lallement²,

Ferron³

et al. 2006

J. Geophys. Res.

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[1] We present results of the total hydrogen ionization rate obtained from the inversion of almost 10 years of full-sky maps of the interplanetary Lyman background measured by the SWAN instrument on SOHO. Thanks to a new estimate of the absolute calibration of the SWAN instrument and its variation during the 10 years of operation of SOHO, we are able to derive absolute values of the ionization rate as well as its latitudinal dependence. We show how the anisotropy of the ionization rate changes from solar minimum to solar maximum. At solar maximum, the so-called ionization groove has completely disappeared and the ionizing fluxes are the same at all heliographic latitudes. We find that the hydrogen ionization cavity which surrounds the Sun increases in size with solar activity. This is evidenced by the low IP Lyman intensities measured during and after the solar maximum. Our model calculation also shows that the increased radiation pressure is not sufficient to explain the larger cavity observed at solar maximum. We find also that ionization rates derived from in situ solar wind measurements do agree with the SWAN results at solar minimum but are significantly smaller at solar maximum. Derived in situ ionization rates do not show the solar cycle dependence we see from the SWAN data. In conclusion, we discuss possible explanations for this discrepancy.

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Solar wind proton flux latitudinal variations: Comparison between Ulysses in situ data and indirect measurements from interstellar Lyman α mapping

Cited by 20 publications

References 14 publications

Ulysses measurements of variations in the solar wind‐interstellar hydrogen charge exchange rate

Ulysses measurements of variations in the solar wind‐interstellar hydrogen charge exchange rate

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

Interplanetary hydrogen absolute ionization rates: Retrieving the solar wind mass flux latitude and cycle dependence with SWAN/SOHO maps

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