Solar photoionization as a loss mechanism of neutral interstellar hydrogen in interplanetary space

Ogawa, Hiromitsu; Wu, C. Y. Robert; Gangopadhyay, P.; Judge, D. L.

doi:10.1029/94ja03234

Cited by 14 publications

(15 citation statements)

References 26 publications

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“…However, using previous estimates, we can see how this affects our results. Numerical estimates of the ecliptic ionization rate are given by Ajello et al [1987] or Ogawa et al [1995]. During solar minimum conditions (1977), Ajello et al [1987] have estimated the photoionization rate to be 0.55 Â 10 À7 s À1 .…”

Section: Solar Wind Flux Valuesmentioning

confidence: 99%

“…To compute the charge exchange ionization rate from these data, we have used the cross section given by Izmodenov et al [2001]. The photoionization rate was computed from the values given by Ogawa et al [1995]. We took the solar minimum and solar maximum values given by these authors and assumed a linear correlation with the solar Lyman flux.…”

Section: Comparison With In Situ Measurementsmentioning

confidence: 99%

“…Case 1 refers to values using the photoionization rates given by Ajello et al [1987] and Case 2 refers to the values given by Ogawa et al [1995]. This table shows example of solar wind mass fluxes at the poles and the equator deduced from the numerical values presented above.…”

mentioning

confidence: 99%

“…Ogawa et al [1995] give larger values for the photoionization rate. The solar minimum rate is equal to 1.5 Â 10 À7 s À1 and the solar maximum rate is found to be 2.4 Â 10 À7 s À1 .…”

mentioning

confidence: 99%

“…[70] Although the photoionization rate is always smaller than the charge-exchange rate, we see that at solar minimum and at the poles, the value for the photoionization rate given by Ogawa et al [1995] represents 30% of the total ionization rate of the interplanetary hydrogen. A more detailed analysis is required here to accurately remove the photoionization component from the total ionization rate.…”

mentioning

confidence: 99%

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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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Section: Solar Wind Flux Valuesmentioning

confidence: 99%

Section: Comparison With In Situ Measurementsmentioning

confidence: 99%

mentioning

confidence: 99%

“…Ogawa et al [1995] give larger values for the photoionization rate. The solar minimum rate is equal to 1.5 Â 10 À7 s À1 and the solar maximum rate is found to be 2.4 Â 10 À7 s À1 .…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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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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Solar Parameters for Modeling the Interplanetary Background

Bzowski

Sokół

Tokumaru

et al. 2013

Cross-Calibration of Far UV Spectra of Solar System Objects and the Heliosphere

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The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE) Working Team of the International Space Science Institute (ISSI) in Bern, Switzerland, was to establish a common calibration of various UV and EUV heliospheric observations, both spectroscopic and photometric. Realization of this goal required a credible and up-to-date model of spatial distribution of neutral interstellar hydrogen in the heliosphere, and to that end, a credible model of the radiation pressure and ionization processes was needed. This chapter describes the latter part of the project: the solar factors responsible for shaping the distribution of neutral interstellar H in the heliosphere. Presented are the solar Lyman-alpha flux and the question of solar Lyman-alpha resonant radiation pressure force acting on neutral H atoms in the heliosphere, solar EUV radiation and the process of photoionization of heliospheric hydrogen, and their evolution in time and the still hypothetical variation with heliolatitude. Further, solar wind and its evolution with solar activity is 1

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Hydrogen atom lifetimes in the three‐dimensional heliosphere over the solar cycle

et al. 2003

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The three‐dimensional (3‐D) structure of the heliosphere is investigated using in situ and remote sensing measurements. The 3‐D structure of both neutral interplanetary gas and solar wind ions are affected by the solar latitude variation of the solar radiation fields (solar wind and solar EUV). Neutral hydrogen atom lifetimes against charge‐exchange with solar wind protons in the 3‐D heliosphere are calculated from measurements of the solar wind proton velocity, density, and mass flux by Ulysses SWOOPS (Solar Wind Observations Over the Poles of the Sun) from 1990–2001. These are compared to in‐ecliptic H atom lifetimes derived from solar wind measurements by the spacecraft IMP (Interplanetary Monitoring Platform) 6, 7, and 8, WIND, and ACE (Advanced Composition Explorer) SWEPAM (Solar Wind Electron Proton Alpha Monitor). Recent observations during the Ulysses rapid solar pole‐to‐solar pole passage (fast‐latitude scan) at solar maximum find a more isotropic rotationally averaged solar wind mass flux (and H atom lifetime) than was found during the previous fast latitude scan at solar minimum. During the solar minimum fast‐latitude scan the 27‐day averaged SWOOPS lifetime passed through two distinct regimes: it doubled from 2 × 106 s at low latitudes to 4 × 106 s at high latitudes in both hemispheres. During the solar maximum pass the 27‐day averaged SWOOPS H atom lifetime (corrected to 1 AU) at all southern latitudes and at all northern latitudes below 60° was (2–2.5) × 106 s, while at the very end of the pass, above 60° N latitude, it rose to 4 × 106 s as polar coronal holes reformed. Remote sensing studies of interplanetary H Lyman‐α emission, white light solar coronal observations, and radio scintillation experiments have also indicated that the time‐averaged solar wind mass flux (and H atom lifetime) is more isotropic at solar maximum than at solar minimum. This enlarges the polar H cavity at solar maximum. Results from in situ measurements are compared to remote sensing data. Ulysses GAS Lyman‐ α maps are modeled, with updated results. Comparisons of the H atom charge exchange loss rate with a weaker H atom loss process, photoionization, are made using the SOLAR2000 model [Tobiska et al., 2000] for in‐ecliptic solar Extreme UltraViolet (EUV) fluxes. The relative latitude invariance of the H atom lifetime at solar maximum is related to the absence of high‐speed solar wind at solar maximum and to the large inclination of the heliospheric current sheet.

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Solar photoionization as a loss mechanism of neutral interstellar hydrogen in interplanetary space

Cited by 14 publications

References 26 publications

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

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

Solar Parameters for Modeling the Interplanetary Background

Hydrogen atom lifetimes in the three‐dimensional heliosphere over the solar cycle

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