Analysis of Jovian Auroral H Ly-α emission (1981-1991)

Walter Harris; John T. Clarke; Melissa A. McGrath; Gilda E. Ballester

doi:10.1006/icar.1996.0164

Analysis of Jovian Auroral H Ly-α emission (1981-1991)

Walter Harris, John T. Clarke, Melissa A. McGrath, Gilda E. Ballester

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Abstract

We present a new analysis of jovian auroral IUE spectra covering the period from 1981 to 1991. To extract integrated auroral H Ly-α emission from these spectra we have developed a new extraction method that bins signal with wavelength while preserving the spatial information provided by the IUE imaging spectrograph. This separates auroral emission from background sources including the jovian dayglow, geocoronal H Ly-α emission, emission from hydrogen in the interplanetary medium (IPH), and grating scattered light in the IUE spectrograph. Auroral H Ly-α emission is compared with H₂ emission covering the bandpasses from 1230 to 1300 Å and 1550 to 1620 Å. Study of H₂ and H Ly-α variability as a function of central meridian longitude (CML) and the results of linear correlative analysis indicates that these features are produced by a common or linked process with a similar spatial distribution. Further comparative analysis of the relative optical depth of the correlated emission using a modified form of the H₂ color ratio of Yung et al. (1982, Astrophys. J. 254, L65-L69) suggest that H₂ and H Ly-α emissions are subject to similar variability in CH₄ extinction with CML. From this a conservative upper limit of 37% is derived for the amount of H Ly-α emission that can be produced above the altitude where the bulk of the H₂ emission is produced. We also discuss how the implied radiative transfer environment for H Ly-α production and the local H/CH₄ ratio can limit the altitude distribution of the emission, the auroral H Ly-α intensity, and the shape and information available from the emergent line profile.

Original language	English (US)
Pages (from-to)	350-365
Number of pages	16
Journal	Icarus
Volume	123
Issue number	2
DOIs	https://doi.org/10.1006/icar.1996.0164
State	Published - Oct 1996

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1006/icar.1996.0164

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@article{b95019a3133a4f13b38d737a08411356,

title = "Analysis of Jovian Auroral H Ly-α emission (1981-1991)",

abstract = "We present a new analysis of jovian auroral IUE spectra covering the period from 1981 to 1991. To extract integrated auroral H Ly-α emission from these spectra we have developed a new extraction method that bins signal with wavelength while preserving the spatial information provided by the IUE imaging spectrograph. This separates auroral emission from background sources including the jovian dayglow, geocoronal H Ly-α emission, emission from hydrogen in the interplanetary medium (IPH), and grating scattered light in the IUE spectrograph. Auroral H Ly-α emission is compared with H2 emission covering the bandpasses from 1230 to 1300 {\AA} and 1550 to 1620 {\AA}. Study of H2 and H Ly-α variability as a function of central meridian longitude (CML) and the results of linear correlative analysis indicates that these features are produced by a common or linked process with a similar spatial distribution. Further comparative analysis of the relative optical depth of the correlated emission using a modified form of the H2 color ratio of Yung et al. (1982, Astrophys. J. 254, L65-L69) suggest that H2 and H Ly-α emissions are subject to similar variability in CH4 extinction with CML. From this a conservative upper limit of 37% is derived for the amount of H Ly-α emission that can be produced above the altitude where the bulk of the H2 emission is produced. We also discuss how the implied radiative transfer environment for H Ly-α production and the local H/CH4 ratio can limit the altitude distribution of the emission, the auroral H Ly-α intensity, and the shape and information available from the emergent line profile.",

author = "Walter Harris and Clarke, {John T.} and McGrath, {Melissa A.} and Ballester, {Gilda E.}",

note = "Funding Information: The authors thank Randy Gladstone, Alex Dessler, Bill Kuhn, Hunter Waite, Tim Livengood, and in particular Daniel Rego, who also supplied supporting model calculations, for many useful discussions about the nature of resonance line radiative transfer and the interpretation of the IUE archival data set, as well as the long set of observers who relentlessly pursued Jupiter{\textquoteright}s aurora with IUE over the years. The precision of their work has made our study possible. We would also like to acknowledge Lotfi Ben Jaffel for his contributions and calculations on the subject of Ly-a limb brightening, Yoo-Jea Kim for her contribution of a model H2 spectrum, and an anonymous referee for useful commentary on time dependence and auroral activity. This research was funded under NASA Grants NAG5–1030 and NAGW-1766 to the University of Michigan.",

year = "1996",

month = oct,

doi = "10.1006/icar.1996.0164",

language = "English (US)",

volume = "123",

pages = "350--365",

journal = "Icarus",

issn = "0019-1035",

publisher = "Academic Press Inc.",

number = "2",

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TY - JOUR

T1 - Analysis of Jovian Auroral H Ly-α emission (1981-1991)

AU - Harris, Walter

AU - Clarke, John T.

AU - McGrath, Melissa A.

AU - Ballester, Gilda E.

N1 - Funding Information: The authors thank Randy Gladstone, Alex Dessler, Bill Kuhn, Hunter Waite, Tim Livengood, and in particular Daniel Rego, who also supplied supporting model calculations, for many useful discussions about the nature of resonance line radiative transfer and the interpretation of the IUE archival data set, as well as the long set of observers who relentlessly pursued Jupiter’s aurora with IUE over the years. The precision of their work has made our study possible. We would also like to acknowledge Lotfi Ben Jaffel for his contributions and calculations on the subject of Ly-a limb brightening, Yoo-Jea Kim for her contribution of a model H2 spectrum, and an anonymous referee for useful commentary on time dependence and auroral activity. This research was funded under NASA Grants NAG5–1030 and NAGW-1766 to the University of Michigan.

PY - 1996/10

Y1 - 1996/10

N2 - We present a new analysis of jovian auroral IUE spectra covering the period from 1981 to 1991. To extract integrated auroral H Ly-α emission from these spectra we have developed a new extraction method that bins signal with wavelength while preserving the spatial information provided by the IUE imaging spectrograph. This separates auroral emission from background sources including the jovian dayglow, geocoronal H Ly-α emission, emission from hydrogen in the interplanetary medium (IPH), and grating scattered light in the IUE spectrograph. Auroral H Ly-α emission is compared with H2 emission covering the bandpasses from 1230 to 1300 Å and 1550 to 1620 Å. Study of H2 and H Ly-α variability as a function of central meridian longitude (CML) and the results of linear correlative analysis indicates that these features are produced by a common or linked process with a similar spatial distribution. Further comparative analysis of the relative optical depth of the correlated emission using a modified form of the H2 color ratio of Yung et al. (1982, Astrophys. J. 254, L65-L69) suggest that H2 and H Ly-α emissions are subject to similar variability in CH4 extinction with CML. From this a conservative upper limit of 37% is derived for the amount of H Ly-α emission that can be produced above the altitude where the bulk of the H2 emission is produced. We also discuss how the implied radiative transfer environment for H Ly-α production and the local H/CH4 ratio can limit the altitude distribution of the emission, the auroral H Ly-α intensity, and the shape and information available from the emergent line profile.

AB - We present a new analysis of jovian auroral IUE spectra covering the period from 1981 to 1991. To extract integrated auroral H Ly-α emission from these spectra we have developed a new extraction method that bins signal with wavelength while preserving the spatial information provided by the IUE imaging spectrograph. This separates auroral emission from background sources including the jovian dayglow, geocoronal H Ly-α emission, emission from hydrogen in the interplanetary medium (IPH), and grating scattered light in the IUE spectrograph. Auroral H Ly-α emission is compared with H2 emission covering the bandpasses from 1230 to 1300 Å and 1550 to 1620 Å. Study of H2 and H Ly-α variability as a function of central meridian longitude (CML) and the results of linear correlative analysis indicates that these features are produced by a common or linked process with a similar spatial distribution. Further comparative analysis of the relative optical depth of the correlated emission using a modified form of the H2 color ratio of Yung et al. (1982, Astrophys. J. 254, L65-L69) suggest that H2 and H Ly-α emissions are subject to similar variability in CH4 extinction with CML. From this a conservative upper limit of 37% is derived for the amount of H Ly-α emission that can be produced above the altitude where the bulk of the H2 emission is produced. We also discuss how the implied radiative transfer environment for H Ly-α production and the local H/CH4 ratio can limit the altitude distribution of the emission, the auroral H Ly-α intensity, and the shape and information available from the emergent line profile.

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U2 - 10.1006/icar.1996.0164

DO - 10.1006/icar.1996.0164

M3 - Article

AN - SCOPUS:0030268250

SN - 0019-1035

VL - 123

SP - 350

EP - 365

JO - Icarus

JF - Icarus

IS - 2

ER -

Analysis of Jovian Auroral H Ly-α emission (1981-1991)

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