The atmosphere of Neptune

Results of radio occultation measurements with the Voyager 2 spacecraft

G. F. Lindal, James Lyons, D. N. Sweetnam, V. R. Eshleman, D. P. Hinson, G. L. Tyler

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Radio tracking data acquired during Voyager 2's occultation by Neptune have been used to study the thermal structure and composition of Neptune's troposphere and stratosphere. The occultation began near 62° North planetographic latitude and aided near 45°South latitude. The data cover an altitude interval of about 250 km. A comparison with infrared observations indicates that the gas at the tropopause, which was observed near the 100 mbar level, consists of 77 to 85 % hydrogen by number density with the remainder being mostly helium. A layer with a small refractivity scale height that was detected approximately 50 km below the tropopause, may be a region where the CH4 mixing ratio is decreasing with increasing altitude due to condensation effects. This interpretation leads to a CH4 mixing ratio of 1 to 2 % by number density at the base of the layer where the pressure is approximately 1.7 bars. The depth of the occultation measurements was limited by microwave absorption. By assuming that the absorption was caused by saturated NH3 vapor, one obtains a pressure, temperature, and NH3 mixing ratio of 6 bars, 130 K, and 600 parts per billion, respectively, at the lowest level where the radio link was detected. For internal consistency, this solution requires an atmospheric rotation period of 14.2 ± 0.5 hours near 60° North latitude which corresponds to a prograde zonal wind velocity of 170 ± 50 m/sec relative to the magnetic field. The 1 bar isobaric surface has an equatorial radius of 24,764 ± 15 km and a polar radius of 24,341 ± 30 km. The corresponding oblateness, (Req‐Rp)/Req, is 0.0171 ± 0.0014.

Original languageEnglish (US)
Pages (from-to)1733-1736
Number of pages4
JournalGeophysical Research Letters
Volume17
Issue number10
DOIs
StatePublished - Jan 1 1990
Externally publishedYes

Fingerprint

Voyager 2 spacecraft
radio occultation
Neptune (planet)
Neptune
occultation
mixing ratios
mixing ratio
tropopause
spacecraft
radio
atmospheres
atmosphere
radio tracking
radii
scale height
wind velocity
microwave absorption
thermal structure
zonal wind
stratosphere

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

Cite this

The atmosphere of Neptune : Results of radio occultation measurements with the Voyager 2 spacecraft. / Lindal, G. F.; Lyons, James; Sweetnam, D. N.; Eshleman, V. R.; Hinson, D. P.; Tyler, G. L.

In: Geophysical Research Letters, Vol. 17, No. 10, 01.01.1990, p. 1733-1736.

Research output: Contribution to journalArticle

Lindal, G. F. ; Lyons, James ; Sweetnam, D. N. ; Eshleman, V. R. ; Hinson, D. P. ; Tyler, G. L. / The atmosphere of Neptune : Results of radio occultation measurements with the Voyager 2 spacecraft. In: Geophysical Research Letters. 1990 ; Vol. 17, No. 10. pp. 1733-1736.
@article{a5bbc4f1d25a4b0d9e08837b084e4363,
title = "The atmosphere of Neptune: Results of radio occultation measurements with the Voyager 2 spacecraft",
abstract = "Radio tracking data acquired during Voyager 2's occultation by Neptune have been used to study the thermal structure and composition of Neptune's troposphere and stratosphere. The occultation began near 62° North planetographic latitude and aided near 45°South latitude. The data cover an altitude interval of about 250 km. A comparison with infrared observations indicates that the gas at the tropopause, which was observed near the 100 mbar level, consists of 77 to 85 {\%} hydrogen by number density with the remainder being mostly helium. A layer with a small refractivity scale height that was detected approximately 50 km below the tropopause, may be a region where the CH4 mixing ratio is decreasing with increasing altitude due to condensation effects. This interpretation leads to a CH4 mixing ratio of 1 to 2 {\%} by number density at the base of the layer where the pressure is approximately 1.7 bars. The depth of the occultation measurements was limited by microwave absorption. By assuming that the absorption was caused by saturated NH3 vapor, one obtains a pressure, temperature, and NH3 mixing ratio of 6 bars, 130 K, and 600 parts per billion, respectively, at the lowest level where the radio link was detected. For internal consistency, this solution requires an atmospheric rotation period of 14.2 ± 0.5 hours near 60° North latitude which corresponds to a prograde zonal wind velocity of 170 ± 50 m/sec relative to the magnetic field. The 1 bar isobaric surface has an equatorial radius of 24,764 ± 15 km and a polar radius of 24,341 ± 30 km. The corresponding oblateness, (Req‐Rp)/Req, is 0.0171 ± 0.0014.",
author = "Lindal, {G. F.} and James Lyons and Sweetnam, {D. N.} and Eshleman, {V. R.} and Hinson, {D. P.} and Tyler, {G. L.}",
year = "1990",
month = "1",
day = "1",
doi = "10.1029/GL017i010p01733",
language = "English (US)",
volume = "17",
pages = "1733--1736",
journal = "Geophysical Research Letters",
issn = "0094-8276",
publisher = "American Geophysical Union",
number = "10",

}

TY - JOUR

T1 - The atmosphere of Neptune

T2 - Results of radio occultation measurements with the Voyager 2 spacecraft

AU - Lindal, G. F.

AU - Lyons, James

AU - Sweetnam, D. N.

AU - Eshleman, V. R.

AU - Hinson, D. P.

AU - Tyler, G. L.

PY - 1990/1/1

Y1 - 1990/1/1

N2 - Radio tracking data acquired during Voyager 2's occultation by Neptune have been used to study the thermal structure and composition of Neptune's troposphere and stratosphere. The occultation began near 62° North planetographic latitude and aided near 45°South latitude. The data cover an altitude interval of about 250 km. A comparison with infrared observations indicates that the gas at the tropopause, which was observed near the 100 mbar level, consists of 77 to 85 % hydrogen by number density with the remainder being mostly helium. A layer with a small refractivity scale height that was detected approximately 50 km below the tropopause, may be a region where the CH4 mixing ratio is decreasing with increasing altitude due to condensation effects. This interpretation leads to a CH4 mixing ratio of 1 to 2 % by number density at the base of the layer where the pressure is approximately 1.7 bars. The depth of the occultation measurements was limited by microwave absorption. By assuming that the absorption was caused by saturated NH3 vapor, one obtains a pressure, temperature, and NH3 mixing ratio of 6 bars, 130 K, and 600 parts per billion, respectively, at the lowest level where the radio link was detected. For internal consistency, this solution requires an atmospheric rotation period of 14.2 ± 0.5 hours near 60° North latitude which corresponds to a prograde zonal wind velocity of 170 ± 50 m/sec relative to the magnetic field. The 1 bar isobaric surface has an equatorial radius of 24,764 ± 15 km and a polar radius of 24,341 ± 30 km. The corresponding oblateness, (Req‐Rp)/Req, is 0.0171 ± 0.0014.

AB - Radio tracking data acquired during Voyager 2's occultation by Neptune have been used to study the thermal structure and composition of Neptune's troposphere and stratosphere. The occultation began near 62° North planetographic latitude and aided near 45°South latitude. The data cover an altitude interval of about 250 km. A comparison with infrared observations indicates that the gas at the tropopause, which was observed near the 100 mbar level, consists of 77 to 85 % hydrogen by number density with the remainder being mostly helium. A layer with a small refractivity scale height that was detected approximately 50 km below the tropopause, may be a region where the CH4 mixing ratio is decreasing with increasing altitude due to condensation effects. This interpretation leads to a CH4 mixing ratio of 1 to 2 % by number density at the base of the layer where the pressure is approximately 1.7 bars. The depth of the occultation measurements was limited by microwave absorption. By assuming that the absorption was caused by saturated NH3 vapor, one obtains a pressure, temperature, and NH3 mixing ratio of 6 bars, 130 K, and 600 parts per billion, respectively, at the lowest level where the radio link was detected. For internal consistency, this solution requires an atmospheric rotation period of 14.2 ± 0.5 hours near 60° North latitude which corresponds to a prograde zonal wind velocity of 170 ± 50 m/sec relative to the magnetic field. The 1 bar isobaric surface has an equatorial radius of 24,764 ± 15 km and a polar radius of 24,341 ± 30 km. The corresponding oblateness, (Req‐Rp)/Req, is 0.0171 ± 0.0014.

UR - http://www.scopus.com/inward/record.url?scp=84989591920&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84989591920&partnerID=8YFLogxK

U2 - 10.1029/GL017i010p01733

DO - 10.1029/GL017i010p01733

M3 - Article

VL - 17

SP - 1733

EP - 1736

JO - Geophysical Research Letters

JF - Geophysical Research Letters

SN - 0094-8276

IS - 10

ER -