Constraints on Titan's middle atmosphere ammonia abundance from Herschel/SPIRE sub-millimetre spectra

N. A. Teanby*, P. G. J. Irwin, C. A. Nixon, R. Courtin, B. M. Swinyard, R. Moreno, E. Lellouch, M. Rengel, P. Hartogh

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

Sub-millimetre spectra measured with Herschel's SPIRE Fourier Transform Spectrometer were used to search for ammonia (NH3) in Titan's stratosphere. Observations were taken during 2010 and 2011, just after Titan's northern spring equinox, which occurred in mid-2009. In our analysis we used high spectral resolution data (0.074 cm−1 apodised) from the SPIRE shortwave spectrometer array (SSW), which provided the best possible signal-to-noise ratio for detecting any NH3 emission features. These data have the most sensitivity to NH3 spectral emission of any currently available observations, although despite this we did not detect any significant emission features above the noise. However, we can place an improved 3-sigma upper limit on NH3 abundance of  for altitudes 65–110  km (75 km peak sensitivity), or alternatively a column abundance of . These observations provide modest constraint for future photochemical models and are consistent with most current stratospheric predictions. Scaling of photochemical model profiles, in order to fit elevated abundances observed at 1100 km by Cassini's INMS instrument, are for the most part also consistent with our observations.
Original languageEnglish
Pages (from-to)136-147
Number of pages12
JournalPlanetary and Space Science
Volume75
Early online date29 Nov 2012
DOIs
Publication statusPublished - Jan 2013

Keywords

  • Photochemistry
  • CASSINI-CIRS DATA
  • FAR-INFRARED SPECTRA
  • 300-K
  • Herschel
  • PAIRS
  • ROTOTRANSLATIONAL ABSORPTION-SPECTRA
  • Atmosphere
  • SPECTROMETER
  • Sub-millimetre
  • Titan
  • TEMPERATURES
  • STRATOSPHERE
  • HYDROCARBONS
  • RADIATIVE-TRANSFER
  • Composition

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