INMS-derived composition of Titan's upper atmosphere: Analysis methods and model comparison

Magee, B.; Waite, J. H.; Mandt, K.; Westlake, J. H.; Bell, J. M.; Gell, D. A.

doi:10.1016/j.pss.2009.06.016

Cited by 167 publications

(333 citation statements)

References 19 publications

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“…This is seen in Table 3 As seen in Figure 2c, the different T-GITM simulations match different 40 Ar data sets. Model A matches the mixing ratios derived by Magee et al [2009], while models B and B (HE) both match those determined by Yelle et al [2008]. Figure 2d contains a comparison between the isotopic ratios simulated by T-GITM and measured by INMS.…”

Section: Eddy Diffusion: Homopausementioning

confidence: 53%

“…Operationally, models parameterize turbulence using an adjustable eddy diffusion coefficient, and, thus, most studies use the inert gas 40 Ar to constrain it. When comparing different studies of atmospheric escape, one notices two major differences among them: (1) the method for including turbulence (i.e., how they parameterize it) and (2) the source for their 40 Ar data (either that of Magee et al [2009] or Cui et al [2008Cui et al [ , 2012). Fortunately, as seen in section 4.1 and Figure 1, the dynamical effects on 40 Ar are almost completely method invariant, whether you choose to use a hydrostatic diffusion approach (as in Cui et al [2012] or Yelle et al [2008]), include eddy diffusion in the continuity equation (as in Strobel [2009(as in Strobel [ , 2010(as in Strobel [ , 2012), or include turbulence directly in the momentum equation (as in Bell et al [2010a(as in Bell et al [ , 2010b(as in Bell et al [ , 2011b).…”

Section: Discussionmentioning

confidence: 99%

“…Figures 2a and 2b show the simulated major neutral densities and mixing ratios, respectively. The black lines represent T-GITM simulations, and the red circles represent the average INMS measurements during the prime mission as determined by Magee et al [2009] (please note that horizontal uncertainties are a convolution of both counting statistical uncertainties and geophysical variabilities). The CIRS and GCMS ranges for these species are shown as horizontal yellow and cyan bars, respectively.…”

Section: Eddy Diffusion: Homopausementioning

confidence: 99%

“…The CIRS and GCMS ranges for these species are shown as horizontal yellow and cyan bars, respectively. Figure 2c shows the T-GITM simulated 40 Ar mixing ratios (black) lines and the INMS measurements reported by Magee et al [2009] (red circles with horizontal uncertainties) and those of Yelle et al [2008] (blue circles and horizontal uncertainties). Similarly, Figure 2d shows the simulated and measured major stable isotopic ratios of 14 N/ 15 N in N 2 .…”

Section: Eddy Diffusion: Homopausementioning

confidence: 99%

“…In the originally published version of this article, Figure 2 was mistakenly replaced by a copy of Figure 5 Magee et al [2009], and blue data are from Yelle et al [2008]. GCMS and CIRS constraints are cyan and yellow lines.…”

Section: Erratummentioning

confidence: 99%

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Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×1011 CH4 m−2 s−1 and 1.08 ×1014 H2 m−2 s−1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.

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Section: Eddy Diffusion: Homopausementioning

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Section: Eddy Diffusion: Homopausementioning

confidence: 99%

Section: Eddy Diffusion: Homopausementioning

confidence: 99%

Section: Erratummentioning

confidence: 99%

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Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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Density waves in Titan's upper atmosphere

Cui

Yelle

et al. 2014

JGR Space Physics

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Analysis of the Cassini Ion Neutral Mass Spectrometer data reveals the omnipresence of density waves in various constituents of Titan's upper atmosphere, with quasi‐periodical structures visible for N2, CH4,29N2, and some of the minor constituents. The N2 amplitude lies in the range of ≈4%–16%with a mean of ≈8%. Compositional variation is clearly seen as a sequence of decreasing amplitude with increasing scale height. The observed vertical variation of amplitude implies significant wave dissipation in different constituents, possibly contributed by molecular viscosity for N2but by both molecular viscosity and binary diffusion for the others. A wave train with near horizontally propagating wave energy and characterized by a wavelength of ≈730 km and a wave period of ≈10 h is found to best reproduce various aspects of the observations in a globally averaged sense. Some horizontal and seasonal trends in wave activity are identified, suggesting a connection between the mechanism driving the overall variability in the background atmosphere and the mechanism driving the waves. No clear association of wave activity with magnetospheric particle precipitation can be identified from the data.

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An empirical approach to modeling ion production rates in Titan's ionosphere I: Ion production rates on the dayside and globally

et al. 2015

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Titan's ionosphere is created when solar photons, energetic magnetospheric electrons or ions, and cosmic rays ionize the neutral atmosphere. Electron densities generated by current theoretical models are much larger than densities measured by instruments on board the Cassini orbiter. This model density overabundance must result either from overproduction or from insufficient loss of ions. This is the first of two papers that examines ion production rates in Titan's ionosphere, for the dayside and nightside ionosphere, respectively. The first (current) paper focuses on dayside ion production rates which are computed using solar ionization sources (photoionization and electron impact ionization by photoelectrons) between 1000 and 1400 km. In addition to theoretical ion production rates, empirical ion production rates are derived from CH 4 , CH 3 + , and CH 4 + densities measured by the INMS (Ion Neutral Mass Spectrometer) for many Titan passes.The modeled and empirical production rate profiles from measured densities of N 2 + and CH 4 + are found to be in good agreement (to within 20%) for solar zenith angles between 15 and 90°. This suggests that the overabundance of electrons in theoretical models of Titan's dayside ionosphere is not due to overproduction but to insufficient ion losses.

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INMS-derived composition of Titan's upper atmosphere: Analysis methods and model comparison

Cited by 167 publications

References 19 publications

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Density waves in Titan's upper atmosphere

An empirical approach to modeling ion production rates in Titan's ionosphere I: Ion production rates on the dayside and globally

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