Effects of Saturn's magnetospheric dynamics on Titan's ionosphere

Edberg, Niklas J. T.; Andrews, David; Bertucci, C.; Gurnett, D. A.; Holmberg, Mika; Jackman, C. M.; Kurth, W. S.; Menietti, J. D.; Opgenoorth, H. J.; Shebanits, Oleg; Vigren, Erik

doi:10.1002/2015ja021373

Cited by 14 publications

(23 citation statements)

References 65 publications

(93 reference statements)

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“…The fitting coefficients, a z and b z , for CH 3 + and the corresponding 95% confidence uncertainties are shown in Figure c. The average b z is about 0.6, compared to 0.5 for electrons [ Edberg et al ., ]. Analysis of HCNH + (not shown) also produced slightly different coefficients.…”

Section: Ion Density Datamentioning

confidence: 93%

“…In Figure , the drop in HCNH + density from day to night is about 65%, whereas in the C 3 H 5 + case, density decreases by about 75% over the same time period and the same number of flybys. Edberg et al [] introduced a method to remove the SZA dependence from RPWS‐LP electron density measurements. We applied a similar method on the INMS ion densities, in an attempt (only partially successful) to detrend the data and further isolate the solar activity effects.…”

Section: Ion Density Datamentioning

confidence: 99%

“…In the next step, the ion densities are corrected for SZA according to

n_{i_{S Z A}} ((), z) = \frac{n_{i_{italicinitial}} ((), z)}{normalcos ((), b_{z} \times sza)}

In this equation

n_{i_{italicinitial}}

is the density of ion species i , sza is the solar zenith angle at the time of measurement, b z is one of the fitting parameters in equation , and

n_{i_{S Z A}}

is the corrected density of the ion species as if the solar zenith angle was at 0°. This quantity for electrons is referred to as N e,EUV by Edberg et al [].…”

Section: Ion Density Datamentioning

confidence: 99%

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Solar cycle variations in ion composition in the dayside ionosphere of Titan

et al. 2016

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One Titanian year spans over two complete solar cycles, and the solar irradiance has a significant effect on ionospheric densities. Solar cycle 24 has been one of the quietest cycles on record. In this paper we show data from the Cassini ion and neutral mass spectrometer (INMS) and the radio and plasma wave science Langmuir probe spanning the time period from early 2005, at the declining phase of solar cycle 23, to late 2015 at the declining phase of solar cycle 24. Densities of different ion species measured by the INMS show a consistent enhancement for high solar activity, particularly near the ionospheric peak. The density enhancement is best seen in primary ion species such as CH3+ rather than heavier ion species such as HCNH+. Unlike at Earth, where the ionosphere and atmosphere thermally expand at high solar activity, at Titan the altitude of the ionospheric peak decreases, indicating that the underlying neutral atmosphere was less extensive. Among the major ion species, CH5+ shows the largest decrease in peak altitude, whereas heavy ions such as C3H5+ show very little decrease. We also calculate the ion production rates using a theoretical model and a simple empirical model using INMS data and show that these effectively predict the increased ion production rates at high solar activity.

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Section: Ion Density Datamentioning

confidence: 93%

Section: Ion Density Datamentioning

confidence: 99%

“…In the next step, the ion densities are corrected for SZA according to

n_{i_{S Z A}} ((), z) = \frac{n_{i_{italicinitial}} ((), z)}{normalcos ((), b_{z} \times sza)}

In this equation

n_{i_{italicinitial}}

is the density of ion species i , sza is the solar zenith angle at the time of measurement, b z is one of the fitting parameters in equation , and

n_{i_{S Z A}}

is the corrected density of the ion species as if the solar zenith angle was at 0°. This quantity for electrons is referred to as N e,EUV by Edberg et al [].…”

Section: Ion Density Datamentioning

confidence: 99%

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Solar cycle variations in ion composition in the dayside ionosphere of Titan

et al. 2016

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“…Upstream electron fluxes at Titan can indeed vary substantially (see in particular Rymer et al 2009;Arridge et al 2011), and the electron precipitation also depends strongly on the magnetic field topology (Gronoff et al 2009;Simon et al 2013;Snowden et al 2013;Edberg et al 2015;Richard et al 2015b). Clearly, from the limited set of flybys and locations investigated here we cannot state that magnetospheric electrons preferably are directed toward Titanʼs nightside.…”

Section: Caps/els-derived Electron-impact Ionization Frequencies On Tmentioning

confidence: 99%

“…It is noted that Edberg et al (2015) performed a somewhat similar study, but with the focus on electron number densities measured by RPWS/LP. Using data from 109 Titan flybys and correcting for solar zenith angle and solar EUV variations, they reported that electron number densities in the altitude range 1600-2400 km are elevated by a factor of ∼2.5 when Titan is located on Saturnʼs nightside compared with when located on the dayside.…”

Section: Caps/els-derived Electron-impact Ionization Frequencies On Tmentioning

confidence: 99%

Suprathermal Electrons in Titan’s Sunlit Ionosphere: Model–observation Comparisons

Vigren

Galand

Wellbrock

et al. 2016

ApJ

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The dayside ionosphere of the Saturnian satellite Titan is generated mainly from photoionization of N 2 and CH 4 . We compare model-derived suprathermal electron intensities with spectra measured by the Cassini Plasma Spectrometer/Electron Spectrometer (CAPS/ELS) in Titanʼs sunlit ionosphere (altitudes of 970-1250 km) focusing on the T40, T41, T42, and T48 Titan flybys by the Cassini spacecraft. The model accounts only for photoelectrons and associated secondary electrons, with a main input being the impinging solar EUV spectra as measured by the Thermosphere Ionosphere Mesosphere Energy and Dynamics/Solar EUV Experiment and extrapolated to Saturn. Associated electron-impact electron production rates have been derived from ambient number densities of N 2 and CH 4 (measured by the Ion Neutral Mass Spectrometer/Closed Source Neutral mode) and related energy-dependent electron-impact ionization cross sections. When integrating up to electron energies of 60 eV, covering the bulk of the photoelectrons, the model-based values exceed the observationally based values typically by factors of ∼3 ± 1. This finding is possibly related to current difficulties in accurately reproducing the observed electron number densities in Titanʼs dayside ionosphere. We compare the utilized dayside CAPS/ELS spectra with ones measured in Titanʼs nightside ionosphere during the T55-T59 flybys. The investigated nightside locations were associated with higher fluxes of high-energy (>100 eV) electrons than the dayside locations. As expected, for similar neutral number densities, electrons with energies <60 eV give a higher relative contribution to the total electron-impact ionization rates on the dayside (due to the contribution from photoelectrons) than on the nightside.

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Ion and aerosol precursor densities in Titan's ionosphere: A multi‐instrument case study

et al. 2016

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The importance of the heavy ions and dust grains for the chemistry and aerosol formation in Titan's ionosphere has been well established in the recent years of the Cassini mission. In this study we combine independent in situ plasma (Radio Plasma and Wave Science Langmuir Probe (RPWS/LP)) and particle (Cassini Plasma Science Electron Spectrometer, Cassini Plasma Science Ion Beam Spectrometer, and Ion and Neutral Mass Spectrometer) measurements of Titan's ionosphere for selected flybys (T16, T29, T40, and T56) to produce altitude profiles of mean ion masses including heavy ions and develop a Titan‐specific method for detailed analysis of the RPWS/LP measurements (applicable to all flybys) to further constrain ion charge densities and produce the first empirical estimate of the average charge of negative ions and/or dust grains. Our results reveal the presence of an ion‐ion (dusty) plasma below ~1100 km altitude, with charge densities exceeding the primary ionization peak densities by a factor ≥2 in the terminator and nightside ionosphere (ne/ni ≤ 0.1). We suggest that ion‐ion (dusty) plasma may also be present in the dayside ionosphere below 900 km (ne/ni < 0.5 at 1000 km altitude). The average charge of the dust grains (≥1000 amu) is estimated to be between −2.5 and −1.5 elementary charges, increasing toward lower altitudes.

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Effects of Saturn's magnetospheric dynamics on Titan's ionosphere

Cited by 14 publications

References 65 publications

Solar cycle variations in ion composition in the dayside ionosphere of Titan

Solar cycle variations in ion composition in the dayside ionosphere of Titan

Suprathermal Electrons in Titan’s Sunlit Ionosphere: Model–observation Comparisons

Ion and aerosol precursor densities in Titan's ionosphere: A multi‐instrument case study

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