The near-surface methane humidity on Titan

Lora, Juan M.; Ádámkovics, Máté

doi:10.1016/j.icarus.2016.10.012

Cited by 30 publications

(18 citation statements)

References 47 publications

(67 reference statements)

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“…Matching these patterns over almost half a Titan year with GCM results suggests that although liquids are only observed to cover parts of the surface at high latitudes, primarily in the north, there may be a substantial subsurface methane table at each pole above 60°latitude that is available for exchange with the atmosphere. This interpretation is consistent with other results based on a variety of data and techniques (e.g., RADAR imaging and topography, ISS and VIMS surface imaging and spectra, subsurface transport models, surface temperatures, and tropospheric methane mole fractions) that suggest connected subsurface hydrology at Titan's north pole (e.g., Birch et al, 2017;Hayes et al, 2008Hayes et al, , 2017Horvath et al, 2016;Jennings et al, 2016;Lora & Ádámkovics, 2017).…”

Section: Discussionsupporting

confidence: 90%

Titan's Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs

Turtle

Perry

Barbara

et al. 2018

Geophysical Research Letters

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Cassini observations of Titan's weather patterns over >13 years, almost half a Saturnian year, provide insight into seasonal circulation patterns and the methane cycle. The Imaging Science Subsystem and the Visual and Infrared Mapping Spectrometer documented cloud locations, characteristics, morphologies, and behavior. Clouds were generally more prevalent in the summer hemisphere, but there were surprises in locations and timing of activity: Southern clouds were common at midlatitudes, northern clouds initially appeared much sooner than model predictions, and north polar summer convective systems did not appear before the mission ended. Differences from expectations constrain atmospheric circulation models, revealing factors that best match observations, including the roles of surface and subsurface reservoirs. The preference for clouds at mid‐northern latitudes rather than near the pole is consistent with models that include widespread polar near‐surface methane reservoirs in addition to the lakes and seas, suggesting a broader subsurface methane table is accessible to the atmosphere.

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Section: Discussionsupporting

confidence: 90%

Titan's Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs

Turtle

Perry

Barbara

et al. 2018

Geophysical Research Letters

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“…Using photometric observations collected in 2014, Lora and Ádámkovics (2017) found with certainty a very humid north polar region and, consistent with Tokano (2014) but not in a significant way, a methane humidity increasing from the north (30-60 o N) to the southern hemisphere (30 o S to equator). However clear conclusions at global scale could not be drawn due to uncertainties in methane retrievals.…”

mentioning

confidence: 57%

Convection behind the Humidification of Titan’s Stratosphere

Rannou

Coutelier

Rivière

et al. 2021

ApJ

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On Titan, methane is responsible for the complex prebiotic chemistry, the global haze, most of the cloud cover, and the rainfall that models the landscape. Its sources are located in liquid reservoirs at and below the surface, and its sink is the photodissociation at high altitude. Titan’s present and past climates strongly depend on the connection between the surface sources and the atmosphere upper layers. Despite its importance, very little information is available on this topic. In this work, we reanalyze two solar occultations made by Cassini before the northern spring equinox. We find a layer rich in methane at 165 km and at 70°S (mixing ratio 1.62% ± 0.1%) and a dryer background stratosphere (1.1%–1.2%). In the absence of local production, this reveals an intrusion of methane transported into the stratosphere by convective circulation. On the other hand, methane transport through the tropopause at a global scale appears quite inhibited. Leaking through the tropopause is an important bottleneck of Titan’s methane cycle at all timescales. As such, it affects the long-term evolution of Titan’s atmosphere and the exchange fluxes with the surface and subsurface reservoirs in a complex way. Global climate models accounting for cloud physics, thermodynamical feedbacks, and convection are needed to understand the methane cycle, and specifically the humidification of the stratosphere, at the present time, and its evolution under changing conditions at a geological timescale.

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“…We use the Titan Atmospheric Model (TAM; Lora et al, ) to investigate the relative effect of the TIUs defined above on the state of Titan's lower atmosphere. TAM is a fully three‐dimensional GCM that has been used to simulate Titan's middle and lower atmosphere (Lora et al, ), as well as investigate its paleoclimate (Lora et al, ) and various aspects of the methane cycle (Faulk et al, ; Lora & Mitchell, ; Lora & Ádámkovics, ; Mitchell & Lora, ).…”

Section: Incorporating Thermal Inertia Map Into a Gcmmentioning

confidence: 99%

A Thermal Inertia Map of Titan

2019

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Like Earth, the atmosphere of Titan, Saturn's largest moon, is affected by the ability of the surface to store and release heat. Modeling efforts have shown that global temperature distributions and wind profiles differ between simulations describing Titan's surface with a uniform thermal inertia. Cassini‐Huygens demonstrated, however, that a variety of morphologies and compositions make up the Titanian landscape. Using data from Cassini RADAR and the Visible and Infrared Mapping Spectrometer, we classified the surface into five terrain types: dune, lake, hummocky, plains, and labyrinth. We estimated the thermal and physical properties (conductivity, specific heat, and density) for each type, creating a 1° × 1° global map of thermal inertia values. For the lakes, as the depth of convection is not yet known, we considered both still and convective bodies. Four simulations of the Titan Atmospheric Model were run with different surface thermal properties: a low homogeneous thermal inertia, a moderate homogeneous, the heterogeneous map with still lakes, and the heterogeneous map with convective lakes. In dry regimes (i.e., without the hydrological cycle), the differences between the four cases were generally minimal, suggesting that general circulation models can use a single (moderate) value for surface thermal inertia value for large‐scale investigations that do not consider diurnal variations. Given the importance of hydrological processes and regional spatial diversity on Titan, future work should consider the effects of nonuniform thermal inertia on Titan's climate on local and regional scales.

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The near-surface methane humidity on Titan

Cited by 30 publications

References 47 publications

Titan's Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs

Titan's Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs

Convection behind the Humidification of Titan’s Stratosphere

A Thermal Inertia Map of Titan

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