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Simulating the Production of Stratospheric Ice Clouds over Titan’s Winter Pole with the Titan Atmospheric Model

Presentation #208.06 in the session Titan I: Atmosphere (Oral Presentation)

Published onOct 23, 2023
Simulating the Production of Stratospheric Ice Clouds over Titan’s Winter Pole with the Titan Atmospheric Model

Titan’s middle atmosphere exhibits a nearly pole-to-pole meridional overturning circulation that delivers air from the summer hemisphere to the winter pole [1]. This circulation involves an ascending branch at summer latitudes, high altitude transport from the summer hemisphere to the winter hemisphere, and a descending branch that delivers high altitude air into the lower stratosphere above the winter pole [2]. Through this process trace molecules, which are typically more abundant at high altitudes, are delivered to the lower stratosphere, resulting in a steep meridional gradient in abundance [3]. This chemically enriched polar air mass is trapped by the polar jet, a region of strong zonal winds that exists from autumn through early spring [1,2]. Trace species that are delivered to the lower winter stratosphere are removed from the atmosphere via saturation, and produce stratospheric ice clouds throughout autumn and winter. The altitudes at which these clouds are produced depends on the molecule, with nitriles typically condensing at higher altitudes than hydrocarbons. Two such clouds have been observed, including an HCN cloud observed near 300 km during southern autumn in 2012 [4] and a C2H6 cloud observed near 150 km during late northern winter in 2004 [5].

Here, using a new capability within the three-dimensional Titan Atmospheric Model (TAM; [6, 7]) to simulate the idealized production, transport, photochemical decay, and saturation of trace species, we explore the latitudes, altitudes, and seasonal coverage of stratospheric ice cloud production. We compare our results to observed occurrences of stratospheric clouds and assess the possibility of the production of ice clouds with compositions yet to be observed on Titan.

References

[1] Teanby, N.A. et al., (2017), Nat Comm 8, 11586

[2] Lombardo, N.A., et al., submitted to JGR Planets

[3] Mathé, C. et al., (2020), Icar 344, 113547

[4] de Kok, R. J., et al., (2014), Nature 514, 65 — 67

[5] Griffith, C. A., et al., (2005), Science 313, 1620 – 1622

[6] Lombardo, N.A. et al., (2023), Icar 390, 115291

[7] Lora, J.M. et al., (2015), Icar 250, 516 — 528

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