The Energy and Momentum Balance of Titan’s Stratospheric Polar Vortex as Simulated in a General Circulation Model

Titan’s stratospheric polar vortex is a prominent phenomenon of Titan’s global wind field, consisting of a westerly jet achieving speeds of nearly 200 m s^-1 [1, 2].  The strong westerly winds have been hypothesized to serve as a mixing barrier to molecules transported to the high winter latitudes by Titan’s stratospheric meridional overturning circulation [2].  Similar to Earth’s stratospheric polar vortex, the vortex on Titan is primarily driven by diabatic cooling at high winter latitudes, resulting in a steep meridional temperature gradient and, via the thermal wind relation, a strong vertical wind shear [3].  While the existence and evolution of the vortex has been constrained for one half of a Titan year by observations from the Cassini spacecraft, a rigorous analysis of the potential mechanisms that give rise to the strong stratospheric jet has not yet been performed.

Here, using simulations from the Titan Atmospheric Model [4], which has recently been updated to better simulate Titan’s stratosphere [5], we study the temporal evolution of processes proposed to be responsible for the evolution of Titan’s stratospheric polar vortex, including: solar shortwave heating (largely controlled by the presence of stratospheric aerosols), adiabatic heating from the descending branch of the meridional overturning circulation, and molecular longwave cooling [3].

References

[1] Sharkey, J. et al, (2021) Icar 354, 114030

[2] Schultis, J., et al., (2022) PSJ 3, 73

[3] Teanby, N. A., et al, (2017), Nat Comm 8, 1586

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

[5] Lombardo, N. A., et al., (in review), Icar