The Energy and Momentum Budgets of Titan’s Stratospheric Polar Vortex

Titan’s stratosphere exhibits significant seasonality over the course of its year, including the development of a westerly jet near its autumn and winter pole, with speeds approaching 200 m s^-1 [1, 2]. The jet, also referred to as the stratospheric polar vortex, has been hypothesized to act as a mixing barrier which traps trace species above the winter pole, the location of the descending branch of the stratospheric meridional overturning circulation [2]. Titan’s polar vortex is primarily driven by diabatic cooling caused by decreased solar insolation at high winter latitudes, which results in a steep meridional thermal gradient and, consequently, a strong wind shear [3]. Though the evolution of the vortex has been documented for one half of a Titan year by observations from the Cassini spacecraft, quantification of the proposed mechanisms that are responsible for generating the stratospheric jet has not been performed. Here, we study the seasonal variations of potential processes proposed to be responsible for the evolution of the stratospheric polar vortex. Using simulations from the Titan Atmospheric Model [4], which has been recently updated to better simulate Titan’s stratosphere [5], we describe the evolution of solar shortwave heating (driven by absorption of solar light by atmospheric aerosol), heating from the adiabatic descent of the stratospheric meridional overturning circulation, longwave cooling from enhanced trace molecules, and the transport of zonal momentum by both the mean flow and eddies.

References

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

[2] Shultis, 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. & Lora, J. M., (in review), Icar