Angular Momentum Transfer Events in Titan's Stratosphere

Using a combination of space-time cross spectral wave analysis, 1D Fourier transformation and spherical harmonic wave analysis techniques, we characterize the dominant atmospheric wave modes driving and maintaining superrotation in Titan's stratosphere. We evaluate the strength of temperature and wind perturbations in TitanWRF GCM simulations during strong angular momentum transfer events at Ls = 115°, 191°, and 260° as well as during quiescent periods. From the space-time cross spectral analysis, we extract dominant horizontal wave modes with properties including phase speed and wavenumber, as indicated by maximum power spectral density of eddy heat and eddy momentum fluxes. From 1D Fourier transformation, we obtain dominant vertical wave modes (characterized by wave amplitude and wavelength) that may correlate to the dominant horizontal wave modes. And from the spherical harmonic analysis, we decompose temperature and winds and on a spherical surface to identify the dominant wave modes that transfer energy to and take energy away from the zonal flow. We demonstrate that the amplitude of temperature and wind perturbations are stronger during angular momentum transfer events, and the net effect of the waves associated with these perturbations drive the stratospheric superrotation.

In addition, we will present an orbital submillimeter spectrometer point design for use at Titan to measure the vertical profiles of temperature, winds, and trace gases in the atmosphere. We preliminarily evaluate the efficacy of such an instrument for measuring these quantities and for detecting wave structures and their impacts in Titan's atmosphere via our pseudo-Observation System Simulation Experiment (OSSE) methodology. Direct observations of waves and their impact on superrotation in Titan's atmosphere would greatly improve our understanding of the atmospheric circulation of Titan, and other slow rotating planetary bodies.