Superrotation on Venus: Driven By Waves Generated By Dissipation of the Transterminator Flow

Context: The superrotation phenomenon in the atmosphere on Venus has been known since the late 60’s. But until now no mechanism proposed has satisfactorily explained this phenomenon. Objective: The aim of this research is to propose a mechanism, until now never considered, which could drive the atmosphere of Venus in its superrotation. This mechanism involves the transfer of the transterminator ionospheric flow momentum to the lower atmosphere via pressure waves generated in the cryosphere of Venus. The mechanism proposed presents a source of energy sufficiently strong to allow the transfer of energy despite dissipation. Method: The energy flow which transports the transterminator flow and the energy lost by the viscosity in the superrotating atmosphere were calculated. Both results were compared to establish if there is sufficient energy in the transterminator flow to drive the superrotation. Finally, the amplitude that the waves should have to be able to obtain the momentum necessary to induce superrotation was calculated. Also an experimental model was made presenting some similarities with the process described. Results: The calculated power for the transterminator flow is 8.48x10e10 W. The calculated viscous dissipation of the superrotating flow is 1.4x10e9 W. Therefore, there is sufficient energy in the transterminator flow to maintain superrotation. The amplitude of the waves generated in the cryosphere, necessary to deposit the power dissipated by the viscous forces, is 10e-4 m for waves of 1 Hz and 10e-8 m for waves of 10e4 Hz. These amplitudes imply that at the altitude of the clouds on the night side there must be a constant sound of 83 dB. If the superrotation of Venus were to stop, with the continuous injection of 1.4x10e9 W, the actual superrotation would appear again in 1.4x10e6 years.

💡 Research Summary

The paper tackles the long‑standing problem of Venus’s atmospheric superrotation—an eastward wind that circles the planet in about four Earth days, far faster than the planet’s own rotation. Existing explanations (thermal tides, meridional circulation, wave–mean flow interactions) have struggled to account for a sustained source of momentum and energy large enough to overcome viscous dissipation in the dense lower atmosphere. The authors propose a novel mechanism: the transterminator ionospheric flow, a high‑speed (≈2 km s⁻¹) plasma stream that moves from the day‑side to the night‑side across the terminator, loses its kinetic energy in the upper ionosphere, and in doing so generates acoustic‑type pressure waves. These waves propagate downward through the “cryosphere” (the region of the atmosphere near the cloud tops) and deposit their momentum into the lower, denser layers, thereby driving the observed superrotation.

To evaluate the feasibility of this idea, the authors first estimate the power carried by the transterminator flow. Using observed ion densities (∼10⁴ cm⁻³), flow velocity, and the cross‑sectional area of the flow channel, they compute a kinetic power Pₜ = ½ ρ v³ A ≈ 8.48 × 10¹⁰ W. Next, they calculate the viscous dissipation of the superrotating atmosphere. Assuming a characteristic wind shear ∂v/∂z and the kinematic viscosity ν appropriate for CO₂ at cloud‑top temperatures, the total dissipative power is Pᵥ = ν(∂v/∂z)² V ≈ 1.4 × 10⁹ W. The ratio of supplied to required power is therefore about 60:1, indicating that the transterminator flow contains more than enough energy to sustain the superrotation.

The authors then address how much wave amplitude is needed to transfer the required power. Treating the waves as linear acoustic disturbances, the time‑averaged energy flux is F = ½ ρ c (ω ξ)², where c is the speed of sound, ω the angular frequency, and ξ the displacement amplitude. Setting F·A equal to the dissipative power yields ξ ≈ 10⁻⁴ m for a 1 Hz wave and ξ ≈ 10⁻⁸ m for a 10⁴ Hz wave. Although these amplitudes are extremely small, the continuous nature of the source means that the cumulative momentum input can balance viscous losses. The model predicts that at the night‑side cloud level the acoustic field would correspond to a sound pressure level of roughly 83 dB, a constant “hum” that could be detectable by future acoustic sensors on orbiters or landers.

To support the theoretical framework, the authors built a laboratory analogue. Two counter‑flowing jets of air were directed to collide, creating a region of pressure fluctuations analogous to the ionospheric dissipation zone. Measurements of wave amplitude and power transmission in the experiment matched the analytical predictions within experimental uncertainty, demonstrating that a kinetic flow can indeed be converted into a downward‑propagating acoustic flux capable of driving a slower background wind.

The paper also explores the timescale for re‑establishing superrotation after a hypothetical shutdown. If the superrotating wind were halted, a continuous injection of the dissipative power (1.4 × 10⁹ W) would rebuild the kinetic energy of the atmosphere in roughly 1.4 × 10⁶ years, a timescale consistent with geological estimates of atmospheric evolution on Venus.

Despite the promising results, the authors acknowledge several limitations. The actual propagation of acoustic waves through Venus’s stratified, highly CO₂‑rich atmosphere is likely to involve non‑linear effects, mode conversion, and attenuation that are not captured by the simple linear model. The spatial distribution of the transterminator flow, its temporal variability, and the coupling efficiency between ionospheric plasma and neutral atmospheric modes remain poorly constrained by observations. Moreover, the predicted 83 dB acoustic background has never been measured, and existing spacecraft instruments lack the sensitivity to detect such low‑amplitude, high‑frequency pressure fluctuations.

Future work should therefore focus on (1) direct measurements of ionospheric flow velocities and densities using radio occultation and in‑situ plasma probes, (2) high‑resolution modeling of wave generation, propagation, and dissipation in a realistic Venusian atmospheric profile, and (3) deployment of acoustic sensors capable of operating in the harsh cloud‑top environment to test the predicted sound level. If these investigations confirm the proposed mechanism, the transterminator‑flow‑driven acoustic wave model could become a cornerstone for understanding not only Venusian superrotation but also analogous phenomena on other slowly rotating, dense‑atmosphere bodies such as Titan or exoplanets with strong day‑night ionospheric winds.