Prograde and retrograde atmospheric rotation of cloud-covered terrestrial planets

Abstract

Context. Cloud-covered middle-atmospheric dynamics are important in the strong prograde rotation (i.e. superrotation) observed in some terrestrial-planet atmospheres, such as Venus and Titan. In addition, the unified theory and the mechanism driving the general circulation could be extended to as yet unknown extrasolar Earth-sized habitable planet atmospheres. Aims. We elucidate the dynamical process controlling prograde and retrograde atmospheric rotation induced by cloud heating in the middle atmosphere of terrestrial planets. Methods. The terrestrial middle-atmospheric circulation is examined using a general circulation model in which astronomical parameters are varied. Results. Middle-atmospheric circulation is strongly controlled by seasonal variation of the meridional circulation. Prograde and retrograde atmospheric rotation is determined by the direction of vertical angular momentum transport due to the meridional circulation resulting from tilting of the planetary rotation axis. The retrograde rotation rate is limited to −Ω for slowly rotating planets (where Ω is the planetary rotation rate).

General circulation driven by baroclinic forcing due to cloud layer heating: Significance of planetary rotation and polar eddy heat transport

“…The mean zonal flows in Exps. V, T, and E are weaker than those in Figure 2a of Yamamoto and Takahashi [], because there are large differences in horizontal resolution and radiative heating. In the low‐resolution GCM of T21 [ Yamamoto and Takahashi , ], the polar indirect cell and multiple meridional circulations are not fully resolved, and the strong equatorial superrotation and midlatitude jets are formed in and around the cloud layer.…”

“…V, T, and E are weaker than those in Figure 2a of Yamamoto and Takahashi [], because there are large differences in horizontal resolution and radiative heating. In the low‐resolution GCM of T21 [ Yamamoto and Takahashi , ], the polar indirect cell and multiple meridional circulations are not fully resolved, and the strong equatorial superrotation and midlatitude jets are formed in and around the cloud layer. This is different from the results of the present simplified high‐resolution (T106) model; the cloud level jet extends to the lower atmosphere in Exp V, and the midlatitude jet forms in the upper atmosphere above the cloud layer in Exp.…”

“…However, the model does not resolve the middle atmosphere above the troposphere. Although Yamamoto and Takahashi [, ] investigated the effects of changing the obliquity angle of the planetary rotation axis on superrotation and subrotation in the planetary middle atmosphere, the horizontal resolution was too low to fully resolve the polar circulation. By improving the baseline run of the ISSI project [ Lebonnois et al ., ] to higher resolution, the idealized AGCM enables us here to conduct long‐term (~50,000 Earth days) simulations of the middle atmosphere and polar dynamics in a cloud‐covered planet.…”

Rossby Number Dependence of Venus/Titan‐Type Superrotation and Its Related Intermittency

“…Although a few previous studies (Yamamoto & Takahashi, 2008, 2016) have investigated the sensitivity of Venus/Titan‐type superrotation to planetary rotation, superrotation dynamics with high Rossby numbers in cloud‐covered atmospheres like those of Venus and Titan are not yet fully understood. Hence, the sensitivity of superrotation to planetary rotation and size is investigated here for a wide range of Rossby numbers to gain understanding of the geophysical fluid dynamics of slowly rotating and/or small‐sized terrestrial planets.…”

Dynamical effects of solar heating below the cloud layer in a Venus‐like atmosphere

“…Recently, Yamamoto and Takahashi [2007a, 2008] investigated the sensitivity of terrestrial superrotation to astronomical parameters. In the work of Yamamoto and Takahashi [2007a], we found the long‐period variation between the fast and slow superrotation states.…”