The Hadley Cells Across Seasons and the Solar System

The Hadley cells shape Earth's climate and vary across seasons, years, and planetary bodies. Using a simple theory linking their poleward extent to baroclinic instability, we capture the climatological seasonal cycle and interannual variations of Earth's Hadley cells---in both cases determined primarily by each cell's mean Rossby number and secondarily by the poleward displacement of their shared ascending edge. For Mars and Titan, we further capture the seasonal cycle of ascent with a simple theory linking it to tropical supercriticality, yielding a combined theory capturing the full climatological extent of each Hadley cell across seasons. Examining Hadley cell extent in terms of the mean Rossby number and ascending edge could be useful for outstanding questions regarding global warming, paleoclimate, and terrestrial exoplanets.