Uranus’ many unique attributes provide insights into planetary atmospheric dynamics. Uranus’ spin axis lying nearly in its orbital plane curtails hemispheric redistribution of solar influx over each 21 Julian-year long winter. Hence, flux calculations overestimate Uranus’ average surface temperature. Location of Uranus’ H 2 -rich atmosphere on the H 2 gas-liquid (∼32 K) or fluid-ice (∼15 K) phase boundary buffers its emissions, reducing temperature variations, while creating the imaged, permanent ice caps that dominate atmospheric dynamics. Due to immense size and extreme cold, summertime sublimation slightly reduces the size of H 2 ice caps, while also releasing minor amounts of methane and creating haze. Uranus’ and Neptune’s absolute zonal wind speeds are fit by v max cos(latitude) 1- n , where v max is measured equatorial windspeed and the sole fitting parameter n describes drag. We show top-heating provides meridional circulation with the same sense as bottom-heating, but with far less vigor. Based on the above findings, edges of Uranus’ sunlit ice caps define a polar front, which yields a single, weak Ferrel cell near solstice. Permanent ice caps maintain polar fronts near ±30°, leading to paired Ferrel and Polar cells near equinox. Based on Uranus’ seasonally changing atmospheric circulation, and because oceanic warming preceded observed shifts in Earth’s climate belts during the last ice age, we propose that global warming increases atmospheric vigor, triggering Earth’s three pairs of meridional cells to increase to four. Four pairs provide high polar precipitation but foster consequent cooling which reduces vigor: Hence, cell number reverts and warming recommences. Our explanations of Uranus’ behavior and Earth’s Ice Age periodicity are analogous to thermal cycling in biological and engineered systems. A specific cause of global warming is not required. • Uranus’ spin orientation makes Solar heating ineffective and Uranus surprisingly cold • A phase transition defining Uranus’ surface conditions masks its emissions • Uranus’ equatorial atmosphere rotates with the interior, confirming frigidity • Unearthlike top-heating of optically thick atmospheres provides weak Hadley cells • Earth’s Ice age periods are thermoregulated due to feedback: control theory holds
Hofmeister et al. (Sun,) studied this question.