Exploring the Giant Saturnian Storm in 2010: A Model of Moist Convection

A giant planet-encircling storm occurred on Saturn at the end of year 2010. The storm produced lightning at a rate greater than 10 SEDs per second. It stirred up its latitude band and wrapped around the planet, and after 6 months it died. These kinds of storms are rare and episodic. They happen every 20-30 years. In this study, we discuss the role of moist convection to the development of the storm. The study is composed of three parts. First, thermodynamics on Saturn suggests that strong convection is prohibited by the water-loading-effect when the troposphere is warm. After 20~30 years, the troposphere has cooled below a critical value so that deep convection starts to develop at the base of the cloud. Second, a linear perturbation analysis of Rossby waves in an easterly jet is performed to narrow down the choices of free parameters. Based on the observed features of the storm (propagation phase speed, typical wave length, etc), the Rossby radius of deformation is calculated to be around 2000 km. Third, a 2D numerical model is developed to simulate the propagation of the storm, with moist convection parameterized as an anticyclonic vorticity source. The simulated storm has a well-defined head and a wavy tail that resemble the observation.