Speaker:Nathan Arnold from NASA, Goddard Space Flight Cen.

Title: “Non-rotating convective aggregation and the Madden-Julian Oscillation.”

Abstract: “The Madden-Julian oscillation (MJO) is the dominant mode of tropical intraseasonal variability, but its dynamics remain poorly understood.  It has been suggested that the MJO is a form of convective self-aggregation, similar to that seen in non-rotating cloud resolving simulations but on a larger spatial scale.  In this talk I will present support for that hypothesis based on SPCAM simulations with globally uniform SST.  Under non-rotating conditions, convection self-organizes into large (~4000km) clusters surrounded by dry regions, while with Earth-like rotation the model produces a robust MJO.  The non-rotating aggregation and MJO are found to have similar budgets of moist static energy, both being supported by diabatic feedbacks, particularly cloud-longwave feedbacks.  Mechanism denial experiments confirm that interactive longwave heating is essential to both phenomena.  Non-rotating simulations using the conventional CAM with a weak MJO show a much weaker tendency to aggregate, and both MJO activity and aggregation intensity are found to depend on the parameterized convective entrainment rate. Processes controlling the spatial scale of aggregated convection will also be explored.”