Circumnavigating Kelvin Waves that Initiate and Dissipate the Madden-Julian Oscillation

Radiosonde observations and Lagrangian model simulations show that an active Madden-Julian Oscillation event initiates when a dry, first baroclinic Kelvin wave enters a region in which large-scale upward motion is largely balanced by convective heating. As the MJO matures, an opposite-signed Kelvin wave emanates from its eastern edge, and transitions from a moist to a dry wave, with consequent changes in its phase speed. This wave rapidly propagates around the world and dissipates the previously active MJO convection. The Kelvin wave that initiates an active MJO can originate either from the inactive phase of a previous MJO, or from any process that suppresses convection in the western Pacific long enough to excite a deep Kelvin wave response.