Influence of Convectively Coupled Equatorial Waves, the MJO, and ENSO on the Environment of Tropical Cyclones in Coupled Atmosphere–Ocean Subseasonal Prediction Systems

Tropical convection is modulated by convectively coupled equatorial waves (CCEWs), the Madden Julian Oscillation (MJO), and the El Nino Southern Oscillation (ENSO). Coupled atmosphere-ocean subseasonal prediction systems such as the Navy Earth System Model (NESM) have demonstrated an ability to produce intraseasonal convective variability consistent with the MJO. However, less is known about the ability of subseasonal prediction systems to simulate the interannual variability of the MJO and the modulation of higher-frequency modes of variability such as easterly waves and Kelvin waves by the MJO. These various modes of convective variability are also known to modulate environmental conditions relevant to tropical cyclones.

In this study, the ability of the NESM and models in the Subseasonal to Seasonal (S2S) database to predict convective variability across a range of spatiotemporal scales and its connection to variability in environmental conditions relevant to TC formation and intensity (e.g. humidity, shear, relative vorticity, and maximum potential intensity) are evaluated using 1999-2015 boreal summer hindcasts. Implications for tropical cyclone prediction on subseasonal time scales are also discussed.