RESUMEN
Tropical cyclone Seroja was one of the first tropical cyclones to significantly impact Indonesian land, and the strongest one in such close proximity to Timor Island. In April 2021 Seroja brought historic flooding to near-equatorial regions of Indonesia and East Timor, as well as impacting Western Australia. Here we show that the unusual near-equatorial cyclogenesis in close proximity to a land mass was due to "perfect storm" conditions associated with multiple wave interactions. Specifically, this was associated with enhanced equatorial convection on the leading edge of a Madden-Julian Oscillation (MJO) event. Within the MJO, the interaction between a convectively coupled equatorial Rossby wave and two convectively coupled Kelvin waves span up the initial vortex and accelerated cyclogenesis. On average, such favorable atmospheric conditions can occur once per year. These results indicate the potential for increased predictability of tropical cyclones over the Maritime Continent.
RESUMEN
Sea surface temperature (SST) is a fundamental driver of tropical weather systems such as monsoon rainfall and tropical cyclones. However, understanding of the factors that control SST variability is lacking, especially during the monsoons when in situ observations are sparse. Here we use a ground-breaking observational approach to determine the controls on the SST variability in the southern Bay of Bengal. We achieve this through the first full closure of the ocean mixed layer energy budget derived entirely from in situ observations during the Bay of Bengal Boundary Layer Experiment (BoBBLE). Locally measured horizontal advection and entrainment contribute more significantly than expected to SST evolution and thus oceanic variability during the observation period. These processes are poorly resolved by state-of-the-art climate models, which may contribute to poor representation of monsoon rainfall variability. The novel techniques presented here provide a blueprint for future observational experiments to quantify the mixed layer heat budget on longer time scales and to evaluate these processes in models.
RESUMEN
Using the new Argo array of profiling floats that gives unprecedented space-time coverage of the upper 2000 meters of the global ocean, we present definitive evidence of a deep tropical ocean component of the Madden-Julian Oscillation (MJO). The surface wind stress anomalies associated with the MJO force eastward-propagating oceanic equatorial Kelvin waves that extend downward to 1500 meters. The amplitude of the deep ocean anomalies is up to six times the amplitude of the observed annual cycle. This deep ocean sink of energy input from the wind is potentially important for understanding phenomena such as El Niño-Southern Oscillation and for interpreting deep ocean measurements made from ships.
