Convective Bursts Episode of the Rapidly Intensified Typhoon Mujigae (2015)

Abstract

Convective burst (CB) characteristics at distinct stages of a rapidly intensified Typhoon Mujigae (2015), are investigated based on a 72-h simulation. The spatial features show that almost all CB elements develop in the eyewall. The number of CBs in the inner-core region within a 100 km radius——which account for a large proportion of the total CBs, with a sharp increase about 6 h before the onset of rapid intensification (RI)——provides some indication of the RI of the typhoon. The CBs during pre-RI and RI are examined from dynamic and thermodynamic viewpoints. The combination of lower-level convergent inflow and upper-level divergent outflow pushes a relay-race-like transmission of convective activity, favorable for the development of deep convection. A double warm-core structure is induced by the centripetal outflow sinking and warming associated with CBs, which directly accelerates RI by a sudden decrease in hydrostatic pressure. By utilizing the convection activity degree (CAD) index derived from the local total energy anomaly, a correlation formula between CBs and CAD is deduced. Furthermore, an intense CAD (ICAD) signal threshold (with a value equal to 100) to predict CBs is obtained. It is verified that this ICAD threshold is effective for estimating the occurrence of a CB episode and predicting RI of a typhoon. Therefore, this threshold may be a valuable tool for identifying CB episodes and forecasting rapidly intensified typhoons.