Mechanism of periodic convective bursts during tropical cyclogenesis and impact of radiation
The statistical analysis of observation shows that there is a periodic characteristic of convective activity before the formation of tropical cyclones,with periods concentrated between 18-26 hours and peaks mostly occurring at night.This article discussed the causes of periodic convective bursts during tropical cyclogenesis and the impact of daily variations in radiation during this process through a series of idealized cloud-resolved numerical control experiments and comparative experiments of radiation sensitivity.Results indicate that under a constant solar radiation without daily variation,periodic convective bursts may also occur during tropical cyclogenesis as in observation,indicating that diurnal radiation cycle is not only the controlling factor of the periodic convection.The analysis of the budget of moist static energy anomaly reveals that the periodic increase or decrease of moist static energy in the boundary layer is a key factor affecting the occurrence of periodic deep convection.The cold pool formed by the outbreak of deep convection reduces the moist static energy in the boundary layer through advection,which needs to be recovered through radiation and surface flux processes in order to trigger convection again.The diurnal variation of radiation has a modulating effect on some weaker tropical depressions,which can cause the peak time phase of periodic convective bursts to change and to appear at night;but for strong vortices,the modulation effect of radiation is not significant,and vortices will maintain their initial period and peak time phase of convective burst.This study can provide a reasonable explanation for the observed occurrence of convective peaks during the daytime or nighttime during the tropical cyclogenesis,and also advance the understanding of scientific issues on the role and impact of convection and radiation on tropical cyclogenesis.
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