On the rapid intensification for Typhoon Meranti (2016): convection, warm core, and heating budget

Abstract

Through a cloud-resolving simulation of the rapid intensification (RI) of Typhoon Meranti (2016), the convections, warm core, and heating budget are investigated during the process of RI. By investigating the spatial distributions and temporal evolutions of both convective-stratiform precipitation and shallow-deep convections, we find that the inner-core convections take mode turns, from stratiform-precipitation (SP) dominance to convective-precipitation (CP) prevalence during the transition stages between pre-RI and RI. For the CP, it experiences fewer convections before RI, and the conversion from moderate/ moderate-deep convections to moderate-deep/deep convections during RI. There is a clear upper-level warm-core structure during the process of RI. However, the mid-low-level warming begins first, before the RI of Meranti. By calculating the local potential temperature (θ) budget of various convections, the link between convections and the warm core (and further to RI via the pressure drop due to the warming core) is established. Also, the transport pathways of heating toward the center of Meranti driven by pressure are illuminated. The total hydrostatic pressure decline is determined by the mid-low-level warm anomaly before RI, mostly caused by SP. The azimuthal-mean diabatic heating is the largest heating source, the mean vertical heat advection controls the vertical downwards transport by adiabatic warming of compensating down-drafts above eye region, and then the radial θ advection term radially transports heat toward the center of Meranti in a slantwise direction. Accompanying the onset of RI, the heating efficiency of the upper-level warming core rises swiftly and overruns that of the mid-low-level warm anomaly, dominating the total pressure decrease and being mainly led by moderate-deep and deep convections. Aside from the characteristics in common with SP, for CP, the eddy component of radial advection also plays a positive role in warming the core, which enhances the centripetal transport effect and accelerates the RI of Meranti.