Radial Ventilation and the Rapid Intensity Changes of Hurricane Sam (2021)

Using a method to diagnose radial ventilation, the horizontal flux of relatively low-θ_e air into tropical cyclones, from dropsonde observations, we investigate ventilation changes over three consecutive aircraft sampling periods in Hurricane Sam (2021). Sam underwent substantial intensity changes over three days. During the first and last periods, coinciding with intensification, the ventilation was relatively small due to a lack of spatial correlation between radial flow and θ_e azimuthal asymmetries. During the second period, coinciding with weakening, the ventilation was relatively large. The increased ventilation was caused by greater shear associated with an upper-level trough, tilting the vortex, along with dry, low-θ_e air wrapping in upshear. The spatial correlation of the tilt-induced radial inflow and anomalously low-θ_e air resulted in large ventilation at mid-to-upper levels. Additionally, at low-to-mid levels, there was evidence of mesoscale inflow of low-θ_e air in the stationary band complex. More generally, this method offers a way to monitor ventilation changes in tropical cyclones, particularly when there is full-troposphere sampling around and within a tropical cyclone's core.