Diagnosing radial ventilation in dropsonde observations of Hurricane Sam (2021)

This study presents a method to diagnose radial ventilation, the horizontal flux of relatively low-9e 9 e air into tropical cyclones, from dropsonde observations. We used this method to investigate ventilation changes over three consecutive sampling periods in Hurricane Sam (2021), which underwent substantial intensity changes over 3 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 9e 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-9e 9 e air wrapping in upshear. The spatial correlation of the radial inflow flow and anomalously low-9e 9 e air resulted in large ventilation at mid- to upper levels. Additionally, at low to midlevels, there was evidence of mesoscale inflow fl ow of low-9e 9 e air in the stationary band complex. The location of these radial ventilation pathways and their effects on Sam's intensity are consistent with previous idealized and real-case modeling studies. 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.