Negative Pressure Perturbations Associated With Tornado-Scale Vortices in the Tropical Cyclone Boundary Layer

Dangerous turbulences were observed in the eyewall of category 5 Hurricane Hugo (1989) and the surface pressure associated with the turbulence was 8 hPa lower than the mean pressure in the eye. In this study, it is demonstrated that small scale, negative pressure perturbations in the tropical cyclone eyewall are associated with the tornado-scale vortex (TSV) simulated with the large-eddy simulation technique in a semi-idealized numerical experiment. The negative pressure perturbation associated with TSVs is nonhydrostatic, dynamically resulting from the shearing effect. As a result, the negative pressure perturbation is linearly correlated with the vertical component of relative vorticity and maximum wind perturbation. Since the TSV is prevalent near the inner edge of the tropical cyclone eyewall, it is suggested that caution should be taken to estimate the central pressure of tropical cyclones with the extremely low pressure observed in the eyewall. Plain Language Summary A National Oceanic and Atmospheric Administration (NOAA) research aircraft encountered dangerous turbulences in the eyewall of category 5 Hurricane Hugo (1989) and the observed surface pressure associated with the turbulence sharply decreased to 916 hPa in the eyewall, 8 hPa lower than the mean pressure of 924 hPa in the eye. This study demonstrates that the small-scale pressure perturbation in the eyewall are associated with the tornado-scale vortex. The negative pressure perturbation is linearly correlated with the vertical component of relative vorticity and maximum wind perturbation. Since the perturbation is prevalent near the inner edge of the tropical cyclone eyewall, it is suggested that the extremely low pressure observed in the eyewall is not necessarily associated with the tropical cyclone intensity. Key Points Caution should be taken to estimate the central pressure of tropical cyclones with the extremely low pressure observed in the eyewall. Small scale, negative pressure perturbations are associated with the tornado-scale vortex in the tropical cyclone eyewall. The negative pressure perturbations associated with tornado-scale vortices (TSVs) is nonhydrostatic, dynamically resulting from the shearing effect.