2001/01/01 by Da‐Lin Zhang, Da-Lin Zhang, Yubao Liu +1 · 111 citations
Earth and Planetary Sciences · #Angular momentum #Atmospheric sciences #Boundary layer #Classical mechanics #Climatology #Eye #Geology #Inflow #Mechanics #Meteorological Phenomena and Simulations #Meteorology #Momentum (technical analysis) #Ocean Waves and Remote Sensing #Outflow #Physics #Pressure gradient #Pressure-gradient force #Tropical and Extratropical Cyclones Research #Tropical cyclone
paper · pdf · doi:10.1175/1520-0493(2001)129<0092:amnsoh>2.0.co;2
published in Monthly Weather Review 129(1), 92-107 (American Meteorological Society)
openalex publication_date 2001/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Despite considerable progress in understanding the hurricane vortex using balanced models, the validity of gradient wind balance in the eyewall remains controversial in observational studies. In this paper, the structure and development of unbalanced forces and flows in hurricanes are examined, through the analyses of the radial momentum and absolute angular momentum (AAM) budgets, using a high-resolution (i.e., Δx = 6 km), fully explicit simulation of Hurricane Andrew (1992). It is found from the radial momentum budgets that supergradient flows and accelerations, even after temporal and azimuthal averaging, are well organized from the bottom of the eye center to the upper outflow layer in the eyewall. The agradient accelerations are on average twice greater than the local Coriolis force, and caused mainly by the excess of the centrifugal force over the pressure gradient force. It is shown by the AAM budgets that supergradient flows could occur not only in the inflow region as a result of the inward AAM transport, but also in the outflow region through the upward transport of AAM. The eyewall is dominated by radial outflow in which the upward transport of AAM overcompensates the spindown effect of the outflow during the deepening stage. The intense upper outflow layer is generated as a consequence of the continuous outward acceleration of airflows in the eyewall updrafts. In spite of the pronounced agradient tendencies, results presented here suggest that the azimuthally averaged tangential winds above the boundary layer satisfy the gradient wind balance within an error of 10%. The analyses of instantaneous fields show pronounced asymmetries and well-organized wavenumber-2 structures of the agradient flows and forces in the form of azimuthally propagating vortex–Rossby waves in the eyewall. These waves propagate cyclonically downstream with a speed half the tangential winds near the top of the boundary layer and vertically upward. Agradient flows/forces and AAM transport in the eye are also discussed.