THE MOTION OF HURRICANE GLORIA - A POTENTIAL VORTICITY DIAGNOSIS

Multilevel, multinested analyses of Hurricane Gloria of 1985 are the m ost comprehensive kinematic dataset yet developed for a single hurrica ne. A piecewise inversion technique is used with these analyses and th e nonlinear balance equation to deduce the three-dimensional distribut ion of potential vorticity (PV) that contributed to the deep-layer mea n (DLM) how that steered Gloria toward the northwest. The background s tate is taken to be the azimuthally averaged winds in balance with a g eopotential distribution on an f plane. Advantage is taken of the near -linearity of the weak asymmetries near the hurricane's core and of PV in the environment. Thus, ad hoc aspects of the linearization require d by other investigators are effectively eliminated. Removal of the hu rricane Vortex and the use of a climatological mean background state a re avoided as well. The insensitivity of the results to the imposed la teral boundary conditions is also demonstrated. Wind anomalies attribu table to pieces of anomalous PV restricted to cylinders of different r adii centered on the hurricane are evaluated. The DLM wind that steere d Gloria to the northwest is primarily attributable to PV anomalies co nfined within a cylinder of radius 1000 km and levels 500 mb and above , including positive anomalies associated with a cold low over Cuba. T he vector difference between the hurricane's observed motion and the D LM wind at Gloria's center attributable to these PV anomalies is 1.0 m s(-1), explaining more than five-sixths of the hurricane's 6.2 m s(-1 ) motion. Implications for measurements required to establish short-te rm changes of the environmental steering dow are considered. Difficult ies in the interpretation of results are discussed for PV anomalies th at are confined to noncircular regions; the implication for other stud ies is considered as well.