A Computational Study of Binary Mesoscale Vortex Interactions on the Tropical Oceanic F-Plane: The Consequences on Hurricane Formation

The evolution of two symmetric mid-level mesoscale vortices (MVs) over a tropical ocean is systematically examined with an idealized configuration of a standard cloud model. The ambient conditions correspond to either the Jordan mean sounding (JMS) for hurricane season in the West Indies or a variant of the JMS that is humidified in the middle-troposphere to provide a setting conducive to rapid vortex intensification. In the humidified atmosphere, the MVs generally develop into one or two hurricanes with the pathway depending on the horizontal separation distance D. The time-scale for the early stage of intensification tends to decrease with D, but the timing of merger disrupts intensification for intermediate values of D. In the drier atmosphere corresponding to the JMS, an intermediate value of D can surprisingly suppress hurricane formation for at least 300 hours. The suppression is apparently connected to the detachment (outward radial ejection) of low-level potential vorticity from the two MVs as they merge in the middle-troposphere. A potentially important caveat regarding complete suppression at intermediate D is that the simulation set producing this result uses warm-rain Kessler microphysics, a Smagorinsky subgrid turbulence scheme, select constant values of the surface exchange coefficients (within observational bounds), and no parameterization of atmospheric radiation. It should be emphasized, however, that hurricanes readily form from a single MV (or two MVs with D outside the suppression interval) when using the same model physics. Sensitivity of suppression to model physics is currently under investigation. The structural dependence of a recently formed hurricane on D is also being examined. This work is supported by NSF grant AGS-1250533.