The Use of a Vortex Insertion Technique to Simulate the Extratropical Transition of Hurricane Michael (2000)

Abstract

On 19 October 2000, Hurricane Michael merged with an approaching baroclinic trough over the western North Atlantic Ocean south of Nova Scotia. As the hurricane moved over cooler sea surface temperatures (SSTs; less than 25°C), it intensified to category-2 intensity on the Saffir-Simpson hurricane scale [maximum sustained wind speeds of 44 m s Ϫ1 (85 kt)] while tapping energy from the baroclinic environment. The large "hybrid" storm made landfall on the south coast of Newfoundland with maximum sustained winds of 39 m s Ϫ1 (75 kt) causing moderate damage to coastal communities east of landfall. Hurricane Michael presented significant challenges to weather forecasters. The fundamental issue was determining which of two cyclones (a newly formed baroclinic low south of Nova Scotia or the hurricane) would become the dominant circulation center during the early stages of the extratropical transition (ET) process. Second, it was difficult to predict the intensity of the storm at landfall owing to competing factors: 1) decreasing SSTs conducive to weakening and 2) the approaching negatively tilted upper-level trough, favoring intensification. Numerical hindcast simulations using the limited-area Mesoscale Compressible Community model with synthetic vortex insertion (cyclone bogus) prior to the ET of Hurricane Michael led to a more realistic evolution of wind and pressure compared to running the model without vortex insertion. Specifically, the mesoscale model correctly simulates the hurricane as the dominant circulation center early in the transition process, versus the baroclinic low to its north, which was the favored development in the runs not employing vortex insertion. A suite of experiments is conducted to establish the sensitivity of the ET to various initial conditions, lateral driving fields, domain sizes, and model parameters. The resulting storm tracks and intensities fall within the range of the operational guidance, lending support to the possibility of improving numerical forecasts using synthetic vortex insertion prior to ET in such a model.

Using atmospheric model output to simulate the meteorological tsunami response to Tropical Storm Helene (2000)

“…vortex is completely missing from the GEM analysis. The importance of vortex insertion has been shown previously by Fogarty et al [2006], when simulating Hurricane Juan (2003), and Fogarty et al [2007], when simulating Hurricane Michael (2000).…”

“…The parameters used to create the vortex are the minimum sea level pressure, the position of the storm, the radius of 15 m s −1 winds (R 15 ), and the speed of the storm motion, which are all parameters available when preparing forecasts of tropical cyclones. The use of synthetic vortex insertion with the MC2 model has been shown to be successful with a number of storms [ Fogarty et al , 2006, 2007]. The MC2 model, with synthetic vortex insertion, is currently run experimentally on a real‐time basis at the Canadian Hurricane Center when storms are active.…”

“…The atmospheric forcing is taken from a simulation of Tropical Storm Helene that uses the Mesoscale Compressibility Community (MC2) model [ Benoit et al , 1997] together with a vortex insertion method [cf. Fogarty et al , 2007]. The latter uses data available from the National Hurricane Center and satellite imagery to create a vortex specified by intensity, size, and initial position, which is then inserted into the atmospheric fields as the initial condition for the MC2 model.…”

Aircraft Observations of Tropical Cyclones

“…Ice water concentrations on the western side of the storm in the stratiform precipitation region were very high, and more characteristic of concentrations seen in the center of continental cumulonimbus clouds. Data from the mission led to improved initialization techniques for numerical models (Fogarty et al, 2007).…”

The elliptical vortices, integrable Ermakov structure, Schrödinger connection, and Lax pair in the compressible Navier–Stokes equation

“…Based on the Ermakov structure, they derived a class of vortex solutions termed pulsrodons. Investigations reveal that such pulsrodons are very useful in studying warm‐core eddies, tidal oscillations, geophysics, oceanic and atmospheric dynamics, and so forth 39–46 . It is noticed that the works of Refs.…”