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The Detection of Flow Asymmetries in the Tropical Cyclone Environment

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  • 1 Meteorological Institute, University of Munich, Federal Republic of Germany
  • | 2 National Meteorological Center, NOAA, Washington, D.C.
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Abstract

Data from a numerical simulation of a moving barotropic vortex on a sphere with 10-km resolution are used to assess the ability of a state-of-the-art objective analysis scheme to detect certain large-scale tropical cyclone asymmetries, the so-called “beta gyres” to which the cyclone motion appears to be attributed.

A series of analyses is conducted, first using the entire dataset and then taking subsets of it. Four subsets were considered in which data at a regular array of points were extracted, progressively increasing the separation between points. A fifth calculation was considered in which data were selected at points corresponding to the proposed upgraded upper-air network for a tropical cyclone motion experiment in the northwest Pacific region.

It is shown that for a moderate-sized tropical cyclone-scale vortex, a regular grid spacing on the order of 100–150 km is required to adequately define the gyres, at least when the ambient flow is weak. The upgraded upper-air network was found to be inadequate by itself for this purpose, suggesting that aircraft dropwindsonde data are a prerequisite for this task.

Abstract

Data from a numerical simulation of a moving barotropic vortex on a sphere with 10-km resolution are used to assess the ability of a state-of-the-art objective analysis scheme to detect certain large-scale tropical cyclone asymmetries, the so-called “beta gyres” to which the cyclone motion appears to be attributed.

A series of analyses is conducted, first using the entire dataset and then taking subsets of it. Four subsets were considered in which data at a regular array of points were extracted, progressively increasing the separation between points. A fifth calculation was considered in which data were selected at points corresponding to the proposed upgraded upper-air network for a tropical cyclone motion experiment in the northwest Pacific region.

It is shown that for a moderate-sized tropical cyclone-scale vortex, a regular grid spacing on the order of 100–150 km is required to adequately define the gyres, at least when the ambient flow is weak. The upgraded upper-air network was found to be inadequate by itself for this purpose, suggesting that aircraft dropwindsonde data are a prerequisite for this task.

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