Tuesday, 30 April 2002: 11:45 AM
Comparison of Hurricane intensity as realized in an axisymmetric model with MPI theory
The language of hurricane intensity theory is used to assess the important
controls and resolution dependence of intensity in axisymmetric numerical
models. Specifically, the energetically-based maximum intensity theory (E-MPI)
of K. Emanuel is used since it has many dynamical elements and is constructed
solely on axisymmetric principles. Certain elements of the E-MPI theory are
found difficult to apply to model output. One example is the value of boundary
layer relative humidity, since the tendency of one cloud-resolving axisymmetric
model (the Rotunno and Emanuel 1987 model) is to saturate the lowest grid level.
In this case, the assumptions of E-MPI can be relaxed and a point in the
derivation can be found where relative humidity does not appear. This earlier
point in the derivation is not a new a priori MPI, but rather a local diagnosis
of the assumptions used to derive E-MPI. Discrepancies between the assumptions
of E-MPI and the modeled intensity of the storm point to the important physical
processes in the model that regulate intensity. We see this work as a first
step toward analyzing the processes that regulate intensity in more realistic
three-dimensional cloud-resolving models.
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