Examination of the New Mesocyclone Detection Algorithm
Proposed for the WSR-88D Radar Network (99)
Brandon Smith, Cooperative
Institute for Mesoscale Meteorological Studies / National Severe Storms
Laboratory, Norman, OK
Matthew Mahalik, Cooperative
Institute for Mesoscale Meteorological Studies / National Severe Storms
Laboratory
Abstract:
The NSSL/ROC Tech Transfer
MOU—Severe Storms Section, allows staff at the ROC and NSSL/CIMMS to
work together to develop new thunderstorm-related algorithms and improve
existing algorithms for the WSR-88D network. One of the current MOU projects is
the development of a New Mesocyclone Detection Algorithm (NMDA) for the WSR-88D
network that when completed, will be proposed to replace the current legacy MDA
that was developed in the late 1990s. While the legacy MDA utilized raw radial
velocity fields to find and analyze storm-scale circulations, the NMDA uses
velocity-derived azimuthal shear (AzShear), in conjunction with
velocity-derived shear diameter and half-velocity fields. AzShear is created
using a linear least-squares derivative (LLSD) technique to compute velocity
gradients across a radar beam for a neighborhood of gates. This produces a
rotation estimation field that effectively mitigates a vast majority of the
noise and extreme outliers that are present in raw radial velocity data, which
can cause circulation identification errors in the legacy MDA. Although the
internal workings of the legacy MDA are being replaced, the NMDA is maintaining
the existing visual display and output attributes of the legacy MDA familiar to
many NWS forecasters. This presentation will describe the methods used by the
NMDA for both the 2D and 3D detection of storm-scale circulations, as well as
those used to track and derive trend information for each identified
circulation. A comparison of performance will also be shown between the NMDA
and the legacy MDA across a multitude of severe weather event types, providing
a first look of this newly developed WSR-88D algorithm.