A Multiscale Numerical Study of Hurricane Andrew 1992' Part I: Explicit Simulation and Verificantion

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A Multiscale Numerical Study of Hurricane Andrew
(1992). Part I Explicit Simulation and
Verificantion

• Liu, Y., D.-L. Zhang, and M. K. Yau, 1997, Mon.
  Wea. Rev., 125, 3073-3093

??? 2004/03/08
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Introduction

• The hurricane is a violent atmospheric vortex
  characterized by strong multiscale interactions.
• Previous studies have shown that the tropical
  synoptic conditions and the sea surface
  temperature (SST) tend to control the general
  development of a hurricane(Gray 1979.) .
• Its track and intensity can be affected by its
  internal dynamics and thermodynamics, the
  formation and distribution of clouds and
  precipitation, and the interaction between the
  hurricane and its larger-scale environment
  (Holland and Merrill 1984.)
• Observations reveal many interesting phenomena
  and structures of mature hurricanes.

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Overview of Hurricane Andrew

• Hurricane Andrew cost a total of 25 billion in
  damages.
• The storm originated from a tropical disturbance
  near the west coast of Africa on 1992/08/14, and
  deep convection began to organize into a narrow,
  spiral cloud band an 08/17.

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http//www.nhc.noaa.gov/1992andrew.html
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• Model integration is initialized at 08/21/1200
  UTC (began to intensify) 08/24/1200 UTC(about
  move out Florida)
• Its rapid deepening stage, the mature stage, the
  maximum intensity stage near Bahamas, and its
  landfall stage over Florida.

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Model description and initial conditions

• An improved version of the PSU-NCAR
  nonhydrostatic, movable, triply nested grid, 3D
  mesoscale model (MM5).
• 23 s layers, a two-way interaction, movable,
  triply nested grid.
• The Betts-Miller parameterization for shallow
  convection is applied over mesh C to treat
  reasonably shallow convective clouds at the outer
  edge of the hurricane.
• The SST is held constant, and use the NCEP
  data(2o).
• The NCEP analysis is always too dry, particularly
  in the lower troposphere, as compared with the
  Omega dropwindsondes (ODWs) observation that were
  taken during Andrews development stage.

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Model verification
C5(gt68)
parameterized deep convection over the mesh B
domain
C4(gt57)
C3(gt48)
The storm translates at a speed of 6-8 ms-1, the
deviation in track less than 100 km at the time
of landfall.
C2(gt41)
C1(gt33)
922 hPa
919 hPa
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08/23/0000 UTC
CTL compared with 49 ODWs (released at 400 hPa
level).
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Miami WSR-57 radar at 08/24/0830 UTC
CTL at08/24/0800 UTC
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Andrew moves over land(1) the eye begins to
fill,(2) the eyewall expands in size, and(3)
the radar reflectivities or the rainfall rates
weaken rapidly.
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From Powell and Houston(1996)
The strong-wind zone near the coastline to the
north results from the intensified deep
convection, which is in turn attributable to the
rapid increase in surface friction and the
enhanced low-level convergence of mass and
moisture.
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Vertical structures
08/23/2000 UTC
08/23/2000 UTC
08/24/0800 UTC
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08/23/2000 UTC
cloud water(0.8-2.0 g kg-1)/ice (0.8-1.2 g kg-1)
rain water (4-6 g kg-1) /snow (0.5-0.8 g kg-1)
graupel (2-4 g kg-1)
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08/23/2000 UTC
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08/23/2000 UTC
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08/23/2000 UTC at the center (eye)
08/23/2000 UTC at the eyewall
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08/23/2000 UTC
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Summary and conclusions

• The model captures successfully the track,
  propagation, and rapid deepening of the storm
  during the 3-day period, as verified against the
  best track analysis.
• The model simulates well the larger-scale
  environment in which Andrew is embedded.
• The model reproduces the visible cloud structures
  in terms of their size, shape, and intensity, as
  compared to the satellite and radar imagery.
• It is found that Hurricane Andrew is
  characterized by a shallow layer of intense
  cyclonic inflows in the PBL and intense outflows
  above 300 hPa, with much weaker and less
  organized radial flows in between.
• The streamlines in the central core tend to
  rotate cyclonically outward and converge in the
  eyewall with the cyclonic inflows from the far
  distance.