DualAircraft Investigation of the inner Core of Hurricane Norbert' Part: Water Budget

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Dual-Aircraft Investigation of the inner Core of
Hurricane Norbert. Part? Water Budget

• Gamache, J. F., R. A. Houze, Jr., and F. D.
  Marks, Jr., 1993 J. Atmos. Sci.,50, 3221-3243.

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Introduction

• Better understanding of microphysical process
  involved in production hurricane precipitation.
• They found that cooling associated with the
  melting of frozen precipitation in the stratiform
  regions outside the eye wall produced mesoscale
  downdrafts.
• The relationship of compute water budget to storm
  inner core structure and dynamics is evaluated.

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Description of water budget

• The continuity equation of condensed water and
  ice

r
?
z
4

• The bulk water budget is the volume integral

condensation
evaporation
Divergence (horizontal)
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Divergence (vertical)
Mass of precipitation
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Diffusion (horizontal)
Diffusion (vertical)
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Strom description

• Hurricane Norbert formed in the eastern Pacific
  Ocean on 16 September 1984.
• It made landfall on 26 September along the
  northern Baja Peninsula.
• The hurricane Norbert was weaken at 0018-0215 UTC
  25.
• The data used in this paper were obtained in the
  middle of the last filght.

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Data

• The Doppler radar was located on the aircraft the
  flew at an altitude about 3 Km.
• Radial precipitation velocities were obtained in
  the scan perpendicular to this axis.
• Data for the two horizontal wind components were
  obtained by flying in two roughly perpendicular
  direction.
• Vertical wind was obtained by integrating
  horizontal divergence and then iteratively to
  correct the horizontal wind.

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Retrieval methods
Method 1 Precipitation content is determined
form a reflectivity mass relationships.
(Jorgense and Willis 1982)
Rain?a14630, b1.4482 (Jorgense and Willis
1982) ice ? a670, b1.79 (Black 1990) Z is the
radar reflectivity (10-18 m3) M is the
precipitation content (g/m-3) R is rainfall
(kgm-2h-1)
Precipitation content is the function of
terminal velocity and precipitation production P
is form M, the Doppler winds and VT .
The first term is three dimensional advective
flux divergence of precipitation The second term
is the flux divergence owing to the terminal
fallspeed relative to the air motion.
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The distribution of precipitation particles
(Marshall-Palmer 1948)
N0 is the zero intercept D is the particle
diameter N is the number concentration for a
given size interval.
The resulting precipitation content is
When Pgt0, precipitation production is given by
Mc is cloud content. Mc0 is the autoconversion
threshold. a is the switch function.
Note Ec is the collection efficiency. In this
study Ec was set 1 for rain and 0.1 for frozen
precipitation. Autoconversion of cloud to
precipitation was set 0.001 s-1 and 0.0001 s-1
for water and ice (threshold0.0005kgkg-1)
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Method 2
The acceleration of wind in a steady-state storm
in a moving coordinate system is
Those accelerations are used in the thermodynamic
retrieval
The steady-state equation in three domain are
Roux et al. (1984) and Roux (1985, 1988)
The perturbation total water mixing ratio
is
qs0 is the level mean saturation specific humidity
Note it is assumed the only one kind of
precipitation can exist at a given location ,
either rain (Tgt0) or precipitation ice (Tlt0).
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Axisymmetric budget

• The mean of all the winds at a given height and a
  given radius form storm center.
• These values were then interpolated to a
  Cartesian grid of the same size as used for
  methods 1 and 2.
• The temperature and pressure were then retrieved
  for this axisymmetric wind field.

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Result

• Definitions
• Precipitation and radar reflection
• Cloud content
• Condensation and evaporation
• Azimuthally average mean structure and advection
• Azimuthally average advection by quadrant
• Constant radius analyses of radial advection
• Bulk water budgets
• Water vapor convergence
• Comparison with earlier budget studies

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Definition
(a)
(b)
6 ms-1
6 ms-1
Vertical wind in meter per second at (a) 3 km and
(b) 6km.
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Precipitation and radar reflection
Radial wind in meters per second at constant
radii form storm center of (a) 25 km (b) 37.5 km
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(a)
(b)
(c)
Observed
MAX
Horizontal cross sections of the
three-dimensional composite of radar reflectivity
at (a) 0.5 km (b) 3km (c) 6 km
(c)
(b)
(a)
Method 2
MAX
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Cloud content
3 km
More cloud content
Method 1
Method 2
6 km
Constant height analyses of 3-km and 6-km
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Condensation and evaporation
3 km
Method 1
Method 2
Bright band error
6 km
Constant height condensation and evaporation of
3-km and 6-km
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Azimuthally averaged mean structure and advection
Method 1
Method 1
Radius-height mean advection of water (left) and
Radius-height mean evaporation and precipitation
(right) in the radial direction
Method 2
Method 2
Symmetric wind field (Method 2)
Symmetric wind field (Method 2)
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Azimuthally averaged advection by quadrant
RF
RR
RF
LF
Method 1
RR
LR
LR
LF
RR
RF
Radius-height mean advection of water in the
radial direction
RF327 - 57 RR57 - 147 LR147 - 237
LF237 - 327
LR
LF
Method 2
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Constant radius analyses of radial advection
Method 1
Method 2
Constant radius plot of radial advection of water
for radius form storm center equal to 25 km and
37.5 km
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Bulk water budget
Method 1
Method 2
Bulk water budget by quadrant (a) method 1 (b)
method 2 Arrows indicate bulk advection through
the indicated boundary.
Different 1. the assumption of steady state
storm structure 2. the strong
attenuation of the X band radar
3. Radar calibration (2- 4 dbz error)
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Water vapor convergence
Global saturation condensation
Global saturation evaporation
Completely saturate
Method 2 condensation
Method 2 evaporation
Method 2
Vertical profiles of the mean condensation and
evaporation rate for the budget region bound by a
distance 37.5 km for storm center.
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Comparison with earlier budget studies
Method 2 vapor budget for the annulus form 10-20
nautical miles (18-37 km) for direct comparison
with Hawkins and Rubsam (1968).
Although budget is similar to that found in
Hurricane Hilda (1964), the Hurricane Hilda was
intensifying when Hurricane Norbert was
dissipation
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Conclusions

• Moisture primarily form the front of the storm,
  most of the condensation occurred on the left
  side of the storm, and most precipitation
  occurred in the left rear quadrant of the storm.
• Most of the vapor entering the budget volume
  entered through the bottom boundary (500 m), and
  it greatly exceeded the low level horizontal
  vapor convergence. Either the inflow form the
  surface to 500 m, which could not be determined
  well from Doppler.
• The similarity in bulk budget between Hurricane
  Norbert, a dissipating storm, and Hurricane
  Hilda, an intensifying storm, indicates the need
  to understand the role of hurricane asymmetries
  in a number of different cases.
• The documentation of the asymmetric structure of
  Hurricane Norbert has allowed the hydrometer
  budget to be related to the cloud microphysical
  structure of the storm analyzed in Part ?

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