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Mesoscale and Convective Structure of a Hurricane Rainband

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					Mesoscale and Convective
 Structure of a Hurricane
        Rainband

 Barnes, G. M., E. J. Zipser, D. Jorgensen, and F.
 Marks, Jr., 1983: J. Atmos. Sci., 40, 2125-2137.
                       Introduction
• History
  Gentry(1964), Simpson(1965), Willoughby(1982), Leary and Houze(1979)
  Fitzjarrald and Grastang(1981), Zipser(1981)

• Objectives
 Structure, motion, mesoscale airflow, convection and the barrier in the
 rainband
                   Sampling strategy
• Flight pattern, aircraft sensors
1. Flying twice at a given altitude.
2. Each flight leg was 60KM.
3. A total of 26 legs were flown at the levels: 150, 600, 1500, 2400, 3000, 4800 and
   6400 m.
4. The experiment was made form 1400-1700 GMT on 7 September 1981.
5. Aircraft instrumentation includes an inertial navigation system, partial measuring
   system, the Johnson- Williams liquid water sensor, two Rosemount temperature
   sensors, an experimental CO2 radiometer, a dew point hygrometer, and aircraft
   pressure/height sensors.

• General weather situation
1. The Hurricane Floyd is asymmetric, and is moving northeast at 4.7 (m/s).
2. Aircraft penetrations of the eye estimate the central pressure to be 975 (mb).
The Hurricane Floyd in a visible picture at 1300 GMT.
                      Results
•   Radar structure and definitions of rainband.
•   Kinematic fields
•   Thermodynamic fields
•   D-value ≡ the height of a given pressure surface
    minus the height of the same surface in a
    reference atmosphere.
            RMW  A1 B
                                     A RB
            p  pc  ( pn  pc )e
Reflective levels are 25, 30, 35, and 38 dBz.
The domain size is 240 km × 240 km.
Altitude is 1.5 km, derived between 1155 and 1347 GMT.
a
                       b
    (a) 1413-1417GMT           (b) 1506-1524GMT




c                          d
    (c) 1539-1554GMT
                           (d) 1645-1658GMT
                      Results
•   Radar structure and definitions of rainband.
•   Kinematic fields
•   Thermodynamic fields
•   D-value ≡ the height of a given pressure surface
    minus the height of the same surface in a
    reference atmosphere.
            RMW  A1 B
                                     A RB
            p  pc  ( pn  pc )e
                                                                 L

                                                          L
                                                                 H
                          H
                                                                 L

The composite field of relative normal   Divergence associated with the rainband.
velocity component ( VR ).




     -          +             -
                      Results
•   Radar structure and definitions of rainband.
•   Kinematic fields
•   Thermodynamic fields
•   D-value ≡ the height of a given pressure surface
    minus the height of the same surface in a
    reference atmosphere.
            RMW  A1 B
                                     A RB
            p  pc  ( pn  pc )e
                        The change in θe with
                        height as one travels
                        from outside to inside
                        the rainband.




The θe fields associated with the rainband.      Skew T-log P diagram
                      Results
•   Radar structure and definitions of rainband.
•   Kinematic fields
•   Thermodynamic fields
•   D-value ≡ the height of a given pressure surface
    minus the height of the same surface in a
    reference atmosphere.
            RMW  A1 B
                                     A RB
            p  pc  ( pn  pc )e
               The composite D-value for 150,
               2400 and 6400m.




RMW  A1 B
                           A RB
p  pc  ( p n  pc ) e
RMW  the radius of maximum wind (km).
pc  the central pressure(mb).
pn  the pressureof the environment (mb).
R  the radius (km).
                 Discussion
• Estimates of mesoscale vertical motion.
       b        m  VR VR 
  wt      wb               Z
       t       t  R R 
  w  vertical velocity. R  the radius. Z  the hight.
  ρ  the density. VR  the radial componentof the wind.
  t,m,b  top, middle and bottom of the given layer.
• Subgrid-scale fluxes
• Hypothesized motions in the rainband.
                ?
                                          ?




Mesoscale vertical velocity field derived from Divergence
diagram.
                 Discussion
• Estimates of mesoscale vertical motion.
       b        m  VR VR 
  wt      wb               Z
       t       t  R R 
  w  vertical velocity. R  the radius. Z  the hight.
  ρ  the density. VR  the radial componentof the wind.
  t,m,b  top, middle and bottom of the given layer.
• Subgrid-scale fluxes
• Hypothesized motions in the rainband.
  1504:02-1510:22




              1512:12-1521:32


            1538:47-1544:32 (feg11)




           1546:47-1550:47 (feg12)    (a) Histograms of drafts as a function
                                          of radial distance.
                                      (b) Reflectivity cells as a function of
Vertical velocity measured.               radial distance.
                 Discussion
• Estimates of mesoscale vertical motion.
       b        m  VR VR 
  wt      wb               Z
       t       t  R R 
  w  vertical velocity. R  the radius. Z  the hight.
  ρ  the density. VR  the radial componentof the wind.
  t,m,b  top, middle and bottom of the given layer.
• Subgrid-scale fluxes
• Hypothesized motions in the rainband.
Rainband in x, y coordinates.

                                A schematic of the rainband in r, z
                                coordinates
              Conclusions
• A partial mesoscale barrier to the inflow is
  associate with rainband.
• Reflectivity observations show that band
  has both a stratiform and convective
  structure.
• A weak mesoscale high pressure area is
  nearly coincident with the rainband near
  the surface.

				
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posted:2/26/2012
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