EnKF OSSE experiments with radar locations Using more realistic radar configurations than in Tong an

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EnKF OSSE experiments with radar locationsUsing
more realistic radar configurations than in Tong
and Xue (2004, submitted to MWR), which assumed
radar data at model grid pointsMing Xue and
Mingjing Tong7/23/2004
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Radar data processing

• Assume the radar is a WSR-88D radar, which has 14
  elevation scans 0.5, 1.5, 2.4, 3.4, 4.3,
  5.3, 6.2, 7.5,8.7, 10.0, 12.0, 14.0,
  16.7, 19.5.
• The antenna beamwidth is 1, the maximum range is
  230km.
• Assume that the original radar data were
  interpolated to Cartesian grid in the horizontal
  while remaining on the constant elevation angle
  levels in the vertical.

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Assimilation of PPI data

• For OSSE, Vr observation is calculated from
• (Brewster, MWR 2003), where h is the height
  above the curving earth's surface, s is the
  distance along the earth's surface, and f is the
  radar azimuth angle, and assuming the atmosphere
  has standard refraction.

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Assimilation of PPI data

• The following relation is used to transfer the
  data from the model vertical levels to the
  elevation angle levels
• where is the radial velocity on an
  elevation angle level and
• is the model vertical grid spacing. The
  power gain of the radar beam is give by
• where z is the distance from the center of
  the radar beam and
• is the beam half-width.

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Experiments

• Both Vr (z gt 10dBZ) and Z (full coverage) are
  used in all the experiments. The only difference
  between different experiments is the radar
  location.
• Model domain is (64km, 64km, 16km)
• Radar location data number at the
  last assimilation cycle
• Exp1 (0km, 0km)
  Vr 4820, Z 12177
• Exp2 (-40km, -40km)
  2925, 8510
• Exp3 (32km, 32km)
  4685, 11672
• Exp4 (48km, -80km)
  2711, 7788
• Exp5 (-80km,48km)
  2765, 7788

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Results time series of analysis error
Exp1 (black)
Exp2 (red)
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Results time series of analysis error
When the radar is located near the center of the
storm (exp3), the retrieval is not successful,
because some parts of the storm can not be seen
by the radar
Exp3(red)
Exp1(black)
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Results time series of analysis error
The main difference is the retrieved horizontal
wind components u and v.
Exp5(red)
Exp4(black)
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Vertical profile of analysis error
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Vertical profile of analysis error
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Specifically for CASA

• Use emulators for X-band radars
• Apply to 4 OK radar locations
• Assume different storm locations and propagation
  speeds
• Using different scanning strategies
• Include attenuation
• Etc. etc. etc.