Consistency of horizontal and vertical resolution of atmospheric parameters measured with GPS radio

1
Consistency of horizontal and vertical resolution
of atmospheric parameters measured with GPS radio
occultations

• Marcello Petitta
• Physics Department
• University of Rome
• La Sapienza

Summer Colloquium on Atmospheric Remote Sensing
Using the Global Positioning System. 20 June-3
July 2004 Boulder, Colorado
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Radio occultation measurement resolution

• Are vertical and horizontal resolution of Radio
  Occultation data accurate enough for atmospheric
  study?

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Task

• Theoretical relationship between horizontal and
  vertical resolution for meteorological variables.
  
• Evaluation of horizontal scale variability of
  temperature and water vapor fields.
• Evaluation of radiative effects of different
  vertical resolutions to understand their impacts
  on the equilibrium state of the atmosphere.
• Sensitivity analysis of the tropopause height
  measurements for different vertical resolutions.
• Evaluation of horizontal and temporal scale
  variability of the tropopause height field

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1/1 - Theoretical relationship between horizontal
and vertical resolution

• The basic equation for quasi-geostrophic flow is
  the geostrophic conservation of pseudo-potential
  vorticity on horizontal surface (Charney, 1979).
  The pseudo-potential vorticity, q, in a ß plane
  is given by

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1/2 - Theoretical relationship between horizontal
and vertical resolution

• Following Lindzen and Fox-Rabinovitz (1989) we
  find
• While at tropical regions

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Vertical resolution ?z as a function of ?? for
different latitudes
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Relationship between horizontal and vertical
resolution
Adapted from Lindzen and Fox-Rabinovitz (1989)
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2 Horizontal scale of refractivity

• From NCEP/NCAR data, daily means of temperature
  and specific humidity
• Refractivity index
• Evaluation of Spatial Correlation
• Function (SCF)

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SCF (mean and variance 1)
N NT NV
Mean Variance
Mean Variance
Mean Variance
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SCF (mean and variance 2)
N NT NV
Mean variance
Mean variance
Mean variance
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Maps of N, NT and NV for 1st January 1991 at
1000hPa
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Maps of N, NT and NV for 1st January 1991 at
500hPa
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Maps of N, NT and NV for 1st January 1991at
300hPa
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3 Sensitivity to variations of the vertical
resolution

• 1 reference atmospheric profile with high
  vertical resolution 5 atmospheric profiles with
  less vertical resolution
• Compute radiative equilibrium for each
  atmospheric profile
• Comparison between the radiative fluxes at TOA
  for the 6 profiles

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Vertical resolutions
25
33
43
63
89
27
25
33
43
63
89
27
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Experiments

• Standard tropical profile
• Water vapor perturbation between 2km and 3km
  (columnar amount remains constant)
• Water vapor perturbation between 2km and 3km
  (columnar amount not constant)
• Water vapor perturbation between 6km and 8km

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Water vapor perturbation
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Results
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4 - Tropopause detection

• Evaluate the changes in tropopause height varying
  vertical resolution
• The same atmospheric profiles at radiative
  equilibrium
• The same 4 experiments with water vapor
  perturbation
• Analysis of the horizontal structure of the
  tropopause height

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Results
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Tropopause meridional structure
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Eddy and standard deviation fields of tropopause
in DJF Northern Hemisphere
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Eddy and standard deviation fields of tropopause
in JJA Southern Hemisphere
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Zonal power spectrum and correlation function for
the standard deviation of tropopause DJF Northern
Hemisphere
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Zonal power spectrum of the standard deviation of
tropopause and correlation function JJA Southern
Hemisphere
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Conclusions

• Radio occultation measurements are consistent
  with the theoretical relationship between
  horizontal and vertical resolution for
  mid-latitude.
• Horizontal resolution of radio occultation data
  is accurate enough (compared with the horizontal
  scale of refractivity)
• Accurate vertical resolution of radio occultation
  measurements can be handled by general
  circulation models

• Measurements with high vertical resolution in the
  troposphere better describes radiative processes
  in the atmosphere
• Tropopause height measurements are sensitive to
  vertical resolution of data and the its
  horizontal variability can be observed with very
  high accuracy through R.O. technique.