Effect of the Super Refraction and Small Scale Refractivity Irregularities on Inversions of Radio Oc

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Effect of the Super Refraction and Small Scale
Refractivity Irregularities on Inversions of
Radio Occultation Signals

• S. Sokolovskiy
• University Corporation for Atmospheric Research

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1) Treatment of the super refraction (SR) in
geometric optics (GO) 2) SR and canonical
transform (CT) inversions 3) Effect of the small
scale refractivity irregularities on the CT
inversions 4) Effect of the duration of radio
occultation (RO) signal tracking on the CT
inversions
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Super Refraction in Geometric Optics Ray
curvature radius at tangent point lt Earths radius
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SR most often occurs on top of moist
PBL. Radiosonde refractivity profiles from St.
Helena Island.
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In case of SR Abel inversion strictly is not
applicable. Formal application results in
negative bias below the upper point of critical
refraction.
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RO signals simulated for two radiosonde
profiles St. Helena Island
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Statistic of SR is different in different
geographic regions
Knowledge of the SR statistics can be useful for
discarding or assimilating RO data in the moist
PBL
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RO inversion in case of SR is an ill-conditioned
problem both true and Abel-retrieved
refractivity profiles yield one bending angle
profile
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The generalized Abel inversion can be applied
below the SR layer (the modified bending angle
is defined inside the finite spherical layer)
j
known from RO observations
calculated from the Abel-retrieved refractivity
above the SR layer
needs ancillary information
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RO signals simulated for mean rafractivity with
imposed random, small scale, 1-D and 2-D
irregularities
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Reconstruction of bending angles by CT method
A) 1-D refractivity B) 2-D refractivity
RO signals were used down to -150 km altitude of
line-of-sight
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Retrieval of refractivity by Abel inversion
true GO CT
true mean CT
RO signals were used down to -150 km altitude of
line-of-sight
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RH inversions no mapping of a point on LEO
trajectory to an altitude in the atmosphere.
N-profile formally can be retrieved down to
surface from RO signal of different length.
RO signals were used down to -75 km of altitude
of line-of-sight
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(No Transcript)
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Inversions of the full (85 sec) and truncated (at
70 sec) GPS/MET signal
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Conclusions
1) RO inversion in the presence of the SR is an
ill-conditioned problem (two different
refractivity profiles yield the same bending
angle as the function of impact parameter). 2)
Abel inversion results in negative bias inside
and below the SR layer (the generalized Abel
inversion below the SR layer requires knowledge
of the refractivity inside the SR layer). 3)
Statistic of the SR on top of PBL is different in
different geographic regions (this information
can be used for discarding, or for aiding
assimilation of the RO data affected by the
SR). 4) CT method allows accurate reconstruction
of ray structure of the diffracted field in case
of the SR and does not introduce inversion
errors additional to those existing in GO. 5) The
small scale refractivity irregularities with
small aspect ratio do not introduce bias in CT
inversions. But they result in strong fluctuation
of the CT amplitude and do not allow accurate
detection of the cut-off altitude. 6) Tracking RO
signals down to insufficiently low altitude may
introduce the additional bias in RO inversions.
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What can potentially be used as an indicator of
the SR in RO data ? 1) Large positive spike in
the CT bending angle ? 2) Break point in the
Abel-retrieved refractivity profile with the
gradient close to the critical ? 3) Deep dip
with the following splash in amplitude ? 4) The
Abel-retrieved refractivity profile ? 5) The
structure of caustics of the BP field ?
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Caustics of the BP field in case of 1-D (A) and
2-D (B) small scale refractivity irregularities
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A single SR layer
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A single SR layer
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A single SR layer
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A single SR layer
T
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