OSIRIS observations of O3, NO2, and NO3 at large solar zeniths angles

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OSIRIS observations of O3, NO2, and NO3 at large
solar zeniths angles

• Chris A. McLinden
• Environment Canada, Toronto, Canada

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Introduction (1)

• To date, OSIRIS data analysis focused on O3 and
  NO2 at SZA ? 90
• But does OSIRIS possess SNR sufficient for
  retrievals at SZA gt 90?
• If so, are current algorithms sufficient?
• Observations at SZA gt 90 more difficult to
  interpret may need true 3D RT models

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Introduction (2)

• Furthermore, do SZA gt 90 give us a chance at
  detecting NO3 (600-700 nm) ?

Box model calculations 35N, 15 December
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VECTOR (1)

• VECTOR VECTor Orders-of-scattering Radative
  transfer model (see McLinden et al., Can. J.
  Phys., 2002 JGR, in press)
• Uses multiple plane-parallel computations to
  construct source function along line-of-sight
  (LOS) (i.e., account for varying SZA, albedo,
  atmosphere)

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VECTOR (2)

• Limb radiation and polarization obtained by
  integrating RTE along LOS

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VECTOR (3)

• Includes coupled stratospheric chemical box model
  (UCI Prather) LBL code
• Archived atmospheres ?t2 weeks, ?lat2.5,
  ?z2 km (10-58 km, 0-76 km), 34 SZAs (z, p, T,
  O3, families, NO2, NO3, ClO, BrO, )

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OSIRIS NO3 (1)

• Would need to look at light that has traversed
  through night air SZAgt93-95
• Ideally have photons scattered into LOS at
  small SZAs and then pass through air at large
  SZAs
• Require scattering angles to be as small as
  possible (Dec ascending/am Jun descending/pm)

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OSIRIS NO3 (2)
Spectral fit Haley et al. (2003) code, 592-680
nm NO3 (Orphal et al., 2003), O3, NO2, O4, H2O,
Ray, d?H2O/dT, tilt, ?0, ?1, ?2
O2-?, red line
?
SZA 95.4 SCD 7.7?1014 cm-2
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OSIRIS NO3 (3)
Mean OSIRIS SCDs - binned by SZA(TH)
Dec 2003 25-45N sunrise
Jun 2004 5S-5N sunset
No sign of shadow
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OSIRIS NO3 (4)
VECTOR SCDs using climatological atmosphere
Dec 2003 35N sunrise SSA76
Jun 2004 0N sunset
SSA60
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OSIRIS NO3 (5)
Comparison of SCDs on successive orbits
Same SZA (95.5) Same latitude (40.0N) NO2 O3
?k NO3 O2 k(T1)/k(T2) 2 for T1-T215 K
T1-T2
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Observations at large SZAs (1)

• What should be the maximum SZA considered for
  retrievals?
• Currently performed up to 92 but not really
  considered above 90
• At 94, shadow at about 10 km so perhaps this is
  a better cut-off would lead to additional 2
  scans per half orbit, or up to 8º of additional
  latitude

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Observations at large SZAs (2)
RMS Fit residuals tend to remain constant up to
SZA?95
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Observations at large SZAs (3)
O3
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Observations at large SZAs (4)

• Signals remain strong up to 97 (largest
  examined)
• Geometry getting very complex can current
  models account for this?

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Observations at large SZAs (5)
NO2
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Observations at large SZAs (6)
O3 profile retrievals, 10-46 km
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Observations at large SZAs (7)
O3 profile retrievals, 18-46 km
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Summary

• OSIRIS possesses good SNR out to large SZAs,
  96-97
• NO3 signature clear SCDs consistent with models
• O3 and NO2 retrievals seem promising out to 94
  for some geometries, possibly larger over reduced
  altitude range
• Twilight studies looking at O3, NO2, NO3