ARM Site Atmospheric State Best Estimates for Aqua:

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• ARM Site Atmospheric State Best Estimates for
  Aqua
• Retrieval, Radiance, and Forward Model Validation
• David Tobin, Wayne Feltz, Bob Knuteson, Hank
  Revercomb
• CIMSS / SSEC / University of Wisconsin-Madison
• Tasks
• Development and production of ARM Site Best
  Estimate Products (SGP, TWP, and NSA sites)
• Improved cloud detection/mask
• Improved surface emissivity estimates
• Improved uncertainty estimates
• Improved temporal and large scale gradient
  estimates for TWP and NSA sites
• Aqua validation studies using ARM site overpass
  datasets
• AIRS and MODIS clear sky radiance and forward
  models
• AIRS cloud cleared radiance
• AIRS and MODIS Temperature and Moisture retrievals

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ARM Site Atmospheric State Best Estimates
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• Presentation Outline Status and near term plans
• ARM upper level water vapor accuracy
• Phase 2 of dedicated sondes
• North Slope of Alaska site
• Surface emissivity

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• Accuracy of ARM Best Estimate Profiles for AIRS
  Upper Level Water Vapor Validation and Forward
  Model Validation/Development
• ARM FIRE Water Vapor Experiment (AFWEX) SGP ARM
  Site, December 2000
• Established upper level water vapor truth,
  through deployment of aircraft based reference
  sensors. Upper level agreement of 5 or better
  found between
• LASE (aircraft based DIAL, NASA LaRC)
• DLH (aircraft based in-situ Diode Laser
  Hygrometer, NASA LaRC)
• ARM and GSFC Raman Lidars with T-dependent cross
  section corrections
• Vaisala RS-80 radiosondes with physical
  corrections
• Confirmed understanding of RS-80 sensor physics
  and accuracy of Miloshevich corrections.
• ARM Raman Lidar / RS-90 radiosonde comparisons
  show good agreement to 10km. Ties RS-90s into
  AFWEX analysis and suggests upper level
  uncertainty of 5 or less.
• Prescribed (time-lag) corrections for Vaisala
  RS-90 radiosondes are small insignificant for
  interpretation of AIRS observed minus calculated.
• Using AIRS as the transfer standard, evaluation
  of clear sky spectral residuals shows very good
  absolute agreement between the ARM and Voemel
  validation profile sets 0K differences for
  in-between line channels implies very good
  agreement below 10km 0.5K differences for
  on-line channels is suggestive of a 5 bias
  (RS-90s drier) above 12 km.
• At the n2 band center, where the forward model
  has best absolute accuracy, very good (0 K) AIRS
  clear sky residuals are obtained when using the
  ARM and Voemel validation profiles.
• My current assessment SGP and TWP absolute water
  vapor uncertainty

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Example AFWEX flight, 5 December 2000
10 minute CART Raman Lidar data

• AFWEX design
• Aircraft based sensors provide accurate
  measurements of upper level water for evaluation
  of radiosonde and ground based Lidar
  measurements.
• IR satellite-like measurements (S-HIS, NAST-I,
  -M, FIRSC) to assess radiative impacts.
• Continuous ground based Lidars used to track
  variability and interpolate in time.
• Clear sky flights flown directly over ARM site at
  various altitudes with many coincident
  radiosondes (RS-80s)

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AFWEX analysis, previous slide
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Summary of Impact of RS-90 Time-lag corrections
(TWP Nighttime) corrections c/o L. Miloshevich,
NCAR
These corrections are not currently included in
the ARM best estimate products provided to the
team
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Summary of AIRS Clear Sky Spectral
Residuals Mean Obs and Obs-Calc for various
validation datasets
Transparent Band Center
legend Voemel ARM SGP
Night ARM SGP Day ARM TWP Night ARM TWP Day GSFC
SRL ABOVE
Early SRL calibration bias?
Cloud contamination in ABOVE dataset?
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Comparison of ARM TWP and Voemel Mean Obs-Calcs
Good agreement in WV column at Transparent Band
Center
Tb difference between ARM TWP and Voemel ensembles
In-between line ARM obs-calcs are in very good
agreement with Voemel obs-calcs. On-line ARM
obs-calcs are slightly more negative (0.5K) than
Voemel, implying a slight dry bias (5 RH) of
ARM RS-90s w/r/t Voemel above 12 km.
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H2O Continuum Measurements and Models at n2 Band
Center
The biggest uncertainty w/r/t the forward model
for upper level water vapor channels is the
knowledge and parameterization of the foreign
broadened water vapor continuum component of the
absorption (Cf0). For these channels, the
forward model is most certain at the n2 band
center, where a convergence of Cf0 measurements
and models exists. (CKDv2.4 is/was known to be
in error in this region and has since been
fixed.) The ARM and Voemel ensemble residuals
(obs-calcs) are very close to zero for these
channels.
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• Remaining on-line AIRS observed minus calculated
  residuals are consistent with
• previous and on-going atmospheric and laboratory
  investigations of a super-Lorentzian near-wing
  water vapor spectral lineshape
• a height dependent water vapor bias (present in
  both character and magnitude in the ARM SGP, ARM
  TWP, and Voemel ensembles)
• some combination of a and b.
• These residuals were tuned out in latest version
  of the fast model (using emperical channel
  optical depth adjustments to the TWP nighttime
  obs-calcs). Tracing the cause back to the
  spectroscopy will require further investigation.

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TWP Nighttime Mean Obs and Obs-Calc
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• Other near term plans regarding ARM Water Vapor
• Resolve RS-90 Diurnal issue (Daytime sondes
  dryer, with an apparent altitude dependence.
  Details presented at May 2003 AIRS STM)
• Investigate why RS-90 radiosondes for ABOVE site
  are significantly too dry. Probably includes
  some cloud contaminated scenes that can be
  removed.
• Assess and incorporate AWEX findings when
  appropriate
• Improved characterization of North Slope of
  Alaska measurements

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• Phase 2 of Aqua dedicated sondes
• Launches recently completed on 19 February
• Now working to process best estimate files for
  all three sites
• North Slope of Alaska site
• Water Vapor characterization experiment recently
  conducted. Plan is to incorporate the
  lessons-learned.
• MWR water vapor accuracy for low water amounts
  in question
• Radiosonde characterization
• Surface emissivity
• Plan is to assess and improve characterization at
  each site.
• TWP currently using Wu/Smith model (not Masuda)
• SGP currently using linear combination of pure
  bare soil and pure vegetated spectral
  emissivities. Working to refine vegetation
  weights.
• NSA plan is to follow SGP approach with various
  pure land, water, and ice emissivities.
• Done in collaboration with Knuteson led effort.