Concurrent measurements of the PMC mass on the limb and in the nadir

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Concurrent measurements of the PMC mass on the
limb and in the nadir
M.H. Stevens and C.R. Englert Naval Research
Laboratory S.M. Bailey University of Alaska,
Geophysical Institute   M.T. DeLand SSAI
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Objectives

• Quantify the difference in the PMC mass (cloud
  frequency and column ice mass) measured by a limb
  viewing and a nadir viewing satellite experiment
  70 2.5º N.

2. Find any hemispheric asymmetry in the PMC mass
between 70 N and 70 S.
3. Find the ice mass variation with latitude and
compare to results from a global
chemical-dynamical model with PMCs parameterized.
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Outline
1. The PMC Observations a. Nadir Solar
Backscatter Ultraviolet (SBUV) instruments. b.
Limb Student Nitric Oxide Explorer (SNOE)
experiment.

• Approach
• a. Cloud brightness ? column ice mass Englert
  et al., 2006.
• b. Cloud frequency fractional spatial
  coverage.
• c. Surface area ? zonally integrated ice mass
  (5 lat. bins).

• Results and Implications
• a. The NH Observed PMC mass (SNOE vs. SBUV).
• b. NH vs. SH PMC mass (SBUV).
• c. Comparison with model results.

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The Observations
Used in this study.
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NH Data Selected for This Study

• SBUV data are selected for limited local times
  (11.1 1.0 h), scattering angles (131 1),
  latitudes (70 2.5) and days ( 15).
• SNOE data are averaged over the same latitudes
  and nearly the same local times (9-14).
• Only backscattered observations are used (? gt
  90).

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SNOE (limb) vs. SBUV (nadir) PMC mass
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SNOE Much More Sensitive to PMCs Than SBUV
Annual PMC Frequency SBUV vs. SNOE

• We make two different comparisons
• SNOE PMC Mass vs. SBUV PMC mass
• SNOE PMC Mass (brightest clouds) vs. SBUV PMC mass

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Two Subsets of SNOE Data Considered
SNOE Observations 2002

• We select only the brightest SNOE PMCs so
  average PMC frequency is same as SBUV.

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Annual SBUV Cloud Albedo

• PMCs brightest at shortest UV wavelengths (252
  nm).
• Color ratios with other wavelengths determines
  particle size.
• Size derived from Mie theory (spherical water ice
  particles).

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Annual Vertical Ice Mass Column
SBUV
SNOE

• Represents amount of ice in an average PMC
  observation.
• SNOE slant column has been converted to a
  vertical column.
• SNOE average and SNOE bright subset both shown.

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Annual PMC Mass SBUV vs. SNOE

• Mass of bright SNOE PMCs SBUV PMC mass to
  within 10.
• SNOE observes 3.8 (-1.2/6.3) times more mass
  than SBUV.
• Solar cycle variation of mass is at least a
  factor of two.

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Northern vs. Southern PMC mass
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NH vs. SH SBUV PMC Frequency
SNOE SH

• Average SH frequency is 54 than NH for
  conditions shown.
• SNOE measurements of backscattered sunlight
  obtained during one season in SH winter
  2000-2001.
• Brightest SNOE PMCs directly compared w/ SBUV.

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NH vs. SH Column Ice Mass
SNOE SH

• SH column ice mass not significantly different
  than NH.
• SNOE SH column ice mass from brightest clouds in
  agreement w/ SBUV for 2000-2001.

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NH vs. SH SBUV PMC Mass
SNOE SH

• SH SNOE PMC mass (brightest clouds) within 10 of
  SBUV.
• NH PMC mass factor of 2.5 (-1.7/8.8) greater
  than SH mass.
• SH SNOE PMC mass factor of 10 greater than SH
  SBUV mass

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Latitude Dependence of PMC Mass and Comparison
with Model Results
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First Model-Data Comparison of Ice Mass 55-80º N

• Uncertainties (shaded) are from both the size
  distribution and an estimate of the
  invisible ice.
• A 2D global chemical/dynamical model with a
  monodisperse size distribution of 30 nm
  yields results consistent with our observations
  poleward of 70 N.

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Summary

• We have inferred the PMC mass in the Arctic
  summer using satellite observations viewing the
  limb and the nadir at 702.5 N, 11.11.0 LT.

2. SNOE (limb sounder) measures 3-10 times more
mass than the less sensitive SBUV (nadir)
instruments.
3. SBUV solar cycle mass variation is at least a
factor of two.
4. NH PMC mass is 1-11 times greater than SH mass.