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PMC Particle Size from 14 Years of HALOE Observations

PMC Particle Size from 14 Years of HALOE Observations. Mark Hervig GATS Inc. Halogen Occultation Experiment (HALOE). Solar Occultation observations in both hemispheres Operated from 11 October 1991 - 21 November 2005 Profile retrievals: H 2 O, O 3 , NO, CH 4

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PMC Particle Size from 14 Years of HALOE Observations

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  1. PMC Particle Size from 14 Years of HALOE Observations Mark Hervig GATS Inc. Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  2. Halogen Occultation Experiment (HALOE) • Solar Occultation observations in both hemispheres • Operated from 11 October 1991 - 21 November 2005 • Profile retrievals: • H2O, O3, NO, CH4 • PMC extinction at 5 wavelengths (2.45, 3.40, 3.46, 5.26, 6.26 m) • Temperature • 1.8 km vertical resolution • This work uses HALOE “Vpmc” data Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  3. HALOE PMC Measurements HALOE multi-wavelength extinctions are consistent with modeled PMC spectra 60-70N Mie theory and a lognormal size distribution with rm = 50 nm,  = 1.4 Ice refractive indices measured at various temperatures Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  4. HALOE PMC Size Information The HALOE 2.45 m PMC measurement is 50% scattering The longer wavelength PMC measurements are pure absorption Absorption - scattering contrast yields PMC size information Median radius can be determined if size distribution width is fixed Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  5. Modeling PMC Optics • The extinction calculations are sensitive to: • Ice refractive index • 266K: Waren et al., 1984 (0.05 - 2000 m) • 163K: Toon et al., 1994 (1.4 - 20 m) • 130-210K: Clapp et al., 1995 (2.5 - 12.5 m) • 100K: Bertie et al., 1969 (1.2 - 333 m) • Particle shape • Spheres (Mie theory) • Non-spherical (T-matrix) • Size distribution • Lognormal: total conc. (N), median radius (rm), width () • Gausian: total conc. (N), median radius (rm), width (r) Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  6. Spheres vs. Spheroids • Oblate and prolate spheroids were considered in these results • Random orientation • Aspect ratios (AR) from 0.2 to 5 • Cross section differences less than 12% compared to spheres Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  7. PMC Size Distributions • Lognormal has precedence • CARMA suggests Gaussian • Comparison of lognormal and Gaussian size distributions • Both use rm = 50 nm • Typical widths • IR extinction is proportional to volume • Volume weighted mean radii: • Lognormal: 75 nm • Gaussian: 58 nm Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  8. PMC Median Radii Determined from HALOE • Median radius can be determined from measured extinction ratios • R = () / (2.45 m) • if the distribution width is fixed. • We can use  = 3.40, 3.46, 5.26, or 6.26 m, but(3.40) has the highest signal-to-noise • Examine sensitivity to: • Particle shape • Size distribution • Refractive index Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  9. HALOE PMC and Background Signals The background is less than 10% for  > 2.45 m At 2.45 m, the background is roughly 50% of the PMC signal Background was subtracted from all HALOE PMC measurements Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  10. PMC Radii Results • Median radii profiles were determined from yearly averaged extinctions. • 60 - 70N, -20 to 50 days from solstice • The calculations used two sets of assumptions: Spheres - lognormal ( = 1.3, 1.5, 1.7) Spheroid (AR=0.2) - Gaussian (r = 10, 15, 20 nm) Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  11. PMC Radius Time Series The median value of rm for all altitudes in each annual profile Results based on sphere - lognormal and spheroid - gaussian models Grand Averages: Spheroid - Gaussian: 141 nm Sphere - lognormal: 62 nm Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  12. Mission average median radius profiles • Average of yearly profiles from 1993 - 2005 • Inversions assume either: • Spheres - lognormal ( = 1.3, 1.5, 1.7) • rm = 70  34 nm (83 km) • Vertical mean rm = 40  28 nm • Spheroid (AR=0.2) - Gaussian (r = 10, 15, 20 nm) • rm = 140  39 nm (83 km) • Vertical mean rm = 79  58 nm • and use ice refractive indices for 163K. • Error bars indicate the variation in rm • over time and for changing distribution width Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  13. Comparisons with CARMA Model Results Particle radii from CARMA are perhaps most sensitive to H2O A quick survey of H2O in the polar summer mesosphere: Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  14. Water Vapor and PMCs There is evidence for a little more H2O in the polar summer mesosphere How does this affect PMCs? HALOE - ACE H2O Comparisons at 66N during summer Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  15. HALOE Radii Compared to CARMA • CARMA model runs using two sources of H2O: • CHEM2D: 3 ppmv (83 km) • CARMA rm : 20 - 70 nm (83 km) • HALOE: 6 ppmv (83 km) • CARMA rm : 70 - 140 nm (83 km) • CARMA notes: • FS Temperatures, CHEM2D vertical winds, averages of 24 - 96 hr cloud age, rm is the number weighted mean, courtesy Mike Stevens (NRL) • HALOE results as before, averages from 1993 - 2005 • Inversions assuming either: • Spheres - lognormal • Spheroid (AR=0.2) - gaussian Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  16. The Range of Observed PMC Extinctions • The HALOE PMC detection threshold is 3.40 m extinction > 2  10-6 km-1 • HALOE extinctions predicted from CARMA results for H2O from: • CHEM2D: 3 ppmv at 83 km, does not cover the HALOE range • HALOE: 6 ppmv at 83 km, easily covers the HALOE observations • Notes: • HALOE PMC frequency for 60-70N and -10 to 40 days from solstice is 23%. • The corresponding SME PMC frequency is about 33% (1.4 times as many). • Stevens et al. [2005] estimated that HALOE detects about 50% of the PMC mass that is present. 60-70N Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

  17. Summary • HALOE PMC median radii, mission averages, 60 - 70N • Spheres - lognormal: • 70 nm at 83 km, 40 nm vertical mean Spheroid - Gaussian: 140 nm at 83 km, 79 nm vertical mean • The Gaussian size distribution requires larger median radii. • Spheroids lead to slightly larger radii, but this is a small effect. • HALOE PMC measurements are consistent with HALOE H2O CARMA results using HALOE H2O can reproduce HALOE PMC radii HALOE extinction magnitude Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006

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