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

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Presentation on theme: "Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 PMC Particle Size from 14 Years of HALOE Observations Mark Hervig GATS Inc."— Presentation transcript:

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

2 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 Halogen Occultation Experiment (HALOE) Solar Occultation observations in both hemispheres Operated from 11 October November 2005 Profile retrievals: H 2 O, O 3, NO, CH 4 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

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

4 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 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

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

6 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 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

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

8 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 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

9 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 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

10 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 PMC Radii Results Median radii profiles were determined from yearly averaged extinctions  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)

11 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 PMC Radius Time Series The median value of r m 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

12 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 Mission average median radius profiles Average of yearly profiles from Inversions assume either: 1.Spheres - lognormal (  = 1.3, 1.5, 1.7) r m = 70  34 nm (83 km) Vertical mean r m = 40  28 nm 2.Spheroid (AR=0.2) - Gaussian (  r = 10, 15, 20 nm) r m = 140  39 nm (83 km) Vertical mean r m = 79  58 nm and use ice refractive indices for 163K. Error bars indicate the variation in r m over time and for changing distribution width

13 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 Comparisons with CARMA Model Results Particle radii from CARMA are perhaps most sensitive to H 2 O A quick survey of H 2 O in the polar summer mesosphere: SourceApproximate 83 km Mixing Ratio (ppmv) Korner & Sonnemann (model)3 CHEM2D model (Siskind)3 ALOMAR 22 GHz (Seele)3 - 4 Odin 557 GHz (Lassow)5 HALOE (Hervig)5 - 7 ACE4 - 7 OSIRIS Limb OH (Gattinger)1 - 7

14 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 Water Vapor and PMCs There is evidence for a little more H 2 O in the polar summer mesosphere How does this affect PMCs? HALOE - ACE H 2 O Comparisons at 66  N during summer

15 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 HALOE Radii Compared to CARMA CARMA model runs using two sources of H 2 O: CHEM2D: 3 ppmv (83 km) CARMA r m : nm (83 km) HALOE: 6 ppmv (83 km) CARMA r m : nm (83 km) CARMA notes: FS Temperatures, CHEM2D vertical winds, averages of hr cloud age, r m is the number weighted mean, courtesy Mike Stevens (NRL) HALOE results as before, averages from Inversions assuming either: Spheres - lognormal Spheroid (AR=0.2) - gaussian

16 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 The Range of Observed PMC Extinctions The HALOE PMC detection threshold is 3.40  m extinction > 2  km -1 HALOE extinctions predicted from CARMA results for H 2 O 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  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  N

17 Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 Summary HALOE PMC median radii, mission averages,  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 H 2 O CARMA results using HALOE H 2 O can reproduce HALOE PMC radii HALOE extinction magnitude


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