Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 PMC Particle Size from 14 Years...
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Transcript of Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006 PMC Particle Size from 14 Years...
Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006
PMC Particle Size from 14 Years of HALOE Observations
Mark Hervig
GATS Inc.
Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006
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
HALOE PMC Measurements
HALOE multi-wavelength extinctions are consistent with modeled PMC spectra
60-70N
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
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
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
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
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
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
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
PMC Radii ResultsMedian radii profiles were determined from yearly
averaged extinctions.
60 - 70N, -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
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
Mission average median radius profiles
Average of yearly profiles from 1993 - 2005
Inversions assume either:
1. Spheres - lognormal ( = 1.3, 1.5, 1.7)
rm = 70 34 nm (83 km)
Vertical mean rm = 40 28 nm
2. 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
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:
Source Approximate 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
ACE 4 - 7
OSIRIS Limb OH (Gattinger)
1 - 7
Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006
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 66N during summer
Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006
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
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 observationsNotes:
•HALOE PMC frequency for 60-70N 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.
60-70N
Mark Hervig, CAWSES Ice Layer Workshop, Kuehlungsborn, May 15, 2006
Summary• HALOE PMC median radii, mission averages, 60 - 70N
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