PMC Particle Size from 14 Years of HALOE Observations

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

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:

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


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


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


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)


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


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


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


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


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)


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


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


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


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


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


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


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

Documents

PMC Particle Size from 14 Years of HALOE Observations