This section summarizes the scientific questions which originated with participation in FIRE II in Coffeyville KA, evolved through participation in several field projects related to FIRE and culminated in participation in FIRE III in the Arctic in March / May 1998. It is noted that many of the ideas generated in FIRE II 1992 - 1995 and published under the grant involving the role of CCN in cirrus formation have been followed through in this grant and have also been central in the ideas for work under the SUCCESS project and the laboratory work currently supported by NSF

Arnott, W. P.

Hallett, John

English

NASA Technical Reports Server

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1. Microphysics and Radiative Properties of Cirrus: Instrumentation and Analysis
2. Summary of Research
3. W.P. Arnott and John Hallett
4. May 4 1995 - May 3 1998
5. Desert Research Institute, PO Box 60220, Reno NV 89506
6. NAG-l-1707
Final Report FIRE 1995 - 1998: Research Summary.
I. Introduction
This section summarizes the scientific questions which originated with
participation in FIRE II in Coffeyville KA, evolved through participation in several field
projects related to FIRE and culminated in participation in FIRE III in the Arctic in March
/ May 1998. It is noted that many of the ideas generated in FIRE II 1992 - 1995 and
published under the grant involving the role of CCN in cirrus formation have been
followed through in this grant and have also been central in the ideas for work under the
SUCCESS project and the laboratory work currently supported by NSF.
II. Scientific Questions
The basic question addressed is the origin and evolution of ice, primarily as
cirrus, from the viewpoint of determining its role in the solar/thermal radiation budget of
the earth. A theme running through the approach has been to assess any significant
differences between cirrus formed under different conditions - tropical convection, mid
latitude convection and frontal cirrus and arctic low level ice clouds which, although
forming at typical cirrus temperatures, form at much lower levels, near surface pressure.
A further consideration has been the role of anthropogenic aerosol, as in aircraft
contrails at altitudes in the upper troposphere and industrial produced aerosol at low
levels in the Arctic.
Specifically, instrumentation has been devised to characterize cirrus particles
and the nuclei on which they form, to be carried by aircraft into sensitive regions where
cirrus cloud formation is - or is not - taking place. The instruments have complemented
more conventional instruments (PMS probes) providing information capable of being
used in a predictive sense in a mesoscale or larger scale dynamical setting. Analysis
has given rise to the following precepts, which are discussed in formal publications,
past, current and pending.
https://ntrs.nasa.gov/search.jsp?R=19980210481 2020-06-16T00:15:33+00:00Z
III. Results
Below are general results that follow from the listed publications and are guiding
the initial analyses of FIRE III data:
t Comparison between data obtained from probes mounted even in close proximity on
the same aircraft must be interpreted in terms of the spatial variability along the flight
track. This is particularly important in sampling cirrus and contrail modified cirrus in
view of its high variability (see particularly Arnott et al 1998). This represents a
major effort of this work; it will be submitted for formal publication shortly.
• The occurrence of giant (diameter > few m) hygroscopic nuclei in concentrations of
cloud physics significance under some conditions (see particularly Meyers and
Hallett 1998);
• The critical supersaturation for initiation of droplets in a lenticular cloud is small -
05% over water, comprising the tail of the CCN spectrum (see Jensen et al 1998);
• The occurrence of 'large' (1001_m) and 'small' (5 _m) ice particles in close proximity
(< 1 m) during sampling, (Meyers and Hallett 1998);
• The occurrence of multiple habit crystals in close proximity (10 p.m equiaxed
particles and extreme, 1:100, 1:1 habit 100 l_m plates or columns), (Bailey and Hallet
1998);
• Aggregates are a rare but not completely absent phenomena; biaxial crystals occur;
trigonal (3-fold symmetry) and 4 fold symmetry crystals sometimes occur (in
preparation);
• Comparative rarity of regions with entirely 'pristine' crystals - that is having well
formed low index plane crystal facets and single crystals, as plates or columns (in
preparation).
IV. Projects from which aircraft data have been obtained:
FIRE II Coffeyville, KA, UND Citation, Nov/Dec 1991.
TOGA COARE From Townsville, over W. Pacific warm pool, January-February 1993,
NASA DC-8.
ARM Mission from Ponca City, OK, UND Citation, October 1994.
ARM Mission from Ponca City, OK, UND Citation, September 1997.
ARM Mission from Ponca City, OK, UND Citation, April 1998.
Planning for FIRE II1:
Canadian Convair: Over Beaufort Sea and to SHEBA from Inuvik, NT, April 1998.
NCAR C130: Over Beaufort Sea and to SHEBA from Fairbanks, AK, May 1998.
Other:
NASA DC-8: Cirrus from tropical storms Patrick AFB, FL, (CAMEX), September 1998.
2
V. Instrumentation Development.
Efforts have been made in two specific directions from the viewpoint of improving
the characterization of ice.
A. Formvar Replicator. This is an old technology (Hallett 1976) which is used for
providing both "air truth" for electro-optical systems (FSSP, 2DC and 2DP), for
collecting particles in the size range 5 -100 m which are not sampled by the other
probes and also provide detail of ice particles by both optical microscopy and also
scanning electron microscopy, if required. Major improvements have been made in
recording frame location in the film in flight and in a laboratory system for automated
frame advance to locate specific times for analysis. A frame grab system is in place
to provide and classify images by habit; size, area and if required, volume from an
empirical relationship. Plots of such data give distributions for these variables as
required (Arnott et al 1998). Evidence is mounting that the sample volume estimates
for the PMS system may be in error, resulting in an underestimate of particle
concentration, (see Fig. 1).
B. A different replicator is used on the NASA DC-8 and the Canadian Convair which fits
a PMS canister and faces into the airstream (as opposed to a cylinder at 90 ° to the
airstream), has a higher collection efficiency and collects particles down to 2 -3 m.
This was modified to operate at slower and higher speed to be more effective both at
lower and higher particle concentration.
C. The DRI cloudscope has been under development for the last 3 years (Arnott et al
1994) and was developed further for FIRE projects. This primarily involved improving
illumination to enable data collection at high illumination in the bright environment of
cloud top and over ice and snow below. A further development enabled the
collecting window to be set to a given, higher, temperature (recorded) and evaporate
particles more rapidly for the case of high liquid water content so that image overlap
did not occur. Automated analysis initially gives size distribution and habit; more
detailed analysis gives particle density, mass, and residue volume of evaporated
particles. It is usually possible to obtain some estimate of the hygroscopicity of such
particles (Arnott et al 1998).
D. A further development made the same improvements on a cloudscope with much
larger format having a field of view nearly 2 cm as opposed to a field of view of 1/2
mm for the standard instrument. This enabled much better statistics to be obtained
for larger particles and also better information on the spatial distribution of ice
particles of different size collected at nearly the same time. The instrument has been
used on the C130 in FIRE III and is anticipated to be used in the Florida CAMEX
mission.
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F J g u r' e 1. Size distributionstandarddeviation normalized
by the average distributions for replicator and 2DC
(thicklines), for the indicatedtemperatureranges•
•
Problems resulting from relating data from two probes located on the same
aircraft - even if nearly collocated - are non trivial and are addressed in various
publications listed below (Arnott et al 1998; Kinne et al 1998). Distant probes, as on
opposite wing tips or fuselage and wing tip, obviously sample regions separated by
some 50m and direct comparison at the same time (1 second) may be an exercise in
futility when variability in the aircraft flight direction varies on this scale. This indeed may
be the case in cirrus as even a casual inspection of high-resolution data - and indeed a
view from the ground - suggests. Thus an averaging of the data needs to be
undertaken, and the detail of such averaging needs careful attention as the statistics of
the occurrence of larger, rarer, particles may require a time well in excess of the scale
of the cloud element being considered. Such considerations point to instruments with
much larger sample volumes for the large particles with data combined with instruments
with much smaller sample volumes for the smaller particles - and herein lies the
problem. Even if the two instruments are in the same pod cluster, the problem is far
from solved as different airflow at the different sampling sites often occur, depending on
the flight characteristics of the aircraft. The conclusion is that measurements to be
combined need to be made with truly collocated instruments - and probably by different
measurements of the same air volume. These themes run through the data as it is
analyzed.
Vl. Field Preparation:
Major efforts were undertaken in this project in preparation, installation and
operation of instruments in aircraft for FIRE III from Inuvik (Canadian Convair replicator
and small format cloudscope) and Fairbanks (NCAR C130 - small and large format
cloudscope). We participated in both field programs and data was obtained in most
flights of the above aircraft. Initial analysis of the data is currently underway in
collaboration with the Canadian group.
VII. Related Project:
In parallel with this FIRE study, a NSF funded laboratory study has been
underway of the habit of ice crystals growing from the vapor under cirrus conditions.
Specifically, a water vapor diffusion chamber has been constructed which enables
temperature, air pressure and ice supersaturation to be varied independently over -30C
to -70C, supersaturation from a few % to over 200% over ice, and air pressure from 700
to below 50 mb. Thus the observed cirrus habits can be related to environmental
conditions through a map as in Fig. 2, with the effective supersaturation being corrected
for fall velocity through a ventilation coefficient, (Bailey & Hallett, 1998).
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References:
Arnott, W.A., Y.Y.Dong, J.Hallett, 1994, Observations and importance of small ice
crystals in a cirrus cloud from FIRE II. JGR 9._9.91371- 1381.
Hallett, J. 1976 Measurement Size Concentration and Structure of Atmospheric
Particulates by the Airborne Continuous Replicator, Final Report. AFGL-TR-76-
1149.
Publications resulting directly* from or related t to this grant:
*Hallett, J. J.G. Hudson and R. Puesche11996 Aerosol in Tropical Cirrus, In 14th
Conference on Nucleation and Atmospheric Aerosols, Ed. Kulmala and Wagner,
Helsinki. 880 - 883.
*Hallett, J., J.G. Hudson, F. Rogers, E. Teets, S.S. Yum and Y. Xie, 1997, The Influence
of Natural and Aircraft Exhaust on Aerosol and Cirrus Formation. Third
Conference on Atmospheric Chemistry, AMS, February 1997, Long Beach CA 45
- 53.
*Pueschel, R.F., J.Hallett, A.W. Strawa, S.D. Howard, G.F.Ferry, T.Foster and W.P.
Arnott. 1997, Aerosol and Cloud Particles in Tropical Cirrus Anvil: Importance to
Radiation Balance. 1997: J. Aerosol Science, 2._881123- 1136.
tHallett, J., W.P. Arnott, R. Purcell and C.S Schmidt: 1998, A Technique for
Characterizing Aerosol and Cloud Particles by Real time Processing. In
Proceedings, PM2. 5 Conference, Long Beach CA, February 1998, 318 - 339.
tPoellot, M.R., W.P. Arnott and J. Hallett, 1998, In Situ Observations of Contrail
Microphysics and Implications for their Radiative Budget. J.G.R., In Press.
tJensen, E.J., O.B. Toon, A. Tabazadeh,G.W. Sachse, B.E.Anderson K.R.Chan,
C.W.Twohy, B.Gandrud, S.M.Aulenbach, A.Heymsfield, J. Hallett and B.Gary,
1998; Ice nucleation processes in upper tropospheric waveclouds observed
during SUCCESS. G.R.L.2__5_51363-1366.
*Pueschel R.F., J.Hallett, A.W. Strawa, S.D. Howard, G.F.Ferry, T.Foster and
W.P.Arnott, 1997; Aerosol and Cloud Particles in Tropical Cirrus Anvil:
Importance to Radiation Balance. 1997; J. Aerosol Science, 2__881123- 1136.
*Sassen, K., G.G. Mace J. Hallett and M. Poellot: 1998; Corona - producing ice clouds:
a case study of a cold mid-latitude cirrus layer. Appl. Optics, 37' 1477 - 1485.
7
Papers to be presented at the AMS Cloud Physics Conference, Everett WA
August 1998:
*Arnott, W.P., T.J. Ulrich, R.Cole and J.Hallett: 1998; Summary of in-situ observations
of Cirrus Microphysics During FIRE I1: Instrumental Response. Conference on
Cloud Physics, Everett, WA, August 1998.
tBailey, M. and J. Hallett, 1998; Laboratory investigation ice growth from the vapor
under cirrus conditions between -30C and -70C, Conference on Cloud Physics,
Everett, WA, August 1998.
tMeyers, M. and J. Hallett 1998 Ice crystal Morphology in Aircraft contrails and Cirrus,
Conference on Cloud Physics, Everett, WA, August 1998.
tSchmitt,C., W.P. Arnott and J. Hallett,1998; Infrared Extinction and Emission by
Laboratory Ice Clouds: Simulation of Cold Cirrus and Contrail Radiative
Properties. Conference on Cloud Physics, Everett, WA, August 1998.
*Presentation to be made at AMS Dallas Meeting, Polar Symposium, (Jan 1999):
Meyers, Mo and J. Hallett Aircraft Observations of Giant Nuclei in Arctic Regions.
Presentations to be made at the CIRRUS Conference in Baltimore, October 1998:
*Shape and Fall of Cirrus Particles.
(Invited paper) John Hallett and Pat Arnott (DRI).
*New Insight for in situ quantification of cirrus
W. Patrick Arnott and John Hallett (DRI) and Michael R. Poellot (UND)
Papers in Preparation:
tLaboratory study of cirrus growth habit related to environmental parameters.
Matthew Bailey and John Hallett
tKinne, S., J. Hallett, et al
Intercomparison of aircraft measurements by instruments mounted at different locations.
*Hallett,J., J.G.Hudson, F.Rogers, E.Teets, S.S. Yum and Y. Xie, 1997, The Influence of
Natural and Aircraft Exhaust on Aerosol and Cirrus Formation.
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Microphysics and Radiative Properties of Cirrus: Instrumentation and Analysis

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