February 12, 2004

• Focus primarily on some examples of studies ice and mixed-phase clouds in last 10 years in which IN and ice concentrations were measured.
• Some inferences about our understanding of upper tropospheric ice formation from studies of natural IN and clouds at low temperatures.
• A general realization/validation: mineral dust is an important source of atmospheric IN.
• A few thoughts on future needs.
February 12, 2004

• Heymsfield and Milosevich 1993-1995 papers suggest that there are few heterogeneous IN in upper troposphere and that ice formation by homogeneous freezing dominates in cold wave clouds
• Some during WISP studies (1993-1994): IN collected from around clouds and processed in CFDC and controlled expansion cloud chamber. IN concentrations reasonably consistent with ice in clouds, but method not sufficient to explain variability in time and space. Tests for evaporation IN in controlled expansion cloud chamber find no more than 2-3 enhancement.
• Wave clouds below -40C during SUCCESS (1996) show total ice concentrations consistent with homogeneous freezing, but also evidence consistent with presence of IN up to 100 per liter at low temperatures. Such high IN not always there and sometimes few deposition nuclei present.
• U.K. studies (Field, Cotton, et al.) using SID show evidence of strong ice formation mechanism in evaporation portion of modestly supercooled wave clouds. Does not always occur.
• WAVEICE studies (2000): Little apparent evidence for enhanced ice formation in downstream portion of modestly supercooled wave clouds. IN upstream of wave cloud are reasonably consistent with ice formed in cloud.
Some evidence for springtime dust impacts on cloud ice formation.
February 12, 2004

• WISP 1994
– NCAR Electra,
Wyoming KingAir
– Six wave clouds
– Upwind-downwind penetrations
– Ice concentration from PMS 2DC and
1DC
– Upwind aerosol bag samples, analyzed at
CSU lab with CFD &
Dynamic Cloud
Chamber

Wind 12-25 m s -1
February 12, 2004

200X probe
February 12, 2004

Parcel model uses IN and CCN measurements:
1000
100
10
-15
-20
-25
-30
-35
-40
-5
-10
5
0
Data from Wyo. KA; March 17, 2000 wind 18 m s -1
10 turb
W
100
1D
10 CFD
1
0.1
2D-C
CN
FSSP-100
FSSP-300
T
CFD
DP
17:43 17:44 17:45 17:46 17:47
Time (UTC)

A number of observations have been made of enhanced ice formation in evaporation region of waves
Cooper (1995,
AMS Cloud
Physics
Conf.). See also Cotton and Field
(2002, QJRMS)
February 12, 2004

Preliminary Inferences from AIRS-2 Studies on the
Role of IN in the Evolution of Mixed Phase Clouds
• Extremely inhomogeneous spatial distributions of IN may exist in the atmosphere prior to winter storms.
• This heterogeneity is reflected by the IN detected from cloud particle residuals (sampled by CVI) but the interpretation of these data may not be straightforward.
February 12, 2004

November 14: Lower clouds with and without ice, deeper clouds and cirrus in some areas. Were in process of transitioning CFDC conditions to equal those in lower clouds at this time
-10
-15
0
-5
10
5
-20
-25
-30
16.95
17.45
17.95
Time (hrs GMT)
18.45
% Sat. Water
Aer. Location Temp
February 12, 2004

November 14: Distinct layers with high IN aloft, sometimes reaching down to lower clouds. Some clouds had ice and some not. Likewise, some had IN, some not.
10 ambient inlet On CVI here
Descent from ~500 to
1 cloud level at 800 mb.
High IN at cirrus levels.
Few lower.
I N detected (above background, peak
1/liter) from CVI residuals in this
No IN detected cloud. Ice present
(above background) from in this cloud.
ambient inlet
CVI residuals in this cloud.
0.1
0.01
Exit to slightly higher altitudes before descent. Layer of high IN and larger aerosols, transected.
1
0.9
0.8
0.7
0.6
0.5
0.4
aerosol>0.3um
0.001
0.3
aerosol>0.7um
0.0001
Transit to Cleveland below clouds and descent. No IN detectable above background even in some high aerosol regions.
0.2
0.1
[IN]avgfilter
[IN]avg
CVI = 1 ( on counterflow)
0.00001
16.95
17.45
17.95
Time (hours GMT)
18.45
0
CVCWC(corr)
February 12, 2004

[IN] in deep precipitating cloud system on November
19, 2003 and relation to cloud residual aerosol
400
500
600
700
800
900
1000
0.00001
1942 to 2036 hours ascent sounding
[IN] aerosol > 0.3um
aerosol > 0.7um
CVICN (>0.015um)
CVIWC (g/m3)
Holes like these are filtered sample air tests for validation purposes
0.001
0.1
Concentration (cm
-3
)
10
400
500 Note horizontal variation
2036 to 2124 hours descent sounding
[IN] aerosol > 0.3um
aerosol > 0.7um
CVIWC (g/m3)
CVICN (>0.015um)
600
700
800
900
1000
1000
0.00001
0.001
0.1
Concentration (cm
-3
)
10 1000
CFDC processing T ≈ -12.5°C; RH w
= 102%

• LAKE-ICE : IN relate to cloud ice in lake-effect systems
• FIRE-ACE/SHEBA : Generally lower IN in Arctic, possible sources from open ocean leads, silicate/sulfur chemistry of IN (Rogers et al.
2001).
• North Dakota Tracer Experiment : Bag samples from cumulus cloud base levels and surface sampling suggests agreement between IN and young updraft ice (Stith et al. 1994; DeMott et al.
1995)
February 12, 2004

Free tropospheric sampling of concentration and composition of nuclei for cirrus formation
Storm Peak Laboratory (3220 m
MSL; Steamboat Springs, CO, USA)
Cziczo et al. 2003, AS&T
INSPECT: Nov. 2001 Aerosol processing methodology (Spring 2004)
February 12, 2004

Cirrus ice formation conditions and ice concentrations nucleated on ambient tropospheric aerosol particles
Homogeneous freezing
Heterogeneous ice nucleation
DeMott et al. 2003,
December, PNAS
February 12, 2004

Homogeneous freezing of pure sulfates from
Chen et al. (2000) or Koop et al.
(2000)
NASA-SUCCESS RH i inside/outside cirrus, |w|<|1m/s
(Jensen et al., JGR, 2001)
Ice saturation
February 12, 2004

Heterogeneous nucleation at low temperatures on ambient tropospheric aerosol particles suggest the range of cirrus types impacted
DeMott et al. 2003, PNAS
Smaller scale wave forcing and anvil cirrus w
Synoptic lifting and Subvisual cirrus
Gierens (2003): “critical” concentration of heterogeneous IN triggering a switch of predominant mechanism from homogeneous freezing to heterogeneous nucleation, as a function of T and updraft speed
February 12, 2004

IN formulations for numerical modeling: need for better parameterizations and more fundamental understanding
1000
100
10
1
Meyers et al .
INSPECT (<-38C)
Series1
Series2
Series3
0.1
0.01
-35 -30 -25 -20 -15 -10
INSPECT (>-35C)
-5 0

T = -42 to -46 °C;
RH w
= 90-92%
February 12, 2004

Statistics of PALMS cluster analyses of particle types
Note: Untold story about organic aerosol components and ice nucleation
20%
80% (1/4 with any detectable S)
February 12, 2004

Atmos. Chem. Phys., 3, 1791-1806, 2003 Freezing thresholds and cirrus cloud formation mechanisms inferred from in situ measurements of relative humidity
•
W. Haag, B. Kärcher, J. Ström, A. Minikin, U. Lohmann, J. Ovarlez, and A. Stohl
The analysis of field data taken at northern and southern midlatitudes in fall 2000 reveals distinct differences in cirrus cloud freezing thresholds. Homogeneous freezing is found to be the most likely mechanism by which cirrus form at southern hemisphere midlatitudes. The results provide evidence for the existence of heterogeneous freezing in cirrus in parts of the polluted northern hemisphere, but do not suggest that cirrus clouds in this region form exclusively on heterogeneous ice nuclei.
Atmos. Chem. Phys., 3, 1807-1816, 2003 Cirrus cloud occurrence as function of ambient relative humidity: a comparison of observations obtained during the INCA experiment
•
J. Ström, M. Seifert, B. Kärcher, J. Ovarlez, A. Minikin, J.-F. Gayet, R. Krejci, A. Petzold, F. Auriol, W. Haag, R. Busen, U. Schumann, and H. C.
Hansson
Discusses the cloud presence fraction (CPF) defined as the ratio between the number of data points determined to represent cloud at a given ambient relative humidity over ice (RHI) divided by the total number of data points at that value of RHI. The CPFs taken at Southern
Hemisphere (SH) and Northern Hemisphere (NH) midlatitudes differ from each other. Above ice saturation, clouds occurred more frequently during the NH campaign. Clouds during the SH campaign formed preferentially at RHIs between 140 and 155%, whereas clouds in the NH campaign formed at RHIs somewhat below 130%.
Observed distributions of cloud water content differ only slightly between the NH and SH campaigns and seem to be only weakly, if at all, affected by the freezing aerosols.
Atmos. Chem. Phys., 3, 1037-1049, 2003 In-situ observations of aerosol particles remaining from evaporated cirrus crystals: Comparing clean and polluted air masses
•
M. Seifert, J. Ström, R. Krejci, A. Minikin, A. Petzold, J.-F. Gayet, U. Schumann, and J. Ovarlez
In-situ observations of aerosol particles contained in cirrus crystals are presented and compared to interstitial aerosol size distributions
(non-activated particles in between the cirrus crystals). Size distribution measurements of crystal residuals show that small aerosol particles (Dp< 0.1 um) dominate the number density of residuals. On average the residual size distributions were shifted towards larger sizes and the calculated particle volume was three times larger in the Southern Hemisphere. The form of the residual size distribution did not depend on temperature as one might have expected considering different modes of nucleation.
The observations of ambient aerosol particles were consistent with the expected higher pollution level in the Northern
Hemisphere. The fraction of residual particles only contributes to approximately a percent or less of the total number of particles.
February 12, 2004

Dust and IN: transports affect different parts of the world at different times (E.g., Asian dust in N. America)
VanCuren and Cahill [JGR, 2002].
Continental transect of inferred fine
Asian dust frequency (top) and concentrations (bottom) in ng m -3 .
Fine (PM2.5) soil concentration at the Mt. Zirkel IMPROVE site
(1993-2002).
February 12, 2004

Polarization lidar data in
Salt Lake City, UT on
April 29, 2001
Considerable warmer and lower than climatological means for cirrus
February 12, 2004

Possible dust impacts (Sassen 2002 GRL introduced
PDL evidence) – Also evidence in WAVEICE (2000)
March 25: Hazy day aloft Early morning 3/25 ruby lidar relative backscattered power and linear depolarization ratio at Salt Lake City (FARS-Ken Sassen)
[2D-c] =16 to
206 l -1 ; T= -14 to -37 °C
Mt Zirkel IMPROVE network sampler indicates dust intrusion
10
Onset of
Spring-
Summer
Dustiness
Typical of moderate
Asian dust
1
Typical
Winter values
0.1
0.01
3/19
3/25
0.001
2/24/2000 3/15/2000 4/4/2000 4/24/2000 5/14/2000 6/3/2000
Date
Al
Ca
Si
Fe soil
February 12, 2004

February 12, 2004

Recent Lab Studies Corroborate Ice Formation by Dust
Particles (resuspended Asian dust – Cassie Archuleta thesis)
180
175
RH w
= 100%
Ca, Si, S, Mg
Homogeneous freezing points of sulfuric acid aerosols
170
165
160
155
200 nm
Heterogeneous nucleation by dust
150
145
140
135
130
125
120
-65
50 nm
100 nm
200 nm
-60 -55 -50
Temperature (°C)
-45 -40
Si, Al, Fe
200 nm
February 12, 2004

(DeMott et al., GRL, 2003 and Sassen et al., GRL, 2003)
Processing at T =-37
°
C, RH w
= 86%,
RH ice
= 123% assured heterogeneous ice nucleation only
MODIS aerosol optical depth, July
20-27; July 29, 2003 back trajectory
S. Florida PDL lidar data on 7/29
February 12, 2004

July 29: CFDC operating mostly in expected homogeneous freezing regime at low temperature during anvil ascent profile.
Ice Nuclei
10
1
0.1
2D probe
8.7 km
CPI
CWC
9.3 km
Process T impactor collected
Process RHw-100
10
• High IWC contents
0
• No Citation FSSP data during period
9.9 km -10
-20
-30
• CFDC [IN] correspond with
[2D] within factor 2
-40
0.01
65000 66000 67000
Time (UT seconds)
CPI data: C. Scmitt, A. Bansemer, A.
Heymsfield
-50
-60
68000
•
• CPI concentrations also correspond well with [IN]
[IN] up to 600/liter

Dustmix
C-containing
KCl, NaCl
Dust/industrial/oxide
February 12, 2004

PALMS analysis of particles from high tropical cirrus during CRYSTAL-FACE (Source D.J. Cziczo, NOAA)
Sulfates plus
Organics (~70%)
Sea Salt (<5%)
Mineral Dust, Fly Ash, Meteoritic, Etc. (~25%)
• Histogram of the area of the sodium peak in each positive polarity mass spectrum.
• This area can be used as a rough indicator of particle type.
• Most ice residue, particles outside cloud, and interstitial aerosols are sulfate / organics : this is consistent with our understanding of homogeneous freezing .
February 12, 2004

PALMS analyses of anvil cirrus particles (July 29, 2002)
Sulfates plus
Organics
(<10%)
Mineral Dust (~70%)
Sea Salt (20%)
• Ice residue from July 28 -29 2002 have a much higher sodium signal than out of cloud particles or interstitial aerosol.
• ~20% are consistent with frozen sea salt. <10% Sulfates and organics.
• Most of the remainder (70%) are consistent with mineral dust or fly ash heterogeneous freezing…
February 12, 2004

• Still believe that wave clouds have much to offer in understanding ice formation mechanisms.
• Do not yet have IN measurements at appropriate conditions in and around cirrus (Tropical cirrus missions and high altitude capabilities coming).
• Need IN versus ice concentration in convective clouds.
Likely missing an important ice formation mechanism.
• Validate the impacts of mineral dusts on clouds in programs such as AMMA?
• Continued need for laboratory studies of aerosol effects on ice nucleation and more fundamental work.
• Definition of ice versus water is still a critical issue for studies relating IN to ice formation.
• Need to take real-time combined IN and residual composition measurements aloft.
February 12, 2004

-1
0
100
200
300
400
500
600
700
800
900
1000
10 ice (no dust) drops (no dust) ice (dust) drops (dust)
100 1000 10000
Drop Conc (cm
-3
) , Ice Conc ( L
-1
)
0
100
200
300
400
500
600
700
800
900
1000
0.01
IWC (no dust)
LWC (no dust)
IWC (dust)
LWC (dust)
0.1
1
LWC (g m
-3
) , IWC (g m
-3
)
10
February 12, 2004