Observed Microphysical Structure of
Mid-Level, Mixed-Phase Clouds
Robert P. Fleishauer, Vincent E. Larson, J. Adam Kankiewicz, Lawrence
D. Carey, Thomas H. Vonder Haar
CIRA, Colorado State University
Presented by: Vincent E. Larson
Atmospheric Science Group, Univ. of Wisconsin --- Milwaukee
11 July 2001
DOD Center for Geosciences/ Atmospheric Research
Colorado State University
Acknowledgements
ƒThis research was supported by the Air Force Institute of
Technology, the DoD Center for Geosciences/Atmospheric
Research Agreement #DAAL01-98-2-0078, and CIRA
subaward G-7420-2 to University of Wisconsin --- Milwaukee.
A portion of the CPI imagery was obtained through funding by
NASA/EOS (# S-97894-F) to Dr. A. Heymsfield.
DOD Center for Geosciences/ Atmospheric Research
Colorado State University
Why study mid-level clouds?
‹ Hindered


Operations in DESERT STORM.
Difficult to forecast.
Impacts pilots’ visibility, unmanned aerial vehicles,
battlefield damage assessment, refueling.
‹ “Forgotten

‹
Clouds” in Atmospheric Science.
Mid-level clouds are not well understood, but they cover ~
22% of globe.
Mixed-Phase Structure of Clouds Unknown.


30% are mixed-phase --- i.e. contain both ice and liquid.
We need to know ice structure for weather and climate
forecasts, e.g. to compute radiative transfer.
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Colorado State University
Scientific Questions
‹ Where’s
the ice?
‹ Is ice water content (IWC) correlated with
temperature?
‹ Low-level stratocumulus clouds are
associated with strong temperature
inversions and horizontal wind shear at
cloud top. Are mid-level clouds?
DOD Center for Geosciences/ Atmospheric Research
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Cases Discussed: CLEX-5
‹
5 Cloud Cases: 11 Nov 1999, 2 Dec 1999, 5 Dec 1999;
10 Mar 2000,12 Apr 2000



All cases were thin, non-precipitating, mid-level clouds
(altocumulus).
All cases were mixed-phase except for 5 Dec 99, which contained
only liquid.
10 Mar and 12 Apr cases were multi layered; other cases were
single layered.
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Colorado State University
Location of Observations
11 Nov 99: over Montana
Other Cases: over ARM CART site in Oklahoma
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Aircraft Measurements
‹
This talk will focus on aircraft observations





‹
CLEX-5 used two jet aircraft: University of North
Dakota’s Citation and SPEC Inc.’s LearJet
Liquid (King probe), ice (2D-C)
Ice particle imagery (Cloud Particle Imager, or CPI)
3-dimensional wind field and temperature
Pressure, humidity, etc.
There were also ground, radar, and satellite
observations
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First question: Where does
ice occur in mid-level
clouds?
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Ice vs Liquid–Single Layer
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Ice vs Liquid–Single Layer
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In the single-layer clouds
we observed, ice appears
to be located mostly near
cloud base.
What happens in multilayered clouds?
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Ice vs Liquid–Multi-Layers
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Ice vs Liquid–Multi-Layers
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Is IWC Correlated with
Temperature?
Temperature [° C]
Ice Water Content vs. Temperature
Ice Water Content [g m-3]
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One might expect
ice water content
(IWC) to maximize
at low
temperatures. In
fact, IWC
maximizes at
roughly –12 C.
Near this, the
saturation
difference between
liquid and ice is
largest.
Colorado State University
How large are temperature inversions at cloud
boundaries? Unlike low-level stratocumulus, they are
small, perhaps because mid-level clouds are short-lived.
Normalized Height vs.Virtual Potential Temperature
Normalized Height
Cloud top Æ
Moist
Adiabats
10 Mar 00
Middle Layer
10 Mar 00
Top Layer
11 Nov 99
5 Dec 99
2 Dec 99
10 Mar 00
Bottom Layer
Cloud base Æ
Virtual Potential Temperature [K]
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Wind shear at cloud boundaries is small, perhaps
because mid-level clouds are not tied to ground.
Mission
Leg
Case Day
#
11 Nov 99
1
Location
Height
Direction
Speed
[m]
[deg]
[m s-1]
Under
4525
268
23.8
2
In (B)
5279
266
26.4
3
In (T)
5608
269
26.5
4
Above
5794
270
24.5
5
In (M)
5546
270
26.0
6
In (M)
5434
271
25.5
7
I/O (B)
5182
270
27.3
8
Below
4877
273
26.8
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Wind shear at cloud
boundaries is small
Mission
Leg
Case Day
#
2 Dec 99
1
Location
Height
Direction
Speed
[m]
[deg]
[m s-1]
Above
8238
242
27.8
2
In (B)
6711
202
22.5
3
In (T)
7008
205
25.4
4
Above
7314
212
26.9
5
Out (M)
6969
209
24.6
6
I/O (M)
6892
206
27.4
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Wind shear at cloud
boundaries is small
Mission
Leg
Case Day
#
5 Dec 99
1
Location
Height
Direction
Speed
[m]
[deg]
[m s-1]
In (B-M)
2592
346
19.5
2
In (B-M)
2592
353
21.1
3
In (B)
2390
344
18.0
4
In (M)
2625
356
26.2
5
I/O (T)
2810
344
19.3
6
Below
2386
351
20.0
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Wind shear at cloud
boundaries is small
Mission
Leg
Case Day
#
10 Mar 00
1
Location
Height
Direction
Speed
[m]
[deg]
[m s-1]
Above
6408
246
28.2
2
In (M)
3309
223
8.5
3
In (T)
3375
225
10.3
4
I/O (M)
3316
220
9.5
5
I/O (M)
5482
236
26.4
6
In (T)
5594
237
27.1
7
In (M)
5517
239
27.1
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Conclusions
‹ It is not difficult to encounter mixed-phase clouds!
Forecast models need to represent ice processes with
fidelity.
‹Microphysical Structure of Mixed-Phase Clouds
 Single Layers: LWC peak at cloud top; IWC peak at cloud base
ΠIce sediments to cloud bottom.
 Multiple Layers: LWC peak at cloud top; IWC homogeneous
ΠSpeculate that Seeder-Feeder Mechanism causes Difference
‹Ice Concentrations/IWC Not Correlated to Temperature
 Peak IWC between –8 and –20º C
Œ Maximum plate-like growth region; maximum (esl - esi) at –12 to -15º C
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Conclusions (cont’d)
‹ CLEX-5 clouds lacked strong temperature
inversions
 Possibly due to short lifetime of clouds
‹ CLEX-5 clouds lacked strong shear at cloud
boundaries
 Mid-level clouds are not tied to the surface. Hence
they tend to drift with the horizontal wind
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Future Work
‹
More observations are needed
Increase database and verify initial findings
 Use airborne radar to find cloud-scale properties

‹
Numerical simulations would be illuminating
Simulations are a cheap way to ``extend the
dataset” to more cases and thereby permit one to
test hypotheses.
 Lagrangian cases are easier to simulate

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