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Understanding formation and maintenance of mixed-phase Arctic stratus through long-
term observation at two Arctic locations
Gijs de BoerE.W. Eloranta, G.J. Tripoli
The University of Wisconsin - Madison
AGU San Francisco, 14 December, 2007
Introduction
AGU San Francisco, 14 December, 2007
Introduction
AGU San Francisco, 14 December, 2007
IntroductionThese cloud structures are extremely prevalent in the Arctic:
- SHEBA: 48% occurrence in May (Rogers et al., 2001)- Low altitude stratus frequency of up to 70% during transitional seasons (Curry et al., 1996; Herman and Goody, 1976)- From Eureka: over 1700 30 minute cases for September 2005-December 2006.- From M-PACE: over 500 30 minute cases for mid September-mid November, 2004.
2004 (Barrow) 2005 (Eureka) 2006 (Eureka)0
500
1000
1500October Single Layer Stratus
Month
Num
ber o
f Cas
es
AGU San Francisco, 14 December, 2007
Introduction
From ARM Model intercomparison (Klein et al.)
AGU San Francisco, 14 December, 2007
Introduction
From ARM Model intercomparison (Klein et al.)
Introduction
- Ice Formation (Pruppacher and Klett, 1997)
AGU San Francisco, 14 December, 2007
•Homogeneous nucleation
•Heterogeneous nucleation•Deposition freezing•Contact freezing•Condensation freezing•Immersion freezing
•Some Multiplication Processes•Drop shattering•Ice-ice collisions•Splinter ejection during riming
AGU San Francisco, 14 December, 2007
Observations
• UW Arctic High Spectral Resolution Lidar• NOAA ETL Millimeter Cloud Radar• 12-hr. Radiosonde Frequency• In-situ from M-PACE
• Microwave Radiometer• U. Idaho Polar AERI• CALIPSO• CloudSAT
Instruments
Observations
AGU San Francisco, 14 December, 2007
Where does the ice come from?
Low IN, but substantial ice...
Example from M-PACE: CFDC Average out of cloud IN concentration for 9 and 10 October 2004: 0.16 1/LIce particle concentrations: ~10 1/L
So nucleation not by:-Deposition freezing-Condensation freezing -Contact freezingalone
Time (UT)
Altit
ude
(km
)
Lidar backscatter cross section (Masked values shown in black and white)
13 14 15 16 17 18 19 20 21 22 23
1.0
2.0
3.0
4.0
1/(m str)1e!8
1e!7
1e!6
1e!5
1e!4
1e!3
Time (UT)
Altit
ude
(km
)
Radar backscatter cross section (Masked values shown in black and white)
13 14 15 16 17 18 19 20 21 22 23
1.0
2.0
3.0
4.0
1/(m str)1e!14
1e!13
1e!12
1e!11
1e!10
1e!9
1e!8
1e!7
AGU San Francisco, 14 December, 2007
Observations
AGU San Francisco, 14 December, 2007
Observations
Time (UT)
Altit
ude
(km
)
Cloud Mask (Masked values shown in black and white)
13 14 15 16 17 18 19 20 21 22 23
1.0
2.0
3.0
4.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
AGU San Francisco, 14 December, 2007
Observations
230 240 250 260 270 2800
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperature (K)
Norm
alize
d #
Probability Density Function
Cloud Min. Temp.Cloud Max. Temp.
AGU San Francisco, 14 December, 2007
Observations
230 240 250 260 270 2800
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperature (K)
Norm
alize
d #
Probability Density Function
Cloud Min. Temp.Cloud Max. Temp.
Hom
ogen
eous
Fre
ezin
g (<
-35
°C)
(Hag
en e
t al
., 19
81; J
ense
n et
al.,
1998
)
AGU San Francisco, 14 December, 2007
Observations
230 240 250 260 270 2800
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Temperature (K)
Norm
alize
d #
Probability Density Function
Cloud Min. Temp.Cloud Max. Temp.
Hom
ogen
eous
Fre
ezin
g (<
-35
°C)
(Hag
en e
t al
., 19
81; J
ense
n et
al.,
1998
)
Splin
ter
Ejec
tion
(> -
8°C
)(H
eym
sfiel
d an
d M
osso
p, 1
984)
230 235 240 245 250 255 260 265 270!10
!5
0
5
10
15
20
)*c. Tem1erature (7)
(Tcb!T
s*c)/!
< (7
/km
)
AGU San Francisco, 14 December, 2007
Observations
AGU San Francisco, 14 December, 2007
Observations
Why the horizontal variability in ice production?
AGU San Francisco, 14 December, 2007
Observations
Figures courtesy of M. Shupe (NOAA)
Why the horizontal variability in ice production?
Summary
AGU San Francisco, 14 December, 2007
Ice production likely not due to:- Homogeneous Nucleation (too warm)- Condensation, deposition or contact freezing alone (too few IN)- Drop splinter ejection during riming (too cold)
Summary
AGU San Francisco, 14 December, 2007
Ice production likely not due to:- Homogeneous Nucleation (too warm)- Condensation, deposition or contact freezing alone (too few IN)- Drop splinter ejection during riming (too cold)
Key to understanding ice production:- Likely lies with understanding controlling mechanisms for horizontal variability in observed precipitation
Summary
AGU San Francisco, 14 December, 2007
Ice production likely not due to:- Homogeneous Nucleation (too warm)- Condensation, deposition or contact freezing alone (too few IN)- Drop splinter ejection during riming (too cold)
Key to understanding ice production:- Likely lies with understanding controlling mechanisms for horizontal variability in observed precipitation
Future investigation- Numerical sensitivity experiments to look at individual processes.- Evaluate role of vertical velocity in cloud layer
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