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Understanding formation and maintenance of mixed-phase Arctic stratus through long- term observation at two Arctic locations Gijs de Boer E.W. Eloranta, G.J. Tripoli The University of Wisconsin - Madison Introduction AGU San Francisco, 14

SLIDE 1

Understanding formation and maintenance of mixed-phase Arctic stratus through long- term observation at two Arctic locations

Gijs de Boer E.W. Eloranta, G.J. Tripoli The University of Wisconsin - Madison

SLIDE 2

AGU San Francisco, 14 December, 2007

Introduction

SLIDE 3

AGU San Francisco, 14 December, 2007

Introduction

SLIDE 4

AGU San Francisco, 14 December, 2007

Introduction

These 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) 500 1000 1500

October Single Layer Stratus Month Number of Cases

SLIDE 5

AGU San Francisco, 14 December, 2007

Introduction

From ARM Model intercomparison (Klein et al.)

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AGU San Francisco, 14 December, 2007

Introduction

From ARM Model intercomparison (Klein et al.)

SLIDE 7

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

SLIDE 8

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

SLIDE 9

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/L Ice particle concentrations: ~10 1/L So nucleation not by:

Deposition freezing
Condensation freezing
Contact freezing

alone

SLIDE 10

Time (UT) Altitude (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) Altitude (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

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AGU San Francisco, 14 December, 2007

Observations

Time (UT) Altitude (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

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AGU San Francisco, 14 December, 2007

Observations

230 240 250 260 270 280 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Temperature (K) Normalized # Probability Density Function Cloud Min. Temp. Cloud Max. Temp.

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AGU San Francisco, 14 December, 2007

Observations

230 240 250 260 270 280 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Temperature (K) Normalized # Probability Density Function Cloud Min. Temp. Cloud Max. Temp.

Homogeneous Freezing (< -35°C) (Hagen et al., 1981; Jensen et al., 1998)

SLIDE 14

AGU San Francisco, 14 December, 2007

Observations

230 240 250 260 270 280 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Temperature (K) Normalized # Probability Density Function Cloud Min. Temp. Cloud Max. Temp.

Homogeneous Freezing (< -35°C) (Hagen et al., 1981; Jensen et al., 1998) Splinter Ejection (> -8°C) (Heymsfield and Mossop, 1984)

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230 235 240 245 250 255 260 265 270 !10 !5 5 10 15 20 )*c. Tem1erature (7) (Tcb!Ts*c)/!< (7/km)

AGU San Francisco, 14 December, 2007

Observations

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AGU San Francisco, 14 December, 2007

Observations Why the horizontal variability in ice production?

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AGU San Francisco, 14 December, 2007

Observations

Figures courtesy of M. Shupe (NOAA)

Why the horizontal variability in ice production?

SLIDE 18

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)

SLIDE 19

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

SLIDE 20

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