Steven Siems1 and Greg McFarquhar2

1Monash University, Melbourne, VIC, Australia2University of Illinois, Urbana, IL, USA

Workshop on Clouds, Aerosols, Radiation and Air-Sea Interface of Southern Ocean: Establishing Directions for

Future Research,18-19 March 2014, Seattle, WA

Observations of supercooled liquid water from in-situ and remote sensing

observations

Mixed phase clouds occur regularly in Arctic/ Southern Oceans, especially in the spring & fall

Supercooled water contents large enough that they can

cause aircraft instruments to ice up in Arctic

Supercooled water contents large enough that they can

cause aircraft instruments to ice up in Arctic

We also know that they occur over the Southern Oceans, yet there are not as much in-situ data

Mixed phase clouds occur regularly in Arctic/ Southern Oceans, especially in the spring & fall

Supercooled water contents large enough that they can

cause aircraft instruments to ice up in Arctic

Why do these clouds persist?

Mixed phase clouds occur regularly in Arctic/ Southern Oceans, especially in the spring & fall

Supercooled water contents large enough that they can

cause aircraft instruments to ice up in Arctic

How do aerosols affect these mixed-phase clouds

Mixed phase clouds occur regularly in Arctic/ Southern Oceans, especially in the spring & fall

Supercooled water contents large enough that they can

cause aircraft instruments to ice up in Arctic

Pristine conditions over Southern Oceans provide good contrast to existing Arctic observations

Mixed phase clouds occur regularly in Arctic/ Southern Oceans, especially in the spring & fall

Glaciation indirect effect (Lohmann 2002)

Riming indirect effect (Borys et al. 2004)

Thermodynamic indirect effect (Rangno & Hobbs 2001; Lance et al. 2011

Aerosol Impacts on Mixed-Phase Clouds

Review past Arctic experiments to understand what data needed to study supercooled/mixed-phase clouds over Southern Oceans

Arctic Experiments

M-PACE: Sept. 27 to Oct. 22 2004

Objective:Collect focused set of observations to advance understanding of dynamical and microphysical processes in mixed-phase clouds, including radiative transfer through clouds

Analysis of > 100 vertical profiles conducted

Vertical profiles of Ni & Nw generated from measurements as function of normalized altitude (Zn) used to develop/evaluate models & retrievals

Poor agreement between modeled & measured IWC & ice crystal concentration

Fridlind et al. 2007

zn

zn

0

0

1

1

Fridlind et al. 2007

Better agreement between modeled & observed ice concentration when have

1) formation of ice nuclei from drop evaporation residuals

2) drop freezing during evaporation

zn

zn

0

0

1

1

zn

zn

0

0

1

1

zn

0

1

Ice # [L-1]

M-PACEOctober 2004

• Pristine Conditions– Open ocean– Few cloud droplets– Ice multiplication– Precipitation

• Polluted Conditions– Sea Ice– Many cloud droplets– Ice nucleation– Little precipitation

ISDACApril 2008

NRC NAX radarX band radar Z and Vd crossections

Strong capping inversion between normalized altitude (zn) of 0.8 to 1.2

Strong capping inversion between normalized altitude (zn) of 0.8 to 1.2

Subadiabatic LWC for zn > 0.8 consistent with entrainment of dry air above cloud top or growth of ice at expense of liquid water

- Examined dependence of cloud properties on aerosol amounts above and below cloud base for different surface and meteorological conditions

- Assessed importance of different indirect effects

- Although needed more data, some patterns emerged

Controls of Cloud Properties

ISDAC M-PACEN

orm

aliz

ed F

requ

ency

ISDAC M-PACE

LWC < for ISDAC than M-PACE, consistent with more open water during M-PACE

Nor

mal

ized

Fre

quen

cy

ISDAC M-PACEN

orm

aliz

ed F

requ

ency

ISDAC M-PACE

Nliq > for ISDAC than M-PACE, consistent with presence of more aerosols/CCN

Nor

mal

ized

Fre

quen

cy

ISDAC M-PACEN

orm

aliz

ed F

requ

ency

ISDAC M-PACE

rel < for ISDAC than M-PACE,

Nor

mal

ized

Fre

quen

cy

ISDAC M-PACE

Nice < for ISDAC than M-PACE, consistent with thermoynamic indirect effect

Nor

mal

ized

Fre

quen

cy

Southern Ocean Data

• Need equivalent set of data over Southern Oceans to understand why these clouds persist and to advance our understanding of dynamical & microphysical processes in mixed-phase clouds, including radiative transfer

• Need in-situ cloud microphysics, in-situ aerosols and remote sensing to give context of measurements