Clouds and aerosols: Understanding processes –informing modelsMike Harvey, NIWA, Wellington NZ

S. Hartery, P. Kuma, O. Morgenstern, R. Querel, V. Varma, Jonny Williams, A. McDonald

• An improved understanding of processes is required to adequately represent and model Clouds and Aerosols in the Southern Ocean region

• Observations are sparse, process understanding is incomplete • Here we look at 2 processes and review:

1/Background/history 2/ Results 3/ Model representation• Current Project Plans

Project personnel ESM/C&A: Adrian McDonald1, Olaf Morgenstern2, Roger Davies3, Mike Harvey2, Vidya Varma2, Jonny Williams2, Simon Parsons1, Alex Schuddeboom1, Peter Kuma1

4D drones: Wolfgang Rack1, Josh McCulloch1, Mike Harvey2, Richard Querel2

The Deep South Clouds and Aerosols

31 2

Model Radiation errors CMIP5 model clouds do not reflect enough sunlight over the Southern Ocean.

Ensemble mean error for CMIP5 models in shortwave radiation absorbed by the Earth System. Positive values indicate too much shortwave radiation absorbed at surface (Trenberth and Fasullo 2010).

Incl - IPCC AR5, 2013: Fig 9.5

Wm-2

What is underlying this problem?Candidates:• Model deficiencies in representing cloud microphysical processes, that can

affect both cloud radiative properties and lifetime that are linked to: Aerosol-Cloud Interactions (ACI)

• Model deficiencies in dynamical and convective processes and PBL parameterization

• Inadequate parameterisation of small sub-grid processes

What properties are specific to the Southern Ocean in ACI – 1/ Ice Nuclei 2/ Cloud Condensation Nuclei

Earth System variables (Jan 2016)

Small amount

Large amount

Seasonally small

Seasonally large

Southern Ocean – ice andmixed phase of water in clouds

Probability of cloud containing supercooled liquid water >-40°C McFarquhar et al. SOCRATES (Calipso)

Over the Southern Ocean, observations have shown a predominance of liquid water down to -20°C, a lower temperature than seen elsewhere

More liquid droplets~ brighter clouds

Bigg, 1973

Bigg & Hopwood, 1963

Role of aerosols (ACI) Ice Nuclei measurements

Very low ice nuclei numbers measured from Tangaroa 2015 in Ross Sea region, Antarctica

DeMott, PNAS 2016Sea spray aerosol as a unique source of ice nucleating particles

Proposed Source: organic exudates in sea-spray aerosol

CESM experiments:

Kay et al 2016Experiments with Tice and tuning glaciation temperature from -5°C to -20°C:

Zonal global mean ctl has excessive absorbed solar radiation over Southern ocean

e.g. ESM model experiments with cloud phase

2/ Role of aerosols - ACI Cloud condensation nuclei (CCN)

Aerosol

Cloud

0.01 0.1 1Diameter /µm

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

dN/d

log(

d) /c

m-3

East Antarctic Plateau 1990 / 91Butter Point, Antarctic Coast 1988Baring Head January 1993Pacific Free Troposphere 1987Extended Cape Grim SpectrumEquatorial Boundary Layer Tarawa, 1987Macquarie Island Sea Level (4 m/s wind) 1995Macquarie Is Sea Level (20 m/s wind) 1995

Measured size spectra (Active Scattering Aerosol Spectrometer Probe) ASASP-100X

Sea saltMass mode

AccumulationMode

AitkenMode

MH/NIWA + Cape Grim +Measurements – Aerosol at the surface in Antarctica with air blowing off the continent can contain less particles than in the mid-latitude free troposphere

Southern Ocean Cloud Experiment (SOCEX)

Seasonal cycles of cloud drop concentration (Nd) and CCN concentration over the Southern Ocean.

Nd data are derived from from MODIS (red), limited aircraft flights during winter and summer (black squares), and measurements at Cape Grim (Ayers and Gras 1991).

294 295 296 297θq /K

4.5

4.7

4.9

5.1

5.3

5.5

5.7

5.9

6.1

6.3

Q /g

kg-1

(a) SOCEX-1 flight 930716.a descent 1 sub-cloud

305.5 306.0 306.5 307.0 307.5 308.0 308.5θq /K

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

Q /g

kg-1

(b) SOCEX-2 flight 950201.a descent 2 sub-cloud

300.5 301.0 301.5 302.0 302.5 303.0 303.5θq /K

5.0

5.2

5.4

5.6

5.8

6.0

6.2

6.4

6.6

6.8

Q /g

kg-1

(c) SOCEX-2 flight 950208.b descent 1 sub-cloud

0 20 40 60 80 100 120 140 160 180 200

Number /cm-3

0

500

1000

1500

2000

Pre

ssu

re a

ltitu

de /

m

ASASPFSSP

(a) SOCEX-1 930716.a descent 1

0 20 40 60 80 100 120 140 160 180 200

Number /cm-3

0

500

1000

1500

2000

Pre

ssu

re a

ltitu

de /

m

ASASPFSSP

(b) SOCEX-2 950201.a descent 2

0 20 40 60 80 100 120 140 160 180 200

Number /cm-3

0

500

1000

1500

2000

Pre

ssu

re a

ltitu

de /

m

ASASPFSSP

(c) SOCEX-2 950208.b descent 1

Boundary layer aerosol-cloud soundings

Case studies from the Southern Ocean Cloud Experiment SOCEX (M Harvey)

Blue vertical lineMean in following figure

Grey: Cloud droplets in marine stratocumulus

Red: Aerosol

Aerosol profilediagram

“Paluch” mixingdiagram

CASE1: well-mixed winter

CASE2: poorly mixed summer

CASE3: well mixed summer

Representing aerosol through modal scheme GLOMAP-mode in GCM’sTwo-moment (mass and number) modal microphysicsComponents: Sulfate, sea-salt, black and organic carbonProcesses: nucleation, scavenging, deposition, condensation, coagulation, sulfur chemistry, ageing

Matt Woodhouse, CSIROCSIRO – NIWA collaboration using GLOMAP in meteorological context to look at marine aerosol sources in the SOAP experiment

Summary• Antarctic aerosol climatology and its sources have regionally specific

characteristics• Low IN numbers, low AOD, seasonally varying aerosol (biogenic source in

summer), high frequency of low clouds• Aerosol can strongly influence cloud and climate in the region through aerosol-

cloud interactions but the remoteness means this is sparsely observed• There are specific micro-physical aspects that need special consideration in

modelling cloud in the region• Remote sensing alone cannot determine all key physical and chemical

properties of the aerosol• Organic processes and aerosol have less well quantified role in nucleation and

nuclei properties (and are likely important in summer Southern waters)• Complexities and inherent variability in key components will guide thinking on

observation – model interaction

Southern Sulfur/Aerosol/Cloud StudiesEarly ANZ Antarctic aerosol observation 1960s - 1990SOCEX (1993-95) CCN, Aerosol-Cloud InteractionACE-1 (1995) ACI indirect effects on clouds

SOIREE (1999) Iron, plankton & DMS

SCHeMe (2000-02) nssCa, O3, SO4 aerosol

SAGE (2004) Iron, plankton & DMS

PtoP (2006) Precursors to Particles SOA, halogens

SOAP (2011-12) plankton, DMS, VOC, CN, CCN

RtoR (2016) Reef to Rainforest - coral symbionts to cloud properties, DMS, VOC, CN, CCN,

S-ACI-MEE (2018) TAN1802 Antarctic Marine Environment and Ecosystems voyage ACI

SOCRATES (2018) CCN, Aerosol-Cloud Interaction

CAPRICORN (2018): Clouds, Aerosols, Precipitation Radiation and atmospheric Composition Over the southeRN ocean

AcknowledgementsTAN 2015: Paul deMott1, Tom Hill1, Blake Hornblow2

SOCEX3: Jorgen Jensen, Reinout BoersSOAP: Cliff Law, Sarah Lawson3, Zoran Ristovski4, Luke Cravigan4 et al.GLOMAP: Matthew Woodhouse3

Colorado State Uni (1), Sir Peter Blake trust(2) CSIRO(3) QUT (4)

SOLAS Science Plan2015 - 2025