Arctic Aerosol Research ActivitiesDorothy Koch GISS, Columbia University

I.I. Observations: ARCTASObservations: ARCTAS

1. GEOS-5, MODIS: Chu, Rodriguez, da Silva1. GEOS-5, MODIS: Chu, Rodriguez, da Silva

2. RSP: Cairns2. RSP: Cairns

II.II. Global modeling of aerosolsGlobal modeling of aerosols

3. Transport, HTAP: Shindell, Chin, 3. Transport, HTAP: Shindell, Chin, et al.et al.

4. Climate: Shindell4. Climate: Shindell

5. Climate: Koch 5. Climate: Koch et al.et al.

III.III. Modeling of aerosol - cloud interactionsModeling of aerosol - cloud interactions

6. GCM: Menon 6. GCM: Menon et al.et al.

7. Cloud scale: Fridlind 7. Cloud scale: Fridlind et al.et al.

GSFC Aerocenter March 4, 2008

GEOS-5 AOT on July 21, 2007

MODIS Terra on July 21, 2007ARCTAS – Arctic Research of the Composition of the Troposphere from Aircraft and SatellitesNASA field program based out of Fairbanks, AK (April 2008) and Cold Spring, Canada (June/July 2008) to study the transport pathways of atmospheric pollutants to the ARCTIC. GSFC: real-time aerosol and chemical forecasts with GEOS-5 model and near real-time satellite retrievals of aerosol properties from MODIS.

1. PI’s: Chu, Rodriguez, da Silva1. PI’s: Chu, Rodriguez, da Silva

Summer ARCTAS deployment: focus on forest fires

Frequency and altitude of pyro-convection: from TOMS Aerosol Index (AI).• LIDAR is CPL from McGill/Hlavka

at GSFC• AI is TOMS from Fromm at NRL.

ARCTAS - Summer: Research Scanning Polarimeter (RSP)

2. Cairns2. Cairns

Lidar: CPLLidar: CPL

TOMS AITOMS AI

• The Research Scanning Polarimeter (RSP is a proxy for APS on the NASA Glory mission) will fly on the same platform as the High Spectral Resolution Lidar (B200) during ARCTAS.

• Previous measurements have shown consistency between RSP retrievals of imaginary index, optical depth, size and aerosol top height with lidar (4.5 km) and TOMS AI (8.5).

• ARCTAS in situ measurements: evaluate RSP single scattering albedo. Lidar: evaluate determination of aerosol layer height.

ARCTAS - Summer

2. Cairns2. Cairns

Clear Smokey

RSP AOD

HTAPShindell et al.: A multi-model assessment of pollution transport to the Arctic

European pollution dominates near the surface.Other regions (e.g. SE Asia more important at higher altitudes.

3. Shindell et al.3. Shindell et al.

Shindell (GRL, 2007) Analyzed transient (1880-2000) simulations of Hansen et al. (2007), and found that Arctic surface air temperature changes correlate better to GLOBAL rather than LOCAL radiative forcings.

4. Shindell 4. Shindell

Koch, D., S. Menon, A. Del Genio, I. Alienov, R. Ruedy, G. Schmidt, Distinguishing

Aerosol Impacts on Climate During the Past Century, to be submitted to J. Clim.

5. Koch 5. Koch

Direct Indirect BC-albedo

Series of equilibrium climate experiments in GISS ModelE, with fully coupled aerosols and a slab ocean (1890 and 1995), distinguishing direct, indirect and BC-albedo effects

[Arctic]-

Arctic seasonality: Autumn cryospheric changes have wintertime temperature impact?

Indirect

BC-albedoDirect

5. Koch 5. Koch JAN JUL DEC JUL DEC

New schemeOld scheme

ModelE: New aerosol-cloud approach

Two-moment bulk cloud microphysics scheme (Morrison et al., 2005)

Number concentration and mixing ratio of Cloud drop, Cloud ice, Rain, Snow

First step: Added in prognostic equations for prediction of cloud droplets and ice crystals

Cloud Droplet Number Concentration

6. Menon 6. Menon

Ice crystal number concentration

Processes: heterogeneous freezing via immersion freezing (based on Bigg, 1953), and nucleation by deposition/condensation-freezing via the formulation of

Cooper (1986) as a function of temperature

Or

DeMott et al. (personal communication) as a function of dust aerosol number

.05

.05

Evaluation in progress

Second step: Switch on interactions between hydrometeors and examine changes to clouds.

Processes represented: Melting, freezing, collection, sedimentation, autoconversion, accretion, evaporation, condensation, deposition, sublimation 6. Menon 6. Menon

7. Fridlind, Ackerman: Cloud-scale modeling of field measurements 7. Fridlind, Ackerman: Cloud-scale modeling of field measurements Ice Particle Formation and a NEW Arctic Aerosol Indirect Effect?

• Publication: “Ice Properties of Single-Layer Stratocumulus during M-PACE. Part II: Model Results” by Fridlind, Ackerman, et al. (JGR, 2007)

• NEW AIE: Under polluted conditions, ice formation is inhibited, increasing LWP (important for LW cloud effects) via reduced desiccation

• Detailed simulations of mixed-phase Arctic stratus: known ice formation mechanisms produce two orders of magnitude fewer crystals than measured

• But ice formation mechanisms related to liquid drop evaporation (hypothesized since the 1950’s) are a viable explanation