Precipitation and albedo variability in marine low clouds Robert Wood Duli Chand, Tad Anderson, Louise Leahy, Jayson Stemmler, Robert J Charlson, Terry Kubar, Dennis Hartmann University of Washington

Cloud cover and albedo monthly means, Bender et al. (2009) Mean albedo α and cloud cover fc remarkably linear  near-constancy of mean cloud albedo αcloud

Chand et al. Nature Geosciences (2009) Practical uses..... Chand et al. Nature Geosciences (2009)

Near-constant mean cloud albedo remarkable in the face of significant cloud morphological changes across regions Near coast offshore Far offshore near coast probability LWP

The importance of optically thin low clouds ...the MODIS perspective

The importance of optically thin low clouds ...the CALIPSO perspective Continuum region (Charlson et al. 2007) consists primarily of optically thin low cloud Integrated attenuated backscatter

Do low cloud droplet concentrations favor thin clouds? inconsistent (?) with Jiang, Feingold and Koren, 2009, J. Geophys. Res.

Optically thin low cloud associated with precipitation

Pockets of Open Cells (POCs) October 27/28th 2008 POC Lagrangian - BAe-146 & NSF C-130 100 km

MODIS 250 m visible imagery 100 km Ultraclean region MODIS 250 m visible imagery Optically thick cell walls Optically thin cell centers 10 km 50 km VOCALS NSF C-130, RF06, October 28, 2008. Photo Rob Wood

High clouds and blue sky visible Radar reflectivity Radar data Dave Leon Aircraft track 1.5 1.0 0.5 0.0 height [km] 0 5 10 15 20 km Liquid water content High clouds and blue sky visible Forward camera Cloud droplet concentration Downward camera Mean volume radius of cloud drops Ocean surface visible VOCALS C-130 Flight RF06 in pocket of open cells

GOES cloud effective radius (Minnis) 27 23 20 18 16 14 12 10 8 6 Visible imagery (MODIS)

Ultra-clean layer (UCL) Accumulation mode MBL top All particles aerosol-depleted layer Cumulus cloud Drizzle scavenging critical for understanding aerosol properties in remote marine boundary layer

Precipitation and cloud optical depth SE Pacific 70-110oW, 40oS-0oS dBZ Precip L.Heat [mm day-1] [W m-2] -15 0.15 5 -7.5 0.7 20 0 2.0 60

Precipitation drives cloud mesoscale dynamics Results from EPIC/VOCALS cruises (Bretherton et al. 2004, Wood et al. 2009)

without drizzle with drizzle Savic-Jovcic and Stevens (2007)

Aerosols, Clouds and Drizzle MODIS CloudSat Smelter locations Pollution Dave Leon U Wyoming Leon et al. J. Geophys. Res. (2009)

CloudSat: colors Model: lines Reflectivity in [LWP, Nd] space Kubar et al. (2009, JAS) Wood et al. (2009, JAS) Increasing relative importance of LWP over Nd at high rainrates CloudSat: colors Model: lines see also Suzuki and Stephens (2008)

Summary Remarkable near-constancy of mean cloud albedo Optically thin clouds prevalent (explaining the “continuum region”), often precipitating Precipitation rule rather than exception in low clouds Precipitation in low clouds sensitive to both cloud macrophysics (LWP) and microphysics (Nd)..... .....but as precip increases sensitivity to Nd weakens

Droplet conc, LWC variability, drizzle 300 250 200 150 100 50 1 0.1 0.01 10-3 10-4 10-5 Drizzle LWC Cloud drop conc. 0.2 0.15 0.1 0.05 85 80 75 70 Longitude [deg W] Std. dev of cloud LWC Drop conc. smaller offshore Clouds more variable offshore Drizzle greater offshore 85 80 75 70 Longitude [deg W]

Conceptual model of POC edge Cumulus-coupled MBL Well-mixed MBL Ultra-clean [CN = 20-50 cm-3, CCN = 5-20 cm-3] Clean [CN = 500-1000 cm-3, CCN = 100 cm-3]

POC formation Wood et al., 2008, J. Geophys. Res.

Cloud liquid water path (minnis)

Minimum values assumed in GCMs Distributions, for all VOCALS flights, of cloud droplet concentration (left) and droplet volume radius (right) for low (black), intermediate (blue) and high (red) liquid water content (qL), for coastal regions east of 77.5oW (top) and remote regions west of 77.5oW. Results show that in coastal regions east of 77.5oW cloud droplet growth is as expected from quasi-adiabatic growth, with droplet concentration approximately independent of liquid water content, and with droplet size increasing with qL. However, in remote regions, there is a population of extremely low cloud droplet concentration. These clouds are primarily found in clouds with low liquid water content. Interestingly, it is these low liquid water clouds that have the largest cloud drop sizes. This behavior is quite different from the behavior seen in the coastal clouds. Minimum values assumed in GCMs