A Non-POC HYPOTHESIS (A. Clarke): The persistence of the adjacent Scu clouds that define a POC region is sustained as a result of entrainment of aged aerosol (biomass burning and other) when it overlies the SCu deck. At times this may be a result of above cloud aerosol transport in ESE flow from Chile. POC regions in these clouds are a predictable response to a drizzling Scu cloud deck when the source of aerosol is not being resupplied from entrainment from the FT (or the surface). Drizzle in POC from thin cloud on RF07 What we observe. POCs appear as breakup regions in more persistent stratus. POCs tend to have lower CO (and Ozone) than adjacent SCu regions: suggesting a 15-30% lower enhancement compared to St after background (50pptv) subtracted. Elevated CO and Ozone over strong inversion has large accumulation mode mass mean diameter (300nm) and often a biomass burning signature in AMS and volatility. Boundary layer aerosol size (160nm), composition and concentration in POC is indicative of clean marine air. Probably grown from 90nm FT aerosol subsiding in high near 30S and 95W. About /cm3. Often nearer 300nm above cloudy region and 200nm below (a mix of 150nm and 300nm peaks?) Aerosol concentrations in aged combustion aerosol above cloud have size and number adequate to sustain MBL CCN when entrained and can resupply CCN from smaller sizes as they grow MBL processes that add sulfate etc. NEXT FIGURES SHOW ENHANCED CO and Black Carbon AROUND POCs ON FLIGHTS RF6 and enhanced CO for RF7,RF09 VOCALS RF06 10/28/08 POC Mission CO mixing ratio (pptv) VOCALS RF06 10/28/08 POC Mission CONCN (low shatter CN) #/cc SP2 Black Carbon on Flight RF06 Highest values aloft and under cloudy parts of POC leg. VOCALS RF06 10/28/08 POC Mission Mixing Ratio g/kg and Winds for POC legs NOTE: Wind barbs for above cloud leg (darker track) with higher CO are ESE compared to SE below in MBL. This is also evident in shallow above cloud layer on other flights indicative of possible transport of this layer aloft from Chile. Winds at higher altitudes are typically westerly Above Cloud Below Cloud VOCALS RF07 10/31/08 POC Mission CO (pptv) dark blue ~ background VOCALS RF07 10/31/08 POC Mission CO (pptv) dark blue ~ background VOCALS RF09 10/28/08 POC Mission CO (pptv) Examples of Number Distributions at various altitudes Inside and Outside of POCs NUMBER Droplet Shatter in Cloud Nominal 0.2% More scavenging of aerosol in POC Lower entrainment of aerosol from aloft?? More processing/growth out of POC Higher entrainment of aerosol from aloft?? 70/cc 15/cc 2/cc 10/cc 70/cc 90/cc Copiapo, 1450m 130,000pop Coquimbo, 50m 160,000C Cuiacamata Cu Smelter # worlds largest 2800m # EXAMPLE OF APARRENT CLOUD ENHANCEMENT IN ARC FROM COPAIPO ?ARE SUCH FEATURES RELATED TO AEROSOL OUTFLOW ABOVE CLOUD? SOME RELATED PAPERS Coastal Lows along the Subtropical West Coast of South America: Numerical Simulation of a Typical Case, R. Garreaud and J. Ruttlant, Monthly Weather Review, v131, May, Mesoscale Wind Regimes in Chile at 30S, N. Kalthoff et al. Jour. Appl. Met., 41, Sept Diurnal Circulation of the Bolivian Altiplano. Part 1- Observations, J. Egger et al. Monthly Weather Review, April 2005.