John E. Yorks, M. McGill, S. Rodier, M. Vaughan, Y. Hu, D. Hlavka African Dust and Smoke Influences on Radiative Effects in the Tropical Atlantic Using CERES and CALIPSO Data Paper 8.3, AMS 2009 Annual Meeting, January 15, 2009, Phoenix, AZ

INTRODUCTION Complex cloud-aerosol interactions and their effects on the radiation budget are a major uncertainty in understanding climate –Aerosol direct effect –Aerosol indirect effects –Aerosol semi-direct effect –Elevated aerosol layers can limit solar radiation reaching clouds These interactions have been investigated previously using models and imaging sensors like MODIS and CERES –Dust from Asian dust storms has caused changes in cloud microphysics, resulting in a weakening of cloud SW and net radiative forcing (Huang et al., 2006) Africa is a primary source of atmospheric desert dust and smoke from biomass burning –Projects such as SAFARI (2000) and NAMMA (2006) have been dedicated to studying African aerosols J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

COLLOCATED DATA CALIPSO & CERES data from the month of July, was collocated (Track between UTC for each day) CERES: imager on Aqua satellite that measures broadband top- of-atmosphere (TOA) radiances CALIPSO: satellite w/ CALIOP dual wavelength backscatter lidar –Has advantages over imagers such as MODIS Provides vertical profiles of clouds and aerosols w/ 60 m vertical resolution Better detection of multiple cloud/aerosol layers in same profile Allows for more accurate user classification of aerosol and cloud type using optical depth, layer height, depolarization ratio J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

PROFILE TYPES Cirrus: optically thin (0.1<COD<1.0) cloud with base height above 8 km Low Cloud: cloud with base height below 5 km (COD>0.1) Dust: Profiles with an aerosol layer of AOD>0.03 and depolarization ratio greater than 0.2 OR 0.07<depolarization ratio<0.2 and 40<S-ratio<60 Smoke: Profiles with an aerosol layer of AOD>0.03 and depolarization ratio less than 0.07 OR Cirrus Dust Smoke Low Cloud J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

PROFILE TYPES Profile Type ConstraintsSamples Pristine/Clearno cloud or aerosol layers present722 Cirrusaerosol-free profile with cirrus cloud1447 Low Cloudaerosol-free profile with low cloud5682 Dustcloud-free profile with dust layer2505 Smokecloud-free profile with smoke layer8476 Dust-Low Cloud (DLC)profile with a low cloud and dust layer3014 Smoke-Low Cloud (SLC)profile with a low cloud and smoke layer1261 Dust-Cirrus Cloud (DC)profile with a cirrus cloud and dust layer304 Smoke-Cirrus Cloud (SC)profile with a cirrus cloud and smoke layer244 * All profiles based on layers detected by CALIPSO J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

LAYER LOCATION J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

DUST & SMOKE TRANSPORT J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

CLOUD DIRECT EFFECTS Low cloud profiles have a greater SW cooling effect than thin cirrus –likely due to larger optical depths of low clouds (2.00) than cirrus (0.53). Cirrus have a stronger greenhouse effect than low clouds –LW radiative flux for cirrus clouds is W/m 2, which is 15% lower than low cloud profiles and 26% lower than pristine profiles –This is likely attributed to the difference in cloud height between cirrus (11.75 km) and low clouds (1.91 km) J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

LOW CLOUDS Dust decreases the SW flux of low clouds ~60 W/m 2 (23%) –Likely due to dust located above the cloud SLC profiles have mean SW TOA radiative flux that is ~30 W/m 2 lower than Low Cloud profiles –Changes in cloud microphysics likely dominant factor LW flux relatively insensitive to aerosol-low cloud interactions (Change of less than 5%) J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

DUST HEIGHT Majority of dust layers (~70%) in DLC profiles are found above 3 km and above the majority of low clouds Elevated dust layers absorb and scatter solar radiation which can: –Inhibit radiation from reaching the cloud –Warms air in the vicinity of cloud top –Evaporates cloud particles located in the upper part of the cloud (semi-direct effect) Aerosol TypeOptical DepthCIAB (sr-1)Particle Radius (um) DLC Low Cloud J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

SMOKE HEIGHT Majority of smoke layers (~70%) in SLC profiles are found below 3 km, at the same levels as the majority of low clouds (~85% below 3 km) Decreases in cloud optical depth (~25%), cloud integrated attenuated backscatter (~50%), and water particle radius reveal changes in cloud microphysics Aerosol semi-direct effect likely the dominant effect Aerosol TypeOptical DepthCIAB (sr-1)Particle Radius (um) SLC Low Cloud J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

CIRRUS CLOUDS The 3-year mean SW radiative fluxes for DC and SC profiles are 12% and 20% less than Cirrus profiles, respectively –Likely due to aerosol absorption below cloud or meteorological conditions –Changes in cloud microphysics occur, but not likely caused by aerosols SC and DC profiles have mean LW radiative fluxes of 235 W/m 2, nearly 7% greater than aerosol-free cirrus cloud profiles –Likely a results of a lower mean cloud height for aerosol-free cirrus cloud profiles J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

SUMMARY Dust and smoke aerosols pollute the Tropical Atlantic in July Low Clouds influence radiative effects over Tropical Atlantic more so than thin cirrus –Greater SW cooling and weaker Greenhouse effect Cloud-aerosol interactions have significant impact on climate of Tropical Atlantic through aerosol absorption above clouds and aerosol semi-direct effect –The decrease in low cloud SW radiative flux due to elevated Saharan dust layers can lead to a weakening of low cloud net cooling in excess of 30% Aerosol layer height and type are important factors in determining cloud-aerosol interactions –These factors are more accurately detected using the CALIPSO lidar than imagers such as MODIS J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ

Acknowledgments NASA’s Radiation Sciences Program funded this study. Special thanks to all the members of the CALIPSO and CERES science team for making the instrument data available. References Huang, J., P. Minnis, B. Lin, T. Wang, Y. Yi, Y. Hu, S. Sun-Mack, and K. Ayers, 2006: Possible influences of Asian dust aerosols on cloud properties and radiative forcing observed from MODIS and CERES. Geophys. Res. Lett., 33, L06824, doi: /2005GL Wielicki, B. A., et al.,1996: Clouds and the Earth’s radiant energy system (CERES): An Earth observing system experiment. Bull. Am. Meteorol. Soc., 77, 853– 868. Winker, D. M., J. R. Pelon, and M. P. McCormick, 2003: The CALIPSO mission: Spaceborne lidar for observation of aerosols and clouds, in Lidar Remote Sensing for Industry and Environment Monitoring III. edited by U. Singh, T. Itabe, and Z. Liu, Proc. SPIE Int. Soc. Opt. Eng., 4893, 1–11. Back trajectories from NOAA HYSLPIT and EDAS 40 km Meteorological fields ( MODIS daily active fire detection product for 17 July 2007 ( J. Yorks, Paper 8.3, AMS 2009 Annual Meeting, 15 January 2009, Phoenix AZ