April 2007EGU Assessment of Global Cloud Climatologies Claudia Stubenrauch + GEWEX cloud assessment group (S. Ackerman, R. Eastman, A. Evans, A. Heidinger, B. Maddux, P. Minnis, J. Norris, W. B. Rossow, S. Sun-Mack, P.-H. Wang, S. Warren, D. Wylie)Co-chairs: B. Baum, SSEC, University of Wisconsin, USA C. Stubenrauch, CNRS/IPSL - Laboratoire de MtorologieDynamique, France project of GEWEX Radiation Panel / WCRP April 2007EGU Satellite radiometers measure: emitted, reflected, scattered emitted, reflected, scattered radiation cloud detection inverse radiative transfer INVERSION cloud properties GEO (3hrs)+polar polar satellites (12/6 hrs) ISCCPPATMOS-xUW HIRSTOVS Path-B ISCCP PATMOS-x UW HIRS, TOVS Path-B IR,VIS IR,NIR,VIS IR Vertical Sounder: CO 2 -band MODISAIRS MODIS AIRS April 2007EGU Climate monitoring: Climate monitoring: trends and where they can originate from Evaluation & analysis of cloud properties: average, regional, seasonal and interannual variations, diurnal cycle Longterm cloud climatologies: ISCCP ISCCP GEWEX cloud dataset (Rossow et al. 1999) PATMOS-x PATMOS-x AVHRR (NESDIS/ORA; Heidinger) UW-HIRS UW-HIRS 13h30/1h (Wylie et al. 2005) TOVS Path-B TOVS Path-B 7h30/19h (Stubenrauch et al. 2006) SAGE SAGE limb solar occultation , (Wang et al. 1996, 2001) SOBS SOBS (Surface Observations): (sea), (land) (Hahn & Warren 1999; 2003) EOS cloud climatologies : EOS cloud climatologies (since 2000, 2002) : MODIS CERES-MODIS MODIS (Ackerman et al.) CERES-MODIS (Minnis et al.) AIRS AIRS (Susskindet al.; Stubenrauch et al.) workshop: 6-7 July 2006 in Madison, USA: 20 presentations, 50 participants April 2007EGU ISCCP ISCCP (Rossow & Schiffer BAMS, 1999) night: +75 hPa p cld bias (Stubenrauch et al. 1999) uncertainties depend on cloud type: Stratus ( cld >5): p cld hPa within radiosonde meas., ~ -65 hPa bias; err T cld 5, with diffuse top ): p cld 150 hPa (trp)/ 50 hPa (midl) above top isolated thin Cirrus: difficult to detect thin Cirrus above low clouds: often identified as midlevel or lowlevel cloud 15% cld decrease for doubling droplet size TOVS Path-B TOVS Path-B (Stubenrauch et al. J. Clim. 2006) p cld uncertainty 25 hPa over ocean, 40 hPa over land (2 nd 2 solution) p cld = mid-cloud p cld, : 600m/ 2 km below cloud-top (low/high clouds) (LITE, Stubenrauch et al. 2005) Sensitivity study for D e of Ci (Rdel et al. 2003) UW HIRS UW HIRS (for Wylie & Menzel J. Clim. 1999, not yet for Wylie et al. J. Clim. 2005) p cld 70 hPa above top (lidar, Wylie & Menzel 1989) 100 hPa above for transmissive cloud overlying opaque cloud (Menzel et al. 1992) Evaluation April 2007EGU JanuaryJuly Geographical distribution of HCA ISCCP TOVS Path-B UW-HIRS ITCZ winter strom tracks SAGE DJFSAGEJJA April 2007EGU Average CA 70 % (5%) cloud amount: 5-15% more over ocean than over land CE-MODIS low, PATMOS low over land, SAGE CA (200km, clds >0.03) 1/3 higher 40% single-layer low clouds: more over ocean than over land; SOBS 40% high clouds: only 3% thick Ci; more over land than over ocean IR sounders ~ 10% more sensitive to Ci than ISCCP SAGE cloud vertical structure in good agreement with IR sounders HCA/CA: SAGE,TOVS/HIRS > CE-MODIS > PATMOS > ISCCPday > MODIS > ISCCPnght diurnal sampling, time period for ISCCP / TOVS-B : 1% effect; low-level over land: 2% can be more important if using afternoon satellites (D. Wylie, A. Evan) April 2007EGU CA seasonal cycle over land Seasonal (& diurnal) cycles: stronger over land than over ocean and strongest in subtropics (ITCZ) seasonal cycles similar, exception: SH polar land and newer datasets (PATMOS, MODIS) TOVS/HIRS CA 5-12% larger than ISCCP & PATMOS UW-HIRS TOVS-B ISCCP PATMOS-x MODIS CE-MODIS SOBS 30-60N 0-30N 0-30S April 2007EGU HCA seasonal cycle : 7-15%,10-27%, 18-45% ISCCP underestimates seasonal cycle of HCA by up to 20% UW-HIRS slightly smaller seasonal cycle than TOVS-B PATMOS & MODIS HCA too low in NH midlatitudes SOBS HCA seasonal cycle modulated by clouds underneath HCA seasonal cycle over land UW-HIRS TOVS-B ISCCP PATMOS-x MODIS CE-MODIS SOBS 30-60N 0-30N 0-30S HCAHCA April 2007EGU TOVS Path-B: diurnal cycle of high clouds max. thin cirrus in early afternoon max Cb (ISCCP) in early evening max. cirrus and thick (large-scale) cirrus in evening cirrus occurrence continues during night and decreases during day TOVS-B extends ISCCP during night NOAA10/12 7h30 AM&PM, NOAA11 2h00 AM&PM( ) NOAA11 4h30 AM&PM( ) strongest diurnal cycles over land, in tropics (& in midlat summer) Stubenrauch et al. J. Climate 2006 April 2007EGU Global CA anomalies E 3 sat 4 sat.5 sat. global CLA within 2.5% UW-HIRS: more or less stable ISCCP: ~5% decrease from 1987 to 2000 related to increasing nb of GEO satellites ? SOBS: increasing over ocean, stable over land >1985 (Warren et al. J. Clim. 2006) April 2007EGU CA change : cluster analysis correcting for artefacts J. Norris6 clusters out of 7 related to artificial satellite features: sea-ice: Oct-Dec 2004, high lat land: > Oct 2001(NOAA16) nb of GEOs - view angle, GEO view area also (Evan et al. GRL 2007) April 2007EGU Changes in Cloud Property Distribution : decreasing of low clouds -> below detection ( Tselioudis et al : decreases with T) CUMULUS Anomaly per cloud type W. B. Rossow April 2007EGU Trend analysis of high clouds: synergy of different variables Tropics (Wang et al., J. Clim., 2007, in rev.) : decreasing NCEP humidity suggests decrease in HCA SAGE: thinner & lower high clouds in tropics rather than simple HCA decrease cause of UTH drop? Is it real? stronger increase related to contrails in NH RH ice 0.4 RH* crit increase of thin Ci in both hemispheres Midlatitudes (Stubenrauch & Schumann, GRL 2005) : April 2007EGU Satellite observations: unique possibility to study cloud properties over long period Intercomparisons: average cloud properties: in general good agreement 70% (5%) clouds: ~ 40% high clouds & ~40% single-layer low clouds HCA/CA: SAGE > TOVS/HIRS > CE-MODIS > PATMOS > ISCCPday > MODIS > ISCCPnght PATMOS-x & EOS datasets still in validation process seasonal cycle: CA good agreement (except SH polar land) ISCCP HCA cycle in tropics underestimated SOBS LCA cycle over ocean smaller; absolute value 18% larger regional differences (latitudinal, ocean/land): linked to cirrus sensitivity: IR sounders & SAGE : HCA +4% (midl) to +20 % (trp) atmos. profiles: TOVS B less HCA in SH compared to SAGE & HIRS diurnal cycle: TOVS-B extends ISCCP during night Trend analysis: careful of satellite drifts, calibration etc. synergy of different variables important ! Evaluation continues & WMO report in preparation