1
synoptic only covariance 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.15 −0.1 −0.05 0 0.05 0.1 0.15 Covariance of ISCCP adjusted low cloud with EIS. Posi9ve values (red) in the subtropics and eastern tropical Atlan9c and Pacific Oceans indicate cloud amounts are greater for more stable condi9ons. Nega9ve values (blue) poleward of 45° la9tude show cloud amount increases for unstable condi9ons. • Synop9c (130 day) covariance is responsible for most of the total covariance (posi9ve and nega9ve) poleward of ±15° la9tude, including in the stratus regions. • In the deep tropics, seasonal covariance of cloud and EIS is responsible for much of the total covariance, especially over the eastern tropical Pacific and Atlan9c Oceans. Amplitudes are normalized to represent cloud frac9on anomalies associated with a standard devia9on of EIS. References Clement, A. C., R. Burgman, and J. R. Norris, 2009: Observa9onal and Model Evidence for Posi9ve LowLevel Cloud Feedback. Science, 325, 460464. Klein, S. A., and D. L. Hartmann, 1993: The seasonal cycle of low stra9form clouds. J. Climate, 6, 15881606. Rossow, W. B., and R. A. Schiffer, 1999: Advances in understanding clouds from ISCCP. Bull. Amer. Meteorol. Soc., 80, 22612287. Wood, R., and C. S. Bretherton, 2006: On the Rela9onship between Stra9form Low Cloud Cover and LowerTropospheric Stability. J. Climate, 19, 64256432, 10.1175/ JCLI3988.1. The authors acknowledge Joel Norris for his guidance in adjus@ng for satellite ar@facts in ISCCP cloud. This work was supported by the Office of Science (BER) U.S. Department of Energy grant DOE ASR DESC0006994. Marine low clouds and inversion strength Simon P. de Szoeke 1* , Sandra E. Yuter 2 , David B. Mechem 3 1 Oregon State University, Corvallis. 2 North Carolina State University, Raleigh. 3 University of Kansas, Lawrence. *corresponding author email address: [email protected] low cloud standard deviation 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 0 0.1 0.2 0.3 low cloud synoptic standard deviation 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 0 0.1 0.2 0.3 low cloud seasonal standard deviation 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 0 0.1 0.2 0.3 CERES "D1" 2000−2011 daylight low cloud amount 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 0 0.2 0.4 0.6 0.8 Top: Mean low cloud amount (CERES daylightonly) shows subtropical marine stra9form cloud decks near the Klein and Hartmann (1993) stratus regions (squares). Low cloud is defined to have cloud top below 560 hPa to include clouds in deep boundary layers. Right: ISCCP standard devia9on of low cloud amount (~0.3) is dominated by synop9c varia9ons, with a 0.1 contribu9on from the seasonal cycle in the southern stratus decks. 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.02 −0.01 0 0.01 0.02 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.015 −0.01 −0.005 0 0.005 0.01 0.015 Low clouds cool the climate by reflec9ng sunlight, shading the ocean surface, and emijng thermal radia9on at a warm temperature. Marine low cloud amount is correlated to lower tropospheric stability (θ 700hPa θ sfc ) on seasonal and interannual 9me scales (Klein and Hartmann 1993). Low cloud parameteriza9ons in many models are ac9vated by lower tropospheric stability criteria. Es9mated inversion strength (EIS, Wood and Bretherton 2006) measures inversion strength using standard analysis levels. A stronger inversion is presumed to limit entrainment of dry air into the boundary layer, aiding cloud forma9on and limi9ng cloud evapora9on. As surface climate warming would reduce inversion strength and thus cloud amount, the control of the inversion strength on marine low cloud represents a posi9ve climate feedback. We inves@gate the low cloudEIS rela@on on sub daily to interannual 9me scales with 26years of ISCCP D1 adjusted low cloud frac9on (Rossow and Schiffer 1999, Clement et al. 2009) and EIS from NCEP reanalysis. We find: 1. Synop@c variability is responsible for most EISlow cloud covariance throughout the subtropics and midla9tudes. Nega9ve synop9c covariance (unstablecloudy) is found at 4560° la9tude. Synop9c storm structure explains the midla9tude covariance. 2. The seasonal EISlow cloud (stablecloudy) correla9on (Klein and Hartmann 1993) dominates only in the southeastern tropical Atlan9c and Pacific Oceans. Beware of using Kleinline low cloud parameteriza@ons on @mescales other than seasonal. 3. Diurnal and interannual low cloudEIS covariance are 10x smaller than seasonal or synop9c variability. 4. Synop9c covariance of low cloud with downward ver@cal velocity is found in midla9tude storm tracks, especially over the western north Pacific and Atlan9c Oceans. The seasonal inversion strength varia@ons explain a small frac@on of low cloud variance around the globe. The processes responsible for marine low cloud correla@ons should be considered carefully when extrapola@ng these correla@ons to climate feedbacks. Interannual to diurnal power spectra of ISCCP adjusted cloud, EIS, and 700 hPa pressure velocity in the tropical stratus regions. Considerable energy lies in the broad synop9c band around 10 day period. We separate EIS and low cloud amount covariance into orthogonal interannual, seasonal, synop9c, and diurnal bands. longitude la9tude Low cloud varia9ons associated with diurnal and interannual varia9ons of EIS are small. longitude la9tude full low cloud covariance per standard deviation of omega 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.15 −0.1 −0.05 0 0.05 0.1 0.15 la9tude 4. longitude upwardcloudy downwardcloudy 3. What is responsible for the synop@c midla@tude lowcloud EIS covariance? Synop9c pamerns of EIS and low cloud regressed on downward 700hPa pressure velocity at 44°S, 61°E (cross). The EIS regression on pressure velocity 9lts northeastsouthwest in the southern hemisphere, while low cloud amount 9lts northwestsoutheast. Thus more low clouds are found in stable condi9ons equatorward of 45° and more low clouds are found in unstable condi9ons poleward of 45°, explaining the synop9c low cloudEIS correla9on (1) at len. Low clouds increase ~0.15 for a standard downward anomaly of 700 hPa pressure velocity (ω 700 ) in midla9tudes, especially the western Pacific and Atlan9c storm tracks, and the Atlan9c and Indian Southern Ocean. Low cloud response to ver9cal velocity is weak outside the midla9tudes, with clouds increasing slightly for upward mo9on outside of tropical convergence zones. low cloud−EIS covariance per standard EIS anomaly 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.1 −0.05 0 0.05 0.1 synoptic 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.1 −0.05 0 0.05 0.1 seasonal 60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60 −60 −45 −30 −15 0 15 30 45 60 −0.1 −0.05 0 0.05 0.1 less stable cloudy more stable cloudy longitude la9tude 1. 2. la9tude la9tude 10 -3 10 -2 10 -1 10 0 NEP 20-30°N 120-130°W 10 -3 10 -2 10 -1 10 0 NEA 15-25°N 25-35°W 10 -3 10 -2 10 -1 10 0 SEP 10-20°S 80-90°W 10 -3 10 -2 10 -1 10 0 SEA 10-20°S 0-10°E 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 -4 10 -3 10 -2 10 -1 -1 10 0 10 1 10 2 10 3 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 power spectral density [power / day ] -1 frequency [day ] inversion strength [K] cloud amount ω [Pa s ] 700 hPa -1 seasonal diel 20 40 60 80 100 120 −70 −65 −60 −55 −50 −45 −40 −35 −30 −25 −1 −0.5 0 0.5 1 K EIS anomaly correlated to downward velocity at H L 20 40 60 80 100 120 −70 −65 −60 −55 −50 −45 −40 −35 −30 −25 −0.15 −0.1 −0.05 0 0.05 0.1 0.15 H L la9tude stablecloudy unstablecloudy low cloud anomaly correlated to downward velocity longitude geopoten9al height contours every 10 m rms: 0.12 rms: 0.09 rms: 0.04 rms: 0.05 rms: 0.005 diurnal interannual ! ! room 1 poster 57 45°S c low ’s’ < 0 c low ’s’ > 0 ____ ____ – – – – – – – + + + + + + + – + + + + + + + + + – – – – – – – – – – – – – + + + + + + southern hemisphere
