[1] The first 2 year measurements from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and CloudSat radar were analyzed to study the distribution and phase partition of midlevel liquid-layer topped stratiform clouds (MLTSC, top higher than 2.5 km above the Earth's surface and top temperature warmer than À40°C) globally. The global mean MLTSC occurrence was $7.8% and the global mean MLTSC percentage fraction related to all midlevel clouds was $33.6%. Strong seasonal and day-night variations of MLTSC occurrence were observed over different latitude regions. In the polar regions, the maximum occurrence was in summer, while the minimum occurred in winter, with small day-night differences. In the tropics, a high MLTSC occurrence band shifted southward from June -July -August to DecemberJanuary -February with significantly more MLTSC during the nighttime. The global mean MLTSC top height and temperature were $4.5 km above the surface and À13.6°C. Overall, 61.8% of MLTSCs were mixed phase and 12.4% were supercooled liquid (contains only liquid phase or with ice below the detection limit). The fraction of mixed-phase MLTSC increased as the cloud top temperature decreased, with a sharp increase between À10 and À15°C and a noticeable latitude difference. This temperature dependence indicated that ice nucleation is active at À10°C in these clouds. The global mean ice water path (IWP) of mixed-phase MLTSCs, estimated based on an empirical temperature -radar reflectivity -ice water content relationship, was $13.4 g/m 2 , and the IWP increased as cloud top temperature decreased. To improve MLTSC parameterizations in global climate models, further studies are needed to better understand the latitude dependence of MLTSC distributions and microphysical properties and how aerosol and water phase cloud properties affecting ice generation in MLTSCs.Citation: Zhang, D., Z. Wang, and D. Liu (2010), A global view of midlevel liquid-layer topped stratiform cloud distribution and phase partition from CALIPSO and CloudSat measurements,
[1] A survey of the frequency and characteristics of precipitation from low clouds over the oceans based on data from CloudSat and CALIPSO from July 2006 through June 2007 is presented. The low-cloud fraction, drizzle occurrence, and estimated cloud base precipitation rate are examined globally and for eight subtropical and midlatitude stratocumulus (Sc) regions. This analysis is restricted clouds below 4 km. Drizzle detection and characterization is further restricted to clouds with tops above 1 km altitude. The maximum radar reflectivity within an individual CloudSat profile (Z max ) is used to classify the profile as precipitating or nonprecipitating. The distribution of Z max for all profiles is bimodal with peaks around À23 and À12 dBZ interpreted as originating from populations of nondrizzling and drizzling clouds, respectively. Profiles where Z max exceeds À18 dBZ are classified as drizzling. Drizzle is detected for 19-34% of cloudy profiles in the subtropical Sc regions and 37-44% of profiles from the midlatitude Sc regions. The cloud base precipitation rate is estimated using the relation: R cb = 2 Á Z max 0.7 . The lower quartile/median/upper quartile precipitation rates are 0.25/0.6/2.0 mm d À1 for the subtropical Sc regions and 0.28/0.7/2.3 mm d À1 for midlatitude regions. A consistent nighttime increase in low-cloud fraction and drizzle occurrence is observed for the subtropical Sc regions. For clouds with r eff > 17 mm the drizzle occurrence can be treated as a function of LWP alone and exceeds 50% (75%) for a LWP of 50 (110) g m À2 . For r eff < 17 the drizzle occurrence is strongly dependent on both LWP and r eff .
Abstract. This paper is an overview of the progress in sky radiometer technology and the development of the network called SKYNET. It is found that the technology has produced useful on-site calibration methods, retrieval algorithms, and data analyses from sky radiometer observations of aerosol, cloud, water vapor, and ozone. A formula was proposed for estimating the accuracy of the sky radiometer calibration constant F0 using the improved Langley (IL) method, which was found to be a good approximation to observed monthly mean uncertainty in F0, around 0.5 % to 2.4 % at the Tokyo and Rome sites and smaller values of around 0.3 % to 0.5 % at the mountain sites at Mt. Saraswati and Davos. A new cross IL (XIL) method was also developed to correct an underestimation by the IL method in cases with large aerosol retrieval errors. The root-mean-square difference (RMSD) in aerosol optical thickness (AOT) comparisons with other networks took values of less than 0.02 for λ≥500 nm and a larger value of about 0.03 for shorter wavelengths in city areas and smaller values of less than 0.01 in mountain comparisons. Accuracies of single-scattering albedo (SSA) and size distribution retrievals are affected by the propagation of errors in measurement, calibrations for direct solar and diffuse sky radiation, ground albedo, cloud screening, and the version of the analysis software called the Skyrad pack. SSA values from SKYNET were up to 0.07 larger than those from AERONET, and the major error sources were identified as an underestimation of solid viewing angle (SVA) and cloud contamination. Correction of these known error factors reduced the SSA difference to less than 0.03. Retrievals of other atmospheric constituents by the sky radiometer were also reviewed. Retrieval accuracies were found to be about 0.2 cm for precipitable water vapor amount and 13 DU (Dobson Unit) for column ozone amount. Retrieved cloud optical properties still showed large deviations from validation data, suggesting a need to study the causes of the differences. It is important that these recent studies on improvements presented in the present paper are introduced into the existing operational systems and future systems of the International SKYNET Data Center.
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