David Painemal

Assessment of MODIS cloud effective radius and optical thickness retrievals over the Southeast Pacific with VOCALS-REx in situ measurements

[1]xa0Cloud microphysical observations collected in situ during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment within the Chile-Peru stratocumulus cloud deck during October–November 2008 were used to assess MODIS Level 2 cloud property retrievals. The in situ aircraft-derived cloud property values were constructed from the drop size distributions measured by the Cloud Droplet Probe (drop diameter <52 micron) and Two-Dimensional Cloud Probe (drop diameters up to 1600 micron) during 20 vertical profiles. Almost all of the MODIS cloud scenes were highly homogeneous. MODIS cloud optical thickness correlated well with the aircraft-derived value with a slight offset within instrumental/retrieval uncertainties. In contrast, the standard 2.1 micron-derived MODIS effective radius (re) systematically exceeded the in situ cloud top reby 15%–20%, for an absolute error that increased with droplet size. The individual effective radius retrievals at 1.6, 2.1, and 3.7 micron did not provide additional information on cloud vertical structure for our data sample. The secondarily derived MODIS liquid water path also exceeded the in situ value. A MODIS-derived cloud droplet number concentration (Nd) estimate agreed the best of the four MODIS variables with the aircraft observations. The analysis also highlighted a lack of agreement in published satellite-derivedNd values, despite drawing on the same sources. A best a priori formula choice for Nd is likely to vary regionally. Four sources of errors within the MODIS reretrieval were investigated further: the cloud mode droplet size distribution breadth, the presence of a drizzle mode, above-cloud water vapor absorption, and sensor viewing angles. These processes combined conspired to explain most of the observed bias. The above-cloud water vapor paths were poorly specified, primarily because the cloud top heights are placed too high, and secondarily because the water vapor paths are unrealistic. Improvement of the above-cloud water vapor path specification can most easily and systematically improve the MODIS effective radius and liquid water path retrievals.

Stratocumulus Cloud-Top Height Estimates and Their Climatic Implications

A depth-dependent boundary layer lapse rate was empirically deduced from 156 radiosondes released duringsixmonth-longresearchcruisestothe southeastPacificsamplingavarietyofstratocumulusconditions. Thelapse-ratedependenceonboundarylayerheightisweak,decreasingfromabestfitof7.6to7.2K km 21 as theboundarylayerdeepensfrom800mto2km.Ship-basedcloud-baseheightsupto800mcorrespondwellto liftingcondensationlevels,indicatingwell-mixedconditions, withcloud bases .800moften 200‐600m higher than the lifting condensation levels. The lapse rates were combined with Moderate Resolution Imaging Spectrometer 11-mm-derived cloud-top temperatures and satellite microwave-derived sea surface temperatures to estimate stratocumulus cloud-top heights. The October-mean cloud-top height structure of the southeast Pacific was then spatially and diurnally characterized. Coastal shoaling is apparent, but so is a significant along-coast cloud-top height gradient, with a pronounced elevation of the cloud-top heights above theAricaBightat ;208S.Diurnalcloud-topheightvariations(inferredfromirregular4-times-dailysampling) can locally reach 250 m in amplitude, and they can help to visualize offshore propagation of free-tropospheric vertical motions. A shallow boundary layer associated with the Chilean coastal jet expands to its north and west in the afternoon. Cloud-top heights above the Arica Bight region are depressed in the afternoon, which may mean that increased subsidence from sensible heating of the Andes dominates an afternoon increase in convergence/upward motion at the exit of the Chilean coastal jet. In the southeast Atlantic during October, thestratocumuluscloud-topheightsaretypicallylowerthanthoseinthesoutheastPacific.Acoastaljetregion can also be identified through its low cloud-top heights. Coastal shoaling of the South Atlantic stratocumulus region is mostly uniform with latitude, in keeping with the more linear Namibian/Angolan coastline. The southeast Atlantic shallow cloudy boundary layer extends farther offshore than in the southeast Pacific, particularly at 158S.

Mean Structure and Diurnal Cycle of Southeast Atlantic Boundary Layer Clouds: Insights from Satellite Observations and Multiscale Modeling Framework Simulations

AbstractThe mean structure and diurnal cycle of southeast (SE) Atlantic boundary layer clouds are described with satellite observations and multiscale modeling framework (MMF) simulations during austral spring (September–November). Hourly resolution cloud fraction (CF) and cloud-top height (HT) are retrieved from Meteosat-9 radiances using modified Clouds and the Earth’s Radiant Energy System (CERES) Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms, whereas liquid water path (LWP) is from the University of Wisconsin microwave satellite climatology. The MMF simulations use a 2D cloud-resolving model (CRM) that contains an advanced third-order turbulence closure to explicitly simulate cloud physical processes in every grid column of a general circulation model. The model accurately reproduces the marine stratocumulus spatial extent and cloud cover. The mean cloud cover spatial variability in the model is primarily explained by the boundary layer decoupling strength, whereas a boundary layer ...

Southeast Pacific Stratocumulus: High-Frequency Variability and Mesoscale Structures over San Felix Island

Abstract Stratocumulus cloud cover patterns and their relationship to drizzle were characterized at San Felix Island (SFI; 26.5°S, 80°W) in the southeast Pacific Ocean. Small closed, large closed, and open cells were identified in about 65% of the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images during 2003. The MODIS imagery was combined with ceilometer and surface meteorological measurements, human observations of cloud types and drizzle, and large-scale meteorological analyses for January through June. The authors identified two drizzle regimes: a synoptically quiescent summer (January–March) regime characterized by a strong anticyclone, large closed cells, and frequent drizzle, and an autumn (April–June) regime characterized by a weaker anticyclone, small closed cells and open cells, and precipitation that was mainly associated with synoptic activity. The large closed cells had higher mean cloud bases and tops than the small closed cells and accounted for 45% of the cumulus-under...

The Diurnal Cycle of Cloud-Top Height and Cloud Cover over the Southeastern Pacific as Observed by GOES-10

The diurnal cycles in cloud-top height Htop and cloud fraction (CF) in the southeastern Pacific stratocumulus region were determined for October–November 2008 by analyzing data from Geostationary Operational Environmental Satellite-10 (GOES-10) according to a diurnal/semidiurnal harmonic fitting technique. The value of Htop was obtained by applying a formula based on a linear regression of the differences between GOES-10 cloud-top temperature and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) satellite sea surface temperature, with a common 0.25 83 0.258 spatial resolution. A satellite liquid water path (LWP) climatology complemented this dataset. Southwestward transects ofHtopandLWPanomaliesreveala coherentpropagatingsignalfrom thecoast in the afternoon, with a typical phase speed of 25ms 21 . This pattern is preceded by a subsidence wave that reaches its peak a few hours before the maximum in Htop and LWP anomalies. Coincident increases in LWP and Htop after the subsidence wave passes suggest that the boundary layer deepening promotes cloud thickening and increased LWP, which are likely maintained through a well-mixed boundary layer and sufficient moisture fluxes that can counteract the effect of dry air entrainment. The interference between the radiatively and subsidence wave–driven cycles gives rise to a semidiurnal cycle in Htop along the coast. While thesemidiurnalamplitudeisnear80m closetothecoastwithafractionofexplainedvariancegreaterthan0.4, it decreases to 30m offshore (808W). Similar to Htop, CF also exhibits contrasting zonal differences, but with a smaller semidiurnal component. The phase of the semidiurnal harmonic resembles the subsidence propagation westward, and the noticeable land–sea breeze circulation at 268S that extends 200km offshore.

Cloud occurrences and cloud radiative effects (CREs) from CERES‐CALIPSO‐CloudSat‐MODIS (CCCM) and CloudSat radar‐lidar (RL) products

Two kinds of cloud products obtained from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) are compared and analyzed in this study; Clouds and the Earths Radiant Energy System (CERES)-CALIPSO-CloudSat-MODIS (CCCM) product and CloudSat radar-lidar (RL) products such as GEOPROF-LIDAR and FLXHR-LIDAR. Compared to GEOPROF-LIDAR, low-level ( 40°). The difference occurs when hydrometeors are detected by CALIPSO lidar but are undetected by CloudSat radar. In the comparison of cloud radiative effects (CREs), global mean differences between CCCM and FLXHR-LIDAR are mostly smaller than 5 W m-2, while noticeable regional differences are found. For example, CCCM shortwave (SW) and longwave (LW) CREs are larger than FXLHR-LIDAR along the west coasts of Africa and America because the GEOPROF-LIDAR algorithm misses shallow marine boundary layer clouds. In addition, FLXHR-LIDAR SW CREs are larger than CCCM counterpart over tropical oceans away from the west coasts of America. Over midlatitude storm-track regions, CCCM SW and LW CREs are larger than FLXHR-LIDAR counterpart.