scholarly journals Statistical Analyses of Satellite Cloud Object Data from CERES. Part V: Relationships between Physical Properties of Marine Boundary Layer Clouds

2008 ◽  
Vol 21 (24) ◽  
pp. 6668-6688 ◽  
Author(s):  
Zachary A. Eitzen ◽  
Kuan-Man Xu ◽  
Takmeng Wong
Keyword(s):  
Boundary Layer ◽  
Cluster Analysis ◽  
Physical Properties ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Radiant Energy ◽  
Cloud Fraction ◽  
Cloud Radiative Forcing ◽  
Boundary Layer Clouds ◽  
Shallow Cumulus

Abstract Relationships between physical properties are studied for three types of marine boundary layer cloud objects identified with the Clouds and the Earth’s Radiant Energy System (CERES) footprint data from the Tropical Rainfall Measuring Mission satellite between 30°S and 30°N. Each cloud object is a contiguous region of CERES footprints that have cloud-top heights below 3 km, and cloud fractions of 99%–100% (overcast type), 40%–99% (stratocumulus type), or 10%–40% (shallow cumulus type). These cloud fractions represent the fraction of ∼2 km × 2 km Visible/Infrared Scanner pixels that are cloudy within each ∼10 km × 10 km footprint. The cloud objects have effective diameters that are greater than 300 km for the overcast and stratocumulus types, and greater than 150 km for the shallow cumulus type. The Spearman rank correlation coefficient is calculated between many microphysical/optical [effective radius (re), cloud optical depth (τ), albedo, liquid water path, and shortwave cloud radiative forcing (SW CRF)] and macrophysical [outgoing longwave radiation (OLR), cloud fraction, cloud-top temperature, longwave cloud radiative forcing (LW CRF), and sea surface temperature (SST)] properties for each of the three cloud object types. When both physical properties are of the same category (microphysical/optical or macrophysical), the magnitude of the correlation tends to be higher than when they are from different categories. The magnitudes of the correlations also change with cloud object type, with the correlations for overcast and stratocumulus cloud objects tending to be higher than those for shallow cumulus cloud objects. Three pairs of physical properties are studied in detail, using a k-means cluster analysis: re and τ, OLR and SST, and LW CRF and SW CRF. The cluster analysis of re and τ reveals that for each of the cloud types, there is a cluster of cloud objects with negative slopes, a cluster with slopes near zero, and two clusters with positive slopes. The joint OLR and SST probability plots show that the OLR tends to decrease with SST in regions with boundary layer clouds for SSTs above approximately 298 K. When the cloud objects are split into “dry” and “moist” clusters based on the amount of precipitable water above 700 hPa, the associated OLRs increase with SST throughout the SST range for the dry clusters, but the OLRs are roughly constant with SST for the moist cluster. An analysis of the joint PDFs of LW CRF and SW CRF reveals that while the magnitudes of both LW and SW CRFs generally increase with cloud fraction, there is a cluster of overcast cloud objects that has low values of LW and SW CRF. These objects are generally located near the Sahara Desert, and may be contaminated with dust. Many of these overcast objects also appear in the re and τ cluster with negative slopes.

scholarly journals Switching cloud cover and dynamical regimes from open to closed Benard cells in response to the suppression of precipitation by aerosols

2006 ◽  
Vol 6 (1) ◽  
pp. 1179-1198 ◽  
Author(s):  
D. Rosenfeld ◽  
Y. J. Kaufman ◽  
I. Koren
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Cloud Cover ◽  
Marine Boundary Layer ◽  
Background Level ◽  
Dynamic Structure ◽  
Positive Feedbacks ◽  
Cloud Radiative Forcing ◽  
Cloud Regime ◽  
Dynamical Regimes

Abstract. The dynamic structure of the atmospheric marine boundary layer (MBL) supports two distinct states of cloud cover: closed and open Benard cellular convection. Closed cells are nearly fully cloud covered, while the open cells have <40% cloud cover. Here we show that aerosols have a greater than expected impact on the cloud cover by changing the mode of cellular convection. By suppressing precipitation aerosols can reverse the direction of the airflow, converting the cloud structure from open to closed cells and doubling the cloud cover. The two states possess positive feedbacks for self maintenance, so that small changes of the conditions can lead to bifurcation of the MBL cloud regime. The transition occurs at near pristine background level of aerosols, creating a large sensitivity of cloud radiative forcing to very small changes in aerosols at the MBL. This can have a major impact on global temperatures.

scholarly journals Regional Model Simulations of Marine Boundary Layer Clouds over the Southeast Pacific off South America. Part II: Sensitivity Experiments*

2004 ◽  
Vol 132 (11) ◽  
pp. 2650-2668 ◽  
Author(s):  
Yuqing Wang ◽  
Haiming Xu ◽  
Shang-Ping Xie
Keyword(s):  
Boundary Layer ◽  
South America ◽  
Marine Boundary Layer ◽  
Layer Structure ◽  
Temperature Inversion ◽  
Cloud Layer ◽  
Boundary Layer Structure ◽  
Boundary Layer Clouds ◽  
Shallow Cumulus ◽  
Southeast Pacific

Abstract The sensitivity of a regional climate model to physical parameterizations and model resolution is investigated in terms of its simulation of boundary layer stratocumulus (SCu) clouds over the southeast Pacific. Specifically, the physical schemes being tested include shallow cumulus convection, subgrid vertical mixing, cloud droplet number concentration (CDNC), and drizzle. As described in Part I, the model with standard settings captures the major features of the boundary layer in the region, including a well-mixed marine boundary layer, a capping temperature inversion, SCu clouds, and the boundary layer regime transition from the well-mixed layer near the coast of South America to a decoupled cloud layer over warmer water to the west. Turning off the shallow cumulus parameterization results in a dramatic increase in the simulated SCu clouds while the boundary layer structure becomes unrealistic, losing the decoupled regime over warm water. With reduced penetrative mixing at the top of shallow cumuli, the simulated SCu clouds are somewhat increased while the boundary layer structure remained largely unchanged. Reducing the CDNC increases the size of cloud droplets and reduces the cloud albedo but has little effect on the vertical structure of the boundary layer and clouds. Allowing more drizzle decreases boundary layer clouds considerably. It is also shown that the simulated depth of the boundary layer and its decoupling is highly sensitive to the model horizontal and vertical resolutions. Insufficient horizontal or vertical resolutions produce a temperature inversion and cloud layer too close to the sea surface, a typical problem for global general circulation models. Implications of these results for global and regional modeling of boundary layer clouds and the areas that need more attention in future model development are discussed.

scholarly journals An Evaluation of Marine Boundary Layer Cloud Property Simulations in the Community Atmosphere Model Using Satellite Observations: Conventional Subgrid Parameterization versus CLUBB

2018 ◽  
Vol 31 (6) ◽  
pp. 2299-2320 ◽  
Author(s):  
Hua Song ◽  
Zhibo Zhang ◽  
Po-Lun Ma ◽  
Steven J. Ghan ◽  
Minghuai Wang
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Detection Threshold ◽  
Satellite Observation ◽  
Cloud Fraction ◽  
Cloud Properties ◽  
Community Atmosphere Model ◽  
Direct Model ◽  
Atmosphere Model

This paper presents a satellite-observation-based evaluation of the marine boundary layer (MBL) cloud properties from two Community Atmosphere Model, version 5 (CAM5), simulations, one with the standard parameterization schemes (CAM5–Base) and the other with the Cloud Layers Unified by Binormals scheme (CAM5–CLUBB). When comparing the direct model outputs, the authors find that CAM5–CLUBB produces more MBL clouds, a smoother transition from stratocumulus to cumulus, and a tighter correlation between in-cloud water and cloud fraction than CAM5–Base. In the model-to-observation comparison using the COSP satellite simulators, the authors find that both simulations capture the main features and spatial patterns of the observed cloud fraction from MODIS and shortwave cloud radiative forcing (SWCF) from CERES. However, CAM5–CLUBB suffers more than CAM5–Base from a problem that can be best summarized as “undetectable” clouds (i.e., a significant fraction of simulated MBL clouds are thinner than the MODIS detection threshold). This issue leads to a smaller COSP–MODIS cloud fraction and a weaker SWCF in CAM5–CLUBB than the observations and also CAM5–Base in the tropical descending regions. Finally, the authors compare modeled radar reflectivity with CloudSat observations and find that both simulations, especially CAM5–CLUBB, suffer from an excessive drizzle problem. Further analysis reveals that the subgrid precipitation enhancement factors in CAM5–CLUBB are unrealistically large, which makes MBL clouds precipitate too excessively, and in turn results in too many undetectable thin clouds.

Modeling cloud fraction and horizontal variability in marine boundary layer clouds

1997 ◽  
Vol 102 (D12) ◽  
pp. 13517-13525 ◽  
Author(s):  
Geoffrey Considine ◽  
Judith A. Curry ◽  
Bruce Wielicki
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Fraction ◽  
Boundary Layer Clouds

scholarly journals Effect of biomass burning on marine stratocumulus clouds off the California coast

2009 ◽  
Vol 9 (22) ◽  
pp. 8841-8856 ◽  
Author(s):  
J. Brioude ◽  
O. R. Cooper ◽  
G. Feingold ◽  
M. Trainer ◽  
S. R. Freitas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Cloud Fraction ◽  
Marine Stratocumulus ◽  
Cloud Albedo ◽  
Stratocumulus Clouds ◽  
Absorbing Aerosols ◽  
Indirect Radiative Forcing

Abstract. Aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system. Biomass burning aerosols are of special interest due to their radiative impact (direct and indirect effect) and their potential to increase in the future due to climate change. Combining data from Geostationary Operational Environmental Satellite (GOES) and MODerate-resolution Imaging Spectroradiometer (MODIS) with passive tracers from the FLEXPART Lagrangian Particle Dispersion Model, the impact of biomass burning aerosols on marine stratocumulus clouds has been examined in June and July of 2006–2008 off the California coast. Using a continental tracer, the indirect effect of biomass burning aerosols has been isolated by comparing the average cloud fraction and cloud albedo for different meteorological situations, and for clean versus polluted (in terms of biomass burning) continental air masses at 14:00 local time. Within a 500 km-wide band along the coast of California, biomass burning aerosols, which tend to reside above the marine boundary layer, increased the cloud fraction by 0.143, and the cloud albedo by 0.038. Absorbing aerosols located above the marine boundary layer lead to an increase of the lower tropospheric stability and a reduction in the vertical entrainment of dry air from above, leading to increased cloud formation. The combined effect was an indirect radiative forcing of −7.5% ±1.7% (cooling effect) of the outgoing radiative flux at the top of the atmosphere on average, with a bias due to meteorology of +0.9%. Further away from the coast, the biomass burning aerosols, which were located within the boundary layer, reduced the cloud fraction by 0.023 and the cloud albedo by 0.006, resulting in an indirect radiative forcing of +1.3% ±0.3% (warming effect) with a bias of +0.5%. These results underscore the dual role that absorbing aerosols play in cloud radiative forcing.

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