Environmental and internal controls on Lagrangian transitions from closed cell mesoscale cellular convection over subtropical oceans

2021 ◽  
Author(s):  
Ryan Eastman ◽  
Isabel L. McCoy ◽  
Robert Wood
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Amount ◽  
Cloud Droplet ◽  
Boreal Summer ◽  
Liquid Water Path ◽  
Austral Spring ◽  
Annual Cycles ◽  
Closed Cell ◽  
Subtropical Oceans

AbstractClassifications of mesoscale cellular convection (MCC) for marine boundary layer clouds are produced using a supervised neural network algorithm applied to MODIS daytime liquid water path data. The classifier, used in prior studies, distinguishes closed, open, and cellular, but disorganized MCC. This work uses trajectories in four eastern subtropical ocean basins to compare meteorological variables and the structures of boundary layers for trajectories that begin as closed cells, but evolve either into open cells, disorganized cells, or remain closed cells over one afternoon-afternoon cycle.Results show contrasts between the trajectory sets: Trajectories for MCC that remain closed cells are more frequently observed nearer coasts, while trajectories that break into open and disorganized cells begin farther offshore. The frequency at which closed cells transition to open cells is seasonally invariant. The fraction of trajectories that stay as closed MCC varies throughout the year in opposition to those that break into disorganized cells, so that their annual cycles are 180° out of phase. Trajectories remain as closed cell more frequently in austral spring and boreal summer when the trade inversion is stronger.The closed-disorganized MCC breakup is associated with weaker subsidence, a weaker inversion, a drier free troposphere, and enhanced nighttime boundary layer deepening, consistent with a warming-drying mechanism. The closed-open transition occurs in meteorological conditions similar to closed-closed trajectories. However, prior to the transition, the closed-open trajectories exhibit stronger surface winds, lower cloud droplet concentrations, and rain more heavily overnight. Results suggest that multiple, independent mechanisms drive changes in cloud amount and morphology.

scholarly journals Probability Density Functions of Liquid Water Path and Cloud Amount of Marine Boundary Layer Clouds: Geographical and Seasonal Variations and Controlling Meteorological Factors

2010 ◽  
Vol 23 (8) ◽  
pp. 2079-2092 ◽  
Author(s):  
Hideaki Kawai ◽  
João Teixeira
Keyword(s):  
Boundary Layer ◽  
Seasonal Variations ◽  
Marine Boundary Layer ◽  
Meteorological Factors ◽  
Cloud Amount ◽  
Probability Density Functions ◽  
Density Functions ◽  
Subgrid Scale ◽  
Liquid Water Path ◽  
Boundary Layer Clouds

Abstract The subgrid-scale variability of the liquid water path (LWP) of marine boundary layer clouds in areas that correspond to the typical grid size of large-scale (global climate and weather prediction) atmospheric models (200 km × 200 km) is investigated using geostationary satellite visible data. Geographical and seasonal variations of homogeneity, skewness, and kurtosis of probability density functions (PDFs) of LWP are discussed, in addition to cloud amount. It is clear that not only cloud amount but also these subgrid-scale statistics have well-defined geographical patterns and seasonal variations. Furthermore, the meteorological factors that control subgrid-scale statistics of LWP that are related to boundary layer clouds are investigated using reanalysis data and PDFs of LWP data from satellites. Meteorological factors related to stability between 850 and 1000 hPa show high correlations with cloud amount and with the homogeneity, skewness, and kurtosis of PDFs of LWP of marine boundary layer clouds. The corrected gap of low-level moist static energy (CGLMSE) index, which is related to cloud-top entrainment instability, shows the highest correlation with the shape of LWP PDFs.

scholarly journals Manipulating marine stratocumulus cloud amount and albedo: a process-modelling study of aerosol-cloud-precipitation interactions in response to injection of cloud condensation nuclei

2011 ◽  
Vol 11 (1) ◽  
pp. 885-916 ◽  
Author(s):  
H. Wang ◽  
P. J. Rasch ◽  
G. Feingold
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Cloud Amount ◽  
Number Concentration ◽  
Condensation Nuclei ◽  
Liquid Water Path ◽  
Water Path ◽  
Injection Method

Abstract. We use a cloud-system-resolving model to study marine-cloud brightening. We examine how injected aerosol particles that act as cloud condensation nuclei (CCN) are transported within the marine boundary layer and how the additional particles in clouds impact cloud microphysical processes, and feedback on dynamics. Results show that the effectiveness of cloud brightening depends strongly on meteorological and background aerosol conditions. Cloud albedo enhancement is very effective in a weakly precipitating boundary layer and in CCN-limited conditions preceded by heavy and/or persistent precipitation. The additional CCN help sustain cloud water by weakening the precipitation substantially in the former case and preventing the boundary layer from collapse in the latter. For a given amount of injected CCN, the injection method (i.e., number and distribution of sprayers) is critical to the spatial distribution of these CCN. Both the areal coverage and the number concentration of injected particles are key players but neither one always emerges as more important than the other. The same amount of injected material is much less effective in either strongly precipitating clouds or polluted clouds, and it is ineffective in a relatively dry boundary layer that supports clouds of low liquid water path. In the polluted case and "dry" case, the CCN injection increases drop number concentration but lowers supersaturation and liquid water path. As a result, the cloud experiences very weak albedo enhancement, regardless of the injection method.

scholarly journals Probability Density Functions of Liquid Water Path and Total Water Content of Marine Boundary Layer Clouds: Implications for Cloud Parameterization

2012 ◽  
Vol 25 (6) ◽  
pp. 2162-2177 ◽  
Author(s):  
Hideaki Kawai ◽  
João Teixeira
Keyword(s):  
Boundary Layer ◽  
Water Content ◽  
Marine Boundary Layer ◽  
Cloud Amount ◽  
Probability Density Functions ◽  
Total Water Content ◽  
Total Water ◽  
Liquid Water Path ◽  
Boundary Layer Clouds ◽  
The Stability

Abstract Mathematical forms of probability density functions (PDFs) of liquid water path (LWP) and total water content for marine boundary layer clouds are investigated using the homogeneity, skewness, and kurtosis of PDFs of LWP obtained from observations described in a companion paper. First, observed LWP PDF data are divided into four categories depending on the stability between 775 and 1000 hPa in order to investigate the characteristics of the PDFs of LWP depending on stability of the atmospheric boundary layer (ABL). The relationships between cloud amount and higher moments of LWP PDFs for different ABLs show different features. When the stability becomes larger, the LWP PDFs have larger homogeneity, smaller skewness, and smaller kurtosis for similar cloud amounts. To extract useful information about the PDFs of total water content for strongly and moderately stable ABLs, the relationship between LWP PDFs and PDFs of total water content is determined by introducing a set of simple assumptions for the vertical structure of total water content in well-mixed boundary layers. By comparing the observed relationships between cloud amount and higher moments of LWP PDFs, with similar relationships deduced theoretically from various forms of PDFs of total water content, it is found that, in general, the triangular and Gaussian PDFs are a realistic approximation for PDFs of total water content in marine boundary layer clouds for strongly and moderately stable ABLs. Results concerning the correction ratio for the autoconversion rate of cloud water content to precipitation and the reduction factor for shortwave reflectance, as functions of cloud amount, are also discussed.

scholarly journals Response of Marine Boundary Layer Cloud Properties to Aerosol Perturbations Associated with Meteorological Conditions from the 19-Month AMF-Azores Campaign

2016 ◽  
Vol 73 (11) ◽  
pp. 4253-4268 ◽  
Author(s):  
Jianjun Liu ◽  
Zhanqing Li ◽  
Maureen Cribb
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Effective Interaction ◽  
Atmospheric Stability ◽  
Cloud Droplet ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Cloud Properties ◽  
Stable Conditions

Abstract This study investigates the response of marine boundary layer (MBL) cloud properties to aerosol loading by accounting for the contributions of large-scale dynamic and thermodynamic conditions and quantifies the first indirect effect (FIE). It makes use of 19-month measurements of aerosols, clouds, and meteorology acquired during the Atmospheric Radiation Measurement Mobile Facility field campaign over the Azores. Cloud droplet number concentrations and cloud optical depth (COD) significantly increased with increasing aerosol number concentration . Cloud droplet effective radius (DER) significantly decreased with increasing . The correlations between cloud microphysical properties [, liquid water path (LWP), and DER] and were stronger under more stable conditions. The correlations between , LWP, DER, and were stronger under ascending-motion conditions, while the correlation between COD and was stronger under descending-motion conditions. The magnitude and corresponding uncertainty of the FIE ranged from 0.060 ± 0.022 to 0.101 ± 0.006 depending on the different LWP values. Under more stable conditions, cloud-base heights were generally lower than those under less stable conditions. This enabled a more effective interaction with aerosols, resulting in a larger value for the FIE. However, the dependence of the response of cloud properties to aerosol perturbations on stability varied according to whether ground- or satellite-based DER retrievals were used. The magnitude of the FIE had a larger variation with changing LWP under ascending-motion conditions and tended to be higher under ascending-motion conditions for clouds with low LWP and under descending-motion conditions for clouds with high LWP. A contrasting dependence of FIE on atmospheric stability estimated from the surface and satellite cloud properties retrievals reported in this study underscores the importance of assessing all-level properties of clouds in aerosol–cloud interaction studies.

scholarly journals Manipulating marine stratocumulus cloud amount and albedo: a process-modelling study of aerosol-cloud-precipitation interactions in response to injection of cloud condensation nuclei

2011 ◽  
Vol 11 (9) ◽  
pp. 4237-4249 ◽  
Author(s):  
H. Wang ◽  
P. J. Rasch ◽  
G. Feingold
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Cloud Amount ◽  
Number Concentration ◽  
Condensation Nuclei ◽  
Liquid Water Path ◽  
Water Path ◽  
Injection Method

Abstract. We use a cloud-system-resolving model to study marine-cloud brightening. We examine how injected aerosol particles that act as cloud condensation nuclei (CCN) are transported within the marine boundary layer and how the additional particles in clouds impact cloud microphysical processes, and feedback on dynamics. Results show that the effectiveness of cloud brightening depends strongly on meteorological and background aerosol conditions. Cloud albedo enhancement is very effective in a weakly precipitating boundary layer and in CCN-limited conditions preceded by heavy and/or persistent precipitation. The additional CCN help sustain cloud water by weakening the precipitation substantially in the former case and preventing the boundary layer from collapse in the latter. For a given amount of injected CCN, the injection method (i.e., number and distribution of sprayers) is critical to the spatial distribution of these CCN. Both the areal coverage and the number concentration of injected particles are key players but neither one always emerges as more important than the other. The same amount of injected material is much less effective in either strongly precipitating clouds or polluted clouds, and it is ineffective in a relatively dry boundary layer that supports clouds of low liquid water path. In the polluted case and "dry" case, the CCN injection increases drop number concentration but lowers supersaturation and liquid water path. As a result, the cloud experiences very weak albedo enhancement, regardless of the injection method.

scholarly journals Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign

2013 ◽  
Vol 13 (16) ◽  
pp. 8489-8503 ◽  
Author(s):  
D. Jarecka ◽  
H. Pawlowska ◽  
W. W. Grabowski ◽  
A. A. Wyszogrodzki
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Marine Boundary Layer ◽  
Cloud Droplet ◽  
Droplet Radius ◽  
Subgrid Scale ◽  
Microphysics Scheme ◽  
Local Conditions ◽  
Field Campaign ◽  
Les Model

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) modeling of 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds are advected from the northeast by the prevailing lower-tropospheric winds and featured stratocumulus-over-cumulus cloud formations. An almost-solid stratocumulus deck in the upper part of the relatively deep, weakly decoupled marine boundary layer overlays a field of small cumuli. The two cloud formations have distinct microphysical characteristics that are in general agreement with numerous past observations of strongly diluted shallow cumuli on one hand and solid marine stratocumulus on the other. Based on the available observations, a LES model setup is developed and applied in simulations using a novel LES model. The model features a double-moment warm-rain bulk microphysics scheme combined with a sophisticated subgrid-scale scheme allowing local prediction of the homogeneity of the subgrid-scale turbulent mixing. The homogeneity depends on the characteristic time scales for the droplet evaporation and for the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, mean cloud droplet radius, and humidity of the cloud-free air entrained into a cloud, all predicted by the LES model. The model reproduces contrasting macrophysical and microphysical characteristics of the cumulus and stratocumulus cloud layers. Simulated subgrid-scale turbulent mixing within the cumulus layer and near the stratocumulus top is on average quite inhomogeneous, but varies significantly depending on the local conditions.

scholarly journals Southeast Pacific stratocumulus clouds, precipitation and boundary layer structure sampled along 20° S during VOCALS-REx

2010 ◽  
Vol 10 (21) ◽  
pp. 10639-10654 ◽  
Author(s):  
C. S. Bretherton ◽  
R. Wood ◽  
R. C. George ◽  
D. Leon ◽  
G. Allen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Vertical Structure ◽  
Layer Structure ◽  
Cloud Droplet ◽  
Free Troposphere ◽  
Liquid Water Path ◽  
Typical Structure ◽  
Southeast Pacific ◽  
Over The Top

Abstract. Multiplatform airborne, ship-based, and land-based observations from 16 October–15 November 2008 during the VOCALS Regional Experiment (REx) are used to document the typical structure of the Southeast Pacific stratocumulus-topped boundary layer and lower free troposphere on a~transect along 20° S between the coast of Northern Chile and a buoy 1500 km offshore. Strong systematic gradients in clouds, precipitation and vertical structure are modulated by synoptically and diurnally-driven variability. The boundary layer is generally capped by a strong (10–12 K), sharp inversion. In the coastal zone, the boundary layer is typically 1 km deep, fairly well mixed, and topped by thin, nondrizzling stratocumulus with accumulation-mode aerosol and cloud droplet concentrations exceeding 200 cm−3. Far offshore, the boundary layer depth is typically deeper (1600 m) and more variable, and the vertical structure is usually decoupled. The offshore stratocumulus typically have strong mesoscale organization, much higher peak liquid water paths, extensive drizzle, and cloud droplet concentrations below 100 cm−3, sometimes with embedded pockets of open cells with lower droplet concentrations. The lack of drizzle near the coast is not just a microphysical response to high droplet concentrations; smaller cloud depth and liquid water path than further offshore appear comparably important. Moist boundary layer air is heated and mixed up along the Andean slopes, then advected out over the top of the boundary layer above adjacent coastal ocean regions. Well offshore, the lower free troposphere is typically much drier. This promotes strong cloud-top radiative cooling and stronger turbulence in the clouds offshore. In conjunction with a slightly cooler free troposphere, this may promote stronger entrainment that maintains the deeper boundary layer seen offshore. Winds from ECMWF and NCEP operational analyses have an rms difference of only 1 m s−1 from collocated airborne leg-mean observations in the boundary layer and 2 m s−1 above the boundary layer. This supports the use of trajectory analysis for interpreting REx observations. Two-day back-trajectories from the 20° S transect suggest that eastward of 75° W, boundary layer (and often free-tropospheric) air has usually been exposed to South American coastal aerosol sources, while at 85° W, neither boundary-layer or free-tropospheric air has typically had such contact.

scholarly journals Investigation of Regional and Seasonal Variations in Marine Boundary Layer Cloud Properties from MODIS Observations

2008 ◽  
Vol 21 (19) ◽  
pp. 4955-4973 ◽  
Author(s):  
Michael P. Jensen ◽  
Andrew M. Vogelmann ◽  
William D. Collins ◽  
Guang J. Zhang ◽  
Edward P. Luke
Keyword(s):  
Boundary Layer ◽  
General Circulation ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
General Circulation Models ◽  
Test Bed ◽  
Liquid Water Path ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Peak Versus

Abstract To aid in understanding the role that marine boundary layer (MBL) clouds play in climate and assist in improving their representations in general circulation models (GCMs), their long-term microphysical and macroscale characteristics are quantified using observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the National Aeronautics and Space Administration’s (NASA’s) Terra satellite. Six years of MODIS pixel-level cloud products are used from oceanic study regions off the west coasts of California, Peru, the Canary Islands, Angola, and Australia where these cloud types are common. Characterizations are given for their organization (macroscale structure), the associated microphysical properties, and the seasonal dependencies of their variations for scales consistent with the size of a GCM grid box (300 km × 300 km). MBL mesoscale structure is quantified using effective cloud diameter CD, which is introduced here as a simplified measure of bulk cloud organization; it is straightforward to compute and provides descriptive information beyond that offered by cloud fraction. The interrelationships of these characteristics are explored while considering the influences of the MBL state, such as the occurrence of drizzle. Several commonalities emerge for the five study regions. MBL clouds contain the best natural examples of plane-parallel clouds, but overcast clouds occur in only about 25% of the scenes, which emphasizes the importance of representing broken MBL cloud fields in climate models (that are subgrid scale). During the peak months of cloud occurrence, mesoscale organization (larger CD) increases such that the fractions of scenes characterized as “overcast” and “clumped” increase at the expense of the “scattered” scenes. Cloud liquid water path and visible optical depth usually trend strongly with CD, with the largest values occurring for scenes that are drizzling. However, considerable interregional differences exist in these trends, suggesting that different regression functionalities exist for each region. For peak versus off-peak months, the fraction of drizzling scenes (as a function of CD) are similar for California and Angola, which suggests that a single probability distribution function might be used for their drizzle occurrence in climate models. The patterns are strikingly opposite for Peru and Australia; thus, the contrasts among regions may offer a test bed for model simulations of MBL drizzle occurrence.

scholarly journals Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer

2009 ◽  
Vol 137 (3) ◽  
pp. 1083-1110 ◽  
Author(s):  
Andrew S. Ackerman ◽  
Margreet C. vanZanten ◽  
Bjorn Stevens ◽  
Verica Savic-Jovcic ◽  
Christopher S. Bretherton ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Water ◽  
Large Eddy Simulations ◽  
Cloud Base ◽  
Entrainment Rate ◽  
Liquid Water Path ◽  
Average Maximum ◽  
Large Eddy ◽  
The Mean

Abstract Cloud water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from 11 groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. Including drizzle in the simulations reduces convective intensity, increases boundary layer stratification, and decreases LWP for nearly all models. Including cloud water sedimentation substantially decreases entrainment, decreases convective intensity, and increases LWP for most models. In nearly all cases, LWP responds more strongly to cloud water sedimentation than to drizzle. The omission of cloud water sedimentation in simulations is strongly discouraged, regardless of whether or not precipitation is present below cloud base.

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