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

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.

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Linking large-scale circulation patterns to low-cloud properties

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-7125-2020 ◽

2020 ◽

Vol 20 (12) ◽

pp. 7125-7138

Author(s):

Timothy W. Juliano ◽

Zachary J. Lebo

Keyword(s):

Large Scale ◽

Climate Models ◽

Marine Boundary Layer ◽

Warm Season ◽

Cloud Droplet ◽

Synoptic Scale ◽

Liquid Water Path ◽

Cloud Properties ◽

Circulation Patterns ◽

Satellite Retrievals

Abstract. The North Pacific High (NPH) is a fundamental meteorological feature present during the boreal warm season. Marine boundary layer (MBL) clouds, which are persistent in this oceanic region, are influenced directly by the NPH. In this study, we combine 11 years of reanalysis and an unsupervised machine learning technique to examine the gamut of 850 hPa synoptic-scale circulation patterns. This approach reveals two distinguishable regimes – a dominant NPH setup and a land-falling cyclone – and in between a spectrum of large-scale patterns. We then use satellite retrievals to elucidate for the first time the explicit dependence of MBL cloud properties (namely cloud droplet number concentration, liquid water path, and shortwave cloud radiative effect – CRESW) on 850 hPa circulation patterns over the northeast Pacific Ocean. We find that CRESW spans from −146.8 to −115.5 W m−2, indicating that the range of observed MBL cloud properties must be accounted for in global and regional climate models. Our results demonstrate the value of combining reanalysis and satellite retrievals to help clarify the relationship between synoptic-scale dynamics and cloud physics.

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

Journal of Climate ◽

10.1175/2008jcli1974.1 ◽

2008 ◽

Vol 21 (19) ◽

pp. 4955-4973 ◽

Cited By ~ 34

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.

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

Monthly Weather Review ◽

10.1175/2008mwr2582.1 ◽

2009 ◽

Vol 137 (3) ◽

pp. 1083-1110 ◽

Cited By ~ 163

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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How large-scale subsidence affects stratocumulus transitions

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-17229-2015 ◽

2015 ◽

Vol 15 (12) ◽

pp. 17229-17250 ◽

Cited By ~ 1

Author(s):

J. J. van der Dussen ◽

S. R. de Roode ◽

A. P. Siebesma

Keyword(s):

Boundary Layer ◽

Large Scale ◽

Climate Modeling ◽

Hadley Circulation ◽

Cloud Base ◽

Entrainment Rate ◽

Liquid Water Path ◽

Trade Winds ◽

Enhanced Absorption ◽

Subsidence Rate

Abstract. Some climate modeling results suggest that the Hadley circulation might weaken in a future climate, causing a subsequent reduction in the large-scale subsidence velocity in the subtropics. In this study we analyze the cloud liquid water path (LWP) budget from large-eddy simulation (LES) results of three idealized stratocumulus transition cases each with a different subsidence rate. As shown in previous studies a reduced subsidence is found to lead to a deeper stratocumulus-topped boundary layer, an enhanced cloud-top entrainment rate and a delay in the transition of stratocumulus clouds into shallow cumulus clouds during its equatorwards advection by the prevailing trade winds. The effect of a reduction of the subsidence rate can be summarized as follows. The initial deepening of the stratocumulus layer is partly counteracted by an enhanced absorption of solar radiation. After some hours the deepening of the boundary layer is accelerated by an enhancement of the entrainment rate. Because this is accompanied by a change in the cloud-base turbulent fluxes of moisture and heat, the net change in the LWP due to changes in the turbulent flux profiles is negligibly small.

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Improvement of airborne retrievals of cloud droplet number concentration of trade wind cumulus using a synergetic approach

Atmospheric Measurement Techniques ◽

10.5194/amt-12-1635-2019 ◽

2019 ◽

Vol 12 (3) ◽

pp. 1635-1658 ◽

Cited By ~ 3

Author(s):

Kevin Wolf ◽

André Ehrlich ◽

Marek Jacob ◽

Susanne Crewell ◽

Martin Wirth ◽

...

Keyword(s):

Remote Sensing ◽

Cloud Droplet ◽

Number Concentration ◽

Cloud Base ◽

Trade Wind ◽

Liquid Water Path ◽

Cloud Properties ◽

Research Aircraft ◽

Cloud Droplet Number Concentration

Abstract. In situ measurements of cloud droplet number concentration N are limited by the sampled cloud volume. Satellite retrievals of N suffer from inherent uncertainties, spatial averaging, and retrieval problems arising from the commonly assumed strictly adiabatic vertical profiles of cloud properties. To improve retrievals of N it is suggested in this paper to use a synergetic combination of passive and active airborne remote sensing measurement, to reduce the uncertainty of N retrievals, and to bridge the gap between in situ cloud sampling and global averaging. For this purpose, spectral solar radiation measurements above shallow trade wind cumulus were combined with passive microwave and active radar and lidar observations carried out during the second Next Generation Remote Sensing for Validation Studies (NARVAL-II) campaign with the High Altitude and Long Range Research Aircraft (HALO) in August 2016. The common technique to retrieve N is refined by including combined measurements and retrievals of cloud optical thickness τ, liquid water path (LWP), cloud droplet effective radius reff, and cloud base and top altitude. Three approaches are tested and applied to synthetic measurements and two cloud scenarios observed during NARVAL-II. Using the new combined retrieval technique, errors in N due to the adiabatic assumption have been reduced significantly.

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Evaluation of stratocumulus cloud prediction in the Met Office forecast model during VOCALS-REx

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-10541-2010 ◽

2010 ◽

Vol 10 (21) ◽

pp. 10541-10559 ◽

Cited By ~ 52

Author(s):

S. J. Abel ◽

D. N. Walters ◽

G. Allen

Keyword(s):

Boundary Layer ◽

Diurnal Cycle ◽

Liquid Water ◽

Large Scale ◽

Marine Boundary Layer ◽

Coastal Region ◽

Forecast Model ◽

Good Representation ◽

Liquid Water Path ◽

Water Path

Abstract. Observations in the subtropical southeast Pacific obtained during the VOCALS-REx field experiment are used to evaluate the representation of stratocumulus cloud in the Met Office forecast model and to identify key areas where model biases exist. Marked variations in the large scale structure of the cloud field were observed during the experiment on both day-to-day and on diurnal timescales. In the remote maritime region the model is shown to have a good representation of synoptically induced variability in both cloud cover and marine boundary layer depth. Satellite observations show a strong diurnal cycle in cloud fraction and liquid water path in the stratocumulus with enhanced clearances of the cloud deck along the Chilean and Peruvian coasts on certain days. The model accurately simulates the phase of the diurnal cycle but is unable to capture the coastal clearing of cloud. Observations along the 20° S latitude line show a gradual increase in the depth of the boundary layer away from the coast. This trend is well captured by the model (typical low bias of 200 m) although significant errors exist at the coast where the model marine boundary layer is too shallow and moist. Drizzle in the model responds to changes in liquid water path in a manner that is consistent with previous ship-borne observations in the region although the intensity of this drizzle is likely to be too high, particularly in the more polluted coastal region where higher cloud droplet number concentrations are typical. Another mode of variability in the cloud field that the model is unable to capture are regions of pockets of open cellular convection embedded in the overcast stratocumulus deck and an example of such a feature that was sampled during VOCALS-REx is shown.

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Relating Satellite-Observed Cloud Properties from MODIS to Meteorological Conditions for Marine Boundary Layer Clouds

Journal of Climate ◽

10.1175/2009jcli2897.1 ◽

2010 ◽

Vol 23 (6) ◽

pp. 1374-1391 ◽

Cited By ~ 14

Author(s):

Guang J. Zhang ◽

Andrew M. Vogelmann ◽

Michael P. Jensen ◽

William D. Collins ◽

Edward P. Luke

Keyword(s):

Boundary Layer ◽

Meteorological Parameters ◽

Marine Boundary Layer ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Liquid Water Path ◽

Near Surface ◽

Cloud Properties ◽

Lower Tropospheric Stability

Abstract This study examines 6 yr of cloud properties observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the NASA Terra satellite in five prominent marine boundary layer (MBL) cloud regions (California, Peru, Canary, Angola, and Australia) and investigates their relationships with near-surface meteorological parameters obtained from NCEP reanalyses. About 62 000 independent scenes are used to examine the instantaneous relationships between cloud properties and meteorological parameters that may be used for global climate model (GCM) diagnostics and parameterization. Cloud liquid water path (LWP) generally increases with lower-tropospheric stability (LTS) and lifting condensation level (LCL), whereas cloud drizzle frequency is favored by weak LTS and negligible cold air advection. Cloud fraction (CF) depends strongly on variations in LTS, and to a lesser extent on surface air temperature advection and LCL, although the relationships vary from region to region. The authors propose capturing the effects of these three parameters on CF via their linear combination in terms of a single parameter, the effective lower-tropospheric stability (eLTS). Results indicate that eLTS offers a marked improvement over LTS alone in explaining the median CF variations within the different study regions. A parameterization of CF in terms of eLTS is provided, which produces results that are improved over those of Klein and Hartmann’s LTS-only parameterization. However, the new parameterization may not predict the observed variability correctly, and the authors propose a method that might address this shortcoming via a statistical approach.

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Time-dependent entrainment of smoke presents an observational challenge for assessing aerosol–cloud interactions over the southeast Atlantic Ocean

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-14623-2018 ◽

2018 ◽

Vol 18 (19) ◽

pp. 14623-14636 ◽

Cited By ~ 17

Author(s):

Michael S. Diamond ◽

Amie Dobracki ◽

Steffen Freitag ◽

Jennifer D. Small Griswold ◽

Ashley Heikkila ◽

...

Keyword(s):

Boundary Layer ◽

Atlantic Ocean ◽

Marine Boundary Layer ◽

Climate Modeling ◽

Cloud Droplet ◽

Number Concentration ◽

Cloud Properties ◽

History Of ◽

Cloud Droplet Number Concentration ◽

The Relationship

Abstract. The colocation of clouds and smoke over the southeast Atlantic Ocean during the southern African biomass burning season has numerous radiative implications, including microphysical modulation of the clouds if smoke is entrained into the marine boundary layer. NASA's ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign is studying this system with aircraft in three field deployments between 2016 and 2018. Results from ORACLES-2016 show that the relationship between cloud droplet number concentration and smoke below cloud is consistent with previously reported values, whereas cloud droplet number concentration is only weakly associated with smoke immediately above cloud at the time of observation. By combining field observations, regional chemistry–climate modeling, and theoretical boundary layer aerosol budget equations, we show that the history of smoke entrainment (which has a characteristic mixing timescale on the order of days) helps explain variations in cloud properties for similar instantaneous above-cloud smoke environments. Precipitation processes can obscure the relationship between above-cloud smoke and cloud properties in parts of the southeast Atlantic, but marine boundary layer carbon monoxide concentrations for two case study flights suggest that smoke entrainment history drove the observed differences in cloud properties for those days. A Lagrangian framework following the clouds and accounting for the history of smoke entrainment and precipitation is likely necessary for quantitatively studying this system; an Eulerian framework (e.g., instantaneous correlation of A-train satellite observations) is unlikely to capture the true extent of smoke–cloud interaction in the southeast Atlantic.

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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0277.1 ◽

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.

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Evaluation of Warm-Rain Microphysical Parameterizations in Mesoscale Simulations of the Cloudy Marine Boundary Layer

Monthly Weather Review ◽

10.1175/mwr-d-15-0266.1 ◽

2016 ◽

Vol 144 (6) ◽

pp. 2137-2154 ◽

Cited By ~ 1

Author(s):

Kevin J. Nelson ◽

David B. Mechem ◽

Yefim L. Kogan

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Cloud Condensation Nuclei ◽

Forecast Model ◽

Horizontal Resolution ◽

Naval Research ◽

Liquid Water Path ◽

Cloud Properties ◽

Southeastern Pacific ◽

Warm Rain

Abstract Several warm-rain microphysical parameterizations are evaluated in a regional forecast model setting (using the Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System) by evaluating how accurately the model is able to represent the marine boundary layer (MBL). Cloud properties from a large suite of simulations using different parameterizations and concentrations of cloud condensation nuclei (CCN) are compared to ship-based observations from the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study—Regional Experiment (VOCALS-REx) field campaign conducted over the southeastern Pacific (SEP). As in previous studies, the simulations systematically underestimate liquid water path and MBL cloud depth. On the other hand, the simulations overestimate precipitation rates relative to those derived from the scanning C-band radar on board the ship. Most of the simulations exhibit a diurnal cycle, although details differ somewhat from a recent observational study. In addition to direct comparisons with the observations, the internal microphysical consistency of simulated MBL cloud properties is assessed by comparing simulation output to a number of observationally and theoretically derived scalings for precipitation and coalescence scavenging. Simulation results are broadly consistent with these scalings, suggesting COAMPS is behaving in a microphysically consistent fashion. However, microphysical consistency as defined in the analysis is highly dependent upon the horizontal resolution of the model. Excessive depletion of CCN from large coalescence processing rates suggests the importance of parameterizing a source term for CCN or imposing some form of fixed, climatological background CCN concentration.

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