Clouds, Aerosols, and Precipitation in the Marine Boundary Layer: An Arm Mobile Facility Deployment

Abstract The Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (CAP-MBL) deployment at Graciosa Island in the Azores generated a 21-month (April 2009–December 2010) comprehensive dataset documenting clouds, aerosols, and precipitation using the Atmospheric Radiation Measurement Program (ARM) Mobile Facility (AMF). The scientific aim of the deployment is to gain improved understanding of the interactions of clouds, aerosols, and precipitation in the marine boundary layer. Graciosa Island straddles the boundary between the subtropics and midlatitudes in the northeast Atlantic Ocean and consequently experiences a great diversity of meteorological and cloudiness conditions. Low clouds are the dominant cloud type, with stratocumulus and cumulus occurring regularly. Approximately half of all clouds contained precipitation detectable as radar echoes below the cloud base. Radar and satellite observations show that clouds with tops from 1 to 11 km contribute more or less equally to surface-measured precipitation at Graciosa. A wide range of aerosol conditions was sampled during the deployment consistent with the diversity of sources as indicated by back-trajectory analysis. Preliminary findings suggest important two-way interactions between aerosols and clouds at Graciosa, with aerosols affecting light precipitation and cloud radiative properties while being controlled in part by precipitation scavenging. The data from Graciosa are being compared with short-range forecasts made with a variety of models. A pilot analysis with two climate and two weather forecast models shows that they reproduce the observed time-varying vertical structure of lower-tropospheric cloud fairly well but the cloud-nucleating aerosol concentrations less well. The Graciosa site has been chosen to be a permanent fixed ARM site that became operational in October 2013.

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Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-11447-2014 ◽

2014 ◽

Vol 14 (8) ◽

pp. 11447-11491 ◽

Cited By ~ 2

Author(s):

J. C. Schroder ◽

S. J. Hanna ◽

R. L. Modini ◽

A. L. Corrigan ◽

A. M. Macdonald ◽

...

Keyword(s):

Boundary Layer ◽

Black Carbon ◽

Marine Boundary Layer ◽

Back Trajectory ◽

Cloud Droplets ◽

Back Trajectories ◽

Air Masses ◽

Carbon Particles ◽

Back Trajectory Analysis ◽

La Jolla

Abstract. Size resolved observations of aerosol particles (including black carbon particles) and cloud residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, CA during 2012. A counterflow virtual impactor was used to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling ten hours of in-cloud sampling were analyzed. Since the CVI only sampled cloud droplets larger than &approx;11 μm, less than 100% of the cloud droplets were sampled during the two cloud events (&approx;38% of the cloud droplets for the first cloud event and &approx;24% of the cloud droplets for the second cloud were sampled). Back trajectories showed that air masses for both cloud events spent at least 96 h over the Pacific Ocean and traveled near, or over populated regions just before sampling. Based on bulk aerosol particle concentrations measured from the total inlet the two air masses sampled were classified as polluted marine air, a classification that was consistent with back trajectory analysis and the mass concentrations of refractory black carbon (rBC) measured from the total inlet. The activated fraction of rBC, estimated from the measurements, ranged from 0.01 to 0.1 for core diameters ranging from 70 to 220 nm. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC sampled from the residual inlet show that sub-100 nm rBC cores were incorporated into the droplets in both clouds. The coating analysis shows that the rBC cores had average coating thicknesses of 75 nm for core diameters of 70 nm and 29 nm for core diameters of 220 nm. The presence of sub-100 nm rBC cores in the cloud residuals is consistent with kappa-Köhler theory and the measured coating thicknesses of the rBC cores.

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Quantification of aerosol effects on marine boundary layer clouds with machine learning

10.5194/egusphere-egu21-10754 ◽

2021 ◽

Author(s):

Lukas Zipfel ◽

Hendrik Andersen ◽

Jan Cermak

Keyword(s):

Machine Learning ◽

Boundary Layer ◽

Marine Boundary Layer ◽

Cloud Droplet ◽

Number Concentration ◽

Satellite Observations ◽

Radiative Properties ◽

Cloud Base ◽

Boundary Layer Clouds ◽

Cloud Droplet Number Concentration

Satellite observations are used in regional machine learning models to quantify sensitivities of marine boundary-layer clouds (MBLC) to aerosol changes.MBLCs make up a large part of the global cloud coverage as they are persistently present over more than 20% of the Earth&#8217;s oceans in the annual mean.They play an important role in Earth&#8217;s energy budget by reflecting solar radiation and interacting with thermal radiation from the surface, leading to a net cooling effect. Cloud properties and their radiative characteristics such as cloud albedo, horizontal and vertical extent, lifetime and precipitation susceptibility are dependent on environmental conditions. Aerosols in their role as condensation nuclei affect these cloud radiative properties through changes in the cloud droplet number concentration and subsequent cloud adjustments to this perturbation. However, the magnitude and sign of these effects remain among the largest uncertainties in future climate predictions.In an effort to help improve these predictions a machine learning approach in combination with observational data is pursued:Satellite observations from the collocated A-Train dataset (C3M) for 2006-2011 are used in combination with ECMWF atmospheric reanalysis data (ERA5) to train regional Gradient Boosting Regression Tree (GBRT) models to predict changes in key physical and radiative properties of MBLCs. The cloud droplet number concentration (Nd) and the liquid water path (LWP) are simulated for the eastern subtropical oceans, which are characterised by a high annual coverage of MBLC due to the occurrence of semi-permanent stratocumulus sheets. Relative humidity above cloud, cloud top height and temperature below the cloud base and at the surface are identified as important predictors for both Nd and LWP.&#160; The impact of each predictor variable on the GBRT model's output is analysed using Shapley values as a method of explainable machine learning, providing novel sensitivity estimates that will improve process understanding and help constrain the parameterization of MBLC processes in Global Climate Models.

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Southeast Pacific atmospheric composition and variability sampled along 20° S during VOCALS-REx

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-681-2011 ◽

2011 ◽

Vol 11 (1) ◽

pp. 681-744 ◽

Cited By ~ 5

Author(s):

G. Allen ◽

H. Coe ◽

A. Clarke ◽

C. Bretherton ◽

R. Wood ◽

...

Keyword(s):

Boundary Layer ◽

Land Surface ◽

Trajectory Analysis ◽

Marine Boundary Layer ◽

Model Simulation ◽

Cloud Droplet ◽

Atmospheric Composition ◽

Back Trajectory ◽

Free Troposphere ◽

Back Trajectory Analysis

Abstract. The VAMOS Ocean-Climate-Atmosphere-Land Regional Experiment (VOCALS-REx) was conducted from 15 October to 15 November 2008 in the South East Pacific region to investigate interactions between land, sea and atmosphere in this unique tropical eastern ocean environment and to improve the skill of global and regional models in representing the region. This study synthesises selected aircraft, ship and surface site observations from VOCALS-REx to statistically summarise and characterise the atmospheric composition and variability of the Marine Boundary Layer (MBL) and Free Troposphere (FT) along the 20° S parallel between 70° W and 85° W. Significant zonal gradients in mean MBL sub-micron aerosol particle size and composition, carbon monoxide, ozone and sulphur dioxide were seen over the campaign, with a generally more variable and polluted coastal environment and a less variable, more pristine remote maritime regime. Gradients are observed to be associated with strong gradients in cloud droplet number. The FT is often more polluted in terms of trace gases than the MBL in the mean; however increased variability in the FT composition suggests an episodic nature to elevated concentrations. This is consistent with a complex vertical interleaving of airmasses with diverse sources and hence pollutant concentrations as seen by generalised back trajectory analysis, which suggests contributions from both local and long-range sources. Furthermore, back trajectory analysis demonstrates that the observed zonal gradients both in the boundary layer and the free troposphere are characteristic of marked changes in airmass history with distance offshore – coastal boundary layer airmasses having been in recent contact with the local land surface and remote maritime airmasses having resided over ocean for in excess of ten days. Boundary layer composition to the east of 75° W was observed to be dominated by coastal emissions from sources to the west of the Andes, with evidence for diurnal pumping of the Andean boundary layer above the height of the marine capping inversion. The climatology presented here aims to provide a valuable dataset to inform model simulation and future process studies, particularly in the context of aerosol-cloud interaction and further evaluation of dynamical processes in the SEP region for conditions analogous to those during VOCALS-REx.

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Mind the gap – Part 1: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars

Atmospheric Measurement Techniques ◽

10.5194/amt-13-2363-2020 ◽

2020 ◽

Vol 13 (5) ◽

pp. 2363-2379 ◽

Cited By ~ 3

Author(s):

Katia Lamer ◽

Pavlos Kollias ◽

Alessandro Battaglia ◽

Simon Preval

Keyword(s):

Boundary Layer ◽

Cloud Cover ◽

Marine Boundary Layer ◽

Short Pulse ◽

Pulse Mode ◽

Cloud Base ◽

Boundary Layer Clouds ◽

Highly Sensitive ◽

Eastern North Atlantic ◽

Long Pulse

Abstract. Ground-based radar observations show that, over the eastern North Atlantic, 50 % of warm marine boundary layer (WMBL) hydrometeors occur below 1.2 km and have reflectivities of < −17 dBZ, thus making their detection from space susceptible to the extent of surface clutter and radar sensitivity. Surface clutter limits the ability of the CloudSat cloud profiling radar (CPR) to observe the true cloud base in ∼52 % of the cloudy columns it detects and true virga base in ∼80 %, meaning the CloudSat CPR often provides an incomplete view of even the clouds it does detect. Using forward simulations, we determine that a 250 m resolution radar would most accurately capture the boundaries of WMBL clouds and precipitation; that being said, because of sensitivity limitations, such a radar would suffer from cloud cover biases similar to those of the CloudSat CPR. Observations and forward simulations indicate that the CloudSat CPR fails to detect 29 %–43 % of the cloudy columns detected by ground-based sensors. Out of all configurations tested, the 7 dB more sensitive EarthCARE CPR performs best (only missing 9.0 % of cloudy columns) indicating that improving radar sensitivity is more important than decreasing the vertical extent of surface clutter for measuring cloud cover. However, because 50 % of WMBL systems are thinner than 400 m, they tend to be artificially stretched by long sensitive radar pulses, hence the EarthCARE CPR overestimation of cloud top height and hydrometeor fraction. Thus, it is recommended that the next generation of space-borne radars targeting WMBL science should operate interlaced pulse modes including both a highly sensitive long-pulse mode and a less sensitive but clutter-limiting short-pulse mode.

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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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Why sometimes its simply sunny (in the trades)

10.5194/egusphere-egu21-15408 ◽

2021 ◽

Author(s):

Bjorn Stevens ◽

Ilya Serikov ◽

Anna Lea Albright ◽

Sandrine Bony ◽

Geet George ◽

...

Keyword(s):

Boundary Layer ◽

Water Vapor ◽

Marine Boundary Layer ◽

Cloud Base ◽

Lidar Signal ◽

Cloud Base Height

Cloud free skies are rare in the trades. &#160;We analyze conditions in which cloud-free conditions prevail. &#160;For this purpose Raman water vapor measurements from the Barbados Cloud Observatory, complemented by ship-based measurements during EUREC4A are used to explore water vapor variability in the marine boundary layer. &#160; We explore the consistency of the inferred cloud base height with estimates of temperature and water vapor from the lidar signal, and examine the co-variability of these quantities. &#160;After having established the properties of these measurements, we seek to use them as well as others, to explain in what ways periods of cloud-free conditions are maintained, investigating the hypothesis that only when the wind stills is it simply sunny.

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Lidar-based remote sensing of atmospheric boundary layer height over land and ocean

Atmospheric Measurement Techniques ◽

10.5194/amt-7-173-2014 ◽

2014 ◽

Vol 7 (1) ◽

pp. 173-182 ◽

Cited By ~ 37

Author(s):

T. Luo ◽

R. Yuan ◽

Z. Wang

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Marine Boundary Layer ◽

Mixing Layer ◽

Layer Height ◽

Boundary Layer Height ◽

Lidar Measurements ◽

Mixing Layer Height ◽

Atmospheric Radiation Measurement ◽

Atmospheric Boundary Layer Height

Abstract. Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of the ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and the ABL vertical structure over ocean and land are analyzed. The new methods are then applied to satellite lidar measurements. The aerosol-derived global marine boundary layer heights are evaluated with marine ABL stratiform cloud top heights and results show a good agreement between them.

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Wind speed response of marine non-precipitating stratocumulus clouds over a diurnal cycle in cloud-system resolving simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-5811-2016 ◽

2016 ◽

Vol 16 (9) ◽

pp. 5811-5839 ◽

Cited By ~ 11

Author(s):

Jan Kazil ◽

Graham Feingold ◽

Takanobu Yamaguchi

Keyword(s):

Boundary Layer ◽

Wind Speed ◽

Large Scale ◽

Layer Growth ◽

Radiative Properties ◽

Cloud Base ◽

Latent Heat Release ◽

Marine Stratocumulus ◽

Stratocumulus Clouds ◽

Boundary Layer Growth

Abstract. Observed and projected trends in large-scale wind speed over the oceans prompt the question: how do marine stratocumulus clouds and their radiative properties respond to changes in large-scale wind speed? Wind speed drives the surface fluxes of sensible heat, moisture, and momentum and thereby acts on cloud liquid water path (LWP) and cloud radiative properties. We present an investigation of the dynamical response of non-precipitating, overcast marine stratocumulus clouds to different wind speeds over the course of a diurnal cycle, all else equal. In cloud-system resolving simulations, we find that higher wind speed leads to faster boundary layer growth and stronger entrainment. The dynamical driver is enhanced buoyant production of turbulence kinetic energy (TKE) from latent heat release in cloud updrafts. LWP is enhanced during the night and in the morning at higher wind speed, and more strongly suppressed later in the day. Wind speed hence accentuates the diurnal LWP cycle by expanding the morning–afternoon contrast. The higher LWP at higher wind speed does not, however, enhance cloud top cooling because in clouds with LWP ⪆ 50 g m−2, longwave emissions are insensitive to LWP. This leads to the general conclusion that in sufficiently thick stratocumulus clouds, additional boundary layer growth and entrainment due to a boundary layer moistening arises by stronger production of TKE from latent heat release in cloud updrafts, rather than from enhanced longwave cooling. We find that large-scale wind modulates boundary layer decoupling. At nighttime and at low wind speed during daytime, it enhances decoupling in part by faster boundary layer growth and stronger entrainment and in part because shear from large-scale wind in the sub-cloud layer hinders vertical moisture transport between the surface and cloud base. With increasing wind speed, however, in decoupled daytime conditions, shear-driven circulation due to large-scale wind takes over from buoyancy-driven circulation in transporting moisture from the surface to cloud base and thereby reduces decoupling and helps maintain LWP. The total (shortwave + longwave) cloud radiative effect (CRE) responds to changes in LWP and cloud fraction, and higher wind speed translates to a stronger diurnally averaged total CRE. However, the sensitivity of the diurnally averaged total CRE to wind speed decreases with increasing wind speed.

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The North Atlantic Marine Boundary Layer Experiment(NAMBLEX). Overview of the campaign held at Mace Head, Ireland, in summer 2002

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-2241-2006 ◽

2006 ◽

Vol 6 (8) ◽

pp. 2241-2272 ◽

Cited By ~ 48

Author(s):

D. E. Heard ◽

K. A. Read ◽

J. Methven ◽

S. Al-Haider ◽

W. J. Bloss ◽

...

Keyword(s):

Boundary Layer ◽

North Atlantic ◽

Marine Boundary Layer ◽

Numerical Models ◽

Measurement Data ◽

Air Mass ◽

The North ◽

Trace Species ◽

Wide Range ◽

The North Atlantic

Abstract. The North Atlantic Marine Boundary Layer Experiment (NAMBLEX), involving over 50 scientists from 12 institutions, took place at Mace Head, Ireland (53.32° N, 9.90° W), between 23 July and 4 September 2002. A wide range of state-of-the-art instrumentation enabled detailed measurements of the boundary layer structure and atmospheric composition in the gas and aerosol phase to be made, providing one of the most comprehensive in situ studies of the marine boundary layer to date. This overview paper describes the aims of the NAMBLEX project in the context of previous field campaigns in the Marine Boundary Layer (MBL), the overall layout of the site, a summary of the instrumentation deployed, the temporal coverage of the measurement data, and the numerical models used to interpret the field data. Measurements of some trace species were made for the first time during the campaign, which was characterised by predominantly clean air of marine origin, but more polluted air with higher levels of NOx originating from continental regions was also experienced. This paper provides a summary of the meteorological measurements and Planetary Boundary Layer (PBL) structure measurements, presents time series of some of the longer-lived trace species (O3, CO, H2, DMS, CH4, NMHC, NOx, NOy, PAN) and summarises measurements of other species that are described in more detail in other papers within this special issue, namely oxygenated VOCs, HCHO, peroxides, organo-halogenated species, a range of shorter lived halogen species (I2, OIO, IO, BrO), NO3 radicals, photolysis frequencies, the free radicals OH, HO2 and (HO2+Σ RO2), as well as a summary of the aerosol measurements. NAMBLEX was supported by measurements made in the vicinity of Mace Head using the NERC Dornier-228 aircraft. Using ECMWF wind-fields, calculations were made of the air-mass trajectories arriving at Mace Head during NAMBLEX, and were analysed together with both meteorological and trace-gas measurements. In this paper a chemical climatology for the duration of the campaign is presented to interpret the distribution of air-mass origins and emission sources, and to provide a convenient framework of air-mass classification that is used by other papers in this issue for the interpretation of observed variability in levels of trace gases and aerosols.

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