Lagrangian Evolution of the Northeast Pacific Marine Boundary Layer Structure and Cloud during CSET

Abstract Flight data from the Cloud System Evolution over the Trades (CSET) campaign over the Pacific stratocumulus-to-cumulus transition are organized into 18 Lagrangian cases suitable for study and future modeling, made possible by the use of a track-and-resample flight strategy. Analysis of these cases shows that 2-day Lagrangian coherence of long-lived species (CO and O3) is high (r = 0.93 and 0.73, respectively), but that of subcloud aerosol, MBL depth, and cloud properties is limited. Although they span a wide range in meteorological conditions, most sampled air masses show a clear transition when considering 2-day changes in cloudiness (−31% averaged over all cases), MBL depth (+560 m), estimated inversion strength (EIS; −2.2 K), and decoupling, agreeing with previous satellite studies and theory. Changes in precipitation and droplet number were less consistent. The aircraft-based analysis is augmented by geostationary satellite retrievals and reanalysis data along Lagrangian trajectories between aircraft sampling times, documenting the evolution of cloud fraction, cloud droplet number concentration, EIS, and MBL depth. An expanded trajectory set spanning the summer of 2015 is used to show that the CSET-sampled air masses were representative of the season, with respect to EIS and cloud fraction. Two Lagrangian case studies attractive for future modeling are presented with aircraft and satellite data. The first features a clear Sc–Cu transition involving MBL deepening and decoupling with decreasing cloud fraction, and the second undergoes a much slower cloud evolution despite a greater initial depth and decoupling state. Potential causes for the differences in evolution are explored, including free-tropospheric humidity, subsidence, surface fluxes, and microphysics.

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Temporal Variability of Fair-Weather Cumulus Statistics at the ACRF SGP Site

Journal of Climate ◽

10.1175/2007jcli2266.1 ◽

2008 ◽

Vol 21 (13) ◽

pp. 3344-3358 ◽

Cited By ~ 54

Author(s):

Larry K. Berg ◽

Evgueni I. Kassianov

Keyword(s):

Great Plains ◽

Sensible Heat Flux ◽

Cloud Fraction ◽

Surface Fluxes ◽

Chord Length ◽

Cloud Base ◽

Fair Weather ◽

Cloud Properties ◽

Cloud Thickness ◽

Cloud Base Height

Abstract Continental fair-weather cumuli exhibit significant diurnal, day-to-day, and year-to-year variability. This study describes the climatology of cloud macroscale properties, over the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains (SGP) site. The diurnal cycle of cloud fraction, cloud-base height, cloud-top height, and cloud thickness were well defined. The cloud fraction reached its maximum value near 1400 central standard time. The average cloud-base height increased throughout the day, while the average cloud thickness decreased with time. In contrast to the other cloud properties, the average cloud-chord length remained nearly constant throughout the day. The sensitivity of the cloud properties to the year-to-year variability of precipitation and day-to-day changes in the height of the lifting condensation level (zLCL) and surface fluxes were compared. The cloud-base height was found to be sensitive to both the year, zLCL, and the surface fluxes of heat and moisture; the cloud thickness was found to be more sensitive to the year than to zLCL; the cloud fraction was sensitive to both the low-level moisture and the surface sensible heat flux; and cloud-chord length was sensitive to zLCL. Distributions of the cloud-chord length over the ACRF SGP site were computed and were well fit by an exponential distribution. The contribution to the total cloud fraction by clouds of each cloud-chord length was computed, and it was found that the clouds with a chord length of about 1 km contributed most to the observed cloud fraction. This result is similar to observations made with other remote sensing instruments or in modeling studies, but it is different from aircraft observations of the contribution to the total cloud fraction by clouds of different sizes.

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Thermal Stratification in Simulations of Warm Climates: A Climatology Using Saturation Potential Vorticity

Journal of Climate ◽

10.1175/jcli-d-15-0785.1 ◽

2016 ◽

Vol 29 (14) ◽

pp. 5083-5102 ◽

Cited By ~ 5

Author(s):

Ryan A. Zamora ◽

Robert L. Korty ◽

Matthew Huber

Keyword(s):

Potential Vorticity ◽

Temporal Distribution ◽

Reanalysis Data ◽

Storm Tracks ◽

The Arctic ◽

Moist Convection ◽

Air Masses ◽

Wide Range ◽

Carbon Dioxide Levels ◽

Lapse Rates

Abstract The spatial and temporal distribution of stable and convectively neutral air masses is examined in climate simulations with carbon dioxide levels spanning from modern-day values to very high levels that produce surface temperatures relevant to the hottest climate of the past 65 million years. To investigate how stability with respect to slantwise and upright moist convection changes across a wide range of climate states, the condition of moist convective neutrality in climate experiments is assessed using metrics based upon the saturation of potential vorticity, which is zero when temperature profiles are moist adiabatic profiles along vortex lines. The modern climate experiment reproduces previously reported properties from reanalysis data, in which convectively neutral air masses are common in the tropics and locally at higher latitudes, especially over midlatitude continents in summer and ocean storm tracks in winter. The frequency and coverage of air masses with higher stabilities declines in all seasons at higher latitudes with warming; the hottest case features convectively neutral air masses in the Arctic a majority of the time in January and nearly universally in July. The contribution from slantwise convective motions (as distinct from upright convection) is generally small outside of midlatitude storm tracks, and it declines in the warmer climate experiments, especially during summer. These findings support the conjecture that moist adiabatic lapse rates become more widespread in warmer climates, providing a physical basis for using this assumption in estimating paleoaltimetry during warm intervals such as the early Eocene.

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Building a cloud in the Southeast Atlantic: Understanding low-cloud controls based on satellite observations with machine learning

10.5194/acp-2018-593 ◽

2018 ◽

Cited By ~ 1

Author(s):

Julia Fuchs ◽

Jan Cermak ◽

Hendrik Andersen

Keyword(s):

Machine Learning ◽

Large Scale ◽

Cloud Droplet ◽

Reanalysis Data ◽

Cloud Fraction ◽

Effective Radius ◽

Gradient Boosting ◽

Tropospheric Temperature ◽

Aerosol Cloud ◽

Low Cloud

Abstract. Understanding the processes that determine low-cloud properties and aerosol–cloud interactions (ACI) is crucial for the estimation of their radiative effects. However, the covariation of meteorology and aerosols complicates the determination of cloud-relevant influences and the quantification of the aerosol–cloud relation. This study identifies and analyzes sensitivities of cloud fraction and cloud droplet effective radius to their meteorological and aerosol environment in the atmospherically stable Southeast Atlantic during the biomass-burning season. The effect of geophysical parameters on clouds is investigated based on a machine learning technique, gradient boosting regression trees (GBRTs), using a combination of satellite and reanalysis data as well as trajectory modeling of air-mass origins. A comprehensive, multivariate analysis of important drivers of cloud occurrence and properties is performed and evaluated. The statistical model reveals marked subregional differences of relevant drivers and processes determining low clouds in the Southeast Atlantic. Cloud fraction is sensitive to changes of lower tropospheric stability in the oceanic, southwestern subregion, while in the northeastern subregion it is governed mostly by surface winds. In the pristine, oceanic subregion large-scale dynamics and aerosols seem to be more important for changes of cloud droplet effective radius than in the polluted, near-shore subregion, where free tropospheric temperature is more relevant. This study suggests the necessity to consider distinct ACI regimes in cloud studies in the Southeast Atlantic.

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Satellite-based estimate of the variability of warm cloud properties associated with aerosol and meteorological conditions

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-18187-2018 ◽

2018 ◽

Vol 18 (24) ◽

pp. 18187-18202 ◽

Cited By ~ 1

Author(s):

Yuqin Liu ◽

Jiahua Zhang ◽

Putian Zhou ◽

Tao Lin ◽

Juan Hong ◽

...

Keyword(s):

Cloud Cover ◽

Cloud Droplet ◽

Cloud Fraction ◽

Meteorological Conditions ◽

Liquid Water Path ◽

Time Step ◽

Aerosol Cloud ◽

Cloud Properties ◽

Almost All ◽

Step Over

Abstract. Aerosol–cloud interaction (ACI) is examined using 10 years of data from the MODIS/Terra (morning orbit) and MODIS/Aqua (afternoon orbit) satellites. Aerosol optical depth (AOD) and cloud properties retrieved from both sensors are used to explore in a statistical sense the morning-to-afternoon variation of cloud properties in conditions with low and high AOD, over both land and ocean. The results show that the interaction between aerosol particles and clouds is more complex and of greater uncertainty over land than over ocean. The variation in d(Cloud_X), defined as the mean change in cloud property Cloud_X between the morning and afternoon overpasses in high-AOD conditions minus that in low-AOD conditions, is different over land and ocean. This applies to cloud droplet effective radius (CDR), cloud fraction (CF) and cloud top pressure (CTP), but not to cloud optical thickness (COT) and cloud liquid water path (CWP). Both COT and CWP increase over land and ocean after the time step, irrespective of the AOD. However, the initial AOD conditions can affect the amplitude of variation of COT and CWP. The effects of initial cloud fraction and meteorological conditions on the change in CF under low- and high-AOD conditions after the 3 h time step over land are also explored. Two cases are considered: (1) when the cloud cover increases and (2) when the cloud cover decreases. For both cases, we find that almost all values of d(CF) are positive, indicating that the variations of CF are larger in high AOD than that in low AOD after the 3 h time step. The results also show that a large increase in cloud fraction occurs when scenes experience large AOD and stronger upward motion of air parcels. Furthermore, the increase rate of cloud cover is larger for high AOD with increasing relative humidity (RH) when RH is larger than 20 %. We also find that a smaller increase in cloud fraction occurs when scenes experience larger AOD and larger initial cloud cover. Overall, the analysis of the diurnal variation of cloud properties provides a better understanding of aerosol–cloud interaction over land and ocean.

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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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An emulator approach to stratocumulus susceptibility

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-10191-2019 ◽

2019 ◽

Vol 19 (15) ◽

pp. 10191-10203 ◽

Cited By ~ 6

Author(s):

Franziska Glassmeier ◽

Fabian Hoffmann ◽

Jill S. Johnson ◽

Takanobu Yamaguchi ◽

Ken S. Carslaw ◽

...

Keyword(s):

Initial Conditions ◽

Cloud Amount ◽

Cloud Fraction ◽

Surface Fluxes ◽

Complex Data ◽

Radiative Effect ◽

Liquid Water Path ◽

Cloud Albedo ◽

Cloud Radiative Effect ◽

Wide Range

Abstract. The climatic relevance of aerosol–cloud interactions depends on the sensitivity of the radiative effect of clouds to cloud droplet number N, and liquid water path LWP. We derive the dependence of cloud fraction CF, cloud albedo AC, and the relative cloud radiative effect rCRE=CF⋅AC on N and LWP from 159 large-eddy simulations of nocturnal stratocumulus. These simulations vary in their initial conditions for temperature, moisture, boundary-layer height, and aerosol concentration but share boundary conditions for surface fluxes and subsidence. Our approach is based on Gaussian-process emulation, a statistical technique related to machine learning. We succeed in building emulators that accurately predict simulated values of CF, AC, and rCRE for given values of N and LWP. Emulator-derived susceptibilities ∂ln⁡rCRE/∂ln⁡N and ∂ln⁡rCRE/∂ln⁡LWP cover the nondrizzling, fully overcast regime as well as the drizzling regime with broken cloud cover. Theoretical results, which are limited to the nondrizzling regime, are reproduced. The susceptibility ∂ln⁡rCRE/∂ln⁡N captures the strong sensitivity of the cloud radiative effect to cloud fraction, while the susceptibility ∂ln⁡rCRE/∂ln⁡LWP describes the influence of cloud amount on cloud albedo irrespective of cloud fraction. Our emulation-based approach provides a powerful tool for summarizing complex data in a simple framework that captures the sensitivities of cloud-field properties over a wide range of states.

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A new OCO-2 cloud flagging and rapid retrieval of marine boundary layer cloud properties

10.5194/amt-2020-140 ◽

2020 ◽

Author(s):

Mark Richardson ◽

Matthew D. Lebsock ◽

James McDuffie ◽

Graeme L. Stephens

Keyword(s):

Marine Boundary Layer ◽

A Priori ◽

Cloud Droplet ◽

Lookup Table ◽

Cloud Properties ◽

Cloud Droplet Number Concentration ◽

Boundary Layer Cloud ◽

Priori Information ◽

Heterogeneous Cloud ◽

Cloud Top Pressure

Abstract. The Orbiting Carbon Observatory-2 (OCO-2) carries a hyperspectral A-band sensor that can obtain information about cloud geometric thickness (H). The OCO2CLD-LIDAR-AUX product retrieved H with the aid of collocated CALIPSO lidar data to identify suitable clouds and provide a priori cloud-top pressure (Ptop). This collocation is no longer possible since CALIPSO's coordination flying with OCO-2 has ended, so here we introduce a new cloud flagging and a priori assignment using only OCO-2 data, restricted to ocean footprints where solar zenith angle 1) for a valid retrieval, and agreement with MODIS-CALIPSO is 90.0 %. Secondly, we developed a lookup table to simultaneously retrieve cloud τ, effective radius (re) and Ptop from A-band and CO2 band radiances. Median Ptop difference versus CALIPSO is 12 hPa with interdecile range [−11,87] hPa, substantially better than the MODIS-CALIPSO [−83,81] hPa. The MODIS-OCO-2 τ difference is 0.8 (−3.8,6.9) and re is −0.3 [−2.8,2.1] μm. The tau difference is due to optically thick and horizontally heterogeneous cloud scenes. As well as an improved passive Ptop retrieval, this a priori information will allow a purely OCO-2 based Bayesian retrieval of cloud droplet number concentration (Nd). Finally, our cloud flagging procedure may also be useful for future partial column above-cloud CO2 abundance retrievals.

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An emulator approach to stratocumulus susceptibility

10.5194/acp-2018-1342 ◽

2019 ◽

Author(s):

Franziska Glassmeier ◽

Fabian Hoffmann ◽

Jill S. Johnson ◽

Takanobu Yamaguchi ◽

Ken S. Carslaw ◽

...

Keyword(s):

Initial Conditions ◽

Cloud Amount ◽

Cloud Fraction ◽

Surface Fluxes ◽

Complex Data ◽

Radiative Effect ◽

Liquid Water Path ◽

Cloud Albedo ◽

Cloud Radiative Effect ◽

Wide Range

Abstract. The climatic relevance of aerosol-cloud interactions depends on the sensitivity of the radiative effect of clouds to cloud droplet number N and liquid water path LWP. We derive the dependence of cloud fraction CF, cloud albedo AC and the relative cloud radiative effect rCRE = CF · AC on N and LWP from 159 large-eddy simulations of nocturnal stratocumulus. These simulations vary in their initial conditions for temperature, moisture, boundary-layer height and aerosol concentration but share boundary conditions for surface fluxes and subsidence. Our approach is based on Gaussian process emulation, a statistical technique related to machine learning. We succeed in building emulators that accurately predict simulated values of CF, AC and rCRE for given values of N and LWP. Emulator-derived susceptibilities ∂ ln rCRE/∂ ln N and ∂ ln rCRE/∂ ln LWP cover the non-drizzling, fully-overcast regime as well as the drizzling regime with broken cloud cover. Theoretical results, which are limited to the non-drizzling regime, are reproduced. The susceptibility ∂ ln rCRE/∂ ln N captures the strong sensitivity of the cloud radiative effect to cloud fraction, while the susceptibility ∂ ln rCRE/∂ ln LWP describes the influence of cloud amount on cloud albedo irrespective of cloud fraction. Our emulation-based approach provides a powerful tool for summarizing complex data in a simple framework that captures the sensitivities of cloud field properties over a wide range of states.

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Postfrontal nanoparticles at Cape Grim: impact on cloud nuclei concentrations

Environmental Chemistry ◽

10.1071/en09076 ◽

2009 ◽

Vol 6 (6) ◽

pp. 515 ◽

Cited By ~ 6

Author(s):

John L. Gras

Keyword(s):

Growth Rates ◽

Concentration Ratio ◽

Marine Boundary Layer ◽

Cloud Droplet ◽

Particle Growth ◽

Particle Removal ◽

Cloud Properties ◽

Droplet Nuclei ◽

Background Particle ◽

Cape Grim

Environmental context. Accurate prediction of climate change requires good knowledge of all the contributing processes; those processes controlling clouds and cloud properties are of particular importance. In this study the growth of bursts of nanometre-sized particles observed following cold fronts over the Southern Ocean was modelled to assess their importance as a source of cloud droplet nuclei. This showed that these post-frontal events were responsible for ~8% of the cloud nucleus population in winter but much less in summer. Abstract. Aerosol removal and growth rates were determined for the Cape Grim marine boundary layer (MBL) using local observations. Background particle growth rates, estimated using replacement of condensable sulfur species lost to particle removal are 0.04 nm h–1 (winter) and 0.17 nm h–1 (summer) and for post-frontal nucleation-events growth rates determined using evolution of the concentration ratio of particles with diameter >3 nm and 11 nm are ~0.3–0.4 nm h–1, consistent with reported high-latitude events. A box model using region-specific loss and growth rates predicts free-troposphere/MBL N3 ratios of 1.3–2.1 and 2.4–2.5 for background and event growth rates, compared with observations in the range of 0.7–1.5. Post-frontal nucleation events were found to contribute from <1 to ~8% of the CCN population depending on season and growth rate. However, these events help maintain the MBL Aitken population, contributing up to ~30%.

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Comparing ERA-Interim clouds with satellite observations using a simplified satellite simulator

10.5194/acp-2018-258 ◽

2018 ◽

Cited By ~ 2

Author(s):

Martin Stengel ◽

Cornelia Schlundt ◽

Stefan Stapelberg ◽

Oliver Sus ◽

Salomon Eliasson ◽

...

Keyword(s):

Optical Thickness ◽

Reanalysis Data ◽

Cloud Fraction ◽

Satellite Observations ◽

Vertical Position ◽

Polar Regions ◽

Cloud Properties ◽

Low Clouds ◽

Low Cloud ◽

Cloud Optical Thickness

Abstract. An evaluation of the ERA-Interim clouds using satellite observations is presented. To facilitate such an evaluation in a proper way, a simplified satellite simulator has been developed and applied to six-hourly ERA-Interim reanalysis data covering the period 1982 to 2014. The simulator converts modelled cloud fields, for example those of the ERA-Interim reanalysis, to simulated cloud fields by accounting for specific characteristics of passive imaging satellite sensors such as the Advanced Very High Resolution Radiometer (AVHRR), which form the basis of many long-term observational datasets of cloud properties. It is attempted to keep the simulated cloud fields close to the original modelled cloud fields to allow a quality assessment of the latter based on comparisons of the simulated clouds fields with the observations. Applying the simulator to ERA-Interim data, this study firstly focuses on spatial distribution and frequency of clouds (total cloud fraction) and on their vertical position, using cloud top pressure to express the cloud fraction of high, mid-level and low clouds. Furthermore, the cloud-top thermodynamic phase is investigated. All comparisons incorporate knowledge of systematic uncertainties in the satellite observations and are further stratified by accounting for the limited sensitivity of the observations to clouds with very low cloud optical thickness (COT). The comparisons show that ERA-Interim has generally too low cloud fraction – nearly everywhere on the globe except in the polar regions. This underestimation is caused by a lack of mid-level and/or low clouds – for which the comparisons only show a minor sensitivity to cloud optical thickness thresholds applied. The amount of ERA-Interim high clouds, being higher than in the observations, agrees to the observations within their estimated uncertainties. Removing the optically very thin clouds (COT

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