Postfrontal nanoparticles at Cape Grim: impact on cloud nuclei concentrations

2009 ◽  
Vol 6 (6) ◽  
pp. 515 ◽  
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%.

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

2018 ◽  
Vol 18 (19) ◽  
pp. 14623-14636 ◽  
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.

Postfrontal nanoparticles at Cape Grim: observations

2009 ◽  
Vol 6 (6) ◽  
pp. 508 ◽  
Author(s):  
John L. Gras ◽  
Salah I. Jimi ◽  
Steven T. Siems ◽  
Paul B. Krummel
Keyword(s):  
Global Climate ◽  
Cloud Droplet ◽  
Condensation Nucleus ◽  
Cold Fronts ◽  
Peak Separation ◽  
Cloud Properties ◽  
Mesoscale Structures ◽  
Counter Efficiency ◽  
Essential Components ◽  
Cape Grim

Environmental context. Clouds and the factors controlling cloud properties are essential components in understanding and accurately predicting global climate change. This work examines nanometre-sized atmospheric particles, particularly bursts of enhanced particle concentrations following cold fronts over the Southern Ocean. The properties of these events have been established to enable modelling of their significance as a source of cloud-droplet-forming nuclei. Abstract. Nanoparticles (diameter <10 nm) were studied in clean maritime air at Cape Grim over a 2-year period. Concentrations were determined using a condensation nucleus counter (CNC) and an ultra-CNC (UCNC), requiring careful treatment of drifts in counter efficiency. This is the first extended examination of nanoparticles following cold fronts and shows that nanoparticle enhancements were present following 94% of 121 cold fronts studied. Typical enhancements were ~100 cm–3 with maxima ~300–500 cm–3, occur 9–11 h after the front and contain multiple peaks with peak-to-peak separation of 8–11 h. Most enhancements were associated with drier conditions, indicative of increased entrainment of free-tropospheric air after the front. The quasi-periodicity of the enhancements may be related to mesoscale structures in cloud fields following fronts but this requires testing. This quantification of event properties allows evaluation of the significance of these events for the cloud nucleating particle (CCN) population.

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

2019 ◽  
Vol 147 (12) ◽  
pp. 4681-4700 ◽  
Author(s):  
Johannes Mohrmann ◽  
Christopher S. Bretherton ◽  
Isabel L. McCoy ◽  
Jeremy McGibbon ◽  
Robert Wood ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Layer Structure ◽  
Cloud Droplet ◽  
Reanalysis Data ◽  
Cloud Fraction ◽  
Surface Fluxes ◽  
Strategy Analysis ◽  
Air Masses ◽  
Cloud Properties ◽  
Wide Range

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.

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

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.

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

2018 ◽  
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 ObseRvtions 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. 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 are also expected to obscure the relationship between above-cloud smoke and cloud properties in parts of the southeast Atlantic, although 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.

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 Linking large-scale circulation patterns to low-cloud properties

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.

scholarly journals A new Orbiting Carbon Observatory 2 cloud flagging method and rapid retrieval of marine boundary layer cloud properties

2020 ◽  
Vol 13 (9) ◽  
pp. 4947-4961
Author(s):  
Mark Richardson ◽  
Matthew D. Lebsock ◽  
James McDuffie ◽  
Graeme L. Stephens
Keyword(s):  
Marine Boundary Layer ◽  
A Priori ◽  
Cloud Droplet ◽  
Satellite Observation ◽  
Lookup Table ◽  
Cloud Properties ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Boundary Layer Cloud ◽  
Priori Information ◽  
Heterogeneous Cloud

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 (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) 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 <45∘. Firstly, a multi-layer perceptron network was trained to identify liquid clouds over the ocean with sufficient optical depth (τ>1) for a valid retrieval, and agreement with MODIS–CALIPSO (Moderate Resolution Imaging Spectroradiometer) 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, with the intention that these will act as the a priori state estimate in a future retrieval. Median Ptop difference vs. CALIPSO is 12 hPa with an inter-decile range of [-11,87]hPa, substantially better than the MODIS–CALIPSO range of [-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 τ 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 for 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.

scholarly journals Linking large-scale circulation patterns to low-cloud properties

2019 ◽  
Author(s):  
Timothy W. Juliano ◽  
Zachary J. Lebo
Keyword(s):  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Warm Season ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Synoptic Scale ◽  
Cloud Properties ◽  
Circulation Patterns

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, which yields the frequency at which these regimes occur, reveals two distinguishable patterns – a dominant NPH setup and a land-falling cyclone – and in between a spectrum of regimes. We then use satellite retrievals to elucidate for the first time the explicit dependence of MBL cloud properties (namely cloud droplet number concentration and cloud droplet effective radius) on 850-hPa circulation patterns over the northeast Pacific Ocean. Moreover, we find that shortwave cloud radiative forcing ranges from − 144.0 to − 117.5 W/m2, indicating that the range of MBL cloud properties must be accounted for in global and regional climate models. Our results demonstrate the value of combining reanalysis and satellite observations to help clarify the relationship between synoptic-scale dynamics and cloud microphysics.

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.

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