Dilution of boundary layer cloud condensation nucleus concentrations by free tropospheric entrainment during marine cold air outbreaks

2021 ◽  
Author(s):  
Florian Tornow ◽  
Andrew S. Ackerman ◽  
Ann Fridlind ◽  
Brian Cairns ◽  
Ewan Crosbie ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Condensation Nucleus ◽  
Cloud Condensation Nucleus ◽  
Cold Air ◽  
Boundary Layer Cloud ◽  
Layer Cloud ◽  
Cold Air Outbreaks

scholarly journals Contrasting characteristics of open- and closed- cellular stratocumulus cloud in the Eastern North Atlantic

2021 ◽  
Author(s):  
Michael P. Jensen ◽  
Virendra P. Ghate ◽  
Dié Wang ◽  
Diana K. Apoznanski ◽  
Mary J. Bartholomew ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Open Cell ◽  
Cold Air ◽  
Closed Cell ◽  
Boundary Layer Cloud ◽  
Eastern North Atlantic ◽  
Layer Cloud

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their lifecycle and coverage. In particular, the mesoscale organization, and cellular structure of marine boundary clouds has important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal to identify cloud cases with open- or closed-cellular organization. More than 500 hours of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher-rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than one millimeter were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

scholarly journals Contrasting characteristics of open- and closed-cellular stratocumulus cloud in the eastern North Atlantic

2021 ◽  
Vol 21 (19) ◽  
pp. 14557-14571
Author(s):  
Michael P. Jensen ◽  
Virendra P. Ghate ◽  
Dié Wang ◽  
Diana K. Apoznanski ◽  
Mary J. Bartholomew ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Open Cell ◽  
Cold Air ◽  
Closed Cell ◽  
Boundary Layer Cloud ◽  
Eastern North Atlantic ◽  
Layer Cloud

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their life cycle and coverage. In particular, the mesoscale organization and cellular structure of marine boundary clouds have important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal, to identify cloud cases with open- or closed-cellular organization. More than 500 h of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic, and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than 1 mm were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

Boundary Layer, Cloud, and Drizzle Variability in the Southeast Pacific Stratocumulus Regime

2008 ◽  
Vol 21 (23) ◽  
pp. 6191-6214 ◽  
Author(s):  
Efthymios Serpetzoglou ◽  
Bruce A. Albrecht ◽  
Pavlos Kollias ◽  
Christopher W. Fairall
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Substantial Impact ◽  
Factors Affecting ◽  
Synoptic Conditions ◽  
Southeast Pacific ◽  
Boundary Layer Cloud ◽  
Similar Area ◽  
Earth’S Climate ◽  
Layer Cloud

Abstract The southeast Pacific stratocumulus regime is an important component of the earth’s climate system because of its substantial impact on albedo. Observational studies of this cloud regime have been limited, but during the past 5 yr, a series of cruises with research vessels equipped with in situ and remote sensing systems have provided unprecedented observations of boundary layer cloud and drizzle structures. These cruises started with the East Pacific Investigation of Climate (EPIC) 2001 field experiment, followed by cruises in a similar area in 2003 and 2004 [Pan-American Climate Studies (PACS) Stratus cruises]. The sampling from these three cruises provides a sufficient dataset to study the variability occurring over this region. This study compares observations from the 2004 cruise with those obtained during the previous two cruises. Observations from the ship provide information about boundary layer structure, fractional cloudiness, cloud depth, and drizzle characteristics. This study indicates more strongly decoupled boundary layers during the 2004 cruise than the well-mixed conditions that dominated the cloud and boundary layer structures during the EPIC cruise, and the highly variable conditions—sharp transitions from a solid stratus deck to broken-cloud and clear-sky periods—encountered during PACS Stratus 2003. Diurnal forcing and synoptic conditions are considered to be factors affecting these variations. A statistical evaluation of the macrophysical boundary layer, cloud, and drizzle properties is performed using the 5–6-day periods for which the research vessels remained stationed at the location of 20°S, 85°W during each cruise.

scholarly journals Marine boundary layer cloud regimes and POC formation in a CRM coupled to a bulk aerosol scheme

2013 ◽  
Vol 13 (24) ◽  
pp. 12549-12572 ◽  
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood ◽  
A. Muhlbauer
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Three Dimensional ◽  
Two Dimensional ◽  
State Variables ◽  
Liquid Water Path ◽  
Modeling Framework ◽  
Boundary Layer Cloud ◽  
Cloud Regimes ◽  
Layer Cloud

Abstract. A cloud-resolving model (CRM) coupled to a new intermediate-complexity bulk aerosol scheme is used to study aerosol–boundary-layer–cloud–precipitation interactions and the development of pockets of open cells (POCs) in subtropical stratocumulus cloud layers. The aerosol scheme prognoses mass and number concentration of a single lognormal accumulation mode with surface and entrainment sources, evolving subject to processing of activated aerosol and scavenging of dry aerosol by clouds and rain. The CRM with the aerosol scheme is applied to a range of steadily forced cases idealized from a well-observed POC. The long-term system evolution is explored with extended two-dimensional (2-D) simulations of up to 20 days, mostly with diurnally averaged insolation and 24 km wide domains, and one 10 day three-dimensional (3-D) simulation. Both 2-D and 3-D simulations support the Baker–Charlson hypothesis of two distinct aerosol–cloud "regimes" (deep/high-aerosol/non-drizzling and shallow/low-aerosol/drizzling) that persist for days; transitions between these regimes, driven by either precipitation scavenging or aerosol entrainment from the free-troposphere (FT), occur on a timescale of ten hours. The system is analyzed using a two-dimensional phase plane with inversion height and boundary layer average aerosol concentrations as state variables; depending on the specified subsidence rate and availability of FT aerosol, these regimes are either stable equilibria or distinct legs of a slow limit cycle. The same steadily forced modeling framework is applied to the coupled development and evolution of a POC and the surrounding overcast boundary layer in a larger 192 km wide domain. An initial 50% aerosol reduction is applied to half of the model domain. This has little effect until the stratocumulus thickens enough to drizzle, at which time the low-aerosol portion transitions into open-cell convection, forming a POC. Reduced entrainment in the POC induces a negative feedback between the areal fraction covered by the POC and boundary layer depth changes. This stabilizes the system by controlling liquid water path and precipitation sinks of aerosol number in the overcast region, while also preventing boundary layer collapse within the POC, allowing the POC and overcast to coexist indefinitely in a quasi-steady equilibrium.

Modeling Arctic Boundary Layer Cloud Streets at Grey-zone Resolutions

2019 ◽  
Vol 37 (1) ◽  
pp. 42-56
Author(s):  
Hui-Wen Lai ◽  
Fuqing Zhang ◽  
Eugene E. Clothiaux ◽  
David R. Stauffer ◽  
Brian J. Gaudet ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Grey Zone ◽  
Arctic Boundary Layer ◽  
Boundary Layer Cloud ◽  
Layer Cloud

The Climatology, Meteorology, and Boundary Layer Structure of Marine Cold Air Outbreaks in Both Hemispheres*

2016 ◽  
Vol 29 (6) ◽  
pp. 1999-2014 ◽  
Author(s):  
Jennifer Fletcher ◽  
Shannon Mason ◽  
Christian Jakob
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Pressure Gradients ◽  
Cold Air ◽  
Surface Heat Fluxes ◽  
Cold Air Outbreak ◽  
Wide Range ◽  
Cold Air Outbreaks

Abstract A comparison of marine cold air outbreaks (MCAOs) in the Northern and Southern Hemispheres is presented, with attention to their seasonality, frequency of occurrence, and strength as measured by a cold air outbreak index. When considered on a gridpoint-by-gridpoint basis, MCAOs are more severe and more frequent in the Northern Hemisphere (NH) than the Southern Hemisphere (SH) in winter. However, when MCAOs are viewed as individual events regardless of horizontal extent, they occur more frequently in the SH. This is fundamentally because NH MCAOs are larger and stronger than those in the SH. MCAOs occur throughout the year, but in warm seasons and in the SH they are smaller and weaker than in cold seasons and in the NH. In both hemispheres, strong MCAOs occupy the cold air sector of midlatitude cyclones, which generally appear to be in their growth phase. Weak MCAOs in the SH occur under generally zonal flow with a slight northward component associated with weak zonal pressure gradients, while weak NH MCAOs occur under such a wide range of conditions that no characteristic synoptic pattern emerges from compositing. Strong boundary layer deepening, warming, and moistening occur as a result of the surface heat fluxes within MCAOs.

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