Optical properties of marine stratocumulus clouds modified by ships

1993 ◽  
Vol 98 (D2) ◽  
pp. 2729-2739 ◽  
Author(s):  
Michael D. King ◽  
Lawrence F. Radke ◽  
Peter V. Hobbs
Keyword(s):  
Optical Properties ◽  
Marine Stratocumulus ◽  
Stratocumulus Clouds

scholarly journals Cloud droplets to drizzle: Contribution of transition drops to microphysical and optical properties of marine stratocumulus clouds

2017 ◽  
Vol 44 (15) ◽  
pp. 8002-8010 ◽  
Author(s):  
S. Glienke ◽  
A. Kostinski ◽  
J. Fugal ◽  
R. A. Shaw ◽  
S. Borrmann ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cloud Droplets ◽  
Marine Stratocumulus ◽  
Stratocumulus Clouds

scholarly journals Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem

2011 ◽  
Vol 11 (23) ◽  
pp. 11951-11975 ◽  
Author(s):  
Q. Yang ◽  
J. D. Fast ◽  
H. Wang ◽  
R. C. Easter ◽  
H. Morrison ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Cloud Droplet ◽  
Energy Fluxes ◽  
Microphysics Scheme ◽  
Marine Stratocumulus ◽  
Aerosol Cloud ◽  
Southeast Pacific ◽  
Temperature And Humidity ◽  
Stratocumulus Clouds

Abstract. This study assesses the ability of the recent chemistry version (v3.3) of the Weather Research and Forecasting (WRF-Chem) model to simulate boundary layer structure, aerosols, stratocumulus clouds, and energy fluxes over the Southeast Pacific Ocean. Measurements from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) and satellite retrievals (i.e., products from the MODerate resolution Imaging Spectroradiometer (MODIS), Clouds and Earth's Radiant Energy System (CERES), and GOES-10) are used for this assessment. The Morrison double-moment microphysics scheme is newly coupled with interactive aerosols in the model. The 31-day (15 October–16 November 2008) WRF-Chem simulation with aerosol-cloud interactions (AERO hereafter) is also compared to a simulation (MET hereafter) with fixed cloud droplet number concentrations in the microphysics scheme and simplified cloud and aerosol treatments in the radiation scheme. The well-simulated aerosol quantities (aerosol number, mass composition and optical properties), and the inclusion of full aerosol-cloud couplings lead to significant improvements in many features of the simulated stratocumulus clouds: cloud optical properties and microphysical properties such as cloud top effective radius, cloud water path, and cloud optical thickness. In addition to accounting for the aerosol direct and semi-direct effects, these improvements feed back to the simulation of boundary-layer characteristics and energy budgets. Particularly, inclusion of interactive aerosols in AERO strengthens the temperature and humidity gradients within the capping inversion layer and lowers the marine boundary layer (MBL) depth by 130 m from that of the MET simulation. These differences are associated with weaker entrainment and stronger mean subsidence at the top of the MBL in AERO. Mean top-of-atmosphere outgoing shortwave fluxes, surface latent heat, and surface downwelling longwave fluxes are in better agreement with observations in AERO, compared to the MET simulation. Nevertheless, biases in some of the simulated meteorological quantities (e.g., MBL temperature and humidity) and aerosol quantities (e.g., underestimations of accumulation mode aerosol number) might affect simulated stratocumulus and energy fluxes over the Southeastern Pacific, and require further investigation. The well-simulated timing and outflow patterns of polluted and clean episodes demonstrate the model's ability to capture daily/synoptic scale variations of aerosol and cloud properties, and suggest that the model is suitable for studying atmospheric processes associated with pollution outflow over the ocean. The overall performance of the regional model in simulating mesoscale clouds and boundary layer properties is encouraging and suggests that reproducing gradients of aerosol and cloud droplet concentrations and coupling cloud-aerosol-radiation processes are important when simulating marine stratocumulus over the Southeast Pacific.

scholarly journals Factors Controlling Rapid Stratocumulus Cloud Thinning

2014 ◽  
Vol 71 (2) ◽  
pp. 655-664 ◽  
Author(s):  
J. J. van der Dussen ◽  
S. R. de Roode ◽  
A. P. Siebesma
Keyword(s):  
Moisture Flux ◽  
Steady State Solution ◽  
Cloud Layer ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Buoyancy Reversal ◽  
Stratocumulus Clouds ◽  
Budget Equation ◽  
Heat And Moisture

Abstract The relationship between the inversion stability and the liquid water path (LWP) tendency of a vertically well-mixed, adiabatic stratocumulus cloud layer is investigated in this study through the analysis of the budget equation for the LWP. The LWP budget is mainly determined by the turbulent fluxes of heat and moisture at the top and the base of the cloud layer, as well as by the source terms due to radiation and precipitation. Through substitution of the inversion stability parameter κ into the budget equation, it immediately follows that the LWP tendency will become negative for increasing values of κ due to the entrainment of increasingly dry air. Large κ values are therefore associated with strong cloud thinning. Using the steady-state solution for the LWP, an equilibrium value κeq is formulated, beyond which the stratocumulus cloud will thin. The Second Dynamics and Chemistry of Marine Stratocumulus field study (DYCOMS-II) is used to illustrate that, depending mainly on the magnitude of the moisture flux at cloud base, stratocumulus clouds can persist well within the buoyancy reversal regime.

Can Marine Cloud Brightening Reduce Sea-Surface Temperatures to Moderate Extreme Hurricanes and Typhoons?

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Salter SH ◽  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Sea Water ◽  
Cloud Condensation Nuclei ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Marine Stratocumulus ◽  
Surface Temperatures ◽  
Stratocumulus Clouds ◽  
Cloud Tops

Elevated sea-surface temperatures are a necessary but not sufficient requirement for the formation of hurricanes and typhoons. This paper suggests a way to exploit this. Twomey [1] showed that cloud reflectivity depends on the size-distribution of cloud drops, with a large number of small drops reflecting more than a smaller number of larger ones. Mid-ocean air is cleaner than over land. Latham [2-4] suggested that reflectivity of marine stratocumulus clouds could be increased by releasing a submicron spray of filtered sea water into the bottom of the marine boundary layer. The salt residues left after evaporation would be mixed by turbulence through the full depth of the marine boundary layer and would be ideal cloud condensation nuclei. Those that reached a height where the air had a super-saturation above 100% by enough to get over the peak of the Köhler curve would produce an increased number of cloud drops and so trigger the Twomey effect. The increase in reflection from cloud tops back out to space would cool sea-surface water. We are not trying to increase cloud cover; we just want to make existing cloud tops whiter. The spray could be produced by wind-driven vessels cruising chosen ocean regions. The engineering design of sea-going hardware is well advanced. This paper suggests a way to calculate spray quantities and the number and cost of spray vessels to achieve a hurricane reduction to a more acceptable intensity. It is intended to show the shape of a possible calculation with credible if not exact assumptions. Anyone with better assumptions should be able to follow the process.

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

2016 ◽  
Vol 16 (9) ◽  
pp. 5811-5839 ◽  
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.

Regional flow conditions associated with stratocumulus cloud-eroding boundaries over the southeast Atlantic

2021 ◽  
Author(s):  
Laura M. Tomkins ◽  
David B. Mechem ◽  
Sandra E. Yuter ◽  
Spencer R. Rhodes
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Weather Research And Forecasting ◽  
Marine Stratocumulus ◽  
Boundary Layer Height ◽  
Regional Flow ◽  
Stratocumulus Clouds ◽  
Offshore Flow ◽  
Passive Tracers ◽  
Atmospheric Gravity

AbstractLarge, abrupt clearing events have been documented in the marine stratocumulus cloud deck over the subtropical Southeast Atlantic Ocean. In these events, clouds are rapidly eroded along a line hundreds–to–thousands of kilometers in length that generally moves westward away from the coast. Because marine stratocumulus clouds exert a strong cooling effect on the planet, any phenomenon that acts to erode large areas of low clouds may be climatically important. Previous satellite-based research suggests that the cloud-eroding boundaries may be caused by westward-propagating atmospheric gravity waves rather than simple advection of the cloud. The behavior of the coastal offshore flow, which is proposed as a fundamental physical mechanism associated with the clearing events, is explored using the Weather Research and Forecasting model. Results are presented from several week-long simulations in the month of May when cloud-eroding boundaries exhibit maximum frequency. Two simulations cover periods containing multiple cloud-eroding boundaries (active periods), and two other simulations cover periods without any cloud-eroding boundaries (null periods). Passive tracers and an analysis of mass flux are used to assess the character of the diurnal west-African coastal circulation. Results indicate that the active periods containing cloud-eroding boundaries regularly experience stronger and deeper nocturnal offshore flow from the continent above the marine boundary layer, compared to the null periods. Additionally, we find that the boundary layer height is higher in the null periods than in the active periods, suggesting that the active periods are associated with areas of thinner clouds that may be more susceptible to cloud erosion.

Quantifying how model assumptions affect aerosol-cloud interactions in large-eddy simulations of warm stratocumulus clouds

2021 ◽  
Author(s):  
Matthias Schwarz ◽  
Julien Savre ◽  
Annica Ekman
Keyword(s):  
Number Concentration ◽  
Large Eddy Simulations ◽  
Radiation Balance ◽  
Marine Stratocumulus ◽  
Aerosol Cloud ◽  
Reference Simulation ◽  
Model Aerosol ◽  
Large Eddy ◽  
Stratocumulus Clouds ◽  
Climate Interactions

<p>Subtropical low-level marine stratocumulus clouds effectively reflect downwelling shortwave radiation while having a small effect on outgoing longwave radiation. Hence, they impose a strong negative net radiative effect on the Earth’s radiation balance. The optical and microphysical properties of these clouds are susceptible to anthropogenic changes in aerosol abundance. Although these aerosol-cloud-climate interactions (ACI) are generally explicitly treated in state-of-the-art Earth System Models (ESMs), they are accountable for large uncertainties in current climate projections.</p><p>Here, we present preliminary work where we exploit Large-Eddy-Simulations (LES) of warm stratocumulus clouds to identify and constrain processes and model assumptions that affect the response of cloud droplet number concentration (N<sub>d</sub>) to changes in aerosol number concentration (N<sub>a</sub>). Our results are based on simulations with the MISU-MIT Cloud-Aerosol (MIMICA, Savre et al., 2014) LES, which has two-moment bulk microphysics (Seifert and Beheng, 2001) and a two-moment aerosol scheme (Ekman et al., 2006). The reference simulation is based on observations made during the Dynamics and Chemistry of Marine Stratocumulus Field Study (DYCOMS-II, Stevens et al., 2003) which were used extensively during previous LES studies (e.g., Ackerman et al., 2009).</p><p>Starting from the reference simulation, we conduct sensitivity experiments to examine how the susceptibility (β=dln(N<sub>d</sub>)/dln(N<sub>a</sub>)) changes depending on different model setups. We run the model with fixed and interactive aerosol concentrations, with and without saturation adjustment, with different aerosol populations, and with different model parameter choices. Our early results suggest that β is sensitive to these choices and can vary roughly between 0.6 to 0.9 depending on the setup. The overall purpose of our study is to guide future model developments and evaluations concerning aerosol-cloud-climate interactions.  </p><p> </p><p><strong>References</strong></p><p>Ackerman, A. S., vanZanten, M. C., Stevens, B., Savic-Jovcic, V., Bretherton, C. S., Chlond, A., et al. (2009). Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer. Monthly Weather Review, 137(3), 1083–1110. https://doi.org/10.1175/2008MWR2582.1</p><p>Ekman, A. M. L., Wang, C., Ström, J., & Krejci, R. (2006). Explicit Simulation of Aerosol Physics in a Cloud-Resolving Model: Aerosol Transport and Processing in the Free Troposphere. Journal of the Atmospheric Sciences, 63(2), 682–696. https://doi.org/10.1175/JAS3645.1</p><p>Savre, J., Ekman, A. M. L., & Svensson, G. (2014). Technical note: Introduction to MIMICA, a large-eddy simulation solver for cloudy planetary boundary layers. Journal of Advances in Modeling Earth Systems, 6(3), 630–649. https://doi.org/10.1002/2013MS000292</p><p>Stevens, B., Lenschow, D. H., Vali, G., Gerber, H., Bandy, A., Blomquist, B., et al. (2003). Dynamics and Chemistry of Marine Stratocumulus—DYCOMS-II. Bulletin of the American Meteorological Society, 84(5), 579–594. https://doi.org/10.1175/BAMS-84-5-579</p>

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