scholarly journals Large eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey area ship track experiment

2015 ◽  
Vol 15 (10) ◽  
pp. 5851-5871 ◽  
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for 8 h (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of the cloud into mesoscale rolls. After 8 h, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In that case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

scholarly journals Large-eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey Area Ship Track experiment

2014 ◽  
Vol 14 (17) ◽  
pp. 24387-24439
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large-eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for eight hours (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of cloud into mesoscale rolls. After eight hours, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In this case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

scholarly journals Large Eddy Simulation of the Diurnal Cycle in Southeast Pacific Stratocumulus

2009 ◽  
Vol 66 (2) ◽  
pp. 432-449 ◽  
Author(s):  
Peter Caldwell ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Water Path ◽  
Diurnal Cycles ◽  
Eddy Simulation ◽  
Droplet Concentration ◽  
Large Eddy

Abstract This paper describes a series of 6-day large eddy simulations of a deep, sometimes drizzling stratocumulus-topped boundary layer based on forcings from the East Pacific Investigation of Climate (EPIC) 2001 field campaign. The base simulation was found to reproduce the observed mean boundary layer properties quite well. The diurnal cycle of liquid water path was also well captured, although good agreement appears to result partially from compensating errors in the diurnal cycles of cloud base and cloud top due to overentrainment around midday. At all times of the day, entrainment is found to be proportional to the vertically integrated buoyancy flux. Model stratification matches observations well; turbulence profiles suggest that the boundary layer is always at least somewhat decoupled. Model drizzle appears to be too sensitive to liquid water path and subcloud evaporation appears to be too weak. Removing the diurnal cycle of subsidence had little effect on simulated liquid water path. Simulations with changed droplet concentration and drizzle susceptibility showed large liquid water path differences at night, but differences were quite small at midday. Droplet concentration also had a significant impact on entrainment, primarily through droplet sedimentation feedback rather than through drizzle processes.

Reconciling and Validating the Cloud Thickness and Liquid Water Path Tendencies Proposed by R. Wood and J. J. van der Dussen et al.

2015 ◽  
Vol 72 (5) ◽  
pp. 2033-2040 ◽  
Author(s):  
Mohamed S. Ghonima ◽  
Joel R. Norris ◽  
Thijs Heus ◽  
Jan Kleissl
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Mixed Boundary ◽  
Liquid Water Path ◽  
Water Path ◽  
Large Eddy ◽  
Heat And Moisture ◽  
Cloud Thickness ◽  
Detailed Derivation ◽  
Good Agreement

Abstract A detailed derivation of stratocumulus cloud thickness and liquid water path tendencies as a function of the well-mixed boundary layer mass, heat, and moisture budget equations is presented. The derivation corrects an error in the cloud thickness tendency equation derived by R. Wood to make it consistent with the liquid water path tendency equation derived by J. J. van der Dussen et al. The validity of the tendency equations is then tested against the output of large-eddy simulations of a typical stratocumulus-topped boundary layer case and is found to be in good agreement.

scholarly journals Nocturnal Boundary Layer Erosion Analysis in the Amazon Using Large-Eddy Simulation during GoAmazon Project 2014/5

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 240
Author(s):  
Rayonil Carneiro ◽  
Gilberto Fisch ◽  
Theomar Neves ◽  
Rosa Santos ◽  
Carlos Santos ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Rainy Season ◽  
Nocturnal Boundary Layer ◽  
Enso Event ◽  
Dry Season ◽  
Dry Period ◽  
Additional Energy ◽  
Eddy Simulation ◽  
Large Eddy

This study investigated the erosion of the nocturnal boundary layer (NBL) over the central Amazon using a high-resolution model of large-eddy simulation (LES) named PArallel Les Model (PALM) and observational data from Green Ocean Amazon (GoAmazon) project 2014/5. This data set was collected during four intense observation periods (IOPs) in the dry and rainy seasons in the years 2014 (considered a typical year) and 2015, during which an El Niño–Southern Oscillation (ENSO) event predominated and provoked an intense dry season. The outputs from the PALM simulations represented reasonably well the NBL erosion, and the results showed that it has different characteristics between the seasons. During the rainy season, the IOPs exhibited slow surface heating and less intense convection, which resulted in a longer erosion period, typically about 3 h after sunrise (that occurs at 06:00 local time). In contrast, dry IOPs showed more intensive surface warming with stronger convection, resulting in faster NBL erosion, about 2 h after sunrise. A conceptual model was derived to investigate the complete erosion during sunrise hours when there is a very shallow mixed layer formed close to the surface and a stable layer above. The kinematic heat flux for heating this layer during the erosion period showed that for the rainy season, the energy emitted from the surface and the entrainment was not enough to fully heat the NBL layer and erode it. Approximately 30% of additional energy was used in the system, which could come from the release of energy from biomass. The dry period of 2014 showed stronger heating, but it was also not enough, requiring approximately 6% of additional energy. However, for the 2015 dry period, which was under the influence of the ENSO event, it was shown that the released surface fluxes were sufficient to fully heat the layer. The erosion time of the NBL probably influenced the development of the convective boundary layer (CBL), wherein greater vertical development was observed in the dry season IOPs (~1500 m), while the rainy season IOPs had a shallower layer (~1200 m).

Large Eddy Simulation of the Wake Behind a Turning Ship

2002 ◽  
Author(s):  
Ibrahim Yavuz ◽  
Zeynep N. Cehreli ◽  
Ismail B. Celik ◽  
Shaoping Shi
Keyword(s):  
Large Eddy Simulation ◽  
Sensitivity Study ◽  
West Virginia University ◽  
Vortical Structures ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Flow Generation ◽  
Large Eddy ◽  
Unsteady Inflow ◽  
Random Flow

This study examines the dynamics of turbulent flow in the wake of a turning ship using the large eddy simulation (LES) technique. LES is applied in conjunction with a random flow generation (RFG) technique originally developed at West Virginia University to provide unsteady inflow boundary conditions. As the ship is turning, the effects of the Coriolis and centrifugal forces on vortical structures are included. The effects of the Coriolis force on the flow-field are assessed and a grid sensitivity study is performed. The predicted turbulence structures are analyzed and compared with the wake of a non-turning ship.

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