scholarly journals Relationship between the Vertical Velocity Skewness and Kurtosis Observed during Sea-Breeze Convection

2002 ◽  
Vol 41 (8) ◽  
pp. 885-889 ◽  
Author(s):  
S. Alberghi ◽  
A. Maurizi ◽  
F. Tampieri
Keyword(s):  
Vertical Velocity ◽  
Sea Breeze ◽  
Skewness And Kurtosis ◽  
Velocity Skewness

scholarly journals Idealized Numerical Simulations of the Interactions between Buoyant Plumes and Density Currents

2007 ◽  
Vol 64 (6) ◽  
pp. 2105-2115 ◽  
Author(s):  
Philip Cunningham
Keyword(s):  
Vertical Velocity ◽  
Dynamical Behavior ◽  
Sea Breeze ◽  
Density Current ◽  
Buoyant Plume ◽  
Density Currents ◽  
Buoyant Plumes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Idealized numerical experiments using a large-eddy simulation (LES) model are performed to examine the fundamental dynamical processes associated with the interactions between buoyant plumes and density currents. The aim of these simulations is to provide insight into the rapid changes in the structure of plumes that may be observed during the passage of density current phenomena such as thunderstorm outflows, sea-breeze fronts, or intense cold fronts. The LES model results indicate that when the ambient winds are calm the vertical velocity in the plume decreases with the passage of the density current, but that when the ambient winds oppose the motion of the density current a significant increase in vertical velocity in the plume may occur temporarily. In the latter case, the pressure perturbation and the associated region of horizontal convergence that lead the head of the density current interact with the tilted plume, causing the base of the plume to become vertical and resulting in a dramatic increase in vertical velocity within the plume. This basic dynamical behavior occurs over a relatively broad range of parameters, provided the characteristic velocity in the density current (taken as the densimetric speed) exceeds the ambient wind speed. When this is the case, the interaction is dominated by the effect of the density current on the buoyant plume such that the plume is essentially advected as a passive tracer by the flow due to the density current, and the increase in vertical velocity depends on the inverse of the convective Froude number of the buoyant plume.

scholarly journals Turbulent structure and scaling of the inertial subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar

2015 ◽  
Vol 15 (10) ◽  
pp. 5873-5885 ◽  
Author(s):  
J. Tonttila ◽  
E. J. O'Connor ◽  
A. Hellsten ◽  
A. Hirsikko ◽  
C. O'Dowd ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Marine Boundary Layer ◽  
Turbulent Structure ◽  
Inertial Subrange ◽  
Doppler Lidar ◽  
Turbulent Dissipation ◽  
Additional Information ◽  
Velocity Statistics ◽  
Velocity Skewness

Abstract. The turbulent structure of a stratocumulus-topped marine boundary layer over a 2-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both coupled and decoupled turbulence characteristics are observed. The length and timescales related to the cloud-driven mixing are investigated and shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measurements. For this, the maximum wavelengths that belong to the inertial subrange are studied through spectral analysis of the vertical velocity. The maximum wavelength of the inertial subrange in the cloud-driven layer scales relatively well with the corresponding layer depth during pronounced decoupled structure identified from the vertical velocity skewness. However, on many occasions, combining the analysis of the inertial subrange and vertical velocity statistics suggests higher decoupling height than expected from the skewness profiles. Our results show that investigation of the length scales related to the inertial subrange significantly complements the analysis of the vertical velocity statistics and enables a more confident interpretation of complex boundary layer structures using measurements from a Doppler lidar.

scholarly journals Characterization and Modulation of Langmuir Circulation in Chesapeake Bay

2015 ◽  
Vol 45 (10) ◽  
pp. 2621-2639 ◽  
Author(s):  
Malcolm E. Scully ◽  
Alexander W. Fisher ◽  
Steven E. Suttles ◽  
Lawrence P. Sanford ◽  
William C. Boicourt
Keyword(s):  
Chesapeake Bay ◽  
Mixed Layer ◽  
Vertical Velocity ◽  
Large Scale ◽  
Low Frequency ◽  
Surface Boundary ◽  
Surface Mixed Layer ◽  
Langmuir Circulation ◽  
Salinity Stratification ◽  
Velocity Skewness

AbstractMeasurements made as part of a large-scale experiment to examine wind-driven circulation and mixing in Chesapeake Bay demonstrate that circulations consistent with Langmuir circulation play an important role in surface boundary layer dynamics. Under conditions when the turbulent Langmuir number Lat is low (<0.5), the surface mixed layer is characterized by 1) elevated vertical turbulent kinetic energy; 2) decreased anisotropy; 3) negative vertical velocity skewness indicative of strong/narrow downwelling and weak/broad upwelling; and 4) strong negative correlations between low-frequency vertical velocity and the velocity in the direction of wave propagation. These characteristics appear to be primarily the result of the vortex force associated with the surface wave field, but convection driven by a destabilizing heat flux is observed and appears to contribute significantly to the observed negative vertical velocity skewness.Conditions that favor convection usually also have strong Langmuir forcing, and these two processes probably both contribute to the surface mixed layer turbulence. Conditions in which traditional stress-driven turbulence is important are limited in this dataset. Unlike other shallow coastal systems where full water column Langmuir circulation has been observed, the salinity stratification in Chesapeake Bay is nearly always strong enough to prevent full-depth circulation from developing.

scholarly journals An Improved Double-Gaussian Closure for the Subgrid Vertical Velocity Probability Distribution Function

2019 ◽  
Vol 76 (1) ◽  
pp. 285-304 ◽  
Author(s):  
A. C. Fitch
Keyword(s):  
Distribution Function ◽  
Probability Distribution ◽  
Vertical Velocity ◽  
Probability Distribution Function ◽  
Cumulus Cloud ◽  
Turbulence Statistics ◽  
Shallow Cumulus ◽  
Velocity Probability ◽  
Non Gaussian ◽  
Skewness And Kurtosis

Abstract The vertical velocity probability distribution function (PDF) is analyzed throughout the depth of the lower atmosphere, including the subcloud and cloud layers, in four large-eddy simulation (LES) cases of shallow cumulus and stratocumulus. Double-Gaussian PDF closures are examined to test their ability to represent a wide range of turbulence statistics, from stratocumulus cloud layers characterized by Gaussian turbulence to shallow cumulus cloud layers displaying strongly non-Gaussian turbulence statistics. While the majority of the model closures are found to perform well in the former case, the latter presents a considerable challenge. A new model closure is suggested that accounts for high skewness and kurtosis seen in shallow cumulus cloud layers. The well-established parabolic relationship between skewness and kurtosis is examined, with results in agreement with previous studies for the subcloud layer. In cumulus cloud layers, however, a modified relationship is necessary to improve performance. The new closure significantly improves the estimation of the vertical velocity PDF for shallow cumulus cloud layers, in addition to performing well for stratocumulus. In particular, the long updraft tail representing the bulk of cloudy points is much better represented and higher-order moments diagnosed from the PDF are also greatly improved. However, some deficiencies remain owing to fundamental limitations of representing highly non-Gaussian turbulence statistics with a double-Gaussian PDF.

Inter-individual variability in clopidogrel inhibition effect on platelet aggregation

2018 ◽  
Vol 9 (SPL1) ◽  
Author(s):  
Hussein Ali Sahib ◽  
Bassim Irhiem Mohammed ◽  
Ban A. Abdul Majid
Keyword(s):  
Cardiovascular Disease ◽  
Platelet Aggregation ◽  
Coronary Care Unit ◽  
Light Transmission ◽  
Individual Variability ◽  
Study Group ◽  
Inhibition Effect ◽  
Light Transmission Aggregometry ◽  
Coronary Care ◽  
Skewness And Kurtosis

Despite the unmistakable beneficial effect of clopidogrel on platelet aggregation,still there are some patient poorly responds to clopidogrel that may lead to worse cardiovascular clinical events.One hundred and twenty seven patients with cardiovascular disease (ACS,stroke,or TIA) were enrolled as a study group. Patients were recruited at coronary care unit (CCU) of Al-Yarmouk Teaching Hospital. Paletlet assessment was done by using light transmission aggregometry. between the patients that enrolled in this study there are significant inter-individual variability both skewness and Kurtosis were negative (-0.450,-0.130) respectively. 24% of patient enrolled in this study were hyporesponder.

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