scholarly journals On the Relationship between SST Gradients, Boundary Layer Winds, and Convergence over the Tropical Oceans

2009 ◽  
Vol 22 (15) ◽  
pp. 4182-4196 ◽  
Author(s):  
Larissa E. Back ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Force Balance ◽  
Semiempirical Model ◽  
Pressure Gradients ◽  
Surface Winds ◽  
Layer Model ◽  
Zonal Winds ◽  
Tropical Oceans ◽  
The Relationship

Abstract A linear mixed layer model that skillfully reproduces observed surface winds and convergence over the tropical oceans is used to examine the relative influence of boundary layer and free-tropospheric processes on the distribution of climatological surface winds and convergence. The semiempirical model assumes a subcloud-layer momentum force balance between pressure gradients, Coriolis acceleration, linearized friction, and downward momentum mixing, and it utilizes boundary conditions from the 40-yr ECMWF Re-Analysis (ERA-40). Observed pressure gradients are linearly decomposed into boundary layer (defined as the region below 850 hPa) and free-tropospheric components, and the surface winds and convergence associated with these components are computed. Results show that surface zonal winds are predominantly associated with a combination of free-tropospheric pressure gradients and downward momentum mixing, whereas the distribution of convergence is primarily due to boundary layer temperature gradients, which are closely related to SST gradients. The authors conclude that the climatological distribution of boundary layer convergence is primarily a function of the pattern of SST gradients and is better regarded as a cause rather than a consequence of deep convection.

scholarly journals Effective Buoyancy, Inertial Pressure, and the Mechanical Generation of Boundary Layer Mass Flux by Cold Pools

2015 ◽  
Vol 72 (8) ◽  
pp. 3199-3213 ◽  
Author(s):  
Nadir Jeevanjee ◽  
David M. Romps
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Dominant Role ◽  
Deep Convection ◽  
Force Balance ◽  
Vertical Force ◽  
Inertial Forces ◽  
Buoyancy Forcing ◽  
Cold Pools ◽  
Gust Front

Abstract The Davies-Jones formulation of effective buoyancy is used to define inertial and buoyant components of vertical force and to develop an intuition for these components by considering simple cases. This decomposition is applied to the triggering of new boundary layer mass flux by cold pools in a cloud-resolving simulation of radiative–convective equilibrium (RCE). The triggering is found to be dominated by inertial forces, and this is explained by estimating the ratio of the inertial forcing to the buoyancy forcing, which scales as H/h, where H is the characteristic height of the initial downdraft and h is the characteristic height of the mature cold pool’s gust front. In a simulation of the transition from shallow to deep convection, the buoyancy forcing plays a dominant role in triggering mass flux in the shallow regime, but the force balance tips in favor of inertial forcing just as precipitation sets in, consistent with the RCE results.

Low-level wind profiles at an Antarctic coastal station

1989 ◽  
Vol 1 (2) ◽  
pp. 169-178 ◽  
Author(s):  
J.C. King
Keyword(s):  
Boundary Layer ◽  
Temperature Profiles ◽  
Pressure Gradients ◽  
Synoptic Scale ◽  
Layer Model ◽  
Coastal Station ◽  
One Dimensional ◽  
Dimensional Boundary ◽  
Sloping Surface ◽  
Wind Profiles

Wind and temperature profiles in the lowest 2000 m of the atmosphere at Halley (75°35′S, 26°50′W) have been analysed. Surface winds blow most frequently from the sector 090° ± 45° but the 2000 m wind direction is much more evenly distributed and appears to be determined by synoptic-scale pressure gradients. A simple one-dimensional boundary layer model, which includes the effects of stably-stratified air overlying a sloping surface, is able to reproduce some of the features of the observed profiles.

scholarly journals A Simple Model of Climatological Rainfall and Vertical Motion Patterns over the Tropical Oceans

2009 ◽  
Vol 22 (23) ◽  
pp. 6477-6497 ◽  
Author(s):  
Larissa E. Back ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Diabatic Heating ◽  
Deep Convection ◽  
Vertical Motion ◽  
Central Pacific ◽  
Mode Amplitude ◽  
Tropical Oceans ◽  
Conditional Instability ◽  
Heating Profiles

Abstract A simple model is developed that predicts climatological rainfall, vertical motion, and diabatic heating profiles over the tropical oceans given the sea surface temperature (SST), using statistical relationships deduced from the 40-yr ECMWF Re-Analysis (ERA-40). The model allows for two modes of variability in the vertical motion profiles: a shallow mode responsible for all “boundary layer” convergence between 850 hPa and the surface, and a deep mode with no boundary layer convergence. The model is based on the argument expressed in the authors’ companion paper that boundary layer convergence can be usefully viewed as a forcing on deep convection, not just a result thereof. The shallow mode is either specified from satellite observations or modeled using a simple mixed-layer model that has SST as well as 850-hPa geopotential height, winds, and temperature as boundary conditions. The deep-mode amplitude is empirically shown to be proportional to a simple measure of conditional instability in convecting regions, and is determined by the constraint that radiative cooling must balance adiabatic warming in subsidence regions. This two-mode model is tested against a reanalysis-derived dry static energy budget and in a reanalysis-independent framework based on satellite-derived surface convergence and using SST as a proxy for conditional instability. It can predict the observed annual mean and seasonal cycle of rainfall, vertical motion, and diabatic heating profiles across the tropical oceans with significantly more skill than optimized predictions using a thresholded linear relationship with SST. In most warm-ocean regions, significant rainfall only occurs in regions of monthly-mean boundary layer convergence. In such regions, deep-mode amplitude and rainfall increase linearly with SST, with an additional rainfall contribution from the shallow mode directly tied to boundary layer convergence. This second contribution is significant mainly in the east and central Pacific ITCZ, where it is responsible for that region’s “bottom-heavy” vertical-velocity, diabatic heating, and cloud profiles.

scholarly journals Deep Convective Organization, Moisture Vertical Structure, and Convective Transition Using Deep-Inflow Mixing

2019 ◽  
Vol 76 (4) ◽  
pp. 965-987 ◽  
Author(s):  
Kathleen A. Schiro ◽  
J. David Neelin
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Convective Systems ◽  
Diurnal Cycles ◽  
Mesoscale Convective ◽  
Strong Relation ◽  
Environmental Air ◽  
Open Question ◽  
The Relationship ◽  
Convective Organization

Abstract It is an open question whether an integrated measure of buoyancy can yield a strong relation to precipitation across tropical land and ocean, across the seasonal and diurnal cycles, and for varying degrees of convective organization. Building on previous work, entraining plume buoyancy calculations reveal that differences in convective onset as a function of column water vapor (CWV) over land and ocean, as well as seasonally and diurnally over land, are largely due to variability in the contribution of lower-tropospheric humidity to the total column moisture. Over land, the relationship between deep convection and lower-free-tropospheric moisture is robust across all seasons and times of day, whereas the relation to boundary layer moisture is robust for the daytime only. Using S-band radar, these transition statistics are examined separately for mesoscale and smaller-scale convection. The probability of observing mesoscale convective systems sharply increases as a function of lower-free-tropospheric humidity. The consistency of this with buoyancy-based parameterization is examined for several mixing formulations. Mixing corresponding to deep inflow of environmental air into a plume that grows with height, which incorporates nearly equal weighting of boundary layer and free-tropospheric air, yields buoyancies consistent with the observed onset of deep convection across the seasonal and diurnal cycles in the Amazon. Furthermore, it provides relationships that are as strong or stronger for mesoscale-organized convection as for smaller-scale convection.

Deep Convection and Column Water Vapor over Tropical Land versus Tropical Ocean: A Comparison between the Amazon and the Tropical Western Pacific

2016 ◽  
Vol 73 (10) ◽  
pp. 4043-4063 ◽  
Author(s):  
Kathleen A. Schiro ◽  
J. David Neelin ◽  
David K. Adams ◽  
Benjamin R. Lintner
Keyword(s):  
Water Vapor ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Tropical Ocean ◽  
Tropical Oceans ◽  
Tropical Deep Convection ◽  
Conditional Instability ◽  
Convective Layer ◽  
The Impact ◽  
The Relationship

Abstract The relationships between the onset of tropical deep convection, column water vapor (CWV), and other measures of conditional instability are analyzed with 2 yr of data from the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility in Manacapuru, Brazil, as part of the Green Ocean Amazon (GOAmazon) campaign, and with 3.5 yr of CWV derived from global positioning system meteorology at a nearby site in Manaus, Brazil. Important features seen previously in observations over tropical oceans—precipitation conditionally averaged by CWV exhibiting a sharp pickup at high CWV, and the overall shape of the CWV distribution for both precipitating and nonprecipitating points—are also found for this tropical continental region. The relationship between rainfall and CWV reflects the impact of lower-free-tropospheric moisture variability on convection. Specifically, CWV over land, as over ocean, is a proxy for the effect of free-tropospheric moisture on conditional instability as indicated by entraining plume calculations from GOAmazon data. Given sufficient mixing in the lower troposphere, higher CWV generally results in greater plume buoyancies through a deep convective layer. Although sensitivity of buoyancy to other controls in the Amazon is suggested, such as boundary layer and microphysical processes, the CWV dependence is consistent with the observed precipitation onset. Overall, leading aspects of the relationship between CWV and the transition to deep convection in the Amazon have close parallels over tropical oceans. The relationship is robust to averaging on time and space scales appropriate for convective physics but is strongly smoothed for averages greater than 3 h or 2.5°.

Dyeing Rate of Nylon 6 Fabric and Yarn Assemblies with p-Aminoazobenzene

1992 ◽  
Vol 62 (12) ◽  
pp. 736-741 ◽  
Author(s):  
H. Sasaki ◽  
H. Morikawa ◽  
H. Araki
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Nylon 6 ◽  
Layer Model ◽  
Layer Parameter ◽  
Diffusional Boundary Layer ◽  
Apparent Diffusion ◽  
Boundary Layer Parameter ◽  
The Relationship ◽  
Dyeing Rate

The dyeing rates of p-aminoazobenzene on nylon 6 fabrics and yarn assemblies at 40°C have been investigated. The apparent diffusion coefficient and the diffusional boundary layer parameter are estimated in such a way that the experimental data fit the theoretical rate curve based on the diffusional boundary layer model. Because the boundary layer parameter can be separated into two distinct components, the relationship between each component and the dyeing condition and the structure of the textile assembly is examined. The component concerned with the dye-fiber-dyebath combination or composition is subdivided into several groups. The component determined by the fluid-flow pattern and rate is dependent on the magnitude of the inter-yarn spaces.

Self-preserving development within turbulent boundary layers in strong adverse pressure gradients

1965 ◽  
Vol 23 (4) ◽  
pp. 767-778 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Outer Part ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Pressure Gradients ◽  
Layer Model ◽  
Pressure Distributions ◽  
Two Layer Model ◽  
Local Parameters

The development of a turbulent boundary layer in a strong adverse pressure gradient can be described by the two-layer model proposed by Stratford (1959), in which the outer part of the flow is assumed to be unmodified by the pressure-rise and the inner part described by two local parameters, the surface stress and the pressure gradient. The description suggests that the modification of the original flow is in some sense self-preserving, and it is shown here that self-preserving development of the modification is consistent with the Reynolds equations of turbulent flow in particular pressure distributions. For these distributions, the predictions of the two-layer model are confirmed without any need to make the sharp and arbitrary distinction between the two parts of the boundary layer.

Rough-wall boundary layers in adverse pressure gradients

1963 ◽  
Vol 17 (2) ◽  
pp. 193-211 ◽  
Author(s):  
A. E. Perry ◽  
P. N. Joubert
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Rough Wall ◽  
Pressure Gradients ◽  
Fluid Density ◽  
Duct Flow ◽  
Local Boundary ◽  
Wall Boundary ◽  
The Relationship ◽  
General Method

Smooth- and rough-wall boundary layers and fully developed pipe and duct flow investigations are reviewed. It is shown that the effect of roughness on the flow away from the wall can be accounted for by using an equivalent viscosity νe. This viscosity is thought to depend only on the variables at the wall, such as shear stress τ0, fluid density ρ, viscosity μ and the roughness size and geometry and that the relationship between these variables is the same for both boundary layers and duct flow. However, experiments to date have been confined to the ‘rough régime’ and to boundary layers with a zero pressure gradient.Experiments were performed and the results show that the above finding can be extended to boundary layers with adverse pressure gradients in the rough régime.A general method for measuring the local boundary-layer characteristics, with roughness and pressure gradients present, is developed.

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