Richardson number profiles through shear instability wave regions observed in the lower planetary boundary layer

1973 ◽  
Vol 5 (1-2) ◽  
pp. 19-27 ◽  
Author(s):  
C. B. Emmanuel
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
Shear Instability ◽  
Instability Wave

scholarly journals On the computation of planetary boundary-layer height using the bulk Richardson number method

2014 ◽  
Vol 7 (6) ◽  
pp. 2599-2611 ◽  
Author(s):  
Y. Zhang ◽  
Z. Gao ◽  
D. Li ◽  
Y. Li ◽  
N. Zhang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
Potential Temperature ◽  
Bulk Richardson Number ◽  
Stable Boundary Layers ◽  
Stable Boundary ◽  
Field Campaigns ◽  
Weakly Stable

Abstract. Experimental data from four field campaigns are used to explore the variability of the bulk Richardson number of the entire planetary boundary layer (PBL), Ribc, which is a key parameter for calculating the PBL height (PBLH) in numerical weather and climate models with the bulk Richardson number method. First, the PBLHs of three different thermally stratified boundary layers (i.e., strongly stable boundary layers, weakly stable boundary layers, and unstable boundary layers) from the four field campaigns are determined using the turbulence method, the potential temperature gradient method, the low-level jet method, and the modified parcel method. Then for each type of boundary layer, an optimal Ribc is obtained through linear fitting and statistical error minimization methods so that the bulk Richardson method with this optimal Ribc yields similar estimates of PBLHs as the methods mentioned above. We find that the optimal Ribc increases as the PBL becomes more unstable: 0.24 for strongly stable boundary layers, 0.31 for weakly stable boundary layers, and 0.39 for unstable boundary layers. Compared with previous schemes that use a single value of Ribc in calculating the PBLH for all types of boundary layers, the new values of Ribc proposed by this study yield more accurate estimates of PBLHs.

A numerical investigation of fine particle laden flow in an oscillatory channel: the role of particle-induced density stratification

2010 ◽  
Vol 665 ◽  
pp. 1-45 ◽  
Author(s):  
CELALETTIN E. OZDEMIR ◽  
TIAN-JIAN HSU ◽  
S. BALACHANDAR
Keyword(s):  
Boundary Layer ◽  
Particle Transport ◽  
Fine Particle ◽  
Richardson Number ◽  
Density Stratification ◽  
Shear Instability ◽  
Bulk Richardson Number ◽  
Turbulence Modulation ◽  
Oscillatory Boundary Layer

Studying particle-laden oscillatory channel flow constitutes an important step towards understanding practical application. This study aims to take a step forward in our understanding of the role of turbulence on fine-particle transport in an oscillatory channel and the back effect of fine particles on turbulence modulation using an Eulerian–Eulerian framework. In particular, simulations presented in this study are selected to investigate wave-induced fine sediment transport processes in a typical coastal setting. Our modelling framework is based on a simplified two-way coupled formulation that is accurate for particles of small Stokes number (St). As a first step, the instantaneous particle velocity is calculated as the superposition of the local fluid velocity and the particle settling velocity while the higher-order particle inertia effect neglected. Correspondingly, only the modulation of carrier flow is due to particle-induced density stratification quantified by the bulk Richardson number, Ri. In this paper, we fixed the Reynolds number to be ReΔ = 1000 and varied the bulk Richardson number over a range (Ri = 0, 1 × 10−4, 3 × 10−4 and 6 × 10−4). The simulation results reveal critical processes due to different degrees of the particle–turbulence interaction. Essentially, four different regimes of particle transport for the given ReΔ are observed: (i) the regime where virtually no turbulence modulation in the case of very dilute condition, i.e. Ri ~ 0; (ii) slightly modified regime where slight turbulence attenuation is observed near the top of the oscillatory boundary layer. However, in this regime a significant change can be observed in the concentration profile with the formation of a lutocline; (iii) regime where flow laminarization occurs during the peak flow, followed by shear instability during the flow reversal. A significant reduction in the oscillatory boundary layer thickness is also observed; (iv) complete laminarization due to strong particle-induced stable density stratification.

scholarly journals Impact of planetary boundary layer turbulence on model climate and tracer transport

2014 ◽  
Vol 14 (23) ◽  
pp. 31627-31674
Author(s):  
E. L. McGrath-Spangler ◽  
A. Molod ◽  
L. E. Ott ◽  
S. Pawson
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
Surface Wind ◽  
Specific Humidity ◽  
Boreal Summer ◽  
Tracer Transport ◽  
Bulk Richardson Number ◽  
Turbulent Length Scale ◽  
Near Surface

Abstract. Planetary boundary layer (PBL) processes are important for weather, climate, and tracer transport and concentration. One measure of the strength of these processes is the PBL depth. However, no single PBL depth definition exists and several studies have found that the estimated depth can vary substantially based on the definition used. In the Goddard Earth Observing System (GEOS-5) atmospheric general circulation model, the PBL depth is particularly important because it is used to calculate the turbulent length scale that is used in the estimation of turbulent mixing. This study analyzes the impact of using three different PBL depth definitions in this calculation. Two definitions are based on the scalar eddy diffusion coefficient and the third is based on the bulk Richardson number. Over land, the bulk Richardson number definition estimates shallower nocturnal PBLs than the other estimates while over water this definition generally produces deeper PBLs. The near surface wind velocity, temperature, and specific humidity responses to the change in turbulence are spatially and temporally heterogeneous, resulting in changes to tracer transport and concentrations. Near surface wind speed increases in the bulk Richardson number experiment cause Saharan dust increases on the order of 1 × 10−4 kg m−2 downwind over the Atlantic Ocean. Carbon monoxide (CO) surface concentrations are modified over Africa during boreal summer, producing differences on the order of 20 ppb, due to the model's treatment of emissions from biomass burning. While differences in carbon dioxide (CO2) are small in the time mean, instantaneous differences are on the order of 10 ppm and these are especially prevalent at high latitude during boreal winter. Understanding the sensitivity of trace gas and aerosol concentration estimates to PBL depth is important for studies seeking to calculate surface fluxes based on near-surface concentrations and to studies projecting future concentrations.

scholarly journals Comparison of GEOS-5 AGCM planetary boundary layer depths computed with various definitions

2014 ◽  
Vol 14 (13) ◽  
pp. 6717-6727 ◽  
Author(s):  
E. L. McGrath-Spangler ◽  
A. Molod
Keyword(s):  
Boundary Layer ◽  
Diffusion Coefficient ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
General Circulation ◽  
Circulation Model ◽  
Eddy Diffusion ◽  
Bulk Richardson Number ◽  
Turbulent Length Scale ◽  
Eddy Diffusion Coefficient

Abstract. Accurate models of planetary boundary layer (PBL) processes are important for forecasting weather and climate. The present study compares seven methods of calculating PBL depth in the GEOS-5 atmospheric general circulation model (AGCM) over land. These methods depend on the eddy diffusion coefficients, bulk and local Richardson numbers, and the turbulent kinetic energy. The computed PBL depths are aggregated to the Köppen–Geiger climate classes, and some limited comparisons are made using radiosonde profiles. Most methods produce similar midday PBL depths, although in the warm, moist climate classes the bulk Richardson number method gives midday results that are lower than those given by the eddy diffusion coefficient methods. Additional analysis revealed that methods sensitive to turbulence driven by radiative cooling produce greater PBL depths, this effect being most significant during the evening transition. Nocturnal PBLs based on Richardson number methods are generally shallower than eddy diffusion coefficient based estimates. The bulk Richardson number estimate is recommended as the PBL height to inform the choice of the turbulent length scale, based on the similarity to other methods during the day, and the improved nighttime behavior.

scholarly journals Impact of planetary boundary layer turbulence on model climate and tracer transport

2015 ◽  
Vol 15 (13) ◽  
pp. 7269-7286 ◽  
Author(s):  
E. L. McGrath-Spangler ◽  
A. Molod ◽  
L. E. Ott ◽  
S. Pawson
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
Surface Wind ◽  
Specific Humidity ◽  
Boreal Summer ◽  
Tracer Transport ◽  
Bulk Richardson Number ◽  
Turbulent Length Scale ◽  
Near Surface

Abstract. Planetary boundary layer (PBL) processes are important for weather, climate, and tracer transport and concentration. One measure of the strength of these processes is the PBL depth. However, no single PBL depth definition exists and several studies have found that the estimated depth can vary substantially based on the definition used. In the Goddard Earth Observing System (GEOS-5) atmospheric general circulation model, the PBL depth is particularly important because it is used to calculate the turbulent length scale that is used in the estimation of turbulent mixing. This study analyzes the impact of using three different PBL depth definitions in this calculation. Two definitions are based on the scalar eddy diffusion coefficient and the third is based on the bulk Richardson number. Over land, the bulk Richardson number definition estimates shallower nocturnal PBLs than the other estimates while over water this definition generally produces deeper PBLs. The near-surface wind velocity, temperature, and specific humidity responses to the change in turbulence are spatially and temporally heterogeneous, resulting in changes to tracer transport and concentrations. Near-surface wind speed increases in the bulk Richardson number experiment cause Saharan dust increases on the order of 1 × 10−4 kg m−2 downwind over the Atlantic Ocean. Carbon monoxide (CO) surface concentrations are modified over Africa during boreal summer, producing differences on the order of 20 ppb, due to the model's treatment of emissions from biomass burning. While differences in carbon dioxide (CO2) are small in the time mean, instantaneous differences are on the order of 10 ppm and these are especially prevalent at high latitude during boreal winter. Understanding the sensitivity of trace gas and aerosol concentration estimates to PBL depth is important for studies seeking to calculate surface fluxes based on near-surface concentrations and for studies projecting future concentrations.

scholarly journals Estimating Planetary Boundary Layer Heights from NOAA Profiler Network Wind Profiler Data

2015 ◽  
Vol 32 (9) ◽  
pp. 1545-1561 ◽  
Author(s):  
A. Molod ◽  
H. Salmun ◽  
M. Dempsey
Keyword(s):  
United States ◽  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
Wind Profiler ◽  
Clear Sky ◽  
Hourly Temperature ◽  
Central United States ◽  
Sky Conditions ◽  
Profiler Data

AbstractAn algorithm was developed to estimate planetary boundary layer (PBL) heights from hourly archived wind profiler data from the NOAA Profiler Network (NPN) sites located throughout the central United States. Unlike previous studies, the present algorithm has been applied to a long record of publicly available wind profiler signal backscatter data. Under clear-sky conditions, summertime averaged hourly time series of PBL heights compare well with Richardson number–based estimates at the few NPN stations with hourly temperature measurements. Comparisons with estimates based on clear-sky reanalysis show that the wind profiler (WP) PBL heights are lower by approximately 250–500 m. The geographical distribution of daily maximum PBL heights corresponds well with the expected distribution based on patterns of surface temperature and soil moisture. Wind profiler PBL heights were also estimated under mostly cloudy-sky conditions, and are generally comparable to the Richardson number–based PBL heights and higher than the reanalysis PBL heights. WP PBL heights have a smaller clear–cloudy condition difference than either of the other two. The algorithm presented here is shown to provide a reliable summertime climatology of daytime hourly PBL heights throughout the central United States.

scholarly journals Comparison of GEOS-5 AGCM planetary boundary layer depths computed with various definitions

2014 ◽  
Vol 14 (5) ◽  
pp. 6589-6617 ◽  
Author(s):  
E. L. McGrath-Spangler ◽  
A. Molod
Keyword(s):  
Boundary Layer ◽  
Diffusion Coefficient ◽  
Planetary Boundary Layer ◽  
Richardson Number ◽  
General Circulation ◽  
Circulation Model ◽  
Eddy Diffusion ◽  
Bulk Richardson Number ◽  
Turbulent Length Scale ◽  
Eddy Diffusion Coefficient

Abstract. Accurate models of planetary boundary layer (PBL) processes are important for forecasting weather and climate. The present study compares seven methods of calculating PBL depth in the GEOS-5 atmospheric general circulation model (AGCM) over land. These methods depend on the eddy diffusion coefficients, bulk and local Richardson numbers, and the turbulent kinetic energy. The computed PBL depths are aggregated to the Köppen climate classes, and some limited comparisons are made using radiosonde profiles. Most methods produce similar midday PBL depths, although in the warm, moist climate classes, the bulk Richardson number method gives midday results that are lower than those given by the eddy diffusion coefficient methods. Additional analysis revealed that methods sensitive to turbulence driven by radiative cooling produce greater PBL depths, this effect being most significant during the evening transition. Nocturnal PBLs based on Richardson number are generally shallower than eddy diffusion coefficient based estimates. The bulk Richardson number estimate is recommended as the PBL height to inform the choice of the turbulent length scale, based on the similarity to other methods during the day, and the improved nighttime behavior.

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