scholarly journals Evaluation of Boundary Layer Depth Estimates at Summit Station, Greenland

2013 ◽  
Vol 52 (10) ◽  
pp. 2356-2362 ◽  
Author(s):  
B. Van Dam ◽  
D. Helmig ◽  
W. Neff ◽  
L. Kramer
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Surface Fluxes ◽  
Lower Atmosphere ◽  
Trace Gas ◽  
Polar Regions ◽  
Stable Conditions ◽  
Sonic Anemometers ◽  
Turbulence Data ◽  
Atmospheric Trace Gas

AbstractBoundary layer conditions in polar regions have been shown to have a significant impact on the levels of trace gases in the lower atmosphere. The ability to properly describe boundary layer characteristics (e.g., stability, depth, and variations on diurnal and seasonal scales) is essential to understanding the processes that control chemical budgets and surface fluxes in these regions. Surface turbulence data measured from 3D sonic anemometers on an 8-m tower at Summit Station, Greenland, were used for estimating boundary layer depths (BLD) in stable to weakly stable conditions. The turbulence-derived BLD estimates were evaluated for June 2010 using direct BLD measurements from an acoustic sounder located approximately 50 m away from the tower. BLDs during this period varied diurnally; minimum values were less than 10 m, and maximum values were greater than 150 m. BLD estimates provided a better comparison with sodar observations during stable conditions. Ozone and nitrogen oxides were also measured at the meteorological tower and investigated for their dependency on boundary layer structure. These analyses, in contrast to observations from South Pole, Antarctica, did not show a clear relation between surface-layer atmospheric trace-gas levels and the stable boundary layer.

Sensitivity studies with different formulations for similarity functions used in surface layer scheme, over the tropical region, in a climate model

2020 ◽  
Author(s):  
Prabhakar Namdev ◽  
Maithili Sharan ◽  
Saroj Kanta Mishra
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Climate Model ◽  
Stable Stratification ◽  
Turbulent Fluxes ◽  
Surface Fluxes ◽  
Tropical Region ◽  
Similarity Functions ◽  
Unstable Stratification ◽  
Stable Conditions

<p>The lowest portion of the planetary boundary layer (PBL), where the turbulent fluxes are assumed to be constant, is known as the atmospheric surface layer (ASL). Within the surface layer, the surface exchange processes play an important role in land-atmosphere interaction. Thus, a precise formulation of the surface fluxes is crucial to ensure an adequate atmospheric evolution by numerical models. The Monin–Obukhov Similarity Theory (MOST) is a widely used framework to estimate the surface turbulent fluxes within the surface layer. MOST uses similarity functions of momentum (φ<sub>m</sub>) and heat (φ<sub>h</sub>) for non-dimensional wind and temperature profiles. Over the years, various formulations for these similarity functions have been proposed by the researchers ranging from linear to non-linear forms. These formulations have limitations in the weak wind, stable, and unstable atmospheric conditions. In the surface layer scheme currently available in the Community Atmosphere Model version 5 (CAM5.0), the stable and unstable regimes are divided into four parts, and the corresponding similarity functions are the functions proposed by Kader and Yaglom (1990) for strong unstable stratification, by Businger et al. (1971) for weak unstable stratification, functions by Dyer (1974) for weak stable stratification, and for moderate to strongly stable stratification, the functions from Holtslag et al. (1990) have been utilized. The criteria used for this classification are somewhat ad-hoc, and there is an abrupt transition between different regimes encountered.            </p><p>       In the present study, an effort has been made to implement the similarity functions proposed by Grachev et al. (2007) for stable conditions and Fairall et al. (1996) for unstable conditions in the surface layer scheme of Community Land Model (CLM) for CAM5.0. In the modified version, the similarity functions for unstable conditions are a combination of commonly used Paulson type expressions for near-neutral stratification and an expression proposed by Carl et al. (1973) that takes in to account highly convective conditions. Similarly, the formulation proposed by Grachev et al., for stable conditions, can cover a wider range of stable stratifications. The simulations with CAM5 model using the existing and modified version of surface layer scheme have been performed with 1° resolution for ten years, and the impact of modified functions on the simulation of various important near-surface variables over the tropical region is analyzed. It is found that the scheme with modified functions improving the simulation of surface variables as compared with the existing scheme over the tropical region. In addition, the limitations arbitrarily imposed on particular variables in the existing surface layer scheme can be eliminated or suppressed by using these modified functions.  </p><p>References:</p><p>Fairall CW, Bradley EF, Rogers DP, Edson JB, Young GS (1996) Bulk parameterization of air-sea fluxes for tropical ocean global atmosphere coupled-ocean atmosphere response experiment. J Geophys Res 101(C2):3747–3764</p><p>Grachev, A.A., Andreas, E.L., Fairall, C.W., Guest, P.S. and Persson, P.O.G. (2007a) SHEBA: flux–profile relationships in stable atmospheric boundary layer. Boundary-Layer Meteorology,124, 315–333.</p><p>Keywords:</p><p>Boundary layer, Turbulence, Climate Model, Surface Fluxes</p>

scholarly journals An evaluation of COSMIC radio occultation data in the lower atmosphere over the Southern Ocean

2014 ◽  
Vol 7 (9) ◽  
pp. 9771-9801
Author(s):  
L. B. Hande ◽  
D. H. Lenschow ◽  
S. T. Siems ◽  
M. J. Manton
Keyword(s):  
Boundary Layer ◽  
Southern Ocean ◽  
Radio Occultation ◽  
Layer Structure ◽  
Lower Atmosphere ◽  
Cosmic Radio ◽  
Atmospheric Measurements ◽  
Macquarie Island ◽  
Extensive Evaluation ◽  
Break Points

Abstract. The Global Positioning System (GPS) Radio Occultation (RO) method is a relatively new technique for taking atmospheric measurements for use in both weather and climate studies. As such, this technique needs to be evaluated for all parts of the globe. Here, we present an extensive evaluation of the performance of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) GPS RO observations of the Southern Ocean boundary layer. The two COSMIC products used here are the "wetPrf" product, which is based on 1-D variational analysis with European Centre for Medium-Range Weather Forecasts (ECMWF), and the "atmPrf" product, which contains the raw measurements from COSMIC. A direct comparison of temporally and spatially co-located COSMIC profiles and high resolution radiosonde profiles from Macquarie Island (54.62° S, 158.85° E) highlights weaknesses in the ability of both COSMIC products to identify the boundary layer structure, as identified by break points in the refractivity profile. In terms of reproducing the temperature and moisture profile in the lowest 2.5 km, the "wetPrf" COSMIC product does not perform as well as an analysis product from the ECMWF. A further statistical analysis is performed on a large number of COSMIC profiles in a region surrounding Macquarie Island. This indicates that, statistically, COSMIC performs well at capturing the heights of main and secondary break points. However the frequency of break points detected is lower than the radiosonde profiles suggest, but this could be simply due to the long horizontal averaging in the COSMIC measurements. There is also a weak seasonal cycle in the boundary layer height, providing some confidence in the ability of COSMIC to detect an important boundary layer variable.

scholarly journals Including Atmospheric Layers in Vegetation and Urban Offline Surface Schemes

2009 ◽  
Vol 48 (7) ◽  
pp. 1377-1397 ◽  
Author(s):  
Valéry Masson ◽  
Yann Seity
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Single Layer ◽  
Urban Canopy ◽  
Atmospheric Model ◽  
Surface Fluxes ◽  
Surface Boundary ◽  
Surface Cooling ◽  
Stable Conditions ◽  
Surface Scheme

Abstract A formulation to include prognostic atmospheric layers in offline surface schemes is derived from atmospheric equations. Whereas multilayer schemes developed previously need a complex coupling between atmospheric-model levels and surface-scheme levels, the coupling proposed here remains simple. This is possible because the atmospheric layers interacting with the surface scheme are independent of the atmospheric model that could be coupled above. The surface boundary layer (SBL; both inside and just above the canopy) is resolved prognostically, taking into account large-scale forcing, turbulence, and, if any, drag and canopy forces and surface fluxes. This formulation allows one to retrieve the logarithmic law in neutral conditions, and it has been validated when coupled to a 3D atmospheric model. Systematic comparisons with 2-m observations and 10-m wind have been made for 2 months. The SBL scheme is able to model the 2-m temperature accurately, as well as the 10-m wind, without any use of analytical interpolation. The largest improvement takes place during stable conditions (i.e., by night), during which analytical laws and interpolation methods are known to be less accurate, and in mountainous areas, in which nocturnal low-level flow is strongly influenced by surface cooling. The prognostic SBL scheme is shown to solve the nighttime physical disconnection problem between surface and atmosphere models. The inclusion of the SBL into the urban Town Energy Balance scheme is presented in a paper by Hamdi and Masson in which the ability of the method to simulate the profiles of both mean and turbulent quantities from above the building down to the road surface is shown using data from the Basel Urban Boundary Layer Experiment (BUBBLE). The proposed method will allow the inclusion of the detailed physics of the multilayer schemes (e.g., the interactions of the SBL flow with forest or urban canopy) into a single-layer scheme that is easily coupled with atmospheric models.

scholarly journals Land surface spinup for episodic modeling

2014 ◽  
Vol 14 (15) ◽  
pp. 8165-8172 ◽  
Author(s):  
W. M. Angevine ◽  
E. Bazile ◽  
D. Legain ◽  
D. Pino
Keyword(s):  
Boundary Layer ◽  
Soil Moisture ◽  
Spatial Variability ◽  
Land Surface ◽  
Large Scale ◽  
Layer Structure ◽  
Numerical Models ◽  
Surface Fluxes ◽  
Boundary Layer Structure ◽  
Soil Variables

Abstract. Soil moisture strongly controls the surface fluxes in mesoscale numerical models, and thereby influences the boundary layer structure. Proper initialization of soil moisture is therefore critical for faithful simulations. In many applications, such as air quality or process studies, the model is run for short, discrete periods (a day to a month). This paper describes one method for soil initialization in these cases – self-spinup. In self-spinup, the model is initialized with a coarse-resolution operational model or reanalysis output, and run for a month, cycling its own soil variables. This allows the soil variables to develop appropriate spatial variability, and may improve the actual values. The month (or other period) can be run more than once if needed. The case shown is for the Boundary Layer Late Afternoon and Sunset Turbulence experiment, conducted in France in 2011. Self-spinup adds spatial variability, which improves the representation of soil moisture patterns around the experiment location, which is quite near the Pyrenees Mountains. The self-spinup also corrects a wet bias in the large-scale analysis. The overall result is a much-improved simulation of boundary layer structure, evaluated by comparison with soundings from the field site. Self-spinup is not recommended as a substitute for multi-year spinup with an offline land data assimilation system in circumstances where the data sets required for such spinup are available at the required resolution. Self-spinup may fail if the modeled precipitation is poorly simulated. It is an expedient for cases when resources are not available to allow a better method to be used.

scholarly journals Vertical Velocity Variance Measurements from Wind Profiling Radars

2016 ◽  
Author(s):  
Katherine McCaffrey ◽  
Laura Bianco ◽  
Paul Johnston ◽  
James M. Wilczak
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Planetary Boundary Layer ◽  
Vertical Velocity ◽  
Prediction Models ◽  
Weather Prediction ◽  
Small Scale ◽  
Stable Conditions ◽  
Sonic Anemometers ◽  
Velocity Variance

Abstract. Observations of turbulence in the planetary boundary layer are critical for developing and evaluating boundary layer parameterizations in mesoscale numerical weather prediction models. These observations, however, are expensive, and rarely profile the entire boundary layer. Using optimized configurations for 449 MHz and 915 MHz wind profiling radars during the eXperimental Planetary boundary layer Instrumentation Assessment, improvements have been made to the historical methods of measuring vertical velocity variance through the time series of vertical velocity, as well as the Doppler spectral width. Using six heights of sonic anemometers mounted on a 300-m tower, correlations of up to R2 = 0.74 are seen in measurements of the large-scale variances from the radar time series, and R2 = 0.79 in measurements of small-scale variance from radar spectral widths. The total variance, measured as the sum of the small- and large-scales agrees well with sonic anemometers, with R2 = 0.79. Correlation is higher in daytime, convective boundary layers than nighttime, stable conditions when turbulence levels are smaller. With the good agreement with the in situ measurements, highly-resolved profiles up to 2 km can be accurately observed from the 449 MHz radar, and 1 km from the 915 MHz radar. This optimized configuration will provide unique observations for the verification and improvement to boundary layer parameterizations in mesoscale models.

In situ observations of the near-shore atmospheric boundary layer during ATOMIC/EUREC4A from small Uncrewed Aircraft Systems  

2021 ◽  
Author(s):  
Gijs de Boer ◽  
Radiance Calmer ◽  
Steven Borenstein ◽  
Christopher Choate ◽  
Michael Rhodes ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Internal Variability ◽  
Surface Fluxes ◽  
Lower Atmosphere ◽  
University Of Colorado ◽  
Remotely Piloted Aircraft ◽  
Near Shore ◽  
Aircraft System ◽  
The University

<p>During the 2020 Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) and ElUcidating the Role of Cloud- Circulation Coupling in ClimAte (EUREC4A) field campaigns, a team from the University of Colorado Boulder deployed the RAAVEN Remotely-Piloted Aircraft System (RPAS). The RAAVEN RPAS was equipped with the miniFlux measurement system to observe the marine boundary layer upwind of Morgan Lewis, Barbados.  Over the course of 23 days, the team completed 39 flights covering nearly 80 flight hours.  Flights were conducted in and just above the boundary layer at altitudes between 10 and 1000 m, with a focus on capturing regular thermodynamic and kinematic profiles of the lower atmosphere, along with statistics on vertical transport and spatial variability.  In this presentation, we will give initial details on the observed state of the lower atmosphere.  This includes information on the structure and internal variability of thermodynamic and kinematic properties, turbulence intensity, turbulent surface fluxes and their variability, and details on the structure of vertical velocities in the lower atmosphere.</p>

Trace gas flux measurements at the landscape scale using boundary-layer budgets

1995 ◽  
Vol 351 (1696) ◽  
pp. 357-369 ◽  
Keyword(s):  
Boundary Layer ◽  
Local Area ◽  
Surface Fluxes ◽  
Trace Gas ◽  
Significant Heterogeneity ◽  
Methane Fluxes ◽  
Flux Measurements ◽  
The Mean ◽  
Nocturnal Inversion ◽  
One Year

Methane effluxes from wetland areas of Scotland were estimated by using the boundary-layer budget method by collecting air samples with an aircraft upwind and downwind of an area of extensive peatland. Nocturnal local area methane fluxes were also estimated at a peat bog site, Loch More, located at 58° 24' N 03° 36' W, using the concentration build up under the nocturnal inversion and from profiles of methane concentration using a tethered balloon. The mean daytime flux for the Loch More case studies in 1993 was found to be 128 ± 57 μ mol m -2 h -1 for the NE region of Scotland, comparable to but generally larger than those obtained for the same region one year earlier. The fluxes are smaller than those obtained in Caithness by the same technique. In 1993 the nocturnal fluxes were found to be 38 ± 7 μ mol m -2 h -1 , significantly smaller than those found during 1992. The daytime fluxes measured by the aircraft were generally larger than fluxes measured by micrometeorological techniques at the same time. These differences can be explained in terms of the significant heterogeneity in surface fluxes that exist on scales of a few hundred metres or less and the possibility of additional sources other than peatland in this region.

The variability of mixing at the continental slope

1990 ◽  
Vol 331 (1616) ◽  
pp. 183-194 ◽  
Keyword(s):  
Boundary Layer ◽  
Continental Slope ◽  
Tidal Cycle ◽  
Layer Structure ◽  
Internal Gravity Waves ◽  
Benthic Boundary Layer ◽  
Temperature Structure ◽  
Sea Bed ◽  
Stable Conditions ◽  
Mixed Layers

The benthic boundary layer on the continental slope is a region in which isopycnal surfaces intersect topography. It is, in consequence, particularly subject to variability caused by reflecting internal gravity waves, as well as by trapped baroclinic slope waves. Observations made using an array of moorings off the west slope of the Porcupine Bank reveal the presence there of a northerly along-slope current at depths of 3000-4000 m, which extends to some 20 km off-slope, and of waves of periods 2-9 days trapped within about 10 km ( ca. 1 Rossby radius) of the slope. Lower-frequency variations are dominant at greater distances. The tide has a significant spectral peak, with a first subharmonic apparent near the slope. Measurements of the temperature structure in the boundary layer have been made at 1705 m on the Hebrides slope and at 3447 m off the Porcupine Bank. In both areas the boundary layer structure is dominated by asymmetrical M 2 variations in the isopycnal surfaces, with displacements of50-100 m. Uniform near-bed ‘mixed’ layers appear during the tidal cycle, reaching to some 50 m off the sea bed, but are transient, lasting for only a fraction of the tidal cycle following sharp rises in isotherm levels, later to be replaced by statically stable conditions extending to within a few metres of the sea bed. The slope-trapped waves also modify the mean temperature gradients and are responsible for variations in the locations at which reflecting internal waves of given frequency are critical or resonant.

scholarly journals Analysis of the Influence of the Length Scales in a Boundary-Layer Model

2021 ◽  
Author(s):  
Enrico Ferrero ◽  
Massimo Canonico
Keyword(s):  
Boundary Layer ◽  
Prediction Models ◽  
Weather Prediction ◽  
Layer Model ◽  
Length Scales ◽  
Boundary Layer Model ◽  
Low Wind Speed ◽  
Stable Conditions ◽  
Sonic Anemometers ◽  
Numerical Weather Prediction Models

AbstractWe consider the Janjic (NCEP Office Note 437:61, 2001) boundary-layer model, which is one of the most widely used in numerical weather prediction models. This boundary-layer model is based on a number of length scales that are, in turn, obtained from a master length multiplied by constants. We analyze the simulation results obtained using different sets of constants with respect to measurements using sonic anemometers, and interpret these results in terms of the turbulence processes in the atmosphere and of the role played by the different length scales. The simulations are run on a virtual machine on the Chameleon cloud for low-wind-speed, unstable, and stable conditions.

scholarly journals Interactions among drainage flows, gravity waves and turbulence: a BLLAST case study

2015 ◽  
Vol 15 (8) ◽  
pp. 12821-12865 ◽  
Author(s):  
C. Román-Cascón ◽  
C. Yagüe ◽  
L. Mahrt ◽  
M. Sastre ◽  
G. J. Steeneveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Flux ◽  
Decomposition Methods ◽  
Surface Fluxes ◽  
Drainage Flows ◽  
Sonic Anemometers ◽  
Using Data ◽  
Sloping Terrain ◽  
Wavelet Analyses

Abstract. The interactions among several stable-boundary-layer (SBL) processes occurring just after the evening transition of 2 July 2011 have been analysed using data from instruments deployed over the area of Lannemezan (France) during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. The near-calm situation of the afternoon was followed by the formation of local shallow drainage flows (SDFs) of less than ten meters depth at different locations. The SDF stage ended with the arrival of a deeper wind more associated with the mountain-plain circulation, which caused mixing and destruction of the SDFs. Several gravity wave-related oscillations were also observed on different time series. Wavelet analyses and wave parameters were calculated from high resolution and accurate surface pressure data of an array of microbarometers. These waves propagated relatively long distances within the SBL, which was confined from the surface to 100 m a.g.l. The effects of these phenomena on the surface fluxes have been studied through Multi Resolution Flux Decomposition methods performed on high frequency data from sonic anemometers deployed at different heights and locations. With this method, we were able to detect the different time-scales involved in surface flux generation and separate them from wave contributions, which becomes very important when choosing averaging-windows for surface flux computations using Eddy Covariance methods. The extensive instrumentation allowed us to highlight in detail the peculiarities of the surface fluxes in the SBL, where several of the noted processes were interacting and producing important variations in the fluxes with height and among sites along the sloping terrain.

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