Using Idealized Coherent Structures to Parameterize Momentum Fluxes in a PBL Mass-Flux Model

2005 ◽  
Vol 62 (8) ◽  
pp. 2829-2846 ◽  
Author(s):  
Cara-Lyn Lappen ◽  
David A. Randall
Keyword(s):  
Coherent Structures ◽  
Mass Flux ◽  
Potential Temperature ◽  
Orientation Angle ◽  
Higher Order ◽  
Horizontal Wind ◽  
Spatial Integration ◽  
Momentum Fluxes ◽  
Flux Model ◽  
Horizontal Momentum

Abstract In 2001, the authors presented a higher-order mass-flux model called assumed distributions with higher-order closure (ADHOC), which represents the large eddies of the planetary boundary layer (PBL) in terms of an assumed joint distribution of the vertical velocity and scalars such as potential temperature or water vapor mixing ratio. ADHOC is intended for application as a PBL parameterization. It uses the equations of higher-order closure to predict selected moments of the assumed distribution, and diagnoses the parameters of the distribution from the predicted moments. Once the parameters of the distribution are known, all moments of interest can be computed. The first version of ADHOC was incomplete in that the horizontal momentum equations, the vertical fluxes of horizontal momentum, the contributions to the turbulence kinetic energy from the horizontal wind, and the various pressure terms involving covariances between pressure and other variables were not incorporated into the assumed distribution framework. Instead, these were parameterized using standard methods. This paper describes an updated version of ADHOC. The new version includes representations of the horizontal winds and momentum fluxes that are consistent with the mass-flux framework of the model. The assumed joint probability distribution is replaced by an assumed joint spatial distribution based on an idealized coherent structure, such as a plume or roll. The horizontal velocity can then be determined using the continuity equation, and the momentum fluxes and variances are computed directly by spatial integration. These expressions contain unknowns that involve the parameters of the assumed coherent structures. Methods are presented to determine these parameters, which include the radius of convective updrafts and downdrafts and the wavelength, tilt, and orientation angle of the convective rolls. The parameterization is tested by comparison with statistics computed from large-eddy simulations. In a companion paper, the results of this paper are built on to determine the perturbation pressure terms needed by the model.

Parameterization of Pressure Perturbations in a PBL Mass-Flux Model

2006 ◽  
Vol 63 (7) ◽  
pp. 1726-1751 ◽  
Author(s):  
Cara-Lyn Lappen ◽  
David A. Randall
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Pressure Field ◽  
Companion Paper ◽  
Large Eddy Simulations ◽  
Large Eddy ◽  
Flux Model ◽  
Horizontal Momentum ◽  
Perturbation Pressure ◽  
Pressure Perturbations

Abstract In a companion paper, the authors presented a boundary layer parameterization that was based on the mass-flux concept and included an internally consistent representation of the vertical flux of horizontal momentum. In the present paper, the authors show how the framework of that model can be used to determine the perturbation pressure field, by solving the anelastic pressure equation. The pressure covariances needed to close the parameterization can then be diagnosed. Tests show very encouraging agreement of the pressure statistics with results obtained from large-eddy simulations.

scholarly journals Spatial and seasonal variability of medium- and high-frequency gravity waves in the lower atmosphere revealed by US radiosonde data

2014 ◽  
Vol 32 (9) ◽  
pp. 1129-1143 ◽  
Author(s):  
S. D. Zhang ◽  
C. M. Huang ◽  
K. M. Huang ◽  
F. Yi ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Energy Density ◽  
Gravity Waves ◽  
Seasonal Variability ◽  
High Frequency ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
High Latitudes ◽  
Middle Latitudes ◽  
Momentum Fluxes ◽  
Horizontal Momentum

Abstract. We extended the broad spectral method proposed by Zhang et al. (2013) for the extraction of medium- and high-frequency gravity waves (MHGWs). This method was applied to 11 years (1998–2008) of radiosonde data from 92 stations in the Northern Hemisphere to investigate latitudinal, continuous vertical and seasonal variability of MHGW parameters in the lower atmosphere (2–25 km). The latitudinal and vertical distributions of the wave energy density and horizontal momentum fluxes as well as their seasonal variations exhibit considerable consistency with those of inertial gravity waves. Despite the consistency, the MHGWs have much larger energy density, horizontal momentum fluxes and wave force, indicating the more important role of MHGWs in energy and momentum transportation and acceleration of the background. For the observed MHGWs, the vertical wavelengths are usually larger than 8 km; the horizontal wavelengths peak in the middle troposphere at middle–high latitudes. These characteristics are obviously different from inertial gravity waves. The energy density and horizontal momentum fluxes have similar latitude-dependent seasonality: both of them are dominated by a semiannual variation at low latitudes and an annual variation at middle latitudes; however at high latitudes, they often exhibit more than two peaks per year in the troposphere. Compared with the inertial GWs, the derived intrinsic frequencies are more sensitive to the spatiotemporal variation of the buoyancy frequency, and at all latitudinal regions they are higher in summer. The wavelengths have a weaker seasonal variation; an evident annual cycle can be observed only at middle latitudes.

Impacts of Assimilating Measurements of Different State Variables with a Simulated Supercell Storm and Three-Dimensional Variational Method

2013 ◽  
Vol 141 (8) ◽  
pp. 2759-2777 ◽  
Author(s):  
Guoqing Ge ◽  
Jidong Gao ◽  
Ming Xue
Keyword(s):  
Potential Temperature ◽  
Three Dimensional ◽  
Horizontal Wind ◽  
Cold Pool ◽  
State Variables ◽  
Wind Fields ◽  
Simulation Experiments ◽  
Supercell Storm ◽  
The Impact ◽  
Analysis Quality

Abstract This paper investigates the impacts of assimilating measurements of different state variables, which can be potentially available from various observational platforms, on the cycled analysis and short-range forecast of supercell thunderstorms by performing a set of observing system simulation experiments (OSSEs) using a storm-scale three-dimensional variational data assimilation (3DVAR) method. The control experiments assimilate measurements every 5 min for 90 min. It is found that the assimilation of horizontal wind can reconstruct the storm structure rather accurately. The assimilation of vertical velocity , potential temperature , or water vapor can partially rebuild the thermodynamic and precipitation fields but poorly retrieves the wind fields. The assimilation of rainwater mixing ratio can build up the precipitation fields together with a reasonable cold pool but is unable to properly recover the wind fields. Overall, data have the greatest impact, while have the second largest impact. The impact of is the smallest. The impact of assimilation frequency is examined by comparing results using 1-, 5-, or 10-min assimilation intervals. When is assimilated every 5 or 10 min, the analysis quality can be further improved by the incorporation of additional types of observations. When are assimilated every minute, the benefit from additional types of observations is negligible, except for . It is also found that for , , and measurements, more frequent assimilation leads to more accurate analyses. For and , a 1-min assimilation interval does not produce a better analysis than a 5-min interval.

Evaluating and Improving Parameterizations of the Variance of Temperature Fluctuations Over Heterogeneous Landscapes for Surface Boundary Conditions in Atmospheric Models

2021 ◽  
Author(s):  
Tyler Waterman ◽  
Gabriel Katul ◽  
Andy Bragg ◽  
Nathaniel Chaney
Keyword(s):  
Energy Balance ◽  
Boundary Conditions ◽  
Weather Prediction ◽  
Potential Temperature ◽  
Temperature Fluctuations ◽  
Higher Order ◽  
Parameterization Scheme ◽  
Surface Boundary ◽  
Local Energy ◽  
Temperature Variance

<p>The implementation of higher-order turbulence closure schemes in Earth system models (e.g., the Cloud Layers Unified by Binormals; CLUBB) aims to improve the modeling of convection and radiative transfer in numerical weather prediction and climate models. However, the added value of these schemes is constrained by the specification of boundary conditions on higher-order statistics. At the land surface, many of the higher order turbulence statistics that are required as boundary conditions are parameterized using formulations more appropriate for stationary and planar-homogeneous flow in the absence of subsidence. A case in point is the variance of the potential temperature fluctuations.  Because of the additive nature of variances arising from non-uniformity in surface heating, current parameterizations are not readily generalizable. The current scheme used in CLUBB, as well as other models, relies on limited studies over uniform terrain, with the variance entirely determined by local sensible heat flux, friction velocity, and the Obukhov stability parameter without regard to local site characteristics. This presentation aims to address this weakness by leveraging the National Ecological Observation Network (NEON) network of eddy covariance towers to validate the current parameterization scheme for potential temperature variance, as well as propose improvements for more heterogeneous terrain.</p><p>The turbulence fluctuations of temperature at 39 NEON sites are processed and quality controlled, removing points occurring at night, while precipitation is falling, and with sub-zero temperatures. Results overall indicate the current scheme performs well, especially over flat homogeneous terrain where local flux relationships dominate. When there is sufficiently heterogeneous, rough terrain or non-closure of the local energy balance, however, existing schemes fail to accurately estimate the variances in temperature. In these cases, the parameterization needs to be modified, and initial results suggest simple adjustments can yield improvements and reduce error close to that of the uniform sites with local energy balance closure. The successful improvement of the temperature variance parameterization scheme implies high potential for similar, new, empirically derived parameterizations for the surface boundaries for other higher order turbulent statistics (e.g. temperature skewness) in atmospheric turbulence models.</p>

scholarly journals Gravity wave amplitudes and momentum fluxes inferred from OH airglow intensities and meteor radar winds during SpreadFEx

2009 ◽  
Vol 27 (6) ◽  
pp. 2361-2369 ◽  
Author(s):  
F. Vargas ◽  
D. Gobbi ◽  
H. Takahashi ◽  
L. M. Lima
Keyword(s):  
Gravity Waves ◽  
Horizontal Wind ◽  
Small Scale ◽  
Meteor Radar ◽  
Plasma Bubble ◽  
Spatial And Temporal Scales ◽  
Analysis Technique ◽  
Momentum Fluxes ◽  
Different Types ◽  
Wave Directionality

Abstract. We show in this report the momentum flux content input in the mesosphere due to relatively fast and small scale gravity waves (GWs) observed through OH airglow images. The acquisition of OH NIR images was carried out in Brazil at Brasilia (14.8° S, 47.6° W) and Cariri (7.4° S, 36.5° W) from September 2005 to November 2005 during the SpreadFEx Campaign. Horizontal wind information from meteor radar was available in Cariri only. Our findings showed strong wave activity in both sites, mainly in Cariri. High wave directionality was also observed in both sites during SpreadFEx, which have been observed by other investigators using different analysis' techniques and different types of data during the campaign. We discuss also the possibility of plasma bubble seeding by gravity waves presenting spatial and temporal scales estimated with our novel analysis technique during the SpreadFEx campaign.

Coherent structures in direct numerical simulation of turbulent boundary layers at Mach 3

2007 ◽  
Vol 594 ◽  
pp. 59-69 ◽  
Author(s):  
MATTHEW J. RINGUETTE ◽  
MINWEI WU ◽  
M. PINO MARTÍN
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Boundary Layers ◽  
Coherent Structures ◽  
Mass Flux ◽  
Large Scale ◽  
Turbulent Boundary Layers ◽  
Turbulence Structure ◽  
Taylor’S Hypothesis ◽  
Mach 3

We demonstrate that data from direct numerical simulation of turbulent boundary layers at Mach 3 exhibit the same large-scale coherent structures that are found in supersonic and subsonic experiments, namely elongated, low-speed features in the logarithmic region and hairpin vortex packets. Contour plots of the streamwise mass flux show very long low-momentum structures in the logarithmic layer. These low-momentum features carry about one-third of the turbulent kinetic energy. Using Taylor's hypothesis, we find that these structures prevail and meander for very long streamwise distances. Structure lengths on the order of 100 boundary layer thicknesses are observed. Length scales obtained from correlations of the streamwise mass flux severely underpredict the extent of these structures, most likely because of their significant meandering in the spanwise direction. A hairpin-packet-finding algorithm is employed to determine the average packet properties, and we find that the Mach 3 packets are similar to those observed at subsonic conditions. A connection between the wall shear stress and hairpin packets is observed. Visualization of the instantaneous turbulence structure shows that groups of hairpin packets are frequently located above the long low-momentum structures. This finding is consistent with the very large-scale motion model of Kim & Adrian (1999).

scholarly journals Radar Kinematic Information as a Surrogate for Isentropes in Stratiform Precipitation Systems

2017 ◽  
Vol 145 (9) ◽  
pp. 3763-3774 ◽  
Author(s):  
Bart Geerts ◽  
Jordan I. Christian
Keyword(s):  
Wind Shear ◽  
Doppler Radar ◽  
Potential Temperature ◽  
Vertical Gradient ◽  
Horizontal Wind ◽  
Model Output ◽  
Vertical Resolution ◽  
Equivalent Potential ◽  
Stratiform Precipitation ◽  
Kinematic Information

Abstract This study illustrates that dual-Doppler-derived wind shear (vertical gradient of the horizontal wind) in stratiform, nonturbulent flow is structured in long, thin striations. The reason this has not been documented before is that scanning ground-based radars have inadequate vertical resolution, deteriorating with range. Here data from an airborne radar with a fine, range-independent vertical resolution are used. A comparison of the radar-derived wind shear with model output of isentropes in vertical transects in the comma head of two frontal disturbances suggests that the wind shear layers describe material surfaces. Model output itself further confirms the alignment of isentropes with wind shear in vertical transects. Thus, Doppler-radar-derived wind shear (a kinematic conserved variable) may serve as a suitable proxy for thermodynamic conserved variables such as equivalent potential temperature in stratiform precipitation. Furthermore, the presence of shear striations in vertical transects can be used as a marker for nonturbulent flow, and their persistence as an indicator of limited dispersion in such flow.

scholarly journals Dynamics of the Disrupted 2015/16 Quasi-Biennial Oscillation

2017 ◽  
Vol 30 (15) ◽  
pp. 5661-5674 ◽  
Author(s):  
Lawrence Coy ◽  
Paul A. Newman ◽  
Steven Pawson ◽  
Leslie R. Lait
Keyword(s):  
Lower Stratosphere ◽  
Global Climate ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Wind Variability ◽  
Momentum Fluxes ◽  
Horizontal Momentum ◽  
The Tropics ◽  
Global Reanalysis ◽  
Biennial Oscillation

A significant disruption of the quasi-biennial oscillation (QBO) occurred during the Northern Hemisphere (NH) winter of 2015/16. Since the QBO is the major wind variability source in the tropical lower stratosphere and influences the rate of ascent of air entering the stratosphere, understanding the cause of this singular disruption may provide new insights into the variability and sensitivity of the global climate system. Here this disruptive event is examined using global reanalysis winds and temperatures from 1980 to 2016. Results reveal record maxima in tropical horizontal momentum fluxes and wave forcing of the tropical zonal mean zonal wind over the NH 2015/16 winter. The Rossby waves responsible for these record tropical values appear to originate in the NH and were focused strongly into the tropics at the 40-hPa level. Two additional NH winters, 1987/88 and 2010/11, were also found to have large tropical lower-stratospheric momentum flux divergences; however, the QBO westerlies did not change to easterlies in those cases.

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