|
|
- The Surface Energy Budget of a Wheat Crop: Estimates of Storage
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The residual found by Garratt and Pearman (2020, Boundary-Layer Meteorology 177: 613–641) in the surface energy budget of a winter wheat crop is the result of combining seven separately measured or estimated individual fluxes, each with its own uncertainty. We show that the mean hourly residual as it varies through the day is closely correlated with the rate-of-change of radiative surface temperature. Using the latter as a basis for estimating the hourly storage closes the budget to within 5% of the incident broadband shortwave irradiance, down from 10% when storage is excluded. The storage so calculated both agrees with estimates for a maize crop (Hicks et al. 2020, Agricultural and Forest Meteorology 290: 108035) and with theoretical considerations. However, for storage calculations in the field, soil and canopy temperatures are preferable to surface temperature.
PubDate: 2023-11-21
- The Performance of GRAMM-SCI and WRF in Simulating the Surface-Energy
Budget and Thermally Driven Winds in an Alpine Valley-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Using WRF as a benchmark, GRAMM-SCI simulations are performed for a case study of thermally driven valley- and slope winds in the Inn Valley, Austria. A clear-sky, synoptically undisturbed day was selected when large spatial heterogeneities occur in the components of the surface-energy budget driven by local terrain and land-use characteristics. The models are evaluated mainly against observations from four eddy-covariance stations in the valley. While both models are able to capture the main characteristics of the surface-energy budget and the locally driven wind field, a few overall deficiencies are identified: (i) Since the surface-energy budget is closed in the models, whereas large residuals are observed, the models generally tend to overestimate the daytime sensible and latent heat fluxes. (ii) The partitioning of the available energy into sensible and latent heat fluxes remains relatively constant in the simulations, whereas the observed Bowen ratio decreases continuously throughout the day because of a temporal shift between the maxima in sensible and latent heat fluxes, which is not captured by the models. (iii) The comparison between model results and observations is hampered by differences between the real land use and the vegetation type in the model. Recent modifications of the land-surface scheme in GRAMM-SCI improve the representation of nighttime katabatic winds over forested areas, reducing the modeled wind speeds to more realistic values.
PubDate: 2023-11-10
- Investigation of a Geometric Parameter Corresponding to the Turbulent
Length Scale Within an Urban Canopy Layer-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract In this paper, we identify a new geometric parameter that governs the turbulent length scale within the urban canopy layer. This parameter is the geometric mean ( \(\sqrt[3]{HDX}\) ) of the building height (H), width of the road in the streamwise direction (D), and width of the road in the spanwise direction (X). The turbulent length scales in various cities are estimated and nondimensionalised using the proposed parameter. The proposed parameter ( \(\sqrt[3]{HDX}\) ) corresponds well to the turbulent length scale. It is better than H or D. Additionally, we propose a weighting factor ( \({w}_{var}(z)\) ) using the local plan area index to achieve good correspondence to the turbulent length scale even when the building height varies. The parameter multiplying \(\sqrt[3]{HDX}\) and \({w}_{var}(z)\) corresponds well to the turbulent length scale in cities with various building heights. Furthermore, the proposed parameter \({w}_{var}(z)\sqrt[3]{HDX}\) is combined with the turbulent length scale of the Mellor–Yamada turbulence model. This combined turbulent length scale can capture the characteristics of the vertical profile of the turbulent length scale better than the conventional method, particularly within the urban canopy layer.
PubDate: 2023-10-30
- Impact of Local Terrain Features on Urban Airflow
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Past work has shown that coupling can exist between atmospheric air flows at street scale (O(0.1 km)) and city scale (O(10 km)). It is generally impractical at present to develop high-fidelity urban simulations capable of capturing such effects. This limitation imposes a need to develop better parameterisations for meso-scale models but an information gap exists in that past work has generally focused on simplified urban geometries and assumed the buildings to be on flat ground. This study aimed to begin to address this gap in a systematic way by using the large eddy simulation method with synthetic turbulence inflow boundary conditions to simulate atmospheric air flows over the University of Southampton campus. Both flat and realistic terrains were simulated, including significant local terrain features, such as two valleys with a width about 50 m and a depth about average building height, and a step change of urban roughness height. The numerical data were processed to obtain averaged vertical profiles of time-averaged velocities and second order turbulence statistics. The flat terrain simulation was validated against high resolution particle image velocimetry data, and the impact of uncertainty in defining the turbulence intensity in the synthetic inflow method was assessed. The ratio between realistic and flat terrains of time-mean streamwise velocity at the same ground level height over a terrain crest location can be >2, while over a valley trough it can be <0.5. Further data analysis conclusively showed that the realistic terrain can have a considerable effect on global quantities, such as the depth of the spanwise-averaged internal boundary layer and spatially-averaged turbulent kinetic energy. These highlight the potential impact that local terrain features (O(0.1 km)) may have on near-field dispersion and the urban micro-climate.
PubDate: 2023-10-13
- The Relaxed Eddy Accumulation Method Over the Amazon Forest: The
Importance of Flux Strength on Individual and Aggregated Flux Estimates-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The ability of the relaxed eddy accumulation (REA) method to estimate the kinematic fluxes of temperature, water vapor and carbon dioxide was assessed for the dry season (3 months) at the ATTO (Amazon Tall Tower Observatory) site from turbulence measurements. The measurements were performed at 50 m above ground within the roughness sublayer. Non-conformity with inertial sublayer conditions was confirmed one more time by analyzing dimensionless scalar standard deviations. Over the scale of the whole dry season, REA and EC (eddy covariance) estimates are essentially equal. Recently found results that the REA method outperforms Monin–Obukhov-based approaches are confirmed. However, we also verify that such results fail to reveal significant variability and scatter of the REA estimates when the fluxes are of small magnitude. On the basis of previous studies, we conjecture that this is caused by a likely imbalance between scalar gradient production and molecular dissipation. Confirmation of our results to trace gases, therefore, requires further study.
PubDate: 2023-10-04
- Wake Characterization of Building Clusters Immersed in Deep Boundary
Layers-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Wind tunnel experiments were conducted to understand the effect of building array size (N), aspect ratio (AR), and the spacing between buildings ( \(W_S\) ) on the mean structure and decay of their wakes. Arrays of size 3 \(\times \) 3, 4 \(\times \) 4,and 5 \(\times \) 5, AR = 4, 6, and 8, and \(W_S\) = 0.5 \(W_B\) , 1 \(W_B\) , 2 \(W_B\) and 4 \(W_B\) (where \(W_B\) is the building width) were considered. Three different wake regimes behind the building clusters were identified: near-, transition-, and far-wake regimes. The results suggest that the spatial extent of these wake regimes is governed by the overall array width ( \(W_A\) ). The effects of individual buildings are observed to be dominant in the near-wake regime ( \(0<x/W_A< {0.45}\) ) where individual wakes appear behind each building. These wakes are observed to merge in the transition-wake region ( \({0.45}< x/W_A < 1.5\) ), forming a combined wake in which the individual contributions are no longer apparent. In the far-wake regime ( \(x/W_A > 1.5\) ), clusters’ wakes are akin to those developing downwind of a single isolated building. Accordingly, new local and global scaling parameters in the near- and far-wake regimes are introduced. The decay of the centreline velocity deficit is then modelled as a function of the three parameters considered in the experiment.
PubDate: 2023-10-04
- Quantification of Uncertainties of Radiative Transfer Calculation in Urban
Canopy Models-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Urban canopy models simplify urban morphology and physical processes such as radiative transfer to calculate the urban surface energy balance as a lower boundary condition for atmospheric models at low computational cost. The present study uses a reference model of urban radiative transfer based on the Monte Carlo method, which solves the radiative transfer equation by taking into account the complex geometry of buildings and vegetation. Procedurally-generated urban morphologies similar to the local climate zones (LCZ) are studied to cover the variety of urban forms that exist globally. The uncertainties arising from the simplification of the urban morphology as an infinitely-long street canyon or a regular array of square blocks are quantified. In addition, uncertainties due to the neglect of specular or spectral material reflectivities and the involved atmosphere are investigated. It is found that for all LCZ, the street canyon and block morphologies lead to a systematic overestimation (underestimation) of the fraction of solar radiation absorbed by the walls (ground). The neglect of pitched roofs has a strong influence on the simulated urban solar radiation budget for low solar elevation angles. Neglecting the spectral reflectivity of urban materials does not lead to relevant uncertainties in the broadband radiative fluxes. Specularly reflecting windows only change the urban solar radiation budget for a central business district morphology with a high glazing ratio. The participating atmosphere can strongly influence the urban terrestrial radiation budget, especially for high-rise districts. Future urban canopy models should therefore improve the realism of the urban morphology, and consider a participating atmosphere for the calculation of terrestrial radiation.
PubDate: 2023-09-26
- Celebrating the Career of Evgeni Fedorovich: Explorer of the
Boundary-Layer Realm and Ambassador for the Community-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
PubDate: 2023-09-11
DOI: 10.1007/s10546-023-00828-8
- Understanding Thermally Driven Slope Winds: Recent Advances and Open
Questions-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The paper reviews recent advances in our understanding about the dynamics of thermally driven winds over sloping terrain. Major progress from recent experiments, both in the field and in the laboratory, are outlined. Achievements from numerical modelling efforts, including both parameterized turbulence and large eddy simulation approaches, up to direct numerical simulations, are also reviewed. Finally, theoretical insights on the nature of turbulence in such winds are analyzed along with applications which benefit from progress in understanding of these flows. Open questions to be faced for further investigations are finally highlighted.
PubDate: 2023-09-09
DOI: 10.1007/s10546-023-00821-1
- Atmospheric Small-Scale Turbulence from Three-Dimensional Hot-film Data
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The behavior of small-scale atmospheric turbulence is investigated using the three-dimensional Canopy Horizontal Array Turbulence Study hot-film data. The analysis relies on an in situ calibration versus simultaneous sonic anemometer measurements. The calibration is based on King’s law and geometric relationships between the individual hot-film sensors, and is able to account for the errors associated with sensors’ misalignment and the high turbulence intensity. The details of the calibration are provided, and its performance is validated by comparing results of spectra and structure functions with standard wind-tunnel data and model spectra. A single 3 h block of data was selected, containing 33 subblocks of 2 min data without error gaps, whose statistics were averaged to provide smooth results. These data were measured above canopy under stable conditions, and correspond to a Taylor Reynolds number \(Re_\lambda \approx 1550\) . The agreement with wind tunnel results for a similar \(Re_\lambda \) and with model predictions provides a validation for the in situ calibration method applied. Furthermore, the results indicate a presence of the bottleneck effect in the lateral and vertical spectra, in addition to a lack of inertial range in the second-order structure function due to the low Reynolds number. An additional analysis of the effect of Reynolds number on the inertial range is provided using atmospheric data from the literature.
PubDate: 2023-09-07
DOI: 10.1007/s10546-023-00826-w
- Correction to: Wavelet Analysis of Coherent Structures above Maize and
Soybean Crops-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
PubDate: 2023-09-01
DOI: 10.1007/s10546-023-00817-x
- Wind-Tunnel Reproduction of Nonuniform Terrains Using Local Roughness
Zones-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Wind-tunnel modeling of Atmospheric Boundary Layer flows has primarily consisted of simplified (purely uniform) upwind terrain conditions. This approach is easier to carry out but may not replicate the true wind characteristics of the site. This paper proposes a method to simulate nonuniform terrains in a wind-tunnel and investigates the wind characteristics produced by the method. The proposed method employs the local roughness zones where the given terrain is divided into sub-areas with an approximately uniform roughness length. Next, each sub-area is represented in the wind-tunnel with uniform roughness elements. However, the overall upwind fetch will be composed of roughness elements of various heights. To study the wind characteristics produced by the method, nine different real-world sites were simulated in the Boundary Layer Wind Tunnel at the University of Florida Natural Hazard Engineering Infrastructure Experimental Facility, using a self-configurable (automated) roughness element grid. Compared with the conventional equivalent uniform representation, similarities and differences in the longitudinal mean velocity, turbulence intensity, wind spectrum, and integral length scale profiles are reported and discussed. In particular, a significant difference was observed for the higher-order moments of the longitudinal velocity component, which indicates the need for further studies in wind loads under nonuniform terrains.
PubDate: 2023-08-26
DOI: 10.1007/s10546-023-00822-0
- Turbulence in the Mixed Layer Over an Urban Area: A New York City Case
Study-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This study examines the turbulence characteristics of the boundary layer over New York City. Understanding the urban boundary layer characteristics is key to forecasting weather in cities, where most people live. Although extensive research into urban boundary layer (UBL) processes have been carried out in the past decades, majority of these studies focused on the urban surface layer; our understanding of urban mixed layer characteristics is still incomplete. Here we use Doppler lidar observations from multiple sites in New York City to study turbulent properties in the UBL and their relationship to the heterogeneous urban surface. All three sites were influenced by different levels of urbanization. By investigating turbulent properties such as velocity variances, turbulent intensities, and vertical velocity spectra throughout the UBL, our analysis shows vertical stratification in momentum transport during non-neutral stability periods. The spectral analysis of vertical velocities show vertical stratification in normalized energy density at different heights, with the degree of stratification increasing with increasingly non-neutral surface stability. A comparison of turbulent properties over the study sites reveals a degree of homogeneity in mixed layer characteristics, with similar vertical profiles of the turbulent characteristics among the sites, suggesting horizontal homogeneity in the urban mixed layer.
PubDate: 2023-08-24
DOI: 10.1007/s10546-023-00819-9
- Appropriate Momentum Provision for Numerical Simulations of Horizontally
Homogeneous Urban Canopies Using Periodic Boundary Conditions-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Turbulent flow over urban-like roughness has been numerically studied for various purposes, such as the clarification of turbulent characteristics over rough walls, visualization of turbulent structures around block arrays, and evaluation of urban ventilation and pedestrian winds. In such simulations, a portion of the developing boundary layer is extracted as a numerical domain, assuming periodic boundary conditions in the horizontal direction to reproduce laterally homogeneous rough surfaces. However, the conditions required to drive the airflow by an artificial momentum source uniquely determine the turbulent statistics, which are different from those in developing boundary layers. Therefore, this study presents a new approach for driving the airflow over urban-like block arrays. The new method is based on spatially averaged Navier–Stokes equations to prove the necessity of height-dependent momentum provision. The turbulent flow over a cubical-block array is determined using large-eddy simulations driven by four different momentum sources. Regardless of the driving force, the vertical profiles of the streamwise velocity components are identical. In contrast, slight differences in the vertical Reynolds stress, variances in the velocity components, and turbulence kinetic energy are appropriately reproduced in the new approach. In addition, the budget equations of the turbulent statistics reveal that a change in the vertical Reynolds stress affects the energy production and its redistribution into variance components. The proposed method can contribute to the reproduction of a realistic turbulent flow and provide a theoretical understanding of the momentum provision.
PubDate: 2023-08-22
DOI: 10.1007/s10546-023-00823-z
- The Atmospheric Boundary Layer Above the Marginal Ice Zone: Scaling,
Surface Fluxes, and Secondary Circulations-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The Arctic is undergoing rapid changes due to global warming, including the expansion of the marginal ice zone (MIZ), a zone of mixed ice and open water surfaces. To predict the atmospheric interaction with these surfaces, a critical process in climate models, this paper examines a simplified theoretical framework to non-dimensionalize the dynamics of the atmospheric boundary layer (ABL) over a mixed ice-water surface (MIZ–ABL). A heterogeneity Richardson number, \(\text {Ri}_h\) , is proposed to account for the difference in temperature between the ice and water surface in relation to the synoptic pressure gradient forcing. With the wind angle relative to the ice-water interface, \(\alpha \) , this framework hypothesizes that these two dimensionless numbers, regardless of individual dimensional variables (surface temperature and geostrophic wind speed) are sufficient to predict the MIZ–ABL dynamics. To test this framework, large-eddy simulations were employed over half-ice and half-water surfaces, with varying surface temperatures and geostrophic wind velocities. While the surface heat fluxes over ice, water, and the aggregate surface seem to be captured reasonably well by \(\alpha \) and Ri \(_h\) , the mean wind and turbulent kinetic energy (TKE) profiles were not, suggesting that not only the difference in stability between the two surface, but also the individual stabilities over each surface influence the dynamics. The wind angle had a significant impact on the results, both in terms of heat fluxes at the surface, turbulent and dispersive fluxes in the MIZ–ABL, and the structure of the secondary circulations. When wind blows perpendicular to the water-ice interface, internal boundary layers are favoured except at the highest Ri \(_h\) simulated. For cases with wind parallel to the interface, large rolls parallel to the shore emerge. The paper raises at least as many questions as it answers, highlighting the need for further studies of the MIZ–ABL.
PubDate: 2023-08-21
DOI: 10.1007/s10546-023-00825-x
- Correction to: Evidence of Strong Flux Underestimation by Bulk
Parametrizations During Drifting and Blowing Snow-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
PubDate: 2023-08-01
DOI: 10.1007/s10546-023-00809-x
- The Performance of a Time-Varying Filter Time Under Stable Conditions over
Mountainous Terrain-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Eddy-covariance data from five stations in the Inn Valley, Austria, are analyzed for stable conditions to determine the gap scale that separates turbulent from large-scale, non-turbulent motions. The gap scale is identified from (co)spectra calculated from different variables using both Fourier analysis and multi-resolution flux decomposition. A correlation is found between the gap scale and the mean wind speed and stability parameter z/L that is used to determine a time-varying filter time, whose performance in separating turbulent and non-turbulent motions is compared to the performance of constant filter times between 0.5 and 30 min. The impact of applying different filter times on the turbulence statistics depends on the parameter and location, with a comparatively smaller impact on the variance of the vertical wind component than on the horizontal components and the turbulent fluxes. Results indicate that a time-varying filter time based on a multi-variable fit taking both mean wind speed and stability into account and a constant filter time of 2–3 min perform best in that they remove most of the non-turbulent motions while at the same time capturing most of the turbulence. For the studied sites and conditions, a time-varying filter time does not outperform a well chosen constant filter time because of relatively small variations in the filter time predicted by the correlation with mean flow parameters.
PubDate: 2023-07-29
DOI: 10.1007/s10546-023-00824-y
- Wind-Tunnel Experiments of Turbulent Wind Fields over a Two-dimensional
(2D) Steep Hill: Effects of the Stable Boundary Layer-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Flow separation caused by steep topography remains a significant obstacle in accurately predicting turbulent boundary-layer flows over complex terrain, despite the utilization of sophisticated numerical models. The addition of atmospheric thermal stability, in conjunction with steep topography, further complicates the determination of disrupted turbulent wind patterns. The turbulent separated flows over a two-dimensional (2D) steep hill under thermal stratification has not been extensively addressed in previous experimental studies. Such measurements are crucial for enhancing our comprehension of flow physics and validating numerical models. We measured the turbulent wind flows over a 2D steep hill immersed in a stable boundary layer (of the bulk Richardson Number \(\textrm{Ri}_b\) = 0.256) in a thermally-stratified boundary-layer wind tunnel. The flow separation, re-circulation zone and flow reattachment were characterized by the planar particle image velocimetry technique. Vertical profiles of mean air temperature and its fluctuations are also quantified at representative locations above the 2D steep hill and in the near wake region. Results indicate that the separated shear layer, initiated near the crest of the 2D steep hill, dominates the physical process leading to high turbulence levels and the turbulent kinetic energy production in the wake region for both stable and neutral thermal stability. Although the stable boundary layer does not dramatically change the turbulent flow pattern around the hill, the mean separation bubble is elongated by 13%, and its vertical extent is decreased by approximately 20%. Furthermore, the reduced turbulence intensities and turbulent kinetic energy of the near wake flow are attributed to the relatively low turbulence intensity and low momentum of the stable boundary layer due to buoyancy damping, compared to the neutral boundary layer. Additionally, a distinct low-temperature region—a cold pool—is extended beyond the separation bubble, reflecting the significant sheltering effect of the 2D steep hill on the downwind flow and temperature field.
PubDate: 2023-07-13
DOI: 10.1007/s10546-023-00820-2
- The Role of Vertical Diffusion Parameterizations in the Dynamics and
Accuracy of Simulated Intensifying Hurricanes-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Rotation in hurricane flows can significantly impact the dynamics and structure of the turbulent boundary layer. Despite this unique feature of hurricane boundary layers, the current planetary boundary layer (PBL) schemes in weather models are neither specifically designed nor comprehensively tested for intensifying hurricane flows. The objective of this paper is to bridge this knowledge gap by characterizing the role of vertical diffusion depth and magnitude in simulated hurricane intensity, size, and track. To this end, five major hurricane cases undergoing an intensification period are simulated using two widely used local and non-local PBL schemes in Weather Research and Forecasting (WRF) model. In total, eighty WRF simulations are conducted by varying the grid resolution, PBL scheme, eddy diffusivity depth and magnitude, and PBL height. By decreasing the existing vertical diffusion depth and magnitude, on average, ~ 38 and ~ 24% improvements in hurricane intensity forecasts were obtained compared to the default models. Hence, the results indicate that the current PBL schemes in WRF are overly diffusive for simulating major hurricanes since they do not account for turbulence suppression effects in rotating hurricane flows. The paper yields new insights into the role of vertical diffusion in simulated hurricane dynamics and provides some guidance to enhance the PBL schemes of NWPs for improved hurricane forecasts.
PubDate: 2023-07-12
DOI: 10.1007/s10546-023-00818-w
- Budgets of Second-Order Turbulence Moments over a Real Urban Canopy
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This study analyses budgets of second-order turbulence moments over a real urban canopy using large-eddy simulation. The urban canopy is representative of the City of Boston, MA, United States and is characterized by a significant height variability relative to the mean building height. The budgets of double-averaged Reynolds-stress components, scalar fluxes, and scalar variances are examined with a focus on the importance of the dispersive terms above the mean building height. Results reveal the importance of the wake (dispersive) production term, in addition to the shear production term, in the turbulence kinetic energy (TKE), streamwise velocity variance and scalar variance budgets well above the mean building height. In this region, the turbulent and dispersive transport terms are smaller than the production and dissipation terms. Nonetheless, the dispersive transport terms in the TKE and scalar variance budgets can be as important as their turbulent counterparts. The subgrid-scale dissipation term is the main sink in the TKE, vertical velocity variance and scalar variance budgets. In the momentum and scalar flux budgets, the pressure-strain correlation term and the pressure gradient-scalar interaction term are the significant sink terms, respectively. Our analysis highlights the complexity associated with the budgets of second-order turbulence moments over real urban canopies and has important implications for developing urban parameterizations for weather and climate models.
PubDate: 2023-07-03
DOI: 10.1007/s10546-023-00816-y
|
Hybrid journal (It can contain Open Access articles)
