Planetary Boundary Layer Parameterization Research Articles

Addition of Multilayer Urban Canopy Models to a Nonlocal Planetary Boundary Layer Parameterization and Evaluation Using Ideal and Real Cases

AbstractThe multilayer urban canopy models (UCMs) building effect parameterization (BEP) and BEP + building energy model (BEM; a building energy model integrated in BEP) are added to the Yonsei University (YSU) planetary boundary layer (PBL) parameterization in the Weather Research and Forecasting (WRF) Model. The additions allow for the first analysis of the detailed effects of buildings on the urban boundary layer in a nonlocal closure scheme. The modified YSU PBL parameterization is compared with the other 1.5-order local PBL parameterizations that predict turbulent kinetic energy (TKE), Mellor–Yamada–Janjić and Bougeault–Lacarerre, using both ideal and real cases. The ideal-case evaluation confirms that BEP and BEP+BEM produce the expected results in the YSU PBL parameterization because the simulations are qualitatively similar to the TKE-based PBL parameterizations in which the multilayer UCMs have long existed. The modified YSU PBL parameterization is further evaluated for a real case. Similar to the ideal case, there are larger differences among the different UCMs (simple bulk scheme, BEP, and BEP+BEM) than across the PBL parameterizations when the UCM is held fixed. Based on evaluation against urban near-surface wind and temperature observations for this case, the BEP and BEP+BEM simulations are superior to the simple bulk scheme for each PBL parameterization.

Sensitivity of WRF-simulated 10 m wind over the Persian Gulf to different boundary conditions and PBL parameterization schemes

A sensitivity analysis of the Weather Research and Forecasting (WRF) mesoscale model with the Advanced Research WRF (ARW) dynamical solver for wind simulation at 10 m above ground level was conducted through different initial and boundary conditions datasets, and various planetary boundary layer (PBL) schemes throughout the year 2017 over the Persian Gulf region. Owing to the wide variety of approaches and development periods of analysis and reanalysis data (e.g. assimilation system) as well as different methods for PBL parameterization (closure formulations), this paper aims to obtain an efficient set up of the WRF model configuration in terms of the lowest error in simulating surface wind. Three datasets including ERA-Interim reanalysis, NCEP-R2 reanalysis, and NCEP-FNL analysis as initial and boundary conditions to the model and six PBL schemes including ACM2, BouLac, MYJ, MYNN, QNSE, and YSU accompanied by their relevant surface-layer schemes were used to accomplish this goal. Available observational wind data including 23 synoptic weather stations located in the region were used to compare the model wind simulation. Comparing WRF wind simulations with observations at synoptic weather stations indicates that; irrespective of the type of PBL scheme, ERA-Interim, and NCEP-FNL datasets exhibit better performance than the NCEP-R2. In addition, in the case of considering PBL schemes, results show that the configuration including the YSU scheme and ERA-Interim reanalysis data leads to the best estimation of wind speed and configuration including YSU and NCEP-FNL data produces the least error for wind direction. The performance of the model in summer shows higher errors compared to the winter season. It is due to the obvious differences between initial and boundary conditions data with observation data. The success of the YSU scheme in comparison with other schemes is rooted in the nonlocal closure of this scheme, which includes local gradients correction and entrainment sentences.

Impact of boundary layer simulation on predicting radioactive pollutant dispersion: A case study for HANARO research reactor using the WRF-MMIF-CALPUFF modeling system

Wind plays an important role in cases of unexpected radioactive pollutant dispersion, deciding distribution and concentration of the leaked substance. The accurate prediction of wind has been challenging in numerical weather prediction models, especially near the surface because of the complex interaction between turbulent flow and topographic effect. In this study, we investigated the characteristics of atmospheric dispersion of radioactive material (i.e. 137Cs) according to the simulated boundary layer around the HANARO research nuclear reactor in Korea using the Weather Research and Forecasting (WRF)-Mesoscale Model Interface (MMIF)-California Puff (CALPUFF) model system. We examined the impacts of orographic drag on wind field, stability calculation methods, and planetary boundary layer parameterizations on the dispersion of radioactive material under a radioactive leaking scenario. We found that inclusion of the orographic drag effect in the WRF model improved the wind prediction most significantly over the complex terrain area, leading the model system to estimate the radioactive concentration near the reactor more conservatively. We also emphasized the importance of the stability calculation method and employing the skillful boundary layer parameterization to ensure more accurate low atmospheric conditions, in order to simulate more feasible spatial distribution of the radioactive dispersion in leaking scenarios.

The Effects of Different Planetary Boundary Layer Schemes on the Meteorological and Environmental Elements in winter stable weather of Shenyang

Two planetary boundary layer schemes (YUS and MYJ) in the WRF-CMAQ model, are selected for sensitivity simulation, and the simulation capabilities of different planetary boundary layer schemes to meteorological elements and PM2.5 concentration distribution are analyzed from December 17th to December 20th in 2016. The results show that using the YSU and MYJ schemes can well simulate the spatial distribution and diurnal variation characteristics of temperature, wind speed and PM2.5 concentration on the ground under the background of stable weather in winter. It is sensitive to temperature, wind speed and PM2.5 concentration on the ground using different planetary boundary layer parameterization schemes. The simulated wind speed is relatively large, and the maximum deviation can reach about 2m/s. The deviation of wind speed using the MYJ scheme is relatively small than YSU, which is closer to the real value. There has a lower PM2.5 concentration value using YSU than MYJ at night, however the daytime (mainly from 11:00 to 18: 00) YSU scheme is relatively higher than MYJ. The deviation of PM2.5 concentration on the ground using the MYJ scheme is relatively smaller than YSU, and the characteristics of daily variation is closer to the real situation. Overall, the MYJ scheme is better than YSU in air pollution simulation.

Evaluation of CMAQ modeling sensitivity to planetary boundary layer parameterizations for gaseous and particulate pollutants over a fjord valley

Abstract Three-dimensional chemical transport models are useful for spatial and temporal analyses of outdoor air quality. However, the suitability of boundary-layer parameterizations for air pollution modeling over deep, coastal valleys has seldom been tested. An evaluation of the Community Multiscale Air Quality (CMAQ) model performance for five planetary boundary-layer schemes (PBL) with the Weather Research and Forecasting (WRF) meteorological driver was conducted at 1-km horizontal resolution for fine particulate matter (PM2.5), sulfur dioxide (SO2) and nitrogen dioxide (NO2) over the Terrace-Kitimat valley of northwestern British Columbia, Canada. The top-ranked schemes were Mellor-Yamada-Nakanishi-Niino Level 3 (MYNN3) for PM2.5 and Mellor-Yamada-Janjic for NO2. Both schemes ranked high for absolute SO2 levels, but the MYJ and Asymmetric Convective Model, version 2 (ACM2) schemes qualitatively emulated peak summertime diurnal concentrations in the near field of elevated point sources. Greater nighttime SO2 concentrations with MYNN3 and Yonsei University PBL schemes, in less agreement with station monitoring 8 km downwind of emissions from tall stacks, suggested sustained pollutant mixing and downward transport within the nocturnal boundary layer. Consequently, for these two schemes with representations of nonlocal mass flux transfers between model layers, inland penetrations of pollutant plumes were farther than those of ACM2, MYJ, and University of Washington schemes. For NO2 and PM2.5 that mainly discharged passively from fugitive, ground-level sources, hence are less accurately quantified than SO2 emissions, the fully local MYJ, and semi-local MYNN3 PBL schemes more reasonably reproduced peak season concentrations than other schemes. It is concluded that for air pollution modeling in rugged, remote areas, the mode of pollutant emissions is important for the choice of a PBL scheme. PM2.5 was consistently underestimated by the various PBL schemes, and aspects for improving CMAQ simulations for a complex environment are discussed.

Extreme rainfall event in the Northeast coast of Brazil: a numerical sensitivity study

This study investigates an extreme rainfall event which occurred in Northern Brazil (NEB) between 20 and 30th 2017 May causing several deaths and making thousands homeless. Based on a suite of microphysics and planetary boundary layer (PBL) schemes based on the WRF model, it is demonstrated that anomalous weather conditions are characterized by significant upward and eastward wind flow. Omega differences with respect to climatological conditions showed values up to − 0.04 Pa/s and wind up to 6–8 m/s in consonance with higher precipitation in May in the NEB coast. The cumulative rainfall for 11 days was higher than 500 mm in some locations, as measured by weather stations. These conditions were simulated by the WRF model under different physics parameterization schemes. In total 24 experiments with WRF were implemented. Non-local PBL demonstrated better performance than the local PBL. Moreover, the rainfall was concentrated in small portions of the region, and the local scheme limited the WRF conditions to estimate the correct maximum precipitation location. The Morrison scheme performed better compared to the other schemes. Results presented here show that the correct choices of the microphysics and PBL parameterizations are fundamental to obtain good simulation/forecast, especially for extreme rainfall events. This study demonstrates that regional modeling is crucial to provide accurate information to forecasters and decision makers to plan actions which hamper catastrophic situations such as landslides and floods in high-risk regions.

Evaluation of an E–ε and Three Other Boundary Layer Parameterization Schemes in the WRF Model over the Southeast Pacific and the Southern Great Plains

Abstract To accurately simulate the atmospheric state within the planetary boundary layer (PBL) by PBL parameterization scheme in different regions with their dominant weather/climate regimes is important for global/regional atmospheric models. In this study, we introduce the turbulence kinetic energy (TKE) and TKE dissipation rate (ε) based 1.5-order closure PBL parameterization (E–ε, EEPS) in the Weather Research and Forecasting (WRF) Model. The performances of the newly implemented EEPS scheme and the existing Yonsei University (YSU) scheme, the University of Washington (UW) scheme, and Mellor–Yamada–Nakanishi–Niino (MYNN) scheme are evaluated over the stratocumulus dominated southeast Pacific (SEP) and over the Southern Great Plains (SGP) where strong PBL diurnal variation is common. The simulations by these PBL parameterizations are compared with various observations from two field campaigns: the Variability of American Monsoon Systems Project (VAMOS) Ocean–Cloud–Atmosphere–Land Study (VOCALS) in 2008 over the SEP and the Land–Atmosphere Feedback Experiment (LAFE) in 2017 over the SGP. Results show that the EEPS and YSU schemes perform comparably over both regions, while the MYNN scheme performs differently in many aspects, especially over the SEP. The EEPS (MYNN) scheme slightly (significantly) underestimates liquid water path over the SEP. Compared with observations, the UW scheme produces the best PBL height over the SEP. The MYNN produces too high PBL height over the western part of the SEP while both the YSU and EEPS schemes produce too low PBL and cloud-top heights. The differences among the PBL schemes in simulating the PBL features over the SGP are relatively small.

Simulation of Atmospheric Microbursts Using a Numerical Mesoscale Model at High Spatiotemporal Resolution

AbstractAtmospheric microbursts are low‐level meteorological events that can produce significant damage on the surface and pose a major risk to aircraft flying close to the ground. Studies and ad hoc numerical models have been developed to understand the origin and dynamics of the microburst; nevertheless, there are few researches of the phenomenon using global and mesoscale models. This is mainly due to the limitations in resolution, as microbursts normally span for less than 4 km and 20 min. In this paper, the Weather Research and Forecasting model is used at resolutions of 400 m and 3 min to test if it can properly capture the variables and dynamics of high‐reflectivity microbursts. Several microphysics and planetary boundary layer parametrizations are tested to find the best model configuration for the simulation of this kind of episodes. General conditions are evaluated by using thermodynamic diagrams. Surface and vertical wind speed, reflectivity, precipitation, and other variables for each simulated event are compared with observations, and the model's sensitivity to the variables is assessed. The dynamics and evolution of the microburst is evaluated using different plots of a chosen event. The results show that the model is able to reproduce high‐reflectivity microbursts in accordance with observations, although there is a tendency to underestimate the intensity of variables, most markedly on the wind vertical velocity. Regarding the microphysics schemes, the Morrison parametrization performs better than the WRF single‐moment 6‐class scheme. No major differences are found between the Mellor‐Yamada‐Janjic and the Mellor‐Yamada‐Nakanishi‐Niino planetary boundary layer parametrizations.

Sub-kilometer dispersion simulation of a CO tracer for an inter-Andean urban valley

Air quality planning and management can benefit from the ability of numerical models to produce skillful forecasts. However, obtaining these forecasts is a continuing challenge, particularly in complex terrain. Here we examine the dispersion of traffic emissions in the Aburrá valley (located in the Colombian Andes) during an episode of severe air pollution, using the WRF-Chem and a Lagrangian model at sub-kilometer resolution. We focus on the identification of areas with higher CO concentrations (the pollutant analyzed), and examine the role of local and regional airflows in the distribution of CO inside the valley. The meteorological model performance, considering different planetary boundary layer parameterizations and grid sizes, is evaluated using available observations. Overall, the meteorological model performance is within recommended benchmarks for complex terrain. Model performance improves with increasing grid resolution for surface temperature and wind direction, but not for wind speed. Both dispersion models reproduce important features of the spatial and diurnal variability of CO in the valley, but underestimate CO concentrations throughout the simulation period. The south and southeast areas of the valley present the largest CO concentrations, associated with a prevalent northerly transport along the valley axis and reduced transport on the eastern slope. The representation of CO improves when the model adequately reproduces observed rainfall, due to effects of rainfall on boundary layer height and stability, which condition dispersion. Better simulation of transport processes is crucial for informing decisions on air quality management in critical areas such as urban valleys.

The role of the planetary boundary layer parameterization schemes on the meteorological and aerosol pollution simulations: A review

In the past decades, various planetary boundary layer (PBL) parameterization schemes have been developed. The PBL schemes play an essential role in the simulation of meteorological parameters and PBL structures of the model. This review is aimed at presenting the contemporary state of simulation of the meteorological parameters and PBL structures through different PBL schemes over the world, as well as at identifying the main gaps in the simulation capability of PBL schemes and the impact of PBL schemes on the aerosol pollution. To date, there are a total of twelve PBL schemes embedded in the WRF model. Theoretically, the nonlocal closure schemes (MRF, YSU and SH schemes) are more suitable for unstable stratifications. Due to the nonlocal effects, these schemes will produce stronger turbulent mixing. While the local closure schemes (e.g., MY series schemes) are applicable to stable stratifications and produce smaller turbulent mixing. In general, serious PM 2.5 -haze events are accompanied by calm surface winds, higher relative humidity, stronger anomalous temperature inversion and weaker turbulent diffusion within the PBL. Therefore, the results of different PBL schemes on the meteorological parameters, PBL structures, turbulent diffusion were summarized. In summary, to further understand the shortcoming of PBL schemes during the severe haze periods and simulate influence on pollutants by the PBL schemes, and then to improve them in the future. • Multiple planetary boundary layer parameterization schemes are reviewed. • The influence of these schemes on the meteorological and aerosol pollution is discussed. • The main gaps between these schemes and aerosol pollution are presented. • We suggest that further improve the simulation capability of these schemes during the severe haze periods.

Sensitivity Analysis of Ensemble Simulations on a Torrential Rainfall Case over South China Using Multiple PBL and SL Parameterizations

A good representation of the interaction between the planetary boundary layer (PBL) and the surface layer (SL) in numerical models is of great importance for the prediction of the initiation and development of convection. This study examined an ensemble that consists of the available suites of PBL and SL parameterizations based on a torrential rainfall event over south China. The sensitivity of the simulations was investigated against objective measurements using multiple PBL and SL parameterization schemes. The main causes of the bias from different parameterization schemes were further analysed by comparing the good and bad ensemble members. The results showed that good members tended to underestimate the rainfall amount but presented a decent evolution of mesoscale convective systems that were responsible for the torrential rainfall. Using the total energy mass flux (TEMF) scheme, the bad members overestimated the amount and spatial coverage of rainfall. The failure of the bad member was due to a spurious convection initiation (CI) resulting from the overestimated high-<i>θ</i>e elevated air. The spurious CI developed and expanded rapidly, causing intensive and extensive rainfall over south China. Consistent with previous studies, the TEMF scheme tends to produce a warmer and moister PBL environment. The detailed sensitivity analysis of this case may provide reference for the operational forecast of rainfall over south China using multiple PBL and SL parameterizations.

Three-Dimensional Planetary Boundary Layer Parameterization for High-Resolution Mesoscale Simulations

Wind energy applications including wind resource assessment, wind power forecasting, and wind plant optimization require high-resolution mesoscale simulations. High resolution mesoscale simulations are essential for accurate characterization of atmospheric flows over heterogeneous land use and complex terrain. Under such conditions, the assumption of grid-cell homogeneity, used in one-dimensional planetary boundary layer (1D PBL) parameterizations, breaks down. However, in most numerical weather prediction (NWP) models, boundary layer turbulence is parameterized using 1D PBL parameterizations. We have therefore developed a three-dimensional (3D) PBL parameterization to better account for horizontal flow heterogeneities. We have implemented and tested the 3D PBL parameterization in the Weather Research and Forecasting (WRF) numerical weather prediction model. The new parameterization is validated using observations from the Wind Forecast Improvement 2 (WFIP 2) project and compared to 1D PBL results.

The Uncertainty of Tropical Cyclone Intensity and Structure Based on Different Parameterization Schemes of Planetary Boundary Layer

Based on different parameterization schemes of planetary boundary layer (PBL), the uncertainty of intensity and structure of the Super-strong Typhoon Rammasun (1409) is investigated using the WRF model (v3.4) with six PBL parameterization schemes. Results indicate that PBL uncertainty leads to the uncertainty in tropical cyclone (TC) prediction, which increases with forecast time. The uncertainty in TC prediction is mainly reflected in the uncertainty in TC intensity, with significant differences in the TC intensity forecasts using various PBL schemes. The uncertainty in TC prediction is also reflected in the uncertainty in TC structures. Greater intensity is accompanied by smaller vortex width, tighter vortex structure, stronger wind in the near-surface layer and middle and lower troposphere, stronger inflow (outflow) wind at the lower (upper) levels, stronger vertical upward wind, smaller thickness of the eye wall, smaller outward extension of the eye wall, and warmer warm core at the upper levels of eye. PBL height, surface upward heat flux and water vapor flux are important factors that cause the uncertainty in TC intensity and structure. The more surface upward heat flux and water vapor flux and the lower PBL height, the faster TC development and the stronger TC intensity.

Sensitivity study of the planetary boundary layer and microphysical schemes to the initialization of convection over the Arabian Peninsula

AbstractIn this study, we present a five‐member Weather Research and Forecasting (WRF) physics ensemble over the Arabian Peninsula on the convection‐permitting (CP) scale and investigate the ability to simulate convection and precipitation by varying the applied cloud microphysics and planetary boundary layer (PBL) parametrizations. The study covers a typical precipitation event ocurring during summertime over the eastern part of the United Arab Emirates (UAE). Our results show that the best results are obtained by using water‐ and ice‐friendly aerosols combined with aerosol‐aware Thompson cloud microphysics and the Mellor‐Yamada‐Nakanishi‐Niino (MYNN) PBL parametrization. The diurnal cycle of 2‐m temperature over the desert is well captured by all members, although a cold bias is present during the morning and evening transition. All members are capable of simulating the correct timing of the onset of convection. Simulations with the MYNN PBL and Thompson scheme produce the highest convective available potential energy (CAPE) and convective inhibition (CIN), associated with stronger mixing inside the PBL, leading to the formation of more dense liquid water clouds. The WDM6 microphysics scheme is not a suitable option, as there are hardly any liquid water clouds; mainly ice clouds are simulated. Precipitation is best captured by applying the MYNN and Thomspon scheme. Although the ensemble size is relatively small, this allows for the provision of cloud probability maps suitable for cloud‐seeding applications.

Systematic errors in the WRF model planetary boundary layer schemes for two contrasting monsoon seasons over the state of Odisha and its neighborhood region

This study evaluates the characteristics of systematic errors (up to day 4) in the planetary boundary layer (PBL) parameterization schemes over the state of Odisha and its neighboring regions for two contrasting monsoon seasons, i.e., 2013 (normal) and 2014 (deficit), using the Weather Research and Forecasting (WRF) model. A total of 1112 numerical experiments are carried out, each with initial conditions from May 28 to September 29 using four PBL schemes, i.e., Yonsei University (YSU), Mellor-Yamada-Nakanishi-Niino (MYNN), Asymmetric Convective Model version 2 (ACM2), and Medium Range Forecast (MRF) with horizontal resolutions of 27 and 9 km with a lead time up to 96 h. It is found that the PBL parameterizations significantly impact the basic atmospheric variables (i.e., wind, temperature, moisture, and rainfall) and associated convective processes such as moist static energy. The wind and rainfall forecast skill of MRF showed better agreement with European Re-Analysis (ERAI). However, YSU has better skills for 2-m temperature and specific humidity compared to others. All PBL schemes produced a moist bias at the surface except MRF. The principle cause of this moist bias with mid tropospheric warming is attributed to inherent tendency of the model to overestimate moist static energy leading to intense vertical motion and convective instability. The magnitude of errors for wind forecast is higher for the deficit year compared to the normal monsoon year. However, the strength of the cross equatorial flow is found to be weaker in all the experiments for both the seasons. In general, the spread and magnitude of errors are large for 2013 (normal) as compared to 2014 (deficit) year.

Influence of PBL parameterization schemes in WRF_ARW model on short - range precipitation's forecasts in the complex orography of Peruvian Central Andes

Abstract The study evaluated the sensitivity of the precipitation forecast in the central Andes of Peru of Weather Research and Forecasting (WRF) model to change the planetary boundary layer (PBL) schemes. In that region is located the Mantaro basin, which is one of the most important in the region. Here, the rainfall is very important to the agriculture and to the reserves of drinking water. The simulations were carried out with ten PBL schemes for 19 days in January, February, and March, between 2009 and 2012. Based on the statistical analysis (model vs. observation), the more efficient schemes were determined and analyses of the vertical profiles of some variables are shown. As a result, the schemes that most helped the model in rainfall forecasting were MYNN3 (general and north sector of the basin), Bou-Lac (central sector) and Bretherton-Park (southern sector). The model generally overestimated rainfall in the northern basin, underestimated in the center, and in the south some schemes overestimated and others underestimated. In addition, it was concluded that the boundary layer is more stable in the model than in the observations. The schemes that generated the most rainfall were those that generated a more unstable boundary layer with weaker wind speeds, at least with easterly winds. Another conclusion is that the height of the boundary layer for rainy days in the region at 18 UTC oscillates around 1000 m and that, generally, the wind's velocity changes very little or decreases within the boundary layer and increases above it.

Fast domain-aware neural network emulation of a planetary boundary layer parameterization in a numerical weather forecast model

Abstract. Parameterizations for physical processes in weather and climate models are computationally expensive. We use model output from the Weather Research Forecast (WRF) climate model to train deep neural networks (DNNs) and evaluate whether trained DNNs can provide an accurate alternative to the physics-based parameterizations. Specifically, we develop an emulator using DNNs for a planetary boundary layer (PBL) parameterization in the WRF model. PBL parameterizations are used in atmospheric models to represent the diurnal variation in the formation and collapse of the atmospheric boundary layer – the lowest part of the atmosphere. The dynamics and turbulence, as well as velocity, temperature, and humidity profiles within the boundary layer are all critical for determining many of the physical processes in the atmosphere. PBL parameterizations are used to represent these processes that are usually unresolved in a typical climate model that operates at horizontal spatial scales in the tens of kilometers. We demonstrate that a domain-aware DNN, which takes account of underlying domain structure (e.g., nonlocal mixing), can successfully simulate the vertical profiles within the boundary layer of velocities, temperature, and water vapor over the entire diurnal cycle. Results also show that a single trained DNN from one location can produce predictions of wind speed, temperature, and water vapor profiles over nearby locations with similar terrain conditions with correlations higher than 0.9 when compared with the WRF simulations used as the training dataset.

Impact of Selected Options in the Weather Research and Forecasting Model on Surface Wind Hindcasts in Coastal Ghana

This paper examines the impacts of five planetary boundary layer (PBL) parameterization schemes paired with several compatible surface layer (SL) parameterization schemes in the Weather Research and Forecasting Model on wind hindcasts for resource assessment purposes in a part of Coastal Ghana. Model predictions of hourly wind speeds at 3 × 3 km2 and 9 × 9 km2 grid boxes were compared with measurements at 40 m, 50 m, and 60 m. It was found that the Mellor-Yamada Nakanishi and Niino Level 3 (MYNN3) PBL scheme generally predicted winds with a relatively better combination of error metrics, irrespective of the SL scheme it was paired with. When paired with the Eta surface layer scheme, it often produced some of the relatively fewest errors in estimated mean wind power density (WPD) and Weibull cumulative density. A change in the simulation grid size did not have a significant impact on the conclusions of the relative performance of the PBL-SL pairs that were tested. The results indicate that the MYNN3 PBL and Eta SL pair is probably best for wind speed and energy assessments for this part of coastal Ghana.

Simulation of mid-latitude winter storms over the North Atlantic Ocean: impact of boundary layer parameterization schemes

This study discusses the performance of various planetary boundary layer parameterization (PBL) schemes—the Quasi-Normal Scale Elimination (QNSE), the University of Washington Moist Turbulence (UWMT), and the Yonsei University (YSU)—for the simulation of rapidly developing North Atlantic (NA) mid-latitude winter storms. Sensitivity experiments with the three PBL schemes, YSU, QNSE, and UWMT, indicate that there are minor differences at the center of the storm while simulating the evolution of the three explosive storms Klaus (21–27 January 2009), Xynthia (25 February–03 March 2010), and Gong (16–20 January 2013). The differences are shown in terms of the central minimum pressure, 10-m wind, specific humidity, CAPE, transitional speed, boundary layer height and frictional velocity of these mid-latitude storms. One of the main result shows the capability of QNSE and UWMT PBL schemes to reproduce accurately both the cyclogenesis and explosive stage for these mid-latitude storms during the winter season, better than YSU scheme. Almost all PBL schemes show dry bias from middle to upper troposphere (600 hPa–250 hPa), while YSU scheme carries this bias at the surface boundary layer, for all simulations. Moreover, QNSE, UWMT and YMSU PBL schemes underestimate the tangential winds for these mid-latitude storms. The 24 h accumulated latent heat flux and precipitation from UWMT scheme show modified results as compared to YSU and QNSE PBL schemes. Overall results show the superiority of QNSE and UWMT PBL schemes for an accurate simulation of the explosive stage of these North Atlantic winter storms.

The assessment of the planetary boundary layer schemes in WRF over the central Tibetan Plateau

The planetary boundary layer (PBL) parameterization schemes play a critical role in the weather and climate models, while they describe physical processes associated with the momentum, heat and humidity exchange between land surface and atmosphere. The sensitivity of boundary layer variables to eight PBL parameterization schemes (three non-local and five local closure schemes), available in the Weather Research and Forecasting (WRF) model, is evaluated over the central Tibetan Plateau with field measurements of the Third Tibetan Plateau atmospheric scientific experiment (TIPEX III) in July. Model results showed acceptable behavior, but no particular scheme produced the best performances for all observation stations and meteorological parameters. All PBL schemes underestimated the surface temperature over the central Tibetan Plateau. The BouLac scheme showed the minimum cold bias of the surface temperature. For the surface energy budget components, it was found that the sensible heat flux and the downward longwave radiation were the main factors causing the lower surface temperature. The sub-grid scale gravity wave drag was added to reduce biases result from unresolved topography over the central Tibetan Plateau. It led to smaller cold bias, causing warmer lower-tropospheric temperature, smaller water vapor content and higher PBL height. The modified model results show more close to the observation.