Medium-Range Forecast Scheme Research Articles

Improving the Wind Power Density Forecast in the Middle- and High-Latitude Regions of China by Selecting the Relatively Optimal Planetary Boundary Layer Schemes

As the power generation mode with the lowest carbon emissions, wind power generation plays an indispensable role in achieving the goal of carbon neutralization. To optimize the wind power density (WPD), forecasting is crucial to improve wind power utilization and power system stability. However, because near-surface wind is characterized by notable randomness, diversity, intermittence, and uncontrollability, accurately forecasting the WPD on wind farms remains a challenging task. In this study, we attempted to improve the WPD forecast in the middle- and high-latitude regions of China (wind energy resources are abundant there) by selecting the relatively optimal planetary boundary layer (PBL) scheme, as the PBL processes exert notable effects on the near-surface wind field directly. Based on a whole month in the summer (July 2021), seven PBL schemes were compared quantitatively by using the Weather Research and Forecasting (WRF) model for a total of 70 runs (for each run, the forecast period was 3 days). The results show that no PBL schemes could always show the best performance in forecasting all variables, and the forecast accuracy showed a notable dependence on the evolution of the weather systems. Among the seven PBL schemes, the Medium-Range Forecast (MRF) scheme showed the overall best performance in forecasting the 100 m wind speed, sea level pressure, and 2 m temperature, which ensured that it had the highest forecast skill for the WPD in the middle- and high-latitude regions of China. Further analyses indicate that the background conditions were also well forecasted by the MRF scheme (ranked first or second). This was a crucial reason why the WPD forecast was the best for the MRF scheme.

Improvements of Sea Fog Forecasting Based on CMA-TYM

Based on the operational version of the China Meteorological Administration Typhoon Model (CMA-TYM, formerly known as GRAPES_TYM), a series of numerical tests are conducted by optimizing the boundary layer parameterization scheme, vertical resolution, and boundary conditions. Instead of the sea surface temperature (SST) from the Global Forecast System (GFS) model, more accurate daily SST data reflecting the daily SST variation are used as the boundary condition. The new SST dataset is capable of representing the key points in the area, including the low coastal SST related to upwelling, the intrusion of the Yellow Sea (YS) Warm Current, and the ocean front between the YS and the East China Sea. An analysis of the performances of two boundary layer parameterization schemes (the Yonsei University scheme and the Medium-Range Forecast scheme) in characterizing turbulent heat exchange reveals that the former can more accurately reflect offshore turbulence and forecast the fog area. By increasing the number of vertical layers of the model to 68 and reducing the height of the bottom layer to approximately 10 m, the model presents a better performance in simulating the rapid formation and dissipation of sea fog. With the above improvements, the equitable threat score (ETS) for the hindcasting of eleven sea fog cases in the spring of 2018 increases by 61%, mainly due to the increase in the correctly forecasted fog area.

Exploring the Impact of Planetary Boundary Layer Schemes on Rainfall Forecasts for Typhoon Mujigae, 2015

Sensitivity experiments were conducted on Typhoon Mujigae, which occurred in 2015, wherein the Weather Research and Forecasting Advanced Research (WRF-ARW) model was used to select two local and two nonlocal planetary boundary layer (PBL) parameterization schemes: the quasi-normal scale elimination (QNSE) and Mellor–Yamada–Janjic (MYJ) schemes, and the Yonsei University (YSU) and medium-range forecast (MRF) schemes, respectively. The differences in rainfall response in the typhoon’s inner core and outer region were evaluated by comparing the anomaly rainfall distribution, heat transmission, and mixing processes in the boundary layer among the PBL schemes. The results show that the simulated rainfall in typhoon Mujigae has large uncertainty among the PBL schemes and a significant difference between the inner and outer regions. Compared with the observation, the simulated rainfall was significantly higher in the inner core and slightly lower in the outer region. All PBL schemes accurately identified the rainfall location, although the amounts differed between the schemes. The rainfall levels in the MRF scheme were closest to the observation, followed by those in the YSU and MYJ schemes; the QNSE scheme showed the largest deviation. In general, rainfall simulation using a nonlocal boundary layer scheme such as MRF had the best results for both the inner core and the outer region.

Impacts of PBL schemes on PM2.5 simulation and their responses to aerosol-radiation feedback in GRAPES_CUACE model during severe haze episodes in Jing-Jin-Ji, China

Using the online-coupled Global/Regional Assimilation and Prediction System coupled with the Chinese Unified Atmospheric Chemistry Environment (GRAPES_CUACE) model, numerical experiments are conducted to compare the impacts of three planetary boundary layer (PBL) schemes—Medium Range Forecast (MRF), Yonsei University (YSU), and Mellor-Yamada-Janjic (MYJ)—on PM2.5 simulations and their responses to aerosol-radiation feedback (ARF), under different terrain and weather conditions. The baseline experiments without ARF with all three PBL schemes can reproduce the spatial and temporal distribution characteristics of surface PM2.5 on the whole and show that the model can capture the PM2.5 variation better in unstable conditions (clean days) than in stable conditions (pollution days). The three PBL schemes show differences in the simulations of meteorological factors, e.g., the MRF scheme produces the best 10-m wind speed, the MYJ scheme produces the best 2-m temperature, and the YSU scheme produces the lowest PBL height (PBLH) and vertical diffusivity. Consequently, there is no significant difference among the three PBL schemes in surface PM2.5 simulations due to the combined action of the surface and the PBL structure. However, all the baseline experiments massively underestimate PM2.5 during severe pollution days. The online computing of ARF in the three PBL schemes can substantially improve the underestimation of PM2.5 by reducing sensible heat fluxes, 2-m temperature, friction velocity, and the PBL height. More importantly, the response intensity of three PBL schemes to ARF is very different. For PM2.5 simulations, MYJ has the weakest response, whereas MRF and YSU have similar responses. During the heavy pollution days with more intense aerosol-radiation effect, the increase of PM2.5 induced by ARF in MRF and YSU is about twice that in MYJ, making the PM2.5 simulated by MRF and YSU more consistent with the observations. This result shows the ARF dependence on the PBL processes and suggests the importance of PBL-ARF interaction to the PM2.5 numerical prediction during haze episodes.

Sensitivity of the Summer Precipitation Simulated with WRF Model to Planetary Boundary Layer Parameterization over the Tibetan Plateau and its Downstream Areas

This study examines the sensitivity of simulated precipitation to planetary boundary layer (PBL) schemes over the Tibetan Plateau (TP) and the Yangtze River Valley (YRV). The summer precipitation from 15 June to 30 July 2010 is simulated with the Weather Research and Forecasting (WRF) model over these areas. Three PBL parameterization schemes, Mellor-Yamada-JanjiA‡ (MYJ), Yonsei University (YSU), and Medium-Range Forecast (MRF) are compared in the simulation. The simulated hourly precipitation overestimates the observed precipitation, and the simulation of MRF scheme is more close to the observation. In general, the WRF model shows good (poor) ability in simulating the diurnal cycle of precipitation over the TP (the upper YRV). Although the WRF model simulates a two-peak pattern different from the observed one-peak pattern in the middle YRV, both of them are generally close in trend. The choice of PBL parameterization schemes affects not only the amplitude of the precipitation but also the phase of diurnal cycle, and MRF scheme simulates better in precipitation amount than YSU and MYJ schemes. Among the three PBL schemes, the hourly PBL height of MYJ scheme is higher than those of MRF and YSU schemes. All the three PBL schemes present a similar diurnal cycle of PBL height, and the differences of PBL heights are responsible for the discrepancies in the simulated precipitation amounts. The three largest lakes in the central TP result in three large centers of the minimum PBL heights and of the average hourly PBL heights at the same locations, which are responsible for the maximum centers in the simulated precipitation in the central TP.

The Sensitivity of Wind Forecasts with a Mesoscale Meteorological Model at the Centro de Lançamento de Alcântara

The sensitivity of the planetary boundary layer (PBL) parameterizations is investigated using the hybrid Fifth Generation Penn State University/National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) and its results were compared with observations from two field campaigns held during the dry and wet seasons at the Centro de Lancamento de Alcântara (CLA). The comparisons were made using the integrated zonal and meridional components of observed and forecasted winds. Initially, three boundary layer parameterizations, in addition to the current parameterization, were selected for evaluation: Blackadar (BLK), Medium Range Forecast (MRF), Janjic (ETA) and Burk-Thompson (BT). The MRF and BLK schemes produced better results than the ETA and BT schemes. Nevertheless, MRF and BLK underestimate the zonal and meridional wind components by around 16% in the rainy season and overestimate them by on average 18% in the dry season.

The Importance of the Boundary Layer Parameterization in the Prediction of Low-Level Convergence Lines

AbstractThe importance of the boundary layer parameterization in the numerical prediction of low-level convergence lines over northeastern Australia is investigated. High-resolution simulations of convergence lines observed in one event during the 2002 Gulf Lines Experiment are carried out using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). Calculations using five different parameterizations are compared with observations to determine the optimum scheme for capturing these lines. The schemes that give the best agreement with the observations are the three that include a representation of countergradient fluxes and a surface layer scheme based on Monin–Obukhov theory. One of these, the Medium-Range Forecast scheme, is slightly better than the other two, based on its ability to predict the surface pressure distribution. The findings are important for the design of mesoscale forecasting systems for the arid regions of Australia and elsewhere.

Sensitivity of mesoscale simulations of land–sea breeze to boundary layer turbulence parameterization

The sensitivity of mesoscale simulations of land and sea breeze circulation on the south east coast in the Chennai region of India to boundary layer turbulence parameterizations is studied using the community based PSU/NCAR mesoscale model MM5. High-resolution simulations are carried out with nested domains. Four widely used boundary layer turbulence parameterization schemes are selected for the study. Two of these schemes (Blackadar (BK) and medium range forecast (MRF)) are simple first-order non-local schemes and the other two (Mellor–Yamada (MY) Eta planetary boundary layer (PBL) and Gayno–Seaman (GS)) are more complex 1.5 order local schemes that include a prognostic equation for turbulence kinetic energy. The other physics used in the model are identical. The micro-meteorological tower and flux observations, GP sonde and radiosonde observations from the study region are used to compare the simulated mean variables. In spite of differences in complexity, all the schemes show similar capability in simulating the boundary layer temperature, humidity and winds. The land–sea breeze circulation and internal boundary layer formation, which are special phenomena at the coastal site, could be simulated by all the schemes. The BK, MRF schemes produced boundary layers that are more mixed than those produced with the MY and GS schemes. While all the schemes underestimated surface sensible heat fluxes during stable night conditions they are reasonably simulated during daytime by MRF and BK schemes. Among the tested schemes, the BK scheme has reasonably produced the PBL height, humidity, wind fields and proves suitable for operational forecasting. The results suggest that there is little improvement in overall accuracy of predictions with more complex turbulence parameterizations.

Verification of a Mesoscale Data-Assimilation and Forecasting System for the Oklahoma City Area during the Joint Urban 2003 Field Project

AbstractThe National Center for Atmospheric Research (NCAR) and the U.S. Army Test and Evaluation Command have developed a multiscale, rapid-cycling, real-time, four-dimensional data-assimilation and forecasting system that has been in operational use at five Army test ranges since 2001. This system was employed to provide operational modeling support for the Joint Urban 2003 (JU2003) Dispersion Experiment, conducted in Oklahoma City, Oklahoma, during July 2003. To better support this mission, modifications were made to the nonlocal boundary layer (BL) parameterization (known as the Medium Range Forecast scheme) of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model, in order to improve BL forecasts. The NCEP–Oregon State University–Air Force–Hydrologic Research Laboratory land surface model was also improved to better represent urban forcing. Verification of the operational model runs and retrospectively simulated cases show 1) a significantly reduced low bias in the forecast surface wind speed and 2) more realistic daytime BL heights. During JU2003, the forecast urban heat island, urban dry bubble, and urban BL height agree reasonably well with observations and conceptual models. An analysis of three-dimensional atmospheric structures, based on model analyses for eight clear-sky days during the field program, reveals some interesting features of the Oklahoma City urban BL, including complex thermally induced circulations and associated convergence/divergence zones, a nocturnal thermal shadow downwind of the urban area, and the reduction of low-level jet wind speeds by more vigorous nocturnal mixing over the city.

Implementation of a Stable PBL Turbulence Parameterization for the Mesoscale Model MM5: Nocturnal Flow in Complex Terrain

The difficulties associated with the parameterization of turbulence in the stable nocturnal planetary boundary layer (PBL) have been a great challenge for the nighttime predictions from mesoscale meteorological models such as MM5. As such, there is a general consensus on the need for better stable boundary-layer parameterizations. To this end, two new turbulence parameterizations based on the measurements of the Vertical Transport and Mixing (VTMX) field campaign were implemented and evaluated in MM5. A unique aspect of this parameterization is the use of a stability-dependent turbulent Prandtl number that allows momentum to be transported by the internal waves, while heat diffusion is impeded by the stratification. This improvement alleviates the problem of over-prediction of heat diffusion under stable conditions, which is a characteristic of conventional atmospheric boundary-layer schemes, such as the Medium Range Forecast (MRF) and Blackadar schemes employed in MM5. The predictions made with the new PBL scheme for the complex terrain airshed of Salt Lake City were compared with those made with a default scheme of MM5, and with observations made during the VTMX campaign. The new schemes showed an improvement in predictions, particularly for the nocturnal near-surface temperature. Surface wind predictions also improved slightly, but not to the extent of temperature predictions. The default MRF scheme showed a significantly higher surface temperature than observed, which could be attributed to the enhanced vertical heat exchange brought about by its turbulence parameterization. The modified parameterizations reduced the surface sensible heat flux, thus enhancing the strength of the near-surface inversion and lowering the temperature towards the observed values.

Sensitivity of MM5-Simulated Boundary Layer Characteristics to Turbulence Parameterizations

Abstract The sensitivity of high-resolution mesoscale simulations to boundary layer turbulence parameterizations is investigated using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) and observations from two field campaigns. Three widely used turbulence parameterizations were selected for evaluation, two of which [Blackadar (BK) and Medium Range Forecast (MRF) schemes] are simple first-order nonlocal schemes and one [Gayno–Seaman (GS) scheme] of which is a more complex 1.5-order local scheme that solves a prognostic equation for turbulence kinetic energy (TKE). The two datasets are the summer 1996 Boundary Layer Experiment (BLX96) in the southern Great Plains and the autumn 2000 Vertical Transport and Mixing (VTMX) field campaign in the Salt Lake Valley in Utah. Comparisons are made between observed and simulated mean variables and turbulence statistics. Despite the differences in their complexity, all three schemes show similar skill predicting near-surface and boundary layer mean temperature, humidity, and winds at both locations. The BK and MRF schemes produced daytime boundary layers that are more mixed than those produced by the GS scheme. The mixed-layer depths are generally overestimated by the MRF scheme, underestimated by the GS scheme, and well estimated by the BK scheme. All of the schemes predicted surface latent heat fluxes that agreed reasonably well with the observed values, but they substantially overestimated surface sensible heat fluxes because of a significant overprediction of net radiation. In addition, each parameterization overestimated the sensible and latent heat flux aloft. The results suggest that there is little gain in the overall accuracy of forecasts with increasing complexity of turbulence parameterizations.

Analysis of the role of the planetary boundary layer schemes during a severe convective storm

Abstract. The role played by planetary boundary layer (PBL) in the development and evolution of a severe convective storm is studied by means of meso-scale modeling and surface and upper air observations. The severe convective precipitation event that occurred on 14 September 1999 in the northeast of the Iberian Peninsula was simulated by means of the mesoscale model MM5 (version 3) using three different PBL schemes. The numerical results show a large impact of the PBL schemes on the precipitation fields associated to the convective storm. The schemes are based on different physical assumptions: the nonlocal first order Medium-Range Forecast (MRF) and Blackadar (BLA) scheme and the local, one-and-a-half order ETA scheme. Surface and radar observations are used to validate the model results. The comparison focuses on three aspects: the evolution, the spatial distribution and the 24-h accumulated precipitation. The comparison with rain gauge observations shows that the MRF, BLA and ETA schemes predicted most of the precipitation during the morning, whereas the rain gauge stations recorded rainfall during the evening. The evaluation performed with the radar data shows that all three numerical simulations produced a realistic spatial accumulated precipitation distribution. According to the quantity distribution, all three numerical simulations were able to predict precipitation quantities comparable to the rain gauge measurements. The MRF scheme predicted the largest average accumulated precipitation and the largest average precipitation rate, whereas the ETA scheme predicted the smallest accumulated precipitation and average precipitation rate. However, the ETA scheme yielded the highest extreme precipitation rates. The performance of the three schemes is analyzed in terms of the vertical distribution of potential temperature, specific humidity and conserved variables, like equivalent potential temperature and total water content. The MRF scheme showed more evidence of enhanced mixing than did the other schemes. Due to this process, more moisture was more efficiently transported to the free atmosphere. Consequently, the MRF scheme predicts more widespread precipitation. Furthermore, the enhanced mixing led to a less sharp capping inversion. However, the stronger inversion resulting from suppressed mixing processes in the case of the ETA scheme yielded higher values of convective available potential energy (CAPE) than did the other two schemes. Consequently, the more extreme precipitation rates are simulated by MM5 when the ETA scheme is used.

Sensitivity of High-Resolution Simulations of Hurricane Bob (1991) to Planetary Boundary Layer Parameterizations

The fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model is used to simulate Hurricane Bob (1991) using grids nested to high resolution (4 km). Tests are conducted to determine the sensitivity of the simulation to the available planetary boundary layer parameterizations, including the bulk aerodynamic, Blackadar, Medium-Range Forecast (MRF) model, and Burk–Thompson boundary layer schemes. Significant sensitivity is seen, with minimum central pressures varying by up to 16 mb and maximum winds by 15 m s−1. The Burk–Thompson and bulk aerodynamic boundary layer schemes produced the strongest storms while the MRF scheme produced the weakest storm. Simulated horizontal precipitation structures varied substantially between the different PBL schemes, suggesting that accurate forecasts of precipitation in hurricanes can be just as sensitive to the formulation of the PBL as they are to the cloud microphysical parameterizations. Each PBL scheme is different in its formulation of the vertical mixing within the PBL and the surface fluxes, with the exception of the MRF and Blackadar schemes, which share essentially the same surface flux parameterization. Detailed analyses of the PBL schemes describe the key differences in the surface fluxes and how they impact storm intensity. In order to isolate the effects of vertical mixing and surfaces fluxes, simulations were conducted in which each of the surface flux schemes was used in conjunction with the same vertical mixing scheme, and vice versa. These experiments indicate that simulated intensity is largely determined by the surface fluxes rather than by the vertical mixing, with the exception of the MRF PBL case, in which excessively deep vertical mixing acts to dry the lower PBL and reduce hurricane intensity. Simulations that vary only the surface fluxes suggest that the intensity of the simulated hurricane increases with increasing values of the ratio of the exchange coefficients for enthalpy and momentum, Ck/CD. However, even for identical values of Ck/CD, the simulated intensity varies depending on the wind speed dependence of the surface roughness parameter z0.