The Step-Mountain Eta Coordinate Model: Further Developments of the Convection, Viscous Sublayer, and Turbulence Closure Schemes

Janjić, Zavisă

doi:10.1175/1520-0493(1994)122<0927:tsmecm>2.0.co;2

Cited by 2,629 publications

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“…The model physical configuration is that described in Aligo et al (2007) with the exception of the planetary boundary layer (PBL) scheme and the land surface model (LSM), which in the present study are, respectively, the Mellor-Yamada-Janjic (MYJ; Janjic 2002) scheme and the land surface model Noah (Ek et al 2003). In addition to the above configuration, the 12-km outer nest used the Betts-Miller-Janjic convective scheme (Betts 1986;Betts and Miller 1986;Janjic 1994), which currently is employed operationally at the National Centers for Environmental Prediction (NCEP). Bryan et al (2003) point out that a more realistic depiction of moist convection is likely with a horizontal grid spacing O(100 m), but because such grid spacing is not likely to be used operationally in the near future, the horizontal grid spacing of 4 km used in this study is a compromised choice considering the operational orientation of the paper.…”

Section: Methodsology a Model Setup And Datamentioning

confidence: 99%

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

Aligo

Gallus

Segal

2009

Weather and Forecasting

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Weather Research and Forecast (WRF) model exploratory sensitivity simulations were performed to determine the impact of vertical grid resolution (VGR) on the forecast skill of Midwest summer rainfall. Varying the VGR indicated that a refined VGR, while adopting the widely used North America Regional Reanalysis (NARR) for initial and lateral boundary conditions, does not necessarily result in a consistent improvement in quantitative precipitation forecasts (QPFs). When averaged over a variety of microphysical schemes in an illustrative case, equitable threat score (ETS) and bias values actually worsened with a greater overpredicted rainfall for half of the rainfall thresholds when the VGR was refined. Averaged over strongly forced cases, ETS values worsened for all rainfall thresholds while biases mostly increased, indicating a further overprediction of rainfall when the number of levels was increased. Skill improved, however, for all rainfall thresholds when the resolution above the melting level was increased. Skill also improved for most rainfall thresholds when the resolution in the surface layer was increased, which is attributed to better-resolved surface turbulent momentum and thermal fluxes. Likewise, a refined VGR resulted in improvements in weakly forced cases, which are governed mostly by thermodynamic forcing and are sensitive to vertical profiles of temperature and moisture. Application of the factor separation method suggested that the refined VGR more frequently had a negative impact on skill through the interaction between lower-atmospheric processes and microphysical processes above the melting level. KeywordsAgronomy, atmospheric process, equitable threat score, illustrative case, lateral boundary conditions, melting levels, microphysical process, negative impacts, quantitative precipitation forecast, reanalysis, sensitivity simulation, summer rainfall, surface layers, thermal fluxes, turbulent momentum, vertical grids, WRF model, atmospheric thermodynamics, climate prediction, rainfall, weather forecasting Varying the VGR indicated that a refined VGR, while adopting the widely used North America Regional Reanalysis (NARR) for initial and lateral boundary conditions, does not necessarily result in a consistent improvement in quantitative precipitation forecasts (QPFs). When averaged over a variety of microphysical schemes in an illustrative case, equitable threat score (ETS) and bias values actually worsened with a greater overpredicted rainfall for half of the rainfall thresholds when the VGR was refined. Averaged over strongly forced cases, ETS values worsened for all rainfall thresholds while biases mostly increased, indicating a further overprediction of rainfall when the number of levels was increased. Skill improved, however, for all rainfall thresholds when the resolution above the melting level was increased. Skill also improved for most rainfall thresholds when the resolution in the surface layer was increased, which is attributed to better-resolved surface turbulent momentum ...

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Section: Methodsology a Model Setup And Datamentioning

confidence: 99%

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

Aligo

Gallus

Segal

2009

Weather and Forecasting

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“…While the physics sensitivity experiment will be explored more fully in Part II, we will also reference herein results using the Noah (Chen and Dudhia 2001;Ek et al 2003) and thermal diffusion (TD; Skamarock et al 2008) LSMs, and the Yonsei University (YSU; Hong et al 2006), Mellor-Yamada-Janjic (MYJ) PBL scheme (Janjic 1994), and total energy-mass flux (TEMF; Angevine et al 2010) PBL parameterizations. In particular, the Noah-YSU combination, along with the surface layer scheme derived from MM5 (Noah-YSU), 7 is of interest because it is likely the most commonly used configuration in WRF.…”

Section: B Model Experimental Designmentioning

confidence: 99%

Downslope Windstorms of San Diego County. Part I: A Case Study

Yang

Fovell

2016

Monthly Weather Review

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The “Santa Ana” wind is an offshore flow that affects Southern California periodically during the winter half of the year, typically between September and May. The winds can be locally gusty, particularly in the complex terrain of San Diego County, where the winds have characteristics of downslope windstorms. These winds can cause and/or rapidly spread wildfires, the threat of which is particularly acute during the autumn season before the onset of winter rains. San Diego’s largest fires, including the Cedar fire of 2003 and Witch Creek fire of 2007, occurred during Santa Ana wind events. A case study of downslope flow during a moderately intense Santa Ana event during mid-February 2013 is presented. Motivated by the need to forecast winds impinging on electrical lines, the authors make use of an exceptionally dense network of near-surface observations in San Diego County to calibrate and verify simulations made utilizing the Advanced Research version of the Weather Research and Forecasting (WRF) Model, which in turn is employed to augment the observations. Results demonstrate that this particular Santa Ana episode consists of two pulses separated by a protracted lull. During the first pulse, the downslope flow is characterized by a prominent hydraulic jumplike feature, while during the second one the flow possesses a clear temporal progression of winds downslope. WRF has skill in capturing the evolution and magnitude of the event at most locations, although most model configurations overpredict the observed sustained wind and the forecast bias is itself biased.

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“…In the offline coupled mode, the atmospheric model parameterizes the momentum exchange at the air-sea interface by applying a viscous sublayer scheme (Janjić, 1994), where the roughness z 0 over the sea surface is estimated by the formula…”

Section: The Theoretical Backgroundmentioning

confidence: 99%

“…(1) for the estimation of the sea surface roughness length. According to the Mellor-Yamada-Janjic (MYJ) surface layer parameterization scheme (Janjić, 1994), a viscous sublayer is assumed over the oceans and operates under three sea-state regimes: (i) smooth and transitional, (ii) rough, and (iii) rough with spray, depending on the roughness Reynolds number and finally on the friction velocity, which is a monotonic function of R r (Janjić, 1994) …”

Section: The Theoretical Backgroundmentioning

confidence: 99%

A fully coupled atmosphere–ocean wave modeling system for the Mediterranean Sea: interactions and sensitivity to the resolved scales and mechanisms

et al. 2016

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Abstract. It is commonly accepted that there is a need for a better understanding of the factors that contribute to air-sea interactions and their feedbacks. In this context it is important to develop advanced numerical prediction systems that treat the atmosphere and the ocean as a unified system. The realistic description and understanding of the exchange processes near the ocean surface requires knowledge of the sea state and its evolution. This can be achieved by considering the sea surface and the atmosphere as a continuously crosstalking dynamic system. Following and adapting concepts already developed and implemented in large-scale numerical weather models and in hurricane simulations, this study aims to present the effort towards developing a new, highresolution, two-way fully coupled atmosphere-ocean wave model in order to support both operational and research activities. A specific issue that is emphasized is the determination and parameterization of the air-sea momentum fluxes in conditions of extremely high and time-varying winds. Software considerations, data exchange as well as computational and scientific performance of the coupled system, the so-called WEW (worketa-wam), are also discussed. In a case study of a high-impact weather and sea-state event, the wind-wave parameterization scheme reduces the resulted wind speed and the significant wave height as a response to the increased aerodynamic drag over rough sea surfaces. Overall, WEW offers a more realistic representation of the momentum exchanges in the ocean wind-wave system and includes the effects of the resolved wave spectrum on the drag coefficient and its feedback on the momentum flux.

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The Step-Mountain Eta Coordinate Model: Further Developments of the Convection, Viscous Sublayer, and Turbulence Closure Schemes

Cited by 2,629 publications

References 0 publications

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

Downslope Windstorms of San Diego County. Part I: A Case Study

A fully coupled atmosphere–ocean wave modeling system for the Mediterranean Sea: interactions and sensitivity to the resolved scales and mechanisms

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