scholarly journals The Dependence of QPF on the Choice of Boundary- and Surface-Layer Parameterization for a Lake-Effect Snowstorm

2015 ◽  
Vol 54 (6) ◽  
pp. 1177-1190 ◽  
Author(s):  
Robert Conrick ◽  
Heather Dawn Reeves ◽  
Shiyuan Zhong
Keyword(s):  
Surface Layer ◽  
Sensible Heat Flux ◽  
Moisture Flux ◽  
Precipitation Forecast ◽  
Weather Research And Forecasting ◽  
Sensible Heat ◽  
Stability Function ◽  
Lake Effect ◽  
Quantitative Precipitation Forecast ◽  
Model Layer

AbstractSix forecasts of a lake-effect-snow event off Lake Erie were conducted using the Weather Research and Forecasting Model to determine how the quantitative precipitation forecast (QPF) was affected when the boundary- and surface-layer parameterization schemes were changed. These forecasts showed strong variability, with differences in liquid-equivalent precipitation maxima in excess of 20 mm over a 6-h period. The quasi-normal scale elimination (QNSE) schemes produced the highest accumulations, and the Mellor–Yamada–Nakanishi–Niino (MYNN) schemes produced the lowest. Differences in precipitation were primarily due to different sensible heat flux FH and moisture flux FQ off the lake, with lower FH and FQ in MYNN leading to comparatively weak low-level instability and, consequently, reduced ascent and production of hydrometeors. The different FH and FQ were found to have two causes. In QNSE, the higher FH and FQ were due to the decision to use a Prandtl number PR of 0.72 (all other schemes use a PR of 1). In MYNN, the lower FH and FQ were due to the manner in which the similarity stability function for heat ψh is functionally dependent on the temperature gradient between the surface and the lowest model layer. It is not known what assumptions are more accurate for environments that are typical for lake-effect snow, but comparisons with available observations and Rapid-Update-Cycle analyses indicated that MYNN had the most accurate results.

Operational Precipitation Forecast Over China Using the Weather Research and Forecasting (WRF) Model at a Gray-Zone Resolution: Impact of Convection Parameterization

2021 ◽  
Author(s):  
XU ZHANG ◽  
YUHUA YANG ◽  
BAODE CHEN ◽  
WEI HUANG
Keyword(s):  
Case Studies ◽  
Southern China ◽  
Wrf Model ◽  
Warm Season ◽  
Precipitation Forecast ◽  
Weather Research And Forecasting ◽  
Operational System ◽  
Quantitative Precipitation Forecast ◽  
Geographical Regions ◽  
Convection Parameterization

AbstractThe quantitative precipitation forecast in the 9 km operational modeling system (without the use of a convection parameterization scheme) at the Shanghai Meteorological Service (SMS) usually suffers from excessive precipitation at the grid scale and less-structured precipitation patterns. Two scale-aware convection parameterizations were tested in the operational system to mitigate these deficiencies. Their impacts on the warm-season precipitation forecast over China were analyzed in case studies and two-month retrospective forecasts. The results from case studies show that the importance of convection parameterization depends on geographical regions and weather regimes. Considering a proper magnitude of parameterized convection can produce more realistic precipitation distribution and reduce excessive grid-scale precipitation in southern China. In the northeast and southwest China, however, the convection parameterization plays an insignificant role in precipitation forecast because of strong synoptic-scale forcing. A statistical evaluation of the two-month retrospective forecasts indicates that the forecast skill for precipitation in the 9-km operational system is improved by choosing proper convection parameterization. This study suggests that improvement in contemporary convection parameterizations is needed for their usage for various meteorological conditions and reasonable partitioning between parameterized and resolved convection.

scholarly journals Sensible Heat Fluxes in the Nearly Neutral Boundary Layer: The Impact of Frictional Heating within the Surface Layer

2019 ◽  
Vol 76 (4) ◽  
pp. 1039-1053
Author(s):  
J. M. Edwards
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Frictional Heating ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Simple Modification ◽  
Neutral Boundary Layer ◽  
The Impact

Abstract The effect of frictional dissipative heating on the calculation of surface fluxes in the atmospheric boundary layer using bulk flux formulas is considered. Although the importance of frictional dissipation in intense storms has been widely recognized, it is suggested here that its impact is also to be seen at more moderate wind speeds in apparently enhanced heat transfer coefficients and countergradient fluxes in nearly neutral conditions. A simple modification to the bulk flux formula can be made to account for its impact within the surface layer. This modification is consistent with an interpretation of the surface layer as one across which the flux of total energy is constant. The effect of this modification on tropical cyclones is assessed in an idealized model, where it is shown to reduce the predicted maximum wind speed by about 4%. In numerical simulations of three individual storms, the impacts are more subtle but indicate a reduction of the sensible heat flux into the storm and a cooling of the surface layer.

scholarly journals Energetics of Deep Alpine Valleys in Pooling and Draining Configurations

2017 ◽  
Vol 74 (7) ◽  
pp. 2105-2124 ◽  
Author(s):  
Gabriele Arduini ◽  
Charles Chemel ◽  
Chantal Staquet
Keyword(s):  
Boundary Layer ◽  
Temperature Difference ◽  
Heat Budget ◽  
Sensible Heat Flux ◽  
Volume Effect ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Sensible Heat ◽  
Diabatic Processes ◽  
Surface Sensible Heat Flux

Abstract The Weather Research and Forecasting Model is used to investigate the nocturnal atmospheric boundary layer in a valley that opens either on a wider valley (draining configuration) or on a narrower valley (pooling configuration). One draining case and three weak to strong pooling cases are considered. Results show that the structure of the nocturnal boundary layer is substantially different for the draining and pooling configurations. Greater pooling corresponds with a deeper and colder boundary layer. Down-valley winds are weaker for pooling and draining configurations than in an equivalent valley opening directly on a plain. For the strong pooling case, an up-valley flow develops from the narrower to the wider valley during the evening transition, affecting the mass budget of the wider valley during that period. Considering the heat budget of the valley system, the contribution of the diabatic processes, when appropriately weighted, hardly varies along the valley axis. Conversely, the contribution of advection varies along the valley axis: it decreases for a pooling configuration and increases for a draining configuration. Consequently, for a pooling configuration, the heat transfer between the valley and the plain is reduced, thereby increasing the temperature difference between them. For the strong pooling case, this temperature difference can be explained by the valley-volume effect once the down-valley flow has developed. This occurs in a valley when the “extra” heat loss within the valley due to the surface sensible heat flux balances the heat input due to advection.

scholarly journals The evaluating study of the momentum and heat exchange process of two surface layer schemes during the severe haze pollution in east China

2018 ◽  
Author(s):  
Yue Peng ◽  
Hong Wang ◽  
Yubin Li ◽  
Changwei Liu ◽  
Tianliang Zhao ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Momentum Flux ◽  
Roughness Length ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Chemical Model ◽  
East China ◽  
Sensible Heat ◽  
Haze Pollution

Abstract. The turbulent flux parameterization schemes in surface layer are crucial for air pollution modeling. The pollutants prediction by atmosphere chemical model exist obvious deficiencies, which may be closely related to the uncertainties of the momentum and sensible heat fluxes calculation in the surface layer. In this study, a new surface layer scheme (Li) and a classic scheme (MM5) were compared and evaluated based on the observed momentum and sensible heat fluxes in east China during a severe haze episode in winter. The results showed that it is necessary to distinguish the thermal roughness length z0h from the aerodynamic roughness length z0m, and ignoring the difference between the two led to large errors of the momentum and sensible heat fluxes in MM5. The error of calculated sensible heat flux was reduced by 54 % after discriminating z0h from z0m in MM5. Besides, the algorithm itself of Li scheme performed generally better than MM5 in winter in east China and the momentum flux bias of the Li scheme was lower about 12%, sensible heat flux bias about 5 % than those of MM5 scheme. Most of all, the Li scheme showed a significant advantage over MM5 for the transition stage from unstable to stable atmosphere corresponding to the PM2.5 accumulation. The momentum flux bias of Li was lower about 38 %, sensible heat flux bias about 43 % than those of MM5 during the PM2.5 increasing stage. This study result indicates the ability of Li scheme for more accurate describing the regional atmosphere stratification, and suggests the potential improving possibilities of severe haze prediction in east China by online coupling it into the atmosphere chemical model.

scholarly journals Evaluation of Sensible Heat Flux and Evapotranspiration Estimates Using a Surface Layer Scintillometer and a Large Weighing Lysimeter

Sensors ◽  
2017 ◽  
Vol 17 (10) ◽  
pp. 2350 ◽  
Author(s):  
Jerry Moorhead ◽  
Gary Marek ◽  
Paul Colaizzi ◽  
Prasanna Gowda ◽  
Steven Evett ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Weighing Lysimeter

scholarly journals Improved parameterization of snow albedo in Noah coupled with Weather Research and Forecasting: applicability to snow estimates for the Tibetan Plateau

2021 ◽  
Vol 25 (9) ◽  
pp. 4967-4981
Author(s):  
Lian Liu ◽  
Yaoming Ma ◽  
Massimo Menenti ◽  
Rongmingzhu Su ◽  
Nan Yao ◽  
...  
Keyword(s):  
Heat Flux ◽  
Tibetan Plateau ◽  
Air Temperature ◽  
Land Surface ◽  
Snow Depth ◽  
Sensible Heat Flux ◽  
Weather Research And Forecasting ◽  
The Tibetan Plateau ◽  
Sensible Heat ◽  
Snow Albedo

Abstract. Snow albedo is important to the land surface energy balance and to the water cycle. During snowfall and subsequent snowmelt, snow albedo is usually parameterized as functions of snow-related variables in land surface models. However, the default snow albedo scheme in the widely used Noah land surface model shows evident shortcomings in land–atmosphere interaction estimates during snow events on the Tibetan Plateau. Here, we demonstrate that our improved snow albedo scheme performs well after including snow depth as an additional factor. By coupling the Weather Research and Forecasting (WRF) and Noah models, this study comprehensively evaluates the performance of the improved snow albedo scheme in simulating eight snow events on the Tibetan Plateau. The modeling results are compared with WRF run with the default Noah scheme and in situ observations. The improved snow albedo scheme significantly outperforms the default Noah scheme in relation to air temperature, albedo and sensible heat flux estimates by alleviating cold bias estimates, albedo overestimates and sensible heat flux underestimates, respectively. This in turn contributes to more accurate reproductions of snow event evolution. The averaged root mean square error (RMSE) relative reductions (and relative increase in correlation coefficients) for air temperature, albedo, sensible heat flux and snow depth reach 27 % (5 %), 32 % (69 %), 13 % (17 %) and 21 % (108 %), respectively. These results demonstrate the strong potential of our improved snow albedo parameterization scheme for snow event simulations on the Tibetan Plateau. Our study provides a theoretical reference for researchers committed to further improving the snow albedo parameterization scheme.

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