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.

Mechanisms of Along-Valley Winds and Heat Exchange over Mountainous Terrain

2010 ◽  
Vol 67 (9) ◽  
pp. 3033-3047 ◽  
Author(s):  
Juerg Schmidli ◽  
Richard Rotunno
Keyword(s):  
Heat Flux ◽  
Heat Exchange ◽  
Sensible Heat Flux ◽  
Volume Effect ◽  
Turbulent Heat ◽  
Relative Role ◽  
Sensible Heat ◽  
Dynamic Surface ◽  
Surface Sensible Heat Flux

Abstract The physical mechanisms leading to the formation of diurnal along-valley winds are investigated over idealized three-dimensional topography. The topography used in this study consists of a valley with a horizontal floor enclosed by two isolated mountain ridges on a horizontal plain. A diagnostic equation for the along-valley pressure gradient is developed and used in combination with numerical model simulations to clarify the relative role of various forcing mechanisms such as the valley volume effect, subsidence heating, and surface sensible heat flux effects. The full diurnal cycle is simulated using comprehensive model physics including radiation transfer, land surface processes, and dynamic surface–atmosphere interactions. The authors find that the basic assumption of the valley volume argument of no heat exchange with the free atmosphere seldom holds. Typically, advective and turbulent heat transport reduce the heating of the valley during the day and the cooling of the valley during the night. In addition, dynamically induced valley–plain contrasts in the surface sensible heat flux can play an important role. Nevertheless, the present analysis confirms the importance of the valley volume effect for the formation of the diurnal along-valley winds but also clarifies the role of subsidence heating and the limitations of the valley volume effect argument. In summary, the analysis brings together different ideas of the valley wind into a unified picture.

scholarly journals The Impact of the Temperature Inversion Breakup on the Exchange of Heat and Mass in an Idealized Valley: Sensitivity to the Radiative Forcing

2015 ◽  
Vol 54 (11) ◽  
pp. 2199-2216 ◽  
Author(s):  
Daniel Leukauf ◽  
Alexander Gohm ◽  
Mathias W. Rotach ◽  
Johannes S. Wagner
Keyword(s):  
Radiative Forcing ◽  
Sensible Heat Flux ◽  
Temperature Inversion ◽  
Shortwave Radiation ◽  
Weather Research And Forecasting ◽  
Sensible Heat ◽  
Vertical Fluxes ◽  
Nocturnal Inversion ◽  
Surface Sensible Heat Flux ◽  
The Impact

Abstract The breakup of a nocturnal temperature inversion during daytime is studied in an idealized valley by means of high-resolution numerical simulations. Vertical fluxes of heat and mass are strongly reduced as long as an inversion is present; hence it is important to understand the mechanisms leading to its removal. In this study breakup times are determined as a function of the radiative forcing. Further, the effect of the nocturnal inversion on the vertical exchange of heat and mass is quantified. The Weather Research and Forecasting Model is applied to an idealized quasi-two-dimensional valley. The net shortwave radiation is specified by a sine function with amplitudes between 150 and 850 W m−2 during daytime and at zero during the night. The valley inversion is eroded within 5 h for the strongest forcing. A minimal amplitude of 450 W m−2 is required to reach the breakup, in which case the inversion is removed after 11 h. Depending on the forcing amplitude, between 10% and 57% of the energy provided by the surface sensible heat flux is exported out of the valley during the whole day. The ratio of exported energy to provided energy is approximately 1.6 times as large after the inversion is removed as before. More than 5 times the valley air mass is turned over in 12 h for the strongest forcing, whereas the mass is turned over only 1.3 times for 400 W m−2.

scholarly journals Evaluation of the Weather Research and Forecasting Model in the Durance Valley Complex Terrain during the KASCADE Field Campaign

2016 ◽  
Vol 55 (4) ◽  
pp. 861-882 ◽  
Author(s):  
Peter Christiaan Kalverla ◽  
Gert-Jan Duine ◽  
Gert-Jan Steeneveld ◽  
Thierry Hedde
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Soil Moisture ◽  
Land Surface ◽  
Soil Moisture Content ◽  
Sensible Heat Flux ◽  
Weather Research And Forecasting ◽  
Sensible Heat ◽  
Initial Soil ◽  
Pbl Parameterization

AbstractIn the winter of 2012/13, the Katabatic Winds and Stability over Cadarache for the Dispersion of Effluents (KASCADE) observational campaign was carried out in southeastern France to characterize the wind and thermodynamic structure of the (stable) planetary boundary layer (PBL). Data were collected with two micrometeorological towers, a sodar, a tethered balloon, and radiosoundings. Here, this dataset is used to evaluate the representation of the boundary layer in the Weather Research and Forecasting (WRF) Model. In general, it is found that diurnal temperature range (DTR) is largely underestimated, there is a strong negative bias in both longwave radiation components, and evapotranspiration is overestimated. An illustrative case is subjected to a thorough model-physics evaluation. First, five PBL parameterization schemes and two land surface schemes are employed. A marginal sensitivity to PBL parameterization is found, and the sophisticated Noah land surface model represents the extremes in skin temperature better than does a more simple thermal diffusion scheme. In a second stage, sensitivity tests for land surface–atmosphere coupling (through parameterization of z0h/z0m), initial soil moisture content, and radiation parameterization were performed. Relatively strong surface coupling and low soil moisture content result in a larger sensible heat flux, deeper PBL, and larger DTR. The larger sensible heat flux is not supported by the observations, however. It turns out that, for the selected case, a combination of subsidence and warm-air advection is not accurately simulated, but this inaccuracy cannot fully explain the discrepancies found in the WRF simulations. The results of the sensitivity analysis reiterate the important role of initial soil moisture values.

scholarly journals Land-Use Improvements in the Weather Research and Forecasting Model over Complex Mountainous Terrain and Comparison of Different Grid Sizes

2021 ◽  
Author(s):  
Alessio Golzio ◽  
Silvia Ferrarese ◽  
Claudio Cassardo ◽  
Gugliemina Adele Diolaiuti ◽  
Manuela Pelfini
Keyword(s):  
Boundary Layer ◽  
Land Use ◽  
Land Cover ◽  
Mixing Layer ◽  
Local Area ◽  
Heat Fluxes ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Mountainous Terrain ◽  
Weather Research

AbstractWeather forecasts over mountainous terrain are challenging due to the complex topography that is necessarily smoothed by actual local-area models. As complex mountainous territories represent 20% of the Earth’s surface, accurate forecasts and the numerical resolution of the interaction between the surface and the atmospheric boundary layer are crucial. We present an assessment of the Weather Research and Forecasting model with two different grid spacings (1 km and 0.5 km), using two topography datasets (NASA Shuttle Radar Topography Mission and Global Multi-resolution Terrain Elevation Data 2010, digital elevation models) and four land-cover-description datasets (Corine Land Cover, U.S. Geological Survey land-use, MODIS30 and MODIS15, Moderate Resolution Imaging Spectroradiometer land-use). We investigate the Ortles Cevadale region in the Rhaetian Alps (central Italian Alps), focusing on the upper Forni Glacier proglacial area, where a micrometeorological station operated from 28 August to 11 September 2017. The simulation outputs are compared with observations at this micrometeorological station and four other weather stations distributed around the Forni Glacier with respect to the latent heat, sensible heat and ground heat fluxes, mixing-layer height, soil moisture, 2-m air temperature, and 10-m wind speed. The different model runs make it possible to isolate the contributions of land use, topography, grid spacing, and boundary-layer parametrizations. Among the considered factors, land use proves to have the most significant impact on results.

“Gray Zone” Simulations using a Three-Dimensional Planetary Boundary Layer Parameterization in the Weather Research and Forecasting Model

2021 ◽  
Author(s):  
Timothy W. Juliano ◽  
Branko Kosović ◽  
Pedro A. Jiménez ◽  
Masih Eghdami ◽  
Sue Ellen Haupt ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Three Dimensional ◽  
Grid Cell ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Gray Zone ◽  
Pbl Scheme ◽  
3D Effects ◽  
Mesoscale Simulations

AbstractGenerating accurate weather forecasts of planetary boundary layer (PBL) properties is challenging in many geographical regions, oftentimes due to complex topography or horizontal variability in, for example, land characteristics. While recent advances in high-performance computing platforms have led to an increase in the spatial resolution of numerical weather prediction (NWP) models, the horizontal grid cell spacing (Δ x) of many regional-scale NWP models currently fall within or are beginning to approach the gray zone (i.e., Δ x ≈ 100 – 1000 m). At these grid cell spacings, three-dimensional (3D) effects are important, as the most energetic turbulent eddies are neither fully parameterized (as in traditional mesoscale simulations) nor fully resolved [as in traditional large eddy simulations (LES)]. In light of this modeling challenge, we have implemented a 3D PBL parameterization for high-resolution mesoscale simulations using the Weather Research and Forecasting model. The PBL scheme, which is based on the algebraic model developed by Mellor and Yamada, accounts for the 3D effects of turbulence by calculating explicitly the momentum, heat, and moisture flux divergences in addition to the turbulent kinetic energy. In this study, we present results from idealized simulations in the gray zone that illustrate the benefit of using a fully consistent turbulence closure framework under convective conditions. While the 3D PBL scheme reproduces the evolution of convective features more appropriately than the traditional 1D PBL scheme, we highlight the need to improve the turbulent length scale formulation.

scholarly journals Observation of sensible and latent heat flux profiles with lidar

2020 ◽  
Vol 13 (6) ◽  
pp. 3221-3233 ◽  
Author(s):  
Andreas Behrendt ◽  
Volker Wulfmeyer ◽  
Christoph Senff ◽  
Shravan Kumar Muppa ◽  
Florian Späth ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sensible Heat Flux ◽  
Ground Level ◽  
Sensible Heat ◽  
Flux Divergence ◽  
Convective Boundary ◽  
The Mean

Abstract. We present the first measurement of the sensible heat flux (H) profile in the convective boundary layer (CBL) derived from the covariance of collocated vertical-pointing temperature rotational Raman lidar and Doppler wind lidar measurements. The uncertainties of the H measurements due to instrumental noise and limited sampling are also derived and discussed. Simultaneous measurements of the latent heat flux profile (L) and other turbulent variables were obtained with the combination of water-vapor differential absorption lidar (WVDIAL) and Doppler lidar. The case study uses a measurement example from the HOPE (HD(CP)2 Observational Prototype Experiment) campaign, which took place in western Germany in 2013 and presents a cloud-free well-developed quasi-stationary CBL. The mean boundary layer height zi was at 1230 m above ground level. The results show – as expected – positive values of H in the middle of the CBL. A maximum of (182±32) W m−2, with the second number for the noise uncertainty, is found at 0.5 zi. At about 0.7 zi, H changes sign to negative values above. The entrainment flux was (-62±27) W m−2. The mean sensible heat flux divergence in the observed part of the CBL above 0.3 zi was −0.28 W m−3, which corresponds to a warming of 0.83 K h−1. The L profile shows a slight positive mean flux divergence of 0.12 W m−3 and an entrainment flux of (214±36) W m−2. The combination of H and L profiles in combination with variance and other turbulent parameters is very valuable for the evaluation of large-eddy simulation (LES) results and the further improvement and validation of turbulence parameterization schemes.

Sign in / Sign up

Export Citation Format

Share Document