| 1. |
- Bosveld, Fred C., et al.
(författare)
-
The Third GABLS Intercomparison Case for Evaluation Studies of Boundary-Layer Models. Part B : Results and Process Understanding
- 2014
-
Ingår i: Boundary-layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 152:2, s. 157-187
-
Tidskriftsartikel (refereegranskat)abstract
- We describe and analyze the results of the third global energy and water cycle experiment atmospheric boundary layer Study intercomparison and evaluation study for single-column models. Each of the nineteen participating models was operated with its own physics package, including land-surface, radiation and turbulent mixing schemes, for a full diurnal cycle selected from the Cabauw observatory archive. By carefully prescribing the temporal evolution of the forcings on the vertical column, the models could be evaluated against observations. We focus on the gross features of the stable boundary layer (SBL), such as the onset of evening momentum decoupling, the 2-m minimum temperature, the evolution of the inertial oscillation and the morning transition. New process diagrams are introduced to interpret the variety of model results and the relative importance of processes in the SBL; the diagrams include the results of a number of sensitivity runs performed with one of the models. The models are characterized in terms of thermal coupling to the soil, longwave radiation and turbulent mixing. It is shown that differences in longwave radiation schemes among the models have only a small effect on the simulations; however, there are significant variations in downward radiation due to different boundary-layer profiles of temperature and humidity. The differences in modelled thermal coupling to the land surface are large and explain most of the variations in 2-m air temperature and longwave incoming radiation among models. Models with strong turbulent mixing overestimate the boundary-layer height, underestimate the wind speed at 200 m, and give a relatively large downward sensible heat flux. The result is that 2-m air temperature is relatively insensitive to turbulent mixing intensity. Evening transition times spread 1.5 h around the observed time of transition, with later transitions for models with coarse resolution. Time of onset in the morning transition spreads 2 h around the observed transition time. With this case, the morning transition appeared to be difficult to study, no relation could be found between the studied processes, and the variation in the time of the morning transition among the models.
|
|
| 2. |
- Couvreux, Fleur, et al.
(författare)
-
Boundary-layer turbulent processes and mesoscale variability represented by Numerical Weather Prediction models during the BLLAST campaign
- 2016
-
Ingår i: Atmospheric Chemistry and Physics Discussions. - : Copernicus GmbH. - 1680-7367 .- 1680-7375 .- 1680-7324. ; 16:14, s. 8983-9002
-
Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the ability of three operational models, AROME, ARPEGE and ECMWF, to predict the boundary-layer turbulent processes and mesoscale variability observed during the Boundary Layer Late-Afternoon and Sunset Turbulence (BLLAST) field campaign. AROME is a 2.5 km limited area non-hydrostatic model operated over France, ARPEGE a global model with a 10 km grid-size over France and ECMWF a global model with a 16 km grid-size. We analyze the representation of the vertical profiles of temperature and humidity and the time evolution of near surface atmospheric variables as well as the radiative and turbulent fluxes for a total of 12 24h-long Intensive Observing Periods. Special attention is paid to the evolution of the turbulent kinetic energy that was sampled by a combination of independent instruments. For the first time, this variable, which is a central variable in the turbulence scheme used in AROME and ARPEGE, is evaluated with observations.
|
|
| 3. |
|
|
| 4. |
- Ortega, Pablo, et al.
(författare)
-
Improving Arctic Weather and Seasonal Climate Prediction : Recommendations for Future Forecast Systems Evolution from the European Project APPLICATE
- 2022
-
Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 103:10, s. E2203-E2213
-
Tidskriftsartikel (refereegranskat)abstract
- The Arctic environment is changing, increasing the vulnerability of local communities and ecosystems, and impacting its socio-economic landscape. In this context, weather and climate prediction systems can be powerful tools to support strategic planning and decision-making at different time horizons. This article presents several success stories from the H2020 project APPLICATE on how to advance Arctic weather and seasonal climate prediction, synthesizing the key lessons learned throughout the project and providing recommendations for future model and forecast system development.
|
|
| 5. |
- Solomon, Amy, et al.
(författare)
-
The winter central Arctic surface energy budget : A model evaluation using observations from the MOSAiC campaign
- 2023
-
Ingår i: Elementa. - 2325-1026. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the simulation of wintertime (15 October, 2019, to 15 March, 2020) statistics of the central Arctic near -surface atmosphere and surface energy budget observed during the MOSAiC campaign with short-term forecasts from 7 state-of-the-art operational and experimental forecast systems. Five of these systems are fully coupled ocean -sea ice -atmosphere models. Forecast systems need to simultaneously simulate the impact of radiative effects, turbulence, and precipitation processes on the surface energy budget and nearsurface atmospheric conditions in order to produce useful forecasts of the Arctic system.This study focuses on processes unique to the Arctic, such as, the representation of liquid -bearing clouds at cold temperatures and the representation of a persistent stable boundary layer. It is found that contemporary models still struggle to maintain liquid water in clouds at cold temperatures. Given the simple balance between net longwave radiation, sensible heat flux, and conductive ground flux in the wintertime Arctic surface energy balance, a bias in one of these components manifests as a compensating bias in other terms. This study highlights the different manifestations of model bias and the potential implications on other terms. Three general types of challenges are found within the models evaluated: representing the radiative impact of clouds, representing the interaction of atmospheric heat fluxes with sub -surface fluxes (i.e., snow and ice properties), and representing the relationship between stability and turbulent heat fluxes.
|
|
| 6. |
- Svensson, Jacob, 1978-, et al.
(författare)
-
Evaluation of a TKE diffusion parametrization in IFS Single Column Model
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- An implementation of a diffusion parametrization based on Turbulent KineticEnergy (TKE) in a single column model of the weather forecast model Integrated Forecast System (IFS) is evaluated. Simulations are performed for four test cases GABLS1,GABLS3, DICE and GABLS4. The test cases have different idealization and gives together a comprehensive framework for evaluating the performance for a NWP in representing stably stratified atmospheric boundary layers, diurnal cycles and transition between stable andunstable stratification. The sensitivity to the mixing length scale is evaluated by simulations with alternative formulations and by diagnostic evaluation. An estimation of ageostrophicmass flux is made for idealized test cases.The TKE parametrization is less diffusive than the currently used operational parametrization and shows more realistic stable boundary layers. The magnitude of the diffusivity shows to be very sensitive to length scale formulation. The more diffusive formulations yield weaker gradients of temperature and wind at the surface and smaller angle between surface stress and geostrophic wind. The lower limit of the length scale showed to be ofimportance to avoid unrealistic vertical gradients of wind and temperature close to the surface. Moreover, the diagnosed length scales formulations showed to have very simila rbehaviour when turbulence ceases in stable conditions. The ageostrophic mass flux was higher in simulations with stronger diffusion, except that the new TKE scheme in one test case showed similar values as the operational parametrization.
|
|
