| 1. |
- 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.
|
|
| 2. |
- Pithan, Felix, et al.
(författare)
-
Select strengths and biases of models in representing the Arctic winter boundary layer over sea ice : the Larcform 1 single column model intercomparison
- 2016
-
Ingår i: Journal of Advances in Modeling Earth Systems. - 1942-2466. ; 8:3, s. 1345-1357
-
Tidskriftsartikel (refereegranskat)abstract
- Weather and climate models struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Arctic winter, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. In the radiatively clear state, strong surface radiative cooling leads to the build-up of surface-based temperature inversions. Many large-scale models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. Here, the transformation from a moist to a cold dry air mass is modeled using an idealized Lagrangian perspective. The trajectory includes both boundary layer states, and the single-column experiment is the first Lagrangian Arctic air formation experiment (Larcform 1) organized within GEWEX GASS (Global atmospheric system studies). The intercomparison reproduces the typical biases of large-scale models: some models lack the cloudy state of the boundary layer due to the representation of mixed-phase microphysics or to the interaction between micro- and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models substantially disagree on the amount of cloud liquid water in the cloudy state and on turbulent heat fluxes under clear skies. Observations of air mass transformations including both boundary layer states would allow for a tighter constraint of model behavior.
|
|
| 3. |
- Sandu, Irina, et al.
(författare)
-
Impacts of orography on large-scale atmospheric circulation
- 2019
-
Ingår i: npj Climate and Atmospheric Science. - : Springer Science and Business Media LLC. - 2397-3722. ; 2
-
Tidskriftsartikel (refereegranskat)abstract
- Some of the largest and most persistent circulation errors in global numerical weather prediction and climate models are attributable to the inadequate representation of the impacts of orography on the atmospheric flow. Existing parametrization approaches attempting to account for unresolved orographic processes, such as turbulent form drag, low-level flow blocking or mountain waves, have been successful to some extent. They capture the basic impacts of the unresolved orography on atmospheric circulation in a qualitatively correct way and have led to significant progress in both numerical weather prediction and climate modelling. These approaches, however, have apparent limitations and inadequacies due to poor observational evidence, insufficient fundamental knowledge and an ambiguous separation between resolved and unresolved orographic scales and between different orographic processes. Numerical weather prediction and climate modelling has advanced to a stage where these inadequacies have become critical and hamper progress by limiting predictive skill on a wide range of spatial and temporal scales. More physically based approaches are needed to quantify the relative importance of apparently disparate orographic processes and to account for their combined effects in a rational and accurate way in numerical models. We argue that, thanks to recent advances, significant progress can be made by combining theoretical approaches with observations, inverse modelling techniques and high-resolution and idealized numerical simulations.
|
|
| 4. |
- 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.
|
|
