- J.A. Arrillaga (1)
- Wim Berg van den (1)
- Hugo Hartmann (1)
- Dominikus Heinzeller (1)
- Gert Jan Steeneveld (1)
- Matthijs Kramer (1)
- Gregorio Maqueda (1)
- Gema Morales (1)
- Carlos Román-Cascón (1)
- Mariano Sastre (1)
- Gert-Jan Steeneveld (1)
- Carlos Yagüe (1)
Radiation and cloud-base lowering fog events : Observational analysis and evaluation of WRF and HARMONIE
Román-Cascón, Carlos ; Yagüe, Carlos ; Steeneveld, Gert-Jan ; Morales, Gema ; Arrillaga, J.A. ; Sastre, Mariano ; Maqueda, Gregorio - \ 2019
Atmospheric Research 229 (2019). - ISSN 0169-8095 - p. 190 - 207.
Cloud-base-lowering - Fog - HARMONIE - Model skill - Radiation - WRF
Most of the effects caused by fog are negative for humans. Yet, numerical weather prediction (NWP) models still have problems to simulate fog properly, especially in operational forecasts. In the case of radiation fog, this is partially caused by the large sensitivity to many aspects, such as the synoptic and local conditions, the near-surface turbulence, the aerosol and droplet microphysics, or the surface characteristics, among others. This work focuses on an interesting 8-day period with several alternating radiation and cloud-base lowering (CBL) fog events observed at the Research Centre for the Lower Atmosphere (CIBA) in the Spanish Northern Plateau. On the one hand, radiation fog events are associated with strong surface cooling leading to high stability close to the surface and low values of turbulence, giving rise to shallow fog. The evolution of this type of fog is markedly sensitive to the dynamical conditions close to the surface (i.e., wind speed and turbulence). On the other hand, CBL fog presents deeper thickness associated with higher values of turbulence and less stability. Subsequently, we evaluated the fog-forecasting skill of two mesoscale models (WRF and HARMONIE) configured as similar as possible. Both models present more difficulties simulating radiation fog events than CBL ones. However, the duration and vertical extension of the CBL fog events is normally overestimated. This extended-fog avoids the surface radiative cooling needed to simulate radiation fog events formed the following nights. Therefore, these periods with alternating CBL and radiation fog are especially challenging for NWP models.
Assessment of MPAS variable resolution simulations in the grey-zone of convection against WRF model results and observations : An MPAS feasibility study of three extreme weather events in Europe
Kramer, Matthijs ; Heinzeller, Dominikus ; Hartmann, Hugo ; Berg, Wim van den; Steeneveld, Gert Jan - \ 2018
Climate Dynamics (2018). - ISSN 0930-7575 - p. 1 - 24.
Convection-permitting forecast - Föhn - Grey-zone - Hail - MPAS - Numerical weather prediction - Voronoi grid - WRF
Regional weather forecasting models like the Weather Research and Forecasting (WRF) model allow for nested domains to save computational effort and provide detailed results for mesoscale weather phenomena. The sudden resolution change by nesting may cause artefacts in the model results. On the contrary, the novel global Model for Prediction Across Scales (MPAS) runs on Voronoi meshes that allow for smooth resolution transition towards the desired high resolution in the region of interest. This minimises the resolution-related artefacts, while still saving computational effort. We evaluate the MPAS model over Europe focussing on three mesoscale weather events: a synoptic gale over the North Sea, a föhn effect in Switzerland, and a case of organised convection with hail over the Netherlands. We use four different MPAS meshes (60 km global refined to-3 km (60– 3 km), analogous 30–3 km, 15–3 km, global 3 km) and compare their results to routine observations and a WRF setup with a single domain of 3 km grid spacing. We also discuss the computational requirements for the different MPAS meshes and the operational WRF setup. In general, the MPAS 3 km and WRF model results correspond to the observations. However, a global model at 3 km resolution as a replacement for WRF is not feasible for operational use. More importantly, all variable-resolution meshes employed in this study show comparable skills in short-term forecasting within the high-resolution area at considerably lower computational costs.