Numerical modelling of the evolution of the boundary layer during a radiation fog event

Smith, D.; Renfrew, Ian A.; Price, J. D.; Dorling, Stephen

doi:10.1002/wea.3305

Cited by 15 publications

(17 citation statements)

References 21 publications

(28 reference statements)

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“…Recent studies of IOP 1 have shown that humidity and wind speed in the residual layer control the optical thickening of the fog (Smith et al, 2018), in addition to the hygroscopic growth and the fraction of CCN activated into droplets (Boutle et al, 2018). Over the same case, Poku et al (2019) recently showed, with a two-moment microphysical scheme using a single mode of CCN, that the CCN number concentration has a greater impact on fog water content than the CCN soluble fraction.…”

Section: Discussionmentioning

confidence: 99%

Fog in heterogeneous environments: the relative importance of local and non‐local processes on radiative‐advective fog formation

Ducongé

Lac

Vié

et al. 2020

Quart J Royal Meteoro Soc

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A 100 m resolution simulation of radiation fog observed during the Local And Non‐local Fog EXperiment (LANFEX) was performed over the Shropshire hills (UK) in order to understand the impact of local circulation on valley fog formation. The model correctly resolves all valleys and their different geometries, their associated dynamical features, and the different fog conditions between the measurement sites. Passage of stratocumulus during the night led to fog dissipation and gave the opportunity to study two fog formation stages. In the narrow valleys, fog formed at the valley floor and non‐local drainage‐flow processes acted to dissipate it. This equilibrium determined the fog optical thickness, which varied within and between valleys. Wider basins were more subject to dense fog conditions (due to local formation) than narrower valleys, where advecting fog events are locally observed through basins overflowing. The largest and most open valley of Jay Barns was impacted by numerous circulations from narrower tributary valleys, and their complex interactions affected fog formation differently between events. The impact of cloud microphysics on the simulated fog is studied by comparing simulations with one‐moment and two‐moment schemes. The use of a two‐moment scheme brings improvements when the prognostic number concentration is used to compute cloud optical properties, meaning that the radiative impact of droplet concentration is greater than its gravitational settling effect.

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Section: Discussionmentioning

confidence: 99%

Fog in heterogeneous environments: the relative importance of local and non‐local processes on radiative‐advective fog formation

Ducongé

Lac

Vié

et al. 2020

Quart J Royal Meteoro Soc

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“…At Cardington, fog formed around 1800 utc and remained stable, as well as optically thin, through the duration of the night. IOP1 was chosen as it was one of the cleanest examples of local fog development, with minimal influence by advective processes (see Smith et al , for more details).…”

Section: Model Setupmentioning

confidence: 99%

How important are aerosol–fog interactions for the successful modelling of nocturnal radiation fog?

Poku

Ross

Blyth³

et al. 2019

Weather

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Forecasting and modelling fog formation, development, and dissipation is a significant challenge. Fog dynamics involve subtle interactions between small‐scale turbulence, radiative transfer and microphysics. Recent studies have highlighted the role of aerosol and related cloud microphysical properties in the evolution of fog. In this article, we investigate this role using very high‐resolution large eddy simulations coupled with a newly developed multi‐moment cloud microphysics scheme (CASIM), which has been designed to model aerosol–cloud interactions. The simulation results demonstrate the sensitivity of the fog structure to the properties of the aerosol population (e.g. number concentration). This study also demonstrates the importance of the treatment of aerosol activation in fog formation and discusses future work required to improve the representation of aerosol–fog interactions for simulations of fog.

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“…Deep adiabatic radiation fogs are typically longer‐lived, with a greater potential to persist during the day and thus a greater impact (Price, 2011). The stability transition is sensitive to various conditions, including aerosol concentrations (Boutle et al ., 2018; Poku et al ., 2019), wind speed, and humidity (Smith et al ., 2018).…”

Section: Introductionmentioning

confidence: 99%

Sub‐km scale numerical weather prediction model simulations of radiation fog

Smith

Renfrew

Dorling

et al. 2020

Quart J Royal Meteoro Soc

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The numerical weather prediction (NWP) of fog remains a challenge, with accurate forecasts relying on the representation of many interacting physical processes. The recent Local And Non‐local Fog EXperiment (LANFEX) has generated a detailed observational dataset, creating a unique opportunity to assess the NWP of fog events. We evaluate the performance of operational and research configurations of the Met Office Unified Model (MetUM) with three horizontal grid lengths, 1.5 km and 333 and 100 m, in simulating four LANFEX case studies. In general, the subkilometre (sub‐km) scale versions of MetUM are in better agreement with the observations; however, there are a number of systematic model deficiencies. MetUM produces valleys that are too warm and hills that are too cold, leading to valleys that do not have enough fog and hills that have too much. A large sensitivity to soil temperature was identified from a set of parametrisation sensitivity experiments. In all the case studies, the model erroneously transfers heat too readily through the soil to the surface, preventing fog formation. Sensitivity tests show that the specification of the soil thermal conductivity parametrisation can lead to up to a 5‐hr change in fog onset time. Overall, the sub‐km models demonstrate promise, but they have a high sensitivity to surface properties.

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Numerical modelling of the evolution of the boundary layer during a radiation fog event

Cited by 15 publications

References 21 publications

Fog in heterogeneous environments: the relative importance of local and non‐local processes on radiative‐advective fog formation

Fog in heterogeneous environments: the relative importance of local and non‐local processes on radiative‐advective fog formation

How important are aerosol–fog interactions for the successful modelling of nocturnal radiation fog?

Sub‐km scale numerical weather prediction model simulations of radiation fog

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