Improvement of numerical simulation of fog: Implementation of a novel scheme in WRF Thompson Aerosol Aware module to simulate the activation of aerosol particles
- Institute of Geography and Earth Sciences, University of Pécs, Pécs, Hungary
Operative forecasting of the fog is still a challenge. The numerical weather prediction (NWP) models frequently miss the spatial and temporal location or onset and the dissipation the fog. Even the recently developed microphysics schemes (e.g. Thompson Aerosol Aware scheme (hereafter TAAS)), evaluate the rate of the activation of the hygroscopic aerosol particles as a function of the vertical velocity. However, in the case of fog, the updraft is usually negligible, therefore this method is physically inconsistent.
A novel parameterization technique was developed to evaluate the rate of aerosol activation in fog. This novel scheme was implemented into WRF, TAAS microphysical module. The novel parametrization calculates the activation rate as a function of local cooling rate, and as a function of local change of water vapor content. Furthermore, a diagnostic variable was introduced to evaluate the visibility reduction due to the formation of haze droplets.
A well observed radiative fog event was used, to demonstrate the capabilities of the novel parametrization. Data from standard meteorological stations, and a measurement campaign at Budapest are available to test the numerical model.
The results are as follows: (i) While the original TAAS activates the aerosols homogeneously throughout the fog (the prescribed minimum value for the updraft velocity is constant in both space and time), the novel parameterization scheme results in significant spatial and temporal variability of the droplets concentration. The impact of the cooling is well demonstrated by the enhanced activation rate at the top of the fog. (ii) In the dissipation period the spatial extension of the fog simulated by novel parameterization fit better to the satellite data than that of calculated by the updraft based parameterization. The novel activation scheme increases the life time of the fog by 30 – 60 min. (iii) Gradual decrease and increase of the visibility can be simulated by calculating of the visibility reduction due to the haze (iv) Comparison of the observed and simulated data shows that the early dissipation of the simulated fog not necessarily the consequence of the overestimation of downward short wave flux.
The results of further case studies for different types of fog are planned to present.
How to cite: Peterka, A. and Geresdi, I.: Improvement of numerical simulation of fog: Implementation of a novel scheme in WRF Thompson Aerosol Aware module to simulate the activation of aerosol particles, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-61, https://doi.org/10.5194/ems2023-61, 2023.
