Micrometeorological measurements of foggy situations in Siójut (November – December, 2018)

Fog is defined as a suspension of water droplets and ice particles that reduce the visibility to less than 1 km near the Earth's surface. It is also described as a formation of low status cloud that forms near the Earth's surface. Its depth and horizontal extent depends upon surface characteristics, micro- and mesoscale meteorological factors such as radiation and turbulent characteristics. Fog is a major weather hazard as it reduces visibility and can disrupt road, rail, and air transport. Therefore, reliable fog forecasting becomes essential to prevent interruptions in transportation (Michaelides et al., 2014; Vajda et al., 2014). Accurate fog forecasting relies on correct parameterizations of the radiative, turbulent and surface processes as poor parameterization lead to poor forecasting results (Westerhuis et al., 2020). Statistical investigations of fog formation and development are also important for the climatological background of secure aviation (Wantuch & Michaelides, 2005; Bottyán et al., 2010; Tuba & Bottyán, 2018). Therefore, it is essential to understand the physical, chemical, and meteorological features that lead to fog generation, preservation, and dissipation. As a result, ground-based fog experiments are being conducted in different cities worldwide to formulate better parameterizations for fog modelling. Ground-based fog experiments have been conducted for example in Paris, New Delhi or Wasatch Mountain Range (northern Utah, USA), to measure the fog events, associated thermodynamics, microphysics, and chemical composition of gases and aerosols (Haeffelin et al., 2010; Gultepe et al., 2016; Ghude et al., 2017). This study consists of two main parts. First, a comparison of fog climatology among New Delhi, Budapest, and Siófok is provided. It was done to assess the frequency and occurrence of fog in the three cities. The second part of the manuscript describes the micrometeorological measurement campaign in Siójut (Hungary) from 15th October 2018 till 13th December 2018. Measuring system, main goals of the experiment and few results are presented. The momentum () and sensible heat (H) fluxes were calculated based on eddy covariance methodology using Gill sonic anemometer. Necessary corrections were applied to the raw eddy fluxes as described in the TK3 software manual (Weidinger et al., 1999; Barcza, 2001; Mauder & Foken, 2015 and Horváth et al., 2018). We measured the surface and soil energy budget components together with the heat flux into the soil (G_Soil) and net radiation (Rn). Finally, case studies of fog events are presented to show the daily variation of meteorological variables, radiation, and surface energy budget components.