Human thermal load on foggy and cloudless mornings in the cold season

We investigated the human thermal load in Martonvásár (Hungarian lowland, Carpathian region) in anticyclonic weather conditions in the morning, when a) the sky was completely clear and on the other hand, when b) there was fog. A customizable clothing thermal resistance-operative temperature model was used. The body mass index and the basal metabolic flux density values of the person in the simulations were 25 kgm-2 and 40 Wm-2, respectively. During the observations, weather data was provided by the automatic station of the HungaroMet company and it was accessible on the company's website. We had 77 observations in foggy weather, while we had 46 observations under clear sky conditions in the period between 2019–2023. The following main results should be highlighted: 1) clothing thermal resistance (rcl) varied between 0.5-2.5 clo in the case of fog, while in clear-sky cases rcl was between 0.9-3.5 clo. 2) Based on our data analysis, we estimated that the warming effect of the morning fog was around 0.8 clo. 3) We also showed that the effect of inter-personal variability on rcl was significant when the heat deficit was high (rcl ≥ 2.5 clo) and at this time it was comparable with the degree of the warming effect of fog. It should be mentioned that the analysis of typical weather situations from the point of view of human thermal load is a new field of research, since there is little information available on this subject.