Climatology of fog occurrence over a wide flat area in Serbia based on visibility observations

Abstract

Long‐term analysis of occurrence of fog events at 14 stations across part of fairly flat terrain of Serbia, which includes the area of the Pannonian Plain, is conducted. For the majority of stations (Palić, Novi Sad, Kikinda, Vršac, Belgrade‐Surčin, Smederevska Palanka, Valjevo, Loznica, Negotin) data were available for the 33‐year period, 1973–2005. For the rest of stations, data were available for shorter periods: for Sombor and Veliko Gradište 1982–2005, for Sremska Mitrovica and Belgrade‐Vračar 1983–2005, and for Zrenjanin 1989–2005. Fog event is defined only based on visibility observations. Almost 75% of analysed data sets showed a negative annual trend of low‐visibility events throughout the analysed time periods. This negative trend is increasing as it goes towards the north of Serbia and most of the stations with decreasing trend are rural. Fog is most frequent in the period between October and February and it is likely mostly due to radiative cooling and especially in October when an anticyclonic synoptic situation is prevailing. Stations with higher elevations have more lasting fog events and fog events with more variable mean relative humidity compared to their counterparts, which ranges from 92.1–97.4%. For most of stations December is the month with the highest frequency of occurrence of fog in the presence of a low cloud. Frequency of fog onset during low wind speed (below 2 m/s) is analysed along with its correlation with a frequency of fog onset when the cloud base height is equal to or above 2,000 m. In ~71% of the stations correlations are higher than 0.6, and stations with a lower elevations show a generally better correlation than those with higher elevations.

Regional characteristics of cloudiness in Serbia during the period 1991–2017

“…The maximum annual mean number of clear-sky (cloudy-sky) days is in summer (winter). This is in agreement with mean synoptic conditions over Serbia-a prevailing anticyclone in the summer and cyclonic activities and low clouds and fog in the winter(Radinovi c, 1981;Veljovi c and Vujovi c, 2019).…”

“…Although nighttime observations after 21 local time are not available, certain daily variations of TCA can be inferred using observations at 7, 14, and 21 local time. Regarding this type of distribution by months (Figure 10), it can be seen that in November, all six stations with available daily data show a higher percentage of cloudiness at 7 local time than at 14 local time, which may be related to the frequent occurrence of fog in the morning hours (Veljović and Vujović, 2019). This is similar for the majority of analysed stations in October and in the winter months of December and January, when the percentage of cloudiness is highest and ranges from about 70% in WMV in January to about 78% in the south of EMV in December.…”

Global Comparisons of ERA5 and the Operational HRES Tropospheric Delay and Water Vapor Products With GPS and MODIS

“…It plays a key role in the hydrological cycle with fundamental impacts on the Earth's climate. Good knowledge of PWV is crucial for meteorological forecasting for extreme hydro‐meteorological events (e.g., Millán, 2014), fog occurrences (e.g., Veljović & Vujović, 2019), global lightning activities (e.g., Price, 2000) and tornado‐produced storms (e.g., Georgiev, 2003). The spatial‐temporal variability of PWV also leads to the changes in the tropospheric delay, which is known to be a common error source in geodetic observations including Global Positioning System (GPS) (e.g., Iwabuchi et al., 2003), Interferometric Synthetic Aperture Radar (InSAR) (e.g., Yip et al., 2019), Very Long Baseline Interferometry (VLBI) (e.g., Eriksson et al., 2014), and satellite altimetry (e.g., Obligis et al., 2011).…”

A spatially explicit and temporally highly resolved analysis of variations in fog occurrence over Europe

“…; Avotniece et al ; Veljović and Vujović, ). Although these studies cover long time periods, they are only based on station data with few measurements per day.…”

“…With a decrease in aerosol counts, this effect is diminished. Second, increasing air temperatures in the lower atmospheric layers, especially during winter, lead to the fact that the dew point is exceeded less often and so gaseous water vapour generally condenses less frequently to form fog (Gomez and Smith, 1984;Vautard et al, 2009;Avotniece et al, 2015;Łupikasza and Niedźwiedź, 2016;Veljović and Vujović, 2018). Although these studies cover long time periods, they are only based on station data with few measurements per day.…”