Changes of atmospheric properties over Belgrade, observed using remote sensing and in situ methods during the partial solar eclipse of 20 March 2015 L. Ilic a, * , M. Kuzmanoski a , P. Kolarz a , A. Nina a , V. Sreckovic a , Z. Mijic a , J. Bajcetic b , M. Andric b a Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080, Belgrade, Serbia b University of Defence, Military Academy, Generala Pavla Juri sica Sturma 33, 11000, Belgrade, Serbia ARTICLE INFO Keywords: Solar eclipse Lidar Planetary boundary layer Ground based observations ABSTRACT Measurements of atmospheric parameters were carried out during the partial solar eclipse (51% coverage of solar disc) observed in Belgrade on 20 March 2015. The measured parameters included height of the planetary boundary layer (PBL), meteorological parameters, solar radiation, surface ozone and air ions, as well as Very Low Frequency (VLF, 3–30 kHz) and Low Frequency (LF, 30–300 kHz) signals to detect low-ionospheric plasma perturbations. The observed decrease of global solar and UV-B radiation was 48%, similar to the solar disc coverage. Meteorological parameters showed similar behavior at two measurement sites, with different elevations and different measurement heights. Air temperature change due to solar eclipse was more pronounced at the lower measurement height, showing a decrease of 2.6 C, with 15-min time delay relative to the eclipse maximum. However, at the other site temperature did not decrease; its morning increase ceased with the start of the eclipse, and continued after the eclipse maximum. Relative humidity at both sites remained almost constant until the eclipse maximum and then decreased as the temperature increased. The wind speed decreased and reached minimum 35 min after the last contact. The eclipse-induced decrease of PBL height was about 200 m, with minimum reached 20 min after the eclipse maximum. Although dependent on UV radiation, surface ozone concentration did not show the expected decrease, possibly due to less significant influence of photochemical reactions at the measurement site and decline of PBL height. Air-ion concentration decreased during the solar eclipse, with minimum almost coinciding with the eclipse maximum. Additionally, the referential Line-of-Sight (LOS) radio link was set in the area of Belgrade, using the carrier frequency of 3 GHz. Perturbation of the receiving signal level (RSL) was observed on March 20, probably induced by the solar eclipse. Eclipse-related perturbations in ionospheric D-region were detected based on the VLF/LF signal variations, as a consequence of Lyα radiation decrease. 1. Introduction Abrupt change in the incoming solar radiation flux during solar eclipse induces disturbances in different atmospheric layers (Ger- asopoulos et al., 2008; Aplin et al., 2016). These disturbances are not necessarily similar to those during sunset/sunrise, because of different time scales and initial conditions. They depend on a number of factors, including the percentage of sun obscuration, latitude, season, time of the day, synoptic conditions, terrain complexity and surface properties. Since solar energy impacts the atmosphere primarily by convection of heat from the ground, lower atmospheric layers are more influenced by changes in solar radiation. The layer of the atmosphere in direct inter- action with the surface, thus directly influenced by the Earth's surface forcing, is called the planetary boundary layer (PBL). Since surface is also a source of humidity and pollutants, turbulence within the PBL is responsible for mixing and dispersion of pollutants, while air pollution concentrations in the PBL are generally higher than those in the free troposphere (Stull, 1988). A number of studies have focused on the effect of solar eclipse on various atmospheric properties, mainly in PBL. Changes in meteorolog- ical parameters near the ground level were most extensively investigated, for several eclipse events (Anderson, 1999; Ahrens et al., 2001; Kolarz * Corresponding author. E-mail address: luka@ipb.ac.rs (L. Ilic). Contents lists available at ScienceDirect Journal of Atmospheric and Solar-Terrestrial Physics journal homepage: www.elsevier.com/locate/jastp https://doi.org/10.1016/j.jastp.2017.10.001 Received 31 March 2017; Received in revised form 16 August 2017; Accepted 3 October 2017 Available online xxxx 1364-6826/© 2017 Elsevier Ltd. All rights reserved. Journal of Atmospheric and Solar-Terrestrial Physics xxx (2017) 1–10 Please cite this article in press as: Ilic, L., et al., Changes of atmospheric properties over Belgrade, observed using remote sensing and in situ methods during the partial solar eclipse of 20 March 2015, Journal of Atmospheric and Solar-Terrestrial Physics (2017), https://doi.org/10.1016/ j.jastp.2017.10.001