To achieve the high accuracy in GNSS positioning, the various atmospheric effects on GNSS signals need to be mitigated, where the major part present the ionised atmosphere (ionosphere) and the neutral atmosphere (troposphere). Additional signal scattering can occur from heavy precipitation and from snow accumulation on the antenna and on its surroundings. In this study, irregularities in the ionosphere induced by space weather were analysed, as well as sudden snowfall with its impact on meteorological conditions in the troposphere. State in the ionosphere was characterised by total electron content (TEC) derived from GNSS observation of EUREF Permanent Network (EPN) station SRJV in Bosnia and Herzegovina (B&H). Their impacts on the accuracy of GNSS positioning of the EPN station SRJV were examined by applying post-processing static PPP and network solutions using several software (the open-source and commercial). The study period was March 2015, when the strongest geomagnetic storm of solar cycle 24 (St. Patrick’s Day, March 17) and sudden intense snowfall (beginning of the month) occurred. Ionospheric TEC deviated for more than 20 TECU from the regular values during St. Patrick´s Day. Ionosphere-free combination in applied positioning techniques successfully eliminated most of the ionospheric terms. The highest deviations in Up component (to 7 cm) were observed during sudden snowfall characterised by changes in temperature, atmospheric pressure and humidity in the troposphere.

Key words: GNSS positioning, positional accuracy, ionosphere, total electron content (TEC), troposphere, weather condition, geomagnetic storm