Within the framework of the European Space Agency (ESA) SILEX project, aimed at experimentally demonstrating the feasibility of inter-satellite optical communications links, an Optical Ground Station (OGS) has been built by ESA in the premises of the Instituto de Astrofisica de Canarias (IAC, Institute of Astrophysics of the Canary Islands) Observatory of Teide, in the Tenerife island. The OGS is designed to test the optical communications payload on board the ESA's Artemis satellite and to perform ground-satellite optical communications experiments. As part of the OGS design study, an assessment of the impact of the atmosphere on the ground- satellite links was carried out. This assessment included experimental characterizations of the atmospheric effects through both measurements from stars in positions close to the Artemis one in bands comprising the SILEX wavelengths, using the IAC's Mons telescope in the Observatory of Teide, and measurements on a horizontal link with a transmitter near the IAC's Roque de los Muchachos Observatory in La Palma island, based on a laser diode similar to those to be used in SILEX, and a receiver in the Teide Observatory, almost 150 km apart, in the Tenerife island. The 830-nm wavelength horizontal measurements allowed checking the variations in the behavior of the atmospheric turbulence through the diurnal cycle. Besides the information relevant to assess the OGS performance, the horizontal-propagation experiments allowed to gather a considerable amount of propagation data on a very long path, most of it 2400 m above the sea.