Although he had no formal training he was a keen amateur meteorologist and was chosen to man the Glen Coe Weather Station at the foot of Ben Nevis in 1895/6.In 1902 he was chosen to join the Scottish National Antarctic Expedition under William Spiers Bruce on board the Scotia alongside the geologist Dr Harvey Pirie. Mossman was asked to man a newly built weather station on Laurie Island on the South Orkneys, named Omond House after Robert Traill Omond. However, the British government declined to accept and maintain the station and it was instead passed to the government of Argentina. Three Argentine meteorologists were collected and delivered to serve under Mossman in February 1904. They remained under his charge until February 1905 when Mossman left them to run the station without him. He then joined the Argentine boat Uruguay going to the Gerlache Strait in Graham Land in search of Dr Charcot's ongoing expedition. After a three-year trip he briefly returned to Britain in 1905 before joining a further expedition, this time to the Arctic regions of Greenland