Yanvar means, simply, January. I’m assuming this name was given in reference to Bloody Sunday, 22 January 1905 (9 January Old Style), when the Imperial Guard massacred an unarmed crowd of demonstrators trying to petition the Tsar for better working conditions. It was a huge shock to them when their demonstration was treated like a horrible crime, though the Tsar himself wasn’t around and didn’t give the order to fire. The tide against Tsarism irrevocably turned after these tragic events.
Yunnata means “young naturalist,” derived from the elements yunaya naturalistka. Natural history, biology, and naturalism were very popular in the Soviet era, in keeping with the promotion of scientific research and discovery.
Sources consulted:
http://panzercentral.com/forum/viewtopic.php?f=96&t=36301 (penultimate post)
http://www.namenerds.com/uucn/listofweek/soviet.html
http://horo.mail.ru/namesecret/
http://www.devichnik.ru/9810/imia.html (male)
Onomastics Outside the Box 