Can someone tell why Ullr is associated with Aurora borealis?  In which sources one can read this?
And also I’m interested in etymology of the name WUNJO.  They say it means “pasture,  meadow”.

Ullr is a norse god of winter, the legend is that as he skieed along the snow spray that flew up into the shky became the Aurora, the effect of ice crystals in the sky creates a  similar effect.
Wunjo has a very interesting history that

Thanks for your answer!
Is it a Norwegian legend?

Uller norwegian myth is true to the peace of winter snow and the
median example of the Norwedian setting to Alaska would known
as w0ld be the Norse mythology more likened to the Finnish myth
referring to the regard of Sif and the Uller on promise winter warm
will be forecast by the lights we see are the re-write on promise~n

the Aurora Borealis are the static effect of the modern science AUR
geo-magnetic layer of the festival of peace known to mythology @~
as the lite~ing of snow to be gin the blessing to warm the winter @!!
travel and sedentary accord with Fin Sifa Uller and will be the newer
Modern Accord.t with Germanic term Ja W0rld .,. [ Earth Peace ] #^

known to not be the term : JaWolt <ya-volt> nor Ulster as the forein    {[ Modern Science Mas0ner Volt.a aurora caster ]},
German war effort who wanted Earth Peace amidst tumult agress .,.     sorry for mentioning the German.s .  W0LD .  Evard