Flag of Govisümber Aimag, Mongolia.
Official blason: http://govisumber.gov.mn/?page_id=241

Size ratio 1:2
Bright green background
Divided into three equal parts
Middle part sky blue
In the blue field "Three mountains", "Sun", and "Moon"
Own work; Faithful reproduction of blason. color choice inspired by existing PD flags: http://govisumber.khural.mn/n/xiqon
User:Latebird