godan verb (-ru)
get colder; become chilled
Describes a gradual intensification of cold, often used for weather or bodily sensation. The verb 募る adds a sense of something growing stronger.
夜が更けるにつれて冷え募ってきた。
As the night deepened, it got colder and colder.
冷え募る冬の朝、布団から出る
On a bitterly cold winter morning, it's hard to get out of bed.