There isn't a natural phenomenon that is specifically called "green winter". However, there are a few things that could fit the description depending on your interpretation:

* Evergreen trees: These trees retain their green needles throughout the year, even in winter. This could be considered a "green" aspect of winter.

* Moss and lichen: These organisms can thrive in cool, damp environments, even in winter. They can often be found covering rocks, trees, and other surfaces, giving a green appearance.

* Wintering birds: Some birds, like robins and cardinals, maintain their green plumage even in winter, bringing a splash of color to the landscape.

Ultimately, the term "green winter" is more of a poetic concept than a specific natural occurrence. It evokes a sense of life and color persisting even in the coldest season.