I looked out the window this morning and saw that the dawn had left its mark on the meadow – faint traces of ice coated the grasses and other low-lying vegetation under the power line – the season’s first frost.
Frost is deposition of water vapor directly into ice crystals on a cold surface. Frost typically forms on objects close to the ground, such as blades of grass. At night, a blade of grass loses energy by emitting radiation, but it absorbs energy emitted by surrounding objects. Under clear nighttime skies like we had last night, objects near the ground emit more radiation than they receive from the sky, and so a blade of grass cools due to the net energy loss. When temperatures hover near the freezing point and an object such as a blade of grass gets cold enough, frost will form on it.
Up on the hill above the garden, the frost had formed only on very low-lying objects – mainly the grass that I had recently mowed or objects lying on the grass such as a few feathers near the bird feeder station.
As I walked downhill the frost had reached higher and by the time I reached the low point of the power line meadow, it had touched vegetation up to 2 feet off the ground (tree saplings, tall grasses, etc.) probably due to the sinking and collecting of cold, humid air in these low pockets overnight.
Even the aptly-named Frost Aster flowers had a coating of crystals at the base of the hill, but not up near the garden. As the sun rose higher, the icy filigree began its retreat until it finally lingered in only the deepest shade in the valley, and even there, it would soon succumb and have to wait for another dawn to be reborn. I welcome the first frost as a sign of good things to come – campfires under a starry sky, the simple pleasure of heating with wood that you cut and split yourself, and the return of migrants from the far north. It is just the beginning, but the cold, crisp nights of winter are not far behind, and with them, a new set of adventures. On the next chilly morning, go outside and look at the handiwork of frost and you will be amazed at her delicate attention to detail as she paints the landscape.