In Samuel Taylor Coleridge’s 1798 poem, The Rime of the Ancient Mariner, the image of an ice-covered ship near the South Pole makes one shudder with cold.

The ice was here, the ice was there/The ice was all around.

But what exactly is rime, referred to in the title? Other than the ancient mariner with a “long, grey” ice-like beard, reciting an incredulous story to a wedding guest, and other than rime being a homophone with rhyme, I believe rime is predominantly weather related.

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It wasn’t long ago, on a very cold morning in January, that I came upon frost, sticking outward on tall, amber-colored stalks of Western wheat grass. At first I thought the spikes, like thorns, were part of the grass, but on a closer look I noticed they were of their own form; not part of the grass at all. Thin thorns sticking out, like spikes on a dog collar, made me wonder, what type of frost was that? 

Gary Ellrod, retired NOAA Meteorologist and current senior meteorologist at Weather Extreme, explained to me the basics. First, he detailed the difference between snow and frost. Primarily, snow comes out of the sky, while frost is formed at and near the ground. Snow is to raindrops as frost is to dew. 

RIME TIME: When moist air comes into contact with a below-freezing-temperature surface, rime frost forms. This occurs when areas of dense fog or low clouds are present.

The dew point is the temperature at which the air gets so cold that the water vapor in the atmosphere turns into liquid. When the temperature reaches the freezing point or below, the dew freezes into little bits of ice, arranged in the form of ice crystals, thus frost. Ellrod said that some people find it confusing when they learn of a temperature that is said to be above freezing, yet they still see frost on leaves, bushes, cars, or fences. Officially, he said, measurements are taken at 6 feet above the ground. Since warmer air rises and cold air sinks, the ground and what’s close to the ground will be colder than at the 6-foot mark.

There are many kinds of frost, but two stand out as the most predominant: hoar frost and rime frost.

Hoar frost or hoarfrost: Hoar frost forms on clear, cold nights, with a dew point below 32 degrees. The droplets in gas form transition directly from a gas to a solid — deposition. Hoar frost tends to have a feathery appearance. The word hoar is an Old English word from hoary, meaning grey- or white-haired.  

Rime frost or rime ice: Rime frost forms in areas of dense fog (or low clouds). When the moist air comes into contact with a surface, it freezes on contact because of the temperatures being below freezing. Another explanation: Water droplets in freezing fog change from liquid to a solid. Rime frost can look like solid ice, as it can build up over time as long as the foggy and cold conditions continue. This is referred to as hard rime. Yes, as in The Rime of the Ancient Mariner. With a calm wind, rime can also appear feathery or needle-like, referred to as soft rime. Collins English Dictionary attributes the origin of the word rime to “Old English hrīm; related to Dutch rijm, Middle High German rīmeln, to coat with frost.”

Hoar frost and rime frost can easily resemble one another, making it difficult to determine which is which. Sometimes they both have a needle-like structure. The difference points to how the frost is developed. Once again, hoar frost is formed directly from water vapor already in the air. Rime frost builds from low cloud or foggy conditions.

DOUBLE TAKE: The two main types of frost — hoar frost and rime frost — often can resemble one another, making it difficult to tell them apart. The key is to know how the frost was developed.

In the West, frost is also known as pogonip, from the Shoshone word payinappih, with a variety of interpretations pointing to “cloud.”  

Of course, science being science, types of frost don’t end with these two. Some of the others are ice-ferns, fern-like ice structures on a window; and the more uncommon frost-flowers, puffy, cloud-like formations like delicate white flowers consisting of long, curling filaments. 

It all goes back to what we learned in our early days about the water cycle: Water vapor in the air, stemming from the evaporation of bodies of water and waterways, cools and condenses into clouds (condensation) and returns to the ground (precipitation) as rain, hail, sleet, and snow. The age-old adage is at play: Evaporation. Condensation. Precipitation. Collection. (Precipitation is collected in oceans, rivers, lakes, and streams.) 

In the case of frost, dew transitions to some of the most beautiful icy art forms: lacy ice, feathery ice, spikes of ice, ice upon ice, ice like diamonds. That day I took photos of the spikes on the wheat grass, I marveled at how things in nature can change so quickly. The day before, there was no such frost; no ice needles seemingly created with brushstrokes of thin, clear crystals. The day before, there was no such fairy-tale forest of frost. 

Author

  • Eve Quesnel

    Eve Quesnel has lived in Truckee for 35 years with her husband Bill, once-upon-a-time daughter Kim-now on her own-and many dogs through the years, currently a Border Collie-Aussi mix. Her favorite pastimes include walking in her neighborhood and nearby woods, hiking in the high Sierra, and reading and writing. Quesnel is now retired from teaching English at Sierra College in Truckee but continues to pursue several writing projects. She is intrigued by the natural world of which she explores and writes about for the column "Nature's Corner" in Moonshine Ink.

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