當(dāng)冬天來臨，我們最盼望的是快點下一場雪！但冬天比你想象的要繽紛多彩。除了皚皚白雪，我們還可以欣賞“雨凇”、“霜花”、“霧凇”……你見過這些自然氣象嗎？你知道它們的英文表達嗎？

HOAR FROST
白霜

One of the first signs of winter is the hoar frost of late autumn. Deriving its name from an Old English word (hoar, meaning “to appear old”), this is the thin, feathery coating of ice that often forms on objects during cool nights with clear skies. The clear skies allow the ground to lose heat more quickly than the surrounding air, and the humidity in the atmosphere condenses and freezes into a solid when it makes contact with surfaces. This frost can occur even when the air a few feet above ground is well above freezing, and usually melts within an hour or two of sunrise.
深秋的白霜（hoar frost）是預(yù)示冬天到來的最早預(yù)告。它的英文名來源于一個“古老”的英語單詞（hoar，意思是“顯得古老”）。白霜是一層薄薄的羽毛狀冰層，通常在晴朗的寒夜凝結(jié)于物體表面。晴天使地面溫度比周圍空氣的溫度下降更快，大氣中的濕氣在與地面接觸時凝結(jié)成固體。即使地面上幾英尺的空氣遠高于冰點，也會形成這種冰霜，并且通常在日出后一兩個小時內(nèi)融化。

FROST FLOWER
霜花

Frost flowers (and the related “ice ribbons” and “ice beards”) are very thin, spindly, unique formations of ice, seen in late autumn or early winter, when plants are first freezing.
霜花（以及相關(guān)的“冰帶”和“冰須”）是一種薄而細長、非常獨特的冰結(jié)構(gòu)，見于深秋或初冬，植物第一次結(jié)冰時。

When the water in the plant stem freezes, it expands to the point where the plant splits open along the side, and the frozen water is extruded from the split. More water is then drawn up through the stem from the ground via capillary action, adding more ice crystals to the frost flower.
當(dāng)植物莖稈中的水凝結(jié)時，會涌到莖稈裂開的地方，凍結(jié)的水從裂口中溢出。由于毛細作用，植物的莖從地面吸收更多水分，從而結(jié)出更多冰晶的霜花。

GLAZE ICE
雨凇

When falling precipitation hits a surface that’s below freezing, it can instantly form what’s known as “glaze ice,” a buildup of smooth, clear, and transparent ice. It can be seen coating tree branches and plants following an ice storm.
當(dāng)雨點落在溫度在冰點以下的表面時，會立即形成所謂的“雨凇”，即光滑、透明的冰層。雨雪過后，可見雨凇覆蓋在樹枝和植物上。

HARD RIME
硬霧淞

As the weather cools, freezing fogs can occur, and when that fog is combined with wind, hard rime can form on windward (wind-facing) surfaces. “Rime” literally means “hoar frost,” and while slightly different on a meteorological level, “soft rime” is very similar to a thick hoarfrost. Hard rime, on the other hand, is much thicker and harder, and consists of fairly dense pellets of irregular ice crystals glommed together.
隨著天氣變冷，可能會出現(xiàn)凍霧，當(dāng)凍霧與風(fēng)結(jié)合時，物體迎風(fēng)面會形成硬霧?。╤ard rime）。Rime字面意思是“白霜”，軟霧凇與厚厚的白霜非常相似，但在氣象層面上略有不同。此外，硬霧凇要更厚更硬，由高密度的不規(guī)則冰晶團聚合在一起形成。

THUNDERSNOW
雷雪

The conditions required to create thundersnow are most common around lakes (it occasionally accompanies lake-effect snow) and coastal areas. In these places, the sun is able to heat the ground and cause relatively warm and humid columns of unstable air to rise up and form turbulent clouds.
在湖泊周圍（偶爾出現(xiàn)湖泊效應(yīng)降雪）和沿海地區(qū)最常出現(xiàn)滿足雷雪天氣的氣候條件。在這些地方，陽光讓地面溫度上升，導(dǎo)致相對溫暖潮濕的不穩(wěn)定空氣柱上升，形成湍流云。

But clouds alone don’t make thundersnow. Only if the layer of air between the clouds and the ground is warmer than the cloud cover, but still cold enough to create snow, and the wind shear is pushing the warmer air slightly upwards, does thundersnow form.
但光有云層并不能產(chǎn)生雷雪。只有當(dāng)云層和地面之間的空氣層比云層溫度高，但仍冷到足以形成降雪，并且風(fēng)向切變將溫暖的空氣稍微向上推時，才會形成雷雪。

The snow can often muffle the thunderclap, meaning that many instances of thundersnow probably go unnoticed.
雪通常會掩蓋雷聲，這意味著許多時候可能聽不到雷聲。

SNOWPACK
積雪

When a place has an extended cold season, snow rarely melts between each subsequent snowfall. Some of it will sublimate—or transition directly from a solid to a gas—especially in areas with lots of sunlight and dry wind, but the majority of it will stay present on the ground. When fresh snow falls on top of the old snow, the crystals of the old snow get packed down under the weight of the new cover. Depending on the length of time, snowflake types, and weather conditions between snowfalls, each layer of the snowpack may have a different thickness and density.
在寒冷季節(jié)漫長的地區(qū)， 每場雪下完之后都不會融化。其中一些雪會升華（直接從固體轉(zhuǎn)變?yōu)闅怏w），特別是在陽光充足和風(fēng)干燥的地區(qū)，但大部分雪會留在地面上。當(dāng)新雪落在舊雪上面，舊雪的晶體會被新雪覆蓋的重量壓下來。根據(jù)每次降雪間隔的時間長度、雪花類型和天氣條件，每層積雪可能具有不同的厚度和密度。

FIRN
粒雪

When years and years of snowpack accumulate, that buildup is called “firn.” It’s much denser than regular snowpack, because of two factors: the partial melting during warmer seasons packs the snow mass closer together; and the new snow falling on top of the ultra-condensed pack pushes the crystals together without melting during the cold season.
當(dāng)積雪一年又一年堆積起來，就形成了“粒雪”。粒雪比普通積雪密度大得多，這是兩個因素導(dǎo)致的：在溫暖的季節(jié)，一部分雪融化使積雪堆積得更緊密；在寒冷的季節(jié)，新雪落在密實的積雪頂部，將晶體推到一起而不融化。

The buildup of firn at high elevations eventually forms glaciers, and replenishes glacial mass to counteract the melting and calving at their lower elevations. The density of firn is between 550830 kilograms per square meter. To put that in perspective, the density of freshly-fallen “powder” snow is around 50 to 70 kilograms per square meter.
高海拔地區(qū)的積雪最終形成冰川，并補充冰川物質(zhì)，以抵消低海拔地區(qū)冰川的融化和崩解。粒雪的密度在每平方米550830公斤之間。這是什么概念呢？剛落下的“粉末”雪的密度約為每平方米50至70公斤。

來源：Mental Floss
編輯：董靜