二十四節(jié)氣之“霜降（frost fall）”

　　霜降二十四節(jié)氣之一，十月中旬以后天氣漸冷，開(kāi)始有霜.霜降一般是在每年公歷的10月23日左右，當(dāng)太陽(yáng)到達(dá)黃經(jīng)210度時(shí)為二十四節(jié)氣中的霜降.霜降時(shí)節(jié)已是深秋，霜降節(jié)氣也是秋季最后一個(gè)節(jié)氣，是在秋季與立冬之間，深秋的夜晚地面的溫度很低，甚至可以低于零度，大氣中的水蒸氣在地面或植物上在夜里低溫的作用下，直接可以凝結(jié)形成細(xì)微的冰針，有的呈現(xiàn)六角形的霜花形狀，色白且結(jié)構(gòu)疏松.

　　《月令七十二候集解》關(guān)于霜降說(shuō)：九月中，氣肅而凝，露結(jié)為霜矣.“霜降”表示天氣逐漸變冷，露水凝結(jié)成霜.我國(guó)古代將霜降分為三候：一候豺乃祭獸；二候草木黃落.三候蜇蟲(chóng)咸俯.豺狼開(kāi)始捕獲獵物，祭獸，以獸而祭天報(bào)本也，方鋪而祭秋金之義.大地上的樹(shù)葉枯黃掉落.蜇蟲(chóng)也全在洞中不動(dòng)不食，垂下頭來(lái)進(jìn)入冬眠狀態(tài)中.

　　古籍《二十四節(jié)氣解》中說(shuō)：“氣肅而霜降，陰始凝也.“可見(jiàn)“霜降“表示天氣逐漸變冷，開(kāi)始降霜.氣象學(xué)上，一般把秋季出現(xiàn)的第一次霜叫做“早霜“或“初霜“，而把春季出現(xiàn)的最后一次霜稱(chēng)為“晚霜“或“終霜.“從終霜到初霜的間隔時(shí)期，就是無(wú)霜期.也有把早霜叫“菊花霜“的，因?yàn)榇藭r(shí)菊花盛開(kāi)，北宋大文學(xué)家蘇軾有詩(shī)曰：“千樹(shù)掃作一番黃，只有芙蓉獨(dú)自芳“.

　　霜是水氣凝成的，水氣怎樣凝成霜呢？南宋詩(shī)人呂本中在《南歌子·旅思》中寫(xiě)道：“驛內(nèi)侵斜月，溪橋度晚霜.“陸游在《霜月》中寫(xiě)有“枯草霜花白，寒窗月新影.“說(shuō)明寒霜出現(xiàn)于秋天晴朗的月夜.秋晚沒(méi)有云彩，地面上如同揭了被，散熱很多，溫度驟然下降到0℃以下，靠地面不多的水汽就會(huì)凝結(jié)在溪邊、橋間、樹(shù)葉和泥土上，形成細(xì)微的冰針，有的成為六角形的霜花.霜，只能在晴天形成，人說(shuō)“濃霜猛太陽(yáng)“就是這個(gè)道理.

　　由于凍則有霜(有時(shí)沒(méi)有霜稱(chēng)黑霜)，所以把秋霜和春霜統(tǒng)稱(chēng)霜凍.

　　霜降節(jié)氣含有天氣漸冷、開(kāi)始降霜的意思.緯度偏南的南方地區(qū)，平均氣溫多在16℃左右，離初霜日期還有三個(gè)節(jié)氣.在華南南部河谷地帶，則要到隆冬時(shí)節(jié)，才能見(jiàn)霜.當(dāng)然，即使在緯度相同的地方，由于海拔高度和地形不同，貼地層空氣的溫度和濕度有差異，初霜期和霜日數(shù)也就不一樣了.霜降時(shí)節(jié)，涼爽的秋風(fēng)已吹到花城廣州.東北北部、內(nèi)蒙東部和西北大部平均氣溫已在0℃以下.

　　在中國(guó)不同的地區(qū)，氣候差異巨大，“霜降始霜“反映的是黃河流域的氣候特征.就全年霜日而言，青藏高原上的一些地方哪怕是在夏季也常有霜雪，年霜日超過(guò)了200天，是我國(guó)霜日最多的地方.XZ東部、青海南部、祁連山區(qū)、川西高原、滇西北、天山、阿爾泰山區(qū)、北疆西部山區(qū)、東北及內(nèi)蒙東部等地年霜日都超過(guò)100天，淮河、漢水以南、青藏高原東坡以東的廣大地區(qū)均在50天以下，北緯25°以南和四川盆地地區(qū)每年的年霜日是10天左右，福州以南及兩廣沿海平均年霜日不到1天，而西雙版納、海南和臺(tái)灣南部及南海諸島低緯度地區(qū)則是沒(méi)有霜降的地方.

　　深秋的初霜對(duì)農(nóng)業(yè)生產(chǎn)至關(guān)重要，初霜愈早對(duì)作物危害愈大.我國(guó)各地的初霜是自北向南、自高山向平原逐漸推遲的.除全年有霜的地區(qū)外，最早見(jiàn)霜的是大興安嶺北部，一般8月底便可見(jiàn)霜.東北大部、內(nèi)蒙和北疆初霜多在9月份.10月初，寒霜已出現(xiàn)在沈陽(yáng)、承德、榆林、昌都至LS一線.11月初山東半島、鄭州、西安到滇西北也已可見(jiàn)霜.我國(guó)東部北緯30°左右、漢水、YN省北緯2°左右的地區(qū)要到12月初才出現(xiàn)霜降現(xiàn)象.而廈門(mén)、廣州到百色、思茅一帶見(jiàn)霜時(shí)，已是新年過(guò)后的1月上旬了.

　　霜是地面的水氣遇到寒冷天氣凝結(jié)成的，所以霜降不是降霜，而是表示天氣寒冷，大地將產(chǎn)生初霜的現(xiàn)象.用科學(xué)的眼光來(lái)看，霜降與冰露是兩回事，冰露是堅(jiān)硬的小冰珠.而霜凍是指由于溫度劇降而引起的作物凍害現(xiàn)象，其致害溫度因作物、品種和生育期的不同而異.而形成霜，則必須地面或地物的溫度降到0℃以下，地表的氣體中水汽含量要達(dá)到某些標(biāo)準(zhǔn)，一朝有霜晴不久，三朝有霜天晴久程度.因此，發(fā)生霜凍時(shí)不一定出現(xiàn)霜，出現(xiàn)霜時(shí)也不一定就有霜凍發(fā)生.但是，因?yàn)橐?jiàn)霜時(shí)的溫度已經(jīng)比較低，要是繼續(xù)冷卻，便很容易導(dǎo)致霜凍的發(fā)生.

　　“霜降殺百草“，嚴(yán)霜打過(guò)的植物，一點(diǎn)生機(jī)也沒(méi)有.這是由于植株體內(nèi)的液體，因霜凍結(jié)成冰晶，蛋白質(zhì)沉淀，細(xì)胞內(nèi)的水分外滲，使原生質(zhì)嚴(yán)重脫水而變質(zhì).“風(fēng)刀霜?jiǎng)?yán)相逼“說(shuō)明霜是無(wú)情的、殘酷的.其實(shí)，霜和霜凍雖形影相連，但危害莊稼的是“凍“不是“霜“。有人曾經(jīng)試驗(yàn)：把植物的兩片葉子，分別放在同樣低溫的箱里，其中一片葉子蓋滿了霜，另一片葉子沒(méi)有蓋霜，結(jié)果無(wú)霜的葉子受害極重，而蓋霜的葉子只有輕微的霜害痕跡。這說(shuō)明霜不但危害不了莊稼，相反，水汽凝華時(shí)，還可放出大量熱來(lái)，1克0℃的水蒸汽凝華成水，放出氣化熱是667卡，它會(huì)使重霜變輕霜、輕霜變露水，免除凍害.眾人認(rèn)為的“霜降殺百草“，實(shí)質(zhì)是“霜凍殺百草“，霜是天冷的表現(xiàn)，凍是殺害莊稼的敵人.由于凍則有霜(有時(shí)沒(méi)有霜稱(chēng)黑霜)，所以把秋霜和春霜統(tǒng)稱(chēng)霜凍.霜降的諺語(yǔ)關(guān)于霜降節(jié)氣農(nóng)諺

　　千樹(shù)掃作一番黃，只有芙蓉獨(dú)自芳

　　夏雨少，秋霜早。夏雨淋透，霜期退后.

　　秋雨透地，降霜來(lái)遲.

　　秋雁來(lái)得早，霜也來(lái)得早.

　　風(fēng)大夜無(wú)露，陰天夜無(wú)霜.

　　今夜霜露重，明早太陽(yáng)紅.

　　霜重見(jiàn)晴天

　　嚴(yán)霜出毒日，霧露是好天。

　　濃霜毒日頭.

　　霜后暖，雪后寒.

　　一夜孤霜，來(lái)年有荒;多夜霜足，來(lái)年豐收。

　　霜降降霜始(早霜)，來(lái)年谷雨止(晚霜)

　　“Frost fall“ of the twenty-four solar terms

　　Frost is one of the twenty-four solar terms. After mid-October， the weather gets colder and frost begins. Frost usually falls around October 23 in the Gregorian calendar every year. When the sun reaches 210 degrees of the yellow longitude， it is the frost in the twenty-four solar terms. The frost season is already late autumn， and the frost solar term is also the last solar term in autumn. It is between autumn and the beginning of winter. The temperature of the ground in late autumn nights is very low， even below zero. The water vapor in the atmosphere cools down on the ground or plants at night. Under the action of ice， it can condense directly to form fine ice needles， some of which are in the shape of hexagonal frost flowers， white in color and loose in structure.

　　“The Collection of Seventy-two Hours of the Moon Order“ said about the frost: in mid-September， the air is solemn and condensed， and the dew turns into frost.“Frost“ means that the weather is getting colder and the dew condenses into frost. In ancient my country， the frost was divided into three parts Hou: The first time jackals are sacrificed to beasts; the second time is when the grass and trees turn yellow and fall. The third time is when the stinging insects are salty. The jackals start to capture prey and sacrifice to the beasts. The withered yellow falls. The stinging insects are all motionless in the hole and do not eat， and hang their heads to enter the hibernation state.

　　The ancient book “An Explanation of the Twenty-Four Solar Terms“ said:“The air is sombre and the frost falls， and the yin begins to condense.“ It can be seen that “frost“ means that the weather is getting colder and frost begins. In meteorology， the first frost that appears in autumn is generally called “Early frost“ or “first frost“， and the last frost that appears in spring is called “l(fā)ate frost“ or “l(fā)ast frost.“ Because the chrysanthemums are in full bloom at this time， Su Shi， a great writer in the Northern Song Dynasty， wrote a poem:“Thousands of trees are swept away to turn yellow， only hibiscus blooms alone“.

　　Frost is condensed by water vapor， how does water vapor condense into frost? Lu Benzhong， a poet of the Southern Song Dynasty， wrote in “Nangezi Travel Thoughts“:“The slanting moon invades the station， and the creek and bridge spend the night frost.“ Lu You wrote in “Frost Moon“ that “the withered grass is frosty and white， and the moon is new in the cold window.“ Explaining the frost Appears on a clear moonlit night in autumn. There are no clouds in the autumn night， and the ground is like a quilt， with a lot of heat dissipation， the temperature suddenly drops below 0°C， and the little water vapor near the ground will condense on the streams， bridges， leaves and soil ， form fine ice needles， and some become hexagonal frost flowers. Frost can only be formed on sunny days， which is why people say “thick frost and fierce sun“.

　　Because there is frost in frost (sometimes there is no frost called black frost)， so autumn frost and spring frost are collectively called frost.

　　Frost’s solar term means that the weather is getting colder and frost is beginning to fall. In the southern regions with a southerly latitude， the average temperature is mostly around 16°C， and there are three solar terms before the date of the first frost. Frost. Of course， even in places with the same latitude， due to the difference in altitude and terrain， the temperature and humidity of the air attached to the stratum are different， and the first frost period and the number of frost days are also different. During the frost season， the cool autumn wind has blown to the flower city of Guangzhou .The average temperature in the northern part of Northeast China， eastern Inner Mongolia and most parts of Northwest China is already below 0°C.

　　In different regions of China， the climate varies greatly.“Frost's first frost“ reflects the climate characteristics of the Yellow River Basin. In terms of annual frost days， some places on the Qinghai-Tibet Plateau often have frost and snow even in summer.