| East Asian rainy season | |||||||||||||||||||||||||
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 Plum rain falling on two clear umbrellas, looking up toward the Tokyo Metropolitan Government Building, in June 2009 | |||||||||||||||||||||||||
| Chinese name | |||||||||||||||||||||||||
| Chinese | 梅雨 | ||||||||||||||||||||||||
| Literal meaning | plum rain | ||||||||||||||||||||||||
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| Korean name | |||||||||||||||||||||||||
| Hangul | 장마 | ||||||||||||||||||||||||
| Hanja | 長마 | ||||||||||||||||||||||||
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| Japanese name | |||||||||||||||||||||||||
| Kanji | 梅雨 | ||||||||||||||||||||||||
| Kana | つゆ / ばいう | ||||||||||||||||||||||||
| Hiragana | つゆ / ばいう | ||||||||||||||||||||||||
| Katakana | ツユ / バイウ | ||||||||||||||||||||||||
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| Russian name | |||||||||||||||||||||||||
| Russian | Восточно-азиатский сезон дождей | ||||||||||||||||||||||||
TheEast Asian rainy season, also called theplum rain, is caused byprecipitation along a persistentstationary front known as theMeiyu front for nearly two months during the late spring and early summer inEast Asia betweenChina,Taiwan,Korea andJapan. Thewet season ends during the summer when thesubtropical ridge becomes strong enough to push this front north of the region. These weather systems can produce heavy rainfall and flooding.
In China, the term "plum rain" (梅雨;meiyu) refers to the rainfall during the fourth and fifth lunar months.[1][2] It originates from the traditional belief that whenplums ripen and begin to fall in the regions south of the Yangtze River during this period, moisture evaporating from the plants transforms into rain.[2]
The term appears in the following poem, dated to 760, byDu Fu:
梅雨
南京犀浦道，四月熟黃梅。
湛湛長江去，冥冥細雨來。
茅茨疏易溼，雲霧密難開。
竟日蛟龍喜，盤渦與岸迴。Plum rain
On the Xipu road from the Southern Capital[a] the fourth month ripens the yellow p[r]unus.
Thelong river goes off surging, and, darkening, a fine rain comes.
Roof-thatch, loosely bound, is easily soaked, clouds and fog are dense and will not lift.
All day long the dragons delight, whirlpools turning with the bank.[1]
In Japanese, the rainy season is called by the native termtsuyu (梅雨); the spelling is borrowed from the Chinese term, and is an example ofjukujikun (a kanji compound whose components are selected for meaning and do not individually represent a sound).
The season is instead commonly calledJangma (장마) in Korea, which means "long rain". The term was originally spelledDyangmah (댱맣) in 1500s, which was the mix of thehanja character 長 ("long") and the old native Korean word 맣 (mah, "rain"). The word Dyangmah eventually transformed fromJyangma (쟝마) in 1700s to the current form ofJangma after the 1900s.[3]
An east–west zone of disturbed weather during spring along this front stretches from the east China coast, initially across Taiwan and Okinawa, later, when it has shifted to the north, eastward into the southern peninsula of South Korea and Japan.[4] In Taiwan andOkinawa, the rainy season usually lasts from May to June.[5] In RussianPrimorsky Krai, Japan, and Korea, it lasts from June to July (approximately 50 days). In eastern China (especially theYangtze andHuai River regions), it lasts from mid June to early July.
The weather front forms when the moist air over the Pacific meets the cooler continentalair mass. The front and the formation offrontal depressions along it brings precipitation to Primorsky Krai, Japan, Korea, eastern China, and Taiwan. As the front moves back and forth depending on the strength of cool and warm air masses, there is often prolonged precipitation and sometimes flooding in easternChina. However, in the years that it does not rain as much as usual, a drought might result. The rainy season ends when the warm air mass associated with the subtropical ridge is strong enough to push the front north and away.[citation needed]
The highhumidity in the air during this season encourages the formation ofmold androt not only on food but on fabrics as well.Environmentally, heavy rains encouragemudslides and flooding in all areas affected. The most rain in a one-hour period as recorded in Japan was inNagasaki in 1982 with 153 millimetres (6.0 in). The highest overall recorded rainfall during the rainy season in Japan was in 2003 whenMiyazaki Prefecture recorded rains of 8,670 millimetres (341 in).[citation needed]
In Japan, the rainy season is calledtsuyu (梅雨), and lasts from early June to mid-July in most of the country (Honshu,Kyushu andShikoku), approximately June 7 to July 20 in theKansai andKantō regions in Honshū.[6] Thetsuyu season is roughly a month earlier (early May through mid-June) inOkinawa (the southernmost region of the country). There is no pronouncedtsuyu season inHokkaidō (the northernmost region of the country) because thetsuyu front usually attenuates before it reaches the region so that it cannot produce the abundant rainfall.Tsuyu is also known asSamidare (五月雨, literally "the fifth-month rain (in theJapanese traditional calendar)", roughly corresponding to June in the modern calendar). The pop artistEiichi Ohtaki produced a popular song by this name, and aSecond World WarJapanese naval ship was also given this name.[citation needed]
The rainy season is between June and mid-July. It is caused by hot and humid high pressure forming in theSea of Okhotsk due to the North Pacific anticyclone combining with Asiatic continental high pressure. When the two meteorological events meet they form a longjangmajeonseon (Korean: 장마전선, from장마;lit. rainy season and전선;前線;lit. weather front). Beginning in late May, the North Pacific high pressure forces the weaker continental anticyclone south ofOkinawa Island. This fall to the south then reverses and gradually strengthens as it moves northwards back towards the Korean peninsula. On landfall, heavy monsoon rains lead to torrential downpours and flooding. By August the system has weakened as the southern systems retreat towards the Philippine archipelago.[citation needed]
By early autumn, the North Pacific high-pressure system is pushed away as Asiatic continental cold high pressure moves southwards. This produces inclement weather although not on the scale of the summer monsoons. Korea can, however, be struck by typhoons during this period.[citation needed]
In some years, the rainy season's actual beginning and end are under debate. For example, in 2005, the subtropical ridge moved quickly northward in late June/early July. The weather front skipped theYangtze region and there was no rainy season there. Then, the ridge retreated southward and there was significant rainfall in the region. This gave rise to the question of whether this was the summer-type rainfall pattern that is common after the first rainy season or the second rainy season. Somemeteorologists even argued that the rainy period in late June was not a true rainy season.[7][8][9][10][11]
, Volume 2. De Gruyter Mouton. Pages 298–299.ISBN 978-1-5015-0189-0
