Atmospheric pressure distribution - Atmospheric pressure distribution
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This refers to the state of atmospheric pressure distribution. This term is usually used for surface weather charts, but it can also be referred to as the atmospheric pressure distribution in the upper atmosphere. Each season has a type of atmospheric pressure pattern that is likely to occur, and the weather and climate characteristics of that season can often be explained by this. Also, when atmospheric pressure patterns that are characteristic of other seasons occur in one season, it causes unseasonable weather. For the characteristic atmospheric pressure patterns that occur around Japan, refer to the model diagram ( ). When looking at the atmospheric pressure patterns on an actual weather chart, it is important to grasp the characteristics macroscopically without getting caught up in the details. Also, atmospheric pressure patterns need to be understood not simply as the shape of isobars, but in relation to the movements of air masses and weather changes that they cause. Based on this concept, atmospheric pressure patterns are called weather chart types. [Atsushi Kurashima and Takashi Aoki] High in the west and low in the eastThere is high pressure towards the continent to the west of Japan and low pressure in the Pacific Ocean to the east, and the isobars around Japan form vertical stripes. This is a typical winter pressure pattern, with cold air masses from the continent blowing as northwesterly monsoons across the Japanese archipelago, bringing snow and rain to areas on the Sea of Japan side and sunny weather to areas on the Pacific side. It often appears in winter, lasting for about 3-7 days and sometimes bringing about strong cold waves. When this pattern appears in autumn, it is called "kogashi" (a cold wind that blows in the fall) and "kanashi ga fu" (a cold return) in spring, but neither pattern lasts long, and the strong north winds often die down within half a day or a day. [Atsushi Kurashima and Takashi Aoki] South coast low pressure type (East China Sea low pressure type)This type of low pressure develops in the East China Sea area and moves northeastward while developing in the waters south of Japan. It appears throughout the year, and when it approaches the southern coast, it brings precipitation mainly to areas on the Pacific coast, but when it passes away, the precipitation area does not reach land. When this type appears in spring in particular, it brings rain and snow to areas on the Pacific coast that have been dry and sunny during the winter due to a high pressure area in the west and a low pressure area in the east. As the low pressure often occurs near Taiwan, in the past this type of low pressure was called the Taiwan Bozu, but in recent years it is often called the Taiwan Low or the East China Sea Low. [Atsushi Kurashima and Takashi Aoki] Sea of Japan low pressureThis type of low pressure develops over the Sea of Japan and moves northeastward. It appears throughout the year, but is most common in spring. The warm southerly air currents that blow into this low pressure become southerly winds such as the "first spring wind" and blow across the Japanese archipelago. When this type of wind blows, it is prone to the föhn phenomenon in areas along the Sea of Japan, and avalanches and snowmelt floods in areas with heavy snowfall. Before the cold front stretching southwest from the low pressure passes, the warm southerly winds become particularly strong, and once it passes, northerly winds blow and the temperature drops sharply. Spring thunder, tornadoes, gusts of wind, and localized heavy rain are likely to occur near the front, as well as sandstorms, fires, and marine accidents. When two low pressure systems pass simultaneously along the Sea of Japan and the southern coast or over Honshu, this type is called the "two-ball low pressure system" and brings bad weather. Furthermore, when the south coast low pressure system, the Sea of Japan low pressure system, and the Futatsudama low pressure system move over the ocean east of Japan, they will form a western high pressure system with an eastern low pressure system, which will cause a "return of cold weather" in spring and a "cold wind" in autumn. [Atsushi Kurashima and Takashi Aoki] Mobile high pressure systemThis type of high pressure moves regularly in a fairly constant direction from west to east. It often appears in spring and autumn, and because there is a low-pressure trough between the preceding high pressure system, it changes periodically every 3 to 4 days. [Atsushi Kurashima and Takashi Aoki] High pressure zone or zonal high pressureA type in which several mobile high pressure systems line up almost east to west, without any strong low pressure systems or troughs between them, and move slowly eastward. This is a typical pressure distribution in late spring, early summer, and autumn, and clear skies continue within the high pressure zone. The high pressure zone can stretch from northwest to southeast or southwest to northeast, and in extreme cases, a high pressure zone can stretch north to south. There is often a front on the southern edge of the high pressure zone that stretches east to west. In May, when the mainland is covered in clear early summer skies caused by the high pressure zone, Okinawa and the Ogasawara Islands enter the rainy season due to this front. Generally, when a high pressure zone moves northward and passes, the weather in the areas on its southern edge becomes unsettled. [Atsushi Kurashima and Takashi Aoki] Rainy season typeThe rainy season front between the high pressure system over the Sea of Okhotsk, the northern Sea of Japan, and the sea south of Kamchatka (the so-called Okhotsk Sea high pressure system) and the subtropical high pressure system over the far southeast of Japan (the so-called Ogasawara high pressure system and Pacific high pressure system) extends almost east-west along the southern coast of Japan and stagnates. There are also cases where the Okhotsk Sea high pressure system does not exist and there is only a rainy season front. The standard weather distribution is rain up to about 300 km north of the rainy season front, cloudy with occasional rain 300 to 500 km, cloudy 500 to 800 km, clear skies further north, and strong convective rain in places 100 to 200 km south of the rainy season front, but there are many exceptions. In the late rainy season, the subtropical high pressure system strengthens and spreads to the southern coast of Japan, and the rainy season front is over Japan, often bringing heavy rain to various places. [Atsushi Kurashima and Takashi Aoki] Midsummer typeThe rainy season front moves north from Sakhalin to Primorsky Krai, and the subtropical high pressure system in the Pacific Ocean covers Japan. If the Pacific high pressure system is likened to the lower half of a whale's body, the bulge over Western Japan is the tail, so this type is called the "whale tail type." Above this tail, there is an upper-level high pressure system with an independent center, which is connected to the Tibetan high pressure system. This type is persistent, and within the high pressure area, the scorching heat of midsummer continues, making it prone to drought. The southerly air currents that blow into the continent from the Pacific high pressure system are the southeasterly monsoon in summer, as opposed to the northwesterly monsoon in winter. The intratropical convergence zone is drawn from the southern China to Taiwan area, which is the where the northeasterly trade winds and the tropical southwesterly monsoon converge, and typhoons often occur here as "tropical cyclones." [Atsushi Kurashima and Takashi Aoki] Typhoon typeIn autumn, the midsummer Pacific high pressure system retreats to the southeast, while the continental high pressure system develops to the northwest, and Japan finds itself in the valley between the summer and autumn high pressure systems. Typhoons then move north through this valley. During the summer, the ocean surface in the Southern Ocean region absorbs a large amount of solar energy, and areas with high sea temperatures spread northward. In addition, autumn typhoons occur at relatively low latitudes compared to summer and travel widely around warm tropical waters, making them more likely to develop and become large. [Atsushi Kurashima and Takashi Aoki] Northward shift of continental high pressureA continental high pressure system moves northward and stretches out near Japan, and the front between this system and the Pacific high pressure system stretches from east-northeast to west-southwest along the southern coast of Japan, remaining stationary, with a low pressure system moving east-northeast above it. When this front appears between mid-September and mid-October, it is called the autumn rain front, and brings long autumn rains (autumn rains) similar to the rainy season to the southern coast of Japan. In addition, if a typhoon approaches this front, or if moist air from the south flows into the temperate low pressure system on the front, it is likely to become an autumn rain front heavy rain. [Atsushi Kurashima and Takashi Aoki] Southerly shifting continental highWhen the continental high pressure system shifts southward and extends into Japan, and the autumn rain front moves south and away from Japan, the "long autumn rains" come to an end and the season of clear autumn skies begins. [Atsushi Kurashima and Takashi Aoki] Kitako typeWhen a migratory high pressure system or high pressure belt passes north of a region and that region is near the front of the southern edge of the high pressure system to the north, cloudy and rainy weather continues. In this case, it is called a northerly high pressure system. The northward shift of the continental high pressure system and the rainy season type (early stage) can also be considered a type of northerly high pressure system. [Atsushi Kurashima and Takashi Aoki] Northeasterly air currentIn the case of the Northern High Type, northeasterly winds prevail on the southern edge of the high pressure system. To emphasize this point, the Northern High Type is sometimes called the Northeasterly Airflow Type. In particular, the northward shift of the continental high pressure system is called the Northeasterly Airflow Type, and this term is sometimes used to refer to the northeasterly airflow that brings localized cloudy and rainy weather to the Kanto region and other areas. [Atsushi Kurashima and Takashi Aoki] South high, north lowAmong the midsummer type and the southward shift type of the continental high, when the southward shift of the high pressure is particularly strong, or when a migratory high pressure or high pressure belt passes south of Japan, it is sometimes called the southern high, northern low type. In the mainland, the weather is generally sunny and warm. Note that when referring to the northern high and southern high, the north and south refer to the region in question, and when a migratory high pressure passes over Honshu, it becomes the northern high type for Okinawa. [Atsushi Kurashima and Takashi Aoki] East high, west lowThis type corresponds to the midsummer type and some of the rainy season types where there is high pressure to the east of Japan. [Atsushi Kurashima and Takashi Aoki] "How to Read and Enjoy Weather and Weather Charts" edited by Kimura Ryuji (2004, Seibido Publishing) " ▽ "Weather Class for a Million People" by Shiraki Masanori (2007, Seizando Bookstore)" ▽ "Weather Forecaster Handbook" edited by the Japan Weather Forecasters Association (2008, Ohmsha)" ▽ "Illustrated Encyclopedia of How Weather and Weather Work" edited by Aoki Takashi (2009, Seibido Publishing) [Reference] | | |©Shogakukan "> Pressure distribution model around Japan (Figure) Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
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気圧分布の状態をいう。通常このことばは地上天気図について用いられるが、上空の気圧配置という言い方もありうる。 各季節には、それぞれ現れやすい気圧配置の型があり、その季節の天気や気候の特徴は、それによって説明できることが多い。また、ある季節に、他の季節に特徴的な気圧配置が現れると、季節外れの天気になる。日本付近に現れる特徴的な気圧配置は、モデル図（）を参照のこと。実際の天気図で気圧配置の型をみるときは、あまり細かい部分にとらわれずに、巨視的にその特徴をとらえることがたいせつである。また、気圧配置は、単に等圧線の形としてではなく、それによっておこされる気団の動きや天気の変化などと関連させて理解する必要がある。このような考え方から、気圧配置の型を天気図型とよぶ。 ［倉嶋 厚・青木 孝］ 西高東低型日本の西の大陸方面に高気圧、東の太平洋に低気圧があって、日本付近の等圧線は縦縞(たてじま)になっている。代表的な冬型気圧配置で、大陸からの寒気団が北西季節風となって日本列島を吹き抜け、日本海側の地方は雪や雨、太平洋側の地方は晴れの天気が卓越する。冬によく現れ、3～7日間ほど持続して、ときには強い寒波をもたらす。秋にこの型が現れると「木枯し」、春は「寒の戻り」になるが、いずれも長続きせず、強い北風は半日か1日で吹きやむことが多い。 ［倉嶋 厚・青木 孝］ 南岸低気圧型（東シナ海低気圧型）東シナ海方面に発生した低気圧が、日本の南の近海を発達しながら北東進する型。四季を通じて現れ、南岸に接近して通ると、太平洋側の地方を中心に降水があり、離れて通ると、降水域は陸地にかからない。とくに春にこの型が現れると、冬の間、西高東低型で乾燥し、晴天の続いてきた太平洋側の地方に、雨や雪が降る。低気圧の発生位置が台湾付近のことが多いため、昔はこの低気圧を台湾坊主とよんだが、近年は台湾低気圧とか東シナ海低気圧といいかえられることが多い。 ［倉嶋 厚・青木 孝］ 日本海低気圧型低気圧が日本海を発達しながら北東進する型。四季を通じて現れるが、典型的なものは春に多い。この低気圧に吹き込む気温の高い南寄りの気流は、「春一番」などの南風となって、日本列島を吹き抜ける。この種の風が吹くと、日本海側の地方でフェーン現象、多雪地帯では雪崩(なだれ)や融雪洪水がおこりやすい。低気圧から南西に伸びる寒冷前線が通る前は、暖かい南風がとくに強まり、通り過ぎると北寄りの風が吹いて気温が急降する。前線の近くでは春雷、竜巻(たつまき)、突風、局地的豪雨があり、砂嵐(あらし)、火災、海難などがおこりやすい。なお、日本海と南岸沿いまたは本州上を二つの低気圧が同時に通る型を、「二つ玉低気圧型」といい、悪天をもたらす。また南岸低気圧、日本海低気圧、二つ玉低気圧が日本の東の海上に進むと西高東低型になり、春ならば「寒の戻り」、秋ならば「木枯し」になる。 ［倉嶋 厚・青木 孝］ 移動性高気圧型高気圧が、西から東へほぼ一定方向に規則的に動く型。春と秋に現れることが多く、先行する高気圧との間に挟まれた気圧の谷があるので、3～4日の周期変化を伴う。 ［倉嶋 厚・青木 孝］ 高圧帯型または帯状高気圧型いくつかの移動性高気圧が、それぞれの間に強い低気圧や気圧の谷を伴うことなく、ほぼ東西に並んで、ゆっくりと東進する型。晩春、初夏や秋の代表的気圧配置で、高圧帯の域内では晴天が持続する。高圧帯は、北西から南東、あるいは南西から北東に伸びることもあり、極端な場合は南北に伸びる高圧帯もありうる。東西に伸びる高圧帯の南縁には前線があることが多い。5月に本土が高圧帯による初夏の晴天に覆われているとき、沖縄や小笠原(おがさわら)諸島は、この前線によって梅雨に入る。一般に高圧帯が北偏して通ると、その南縁にあたる地方では天気がぐずつく。 ［倉嶋 厚・青木 孝］ 梅雨型オホーツク海、日本海北部、カムチャツカの南方海上などの高気圧（いわゆるオホーツク海高気圧）と、日本のはるか南東洋上の亜熱帯高気圧（いわゆる小笠原高気圧、太平洋高気圧）の間の梅雨前線が、日本の南岸沿いにほぼ東西に伸びて停滞する型。オホーツク海高気圧が存在せず、梅雨前線だけの場合もある。梅雨前線の北側300キロメートルぐらいまでは雨、300～500キロメートルでは曇り所々雨、500～800キロメートルぐらいは曇り、それより北では快晴、また梅雨前線の南側100～200キロメートルでは所々で対流性の強い雨というのが標準的な天気分布であるが例外も多い。梅雨後期には亜熱帯高気圧が強まり、その範囲が日本の南岸まで広がり、梅雨前線は日本の上にあって、各地に集中豪雨を降らせることが多い。 ［倉嶋 厚・青木 孝］ 盛夏型梅雨前線帯が樺太(からふと)（サハリン）から沿海州方面まで北上し、太平洋の亜熱帯高気圧が日本を覆う型。太平洋高気圧をクジラの胴体の下半分に見立てると、西日本の膨らみの部分は尾にあたるので、「鯨(くじら)の尾型」とよばれている。この尾の上空には、独立の中心をもつ上層高気圧があり、チベット高気圧に連なっている。この型には持続性があり、高気圧域内では盛夏の炎天が続き、干魃(かんばつ)になりやすい。太平洋の高気圧から大陸に吹き込む南寄りの気流は、冬の北西季節風に対する、夏の南東季節風である。なおで、華南、台湾方面にかけて熱帯内収束帯が描かれているが、これは北東貿易風と熱帯の南西モンスーンの収束する線で、台風はここで「熱帯低気圧」として発生することが多い。 ［倉嶋 厚・青木 孝］ 台風型秋になると盛夏の太平洋高気圧は南東方に後退し、一方、北西方では大陸高気圧が発達して、日本は夏と秋の高気圧の谷間にあたるようになる。そして、台風がこの谷間を北上する。南洋方面の海面は夏の間、太陽エネルギーを多量に吸収して、海水温の高い区域が北に広がっているうえに、秋の台風は夏に比べると比較的低緯度帯で発生し、暖かい熱帯海域を大きく回ってくるので発達し大型になりやすい。 ［倉嶋 厚・青木 孝］ 大陸高気圧北偏型大陸の高気圧が北偏しながら日本付近に張り出し、これと太平洋高気圧との間の前線が、日本の南岸沿いに東北東から西南西に伸びてほぼ停滞し、その上を低気圧が東北東進する型。9月中ごろから10月中ごろにかけて現れる場合には、この前線は秋雨前線(あきさめぜんせん)とよばれ、日本の南岸にあたる地方に、梅雨に似た「秋の長雨（秋霖(しゅうりん)）」をもたらす。また、この前線に台風が近づいたり、前線上の温帯低気圧に南からの湿った気流が流入すると、秋雨前線豪雨になりやすい。 ［倉嶋 厚・青木 孝］ 大陸高気圧南偏型大陸高気圧が南偏して日本に張り出し、秋雨前線が南下して日本から遠ざかると、「秋の長雨」が明けて、秋晴れの季節に入る。 ［倉嶋 厚・青木 孝］ 北高型移動性高気圧や高圧帯が、ある地域の北を通り、その地域が北の高気圧の南縁の前線の近くにあたると、曇雨天が続く。このような場合を北高型という。大陸高気圧北偏型や梅雨型（前期）も、北高型の一種とみなすことができる。 ［倉嶋 厚・青木 孝］ 北東気流型北高型の場合、高気圧の南縁では北東風が卓越する。その点を強調して、北高型を北東気流型ということがある。またとくに大陸高気圧北偏型を北東気流型とよんだり、関東地方などに局地的に曇雨天をもたらす北東気流に限定して、この呼称を用いたりする。 ［倉嶋 厚・青木 孝］ 南高北低型盛夏型や大陸高気圧南偏型のなかで、とくに高気圧の南偏度の強い場合や、移動性高気圧や高圧帯が日本の南を通る型を南高北低型とよぶことがある。本土では一般に気温の高い晴天が続く。なお、北高、南高と表現する場合の北、南は、当該地域についてであり、本州を移動性高気圧が通る場合、それは沖縄にとっては北高型になる。 ［倉嶋 厚・青木 孝］ 東高西低型日本の東方に高気圧がある盛夏型、梅雨型の一部が、この型に相当する。 ［倉嶋 厚・青木 孝］ 『木村龍治監修『気象・天気図の読み方・楽しみ方』（2004・成美堂出版）』▽『白木正規著『百万人の天気教室』（2007・成山堂書店）』▽『日本気象予報士会編『気象予報士ハンドブック』（2008・オーム社）』▽『青木孝監修『図解 気象・天気のしくみがわかる事典』（2009・成美堂出版）』 [参照項目] | | |©Shogakukan"> 日本付近の気圧配置モデル〔図〕 出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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