Baiu Season Research Articles

モモ及びニホンナシ生産と雨量の変動との関係

Correlations between total rainfall variation in growing seasons and yields (kg/10a) of Peach and Japanese Pear at 3 typical production Prefectures were examined, and approximate quadratic equations were derived for Japanese Pear.Rainfall variations in Baiu seasons (much rain in June and July) and midsummer (little rain in August), which were closely related to fruits culture distribution and management, were analysed using the Quintile Grouping of rainfall data. Ratios of rainfall/potential evapotranspiration were derived and compared by distribution maps with fruits culture regions in normal year, more rainy year (once in 5 years level) and less rainy year (same above).From the prospect of climatic change in near future, the author appointed that warmer temperature and activiation or going north of Baiu Front might cause earlier outburst of pests and diseases and intensification of midsummer drought, which necessitated sufficient irrigation fascilities and water.

梅雨季の中国大陸上における降水帯の形成過程と前線構造

東アジアの梅雨季 (6, 7月)における降水分布の日々変化を類型化し,タイプごとの降水帯の形成過程ならびに梅雨前線の構造について解析を行なった.降水帯は温度傾度を伴わない収束帯に対応する場合と,大気下層に出現した低温域に伴う温度傾度の比較的大きい前線に対応する場合とがある.前者の場合,総観規模低気圧の後面における北～西よりの乾燥した気流と南よりの多湿な気流とによる対流不安定性の生成が降水帯の形成に寄与していると考えられる.後者については,下層に現われた低温域により湿潤気流の対流不安定性が解消され,降水が発生していると考えられる.さらに,降水帯が華中・華北に形成される場合と華南に形成される場合とでは低温域の進入経路や前線面の傾き,あるいは前線の位置に対する相対的な降水分布などが異なる.南北の温度傾度が通常小さな中国大陸上では低温域の出現や総観規模低気圧通過後の収束の開始が降水帯形成のトリガーとなっていると考えられる.

２０世紀の寒冷期・温暖期・変動期における東アジア地上気圧配置の季節内変動と特異性

Surface weather charts have been analyzed nearly for one century on a hemisphere scale. The present study tries to demonstrate characteristics of the occurrence frequency of pressure patterns in the global cold, warm, and recent variable periods, which correspond to or are responsible for anomalies in air temperature and precipitation, and to investigate the intraseasonal variations and singularities of pressure patterns over East Asia. This study defines the period from 1906 to 1920 as a cold period, that from 1936 to 1950 as a warm period, and that from 1971 to 1985 as a recent variable period. According to the classification of pressure pattern types by Yoshino (1968), a calendar of pressure patterns during the periods 1906-1920 and 1936-1940 was originally made on the basis of “Daily Synoptic Series, Historical Weather Maps, Northern Hemisphere Sea Level”. The statistics of this study are also based on the calendars for the periods 1941-1950 (Yoshino and Kai, 1974), 1971-1980 (Yoshino and Yamakawa, 1985) and 1981-1985 (original).The results of this paper are summarized as follows : The annual frequency of the typical winter type (type W) of west high and east low does not reveal much difference between the cold and warm periods. However, in the warm period, the duration of Type W appearance is shorter, but it occurs more frequently in January than in that of the cold period. The typical summer type (Type S), south high and north low, is most distinguished in August, though it is perceptible from July, in the warm period. The temperate migratory high type (Type H) (excluding highs passing North Japan) is clearly eminent throughout the year in the warm period. Particularly in April, Type H accounts for 43% (13% more than that of the cold period); in October it forms 37% (16% more). In the warm period, singularities of Type H are recorded five times in spring and autumn seasons, respectively. The north high type (Type N), which includes migratory highs in North Japan, southern coastal lows and southern coastal fronts, appears with low frequency in the warm period. The difference in occurrence frequency of Type N between the both periods is large in spring (April, May) and autumn (Sept., Oct.). In the cold period when the onset and end of the Baiu season are quite clear, the frontal zone type, consisting of Types N and L, appears with very high frequency (about 90%) throughout the Baiu season. With regard to the typhoon type (Type T), it tends to appear more frequently in August and September of the cold period ; in October of the warm period. Type T appears less frequently in both the summer and autumn seasons of the recent variable periods. Ratios of anticyclonic singularities to cyclonicones are 43 to 57 in the cold period, 54 to 46 in the warm period and 42 to 58 in the recent variable period. In the last period there are many identical singularities with those in the warm period. Especially from mid-August (Aug. 14-18) to mid-September (Sept. 8-12), a series of common singularities-Types T, S, L, S, L and L-are recognized in this order both in the warm and recent variable periods.

Prediction of long distance migration of rice planthoppers to northern Kyushu considering low-level jet stream.

Rice planthoppers are major pest for rice plants in Asian countries. They immigrates from overseas to Kyushu in Japan in the Baiu season every year. To predict the long distance migration of rice planthoppers to northern Kyushu, a migration model was developed with a hypothesis that rice planthoppers were transported by low-level jet stream at 1,000-2,000 m heights. The weather conditions for the migration period (June to July) were analyzed with the 850 mb chart at 21 h in 1980-1985 and at 09 h and 21 h in 1986, and possible migration days were decided. On the other hand, actual migration flight waves were decided with the number of catches by two nets. The possible migration flights decided by the weather chart agreed approximately with the actual flights. The accuracy of this prediction method was improved by using the 850 mb chart at 09 h additionaly. Finally, the prediction procedure was described.

日本における梅雨季の長期変動について

日本における梅雨季の長期変動について

A Year Climatic study of Hydro-climatological Environment in Yamagata Prefecture, Northeast Japan

climatological conditions were investigated by the year climatic consideration of water balance in Yamagata prefecture, Northeast Japan. The water balance was evaluated by “bookkeeping procedures” based on the Thornthwaite's potential evapotranspiration. The data used here were monthly precipitation amount and monthly mean temperature recorded at 31 meteorological or AMeDAS stations in Yamagata and the surrounding prefectures for sixteen years 1967-1982 (Fig. 1).The amount of the potential evapotranspiration was 700-720mm in the Shonai plain, 680mm-700mm in the Yamagata and Yonezawa basins and about 650mm in the Shinjo basin (Fig. 2). Along the border between the Shinjo basin and the other two regions, the potential evapotranspiration becomes 660mm-680mm.According to the warmth index by Kira (1945), the Shinjo basin was classified into the cool temperate and the other two into the warm temperate zone. These character of temperature regions were also supported by sporadic distribution of vegitaton such as laurel forest (Machilus thunbergii, Quercus salicina) in the Shonai plain and Yamagata basin and the deciduous broadleaved forest (Fagus crenata) in the Shinjo basin. Moreover, it was revealed by the important relatioship between the potential evapotranspiration and paddy rice production that the 670mm of potential evapotranspiration is significant for the paddy rice cultivation (Fig. 6). From the energy-budget equation, the about 50W/m2 of the net radiation can be calculated by using the 670mm of potential evapotranspiration and the zero of Bowen ratio.The number of dry months, which the amount of the potential evapotranspiration exeeds that of the monthly precipitation, is about 1.5 in the Shonai plain and Shinjo basin and reaches 2.5-3.0 in the Yamagata and Yonezawa basins (Fig. 3). The distribution of the maximum values of water deficit for the sixteen years (1967-1982) shows almost the same pattern with that of the number of dry months; it is about 50mm in the Shonai plain and Shinjo basin and reaches above 100mm-200mm in the Yamagata and Yonezawa basins (Fig. 4).At Yamagata the dry months occurred in April to October and most frequently in June and August (Table 3). On the occasion of water deficiency, however, the occurrence frequency of the dry month increases on the whole and specially in July (Table 4). This suggests the significance of the precipitation in the “Baiu Season”, one of the rainy seasons in Japan, for the occurrence of water deficit. Water deficiency occurred thirty six times for ninety-two years (1891-1982) and tends to continue about two years. Taking this tendency into account, it can be said that a drought with water deficiency comes on the average every three to four years. The frequency and the amount of water deficiency tend to increase in the period when the sunspot numbers change from the maximum to the minimum, especially in one to two years after the maximum of sunspot number (Table 2).It can be also considered that the condition of water balance as described above influenced on the distribution of Quercus-forest. The Quercus serrata community is typical of the secondary forest in the low land. This forest shifts into the Quercus-mongolica var. grosseserrata community or Fagus crenata-Quercus mongolica var. grosseserrata community, which is typical of the montane secondary forest, as increasing an altitude. In general, the altitude of this boundary decreases gradually toward north. In Yamagata prefecture, this boundary runs 400m-600m of altitude in the Yamagata and Yonezawa basins, 300m or so in the Shinj

日本における１７８０年代暖候期の天候推移と自然季節区分

A study has been made to classify the natural seasons in Japan for the summer half years (May-October) in the period 1781-90. The weather diagrams and the daily weather distribution maps for that period are described using the data of daily weather records in the official diaries (Fig. 1). The duration of five seasons-spring, the Baiu (summer rainy season), midsummer, the Shurin (autumn rainy season) and autumn-for each year is determined based on the seasonal march of weather (Fig. 2).Average beginning dates of the seasons for 1781-90 were not so different as those for today. However, the year-to-year variability of the beginning dates and the length of natural seasons for that period was large. Among those years, 1783, 1785 and 1786 had extremely unusual weather situations.The climate in 1783 was characterized by the remarkably cool and damp weather conditions in summer (Fig. 3). The beginning and ending dates of the Baiu season were approaximately as usual, whereas the following midsummer, which began on 19 July and ended 4 August in northeastern and central Japan, was extraordinarily short. During the Shurin season which started as early as on 5 August and ended on 10 September, the cloudy and rainy weather caused by the cyclonic and frontal activities prevailed, especially in the northeastern and central Japan. The great historic famine known as “Tenmei no Kikin” could be attributed to those severe weather situations.By contrast, the summer of 1785 was exceptionally hot and dry (Fig. 4). The Baiu season began on 3 June and ended as early as on the beginning of July, and this was followed by the extremely long midsummer which lasted until 3 September. A long spell of hot and dry weather in midsummer was occasionally interrupted by the short spell of stormy weather brought by the approach of typhoons. Those unusual weather conditions caused severe droughts in central and southwestern Japan. The Shurin season followed by midsummer began on 4 September and a rainy weather persisted until the end of October.The weather situations in 1786 were characterized by the long spell of wet weather in the Baiu season and the unstable weather in midsummer (Fig. 5). The Baiu season, the end of which was delayed until the beginning of August, was remarkably long and wet, particularly in southwestern Japan. The duration of midsummer was about 40 days and this was somewhat shorter than as usual. During this season, the heavy rains and floods occured frequently under the influence of typhoons. Those bad weather situations caused the poor harvest of rice cultivation.From these results, we can conclude that the climate in Japan for 1781-90 was extremely variable as for the summer weather situations.

Cloud distribution over East Asia during the summer monsoon season interpreted through satellite pictures

Summer monsoon clouds over East Asia observed by the meteorological satellite “Himawari” and ESSA were analyzed in order to shed light on the dynamic climatology of the area during the Baiu season. The mean cloudiness over Monsoon Asia undergoes little change and is nearly 50%, but the monsoon cloud belt varies in time and space in accordance with the seasonal shift of the strongest westerly flow axis at the 500 mb level. The summer monsoon clouds form a belt in which a major amount of water vapor is transported, extending from South China to the Bering Sea. Monsoon rains occur in Japan when the belt of monsoon cloud is over Japan and ends when the cloud belt moves away.

梅雨期の西日本上空における運動量の対流輸送(序報)

1968年,1969年の梅雨期について西日本上空における運動量の収支解析を行った、解析結果を,対象領域の平均12時間降水量が5mmより多い場合(Case MH)と少ない場合(Case NL)に分け,各々の平均状態を比較検討した.熱収支解析からは,対流活動はCase MHでは対流圏全層で盛んであるが, Case NLでは対流圏下層に限定されることが示される.運動方程式の残差項の評価-特に風に垂直な成分について 系統的な誤差が見出されるけれども,Case MHとCase NLとの比較から, Case MHにおいては西風成分の運動量の対流輸送は下向きで,対流圏中層で最大2～4dyn/cm2,南風成分の下向き輸送は2dyn/cm2を越えないと推定される.1000-100mb層の運動エネルギー全消散量は, Case MHでは約20 w/m2と評価されて, Case NLより1オーダー大きい.全消散量が大きいにも拘らず,Case MHの800-600 mb層では消散率は低い.このことから,大規模からsbgrid規模の運動へのエネルギーの流れ-特に対流圏上層において-があり,また対流運動量輸送を通じて上層から下層へのエネルギー移送があることを示していると考えられる.運動量,熱運動エネルギー収支から示される大規模およびsubgrid規模の運動の相互作用が, Case MHとCase NLにおける観測された風の鉛直分布の差に反映している.

THE DIVISIONS AND CHARACTERISTICS OF THE NATURAL SEASONS OF JAPAN

The fourteen natural seasons are subdivided based on the occurrence frequencies of the daily pressure patterns during the period of 1941-197O as follows: _??_ Spring, summer, autumn and winter are 82 days, 91 days, 97 days and 95 days respectively. For each subdivided season, the mean values of climatic elements, such as air pressure, temperature, daily minimum temperature, daily maximum temperature, vapour pressure, relative humidity, cloud amount, wind speed, precipitation and sunshine hours are also calculated for the four stations; Sapporo, Niigata, Tokyo, Kagoshima, which are climatologically representative stations in Japan. (Early spring) Mean air temperature, the difference between maximum and minimum temperatures and sunshine hours increase from the preceeding season to this season. The combination of the pressure patterns of migratory anticyclones and troughs appears frequently. (Spring) Mean air temperatures and the differences between maximum and minimum temperatures are both larger than those in the early spring season. In the areas of Japan Sea side and the northern part of Japan, relative humidity and precipitation are decreasing. On the contrary, these values indicate an upward tendency in the southern part of Japan and Pacific side. The sunshine hours grow longer. The pressure pattern of migratory anticy-clones is prolonged in contrast to the rare appearance of this combination in early spring. (Late spring) Air pressure decreases. Sunshine hours increase. Especially in Kagoshima, it shows a peak during this season. The maximum values of wind speed during a year appears in Sapporo. The combination of pressure pattern of trough and continuous migratory anticyclone occurs most frequently. (Early summer) The maximum of sunshine hours during a year appears at this time except in Kyushu. The precipitation in Niigata shows a minimum value. The cloud amounts during this time are comparatively small. The continuous trough patterns are common. (Bai-u) The values of relative humidity (higher than 80%), cloud amount, and precipitation reach their maximum, and the sunshine minimum. The daily maximum temperatures are higher than 20°C. These conditions make this season gloomy. The continuous pressure pattern of stationary fronts is characteristic in this season. (Summer) From Bai-u to summer, sunshine hours suddenly become longer for example, it changes from 5.0 hours to 7.9 hours in Kagoshima. The mean values of temperatures increase. The lowest values of air pressure and the patterns of continuous south-high/north-low (summer type) is abundant. (Late summer) The maximum of temperature appears in this season or in summer. Vapour pressure and sunshine hours also attain the maximum. Precipitation, relative humidity and wind speed show smaller values. The combinations of pressure patterns are almost the same as those in summer. (Early autumn) Temperature, vapour pressure, relative humidity, and sunshine hours begin to decrease, but air pressure contrarily increases. In the northern part of Japan, it turns to the season of Aki-same. The combination of the continuous pressure patterns of stationary fronts which are similar to the Bai-u season is most dominant. The continuous typhoon pattern ranks second. (Aki-same) A peak of precipitation appears, except in southern Japan. Sunshine hours decrease rapidly relative to that in early autumn. It is interesting to note that the continuous pattern of migratory anticyclone predominates during this rainy season. The continuous frontal pattern also prevails. (Autumn) Air pressure increases rapidly. Temperatures decrease and the daily range becomes larger. Relative humidity and vapour pressure tend to downward. (Late autumn) Air pressure shows the highest value. Air temperature and vapour pressure decrease. Sunshine hours are shorter than that in autumn.

梅雨期の豪雨帯へ南側面から流入する水蒸気流束

梅雨期の豪雨帯へ南側面から流入する水蒸気流束

梅雨期のレインバンドのメソスケール的構造

梅雨期のレインバンドのメソスケール的構造

梅雨期東支那海域の海水温分布の気団の成層およびエコー分布におよぼす影響

梅雨期東支那海域の海水温分布,気団の成層およびエコー分布の間の関係を,第2次(1969)および第4次(1971)梅雨末期集中豪雨特別観測の資料によって明らかにするのが,この報告の目的である.冷水域上では気団は冷却され,その成層は著しく安定化される.この過程は簡単な数値実験でもよく再現される.この安定化のため冷水域ではエコーの発達は著しく抑制される.一方総観的条件が大雨の発生に適すれば(1969年の如く梅雨前線が停滞して)暖水域ではエコー量が多い.しかし,これは気団変質の結果,成層が不安定化してエコーの発達が強化されるからだとは言えない.このような総観状況下では,暖水域上においてすら,気温は海水温より高く,気層の不安定化は加速されないからである.上記した大きなエコー量は,総観状況が積雲対流の発達に適しているならば,暖水域では,その発達が抑制されないからであると説明され得よう.また,もし総観状況が積雲対流の発達に適しなければ(1971年のごとく),暖水域上でもエコーの発達はみられない.なお,梅雨期にも軽度の寒気吹出がみられるが(これは大雨の発生する状態ではないが)この場合には暖水域では,“気団変質”(冬期のような)がおこり,最下層では,成層の不安定化がひきおこされることもある.

下層jetの北側沿にみられる梅雨期の大雨の頻発

The heavy rainfall over Japan in the Baiu season is usually associated with a well-developed low-level jet stream. The relation between the heavy rainfall and the low-level jet is here examined over southwest Japan throughout the Baiu season of 1968.As for the spatial relation, it is concluded that the occurrence of heavy rainfall is mostly confined within the zone of about 200 km wide along the north side of the low-level jet axis.The wind speed in the heavy rainfall zone is almost vertically uniform in the thick convective layer while the geostrophic wind speed increases with height. This characteristic wind profile suggests that the intensification of the super geostrophic low-level jet is to be attributed to convective momentum mixing.These observational facts about the relation between the heavy rainfall and the low-level jet is explained well from the dynamic model of the low-level jet circulation proposed by MATSUMOTO and NINOMIYA (1971).

梅雨期の大雨をともなう洋上の非地衡風的下層ジェット

梅雨期の大雨をともなう洋上の非地衡風的下層ジェット

Distribution of Cloudy or Rainy Weather in the Northern Tohoku under the Easterly Wind in Baiu Season

During the “Baiu” season, cold and humid easterly wind locally called “Yamase” often prevails over Northeastern Japan. The distribution of frequency of cloudy weather (Fig. 1) or rainy weather (Fig. 2) under such a condition was obtained. Fig. 1 shows the area of cloudy weather extends from the east, and Fig. 2 shows that rainy weather often appears along the Pacific coast and Ou-and Kitakami mountain ranges. Both types of the distribution are influenced by the higher part (>750m) in Ou and Kitakami ranges.

The Distribution of Heavy Rainfall Frequency in Western Half of Japan in Baiu Season

Fig. l and Fig. 2 show the distribution of heavy rainfall frequency in June and July respectively. In June (Fig. 1), high frequency areas are in the Pacific side of the district. In July (Fig. 2), the frequency decreases very much in the Pacific side, but it increases in the Japan Sea side. In this reprot, heavy rainfalls are defined as rainfalls that amounted over 50 mm per day.

FRONTAL ZONES AND PRECIPITATION DISTRIBUTION IN THE RAINY SEASON OVER EAST ASIA

Some climatological aspects of the frontal zones at the ground and 850 mb-surface (Figs. 1_??_3) and the precipitation distributions (Figs. 4_??_6) from decade to decade in May, June and July over East Asia were dealt with. The following results were obtained: (1) In the second decade of May, the rainy season appears in South China and the third decade in Japan. In the first decade of June, a marked frontal zone is formed from South China through East China Sea to the Pacific coast of Japanese Islands. Sometimes the frontal zone tends to disappear in South China, causing a pause of the rainy season. In the second decade of June, the frontal zone develops from the area around the lower course of the Yangtze River to the. Pacific coast of Japan; that is the beginning of the Mai-yu season over China and the Bai-u season over Japan. In the last decade of June it shifts slightly to the north. In the first decade of July, it runs from Middle China crossing over southern part of Korea to southwestern Japan. From the last decade of June to the first decade of July the rainy season reaches to its climax. In the second decade of July the frontal zone goes up further north. The rainy season ceases normally in this decade. (2) The position of the frontal zone at the 850 mb-surface is deviated 2_??_6° latitudinally to the north from that at the ground-surface in the beginning period of the rainy season over China. However, there is no positional correlation over Japan and her eastern sea. In the climax period of the season the latitudinal deviation is 2_??_4° over China and Japan. In the last period of the season, there is no positional correlation over China and, on the contrary, 2_??_4° latitudinal deviation is found in the area around Japan and the Pacific. This change in the tendency of positional deviation of frontal zones between the 850 mb-and ground-surface over China and Japan can be explained in relation to the shifting of the jet stream in the rainy season. (3) Characteristics of the precipitation distribution are analyzed only in the area over Japan and her surroundings. On the distribution maps of decadal precipitation from May to July one can observe always a zonal pattern along the Pacific coast of Japan (Figs. 4_??_6). On the other hand, the beginning of the season defined by the change in precipitation and the appearance of the maximum in the season shift from south to north (Figs. 7_??_8). The amount of maximum precipitation becomes smaller in accordance with the distance from the tonal area along the Pacific coast of Japan (Fig. 9). Therefore, it must be pointed out that the shifting of the frontal zone does correspond to the appearance of the maximum at any points and does not indicate the climatological distribution pattern of precipitation in the rainy season over Japan.

“Moist Tongue” over Japan in the Baiu Season (Preliminary Report)

At the time of heavy rainfall, very humid air named “moist tongue” is found in the upper air levels over Japan. This air, extending as a tongue from a moist air to the west or to the southwest, has been repeatedly observed during the rainy periods. In this paper, the moist air area around Japan was analyzed statistically from the vie wpoint of dew-point distribution during the baiu season (June and July). The observed frequency of dew-points above 6°C., 8°C., 10°C., and 12°C. indicates that between the 1st and the 10th of June in the average of three years, 1960-1962 (Figs. 1-4) the axis of the moist area lies in South China and extends to the east; and that between the 1st and the 10th of July (Figs. 5-8) the axis lies in central China and extends to the east. Each group of figures for June and July shows that the core of the moist area exists approximately in SW China with its axis moves toward the north in the early summer when the baiu frontal zone moves toward the north.The observed frequency of high dew-points is shown in Table. Analyzing each observation, the authors conclude that the “moist tongue” appearing over Japan emanates, in many cases, from the above mentioned moist air area.

Broad-scale and Small-scale Analyses of a Situation of Heavy Precipitation over Japan in the Last Period of Baiu Season 1957

Broad-scale and Small-scale Analyses of a Situation of Heavy Precipitation over Japan in the Last Period of Baiu Season 1957