シベリア高気圧の季節変化と季節区分 [in Japanese] Seasonal Change and Seasonal Division of the Siberian High [in Japanese]
Access this Article
Search this Article
海面更正気圧 (SLP) により定義されるシベリア高気圧の季節変化を半旬を単位として明らかにし,上空の気圧配置および気温分布との関係を明らかにした. 1980年から1992年までの13年平均データを用い,シベリア高気圧の中心部 (50～55°N, 90～95°E) とウラル山脈北部(60～65°N,70～75°E)のSLPの3半旬平均の差により,季節変化のステージ分けを行った.その結果, 1年をステージ1(第39～53半旬),ステージ2(第54～57半旬),ステージ3(第58～64半旬),ステージ4(第65～72半旬),ステージ5(第73～3半旬),ステージ6(第4～7半旬:最盛期),ステージ7(第8～12半旬),ステージ8(第13～15半旬),ステージ9(第16～38半旬)に分割することができ,シベリア高気圧の形成・発達・衰退・消滅に至る時期およびその出現位置をとらえることができた.<br> さらに,上空の気圧配置,気温分布,気温の鉛直構造を考察した.この結果, 500hPa面高度で130°E付近の強いトラフと, 50°Eのトラフ, 80°Eのリッジが強くなっている時に,シベリア高気圧の中心が強まっていることがわかった.すなわち,シベリア高気圧の中心部分が発達・衰弱する時には,上層の気圧配置の影響が見られる.また,バイカル湖周辺がシベリア高気圧の中心となっており,気温の鉛直方向の逆転はステージ6のみで見られる.その西部および北東部では下層の寒気により高気圧が形成される.西部のウラル山脈北部では,シベリア高気圧形成時と衰退時に高気圧の中心になり,北東部のヤクーツク付近では,シ球リア高気庄が発達している時に,地上気温が大陸上で最も低くなるため高気圧が張り出す.シベリア高気圧は,これらの3地域を中心として,強さと形が季節変化することが示された.
The seasonal change in the Siberian High (SH), and the relationship with upper atmospheric pres sure and temperature were investigated.<br> Data utilized in the present study included: 1) daily potential height and temperature at 500 hPa and 850 hPa; 2) daily temperature at 700 hPa and 1000 hPa; and 3) 5-day mean sea level pressure (SLP). Data 1 and 2 were analyzed by the Europe Centre for Medium-Range Weather Forecasts (ECMWF) in a 2.5-degree grid. Data 3 were analyzed by the Japan Meteorological Agency (JMA) in a 5-degree grid. Data 1 and 2 were compiled into pentad data. All these were averaged for 13 years from 1980 to 1992.<br> For the division of the stages in a year, the author analyzed the difference in the 3-pentad mean SLP. The 3-pentad mean SLP of the central area of the SH (50-55°N, 90-95°E) was calculated to form the index of development or decline of the SH. The seasonal change in this index is shown in Fig. 3, in which the 3-pentad mean SLP of the Northern Ural area (NU; 60-65°N, 70-75°E) is included. As a re sult, one year was divided into 9 stages (Fig. 3).<br> The mean SLP pattern in each stage is shown in Fig. 4. The characteristics of the SH in each stage are described in the following in relation to low-pressure systems in the northern hemisphere, namely the Aleutian Low (AL) and Iceland Low (IL).<br> Stage 1 (between 39 and 53 pentad [P39-53]): The pressure is low in the central part of the Eura sian continent, and the Northern Pacific High and Azores High in the Atlantic Ocean are recognized.<br> Stage 2 (P54-57): The center of the High in the Eurasian Continent is located near the NU. The AL can be seen in the southern part of Alaska. Around the western part of the Scandinavian Peninsula, the IL strengthens.<br> Stage 3 (P58-64): The center of the SH moves around 50°N, 90-100°E, and after this stage, it devel ops further. At the northern part of the NU, a low-pressure system develops. The strength of the AL does not change from the previous stage. Around the southern part of Greenland, the IL develops.<br> Stage 4 (P65-72): The SH develops. The AL moves westward to 165°W. The center of the IL is in the Scandinavian Peninsula, while the IL moves to the southern part of Greenland.<br> Stage 5 (P73-3): The SH develops. NNE. The AL and IL move westward and develop. The former cen ter nears 180° longitude and the later center approaches Greenland.<br> Stage 6 (P4-7): This stage is the mature stage of the SH which moves forward the northwest. The AL moves westward, and its center reaches the Kamchatka Peninsula. The IL moves southwestward and develops.<br> Stage 7 (P8-12): The SH declines in the central part, but its influence remains in the western part of Siberia. The AL begins to moves eastward. This stage is the climax of the AL. The IL also develops in the south of Greenland, and this stage is also the climax of the IL.<br> Stage 8 (P13-15): The center of the SH moves westward, approaching east of the NU. The AL declines and moves westward again, with its center coming to the Kamchatka Peninsula. The center of the IL is around the south of Greenland and the IL declines.<br> Stage 9 (P16-38): The SH declines and disappears. The AL also declines and its center moves eastward to the eastern part of Alaska. The IL also disappears.<br> The pressure distribution, temperature distribution, and vertical temperature structure in each stage are analyzed to discuss the cause of seasonal change in the SH at SLP. The vertical temperature profiles at 3 points of the NU (65.0°N, 65.0°vE, 96.0m), SH (57.5°N, 92.5°E, 216.6m), and Yakutsk (Ya: 70.0°N, 135.0°E, 228.3m) are shown in Fig. 5. When strong troughs near 130°E and 50°E, and a ridge near 80°E at 500 hPa are obvious, the center of the SH develops. Therefore it was thought that the SH develops or declines under the influence of the pressure distribution of the mid-troposphere.
- Geographical review of Japan, Series B.
Geographical review of Japan, Series B. 70(8), 526-541, 1997-08
The Association of Japanese Geographers