The purpose of this study is to discuss precipitation distribution in Japan during the winter monsoon from the point of view of the generation of local anticyclones and cyclones (or local high-and low-pressure areas), and the landing of Convective Band Clouds (CBCs).
First, the author divides Japan into three districts: Central Japan, Southwest Japan, and Northeast Japan. Second, he classifies the cloud distribution patterns into either five groups (Central Japan) or four groups (Northeast Japan) according to the landing locations of CBCs. In the discussion of Southwest Japan, he refers repeatedly to the five groups classified in the discussion of Central Japan. These classifications also correspond to those of upper wind directions at 850mb.
The results are summarized as follows:
1) Central Japan
Under the influence of westerly upper winds, a local low-pressure area is generated at Fukui and extends northeastward or east-northeastward. High precipitation is obtained along the eastern side of this local low-pressure area. The landing of CBC from East Korea Bay seldom affects this high-precipitation area, where several heavy-precipitation peaks are found at intervals of 100 kilometers or more. These heavy-precipitation peaks are considered to correspond to the generation of local cyclones at meso-β scale.
Under the influence of northwesterly upper winds, high precipitation is obtained around Tsuruga, where a local cyclone is generated. CBC lands on the coast of Wakasa Bay (Tsuruga is situated on the eastern side of Wakasa Bay); however, when CBC does not land, high precipitation is obtained around Tsuruga. From this, we find that the generation of a local cyclone has a greater influence on the high precipitation around Tsuruga. Also, high precipitation is obtained around Takada, which is situated in the leeward of Toyama Bay; a local low-pressure area is generated at Toyama Bay. High precipitation is also obtained there when V-type Cloud Pattern, which has been considered to bring high precipitation, does not appear. From this, we find that the generation of a local low-pressure area has a greater influence on the high precipitation around Takada.
When an upper wind alternates between westerly and northwesterly, precipitation distribution has both the features mentioned above. This can be attributed to the fact that the local weather map in this case gives both features under westerly and northwesterly upper winds. When the Hokuriku Discontinuity Line is not created, high precipitation is obtained around Takada. From this, we find that its creation seldom has an effect on the high precipitation there.
2) Southwest Japan
High precipitation is obtained extending eastward from the landing location of CBC from East Korea Bay. In this high-precipitation area, several heavy-precipitation peaks are found. These are considered to correspond to the generation of local cyclones at meso-β scale. This high-precipitation area corresponds to the generated location of a local low-pressure area. However, when CBC does not land there, high precipitation is not obtained, in spite of the generation of a local low-pressure area.From this, we find that the landing of CBC has a greater influence on the high precipitation.
3) Northwest Japan
In the Tohoku District, CBC rarely lands and local anticyclones and cyclones are hardly generated. High precipitation is obtained in the mountainous ranges. From this, we find that high precipitation can be attributed to orographic rifting.
In Hokkaido, under west-northwesterly upper winds, high precipitation is obtained around Rumoi, where a local cyclone is generated. CBC from the Mamiya Straits often lands there; however, when it does not land, high precipitation is obtained there. From this, we find that the generation of a local cyclone has a greater influence on the high precipitation around Rumoi. High precipitation is also obtained on Ishikari Plain.
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