RELATIONSHIP BETWEEN RAIN CLOUDS DIRECTION, TOPOGRAPHY AND AMOUNT OF PRECIPITATION IN BETWEEN THE OSAKA PLAIN AND THE SOUTH IKOMA MOUNTAINS, MIDDLE OF JAPAN

Abstract

The area between from the Osaka Plain to the Ikoma Mountains faces sea at only west direction
and is surrounded by mountains at the other directions. Then, rain clouds can directly encounter the Ikoma
Mountains only from west direction before crossing any mountains. On the other hand, rain clouds cannot
encounter the Ikoma Mountains from the other directions before crossing surrounding mountains. Only when
rain clouds migrated from west direction, amounts of precipitation in the Ikoma Mountains were observed to
be 41 % higher than in the Osaka Plain. The altitude difference between both areas is about 400 m. When rain
clouds migrated from the other directions, both amounts of precipitation for the Ikoma Mountains and the
Osaka plain were almost the same. Therefore, altitude effect of amounts of precipitation for foot of mountain
and top of mountain was observed only when rain clouds directly encountered the mountain before crossing
the other mountains.