Characteristics of Atmospheric Vertical Structure on Days with Thunderstorms in the Northern Kanto Plain

[摘要] Vertical conditions on 248 days during two summer seasons are investigated to study the distinctive characteristics of the stratification on days with thunderstorms in the northern Kanto plain. For the sake of convenience atmosphere is divided into two layers, upper layer and lower layer.It is recognized that high degree of conditional instability of an upper layer is not the sufficient condition for the occurrence of thunderstorms. However, there are distinct differences of vertical stabilities of a lower layer between on days with thunderstorms and on days without a thunder-storm when an upper layer is conditionally unstable. Namely, it is shown that vertical movement of an air parcel in a lower layer on the former is easier than on the latter. It is also shown that the ratio of the degree of conditional instability of an upper layer to the degree of stability of a lower layer is an important factor affecting the occurrence of thunderstorms rather than their values.These conditions are interpreted into suggesting an interaction between a convective cloud and its subcloud layer, and an instability index is obtained by assuming the interaction. It is shown that this instability index has higher association with the occurrence of thunderstorms than Showalter stability index has. Therefore, the stronger relation is suggested between the occur-rence of thunderstorms and the stability of the whole atmosphere than it has been pointed out.

[学科分类] 大气科学