Modification of Typhoon 7002 Rainfall by Orographic Effect

Abstract

A case study of the rainfall during the passage of Typhoon 7002 over the Kii Peninsula is made on the assumption that the rainfall R(x,y,t) at each station (x,y) should be interpreted as k(x,y)*f(x,y,t), where f(x,y,t) is the rainfall which would be caused at the station by the traverse of a disturbance if there were no orographic effect and k(x,y) is the amplification factor of the rainfall which would be dependent upon the topographic features around the station and the direction and strength of prevailing wind. The results of analysis show that the distribution of h(x,y,t) whish is roughly proportional to f(x,y,t) and its behavior have a good correspondence to the distribution of moving radar echoes, while the distribution of R (x, y,t) is considerably controlled by topographic features over the peninsula. Examples of the pattern of k(x,y) and f(x,y,t) over the peninsula are presented.

A Study of the Heavy Rainfall over the Ohsumi Peninsula (Japan) Caused by Typhoon 9307

“…However, many previous observations reported that strong rainfall was observed on the windward rather than on the lee (e.g. Sakakibara and Takeda, 1973;. It is considered that the following three conditions were effective in this case to produce heavy rainfall on the lee side.…”

“…In many cases, however, the rainfall increases on the windward side rather than on the lee side. For example, the rainfall of Typhoon 7002 was very large on the windward side of the Kii peninsula, while it was very small on the lee side (Sakakibara and Takeda, 1973). The rainfall over New Zealand caused by Cyclone Bola showed extremely large amounts on the windward side of the mountains (Sinclair, 1993).…”

“…It is well known that the rainfall from a tropical cyclone is enhanced around mountains (Staff Members of Tokyo University, 1969University, , 1970Sakakibara and Takeda, 1973;Sinclair, 1993). In many cases, however, the rainfall increases on the windward side rather than on the lee side.…”

A Case Study of Heavy Rain in Owase Area

“…The amplification of rainfall by orographic effect, which was pointed out by Sakakibara and Takeda (1973), would be associated with processes that water drops which should have fallen from low stratiform clouds can grow larger drops in cumulonimbus or they can be coagulated by larger drops in it and that even small water drops which could not become raindrops neither in stratiform cloud nor in cumulonimbus can grow large sufficiently on account of the interaction of both clouds. Very efficient mechanism of rainfall formation can be said to be made around this region.…”

“…Sakakibara and Takeda (1973) developed the study of Staff Members of Tokyo University quantitatively. They stated that in the rainfall of typhoon 7002 over the Kii Peninsula the rainfall caused by the traverse of a disturbance is subject to amplification process which would be T. Hinodedake.…”