Structure of a Typhoon Rainstorm in the Middle Latitudes Observed by Doppler Radar

Abstract

A rainstorm occurred over the central part of Japan (*36*N/140*E) within Typhoon 8124 (Gay) for 22-23 October 1981 and it was studied mainly using Doppler radar data. The main purposes of the present study are to clarify the structure of the rainstorm and to know whether it was a typhoon spiral band or another type of precipitation system.The typhoon was under transformation into an extratropical cyclone in the southeastern portion of a large-scale trough. Satellite and radar data show that this rainstorm occurred on the southeastern edge of a wide cloud band to the north of the typhoon center. The most outstanding feature of this rainstorm found by Doppler radar was the existence of a slant axis of strong wind from lower levels on the southeastern side to upper levels on the northwestern side. This means the existence of a mesoscale slant updraft. Below the axis of the slantwise updraft, convective-scale vertical motion was embeded in the mesoscale updraft. Above the axis, convective-scale vertical motion was generally small. The middlelevel air intruded into the northwestern portion of the rainstorm in the southern part. It is suggested that the intruded air was cooled by evaporation of precipitation particles and formed a mesoscale downdraft.Although a pronounced surface convergence line was associated with the rainstorm, its effect on the rainstorm was subsidiary except in the southern part.The structure of the rainstorm was partially similar to those of a typhoon spiral band, eyewall clouds and a squall line in the middle latitudes.However, this structure is considered as a characteristic feature of a rainstorm which occurs to the north of a typhoon in extratropical transition.The result and interpretation of a mesoscale budget of condensed water in the form of precipitation particles are also shown to study the relative importance of production and transport of precipitation particles in the rainstorm.

Classification of Precipitation Systems in Mature and Early Weakening Stages of Typhoons around Japan

“…This is the first study that shows delta rain shields generated in all typhoons approaching mid-latitude frontal zones. A case study of a delta rain shield was also made by Sakakibara et al (1985).…”

Typhoon 9707 observations with the MU radar and L-band boundary layer radar

“…Ishihara et al (1986) examined the wind fields and the internal structure of the rainband of Typhoon 8305 using the ground-based Doppler radar and showed that the convergence between the low-level warm inflow and the descending rear flow was associated with the relatively cold air. Sakakibara et al (1985) showed that the structure of the rain band in the extratropical transition of the typhoon was partially similar to that of a squall line at mid-latitudes. Tabata et al (1992) showed the structure of spiral rain bands (outer and inner rain bands) of Typhoon 8514.…”

Structure of a Typhoon Rainband Observed by Two Doppler Radars

“…The characteristics of two Doppler radars of 3-and 5-cm bands of Meteorological Research Institute (MRI) were described by Sakakibara et al (1985). Figure 1 shows the location of these radars and experimental domains.…”

“…They showed that the rainband was organized as a mesoscale precipitation system and included convective-scale vertical motions. Sakakibara et al (1985) studied the structure of a mesoscale disturbance near a typhoon center using single Doppler radar data. Marks and Houze (1986) presented the first use of airborne Doppler radar in the study of a hurricane.…”