A General View of the Structure of Typhoon 8514 Observed by Dual-Doppler Radar

Abstract

The structure of the rainbands and eyewall of Typhoon 8514, which landed at the central region of Japan on 30 August 1985 was observed by two ground-based Doppler radars. The main purpose of the present study is to describe a general view of the structure of the typhoon using data of the dual-Doppler radar.Although the typhoon was a small and weak typhoon, it retained the characteristics of tropical cyclones: it was accompanied by spiral rainbands (an outer rainband and an inner rainband) and had a warm core in its upper part.The outer rainband was a spiral band located about 150 km from the center of the typhoon. This rainband consisted of continuous stratiform clouds and scattered convective clouds. A radar "bright band" was observed in this rainband. Wind perturbation induced by cooling-by-melting was observed just below the bright band. An updraft of 1.5 ms-1 was produced, mainly owing to the convergence of a southeasterly flow on the inner edge of the outer rainband. This updraft maintained the outer rainband.The inner rainband was a convective spiral band located *60 km from the typhoon center. The distribution of reflectivity and vertical velocity of this rainband indicated that an old echo cell existed in the inner part, while young echo cells existed in the outer part of this rainband. An inflow (the airflow toward the typhoon center) was observed in the lower layers of the inner rainband. This inflow reached the inner edge of the young cells, and produced an updraft there. When the depth of this inflow layer became thinner, the inner rainband decayed. This indicates that the inflow had an important role to play in maintaining the inner rainband.Because the flow into the eyewall of the typhoon in the lower layers was weak, the radius of maximum wind (RMW) was located at the outer side of the axis of reflectivity maxima. The eyewall decayed when it moved to the inner area (nearer the typhoon center) of the RMW, where downdraft was predominant.

The Effect of Surface Friction on the Mesoscale Organization of Cumulus Convection in Tropical Cyclones

“…In this case, the rainfall, downdraft and cold pool were located at the outside (larger radius) of the updraft. A similar situation has been observed by Ishihara et al (1986) and Tabata et al (1992). In many cases, observed rainbands were not isolated but coexisted with a few rainbands; in some cases, a merger of two rainbands was observed (Barnes et al, 1983).…”

“…This is also seen in observed hurricane rainbands (Barnes et al, 1983;Barnes and Powell, 1995;Powell, 1990a). Outside the area of large 8e gradient, the layer of high 8e is thicker than inside, as reported by observational studies (Barnes et al, 1983;Tabata et al, 1992;May, 1996). Because of intense low-level inflow, more air with high ee is supplied to the low-level convergence area, and low-level clouds are formed more continuously than in the case of ordinary MC.…”

“…Mesoscale structures with a distinct downdraft and cold pool in spiral rainbands have been reported in many observational studies (Tatehira, 1962;Barnes et al, 1983Barnes et al, , 1991Ishihara et al, 1986;Powell, 1990a,b;Tabata et al, 1992). Structures and phase velocities of the observed spiral rainbands are different from those of gravity waves.…”

“…As mentioned above, the longer lifetime was obtained when the tangential velocity increased and frictional inflow became significant. The importance of frictional inflow on the organization of cumulus convection was also stated in observational studies (Ishihara et al, 1986;Tabata et al, 1992). However, the mechanism by which it affected the mesoscale organization has not been well understood.…”

Structure and Evolution of Convection within Typhoon Yancy (T9313) in the Early Developing Stage Observed by the Keifu Maru Radar

“…However, because of the shortage of period and time intervals of the aircraft radar observation, the evolution process and three dimensional structure were not described in detail. This is contrastive to mesoscale features within mature TCs, such as eyewall clouds and spiral bands, which have been investigated extensively using airborne Doppler radar (e.g., Barns et al, 1983;Marks and Houze, 1987) and ground based dual Doppler radar (e.g., Ishiraha et al, 1986;Tabata et al, 1992;Shimazu, 1997).…”