The Structure of Convective Systems Observed by Phased Array Radar in the Kinki Region, Japan

Localized and short-term heavy rainfall generated by convective systems cause problems in Japan. In particular, urban flash floods, which have short response time of less than an hour, threaten the safety of urban residents. To mitigate the effects of such disasters, real time observation and accurate short-term forecasting (nowcasting) of rainfall is required.

To mitigate the effects of such disasters, Osaka University developed the phased array radar at X band (wave length is near 3cm) in Japan. This radar can scan very rapidly (30 seconds for full volume scan) with the high resolutions of azimuthal 1.2° and range 0.1km.

In this study, it was shown that the vertical structure and development of convective systems which cause localized and short term heavy rainfall.

For analyzing radar data, they were interpolated onto Cartesian coordinates (horizontally: 0.1km, vertically: 0.1km). In addition to phased array radar data, X band multi-parameter (XMP) radar data from Ministry of Land, Infrastructure and Transport and Tourism (MLIT) was used to compare to phased array radar data. For the real time monitoring of severe weather, MLIT installed four XMP radars in Kinki region, where the phased array radar is located. These radars can scan for constant altitude data (almost 1km) in 1 minute and for full volume data in 5 minutes.

Phased array radar captured life cycle of growth and decay of each convective cell. Furthermore detailed vertical structure and time series of convective systems which organized by multiple convective cells were shown. Also, initiation and descending of precipitation cores were captured. Most precipitation cores were initiated at around 5km height and some of them reached on the ground in just few minutes after they detected by phased array radar. To get this behavior, very high time resolution data is needed and volume scan data of XMP radar in MLIT was not enough. It is known that the behavior of precipitation cores relate to surface precipitation. Therefore, catching of the core in real time is prospective to be new index for more accurate nowcasting. Especially, upper height data is essential to forecast developing and/or declining stage of heavy rainfall and make nowcasting method expand considering initiation, development and declining of heavy rainfall which is difficult in conventional method.