2:30 PM - 2:45 PM
[AAS03-16] Evolution and Microphysical Processes of Precipitation Cores Observed by Multi-Parameter Phased Array Weather Radar
Keywords:Isolated Cumulonimbus Clouds, Precipitation Cell, Precipitation Core, Microphysics, Phased Array Weather Radar
With the advancement of high-temporal-resolution weather radar, it has become evident that multiple precipitation cores form and dissipate within a single precipitation cell that constitutes an isolated cumulonimbus cloud. The descent of these precipitation cores to the surface results in intense rainfall. Understanding the microphysical processes within precipitation cores is crucial for comprehending the formation of heavy rainfall associated with isolated cumulonimbus clouds. In this study, we analyzed the temporal evolution and microphysical processes of precipitation cores using a Multi-Parameter Phased Array Weather Radar (MP-PAWR), which enables high-temporal-resolution dual-polarization observations.
We focused on an isolated cumulonimbus cloud that developed in the southern Kanto region on August 31, 2018, unaffected by synoptic disturbances. Precipitation cells were defined as three-dimensionally continuous regions with a reflectivity factor (ZH) of 20 dBZ or higher, and were detected for 96.5 minutes from 14:13:00 to 15:49:30 JST. Precipitation cores were identified using the Contoured Frequency by Altitude Diagram (CFAD) of ZH within the precipitation cells, where the threshold was set at the top 3% of ZH at each altitude. A precipitation core was defined as a region exceeding this threshold and containing a single local maximum. The tracking of precipitation cores was manually conducted for those detected before the peak altitude of the precipitation cell at 14:35 JST. Additionally, median diameter (D0) and intercept parameter (Nw) of the drop size distribution were estimated from ZH, differential reflectivity (ZDR), and specific differential phase (KDP). The precipitation particle fall velocity weighted by ZH (wd) was then derived from D0 and Nw. Surface rainfall intensity was obtained from the Ministry of Land, Infrastructure, Transport and Tourism’s XRAIN composite rainfall data.
During the observation period, a total of seven precipitation cores were tracked. These cores were categorized into two major types: (1) those detected above the 0°C level, persisting for 3–8 minutes before dissipating at a constant altitude, and (2) those forming below the 0°C level, descending to the surface while maintaining altitude near the ground. During the approximately 15-minute period of sustained heavy rainfall (around 80 mm/h), three precipitation cores below the 0°C level successively replaced each other.
Focusing on precipitation core 04, which formed below the 0°C level, we analyzed its temporal evolution and microphysical processes. Precipitation core 04 developed directly beneath and descended from precipitation core 03, which had formed above the 0°C level. The fall velocity of the ZH peak in precipitation core 04 was approximately 10 m/s, and the high-ZDR region decreased along with the descent of the precipitation core. The estimated wd was 8–9 m/s, suggesting that the precipitation core descended as large-diameter particles fell. After reaching the surface, the ZH peak remained at an altitude of approximately 2 km for seven minutes. Vertical variations in ZH and ZDR indicated that coalescence processes persisted in the upper part of the precipitation core, while breakup processes continued in the lower part. This suggests that the precipitation core was maintained even after reaching the ground due to the sustained coalescence from the continuous supply of particles from above and their subsequent breakup below.
We focused on an isolated cumulonimbus cloud that developed in the southern Kanto region on August 31, 2018, unaffected by synoptic disturbances. Precipitation cells were defined as three-dimensionally continuous regions with a reflectivity factor (ZH) of 20 dBZ or higher, and were detected for 96.5 minutes from 14:13:00 to 15:49:30 JST. Precipitation cores were identified using the Contoured Frequency by Altitude Diagram (CFAD) of ZH within the precipitation cells, where the threshold was set at the top 3% of ZH at each altitude. A precipitation core was defined as a region exceeding this threshold and containing a single local maximum. The tracking of precipitation cores was manually conducted for those detected before the peak altitude of the precipitation cell at 14:35 JST. Additionally, median diameter (D0) and intercept parameter (Nw) of the drop size distribution were estimated from ZH, differential reflectivity (ZDR), and specific differential phase (KDP). The precipitation particle fall velocity weighted by ZH (wd) was then derived from D0 and Nw. Surface rainfall intensity was obtained from the Ministry of Land, Infrastructure, Transport and Tourism’s XRAIN composite rainfall data.
During the observation period, a total of seven precipitation cores were tracked. These cores were categorized into two major types: (1) those detected above the 0°C level, persisting for 3–8 minutes before dissipating at a constant altitude, and (2) those forming below the 0°C level, descending to the surface while maintaining altitude near the ground. During the approximately 15-minute period of sustained heavy rainfall (around 80 mm/h), three precipitation cores below the 0°C level successively replaced each other.
Focusing on precipitation core 04, which formed below the 0°C level, we analyzed its temporal evolution and microphysical processes. Precipitation core 04 developed directly beneath and descended from precipitation core 03, which had formed above the 0°C level. The fall velocity of the ZH peak in precipitation core 04 was approximately 10 m/s, and the high-ZDR region decreased along with the descent of the precipitation core. The estimated wd was 8–9 m/s, suggesting that the precipitation core descended as large-diameter particles fell. After reaching the surface, the ZH peak remained at an altitude of approximately 2 km for seven minutes. Vertical variations in ZH and ZDR indicated that coalescence processes persisted in the upper part of the precipitation core, while breakup processes continued in the lower part. This suggests that the precipitation core was maintained even after reaching the ground due to the sustained coalescence from the continuous supply of particles from above and their subsequent breakup below.